Step Growth Polymersization

Dr. S.Ray_Chem Engg_NIT Agratala 3/20/2013

Polymer Processing Engineering 1

Chain growth polymerization : Addition polymerizationmolecular weights increase successively,one by one monomer

Ring-opening polymerization may be either stepor chain reaction

Polymerization Processes

Modern classification of polymerization according topolymerization mechanism

Step growth polymerization : Polymers build up stepwise

Polymerization mechanisms

- Step-growth polymerization



Condensation or step-growth polymerization is entirelyanalogous to condensation in low-molecular-weightcompounds.

In polymer formation the condensation takes placebetween two poly-functional molecules to produce onelarger poly-functional molecule, with the possibleelimination of a small molecule, such as, water.

The reaction continues until almost all of one of thereagents is used up; an equilibrium is established that canbe shifted at will at high temperatures by controlling theamounts of the reactants and products

Condensation or step-reaction polymerization

Stepwise (Condensation) polymerization Reaction

Requirements for Step-Growth Polymerization• High monomer conversion• High monomer conversion• High monomer purity• High monomer purity• High reaction yield• High reaction yield• Stoichiometric equivalence of functional groups• Stoichiometric equivalence of functional groups

The characteristic features of this type of polymer ization The characteristic features of this type of polymer ization process as followprocess as follow .11--Growth occurs throughout the matrix Growth occurs throughout the matrix 22--There is the rapid loss of the monomer speciesThere is the rapid loss of the monomer species33--The molecular weight slowly increases throughou t the reaction The molecular weight slowly increases throughout th e reaction 44-- The same mechanism operate throughout the react ion The same mechanism operate throughout the reaction 55--The polymerization rate decreases as the number of functional The polymerization rate decreases as the number of functional group decreases group decreases 66--No initiator is required to start the reactionNo initiator is required to start the reaction



Step-growth polymerization

• In step-growth polymerization, the stepwise reaction occurs between pairs of chemically reactive or functional groups on the reacting molecules. In most cases, step-growth polymerization is accompanied by the elimination of a small molecule such as water as a by-product.

Stage 1

Consumptionof monomer

n n

Stage 2

Combinationof small fragments

Stage 3

Reaction of oligomers to give high molecular weight polymer

Step-Growth Polymerization




• Step-growth polymerization involves a series of reactions in which any two species (monomers, dimers, trimers, etc.) can react at any time, leading to a larger molecule.

• Most step-growth polymerizations, involve a classical condensation reaction such as esterification, ester interchange, or amidization.

Step-growth polymerization• Step-growth polymerizations generally involve

either one or more types of monomers. In either case, each monomer has at least two reactive (functional) groups.

• In cases where only one type of monomer is involved, which is known as A-B step-growth polymerization, the functional groups on the monomer are different and capable of intramolecular reactions.

• In those cases where more than one type of molecule is involved, the functional groups on each type of monomer are the same, but capable of intermolecular reaction with the other type of monomer. This is known as the A–A/B–B step-growth polymerization




• Step-growth polymerizations can be divided into two main categories:

• polycondensation, in which a small molecule is eliminated at each step,

• polyaddition, in which, monomers react without the elimination of a small molecule.

Polyaddition



Polyaddition



Step-reaction Polymerization

A. Monomer to have difunctional group

1. One having both reactive functional groups in one molecule

A R B R X

HO R CO2H O R C

O

+ H2O

H2N R CO2H NH R C

O+ H2O

2. Other having two difunctional monomers

A R A + B R' B R X R' X

OCN R NCO + HO R' OH

CNH R NHCO R' O

H2N R NH2 + ClCO R' OCCl

CNH R NHCO R' O + 2HCl

O O

O O

O O



B. Reaction : Condensation reaction using functional group

Example - Polyesterification

n HO CO2H O C

O

n+ nH2O

nHO2C CO2H + nHOCH2CH2OH

C

O

COCH2CH2O

O

n + 2nH2O

C. Carothers equation

P =NO N

NO

Or N = NO(1 P)

( NO : number of moleculesN : total molecules after a given reaction period.NO – N : The amount reactedP : The reaction conversion )

( DP is the average number of repeating units of all molecules present)

DP = NO/N

DP =1

1 - P

For exampleAt 98% conversion

DP =1

1- 0.98



A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B(d)

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B(a)

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

(b)

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

(c)

(A) Unreacted monomer

(B) 50% reacted, DP = 1.3

(C) 75% reacted, DP = 1.7

(D) 100% reacted, DP = 3

Step-Growth Polymerization

• Great Industrial Value

Examples

Polyester Linear saturated polyester: plasticizer,Linear unsaturated polyester: glass fiber laminate,

casting resin, solvent-less lacquerNetwork polyester: surface coating



Most of the Polycondensation reactions are the typical Step-Growth

Polymerization.

