Polymers

Views:
 
Category: Entertainment
     
 

Presentation Description

No description available.

Comments

Presentation Transcript

P0LYMER : 

P0LYMER

Introduction : 

Poly means many and mer means units.Polymers are macromolecules consisting of large number of small repeating units called monomers.e.g. nCH2=CH2 Polymerisation (CH2– CH2)n Monomer Polymer Introduction

Degree of Polymerisation Is the number of monomers which combine to form polymers.It is denoted by n : 

e.g. nCH2=CH2 (CH2– CH2)n In the above example,n is the degree of polymerisation. n=M/m,where M is the molecular weight of polymer and m is the moleculer weight of monomer. Functionality is the number of bonding sites present in a monomer.e.g. In CH2=CH2 there are two bonding sites at which bonding may take place,so ethene is bifunctional. Degree of Polymerisation Is the number of monomers which combine to form polymers.It is denoted by n

I Classification of polymers on the basis of structure:- : 

Linear chain polymers are those in which monomers are joined in a linear chain . They have high density , high tensile strength and high melting point e.g. Polythene, Nylon, Polystyrene etc. (ii) Branched chain polymers are the polymers having side chains or branches in addition to the main chain . Branching hinders the close packing I Classification of polymers on the basis of structure:-

of the polymeric chain.That is why branched chain polymers are have less density,less tensile strength and low melting point.e.g. LDPE,starch etc. : 

(iii) Network or cross linked polymers are those in which monomers are cross linked together to form a three dimensional network.e.g. Bakelite of the polymeric chain.That is why branched chain polymers are have less density,less tensile strength and low melting point.e.g. LDPE,starch etc.

These are generally formed by the polymerisation of polyfunctional monomers.Cross linked polymers are hard,rigid and brittle. : 

II Classification based on the stereochemistry or tacticity:-Alkenes of the type H2C=CHZ may undergo polymerisation to form polymer (H2C – CHZ)n . The difference in the configuration of polymers is known as tacticity.There are three types of polymers on the basis of tacticity:- (i) Isotactic Polymers are those in which all the functional group Z are on the same side of the main carbon chain.e.g Cis-polyisoprene These are generally formed by the polymerisation of polyfunctional monomers.Cross linked polymers are hard,rigid and brittle.

Slide 7: 

H Z H Z H Z H Z H Z H H H H H H H H H H H H H Z H H same side H Z H H H Z

(ii) Syndiotactic polymers are thse in which the functional group Z are on the alternate side of the main carbon chain.e.g.trans-polyisoprene : 

Z H H Z Z H H Z H H H H H H H H H Z H H Z H H H H Z (ii) Syndiotactic polymers are thse in which the functional group Z are on the alternate side of the main carbon chain.e.g.trans-polyisoprene

(iii) Atactic polymers are are those in which the functional groups Z are arranged randomely along the main carbon chain.e.g. poly propylene : 

Z H Z H H Z Z H H Z H H H H H H H H H H Z H H H Z H H H H Z H H (iii) Atactic polymers are are those in which the functional groups Z are arranged randomely along the main carbon chain.e.g. poly propylene

III Classification based on the type of monomers:There are two types of polymers:- : 

(i) Homopolymers are formed by the polymerisation of one type of monomer e.g.PE,PMMA,PVC etc. (ii) Copolymers are formed by the polymerisation of more than one type of monomer.e.g.Nylon-6,6,Terylene,Vinyon etc. Nylon-6,6 is formed by the condensation of (hexamethylene diamine)H2N – (CH2)6– NH2 and (adipic acid) HOOC – (CH2)4- COOH III Classification based on the type of monomers:There are two types of polymers:-

Vinyon is formed by the condensation of (vinyl chloride)CH2=CHCl and (vinyl acetate)CH2=CHCOOCH3 : 

Depending upon the arrangement of A and B in the polymeric chain copolymers may be subdivided into four types:- Alternating copolymers:Monomers are arranged alternatively in the polymeric chain. nA + nB -A-B-A-B-A-B-A-B- e.g.Polyester,polyamide Vinyon is formed by the condensation of (vinyl chloride)CH2=CHCl and (vinyl acetate)CH2=CHCOOCH3

