xix

CHAPTER -I

xix

SYMBOLS AND ABBREVIATIONS

13C -NMR 1H-NMR

AIBN

ACU

CaCl2

CDCl3

DCPA

DCPMA

DMF

DMSO

DSC

DTA

E

F-R

G-H

K-T

m.pt.

M1

m1

M2

m2

MACU

Carbon nuclear magnetic resonance

Proton nuclear magnetic resonance

Azobis-isobutyronitrile

7-acryloyloxy-4-methyl coumarin

Calcium Chloride

Deuterated chloroform

2,4-dichlorophenyl acrylate

2, 4-dichlorophenyl methacrylate

Dimethyl formamide

Dimethyl sulphoxide

Differential scanning calorimetry

Differential thermal analysis

Polarisibility parameter of monomer

Fineman-Ross

Ordinate parameter in Fineman-Ross plot

Abscissa parameter in Fineman-Ross plot Kelen-tudos

Melting point

Initial mole fraction of monomer before copolymerization

Mole fraction of monomer in copolymer

Initial mole fraction of comonomer before copolymerization

Mole fraction of comonomer in copolymer

7-methacryloyloxy-4-methyl coumarin

xx

NPAM

PA

Poly (NTA-co-QA)

Poly (NTA-co-QMA)

Poly (NTA-co-DCPA)

Poly (NTA-co-DCPMA)

Poly (NTA-co-ACU)

Poly (NTA-co-MACU)

Poly (NTA-co-PA)

Poly (NTA-co-NPAM)

Q

QA

QMA

r1

r2

T50%

Tf

Tg

TGA

N-phenyl acrylamide

Phenyl acrylate

N-tert-amylacrylamide-co-8-quinolinylacrylate copolymer

N-tert-amylacrylamide-co-8-quinolinylacrylate copolymer

N-tert-amylacrylamide-co-2,4-dichlorophenylacrylate copolymer

N-tert-amylacrylamide-co-2,4-dochlorophenyl methacrylate copolymer

N-tert-amylacrylamide-co-7-acryloyloxy-4-methyl coumarin copolymer

N-tert-amylacrylamide-co-7-methacryloyloxy-4-methyl coumarin copolymer

N-tert-amylacrylamide-co- phenyl acrylate copolymer

N-tert-amylacrylamide-co-N-phenyl acrylamide copolymer

Resonance stabilization parameter of monomer

8-quinolinyl acrylate

8-quinolinyl methacrylate

Reactivity Ratio of monomer

Reactivity Ratio of comonomer

Temperature for 50% weight loss

Final decomposition temperature

Glass transition temperature

Thermogravimetric analysis

1

1. INTRODUCTION

1.1 Polymer

The history of polymers goes back further than that of any other group of

substances known to mankind. From the origin of mankind in the Garden of Eden,

dependence was upon naturally-occurring polymers, for food, clothing, shelter and

counication. On the contrary, the history of synthetic polymers is relatively short. It

was only through the pioneering work of Staudinger and the quantitative studies of

Carothers, the macromolecular concept was accepted. Long before this time, synthetic

polymers were being produced and natural polymers were being altered chemically.

Styrene was first polymerized in 1839 and in the same year the process of

vulcanization of rubber was made successful.

1.2 Description and classification

The word polymer was first used to describe compounds with the same

composition but of different molecular weights. Berzelius1 defined polymer as ‘many

of a unit’. Carothers2 defined polymerization as a reaction that is functionally capable

of proceeding indefinitely. According to IUPAC, a monomer is defined as ‘a

compound, consisting of molecules each of which can provide one or more

constitutional units of a polymer or oligomer’ and a monomeric unit or “mer” is the

‘largest constitutional unit contributed by a single monomer molecule in a

polymerization processes.

2

Classification of polymers

On the basis of different chemical structures, physical properties, mechanical

behaviour, thermal characteristics, stereochemistry, polymers can be classified into

following ways:

Figure 1: Classification of polymers

(i) Based on the Origin or Source

(a) Natural polymer: These polymers are generally obtained from nature. They are

available in nature.

Examples: Rubber, Cotton, Silk, Wool, Cellulose, Starch, Proteins etc.

3

(b) Semisynthetic polymer: They are chemically modified natural polymers. For

example cellulose is naturally occurring polymers, cellulose on acetylation

with acetic anhydride in the presence of sulphuric acid forms cellulose

diacetate polymers. It is used in making thread and materials like films glasses

etc. Vulcanized rubber is also an example of semisynthetic polymers which

are used in making tyres etc.

(c) Synthetic polymer: Manmade polymers prepared synthetically from low

molecular weight compounds.

Example: PVC, polyethylene, Polystyrene, nylon etc.

(ii) Based on the mode of formation

Another classification system (Carothers) is based on the nature of the

chemical reactions employed in the polymerization. Here the two major groups are

the “condensation” and “addition” polymers. This type of classification of

polymerization system was slightly modified by P.J.Flory3 who emphasised on the

mechanism of the polymerization reactions. He reclassified polymerizations as step

and chain polymerization. A notable exception occurs with the synthesis of

polyurethanes which follows step kinetics but without the elimination of a small

molecule.

(a) Addition polymer: An addition polymer is a polymer which is formed by an

addition reaction, where many monomers bond together via rearrangement of

bonds without the loss of any atom or molecule. Addition polymers

4

have -C-C- linkage along the main chain and no other atom appears in the

main chain. They are formed by olefinic diaolefinic mechanism known as

addition or chain growth polymerization.

Example: Polyethylene, polypropylene, PVC, polystyrene etc.

Figure 2: Pictorial representation of Addition polymerization

(b) Condensation polymers: Condensation polymers are formed through a

condensation reaction, releasing small molecules as by-products such as water

or methanol. Condensation polymers are formed from intermolecular reactions

between bifunctional or polyfunctional monomer molecules with the

elimination of small biproduct molecule.

Example: Polyamides, Polyesters, Polyethers etc.

Figure 3: Pictorial representation of condensation polymerization

5

(iii) On basis of Thermal response

One of the methods to classify polymers is by their response to thermal

treatment and to divide them into thermoplastics and thermosets.

(a) Thermoplastic polymer

Thermoset polymers soften when heated and harden when cooled.

Simultaneous application of heat and pressure is required to fabricate these

materials.

On the molecular level, when the temperature is raised, secondary bonding

forces are diminished so that the relative movement of adjacent chains is

facilitated when a stress is applied.

Most Linear polymers and those having branched structures with flexible

chains are thermoplastics.

Thermoplastics are very soft and ductile.

(b) Thermosetting polymer

Thermosetting polymers become soft during their first heating and become

permanently hard when cooled. They do not soften during subsequent heating.

Hence, they cannot be remolded / reshaped.

In thermosets, during the initial heating, covalent cross-links are formed

between adjacent molecular chains. These bonds anchor the chains together

resisting the vibration and rotational chain motions at high temperatures. Cross

6

linking is usually 10 to 15% extensive for chain mer units which are cross

linked. Only heating to excessive temperatures lead to severe breaking of

crosslink bonds and polymer degradation.

Thermosets polymers are harder, stronger, and more brittle than

thermoplastics and have better dimensional stability.

They are more usable in processes requiring high temperatures.

When compared to thermoplastics, thermosets can be used at higher

temperature and are more chemically inert.

(iv) Based on its form and use

(a) Plastics: When a polymer is shaped into hard and tough utility articles by the

application of heat and pressure, it is called plastic.

Example: Polyvinyl chloride, Polystyrene, etc.

(b) Elastomers: When a polymer is vulcanized into rubbery products exhibiting

good strength and elongation, it is called elastomers.

Example: Rubber, synthetic rubber, Silicon rubber etc.

(c) Fibres: When a polymer drawn into long fillament like material, whose length

is at least 100 times of its diameter, it is called fibres.

Example: Nylon, Terylene etc.

7

(d) Liquid resins: When a polymer is used as adhesive, potting compounds,

sealants etc., in a liquid form, it is called liquid resin.

