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

Polymers• Polymerization: When carbon

molecules combine into 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.

                                                                                                                                                            

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

88

MECHANISM

– Initiation

– Propagation

– Termination

1)POLYETHYLENE OR POLYTHENEIt 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)packaging, as insulation for electrical wires.2)In the manufacture of pipes, squeeze bottles & toys.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=CHCH3

atactic: soft, elastic solidisotactic: hard, strong

solid

similar to LDPEcarpet, upholstery

Poly(vinyl chloride)(PVC)

–(CH2-CHCl)n–vinyl chloride

CH2=CHCl strong rigid solid pipes, siding, flooring

Polystyrene(PS)

–[CH2-CH(C6H5)]n–styrene

CH2=CHC6H5

hard, rigid, clear solidsoluble in organic

solvents

toys, cabinetspackaging (foamed)

Polyacrylonitrile(PAN, Orlon, Acrilan)

–(CH2-CHCN)n–acrylonitrileCH2=CHCN

high-melting solidsoluble in organic

solvents

rugs, blanketsclothing

Polytetrafluoroethylene(PTFE, Teflon)

–(CF2-CF2)n–tetrafluoroet

hyleneCF2=CF2

resistant, smooth solid non-stick surfaceselectrical insulation

Poly(methyl methacrylate)(PMMA, Lucite, Plexiglas)

–[CH2-C(CH3)CO2CH3]n–

methyl methacrylate

CH2=C(CH3)CO2

CH3

hard, transparent solid lighting covers, signsskylights

Poly(vinyl acetate)(PVAc)

–(CH2-CHOCOCH3)n–vinyl acetate

CH2=CHOCOCH3soft, sticky solid latex paints, adhesives

Some Common Addition Polymers