(ii)Random copolymers:-Monomers are arranged randomely.e.g. Butadiene and styrene : 

nA+nB A-A-B-A-B-B-B-A (iii) Block coploymers:-One block of one type of monomer is followed by the block of other type of monomer which is then followed by the first block. nA+nB A-A-A-B-B-A-A-A-B-B Ist block IInd Ist block (ii)Random copolymers:-Monomers are arranged randomely.e.g. Butadiene and styrene

Graft copolymers:-One type of monomer segment is grafted on the backbone chain of another type of monomer segment. : 

B B nA+nB -A-A-A-A-A-A- Back bone chain B B Grafted chain B Graft copolymers:-One type of monomer segment is grafted on the backbone chain of another type of monomer segment.

IV Classification on the basis of mode of synthesis:-There are two types of polymers. : 

Addition polymers are those which are formed by the polymerisation of monomers without elimination of atoms or groups. The mechanism of addition polymerisation involves three steps:- Chain initiataion by an initiator. (ii) Chain propagation. (iii) Chain termination. e.g. nCH2= CH2 CH2– CH2 n Polyethylene IV Classification on the basis of mode of synthesis:-There are two types of polymers.

nCH2= CH CH2– CH CH3 CH3 n Polypropylene : 

nCH2=CH CH2- CH C6H5 C6H5 n Polystyrene Condensation polymers are those which are formed by the condensation polymerisation of monomers with elimination of small molecules like NH3, H2O,HCl, etc. nCH2= CH CH2– CH CH3 CH3 n Polypropylene

Examples of condensation polymers are:- : 

n H2N – (CH2)6–NH2+n HOOC – (CH2)4– COOH -n H2O HN – (CH2)6– NH – CO – (CH2)4– CO n Poly hexamethylene adepate Polyamide Nylon 6,6 Examples of condensation polymers are:-

V Classification of polymers based on the action of heat : 

(a) Thermoplastics are those which soften on heating and can be remoulded again and again into desired shape.e.g. They are generally linear chain polymers(witout cross linking ) and the different chains are held together by Vanderwaal,s forces of attraction.e.g. LDPE,HDPE,PVC,PTFE,Nylon 6,6 etc. V Classification of polymers based on the action of heat

Thermosetting Polymers are those which do not soften on heating and can not be remoulded again into any other shape.e.g.Bakelite etc. : 

VI Classification on the basis of origin:- There are two types of polymers. (a) Natural polymers are those polymers which are obtained from the nature.e.g. starch,cellulose,proteins,natural rubber etc. (b) Synthetic polymers are those which are prepared in the laboratory.e,g. PVC,PE,Nylon,PTFE etc. Thermosetting Polymers are those which do not soften on heating and can not be remoulded again into any other shape.e.g.Bakelite etc.

VII Classification on the basis of chemical and geometrical structure:- : 

There are three types of polymers. Elastomers are the group of polymers exhibiting high degree of elasticity (reversible elongation 300% to 1000%),stretching at least twice of their original length under the action of tensile force and recover their dimensions after the removal of the applied force,just like rubber.Elastomers have long ,linear coiled and a few cross links.the polymeric chains are held together by weakest intermolecular forces.e.g. Natural rubber(cis-poly isoprene).There are two types of elastomers(i)Natural Elastomers e.g. Natural rubber (ii) Synthetic Elastomers e.g. synthetic rubber like Buna-S,Buna-N,Neoprene,Butyl rubber etc. VII Classification on the basis of chemical and geometrical structure:-

(ii) Fibres are polymers having thread like structure with high aspect ratio(length to diameter ratio)i.e. about 100:1.They have linear,unbranched symmetrical chains aligned in the direction of length. : 

Fabrics are knitted forms of yarns which are formed by spinning of a number of fibres.Fibre are further classified into:- Natural fibres:They are further classified as:- Plant fibre e.g.Cotton,linen and Animal fibres e.g. wool,silk etc. (ii) Artificial fibres are man made fibres like Polyamides e.g Nylon Polyesters e.g. Terylene Vinyls e.g. Acrylonitrile Rayons e.g. Cellulose acetate rayon (ii) Fibres are polymers having thread like structure with high aspect ratio(length to diameter ratio)i.e. about 100:1.They have linear,unbranched symmetrical chains aligned in the direction of length.