Example: Epoxy adhesive, Polysulphide sealants etc.

(v) Organic and Inorganic Polymers (based on the backbone chain)

A polymer whose backbone chain is essentially made of carbon atoms is

termed as organic polymer. The atoms attached to the side valencies of the backbone

carbon atoms are, however, usually those of hydrogen, oxygen, nitrogen, etc. The

majority of synthetic polymers are organic. In fact, the number and variety of

polymers are so large thats why we refer to ‘polymers’ on the other hand, generally

contains no carbon atom in their chain backbone. Glass and silicone rubber are

examples of inorganic polymers.

(vi) Tacticity (based on the configuration)

On the basis of the stereochemistry of molecules in the arrangement of the

functional group in the chain, polymers can be classified into three categories viz.,

atactic, isotactic (cis-arrangement) and syndiotactic (trans-arrangement).

(a) The polymer in which the arrangement of functional groups are all on the

same side are known as isotactic polymer.

(b) The polymer in which the arrangement of functional groups is in alternating

fashion is termed as syndiotactic polymer.

(c) The polymer in which arrangement of functional groups are at random around

the main chain, are termed as atactic polymer.

8

Figure 4: Pictorial representation of stereo regular polymers

(vii) On basis of structure

(a) Linear: Monomeric units are joined in the form of long straight chains, such

polymers have high densities, high tensile strength and high melting point.

Figure 5: Linear chain polymers

Example: Polyethylene, nylons and polyesters.

(b) Branched chain: These are mainly linear in nature but also possess some

branches along the main chain. Example: low density polyethene (LDPE).

They have densities, lower tensile strength and low melting point.

9

Figure 6: Branched chain polymers

Example: Amylopectin and glycogen.

(c) Crossed Linked polymers: Bi-functional and tri-functional monomeric units

are linked together to constitute a three dimensional network. They are hard,

rigid, and brittle.

Figure 7: Cross linked polymers

Example: Bakelite, Melamine formaldehyde resin, etc.

(viii) Based on the chemical composition

Another classification is based on the nature of the monomeric units present in

the polymers as

10

(a) Homopolymers are made up of same repeating unit (monomer). Its type as

follows:

Figure 8: Pictorial representation of Homopolymers

(b) Copolymers have different repeating units (i.e composed of different mers).

Furthermore, depending on the arrangement of the types of monomers in the

polymer chain, we have the following classification:

Figure 9: Pictorial representation of Copolymers

11

1.3 Copolymers

According to IUPAC, copolymers are polymers that are derived from more

than one species of monomer. As this is a process based definition, source based

nomenclature can be easily adapted to the naming of copolymers. Importance to the

arrangement of the various types of monomeric units has been given and seven types

of arrangements have been defined. The monomer names are linked through

connectives (infix) such as –stat-,-ran-, -alt-, -per-, -block-, -graft-, and –co- for

copolymers, based on their nature statistical, random, alternating, periodic, block,

graft and unspecified respectively.

1.4 Addition polymerization

The addition polymerization can be subdivided into cationic, anionic, co-

ordinated (complexed) anionic and free radical polymerization. The cationic

polymerization involves an attack by a proton on the -electron cloud of the

monomer. The propagation is continued by the formed ‘carbonium ion’ renamed as

carbenium ion.

The anionic polymerization involves an attack by the anion from organo-alkali

compounds, strong base etc., on the -electron cloud of the monomer. The

propagation is continued by the formed carbanion. Potentially active ‘living

polymers’4 are reported with carbanions at the chain ends.

Alkenes and dienes can be polymerized using co-ordinated (complexed)

anionic catalysts. Initially a monomer catalyst complex is formed. The co-ordinated

metal –carbon bond formed in the complex acts as active site and makes propagation

12

to take place. However, the free radical governed addition or chain growth

polymerization is the most coon mode.

1.4.1 Free radical polymerization

The ‘free radical polymerization’ has received more intensive study than any

other chemical chain reaction. Countless investigations have contributed to the

industry and chemistry of free radicals. Advances in both fields continue to be made

with a particular emphasis on the growth of special polymers.

Initiators

An effective initiator is a molecule which, when subjected to heat (example:

dibenzoyl peroxide, AIBN), chemical reaction (example: ferrous ion and hydrogen

peroxide, persulphates etc.) or when exposed to electromagnetic radiation , , and

X-rays, will readily undergo homolytic fission in to radicals of greater reactivity than

the monomer radical.

Azo initiators have a long history in polymer technology. Since nitrogen is

evolved on decomposition, they have been used in Germany as blowing agents in the

preparation of light weight plastics and rubbers. Most of the compounds are

represented by the formula

CH3 C N N C CH3

RR

Q Q

13

Where R = alkyl and Q is a simple carboxylic acid residue or a derivative

(nitrile, ester etc.). 2, 2’-azobisisobutyronitrile (AIBN) (R = CH3, Q = CN) is widely

used as an initiator. 4, 4’-azo-4-cyanopentanoic acid (R = CH3, Q = (CH2)2COOH)

has rather similar initiating properties and is soluble in water unlike AIBN.

Thermal decomposition of AIBN and its analogues is generally considered to

produce cyanoisopropyl radicals (or analogues) according to

(CH3)2C N N C(CH3)

CN CN

2 2(CH3)2C CN + N2

.

The transient existence of the (CH3)2C(CN)-N=N. radical has been suggested

on the basis of ESR observations so that the cleavage of the two CN bonds may occur

consecutively rather than simultaneously.

Monomers in free radical polymerization are coonly mono-substituted or

unsyetrically (1, 1)-disubstituted ethylenes, CH2=CHX or CH2=CXY. The essential

polymerization step is a repeated free radical addition to monomer double bonds,

forming chains of carbon atoms constructed of units, either [-CH2-CHX-] or [-CH2-C

(XY)-], linked in predominantly head to tail fashion. The termination may occur

either by bimolecular coupling of two growing chains or by disproportionation or by

chain transfer.

14

1.5 Techniques of polymerization

Monomers of different structure may be polymerized in any of the three states

of matter: solid, liquid or gas. All large scale addition polymerizations are carried out

in the liquid phase. The polymerization can be done in a homogeneous liquid phase or

in a heterogeneous two phase system like solid-liquid or gas –liquid.

1.5.1 Bulk polymerization

An initiator is added to a bulk of monomer(s) which is subsequently heated to

such a temperature that the desired degree of conversion to soluble polymer is

achieved in a reasonable time of reaction. The product will be pure in the sense that it

will be contaminated only by the chemical initiator. The reaction mass can become

quite viscous in the beginning of the reaction, increasing the difficulty of mixing and

heat transfer. ‘Hot spots’ can form and unless precautions are taken, runaway or

explosive reactions can result.

1.5.2 Suspension polymerization

Suspension polymerization, otherwise called pearl or bead polymerization, can

be considered to be bulk polymerization carried out with the water-insoluble

monomers dispersed in small droplets typically 10-1000 m in diameter. The

dispersion stabilized from coalescing by using suitable water soluble protective

colloids, surface active agents and by stirring. Each monomer droplet is isolated and

is independent of the other droplets and the initiators are monomer soluble. The

product can be isolated merely by filtration.

15

1.5.3 Emulsion polymerization

Emulsion polymerization is an important technological process widely used to

prepare acrylic polymers, poly (vinyl chloride), poly (vinyl acetate) and a large

number of copolymers. The technique differs from the suspension method in that the

particles in the system are smaller, 0.05 to 5 m diameter and the initiator is soluble in

the aqueous phase rather than in the monomer droplets. The process offers unique

opportunity of being able to increase the polymer chain length without altering the

reaction rate, this can be achieved by changing either the temperature or the redox

initiator concentration. The highest concentration of the surfactant wherein all the

molecules are in a dispersed state, beyond which only the formation of hydrated

aggregates viz., “micelles” occurs is known as “critical micelle concentration”.

