Polymer Chemistry-

Polycondensation + Polyaddition

Aims of this part:

Mechanism and Kinetics of Polycondensation

Synthesis of Polyethyleneterephtalat (PET)

Aromatic Polyesters

Preparation of Nylon 6,6 (and similar)

High-Performance Polymers (Aramides, Ladderpolymers)

Synthesis of semi-conducting polymers

Braun, Chedron, Rehann, Ritter, Voit “Polymer Synthesis: Theory and

Practice”, Springer, 5th Edition, 2013. Sections 2.1.2 and 4

Lechner, Gehkre, Nordmeier, „Makromolekulare Chemie“, Springer, 5th

Edition, 2014. Section 3.2

Polymer growth mechanism

Reacting

conditions

u

p

Polymerisation is called step-growth polymerisation

Starting with either an AB molecule, where the reaction needs activation

Or with AA and BB monomers, where activation may or may not be required

Growth of Molecular Mass

Not all chains have the same

length, but are very disperse.

Values of 2-3 are common

1 - up =

1

Polyester formation

AB type monomer, typically done in melt

Polymers of high molecular weight can be yielded (50kDa and above)

Problematic side reaction is the formation of rings (lactones)

Typical Polymers would be P(D/L)LA and PGA amongst others

Ricinoloic acid (copolymerized with Glycerol) emulsifying agent in chocolate

AA+BB type reaction, typically done in melt

Only polymers of low molecular weight can be yielded (below 40 kDa)

Water removal can be rather tideous and slow

Activated Acids or pre-esters are often used as replacements

PET formation

2-step process – 1st step is transesterification:

Methanol distilled off at 150 – 200 °C – must be quantitative!

Excess of ethylene glycole is about 1.5-2 times (3-4 equivilants)

Catalysed by weak basic compounds and traces of Ca, Mg, Zn, Cd, Pb, Co

2nd step – polymer growth:

270-280 °C and 1 mbar are typical final conditions

Efficient stirrer is crucial for this step

Melt viscosity determines end point

Catalysts similar to first reaction and traces of Sb, Ge, Ti, Pb

PET/PBT usage

Aliphatic-Aromatic Polyester

2008: 80 MT/a production of PET in Europe

PET: Use in electrical engineering, automobile construction, bottles, etc.

PBT: Mainly construction materials, insulation

PET/PBT blends: High impact strength (protecting materials), basis for indoor

painting material (with TiO2 based white paint)

Recycling:

Very important for PET – 2012: 81% of the sold bottles were recycled (CH)

Cleaning also via heating – loss in molecular weight

Typically lower-class products (e.g. textiles) are produced then

Aromatic Polyesters

Bisphenol A also drawn like this

Is toxic and promotes cancer – “BPA free” is promoted by industry

Esterification with Terephtalic acid Tg of 175°C! (used for windows)

Known as Polyarylates

Generally known for high tensile strength and Tg!

Reasons: High aromatic content – large pi-pi interactions

Low aliphatic content – low flexibility

for AA/BB Polyesters

for AB Polyesters

Poly(4-hydroxybenzoate)

Very stiff, no softening before 315 °C “High Performance Polymer”

LC Polymers

Thermotropic, main-chain liquid crystalline (LC) polyester

Both aromatic units align after the melting to give crystalline (smectic) phases

Detection: polarized light microscopy or DSC

(1) - melting + LC phase forms

(2) - LC phase gets destroyed

Polarised light:

Thin film of polymer between 2 glass plates

Light transmitted depends on angle

(1)(2)

5 6 7 8 9 10 11 12 13 14 15 16 17 18

Retention Time (min)

WQF1115

No Tailing or Fronting in GPC!

Only one population present

PDI = 1.52

With I. Romano, Q. Wang

Research Example of Polyesters

Polyamide formation

Similar to Polyesters, only AA/BB Type condensation

Readily form hydrogen bonds

Low solubility in classic solvents

Resistant to hydrolysis

High melting T

Melting T decreases with longer C-chain (opposite to polyesters!)

Usually soluble in Cresol, Formic acid, sulfuric acid etc.

