Polymer chemistry

Polymer Chemistry Part Polymer Characteristics and Classifications Polymer Poly many mer repeat unit (building blocks) repeat unit repeat unit H H H H H H C C C C C C H H H H H H H H H H H H C C C C C C H Cl H Cl H Cl Polyethylene (PE) Poly(vinyl chloride) (PVC) repeat unit H C H H H C C CH3 H H H C C CH3 H H C CH3 Polypropylene (PP) Carbon chain backbone Definitions Polymer – A very long molecule composed of repeating units connected by covalent bonds Monomer – A repeated unit in a polymer The reactant for the polymerization reaction Characterizing a Polymer  Structure  Classification  Synthesis Skeletal Structure  Linear – a chain with two ends Skeletal Structure  Branched – have side chains Skeletal Structure  Crosslinked (Networked) – chains are connected to other chains Classification of polymer 1- Based on monomer source Addition and Condensation Polymers The addition polymer is often named according to the monomer that was used to form it Example : poly( vinyl chloride ) PVC is made from vinyl chloride -CH2-CH(Cl)If “ X “ is a single word the name of polymer is written out directly ex polystyrene -CH2-CH(Ph)Poly X If “ X “ consists of two or more words parentheses should be used ex , poly (vinyl acetate ) -CH2-CH(OCOCH3)The most common method for condensation polymers since the polymer contains different functional groups than the monomer Classification by Origin  Synthetic organic polymers  Biopolymers (proteins, polypeptides, polynucleotide, polysaccharides, natural rubber)  Semi-synthetic polymers (chemically modified synthetic polymers)  Inorganic polymers (siloxanes, silanes, phosphazenes) Classification by Monomer Composition Copolymer Homopolymer Block Graft Alternating Homopolymer Consist of only one type of constitutional repeating unit (A) AAAAAAAAAAAAAAA copolymer Consists of two or more constitutional repeating units (A.B ) Statistical Polymers are large molecules made up of repeating units called Monomers The synthetic process is Polymerization E.g H2C CH2 Polymerization Monomer O Monomer CH2 CH2 n Polymer Polymerization CH2 CH2 O Polymer n Note – define repeating unit in terms of monomer structure Degree of Polymerization is the number of monomer units in a Polymer However, for synthetic polymers it is more accurate to state average degree of polymerization (DP ¯) Two main classifications of Polymerization Addition reaction or Chain growth Molecular weight increases by successively adding monomers to a reactive polymer chain end resulting in high molecular weights at low conversions STEP reaction or growth Polymers are formed by linking monomer molecules to form dimers, trimers and higher species in a step-wise fashion The most abundant species react, and thus high molecular weight formed only beyond 99% conversion Polymerization Conversion (p) P = M0 - Mt M0 M0 = initial number of monomer molecules Mt = Number of monomer molecules at time t Ionic Chain (addition)-Growth Polymerization The choice of ionic procedure depends greatly on the electronic nature of the monomers to be polymerized Vinyl monomers with electron-withdrawing groups CN CN CO2R CO2R CO2R Anionic Polymerization Vinyl monomers with electron-donating groups N OR SR Cationic Polymerization Monomers and reagents should be scrupulously purified; water and oxygen should be removed Polymerizations carried out at very low temperatures Anionic Polymerizations Initiators include alkyl lithiums and sodium amide Cationic Polymerization the formed carbocation must be quite stable + Stable tertiary carbocation H+ OR H+ + OR stable oxonium ion E.g proton initiates polymerization of isobutane (2-methylpropene) BF3/H2O n Adhesive, sealant, insulating oil, lubricating oil Reactions of water with reactive carbanions and carbocations H O _ CN CN H H acid CN CN CN CN n + _ OH Note – viable substrates for anionic polymerizations not have α -protons H H O H base H + OMe OMe OMe n OMe OMe + H3O+ OMe n n Chain Reaction: Free Radical Polymerization RO Initiation RO OR RO + RO Ph Propagation Ph RO RO Ph Ph Random Termination n n Ph Ph Dead chains Conventional Radical Polymerization Advantages – 1/wide range of vinyl monomers polymerizable 2/can be carried out in bulk, water, organic solvents and other solvents 3/no rigorous purification or drying of reagents required Conditions: Usually heat required for initiation Initiator decomposition time should be considered - Amount of initiator, reaction temperature and initiator half-life (slow decomposition) Initiation Rate = Termination Rate - “steady state” kinetics apply Overall, [radical concentration] = low Since termination (disproportionation and coupling mechanism) is random, a broad MWD results This polymer is dead (cannot initiate new monomer additions) Examples of Polymers Prepared by Radical Polymerization Monomer H H n H n H H H n C MeO n O Me n O Poly(methylacrylate) OMe H H Poly(acrylonitrile) n CH2CH O H Poly(styrene) CN H H n CH2CH CN H Polymer CH2CH CH2CH n O O C Me O Poly(vinylacetate) Ziegler-Natta Chain (Addition) Polymerization H H C C H H TiCl4/AlEt3 1-4 atm, rt n Milder conditions than radical polymerization HDPE (high density poly(ethylene) is 3-10 times stronger than LDPE Less cross-linking, as terminal DBs less reactive than substituted DBs of radical polymerization Termination reaction H H Cl3Ti Few monomers polymerized by Z/N + Cl H Ti Cl Cl Ziegler-Natta Addition Polymerization Isotactic polymerization TiCl4 / AlR3 R 1-4 atm, rt n R Cl3Ti TiCl4 + AlR3 Cl3Ti AlR2 R + Cl σ−complex Cl AlR2 R Cl3Ti Cl3Ti R Cl3Ti π−complex Cl3Ti R Cl3Ti R Cl3Ti R Cl3Ti n R R Step-growth Polymerization Step-polymers are made by allowing difunctional monomers with complementary functional groups to react with one another Condensation between two molecules O HO O + MeO OMe terephthalic acid O O C C OCH2CH2O n OH ethylene glycol Poly(ethylene terephthalate) This is an example of a poly(ester) The reaction is a transesterification Using a condensation reaction PET Recyclable plastic bottles and textile fabrics Step-growth Polymerization These are poly(amides) – bristles of toothbrishes, stockings, rope, tires, carpet fibre Molten nylon spun into fibres - H 2O 260-280 °C 250 psi First patented by Dupont MW = 10,000, m.pt 250 °C, fibres stretched (to increase strength) to times their length Self-Condensation or Ring-Opening Polymerization Also opened by cations & anions First patented by BASF High temp to drive off water Nylon is made by heating caprolactam to about 250 ºC with about 5-10% water Insulation foam, HP adhesives, sealants, carpet underlay Step-addition – “no by-products” O C N N C O N N H H Lower Temp than condensation reactions O CH2 O BF3 n O O benzoquinone n Cyclic diene held cis is very reactive e.g dicyclopentadiene Chain-growth condensation CH2N2 O O Poly(urethane) rt + bisdiene OH O 180 °C CH2 + O Bayer-patented HO [ CH ] n + N2 Impurity found in diazomethane Condensation  Self condensation: Condensation within the same molecule having two different functional groups  Condensation of amino acid molecule Ring opening: caprolactum to nylon-6  Poly condensation  Polyamides [...]... essential to produce polymer with height average molecular weight Polymers are large molecules made up of repeating units called Monomers The synthetic process is Polymerization E.g H2C CH2 Polymerization Monomer O Monomer CH2 CH2 n Polymer Polymerization CH2 CH2 O Polymer n Note – define repeating unit in terms of monomer structure Degree of Polymerization is the number of monomer units in a Polymer However,... chains :a polymer consisting of a single continuous chain of repeat units Branched chains :a polymer that includes side chains of repeat units connecting onto the main chain of repeat units Hyper branched polymer consist of a constitutional repeating unit including a branching groups Cross linked polymer :a polymer that