Polycondensation reactions are taken as examples to illustrate the Step-Growth Polymerization.

Polycondensation is the abbreviation of

condensation polymerization.

Monomers with functional group

Polymer

many times of repeated condensation

Step-Growth Polymerization: Polycondensation



B. Functionality ( f ) ：：：：

the number of functional groups in the molecule

which take part in the reaction.

(monomer,oligomer).


general reaction：：：：n aRa + n bR’b a[R－－－－R’] nb + (2n－－－－1)ab

a，，，，b－－－－ functional group；；；； R’，，，，R－－－－construction unit；；；；ab－－－－ micromolecule

These reactions involve two different functional groups.

One type of the functional group in each monomer.

� Forming linear polycondensation polymer




1) monomer’s f ≥2；；；；2) Changeable factors :

functional groups ( －－－－OH,－－－－COOH,－－－－COOR,－－－－Cl,－－－－NH2，，，，……),

f (linear or cross linking polycindensation)R, and R’Huge sorts of polycondensation polymers

3) The polycondensation polymers are usually the heterochain polymers with N,O,S,P in the backbone and the functional groups in the end. eg.－－－－O－－－－,－－－－CONH－－－－,－－－－COO－－－－etc


Industrially, polycondensation can bedivided into many types according to thegroup in the polymer chain.

polyester, polyamide, polyether reaction




4) The compositions and structures of the polymers are different from those of the monomer, because of the byproducts in the reaction.

5) The conversion of monomer does not increase with

the reaction time in the polycondensation reactions.


Essentially, the key of polycondensation is the reactions between the function groups. Only with the efficient reaction, the macromolecules can be prepared.

Practically, polycondensation should be described by the extent of reaction.




(2) mixed polycondensation , f = 2,2

� Two kinds of bifunctional monomers.

� Only one type of functional group in each monomer.

Example: diamine / diacid, dihydric alcohol / diacid

n H2N(CH2)6NH2 + HOOC(CH2)4COOH →

[NH(CH 2)6NHOC(CH2)4CO]n + (2n－－－－1)H2O

2.2.4 Classifications of Polycon densation

①①①① linear polycondensation

� Bifunctional monomer

� The chain increases to two directions along the ends of the chain.

2. By Structure of polymer



♦ Systems off = 2 and f = 2, 2 are linear polycondensation.

♦ The key of linear polycondensation is to control the molecular weight of the products.


②②②② cross linking polycondensation

�At least one monomer has more than two functional groups ( f = 2, 3 or 2,4，，，，3,3 …)

�The molecule increases towards more than two directions. The crosslinking polymer forms.

Example:glycerol / phthalic anhydride → alkyd resin,

phenol / formaldehyde → phenolic-formaldehyde resin.



• The viscosity will be suddenly increased as reaction goes to the certain degree, forming the gel. --------gelation

♦ The key of cross-linking polycondensation is to forecast and control the gel point

This critical point is called the gel point.

balanced polycondensation

unbalanced polycondensation

the rate of reverse reaction is not equal to zero

K ＞＞＞＞101010103 3 3 3 .

the rate of reverse reaction is little or equal to zero

K＜＜＜＜ 101010103 3 3 3 .

3. By Thermodynamics




The increasement of macromolecule chain is step by step.

2.3 Characteristic of linear polycondensation

Characteristic I.

Any molecule with different functional group can react to each other.

There are no particular active centers inthe reaction.

The molecular weight of the polymer gra-dually increases with the decrease of the number of the groups.




The monomers dispear at the early stage of reaction far

before forming any polymer with sufficiently high

molecular weight for practical utility.

High conversion of monomer is reached at early stage of

reaction followed by the reaction between oligomers.

As the time increases, increases instead of the

conversion.