(iii) Plastics are the polymers which can be moulded into desired shape by the help of heat and pressure. : 

Resins are the basic binding materials that holds different constituents together in plastics . Resins are generally of low molecular weights. Ion exchange resins done already (iii) Plastics are the polymers which can be moulded into desired shape by the help of heat and pressure.

Phenolic Resins are the condensation products of phenol and formaldehyde.They are also known as PF resins : 

Phenolic Resins are the condensation products of phenol and formaldehyde.They are also known as PF resins CH2 CH2 CH2 CH2 OH OH OH OH CH2 CH2 CH2 CH2 CH2 CH2 OH OH OH OH Bakelite

Urea formaldehyde resins : 

A fully cross linked UF polymer is -N – CH2– N – CH2– N – CH2– O=C O=C O-C N – CH2– N – CH2– N – CH2- Cross linked UF resins Urea formaldehyde resins

Co-ordination Polymerisation or Zeiglar Natta Polymerisation : 

Co-ordination addition polymerisation is catalysed by a special type of catalyst known as Zeiglar Natta catalyst,which comprises of two components:- Co-catalyst Catalyst Al(C2H5)3 + TiCl4 (ii) Al(C2H5)3 + TiCl3 (iii) Al(C2H5)2Cl + TiCl4 Co-ordination Polymerisation or Zeiglar Natta Polymerisation

Slide 25: 

Here Titanium halides(catalyst)act as electron donor whereas Aluminium alkyls (co-catalyst) act as electron acceptor resulting in the formation of coordination complexes. Cl Cl C2H5 Ti Al Cl CH2 C2H5 CH3 Mechanism:- (i) Formation of complex due to overlapping of π-cloud of alkene and the empty orbital of Titanium.

(ii) Insertion of alkene molecule between Ti and C in Ti-C bond. : 

(iii) generation of vacant site at titanium due to intramolecular rearrangement and propagation of chain by step i and ii . (iv) Termination of chain by molecules having active hydrogen. (ii) Insertion of alkene molecule between Ti and C in Ti-C bond.

Slide 27: 

H CH3 C C (alkene) H H Ti – CH2– CH3 InitiationTi – CH2– CH – CH2CH3 CH3 Insertion of alkene between Ti-C bond Propagation nCH2=CHCH3

Slide 28: 

Ti – (CH2 – CH -)n+1 CH2 CH3 CH3 Termination HX H CH3– C –( CH2– CH -)n CH2 CH3 CH3 CH3 Ti - X

Significance of Zeiglar Natta Polymerisation:- : 

(i) This polymerisation is stereoselective i.e. units and substituents are arranged in space in definite pattern.Therefore isotactic polymers are formed ,which have superior properties than atactic polymers which are formed by conventional free radical polymerisation.e.g.Isotactic polypropylene has high m.p. and is hard but atactic polypropylene is soft and elastic. Significance of Zeiglar Natta Polymerisation:-

Slide 30: 

(ii) Unlike free radical polymerisation,Zeiglar Natta polymerisation leads to the formation of linear chain polymers devoid of branching,which have high density and high m.p. Individual polymers:- 1.Polyethylene:PE is a addition polymer and thermoplastic.It is of two types: Low density polyethylene (LDPE):-LDPE is prepared by the polymerisation of high purity ethylene at a pressure of 1000-1500 atm at 250oC in presence of initiator O2.

nCH2= CH2 !000-1500 atm. P ( CH2– CH2 )n 250oC Free radical polymerisation : 

LDPE molecules are highly branched,so they have low density. (b) High density polyethylene(HDPE) is obtained by polymerisation of ethylene molecules in the presence of Zeiglar Natta catalyst at 60-70oC and a pressure of 6-7 atm.The polymer thus obtained has high density. n CH2= CH2 6-7 atm.P ( CH2– CH2)n 60-70oC HDPE TiCl4+(C2H5)3 Al nCH2= CH2 !000-1500 atm. P ( CH2– CH2 )n 250oC Free radical polymerisation

2. Poly Vinyl Chloride PVC is a addition polymer,homopolymer and thermoplastic. : 

It is formed by the polymerisation vinyl chloride. n CH2= CH 40-50oC (CH2– CH)n Cl Persulphate Cl 3. Polymethyl Methacrylate PMMA is a addition polymer,homopolymer and thermoplastic. CH3 CH3 CH2= C CH2– C COOCH3 COOCH3 n Methyl methacrylate PMMA 2. Poly Vinyl Chloride PVC is a addition polymer,homopolymer and thermoplastic.