1.5.4 Solution polymerization

In solution polymerization, the monomer is dissolved in a suitable inert

solvent along with the chain-transfer agent whenever used. The free radical initiator is

also dissolved in the solvent medium, while the ionic and co-ordination catalysts can

be either dissolved or dispersed. The presence of the inert solvent medium helps to

control viscosity increase and promote a proper heat transfer.

The three steps of initiation, propagation and termination interact with the

effective concentration of each species essentially equal to its concentration in the

bulk; i.e., concentrations are maintained at the sites of reaction unimpeded by

diffusion control. The steady-state approximation is readily fulfilled. The choice of

16

solvent for a solution polymerization is conditioned by the possibility of chain

transfer to that solvent and the kinetic considerations assume that it is not significant.

Almost all acrylates, ethylene, vinyl acetate and acrylonitrile are polymerized

in this way. The free-radical initiated polymerization of acrylonitrile in toluene and

the redox-initiated polymerization of acrylonitrile in water are example of

‘precipitation polymerization’. This can lead to undesirable side reactions known as

“popcorn polymerization”, when tough crosslinked nodules of polymer grow rapidly

and foul the feedlines in industrial plants.

1.6 CHARACTERIZATION OF POLYMERS

The characterization is essential at each and every stage for a synthetic work

on polymers. Apart from the utilization of UV, IR, NMR techniques, characterization

of polymers involves several other techniques viz., chemical analysis, fractionation,

thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, gel

permeation chromatography etc..

1.6.1 IR Spectroscopy

IR-spectroscopy is probably the oldest of the spectroscopic methods used in

polymer science. It is basing of the analysis of molecular vibrations. IR absorption

data are very important for the theoretical studies not only for the low molecular

weight compounds but also for polymers5. The application of empirical method is

inevitable in the elucidation of the structure of polymers and for qualitative analysis.

17

The same correlation tables, can be employed for polymers as that for low molecular

weight compounds. Prior to 1960 the few normal coordinate calculations which had

been done by Kri6were limited in their detailed predictive capability by the lack of

asufficiently complete force field for the molecule and by simplifying approximations

made about the structure. The derivation of satisfactory forcefields for polymers,

which is still the most basic problem associated with a normal coordinate analysis,

began in the early 1960s, with the use of extended Urey—Bradley force fields and the

development of a detailed valence force field for hydrocarbons. Since then the

technique of normal coordinate analysis has been applied to the interpretation of the

Infrared spectra of many regular polymer structures.

Quantitative analysis of polymers are carried out by using low molecular

weight compounds or stereoregular polymers having a structure similar to the

repeating units in the sample, as standards7. IR is one of the important tools for the

solution of many problems in the studies of chemical and physical nature of polymers

and of the reactions of macromolecules.

FT-IR is a superb analytical tool for screening and profiling polymer samples.

FT-IR identifies chemical bonds in a molecule by producing an infrared absorption

spectrum. The resulting spectra produces a profile of the sample , a distinctive

molecular fingerprint that can be used to easily screen the samples for many different

components.

18

1.6.2 Nuclear Magnetic Resonance

Polymer characterization by NMR provides detailed structural information on

polymers. Among the earliest applications, NMR spectroscopy was the highly

structure determination of polymers, including both homopolymers and copolymers.

Bovey8 found the use of 1H-NMR to be a fertile field to characterize the

microstructure of hydrocarbon polymers. He used 19F-NMR for the characterization

of fluoropolymers. In addition, Bovey pioneered the use of statistics to explain the

numbers and relative abundances of lines in spectra. From those early days , NMR

continues to be one of the most important instrumental methods for characterizing the

microstructures of polymers.

When dissolved in suitable solvents, polymers give so-called “high-

resolution” – NMR spectra in which the resonance lines are narrow, being only a

small fraction (10-3 to 10-4) of the width produced by the solid state. A series of

investigations has proved that these high resolution NMR spectra of polymers are of

great value in solving certain difficult problems of chain structure9, in estimating the

composition of the constitutent monomeric units in the copolymer. 13C-NMR

technique can be applied easily to problems dealing with oligomers, conformational

sequences and quantitative analysis10 comprising the estimation of composition11 of

monomeric units in copolymers. Currently 13C-NMR, because of its larger

dispersivness, has mostly taken over this task from 1H-NMR.

19

1.6.3 X-ray Diffraction

X – ray diffraction (XRD) provides important solid-state structural

information for polymers and composites. Useful XRD analysis data is obtained from

crystalline, semi-crystalline, amorphous, polymeric and composite materials. It is

almost a century that, X-Ray diffraction (XRD) was being used for the

characterization of metals and relatively, from not very long back it is used for the

polymers as well. Generally, polymers are considered as amorphous materials;

however, it is due to the regularly arranged polymer chains (random crystallite

domains called as crystallite lamella), many polymers exhibit varying amount of

crystallinity and hence can be characterized by X-Ray diffraction technique. XRD

techniques are used to identify the state of polymer, i.e. either crystalline, semi-

crystalline or amorphous etc., to calculate percentage crystallinity, to identify

polymers and llers and their quanti cation12.

This technique is perhaps the ultimate tool in the determination of the

structure of a molecule. The crystal structures of many different polymers have been

determined by X-ray diffraction.

1.6.4 Molecular weight determination

Polymer properties are closely related to their molecular mass, size and

structure. The growth of the polymer chain during their synthesis is dependent upon

the availability of the monomers in the reaction mixture. Thus, the polymer sample

contains chains of varying lengths and hence its molecular mass is always expressed

20

as an average. The molecular mass of polymers can be determined by chemical and

physical methods. One of the challenges polymer scientists face is molecular weight

(avg. chain length) determination of their materials. While membrane osmometry, gel

permeation chromatography, viscosity analysis and mass spectrometry are typically

used for molecular weight determination, the techniques can be time consuming,

inaccurate for the molecular weight ranges involved or require specialized

instrumentation. End group analysis by NMR offers an easy alternative method using

an instrument coonly found in many analytical labs. In addition, NMR analysis can

also be used to accurately determine monomer ratios for various copolymer

molecules.

Through molecular weight determination of polymers by the study of

colligative properties has serious limitiations, osmotic pressure measurements can be

helpful to some extent apart from light scattering, viscosity measurement and ultra

centrifuge methods.Gel permeation chromatography, i.e., size exclusion

chromatography has become a prominent and widely adopted method for estimating

molecular weight distributions13since its discovery by W.R. Moore in 1961.

1.6.5 Thermal analysis

In thermal analysis, the properties are measured as a function of temperature

or time. The various methods used include, Evolved – Gas Analysis (EGA),

Differential Thermal Analysis (DTA), Thermo Gravimetric Analysis (TGA) and

Differential Scanning Calorimetry (DSC). In DTA, the temperature difference

21

measured between the sample and reference chamber is a function of time or

temperature as heat is supplied to both the chambers, while in DSC the heat flow

associated with the sample chamber is compared to the heat flow associated with the

reference chamber as a function of time or temperature.

DSC and TGA methods lead to the determination of quantities like

temperature ranges and heat effects in transitions and degradations of polymers. DSC

also gives information about the molecular ordering, heat of fusion, entropy of fusion,

melting temperature and about glass transition temperature (Tg).

The approximate Tg value for the copolymers can be calculated from a

knowledge of the weight fraction ‘w’ of each monomer type and the Tg of each

homopolymer.

(1)

1.6.6 The copolymer composition equation

After the preliminary and purely theoretical considerations of Dostal14, Wall15

attacked the problem of copolymer composition as a function of monomer ratio.

There are two distinct propagation steps involved in the copolymerization of two

monomers viz., the attack on each of the two monomers by the growing chain free

radicals. No distinction is made between two types of growing free radicals which are

present. If monomer M1 reacts with the growing chain free radicals with a rate

constant k1 and the monomer M2 reacts with the growing chains with a rate constant

22

k2, it is clear that the ratio of the rates of addition of the two monomers will be given

by the expression

------- (1)

where M1 and M2 represent the molar concentrations of the respective monomers.