Contrarily, the conversion increases with time in the

chain polymerization.

nX

HOROH HOOCR`COOH

HOROCOR`COOROH

HOROCOR`COOH

HOROH HOOCR`COOH+

+ H2O

HOOCR`COOROCOR`COOH

trimertetramer

2

dimer

trimer




Firstly, the diol and the di-acid monomer reacts to form dimer.

aAa + bBb a [ A B ] b + ab

Then the dimer reacts with itself to form tetrameror with unreacted monomer to yield trimer.

a[A B]b + aAa a[A B A]a + ab

a[A B]b + bBb b[B A B]b + ab

a[A B]b + + aba[A B]b a[A B A B]b

aAa: dihydric alcohol(diol); bBb: diacid


�The tetramer and trimer continues to react with themselves, with each other, and with monomer and dimer.

�The polymerization proceeds in the stepwise manner, resulting the continuously increases of the molecular weight of the polymer.



�All polycondensations are characterized by the stepwise.

�The mechanism of polycondensation is rather different to that of chain polymerization.

�The reactivity of a functional group is independent of the size of the molecule.

the degree of polymerization

P, the fraction of the functional groups that have

reacted

00

0 1N

N

N

NN−=

−

• where,• N0 ：：：： the total of the certain groups at the initial

stage• N ：：：： the quantity of unreacted groups at time of t




� ：the number averageof construction units in

� each macromolecule

nX

leculesof macromonumberthesction unitof construthe total

X n ====

＝

PP＝＝＝＝＝＝＝＝00. . 99，，，，，，，， = = 1010= = 100 100 ~ ~ 200200，，，，，，，， P P 00. . 99 99 ~ ~ 00. . 995995

P−1

1nX

nX

11P －－－－=

00

0

N

N1

N

NNP －－

==

nXnX

� Linear polycondensation is

reversible equilibrium.

� The equilibrium constants (K) of differentlinear polycondensation is different.

Characteristic II.Characteristic of linear

polycondensation



①①①① K＝＝＝＝4～～～～10, e.g kinds of polyester ，，，，the existence of micromolecule will

greatly affect the degree of polymerization.

②②②② K＝＝＝＝300～～～～400, e.g kinds of polyamide ，，，，the existance of micromolecule will

affect the degree of polymerization to someextent.

③③③③ K≥103，，，， e.g phenol ~ methanalthe reaction is irreversible ，，，，

It is clear that the synthesize art dependson the equilibrium constant, K, will affect.

In the closed system, the high molecular weight polymer is hardly obtained, due to the existence of byproducts and residual micromolecule.

Industrially, the micromolecules can be removed by reducing pressure method in order to change the equilibrium for preparing high molecular weight polymer.

e.g. The vacuum degree of the system, i.e., the quantity of residual micromolecules, control the molecular weight of polyethylene terepthalate (polyester).



P, the fraction of the functional groups that have reacted

00

0 1N

N

N

NN−=

−where,N0 ：：：： the total of the certain groups at the initialstageN ：：：： the quantity of unreacted groups at time of t