4. Polystyrene PS is a addition polymer,homopolymer and thermoplastic. : 

It is prepared by the polymerisation of styrene in the presence of benzoyl peroxide. n CH2= CH CH2– CH n 4. Polystyrene PS is a addition polymer,homopolymer and thermoplastic.

5. Polyacrylonitrile PAN is a addition polymer,homopolymer and thermoplastic. : 

It is prepared by the polymerisation of acrylonitrile in presence of FeSO4and H2O2 as catalyst. n CH2= CH Polymerisation (CH2–CH)n CN H2O2+ FeSO4 CN 5. Polyacrylonitrile PAN is a addition polymer,homopolymer and thermoplastic.

6. Polytetrafluoro ethylene PTFE is addition polymer,homopolymer and thermoplastic. : 

It is prepared by the polymerisation of tetra fluoro ethylene under pressure in presence of benzoyl peroxide. n F2C = CF2 (F2C – CF2)n 6. Polytetrafluoro ethylene PTFE is addition polymer,homopolymer and thermoplastic.

7. Polyamides are the polymers obtained by condensation of bifunctional acids and amines and they contain -CO –NH - i.e. amide group. : 

Nylon 6,6 is a condensation polymer,copolymer and thermoplastic.It is prepared by the poly condensation of hexamethylene diamine and adipic acid. n H2N – (CH2)6- NH2+ n HOOC-(CH2)4-COOH NH- (CH2)6-NH-CO-(CH2)4-CO n Nylon 6,6 7. Polyamides are the polymers obtained by condensation of bifunctional acids and amines and they contain -CO –NH - i.e. amide group.

(b) Nylon 6,10 is prepared by the condensation polymerisation of hexamethylene diamine and sebacic acid. It is thermoplastic. : 

n HOOC-(CH2)8-COOH + n H2N-(CH2)6-NH2 CO-(CH2)8-CO-NH-(CH2)6-NH n (c) Nylon 6 is prepared by (i) self condensation of E-caproic acid or (ii) by ring opening of E-caprolactum.It is a thermoplastic. n H2N-(CH2)5-COOH (NH-(CH2)5-CO)n (b) Nylon 6,10 is prepared by the condensation polymerisation of hexamethylene diamine and sebacic acid. It is thermoplastic.

O C (CO-(CH2)5-NH n NH Polyesters are the polymers formed by the polycondensation of bifunctional acids and alcohol.it is a condensation polymer,copolymer and thermosetting polymer.

Terylene or Dacron It is prepared by the polycodensation of Ethylene glycol and Terephthallic acid. : 

n HO-(CH2)2–OH + n HOOC- -COOH Ethylene glycol Terephthallic acid O O O-(CH2)2-O-C C n Glyptal is obtained by the polymerisation of polybasic acid with polyhydric alcohol.e.g Phthalic anhydride and Glycerol Terylene or Dacron It is prepared by the polycodensation of Ethylene glycol and Terephthallic acid.

Slide 40: 

O C CH2OH 2 O CH OH C CH2OH O Phathallic Anhydride Glycerol O O C-O-CH2-CH-CH2– O-C OH C-OH HO-C O O Alkyd resin

Slide 41: 

CO-O-CH2– CH-CH2–O-CO -O-CO- CO-O- n Polyster Alkyd Resin

Natural Rubber is cis-poly isoprene which is 2-methyl 1,3 butadiene. : 

n CH2=C-CH=CH2 CH2–C=CH-CH2 CH3 CH3 n Synthetic rubber:- Styrene rubber or Buna S is prepared by polymerisation of styrene and 1,3 butadiene nCH2=CH – CH = CH2+ 1,3 Butadiene CH2=CH Styrene Natural Rubber is cis-poly isoprene which is 2-methyl 1,3 butadiene.