The above equation gives directly the ratio of the rates at which the two monomers

are used and hence the chemical composition of the copolymer at the initial

concentration of M1 and M2. At first, experiments of Marvel et.al16. seemed to

confirm the conclusion drawn from the above simple relation. But subsequently more

systematic studies by Mayo et.al17 showed that the ratio k2/k1 varied noticeably with

the initial monomer ratio and this made a more elaborate treatment necessary.

This consisted in the introduction of four propagation steps. Such a

generalization had been suggested earlier by Dostal and by Norish and

Brookman18,19and leads to the following considerations.

A growing chain with a terminal group of the type m1 can react with a

monomer M1 or a monomer M2; likewise the other type of free radical chain end,

having an m2 terminal group, can react with either type of monomer. The four

reactions are as follows:

23

Propagation reactions during copolymerization

Propagation

Reactions Growing

chains Adding

monomer Rate of

Process

Reaction

Product

A ~~~~~ m1. M1 K11(m1

.)( M1) ~~~~ m1m1.

B ~~~~~ m1. M2 K12(m1

.)(M2) ~~~~ m1m2.

C ~~~~~ m2. M2 K22(m1

.)(M2) ~~~~ m2m2.

D ~~~~~ m2. M1 K21(m1

.)(M2) ~~~~ m2m1.

In the steady-state of copolymerization, each type of free radical must be

maintained at a certain characteristic concentration; hence

------- (2)

It is now possible to express m2 in terms if

------- (3)

The rates of consumptions of the monomers M1 and M2 are given by

------- (4)

------- (5)

24

The ratio between the rates of disappearance of M2 and M1 is given by

------- (6)

The unknown absolute values of radical concentrations(m1) and (m2) can be

eliminated from the above equation

------- (7)

If the reactivity ratios r1 and r2 were defined as

and

------- (8)

The above copolymer equation in the differential form is valid at any

conversion for relating the instantaneously forming copolymer with the instantaneous

monomer composition .The ratio of the rates of addition of the two monomers is also

the ratio of the molar concentrations of the two monomers in the resulting copolymer.

This ratio can be expressed by m1/m2. The copolymer composition equation which is

valid only for the composition of the initial copolymer formed at monomer

concentrations M1 and M2 can be expressed as

------- (9)

Considering the penultimate group effects, extension were made later of the

copolymer composition equation20.

25

1.6.7 DETERMINATION OF REACTIVITY RATIOS

The determination of monomer reactivity in copolymerization is entirely

dependent on the accuracy of analysis of the products of low conversion experiments.

Hams method21

The mole-fraction-composition of copolymers is plotted as a function of the

monomer mixture for which it is derived. A judicious selection of r1 and r2 values for

theoretical curves should result in a good fit of the experimental data in a few trials.

1/r1 is equal to the initial slope of the composition curve at 100% A and 1/r2 is equal

to the slope at the curve at 100%B.

Barb’s method22

(y-1), where y is the ration of A and B in copolymer , is plotted against x, the

ratio of the monomers A and B. The limiting slope corresponds to r1. The re-

indexing of monomers is done and (y’-1) is plotted against x’, wherein the limiting

slope corresponds to r2.

Intersecting slopes method23

r1 is allowed to take on selected values in the copolymerization equation for a

single copolymerization result and r2 is plotted as a function of r1. Similar plots are

26

made for other copolymer experiments in the same system and the straight lines

should intersect at a coon point with the co-ordinates of correct r1 and r2.

Fineman-Ross method24

The composition of the copolymer expressed in the copolymer equation is

------- (10)

------- (11)

(upon introduction of the transformed variables x = M1/M2 and y = m1/m2)

(upon rearrangement and division by y)

upon introduction of the transformed variables and

------- (12)

A plot of G Vs. F gives a straight line with a slope equal to r1 and intercept

equal to r2.

27

Kelen-Tudos method

The main advantage of the proposed equation is that it is very well adaptable

for visual determination of the applicability of the copolymer composition equation.

If the experimental data were adequate to the equation, the procedure offers a simple

and reliable method for the graphical determination of copolymerization constants

owing to the following factors;

The relationship applied is invariant with respect to the inversion of data (re-

indexing of monomers and reactivity ratios)

The domain of the independent variable is in the interval (0,1); and

with appropriate choice of the parameters of the equation, the experimental

data are located syetrically along wthe interval (0,1).

(i)The Standard method25,26

The graphically evaluable linear equation is

------- (13)

where the transformed variables are = G / +F and = F / + F

is the geometric mean of the minimum and maximum F values for a set of data ; and

G and F are the variables defined in Fineman -Ross equation. By plotting values

against values, a straight line is obtained which when extrapolated to =0 and = 1

gives –r2/ and r1 (both as intercepts).

28

(ii)The Extended Method27,28

The earlier methods for the determination of copolymerization constants viz.,

Walling – Briggs method and Ezrielev method utilized the factor z.

------- (14)

Where 1 and 2 are the copolymerization constants (often referred to as r1

and r2) and x0 is the actual mole ratio of monomers in the mixture yet to be reacted.

Kelen-Tudos considered the factor z to be constant in the copolymer equation:

------- (15)

Which integrates to

And in turn written as

------- (16)

Where and )

w= wt. % conversion

29

= Molecular weight of monomer 2 / molecular weight of monomer 1

To determine the reactivity ratios, the equation

------- (17)

is worked out wherein

= G /

= F / ` + F

G = (y – 1) / z

F = y /z2

` = Geometric mean of minimum and maximum F values

By plotting the values against values, a straight line is obtained which

when extrapolated to = 0 and = 1 gives –r2 / ` and r1 ( both as intercepts)

compared to the usual experimental errors, the error of approximation is negligible

upto 50% conversion and thus does not affect the reliability of the parameters

determined.

1.6.8 Reactivity ratios and Copolymerization behavior

In the derivation of the copolymer equation, considering the propagation

reactions designated A,B,C and D (c.f. Table 1), r1 = k11/ k12 and r2 = k22 / k21. When

r1 = 1, the propagation rate constants are the same for the reactions A and B. When r2

= 1, the propagation rate constants are the same for the reactions C and D.

30

Depending upon the values of r1 and r2, various copolymerization behaviours are

possible.

(i) When r1 = r2 = 1

All the four propagating reactions A,B,C, and D are equally possible. The

probablility of M1 or M2 adding to ~~~~m1 or ~~~~m2 depends purely on the

monomer concentrations. The copolymer formed will have the same ration of the

monomeric components as that of the initial monomers, with the two components in

the chain in a purely random sequence. This behaviour is known as ideal

copolymerization behaviour.

(ii) When r1 = r2 = 0

The propagation reactions A and C are not at all possible and reactions B and

D are only possible. Hence, the copolymer formed will have an equal. The

propagation reactions A and C are not at all possible and reactions B and D are only

possible. Hence the copolymer formed will have an equal number of M1 and M2

monomeric units arranged alternatively in the formed copolymer chain irrespective of

the initial monomer ratio.

(iii) When r1> 1 and r2< 1

Reactions A and D will be preferred to reactions B and C. Hence, the

probability of M1 entering into the copolymer chain is higher as compared to M2. The

copolymer formed will be richer in M1.

31

(iv) When r1< 1 and r2> 1

Reactions B and C will be preferred to reactions A and D and the probability

of M2 entering into the copolymer chain is more. The copolymer formed will be richer

in M2.

