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 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 polymerization 2)condensation polymerization Addition polymerization : monomers react to form a polymer without net loss o f 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 °C 2000 atm O 2 peroxidespolyethylene H2CH2CH2CH2C CH 2 Free-Radical Addition Polymerization of Ethylene

99 MECHANISM MECHANISM – 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 POLYTHENE It is widely used polymer.It is of two types. (a)Low density polythene:- It is formed by heating ethylene to k under a pressure of 1500 atm in the presence of trace of oxygen. (b)High density polythene:- It is formed by heating ethylene to 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

3) POLYSTYRENE (STYRON) Monomer unit :- Styrene StyrenePOLYSTYRENE (C 6 H 5 CO) 2 O 2 USES :- It is used 1)In making light weight packaging materials. 2)In the manufacture of food containers, egg boxes, etc. 3)In making television cabinets.

Name(s)FormulaMonomerPropertiesUses Polyethylene low density (LDPE ) –(CH 2 -CH 2 ) n – ethylene CH 2 =CH 2 soft, waxy solidfilm wrap, plastic bags Polypropylene (PP) different grades –[CH 2 -CH(CH 3 )] n – propylene CH 2 =CHC H 3 atactic: soft, elastic solid isotactic: hard, strong solid similar to LDPE carpet, upholstery Poly(vinyl chloride) (PVC) –(CH 2 -CHCl) n – vinyl chloride CH 2 =CHCl strong rigid solid pipes, siding, flooring Polystyrene (PS) –[CH 2 -CH(C 6 H 5 )] n – styrene CH 2 =CHC 6 H 5 hard, rigid, clear solid soluble in organic solvents toys, cabinets packaging (foamed) Polyacrylonitrile (PAN, Orlon, Acrilan ) –(CH 2 -CHCN) n – acrylonitril e CH 2 =CHC N high-melting solid soluble in organic solvents rugs, blankets clothing Polytetrafluoroethy lene (PTFE, Teflon) –(CF 2 -CF 2 ) n – tetrafluoro ethylene CF 2 =CF 2 resistant, smooth solid non-stick surfaces electrical insulation Poly(methyl methacrylate) (PMMA, Lucite, Plexiglas) –[CH 2 - C(CH 3 )CO 2 CH 3 ] n – methyl methacrylat e CH 2 =C(CH 3 ) CO 2 CH 3 hard, transparent solid lighting covers, signs skylights Poly(vinyl acetate) (PVAc) –(CH 2 -CHOCOCH 3 ) n – vinyl acetate CH 2 =CHOC OCH 3 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 RESINS These 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