SYNTHETIC POLYMERS. The word, polymer, implies that polymers are constructed from pieces (monomers)...
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Transcript of SYNTHETIC POLYMERS. The word, polymer, implies that polymers are constructed from pieces (monomers)...
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