(v) When r1< 1 and r2< 1

Reactions B and D will be preferred to reactions A and C. M2 can add on to

~~~~m1 and M1 can add on to ~~~~m2 at the same time. The preference for one of

these two will depend on the actual values of r1 and r2 and also on the initial monomer

ratio. When r1 and r2 are equal, the copolymer formed will be richer in M1 upto an N1

value of 0.5 and then onwards the copolymer will be richer in M2. At N1 = 0.5, the

copolymer formed will have an n1 value of 0.5. Since this composition of the initial

monomers results in the formation of a copolymer with the same monomeric

composition, it is called ‘azeotropic composition’. The azeotropic composition will

be above 0.5 if r1> r2 and will be less than 0.5 if r1<r2 ( N1 and n1 refer to M1 and m2

respectively; the terms used later in the thesis for initial mole fraction of monomers

and mole fraction of monomeric units in copolymer).

(vi) When r1> 1 and r2> 1

Such system does not undergo random copolymerization though theoretically

possible. It forms either a mixture of two homopolymers or under favourable

conditions block copolymers having long sequence of M1 followed by a long

sequence of M2.

32

(vii) When either r1 = 0 or r2 = 0

Such a system usually results in a copolymer with a particular azeotropic

composition. If the mole fraction of the monomer with a zero reactivity ratio remains

below the azeotropic composition, the azeotropic copolymer will be formed along

with the homopolymer of the comonomer.

1.6.9 STRUCTURE-ACTIVITY RELATIONSHIP

The chemical composition of a copolymer is determined by the competition

of the two monomers for both types of free radicals viz., growing chain ends. The

reactivity of a monomer in copolymerization depends upon its molecular structure and

the following six important factors contribute to the reactivity.

(i) Steric factor

Monomers which possess substituents on both carbon atoms of the carbon-

carbon double bond (1,2 - disubstituted ethylene) exhibit a certain reluctance to add to

themselves in the growing chain, although they may add to vinyl free radicals quite

readily. This is believed to be a steric effect. These types of monomers exhibit

practically no tendency to polymerize alone but often copolymerize readily with vinyl

monomers. Maleic anhydride reacts with styrene-free-radical about 20 times as fast

as does styrene; although maleic anhydride will not add to the maleic – anhydride –

radical at all. Over a wide range of monomer ratios, the copoly(styrene / maleic

anhydride) is therefore exactly 50 to 50 with a regular alternating structure.

33

The addition of 1,1-disubstituted ethylenes to growing free radicals will be

sterically hindered if the two substituents are sufficiently large. The most coon

monomers of this type, such as vinylidene chloride, methyl methacrylate and

methacrylonitrile add quite readily, both to vinyl radicals and to their own radicals.

Thus 1,1- disubstitution does not introduce nearly as serious a steric effect as does 1,2

– disubstitution. However in –Methylstyrene this is probably beginning to play a

role and in 1,1-diphenyl ethylene it appears to be very significant.

(ii) Conjugation factor

The reactivity is governed by the extent of conjugation of the double bond

with the unsaturated groups in the substituent. Styrene exhibits a strong tendency to

add to any radical-chain-end because the resulting adduct-free-radical is strongly

stabilized by resonance. This effect is identical to the one which makes the triphenyl

methyl radical that much stable. Vinyl acetate, on the contrary exhibits a weaker

tendency to add to any given radical, because the resulting adduct radical, in this case,

is much less stabilized by resonance. When styrene and vinyl acetate must compete

with each other for a given free radical, styrene is 30 to 50 times as reactive as vinyl

acetate.

(iii) Polarity factor

The electronic polarity of the double bond is another important factor. A

substituent such as –C = N which is meta directing in the benzene ring, can be

expected to withdraw electrons from the polarisable double bond thereby giving the

34

terminal carbon a positive character. It seems reasonable to assume that such a group

will also give a positive polarity to a free radical. Other substituents such as –C6H5, -

CH3 or –OCH3 which are electron donating exhibit an opposite effect. A free radical

with a positive character will exhibit a particular preference for a monomer with a

negatively charged double bond and vice versa.

(iv) Haett factor

The effect of meta- and para- substituents in the benzene ring, on reaction

rates and equilibria in many polar reactions is expressed by

Where k and k0 are either rates or equilibrium constants for the side chain

reactions of substituted benzene rings and is the constant related to the substituent

and is a constant related to the specific type of reaction.

It has been found that the relative reactivities of a series of ring substituted

styrenes with styrene-type radical can be correlated with Haett’s value for the

substituent. A very good straight line is obtained when logarithms of the relative

reactivities are plotted against values of the substituents.

35

(v) Formation of ion-radicals

In the case of certain monomers pairs, which exhibit particularly large

alternation tendencies in copolymerization, it has been suggested that the transition

state much involve ion-radical forms, similar to those which contribute to the stability

of certain molecular compounds. Explanation has been given, for the high reactivity

of maleic anhydride for styrene-type radicals, in terms of the stabilizing contribution

of structure such as

Many similar structures can be drawn differing in the location of the positive

charge, the negative charge and the unpaired electron.

(vi) Resonance effect and polar character

A semi-quantative scheme (the Q, e-scheme) has been proposed in which the

specific reactivity of a monomer (determined by the resonance effect) is denoted by

Q, and the polar character of the radical-adduct is denoted by e. In this scheme, the

copolymerization reactivity ratios can be given by the following equations:

r1 = Q1 /Q2 exp [-e1(e1-e2)] ------ (18)

r2 = Q2 /Q1 exp [-e2(e2-e1)] -------(19)

36

The Q-e scheme29 represents an attempt to combine the recognized effects of

resonance stabilization and polarity on the relative reactivities of various monomers,

with various free radicals in, at least, a semi-quantitative fashion.

Initially a scheme was developed which could account for the data reported by

Lewis, Mayo and Hulse on the monomers styrene, methyl methacrylate, acrylonitrile

and vinylidene chloride, while remaining consistent with all other information

available on copolymerization at that time. Styrene was arbitrarily taken as a standard

of general reactivity and given the Q value of unity and e value of negative unity. In

view of the sketchy character of this analysis, it is probably best to consider the Q-e

scheme as an empirical method of correlation which has quasi-theoretical significance

rather than a theoretical equation in the usual physiochemical sense. The Q-e scheme

was then expanded by assigning a different e value (-8) to the monomer, styrene.

Once the Q and e values for different monomers are known, the r1 and r2

values for any chosen pair among these monomers can be computed. The scheme

suggests that:

Monomers with widely differing Q values do not copolymerize.

Monomers with widely differing e values have a tendency to form alternating

copolymers; and

Monomers having roughly equal Q values and almost identical e values will

undergo azeotropic copolymerization.

37

The Q-e scheme was later extended to systems containing three or more

monomers. A modified copolymerization equation has also been developed utilizing

the parameters q and in place of Q and e wherein the equations for r1 and r2 are:

r1 = exp [-(q1-q2)/RT]. exp [-7.23 x 10201 ( 1 - 2) / RT] (20)

r2 = exp [-(q2-q1)/RT]. exp [-7.23 x 10202 ( 2 - 1) / RT] (21)

The advantage of this modification is that the parameters q (expressed in kcal / mole)

and (expressed in e.s.u.) are temperature independent.

1.6.10 Antimicrobial activity

An antimicrobial is a substance that kills or inhibits the growth of

microorganisms30 such as bacteria, fungi, or protozoans. Antimicrobial drugs either

kill microbes (microbiocidal) or prevent the growth of microbes (microbiostatic).

Disinfectants are antimicrobial substances used on non-living objects or outside the

body.

The history of antimicrobials begins with the observations of Pasteur and

Joubert, who discovered that one type of bacteria could prevent the growth of another.