The degree of polymerization

：the number everageof construction units in

each macromolecule

nX


X n ====

Example 1 ：polyester reactionnHO－－－－R－－－－COOH → [ORCO] n + (n－－－－1)H2O

t=0，，，，the total of the initial groups ：：：：－－－－COOH：：：：N0

t=t，，，，the quantity of unreacted groups：－：－：－：－COOH：：：：N

P－－－－OH＝＝＝＝P－－－－COOH＝＝＝＝＝＝＝＝ P (2－－－－2) 00

0 1N

N

N

NN−=

−

＝＝＝＝ (2－－－－3)N

N0


X n ====



from (2 －－－－3)：：：：＝＝＝＝ (2－－－－4)nX

1

0N

N

P ＝ 1－nX

1

＝ (2－－－－5)P−1

1nX

substitutes (2－－－－2) for (2－－－－4)：：：：

＝＝＝＝ (2－－－－3)leculesof macromonumberthe

sction unitof construthe total X n

====N

N0

P－－－－OH＝＝＝＝P－－－－COOH＝＝＝＝＝＝＝＝ P (2－－－－2) 00

0 1N

N

N

NN−=

−

Example 2 ：HOROH + HOOCR’COOH

Case : the same mole ratio

t=0 －－－－OH: N0 ，－，－，－，－COOH：：：： N0,

the total of construction units：：：：N0

t=t －－－－OH: N ，，，，－－－－COOH：：：： Nthe quantity of macromolecules：：：：N

P－－－－OH＝＝＝＝P－－－－COOH＝＝＝＝＝＝＝＝ P 00

0 1N

N

N

NN−=

−

nXN

N0

P−1

1＝＝＝＝＝＝＝＝



In the polycondensation reaction，，，，increase ofthe degree of reaction depends on

1. prolonging the reaction time

2. increasing the reaction temperature

3. removing the micromolecule intensively

4. using high active monomer


The equilibrium polycondensation reactions consist of a series of equilibrium reactions.

As the reactivity of functional groups are assumed to be equal to each other, all reactions can be expressed by the same K ：：：：～－～－～－～－COOH ＋＋＋＋～－～－～－～－OH ～－～－～－～－OCOOCOOCOOCO－～－～－～－～＋＋＋＋ HHHH2222OOOO

K ＝＝1

1

−k

k]][[

]][[ 2

OHCOOH

OHOCO

−－－－

The equilibrium constant (K) and the degree of polymerization



～－～－～－～－COOH ＋＋＋＋～－～－～－～－OH ～－～－～－～－OCOOCOOCOOCO－～－～－～－～＋＋＋＋ HHHH2222OOOOtttt＝＝＝＝0 0 0 0 CCCC0 0 0 0 CCCC0000

tttt＝＝＝＝t Ct Ct Ct C0000((((1111----P)P)P)P) CCCC0000((((1111----P) CP) CP) CP) C0000P CP CP CP C0000PPPP

the closed system

)1()1( 00

00

PCPC

PCPC

−•−•

2

2

)1( P

P

−K = ＝＝＝＝

＝＝＝＝＝＝＝＝K P

P

−1 nXP−1

1

P ＝ (2－－－－6)1+K

K

＝ + 1 (2－－－－7)K

Thus,

has relations not only with P，，，，but also with K.nX

nX



To polyester ：K ＝＝＝＝ 4, P(equilibrium )＝＝＝＝2/3，，，，＝＝＝＝3nX

To polyamide: K ＝＝＝＝ 400, P(equilibrium )＝＝＝＝0.95, ＝＝＝＝21nX

K ＝＝＝＝ 104，，，，＝＝＝＝100nX

Thus：：：：1. In the closed systems especially that with small K,

the high molecular weight polymer is hard to be prepared.

2. Try to remove the micromolecules is key for incre-asing the molecular weight of the polymer.

ExampleExampleformation of polyesternHOnHO--RR--OH + nHOOCOH + nHOOC--R¯R¯--COOH HCOOH H--(O(O--RR--OOCOOC--R¯R¯--COCO--))nnOH+(OH+(22nn--11)H)H22OO

Kinetics of condensation (step Kinetics of condensation (step –– Growth ) polymeriza tionGrowth ) polymerizationConsider the synthesis of polyester from a diol and a diacid. The first Consider the synthesis of polyester from a diol and a diacid. The first step is the reaction of the diol and the diacid mon omers to form step is the reaction of the diol and the diacid mon omers to form dimerdimer ,,HO-R-OH + HOOC-R"-COOH--> HO-R-OCO-R'-COOH + H 2O

The dimer then forms trimer by the reaction with di ol monomer ,HOHO--RR--OCOOCO--R'R'--COOH + HOCOOH + HO--RR--OHOH----> HO> HO--RR--OCOOCO--R'R'--COOCOO--RR--OH +HOH +H22OO

and also with diacid monomer ,HOHO--RR--OCOOCO--R'R'--COOH + HOOCCOOH + HOOC--R'R'--COOHCOOH---->>HOOCHOOC--R'R'--COOCOO--RR--OCOOCO--R'R'--COOH + HCOOH + H22OO



Kinetics of Condensation (Step-Growth) Polymerizatio n•• StepStep--Growth polymerization occurs by consecuti ve reactions in which Growth polymerization occurs by consecutive reactio ns in which

the degree of polymerization and average molecular weight of the the degree of polymerization and average molecular weight of the polymer increase as the reaction proceeds. Usually (although not polymer increase as the reaction proceeds. Usually (although not always), the reactions involve the elimination of a small molecule (e.g., always), the reactions involve the elimination of a small molecule (e.g., water). Condensation polymerization may be represe nted by the water). Condensation polymerization may be represe nted by the following reactions: following reactions:

