Synthesis of Polymers Prof. Paula Hammond Lecture 21: Living Anionic Polymerization, Effects of Initiator and Solvent

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1 Sythesis of Polymers Prof. Paula Hammod Lecture 21: Livig Aioic Polymerizatio, Effects of Iitiator ad Solvet Livig Polymerizatio d M ] R p = = k p M ]M ] dt M ] ] I o (assumes all iitiator is active ad available) R p = k p l M M ]I o M ] ] o = k p M ] t = k p ] I t ] costat log M] o M] slope = k p I] tim me M ] π M ] o ] I ] I p p = = polymer grows at exactly the same rate (moomer iitiated at exactly the same time) p liear with time M] I] 0 time M ] for complete coversio p o = ] I PDI: M w = 1 ν M (ν 1) 2 (ot real PDI, but for statistical purposes) Citatio: Professor Paula Hammod, Sythesis of Polymers Fall 2006 materials, MIT pecourseware ( Massachusetts Istitute of Techology, Date.

2 Citatio: Professor Paula Hammod, Sythesis of Polymers Fall 2006 materials, MIT pecourseware ( Massachusetts Istitute of Techology, Date. Where ν = kietic chai legth M w as ν, 1 M predicts PDI Poisso distributio istead of Gaussia distributio Solvet Characteristics Most commo solvets petae hexae cyclohexae bezee dioxae icreasig polarity 1,2 dimethoxyethae CH 3 CH 2 CH 2 CH 3 tetrahydrofura dimethyl formamide H 3 C N C H CH 3 solvet must solvate moomer polymer fuctio of polarity importat solvet effects i aioic polymerizatio rate of polymerizatio highly depedet o accessibility of (propagatig aio) associatio effects degree of couterio/io dissociatio 1. Associatio Effects: Low dielectric (opolar) solvets are poor eviromets for ios: Possible to form micellelike aggregates: opolar chais aggregatio probabilities as polarity of solvet ad as couterio size depedecy o cocetratio: as coc, agg opolar solvet , Sythesis of Polymers, Fall 2006 Lecture 21 Prof. Paula Hammod Page 2 of 5

3 dyamic structure equilibrium Li uimer this species ca propagate K e { M } M let = # of chais per aggregate bracket deotes aggregate M ] K e = { M ] M ] 1/ M 1/ = K { } ] e ] equilibrium costat R p = d M = k pk e M dt 1/ ]{M ] 1/ (assume all aggregates have same umber of chais) see 1/ depedecy i rate of propagatio with respect to M ] { M } ] M ]= ] I ca assume I] {M } ] R p k p K e 1/ M ] I ] 1/ If aggregatio umber is 2, (=2) R = k K M ]{ M ] p p e 2 k p K e M ] I ] aggregate form 2. Degrees of dissociatio of couterio ad chai (happes much more frequetly) differet degrees of dissociatio: Free ios: , Sythesis of Polymers, Fall 2006 Lecture 21 Prof. Paula Hammod Page 3 of 5 Citatio: Professor Paula Hammod, Sythesis of Polymers Fall 2006 materials, MIT pecourseware ( Massachusetts Istitute of Techology, Date.

4 S S S S S S SS ios are fully dissociated from egative charge assume full availability of charge to react with moomer Versus 2 types of io pairs a) usolvated io pairs (tight pairs) cotact io pairs b) solvet separated io pairs (loose ioio coectios) solvet molecules separate ios thi layer of solvet that separates couterio from charge reactio rates of species are goig to be differet k p rate costat for free ios k pi rate costat for all io pairs ad k pi = yk pll (1y)kp c parallel sig k pll = solvet separated pair y = fractio of solvet separated pair Equilibrium betwee free ad dissociated io pairs: k pi k p polymerize polymerize Dissociated rate costat = ] ] ] assume ] = ] (o additio of Cl that drives up ]) , Sythesis of Polymers, Fall 2006 Lecture 21 Prof. Paula Hammod Page 4 of 5 Citatio: Professor Paula Hammod, Sythesis of Polymers Fall 2006 materials, MIT pecourseware ( Massachusetts Istitute of Techology, Date.

5 = ] 2 ] Give that M ] = cocetratio of all ioic sites (free ad associated) # of dissociated (free) ios α all ios α M ] α M ] = (1 α )M ] = 1 α solve for α: ] α M assumig that α = small eglect 1α term i deomiator k p = αk p (1 α )k pi ] = k pi (k p k pi M ] d M R P = ) ]M dt M ] I] , Sythesis of Polymers, Fall 2006 Lecture 21 Prof. Paula Hammod Page 5 of 5 Citatio: Professor Paula Hammod, Sythesis of Polymers Fall 2006 materials, MIT pecourseware ( Massachusetts Istitute of Techology, Date.

Samples questions on Polymer Chemistry

Samples questions on Polymer Chemistry Samples questios o Polymer Chemistry Symbols carry usual meaigs Module 1: Lecture 1-3 1. For a polydisperse polymer sample rak the M, M w, M z, ad M v accordig to their values. I 10 g of a polystyree sample