They did not know at that time that the reason one bacterium failed to grow was that

the other bacterium was producing an antibiotic. Technically, antibiotics are only

those substances that are produced by one microorganism that kill, or prevent the

growth, of another microorganism. Of course, in today’s coon usage, the term

antibiotic is used to refer to almost any drug that attempts to rid your body of a

38

bacterial infection. Antimicrobials include not just antibiotics, but synthetically

formed compounds as well.

Thus antimicrobials gained interest in both academic research and industry

due to their potential to provide quality and safety benefits to many materials.

Antimicrobial agents of low molecular weight are used for the sterilization of water,

as antimicrobial drugs, as food preservatives, and for soil sterilization. The use of

antimicrobial polymers offers promise for enhancing the efficacy of some existing

antimicrobial agents and minimizing the environmental problems accompanying

conventional antimicrobial agents by reducing the residual toxicity of the agents,

increasing their efficiency and selectivity, and prolonging the lifetime of the

antimicrobial agents.

A variety of methods are found for this purpose and since not all of them are

based on same principles, results obtained will also be profoundly influenced not only

by the method selected, but also by the microorganisms used to carry out the test, and

by the degree of solubility of each test-compound31. The test systems should ideally

be simple, rapid, reproducible, and inexpensive and maximize high sample throughput

in order to cope with a varied number of extracts and fractions. The complexity of the

bioassay must be defined by laboratory facilities and quality available personnel

testing of antifungal natural products, methodologies, comparability of results and

assay choice. Rapid detection and subsequent isolation of bioactive constituents of

crude plant extract have been done32,33. The currently available screening methods for

the detection of antimicrobial activity fall into three groups, including bioautographic,

39

diffusion (disc diffusion and well diffusion), and dilution methods. The

bioautographic and diffusion methods are known as qualitative techniques since these

methods will only give an idea of the presence or absence of substances with

antimicrobial activity. On the other hand, dilution methods are considered quantitative

assays as they determine the minimal inhibitory concentration34

Screening methods

In order to suggest methodologies for screening the antimicrobial activity,

two different qualitative methods were evaluated as follows:

agar diffusion test,employing two different types of reservoirs (filter paper

disc impregnated with compound-test and wells in dishes) and

bioautographic method (agar diffusion and chromatogramlayer).

dilution method used for the determination of minimum inhibitory

concentration (MIC).

Agar diffusion well-variant

The bacterial inoculum was uniformly spread using sterile cotton swab on a

sterile Petri dish MH agar. Nine serial dilutions yielded concentrations of 100, 80, 60,

40, 20, 10, 5, 2.5, and 1.25 mg/mL for extracts and fractions and four serial dilutions

yielded concentrations of 20, 15, 10, 5 mg/mL for pure substances. 50 µL of natural

products were added to each of the 5 wells (7 diameter holes cut in the agar gel, 20

apart from one another). The systems were incubated for 24 h at 36 ± 1ºC, under

40

aerobic conditions. After incubation, confluent bacterial growth was observed.

Inhibition of the bacterial growth was measured in mm35.

Agar diffusion disc-variant

Natural products were dissolved and diluted with solvents as mentioned

previously. Same number of subsequent dilutions was performed as described above.

However, natural products serial dilutions were performed out of initial

concentrations 2.5 greater than the ones performed for well-variant method (i.e.250

mg/mL for extracts and fractions and 50 mg/mL for pure substances); 7 filter paper

discs (Whatman, no. 3) wereimpregnated with 20 mL of each of the different

dilutions. The discs were allowed to remain at room temperature until

completediluent evaporation and kept under refrigeration until ready to be used. Discs

loaded with natural products were placed onto the surface of the agar. Coercial

chloramphenicol discs(30mg) and paper discs impregnated with 20 mL of diluents

used to dilute natural products were used as control. Tests were performed in

duplicate .

Bioautographic method direct-variant (chromatogram layer)

Direct variant of the bioautographic method carried out in this work is

outlined as follows: (1) preparation and application of natural products on thin layer

chromatography plates (TLC) (silica gel G60 F254, Merck); (2) preparation and

application of the bacterial inoculum to TLC plates; (3) incubation; and (4) growth

detection by colorimetric assay (INT) and measurement of growth inhibition

diameters.

41

Dilution Methods

Dilution susceptibility testing methods are used to determine the minimal

concentration of antimicrobial compound to inhibit or kill the microorganisms. This

can be achieved by dilution of antimicrobial compound in either agar or broth media.

REAGENTS

1. Muller Hinton Agar Medium (1 L)

The medium was prepared by dissolving 33.9 g of the coercially available

Muller Hinton Agar Medium (HiMedia) in 1000ml of distilled water. The dissolved

medium was autoclaved at 15 lbs pressure at 121°C for 15 minutes. The autoclaved

medium was mixed well and poured onto 100 petriplates (25-30ml/plate) while still

molten.

2. Potato Dextrose Agar medium ( 1 L )

The coercially available (HiMedia) potato dextrose agar medium (39 g) was

suspended in 1000ml of distilled water. The medium was dissolved completely by

boiling and was then autoclaved at 15 lbs pressure (121ºC) for 15 minutes.

3. Nutrient broth (1L)

One litre of nutrient broth was prepared by dissolving 13 g of coercially

available nutrient medium (HiMedia) in 1000ml distilled water and boiled to dissolve

the medium completely. The medium was 44 dispensed as desired and sterilized by

autoclaving at 15 lbs pressure (121ºC) for 15 minutes.

42

Broth Dilution Method

The Broth Dilution Method is a simple procedure for testing a small number

of isolates, even single isolate. The pure cultures of Escherichia coli, Pseudomonas

aeruginosa Staphylococcus aureus, and Bacillus subtilis are sub-cultured in nutrient

broth. And the inoculated broth tubes were incubated at 37°C for 24 hours. After

completion of incubation period, when growth was observed the tubes were kept into

2-8 C until use.

Anti-fungal assays

Anti-fungal assays were followed as per the National Coittee for Clinical

Laboratory Standards, USA. Samples (crude extracts and sub-fractions) were stocked

in solvent DMSO (<1%). The sample solution was further diluted to 1:10 with

RPMI1640 medium prior to test. Each sample was then 1:2 diluted and divided into

10 tubes. The four strains were grown to 104 CFU per ml and then coincubated with

samples for 72 h at 28 °C. The anti-fungal agent, ketoconazole, was used as the

positive control. For the conventional micro-dilution procedure, the growth in each

sample well was compared with that of growth control with the aid of a reading

mirror. Each micro-dilution well was then given a “numericalscore” shown as

following:

4 meant no reduction in growth;

3 indicated a slight reduction in growth or approximately75% the growth of

the growth control (drug-free medium);

43

2 implied a prominent reduction in growth or approximately 50% the growth

of the growth control;

1 was a slight growth or an approximately only 25% growth relative to the

growth control and

0 showed optically clear or absence of growth.

The minimal inhibitory concentration (MIC) was then determined for each test

sample36.

1.7 REVIEW OF LITERATURE

The hydrolytic release of 5-chloro-8-hydroxyquinoline (HQ) from 5-chloro-8-

quinolinylacrylate (AQ) containing polymers was studied under physiological

conditions (pH 7.2 and 37°C) as well as in acidic and alkaline medium. The

hydrolysis rate was influenced by autocatalytic process with participation by

quinolinyl groups as well as by neighboring groups. For copolymers of AQ and

acrylamide (AM), the release rate increased with increasing pH, temperature, and the

content of hydrophilic monomer. The antimicrobial activity of the copolymers was

found to be related to their hydrolysis behavior. The attachment of a biologically

active agent to a macromolecular carrier can prolong its effect37.

The homopolymer, poly (8-QA) and its copolymers with methyl methacrylate

(A) in different monomer feed ratio were prepared by free radical polymerization