Monomer + Monomer Dimer + H 2OMonomer + Dimer Trimer + H 2OMonomer + Trimer Tetramer + H 2ODimer + Dimer Tetramer + H 2ODimer + Trimer Pentamer + H 2OTrimer + Trimer Hexamer + H 2O

•• Generally, the reactions are reversible, thus the e liminated water must be Generally, the reactions are reversible, thus the e liminated water must be removed if a high molecular weight polymer is to be formed.removed if a high molecular weight polymer is to be formed.

•• Based on the assumption that the polymerization kin etics are Based on the assumption that the polymerization kin etics are independent of molecular size, the condensation rea ctions may all be independent of molecular size, the condensation rea ctions may all be simplified to:simplified to:~~~~COOH + HO~~~~ ~~~~COOH + HO~~~~ →→→→→→→→ ~~~~COO~~~~ + H~~~~COO~~~~ + H22OO

Kinetic analysisKinetic analysis~~~~COOH + HO~~~~ →→→→ ~~~~COO~~~~ + H2OMost step polymerization involve bimolecular reacti on that are often catalyzed~~~~A + B~~~~ + catalyst →→→→ ~~~~AB~~~~ + catalystThe rate is accelerated according to

-d [A]

Byintegration

dtdt= k= k [A[A][B] ][B] [catalyst][catalyst]

--d [A]d [A]

dtdt= k= k '' [A[A][B]][B]

--d [A]d [A]

dtdt= k= k '' [A[A]]22

11

[M][M]--

11= k 't= k 't

[M]o[M]o

OrOr

Where k ‘ =Where k ‘ = kk [catalyst][catalyst]

I f [AI f [A] = [B]] = [B]

****

By use the extent of the reaction P (fraction of A or B functional groupsBy use the extent of the reaction P (fraction of A or B functional groupsthat has reacted at time t )that has reacted at time t )P = extent of the reaction = the fraction of conver sionP = extent of the reaction = the fraction of conver sion



The concentration at any time given by [M]

[M] =[M] = [M]o [M]o -- [M]o P = [M]o ([M]o P = [M]o (11-- P )P )

By substitution in (** )By substitution in (** )

11

((11--p)p)= k= k '' [A[A]o t + ]o t + 11

•Note that experimental data are usually linear only beyond ca. 80% conversion.

Polyesterification Without Acidic Catalyst

dt= k [A] 2[B]

-d [A]

dt= k [A] 3

Or

I f [A] = [B]

1[M] 2

-1

= 2k t[M]o 2**

The rate equation is given by

- d[A]

Byintegration

[M] = [M]o - [M]o P = [M]o (1- P )

By substitution in (** )

1(1-p)2

=2 k [A] 2ot + 1



Uncatalyzed Polyesterification

��Note that experimental data for esterification reac tions show that plots of Note that experimental data for esterification reac tions show that plots of 11/(/(11--p)p)22 vs. time are linear only after ca. vs. time are linear only after ca. 8080% conversion% conversion . .

•• This behavior has been attributed to the reaction m edium changing This behavior has been attributed to the reaction m edium changing from one of pure reactants to one in which the este r product is the from one of pure reactants to one in which the este r product is the solvent. solvent.

•• Thus, the true rate constants for condensation poly merizations Thus, the true rate constants for condensation poly merizations should only be obtained from the linear portions of the plots (i.e., the should only be obtained from the linear portions of the plots (i.e., the latter stages of polymerization).latter stages of polymerization).

•• For example, the kinetic plots for the polymerizati on of adipic acid and For example, the kinetic plots for the polymerizati on of adipic acid and 11,,1010--decamethylene glycol show that at decamethylene glycol show that at 202202 ooC, the thirdC, the third--order rate order rate constant for the uncatalyzed polyesterification is k = constant for the uncatalyzed polyesterification is k = 11..75 75 x x 1010--2 2 (kg/equiv)(kg/equiv) 22 minmin --11..

