SYNTHETIC

POLYMERS

The word, polymer, implies that polymers are constructed from pieces (monomers) that can be easily connected into long chains (polymer). When you look at the above shapes, your mind should see that they could easily fit together.

Polymer

INTRODUCTION

PolymersPolymers

The process in which monomers combine to form long chains.

HOW: This happens when a carbon to carbon double bond in a monomer is broken and new single bonds are formed creating a polymer.

                                                                                                                                                            

POLYMERIZATION

HOMOPOLYMER & COPOLYMER

Homopolymers:- A polymer which is obtained from only one type of monomer is known as homopolymer .Example:- Polyethylene.

Copolymer:- A polymer made from two or more types of monomer is known as copolymer.Example:- Nylon-66

Methods for making polymers

1)Addition polymerization2)condensation polymerization

Addition polymerization: monomers react to form a polymer without net loss of atoms

Most common form: free radical chain reaction of ethylene

n monomers one polymer molecule

The processes involved in the synthesis of polymers can be divided into two categories

200 °C200 °C2000 atm2000 atm

OO22

peroxidesperoxides

polyethylenepolyethylene

HH22CC CHCH22

CHCH22 CHCH22 CHCH22 CHCH22 CHCH22 CHCH22 CHCH22

Free-Radical Addition Polymerization of Ethylene

99

MECHANISMMECHANISM

– Initiation

– Propagation

– Termination

IONIC VINYL POLYMEIZATION

It is further classified as cationic & anionic vinyl polymerization.

1)Cationic vinyl polymeization:- It involve carbocation intermediate. It is initiated by acidic catalyst.

MECHANISM

1) Chain initiating step

carbocation

2) Chain propagating step:-

3) Chain terminating step

(B) Anionic vinyl polymerization:-

It is initiated by the anionic catalysts such as alkali metal amides, alkyl lithium and Grignard reagent. It involves formation of carbanion.

MECHANISM

1) Chain initiating step

2) Chain propagating step:-

3) Chain terminating step

ZIEGLER-NATTA POLYMERIZATION

The polymerization reaction using Ziegler-Natta catalysts are called co-ordination polymerization reactions.

There are three main advantages of using Ziegler-Natta catalysts :-1)Polymerization takes place under relatively milder conditions.2)The polymers obtained are straight chain with almost no branching.3) The polymerization takes place in a stereospecific manner.

EXAMPLE

1)POLYETHYLENE OR POLYTHENE1)POLYETHYLENE OR POLYTHENE

It is widely used polymer.It is of two types. (a)Low density polythene:- It is formed by heating ethylene to 463-483k under a pressure of 1500 atm in the presence of trace of oxygen.(b)High density polythene:- It is formed by heating ethylene to 333-343 under a pressure of 6-7atm in the presence of Zeigler-Natta catalyst.

Monomer unit:- Ethylene

SOME IMPORTANT VINYL POLYMER

CHARACTERISTICS:-

Low density polythene is chemically inert, tough but flexible and poor electrical conductor.High density polythene is also chemically inert but is tougher & harder than low density polythene.

Uses:- It is used for

1)In the manufacture of pipes, squeeze bottles & toys.2)packaging, as insulation for electrical wires.3)In the manufacture of containers & house wares.

2)POLYVINYL CHLORIDE (PVC)Monomer unit :- Vinyl chloride

Characteristics :- PVC is a hard and horny. It is an electrical insulator and is resistant to fire and chemicals.

USES : It is used for making- 1) Rain coats, hand bags, table clothes. 2) Plastic dolls, gramophones records , floor covering. 3) Electrical insulating coating on electrical cables.

Vinyl chloride PVC

CH2CH

3) POLYSTYRENE (STYRON)

Monomer unit:- Styrene

Styrene POLYSTYRENE

(C6H5CO)2O2

USES :- It is used1)In making light weight packaging materials.2)In the manufacture of food containers, egg boxes, etc.3)In making television cabinets.

Name(s) Formula Monomer Properties Uses Polyethylene

low density (LDPE) –(CH2-CH2)n–ethyleneCH2=CH2

soft, waxy solid film wrap, plastic bags

Polypropylene(PP) different grades

–[CH2-CH(CH3)]n–propyleneCH2=CHC

H3

atactic: soft, elastic solid

isotactic: hard, strong solid

similar to LDPEcarpet, upholstery

Poly(vinyl chloride)(PVC)

–(CH2-CHCl)n–vinyl

chlorideCH2=CHCl

strong rigid solid pipes, siding, flooring

Polystyrene(PS)

–[CH2-CH(C6H5)]n–

styreneCH2=CHC6

H5

hard, rigid, clear solid

soluble in organic solvents

toys, cabinetspackaging (foamed)

Polyacrylonitrile(PAN, Orlon, Acrilan)

–(CH2-CHCN)n–

acrylonitrile

CH2=CHCN

high-melting solidsoluble in organic

solvents

rugs, blanketsclothing

Polytetrafluoroethylene

(PTFE, Teflon)–(CF2-CF2)n–

tetrafluoroethyleneCF2=CF2

resistant, smooth solid

non-stick surfaceselectrical insulation

Poly(methyl methacrylate)

(PMMA, Lucite, Plexiglas)–[CH2-C(CH3)CO2CH3]n–

methyl methacrylat

eCH2=C(CH3)

CO2CH3

hard, transparent solid

lighting covers, signsskylights

Poly(vinyl acetate)(PVAc)

–(CH2-CHOCOCH3)n–

vinyl acetate

CH2=CHOCOCH3

soft, sticky solid latex paints, adhesives

Some Common Addition Polymers

CONDENSATION ( STEP GROWTH) POLYMERIZATION

This is a type of polymerization in which the monomer molecules combine together in a stepwise manner with the elimination of some simple molecules like water & methyl alcohol.

Example:- Nylon-66

Some Condensation Polymers

PHENOL-FORMALDEHYDE RESINSThese are formed by condensation of formaldehyde and phenol. The most important polymer of this type is Bakelite.

Bakelite:- It is a condensation polymer manufactured by treating phenol with formaldehyde in the presence of an acidic or basic catalyst.

Bakelite

UREA-FORMALDEHYDE RESINS

These are polymeric substances formed by reaction between urea and formaldehyde.

EPOXY RESINS

These are polymeric substances which are formed from epoxides such as ethylene oxide.Examples

Poly(oxymethylene) glycol,This is an addition polymer obtained by the polymerization of ethylene oxide in the presence of water or ethylene glycol and sodium hydroxide catalyst.

Poly(oxymethylene) glycol

POLYURETHANES

A urethane or carbamate is an ester of carbamic acid which is a monoamide of carbomic acid.

:

A typical polyurethane synthesis is shown below:

NATURAL AND SYNTHETIC RUBBERS

Natural rubber:- It is a natural polymer which is obtained from latex. Latex is a milky liquid which excludes from rubber tree. Natural rubber has been found to be a polymer of isoprene. There may be 11,000-20,000 isoprene units in the polymer chain of natural rubber.

Vulcanization:-

This is a process to improve the elasticity of the rubber. During vulcanization cross links are produced between different polymeric chains through disulphide linkage.

Synthetic rubber

Some of the synthetic rubber are:1) cis-Polybutadiene.

2) Styrene butadiene rubber, SBR

3) Butyl rubber

4) Polyisoprene

Neoprene or Polychloroprene