includes interconnections between chains Net work polymer :a cross linked polymer. .. (vulcanized rubber) Cannot be recycled (burn/scorch with heat) Natural* thermosets – vulcanized rubber Polymer Chemistry Part 2 Polymer Synthesis Polymerization mechanisms Chain Growth The only growth reaction is addition of monomer to a growing chain with a reactive monomer The reaction mixture consists of high polymer and unreacted monomers with very few actively growing chain Monomer concentration decreases... units in a Polymer However, for synthetic polymers it is more accurate to state average degree of polymerization (DP ¯) Two main classifications of Polymerization Addition reaction or Chain growth Molecular weight increases by successively adding monomers to a reactive polymer chain end resulting in high molecular weights at low conversions STEP reaction or growth Polymers are formed by linking monomer... Cationic Polymerization Monomers and reagents should be scrupulously purified; water and oxygen should be removed Polymerizations carried out at very low temperatures Anionic Polymerizations Initiators include alkyl lithiums and sodium amide Cationic Polymerization the formed carbocation must be quite stable + Stable tertiary carbocation H+ OR H+ + OR stable oxonium ion E.g proton initiates polymerization... random, a broad MWD results This polymer is dead (cannot initiate new monomer additions) Examples of Polymers Prepared by Radical Polymerization Monomer H H n H n H H H n C MeO n O Me n O Poly(methylacrylate) OMe H H Poly(acrylonitrile) n CH2CH O H Poly(styrene) CN H H n CH2CH CN H Polymer CH2CH CH2CH n O O C Me O Poly(vinylacetate) Ziegler-Natta Chain (Addition) Polymerization H H C C H H TiCl4/AlEt3... TiCl4/AlEt3 1-4 atm, rt n Milder conditions than radical polymerization HDPE (high density poly(ethylene) is 3-10 times stronger than LDPE Less cross-linking, as terminal DBs less reactive than substituted DBs of radical polymerization Termination reaction H H Cl3Ti Few monomers polymerized by Z/N + Cl H Ti Cl Cl Ziegler-Natta Addition Polymerization Isotactic polymerization TiCl4 / AlR3 R 1-4 atm, rt n R Cl3Ti... Statistical copolymer (Random) ABAABABBBAABAABB two or more different repeating unit are distributed randomly  Alternating copolymer ABABABABABABABAB are made of alternating sequences of the different monomers  Block copolymer AAAAAAAAABBBBBBBBB long sequences of a monomer are followed by long sequences of another monomer  Graft copolymer AAAAAAAAAAAAAAAAAA B B B B B B Consist... _ OH Note – viable substrates for anionic polymerizations do not have α -protons H H O H base H + OMe OMe OMe n OMe OMe + H3O+ OMe n n Chain Reaction: Free Radical Polymerization RO Initiation 2 RO OR RO + RO Ph Propagation Ph RO RO Ph Ph Random Termination n n Ph Ph Dead chains Conventional Radical Polymerization Advantages – 1/wide range of vinyl monomers polymerizable 2/can be carried out in bulk,... disappear early in favor of low oligomer Polymerization mechanisms Chain growth High polymer appears immediately , average molecular weight does not change much as reaction proceeds Step Growth Oligomers steadily increases in size, polymer average molecular weight increases as reaction proceeds Increased reaction time increases overall product yield , but does not affect polymer average molecular weight Long ...  Semi-synthetic polymers (chemically modified synthetic polymers)  Inorganic polymers (siloxanes, silanes, phosphazenes) Classification by Monomer Composition Copolymer Homopolymer Block Graft... Monomer CH2 CH2 n Polymer Polymerization CH2 CH2 O Polymer n Note – define repeating unit in terms of monomer structure Degree of Polymerization is the number of monomer units in a Polymer However,... Polymer – A very long molecule composed of repeating units connected by covalent bonds Monomer – A repeated unit in a polymer The reactant for the polymerization reaction Characterizing a Polymer