Polyesterification Without Acidic Catalyst (continu ed)



The Number Average Molecular Weight in Polycondensation

. The number. The number--average degree of polymerization Xaverage degree of polymerization X n n is given as the total is given as the total number of monomer molecules initially present div ided by the total number number of monomer molecules initially present div ided by the total number of molecules present at time t,of molecules present at time t,

XXnn = N= Noo / N = [ M ]/ N = [ M ] oo / [ M ] [ M ] = [ M ]/ [ M ] [ M ] = [ M ] oo ( ( 1 1 –– P )P )

XXnn = = 1 1 / / 1 1 -- PP

••This relationship is the This relationship is the Carother's EquationCarother's Equation . .

ExampleExampleIf monomer conversion is 99% what is X n ?Xn = 1 / 1 – P = 1 / 1 - 0.99 = 100If P =99.5 % Xn = 1 / 1 - 0.995 = 200If P =99.6 % Xn = 1 / 1 - 0.996 = 250

The numberThe number--average molecular weight Maverage molecular weight M nn, defined as, defined as

MMnn = M= Moo XXnn + M+ Megeg = M= Moo / / 1 1 –– P + MP + Megegwhere Mwhere M o o is the mean of the molecular weights of the structu ral is the mean of the molecular weights of the structu ral units, and Munits, and M egeg is the molecular weight of the end groups. The lat ter is the molecular weight of the end groups. The lat ter becomes negligible at even moderate molecular weigh tbecomes negligible at even moderate molecular weigh tMMnn = M= Moo XXnn + M+ Meg eg = M= Moo / / 1 1 –– PP

1(1-p)

= k '[A] ot + 1

Xn= k '[A] ot + 1

X2n=2 k [A] 2

ot + 1

HH--(O(O--RR--OOCOOC--R¯R¯--COCO--))nnOHOH



Mn as a Function of Conversion

Molecular Weight Control in Linear PolymerizationMolecular Weight Control in Linear PolymerizationIn the synthesis of polymers one is usually interested in obtaining a productof very specific molecular weight since its properties are highly dependent on its molecular weight.

The desired molecular weight can be obtained byThe desired molecular weight can be obtained by11--Quenching the reaction (e.g., by cooling) at th e appropriate time. Quenching the reaction (e.g., by cooling) at the ap propriate time. However, the polymer obtained in this case is unsta ble, since it can However, the polymer obtained in this case is unsta ble, since it can undergo further polymerization if it is heated. Thi s is because the end undergo further polymerization if it is heated. Thi s is because the end groups on the polymer chains are still active and t hey can react with groups on the polymer chains are still active and t hey can react with each other. each other.

22--By increasing one reactant over the other. In t his way the monomer inBy increasing one reactant over the other. In this way the monomer inexcess will block any further increase in the polym er chains.excess will block any further increase in the polym er chains.

Excess HExcess H 22NN--RR--NHNH22 + HOOC+ HOOC--R'R'--COOH COOH ------> H> H--((--NHNH--RR--NHCONHCO--R'R'--COCO--))nn--NHNH--RR--NHNH22

The use of excess diacid accomplishes the same resu lt; the polyamideThe use of excess diacid accomplishes the same resu lt; the polyamidein this case has carboxyl end groupsin this case has carboxyl end groups

ExcessHOOCExcessHOOC--R'R'--COOH+HCOOH+H22NN--RR--NHNH22 ------>HO>HO--((--COCO--R'R'--CONHCONH--RR--NHNH--))nn--COCO--R'R'--COOHCOOH



3- Another method of controlling the molecular weigh t is by addingAnother method of controlling the molecular weight is by addingsmall amounts of monofunctional monomer. (Acetic ac id )small amounts of monofunctional monomer. (Acetic ac id )Type (Type (22))

For the polymerization of bifunctional monomers AFor the polymerization of bifunctional monomers A-- A and BA and B--B where BB where B--BBis present in excess, the numbers of A and B F.gs. are given by Nis present in excess, the numbers of A and B F.gs. are given by N AA and Nand NBB. Notice that N. Notice that N A A and Nand NB B are equal to twice the number of Aare equal to twice the number of A--A and BA and B--BBmolecules, respectively.molecules, respectively.The stoichiometric imbalance r of the two f.gs. is given byThe stoichiometric imbalance r of the two f.gs. is given by

r = Nr = NA A /N/NBB. ≤ . ≤ 11The total number of monomer molecules is given by The total number of monomer molecules is given by

(N(NAA+N+NBB)/)/2 2 or Nor N AA((11++11/r)//r)/22. . , the total number of polymer molecules is one half the total number , the total number of polymer molecules is one half the total number of chain ends or of chain ends or

[N[NAA((11--p)+Np)+NBB((11--rp]/rp]/22..