Slide 43: 

CH2– CH=CH – CH2– CH2–CH n Styrene rubber or Buna S

Nitrile rubber or Buna N is prepared by polymerisation of 1,3butadiene and acrylonitrile. : 

n CH2=CH-CH=CH2+ n CH2=CH CN CH2– CH=CH-CH2–CH2–CH n CN Neoprene is prepared by polymerisation of Chloroprene. n CH2=C-CH=CH2 CH2–C=CH-CH2 n Cl Cl Nitrile rubber or Buna N is prepared by polymerisation of 1,3butadiene and acrylonitrile.

Butyl rubber is formed by copolymerisation of Isobutene and isoprene. : 

CH3 n CH2=C + n CH2=C - CH=CH2 CH3 CH3 CH3 CH2– C –CH2–C = CH – CH2 n CH3 CH3 Butyl rubber is formed by copolymerisation of Isobutene and isoprene.

Conducting Polymers are good conductors of electricity. : 

Principles of conducting Polymers:- (i) Polymers having extensive conjugation of π-bonds (hence π-electrons) in the polymeric backbone or ring structure increases their conductivities to a large extent.This is because in such cases π electrons get excited from valence band to conduction band and the band gap decreases to 0.5 to 1 ev.(Band gap for metals is zero,and for insulating polymer band gap is 1.5 to 4 ev.) Conducting Polymers are good conductors of electricity.

e.g.trans polyacetylenen CH=CH n : 

Polypyrrole n N N n H H (ii) The conductivities of such polymers can be increased by doping with suitable impurities.Depending on the type of dopant used positive or negative charge can be created on polymer backbone by oxidation or reduction.This leads to the formation of p-type (i.e. hole dominant or n-type (i.e. free electron dominant) polymers. p-doping: Polymer + A (Polymer)+n A-n (with extensive (Lewis acid (p-type doped conucting polymer conjugation) Electron acceptor ) obtained by oxidation ) where A=I2,Br2,FeCl2,AsF3etc. e.g.trans polyacetylenen CH=CH n

(b)n-doping: : 

Polymer + B (Polymer)-nB+n With extensive Lewis base Doped conducting conjugation Electron polymer obtained donor by reduction Where B=Na,Li etc. Doping leads to the formation of new energy bands which overlaps with valence and conduction bands.This results in the formation of partially filled conduction and valence band apart from the production of holes or free electrons at room temperature.Therefore conductivity increases. (b)n-doping:

Synthesis of conducting polymers : 

Polypyrrole is obtained by electropolymerisation of pyrrole. Polythiophene is obtained by anodic oxidation of thiophene. n S S Properties of Polypyrrole and Polythiophene The electrical conductivity of polypyrrole and Synthesis of conducting polymers

Slide 50: 

Polythiophene is due to extensive conjugation (and hence π electrons)in the polymeric backbone and doping with BF4-,ClO4- ,p-methyl phenyl sulphonate.They are very stable in air. Applications: 1.In rechargeable batteries. e.g.Lithium poly(p-phenylene) batteries have high reliability,light weight as compared to lead storage batteries. 2.Making conducting paints.

Biodegradable Plastic is defined as a degradable plastic in which degradation occurs by the action of : 

naturally occurring microorganisms such as bacteria,fungi and algae.Degradation is a irreversible change in which there is loss of properties due to change in the structure of polymer by the action of microorganisms.Polymers having weight less than 9000 are generally accessible to bacteria and are converted into dust in the presence of sunlight.A good biodegradable polymer should not produce toxic products. Biodegradable Plastic is defined as a degradable plastic in which degradation occurs by the action of

Slide 52: 

Natural biodegradable polymers are polysaccharides e.g.starch,cellulose,Polyesters,Proteins like wool,silk,natural rubber etc. Synthetic biodegradable polymers are polyvinyl alcohols,polyvinyl esters,Polyamide esters,polyalkylene esters,PHBV(Poly Hydroxybutyrate Hydroxy valerate These polymers are expensive,emit green house gases,toxic gases and may have adverse effect on environment.Efforts are being made to produce such polymers which do not produce harmful effects.