using dimethyl formamide (DMF) as a solvent and 2,2 -azobis-isobutyronitrile

(AIBN) as an initiator. The resulting polymers were characterized by IR spectroscopy,

44

UV-visible spectrophotometry, gel permeation chromatography (GPC), solution

viscosity and thermal analysis (TG and DSC). It was observed from the GPC results

that as the 8-QA content in the copolymer increases, the molecular weight decreases

whereas polydispersity increases with increasing 8-QA content in the copolymers. It

was also observed from the TG data that the initial decomposition temperature (IDT)

of thecopolymers decreases with increasing 8-QA content in the copolymers38.

Copolymers of N-vinylcarbazole and acrylamide were synthesized by the free

radical polymerization using AIBN as initiator39. Copolymer electrodes were prepared

by casting from 3% solution on platinum and stainless steel substrate. The response of

electrodes to dopamine was tested by cyclic voltaetry and results suggest that

depending on conditions the electrode shows reversible and stable behavior during

the 14 days and it seems to be a suitable sensor electrode to dopamine. Stability of

copolymer coating was investigated for stainless steel electrodes in sulfuric acid and it

is found that copolymer coating can inhibit the corrosion of stainless steel up to 94%.

Biocompatibility of novel polyacrylamide copolymer suitable for intra–ocular

lenses was studied by P.D. Hamilton et al.40 Polyacrylamide was chosen for its high

resistance to UV and biodegradation; however, the acrylamide monomer is a known

neurotoxin primarily due to their active carbon–carbon double bond. Since this

double bond is consumed in the polymerization reaction, the formed polymer should

not exhibit this toxicity. Because the re–gelling process allows to exhaustively wash

the formed polymer free of any low molecular weight toxic components, should be

able to produce a biocompatible re–gelled material with little or no toxicity.

45

P.Pazhanisamy et al.41 studied the Copolymerization of

N-cyclohexylacrylamide (NCHA) and n-butyl acrylate (BA) was carried out in

dimethylformamide at 55±1°C using azobisisobutyronitrile as a free radical initiator.

The reactivity ratios of the monomers were determined by both linear and non-linear

methods. Mean sequence lengths of copolymers are estimated from r1 and r2 values. It

shows that the BA units increases in a linear fashion in the polymer chain as the

concentration of BA increases in the monomer feed.

The monomer 4-methylcoumarylacrylate (4-MCA) was synthesized from 7-

hydroxy-4-methylcoumarin and characterized by conventional methods. Homo and

copolymers of 4-methylcoumarylacrylate and styrene were synthesized with different

feed ratios using N,N-dimethylformamide (DMF) as a solvent and 2,2 -

azobisisobutyronitrile as an initiator at 70°C.The resulting polymers were

characterized by infrared spectroscopy. Copolymer compositions were determined by

nuclear magnetic resonance spectroscopy. The monomer reactivity ratios were

determined by applying the conventional linearization method of Fineman–Ross and

Kelen–Tudos. The reactivity ratios values of 4-methylcoumarylacrylate and styrene

obtained from F–R plot are 1.36 and 0.62, respectively, and from K–T plot 1.24 and

0.58, respectively42.

The methacrylic monomer, 4-biphenylmethacrylate (BPM) was synthesized

by reacting 4-biphenyl phenol dissolved in ethyl methyl ketone (EMK) with

methacryloyl chloride in presence of triethylamine as a catalyst. The copolymers of

BPM with glycidyl methacrylate (GMA) were synthesized by free radical

46

polymerization in EMK solution at 70±1 °C using benzoyl peroxide as a free radical

initiator.The thermogravimetric analysis of the polymers showed that the thermal

stability of the copolymer increases with BPM content. The copolymer composition

was determined using 1H-NMR spectra43.

Important heterocyclic acrylic copolymers of 7-acryloyloxy-4-

methylcoumarin (AMC) with vinyl acetate (VAc)44 and with methyl acrylate (MA)45

were synthesized in DMF (dimethyl formamide) solution at 70±1°C using 2,2 -

azobisisobutyronitrile (AIBN) as an initiator with different monomer-to-monomer

ratios in the feed. The polymers showed moderate thermal stability which were

determined by thermogravimetry (TG) and differential thermal anlaysis (DTA).

Copolymers' compositions were determined by 1H-NMR spectra. Further, the

linearization method of Finemann-Ross , Kelen-Tudos and extended Kelen-Tudos

were employed to calculate the monomer reactivity ratios. These values suggest that

MA is more reactive than AMC. Antimicrobial activities of different copolymers

synthesized were also studied against different bacteria, fungi, and yeasts.

Copolymers of 2,4-Dichlorophenyl methacrylate with Styrene was also

studied by N. Patel et al46. The free-radical initiated copolymerization of 2,4-DMA

with styrene was carried out in a toluene solution at 70°C using

2,2 -azobisisobutyronitrile (AIBN) as an initiator with different monomer feed ratios.

The monomer 2,4-DMA and the copolymers were characterized by Fourier transform

infrared spectral studies. Copolymer composition was determined by

UV-spectroscopy. The reactivity ratio of the monomers was obtained employing the

47

conventional linearization method of Fineman–Ross. The molecular weights

(M¯w, M¯n) and polydispersity index of the polymers were determined using gel

permeation chromatography. Thermogravimetric analysis (TGA) of the polymers was

carried out in nitrogen atmosphere. Antimicrobial effects of the homo- and

copolymers were also investigated for various microorganisms.

Copolymerization of different feed compositions of HPA with glycidyl

methacrylate (GMA) was carried out using benzoyl peroxide (BPO) as initiator in

EMK solvent under nitrogen atmosphere at 70±1 °C. Polymers thus synthesized were

characterized by IR and NMR (1H/13C) spectroscopic techniques. Reactivity ratios of

the monomers were calculated from the 1H-NMR data by applying linearization

methods such as Fineman–Ross, Kelen–Tudos and extended Kelen–Tudos methods.

Photocrosslinking property of the polymer samples was studied using the solvent

method. Thermal stability of the polymers were measured using thermogravimetric

analysis. Molecular weights (M w and M n) and polydispersity value of the polymer

were determined using gel permeation chromatographic technique47.

Water-soluble acrylamide copolymers of a series of poly(methacrylamide-co-

acrylamide)s and some homopolymer control products were prepared48. The

copolymer products generally had lower molecular weights than those obtained from

the control polyacrylamide preparations. Copolymer samples with comparable

molecular weights did have larger radii of gyration and intrinsic viscosities than

samples of control polyacrylamides.

48

A new functional activated acrylate, 4-acetamidophenyl acrylate (APA) was

synthesized and characterized by IR, 1H- and 13C-NMR and mass spectra. Homo and

copolymers of APA with A and GMA were prepared by free radical polymerization.

All the copolymer compositions have been determined by 1H-NMR and the reactivity

ratios of the monomer pairs have been evaluated.. Thermal stability and molecular

weights of the copolymers were reported49. The kinetics of the copolymerization of

methyl methacrylate with phenylacrylate in solution at low conversions have been

examined50.

Copolymers of N-(2-hydroxypropyl)methacrylamide which contained up to 20

mol % of p-nitrophenyl esters of N-methacryloylated oligopeptides, and of N-

methacryloylaminophenoxyacetic acids (o-, m-, p-) have been prepared. The

aminolyses of these polymers with tert-butylamine, ampicillin and 6-

aminopenicillanic acid were kinetically characterized. Based on these results polymer

bound ampicillin and polymer bound 6-aminopenicillanic acid were prepared. These

preparations possessed antimicrobial activity; they inhibited the growth of

Staphylococcus aureus51.

Patel et al . studied the Copolymer of monomer 2,4-dichlorophenylacrylate

(2,4-DCPA) and methylmethacrylate (A) were synthesized with different monomer

feed ratio using dimethylformamide (DMF) as a solvent and 2,2(-

azobisisobutyronitrile (AIBN) as an initiator at 70°C. The copolymers were

characterized by IR-Spectroscopy and copolymer composition was determined with

UV-Spectroscopy. The linearization method of Fineman Ross (F-R) and Kelen Tudos

49

(K-T) were used to obtain the monomer reactivity ratios. Thermal analyses of

polymer were carried out in nitrogen atmosphere thermal gravimetric analyses (TGA)

and differential thermal analyses (DTA). The homo and copolymers were tested for

their antimicrobial properties against selected microorganisms52.