The numberThe number--average DP( Xaverage DP( X nn )is the total number of A)is the total number of A--A and BA and B--B molecules B molecules initially present divided by the total number of po lymer molecules:initially present divided by the total number of po lymer molecules:

XXnn = N= NAA((11++11/r)//r)/22. . [N[NAA((11--p)+Np)+NBB((11--rp]/rp]/22..

Xn = 1 + r 1 + r – 2rP

If r = 1Xn = 1 / 1-p

If p = 1Xn = 1 + r / 1 - r

ExampleExampleWhat is XWhat is X nn when P = when P = 1 1 but use but use 00. . 9800 9800 moles of Amoles of A--A and A and 11. . 01000100moles of B moles of B –– BBr = Nr = NAA / N/ NB B = = 00..98 98 x x 2 2 / / 11..01 01 x x 2 2 = = 00..9797XXn n = = 1 1 + r / + r / 1 1 –– r = r = 11..97 97 / / 00..03 03 = = 666 6



Type (Type (33))the molecular weight can also be controlled by addi ng small the molecular weight can also be controlled by addi ng small amounts of monofunctional monomer.amounts of monofunctional monomer.Moles of AMoles of A--A = NA = NAA / / 22Moles of BMoles of B--B = NB = NBB / / 22Moles of mono functional B = NMoles of mono functional B = N BB ¯̄

r = ½ Nr = ½ NAA / ½ N/ ½ NBB + N+ NBB¯ = N¯ = NAA / N/ NBB + + 2 2 NNBB ¯̄

Example Example Find Xn for 1 mole of A-A ,1mole of B-B and 0.01 mole of RB¯ when P = 1r = 1/ 1 + 2x 0.01 = 0.99Xn 1 + r / 1 – r = 1 + 0.99 / 1 – 0.99 = 199

The poly dispersity indexThe poly dispersity indexXXww / X/ Xn n = = 1 1 + P + P XXnn = = 1 1 //11--P XP Xw w = = 1 1 + p / + p / 1 1 -- PP

SummarySummary11

((11--p)p)= k= k '' [A[A]o t + ]o t + 11

1(1-p)2 =2 k [A] 2ot + 1

XXnn = N= No o / N = [ M ]/ N = [ M ] oo / [ M]/ [ M] XXnn = = 1 1 / / 1 1 -- PP

MMnn = M= Moo XXnn + M+ Megeg = M= Moo / / 1 1 –– PP

Xn= k '[A] ot + 1

X2n=2 k [A] 2

ot + 1

r = Nr = NAA /N/NBB. ≤ . ≤ 11Xn = 1 + r

1 + r – 2rP If r = 1Xn = 1 / 1-p

If p = 1Xn = 1 + r / 1 - r

r = ½ Nr = ½ NAA / ½ N/ ½ NBB + N+ NBB¯ = N¯ = NAA / N/ NB B + + 2 2 NNBB ¯̄

The poly dispersity indexThe poly dispersity indexXXww / X/ Xnn = = 1 1 + P + P XXnn = = 1 1 //11--P XP Xww = = 1 1 + p / + p / 1 1 -- PP



Polyesters form a large class of commercially important polymers. A typical polyester is poly(ethylene terephthalate) (PET), the largest volume synthetic fiber. It is also used as film and in bottle applications.

The traditional route for the production of commercial PET is through two successive ester interchange reactions,

POLYESTERPOLYESTER

POLYESTERPOLYESTER



In the 1st step, a 1:2 molar ratio of dimethyl terephthalate to ethylene glycol is heated at temperatures near 200°C in the presence of a catalyst such as calcium acetate.

During this stage, methanol is evolved and an oligomeric product (x = 1 to 4) is obtained.

The 2nd step involves a temperature increase to about 300°C. This results in the formation of high polymer with the evolution of ethylene glycol.

Poly(ethylene terephthalate) is a linear polyester obtained from the reaction of difunctional monomers.

