Macromolecular Chemistry Mw PI Mn Lecture 6 Chemistry

Macromolecular Chemistry Mw PI = Mn Lecture 6 Chemistry 367 L/392 N

Polymer % Molecular Weight Distribution in Polymeric Materials Molecular weight Chemistry 367 L/392 N

Radical Chain Growth Polymerization l Among the initiators used for radical chain-growth polymerization are diacyl peroxides, which decompose as shown on mild heating Chemistry 367 L/392 N

Initiation Chemistry 367 L/392 N

Propagation Chemistry 367 L/392 N

Termination Coupling + Disproportionation Chemistry 367 L/392 N

Radical Generation l Thermolysis Thermal decomposition of azo-compounds 2, 2’-azobis(2 -methylpropanenitrile) (AIBN) 1, 1’-azobis(1 -cyclohexanenitrile) Chemistry 367 L/392 N

Thermolysis of peroxides -O-O- Thermal decomposition of peroxides Benzoylperoxide (BPO) di-tert-butylperoxide sodium persulfate Chemistry 367 L/392 N

Photolysis of benzoin (R=R’=H). Chemistry 367 L/392 N

Redox Initiators Redox decomposition of cumyl hydroperoxide Redox decomposition of persulfate Chemistry 367 L/392 N

Self initiation of monomer Chemistry 367 L/392 N

d[I ] kd = dt kd I → 2 R· -E/k. T e k = k max [I] t = 1/ 2 [Time] ln 2 k = 0. 693/kd d For efficient polymerization rate - need sufficient radicals. Too few - slow, poor conversion with t Too many - exothermic, low mol. wt AIBN 64 82 100 120 Optimum = 75 -90 o C 10 hrs 1 hr 6 mins 1 min --> Reaction Time ~ 2 -3 (t 1/2 ) Chemistry 367 L/392 N

Decomposition of Thermal Initiator kd I → 2 R· Efficiency factor ( f ): di-tert-butylperoxide f = 0. 65 R = i AIBN f = 0. 75 d [ R • ] dt di-tert-butylperoxalate f=0. 95 = 2 f k [ I] d Chemistry 367 L/392 N

Temperature of 1 hr t 1/2 Chemistry 367 L/392 N

Kinetics of free radical polymerization Steady state assumption: Ri = Rt - d[M·] R i= = 2 kt [M·]2 Where kt = ktc+ ktd dt fk d [ I ] 2 fk d [ I ] = 2 k t [ M ×] 2 So… [M·]= kt What is the Propagation rate ( Rp ) -d[M] = kp[M][M·] Rp= dt -d[M] = k p[ M ] Rp= dt fkd[ I ] kt Chemistry 367 L/392 N

Kinetics of free radical polymerization Average kinetic chain length ( Ӯ ) Rp Rp = Ӯ = Ri Rt k p [M ] k p[M ] [ M ][ M ×] = =2 Ӯ=Kp 2 2 kt [ M ×] 2 kt [ M ×] ( fktkd[ I ] Disproportionation : DP = Ӯ Combination : DP = 2Ӯ Chemistry 367 L/392 N

Arthur K. Doolittle Award The Arthur K. Doolittle Award, established by the Union Carbide Corporation, is given to the authors of an outstanding paper presented before the PMSE Division at each national meeting of the ACS. A prize in the amount of $1, 000. 00 is financed with the gift of royalties from A. K. Doolittle's book, Technology of Solvents and Plasticizers. All papers are evaluated on the basis of content, with emphasis on originality and development of new concepts, and on the quality of presentation. Recipients are selected by an anonymous panel of judges appointed by the Chairman of the Doolittle Award Committee. Chemistry 367 L/392 N

TEMPO Controlled Polymerization 1993 M. K. Georges, R. P. N. Veregin, P. M. Kazmaier and G. K. Hamer (Xerox Corporation), "Narrow Molecular Weight Resin by Free Radical Process. " I I O + O N N (2, 2, 6, 6 -tetramethylpiperidinyl-1 -oxy) TEMPO Monomer Polymer + O O N N Chemistry 367 L/392 N

Controlled Free Radical Polymerization Chemistry 367 L/392 N

Control of polymer Architecture Chemistry 367 L/392 N

Chemistry 367 L/392 N