Free-radical copolymerization of 4-nitrophenyl acrylate (NPA) with n-butyl

methacrylate (BMA) was carried out using benzoyl peroxide as an initiator. Seven

different mole ratios of NPA and BMA were chosen for this study. The copolymers

were characterized by IR, 1H-NMR, and13C-NMR spectral studies. The molecular

weights of the copolymers were determined by gel permeation chromatography and

the weight-average (Mw) and the number-average (Mn) molecular weights were

calculated. The reactivity ratios of the monomers in the copolymer were evaluated by

Fineman–Ross, Kelen–Tudos, and extended Kelen–Tudos methods. The product

suggests a random arrangement of monomers in the copolymer chain53.

Copolymers with various proportions of phenacyl methacrylate (PAMA) and

glycidyl methacrylate (GMA) were prepared by free radical-polymerization in

solution in 1,4-dioxane using 2,2 -azobisisobutyronitrile as initiator at 70°C. The

polymers were characterized by infrared and 1H and 13C - nuclear magnetic resonance

(NMR) spectroscopy. The copolymer compositions were determined by 1H-NMR

spectra. The reactivity ratios were calculated by both Fineman–Ross and Kelen–

Tüdös methods. Glass transition and decomposition temperatures of copolymers were

determined54.

50

Glass transition temperature was determined by DSC thermograes of mixtures

of poly(methyl methacrylate-co-ethyl acrylate), PA-EA, of different microstructure of

macromolecular chains, exhibit two glass transition temperatures, Tg, indicating the

presence of two phases. In one phase the copolymer chains are compatible with long

blocks of ethyl acrylate and the second phase is very rich in long chains of methyl

methacrylate55.

Co-polymers of N-phenyl methacrylamide with glycidyl methacrylate56 and

methyl methacrylate57 of different compositions were synthesized by free radical

solution co-polymerization of the monomers in dimethylformamide using benzoyl

peroxide as the initiator at 70°C. Solubility of the co-polymers was tested in various

solvents. The molecular structure of the co-polymers was elucidated by infrared and

proton nuclear magnetic resonance spectroscopy. The composition of the co-polymers

was determined from their 1H-NMR spectra by using the intensities of aliphatic and

aromatic protons present in the co-polymer. The Fineman-Ross and Kelen-Tüdos

models have been employed to determine the reactivity ratios of the monomers.

Copolymers of 4-Propanoylphenyl Acrylate with methyl Methacrylate were

characterized by FT-IR, 1H-NMR and 13C-NMR spectroscopic techniques. The

compositions of the copolymers were determined by 1H-NMR analysis. The reactivity

ratios of the monomers were determined using Fineman-Ross ,Kelen-Tüdös ,and Ext.

Kelen-Tüdös as well as by a nonlinear error-in-variables model (EVM) method using

a computer program, RREVM . Thermogravimetric analysis of the polymers reveals

that the thermal stability of the copolymers increases with an increase in the mole

51

fraction of A in the copolymers. Glass transition temperatures of the copolymers were

found to increase with an increase in the mole fraction of A in the copolymers58 .

Coumarin containing polyamides from 6-{[3(chloroformyl)phenyl]ethynyl}

coumarin-3-carboxylic acid chloride were prepared and characterized for the first

time59. The coumarin containing polyamides showed emission and excitation maxima

peaking at 464 and 398 nm, respectively, in solution and exhibited 10% weight loss

above 400°C.

Photodimerization study was carried out by Rebecca et al.60 in

Coumarincontaining poly(alkyl (meth)acrylates). They were prepared via 70–80%

esterification of hydroxy-containing acrylic copolymers, then solution cast into thin

films and photocrosslinked via the dimerization of coumarin derivatives with UVA

light. The coumarin-modified polymers crosslinked upon exposure and exhibited gel

fractions between 74 and 99%. Coumarin dimerization efficiency increased with

higher polymer mobility at the irradiation temperature. The effects of light intensity

and irradiation time in photo-dimerized systems followed the Bunsen-Roscoe

reciprocity law indicating that coumarin photodimerization depended only on dose.

Thus, low intensities are overcome with longer times. This is an important advantage

over photoinitiated free radical crosslinking which depends on irradiation intensity to

the ½ power.

The chemical structures of the new amphiphilic diblock copolymers was

synthesized using atom transfer radical polymerization (ATRP), which contain

pendent coumarin moieties for the reversible photodimerization and cleavage . While

poly(ethylene oxide) (PEO) isthe hydrophilic block, the hydrophobic block varies. It

52

is either poly(coumarin methacrylate) (PCMA) or a random copolymer of

poly(methyl methacrylate) (PA) and PCMA61.

Coumarin side-chain polymer films used for liquid crystal photoalignment was

discussed62.Two-photon polymerization initiated by a tri molecular initiating system

composed of 7-diethylamino-3-(2- beazimidazolyl)coumarin, Titanocene and N-

phenylglycine was investigated. This photopolymer system has been demonstrated for

fabricating three-dimensional microstructure63.

Poly(3-substituted coumarin ethylene)s (PCE1–8) were prepared by reacting

salicylaldehyde-1,2-dichloroethane polymer (SAL-DE) under Wittig, Knoevenagel

and Perkin reaction conditions. All the polymers were characterized by elemental

analysis, IR spectral studies and thermogravimetric analysis (TGA). The PCEs were

tested for their toxicity effect on various fungi and bacteria64.

A series of copolymers N-cyclohexylacrylamide(NCA) with

8-quinolinylacrylate(QA)65 and 2,4-dichlorophenyl methacrylate66 were prepared by

free radical polymerization. The copolymers werecharacterized by 1H-NMR

spectroscopy and the copolymer compositions were determined by1H-NMR analysis.

Thereactivity ratios of monomers were determined by Fineman-Ross and Kelen-

Tudos methods. The copolymers were tested for their antimicrobial properties against

selected microorganism

Copolymerization of N-tert-butylacrylamide (NTB) and 2, 4-Dichlorophenyl

methacrylate (DCPMA)67, NTB with 7-acryloyloxy-4-methyl coumarin (AMC)68,

NTB with 8-Quinolinyl acrylate (QA)69 was carried out in DMF medium at 70 C

53

using AIBN as initiator. The copolymers were characterized by 1H-NMR

spectroscopy and the copolymer compositions were determined by 1H-NMR analysis.

The reactivity ratios of monomers were determined by Fineman -Ross and Kelen -

Tudos methods. Antimicrobial activities of different copolymers synthesized were

also studied against different bacteria and fungi.

From the review of literature, we come to know that the substituted aryl /

heterocyclic moiety containing copolymers possesses antimicrobial activities. The

above survey inspired us to prepare copolymers of N-cyclohexylacrylamide with 8-

quinolinylacrylate(8-QA), 8-quinolinyl methacrylate(8-QMA), 2,4-dichlorophenyl

acrylate(2,4-DCPA), 2,4-dichlorophenyl acrylamide(2,4-DCPMA), 7-acryloyloxy-4-

methyl coumarin(ACU), 7-methacryloyloxy-4-methyl coumarin(MACU), Phenyl

acrylate (PA), N-phenyl acrylamide(NPAM) and study their antimicrobial properties.

1.8 SCOPE OF THE WORK

Biodegradable polymers applications are numerous. In the medicinal field

their applications are notable like drug delivery systems, wound closure, healing

products and surgical implant devices. In additional to that many of the biodegradable

polymers have good film forming properties, making them suitable for applications in

high performance applications as well as in traditional coodity uses, food containers,

soil retention sheeting, agriculture, waste bags and the use as packaging material. In

general monomers, which we are going to use in the formation of copolymers, have

shown antimicrobial activity. So, all the above survey inspired us to synthesize, the

copolymers of N-tert-amylacrylamide with various comonomers .

54

To prepare the monomer n-tert-amylacrylamide (NTA)

To prepare the comonomers

o 8-quinolinyl acrylate (8-QA)

o 8-quinolinyl methacrylate (8-QMA)

o 2,4-dichloro phenylacrylate (2,4-DCPA)

o 2,4-dichloro phenylmethacrylate ( 2,4-DCPMA)

o 7-acryloyloxy-4-methyl coumarin (ACU)

o 7-methacryloyloxy-4-methyl coumarin (MACU)

o Phenyl acrylate ( PA )

o N-Phenyl acrylamide ( NPAM )

To prepare Copolymers of NTA with each of the comonomers in various feed

ratio ( 0.8 / 0.2 ,0.7/0.3, 0.6/0.4, 0.5/0.5, 0.4/0.6, 0.3/0.7, 0.2 / 0.8 )

Characterization

o Copolymer composition by 1H-NMR spectra

o Reactivity ratio by Fineman-Ross, Kelen-Tudos methods.

o Mean sequence lengths

o Thermal behavior

o Antibacterial and antifungal study

55

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