Branched or network polyesters are obtained if at least one of the reagents is tri- or multifunctional.

This can be achieved either by the use of polyols such as glycerol in the case of saturated polyesters (glyptal) or by the use of unsaturated dicarboxylic acids such as maleic anhydride in the case of unsaturated polyester.

POLYESTERPOLYESTER

In the preparation of glyptal, glycerol and phthalic anhydride react to form a viscous liquid initially, which on further reaction hardens as a result of network formation

Glyptal is used mainly as an adhesive. Glyptal modi.ed with natural or synthetic oils is known as an alkyd resin , which is a special polyester of great importance in the coatings industry.

A typical alkyd resin comprises of pthalic anhydride, glycerol and fatty acid. The fatty acid may be derived from vegetable drying oils (e.g., soybean, linseed oils) or from nondrying oils (e.g., coconut oil).

POLYESTERPOLYESTER



POLYESTERPOLYESTER

Branched or network polyesters

Polyamides, as they are commonly called, are characterized by the presence of amide linkages (–CONH–) on the polymer main chain.

Theoretically, a large number of polyamides can be synthesized based on four main synthetic routes:

(1) condensation reaction between a dicarboxylic acid and a diamine,(2) reaction between a diacid chloride and a diamine, (3) dehydration–condensation reactions of amino acids, (4) ring-opening polymerization of lactams.

Chemically, polyamides may be divided into two categories: those based on synthetic routes (1) and (2); and those based on routes (3) and (4).

The commercial use of polyamides is primarily centered around two products: nylon 6,6 from the first category, and nylon 6 from the second category.

POLYAMIDESPOLYAMIDES



The classical route for the synthesis of nylon 6,6 is the direct reaction between a dicarboxylic acid (adipic acid) and a diamine (hexamethylenediamine).

In practice, however, to achieve an exact stoichiometric equivalence between the functional groups, a 1:1 salt of the two reactants is prepared initially and subsequently heated at a high temperature to form the polyamide.

For nylon 6,6, an intermediate hexamethylene diammonium adipate salt is formed. A slurry of 60 to 80% of the recrystallized salt is heated rapidly. The steam that is released is purged by air. Temperature is then raised to 220°C and finally to 270 to 280°C when the monomer conversion is about 80 to 90% while maintaining the steam pressure generated during polymerization at 200 to 250 psi. The pressure is subsequently reduced to atmospheric pressure, and heating is continued until completion of polymerization.

Since the polymerization reaction occurs above the melting points of both reactants and the polymer, the polymerization process is known as melt polymerization.





Other polyamides of commercial importance are nylons that are higher analogs of the more common types: nylons 11; 12; 6,10; and 6,12.

The numerals in the trivial names refer to the number of carbon atoms in the monomer(s).In designating A–A/B–B nylons, the first number refers to the number of carbon atoms in the diamine while the second number refers to the total number of carbon atoms in the acid.

In 60’s aromatic polyamides were developed to improve the flammability and heat resistance of nylons.

Poly(m-phenyleneisophthalamide), or Nomex, is a highly heat resistant nylon obtained from the solution or interfacial polymerization of a metasubstituted diacid chloride and a diamine

The corresponding linear aromatic polyamide is Kevlar aramid which decomposes only above 500°C. The high thermo-oxidative stability of Kevlar is due to the absence of aliphatic units in its main chain. The material is highly crystalline and forms a fiber whose strength and modulus are higher than that of steel on an equal weight basis.





Formaldehyde is employed in the production of aminoplasts and phenoplasts, which are two different but related classes of thermoset polymers.

Aminoplasts are products of the condensation reaction between either urea (urea–formaldehyde or UF resins) or melamine (melamine–formaldehyde or MF resins) with formaldehyde.

Phenoplasts or phenolic (phenol–formaldehyde or PF) resins are prepared from the condensation products of phenol or resorcinol and formaldehyde.

Formaldehyde ResinsFormaldehyde Resins

Urea–formaldehyde resin synthesis consists basically of two steps.

In the first step, urea reacts with aqueous formaldehyde under slightly alkaline conditions to produce methylol derivatives of urea

In the second step, condensation reactions between the methylol groups occur under acidic conditions, leading ultimately to the formation of a network structure

Formaldehyde ResinsFormaldehyde Resins

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