Applications of synthetic Biodegradable polymers : 

1.PHB or Poly β-hydroxy butyrate is used in the manufacture of shampoo bottles. 2.HB-HV or β-hydroxybutyrate-β-hydroxy valerate are used to make the coatings of controlled release drugs. 3. PLA or polylactic acid easily breaks down in the environment to lactic acid .So it is used to make wound clips and time release coatings for fertilisers and pesticides. Applications of synthetic Biodegradable polymers

Organometallics : 

Compounds which contain carbon metal bond are known as organometallic compounds.Due to the difference in electronegativity of Carbon and metal ,carbon acquires partial negative charge and metal acquires partial positive charge. C– M Cδ– Mδ+ Where M=Mg,Ca,Na,Li,Al,Sn,Pb etc. Organometallics

H Methyl Lithium H – C – Li H : 

Triethyl aluminium C2H5 H5C2– Al C2H5 Tetraethyl lead C2H5 H5C2– Pb – C2H5 C2H5 H Methyl Lithium H – C – Li H

Grignard Reagent is an example of organometallic compound. : 

Classification: Organometallics Simple Mixed Alkyls/aryls groups Groups other than alkyl are attached to metal are attached to metal atoms e.g.(C2H5)4Pb, atom e.g. CH3–Mg-Br CH3Li C2H5– Mg - Br Grignard Reagent is an example of organometallic compound.

Classification on the basis of Carbon Metal bond : 

1.Ionic organometallics are the compounds in which negatively charged part of hydrocarbon part and positively charged part of metal ions are held together by electrostatic forces of attraction e.g. C10H8Na 2.Sigma bonded covalent organometallics are formed by non transition metals with a sigma covalent bond. E.g. Al(CH3)3 Classification on the basis of Carbon Metal bond

3.π-organometallics are also formed by transition metals . : 

Organometallic compounds of transition metals are further subdivided into : Aryl or Alkyl complexes are prepared as follows TiCl4+4LiCH3 Dry ether Ti(CH3)4 + 4 LiCl (b) Alkene complexes contain alkenes. E.g. Ziese,s salt K2PtCl4+ C2H4 K PtCl3(C2H4) + KCl 3.π-organometallics are also formed by transition metals .

(c) Sandwitch Bonded complexes are those in which transition metal is sandwitched with delocalised organic part. : 

e.g. Ferrocene Fe It is prepared by the action of cyclopentadiene with finely divided iron at 300oC Fe +2C5H6 Fe(C5H5)2 (c) Sandwitch Bonded complexes are those in which transition metal is sandwitched with delocalised organic part.

(d) Mixed complexes contain both olefinic as well as symetrically delocalised organic part. : 

Applications of Organometallic compounds: Synthesis of different class of organic compounds. 2. In catalysis:TEL i.e tetra ethyl lead is used as negative catalyst to prevent the knocking of petrol in internal combustion engines.During combustion of petrol ,alkyl free radicals are formed.TEL traps the alkyl free radical and terminates the chain reaction. (C2H5)4Pb 4C2H5. + Pb. R. + .C2H5 R – C2H5 Alkane (d) Mixed complexes contain both olefinic as well as symetrically delocalised organic part.

3.Hydrogenation of alkenes is done in presence of Rhodium catalyst . : 

4. Hydroformylation of alkenes is done using Co or Rh compounds. 5. In polymerisation:Zeiglar Natta catalyst consists of organometallic compound and is widely used as a co-ordination catalyst in the synthesis of isotactic polymers. 3.Hydrogenation of alkenes is done in presence of Rhodium catalyst .

Slide 62: 

Preparation: 1.Organolithium compounds are prepared by the reaction of alkyl halides with Lithium metal in dry ether in inert atmosphere of N2 . CH3– I + 2Li Ether CH3Li + LiI -10 C 2. Tetra ethyl lead is prepared by the action of ethyl magnesium iodide on lead chloride. 4C2H5MgI +2PbCl2 (C2H5)4Pb + Pb+4MgICl

authorStream Live Help