Breaking H-Bonds (aliphatic side chains) reverse the effects above

Used as fibers, High-End thermoplasts, electric insulation, consumer products

Aliphatic Polyamides - Nylon

Nylon is a highly popular synthetic fiber, mainly “Nylon-6,6”

1st number: C-chain of diamine, 2nd number: C-chain of diacid

In water

In chloroform

Fiber production

(Nylon-6,10) from

the interface

Good Demos can be found on youtube:

https://www.youtube.com/watch?v=y479OXBzCBQ

Technical Production via melting polymerisation via AH-salt

Kevlar and Nomex (Polyaramides)

Polyamides with aromatic units are called “Polyaramides”

Higher melting T that aliphatic compounds – higher than decomposition T

Strong tendendency to from crystalline regions

Extremely limited solubility

No melt polymerisation – spun from solution

Nomex: Flame retardant material

Stable until 370 °C

Melting at 375 °C

Used for firemen-outfits

Kevlar: Highly resistant material Stable until 460 °C

Very high Youngs’ modulus

Used for firemen-outfits

High-Perfomance

Polymers

Ladder Polyaramides

Polyimides

Can be used continuously at 350 °C

Reverse approach gives polybenzthiazoles

Ladder = strands of 2 C-O/N/C bonds continue the polymer

Temperature range goes up to 500°C

Tetracarboxylic acids give polymer that can be used up to 600 °C

Stability by large amount of 2 bonds

continuing the main chain

Polycarbonates

Polyesters from carbonic acid – own class of materials!

Schotten-Baumann Reaction:

High use as

optical data

storage devices

Also used in other

parts of

electronics

Polycarbamates (Amine-analogues) exist as High-Perfomance polymers

Interface-polycondensation, done in basic, but ambient conditions

Alternatively via double phenolate of carbonic acid

Melting area around 230 °C

Insulating, impact-resistant, form-stable material, partially crystalline

Other Condensation Types

Monomers can be even more complex!

Chem. Mater., 2016, 28 (22), pp 8366–8378 DOI: 10.1021/acs.chemmater.6b03671

Pd catalyzed cross-coupling reactions – Polythiophenes

Semiconducting polymers for (opto)electronics, e.g. solar cells

Other Condensation Types

Highly complex monomers, which need to be synthesized!

Polym. Chem., 2014,5, 5383-5390 DOI: 10.1039/C4PY00747F

Ladder Polymers are insoluble, but highly T-resistant

Cross-coupling reactions are used to create (semi)conducting polymers

Aliphatic polyamides are named “Nylon N.C” (N,C = Number of C-Atoms)

Aromatic polyamides (Aramides) are high-performance polymers (e.g.

Kevlar, Nomex) for over 300 °C

Polyamides are mainly produced by spinning fibres from a solution.

They readily form hydrogen bonds, meaning: Low solubility in classic

solvents, resistant to hydrolysis, high melting T

Polyesters are mainly produced from melt

PET and PBT are important polyesters – produced in a 2-step process.

Aromatic Polyesters can be designed to be liquid crystalline

Starting with either an AB molecule, where the reaction needs activation,

or with AA + BB monomers, where activation may or may not be required

Summary

Polyaddition

Kinetically the same as polycondensation,

but NO sideproducts formed during the reaction

Basic addition reactions

Polyurethanes

By far the most important class of polyadducts

By far the most important class of polyadducts

H-Bonding and tautomerisation is key to the properties:

Tautomerisation leads to almost planar

and non-rotating (inflexible) bonds

H-Bonding increases stiffness as in

polyamides

Polyurethanes

Thermoplastic elastomers (TPEs):

• Aliphatic main chains are mainly used (soft segments)

• H-Bonds of urethane unit (hard segments) break at higher temperatures,

but act as cross-linkers at lower temperatures

• Aromatic main chains leads to hard duromer-like behavior

Foam softness regulated by R-units (see above)

Polyol leads to basic network which can be tuned by TPE character

Example 1: PUR-foam in pillows/matresses

Example 2: Auto-fitting ski boot

Adding water traces - Polyurethane foams: