Chemistry 367L/392N Macromolecular Chemistry Lecture 6 M M PI n w 

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

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

Chemistry 367L/392N Initiation

Propagation

Termination Disproportionation Coupling +

Radical Generation Thermolysis Thermolysis Thermal decomposition of azo-compounds 2,2’-azobis(2-methylpropanenitrile)1,1’-azobis(1-cyclohexanenitrile) (AIBN)

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

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

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

Chemistry 367L/392N Self initiation of monomer

Chemistry 367L/392N = 0.693/k d For efficient polymerization rate - need sufficient radicals. Too few - slow, poor conversion with t Too many - exothermic, low mol. wt AIBN hrs hr 1 hr mins 6 mins min 1 min Optimum = o C --> Reaction Time ~ 2-3 (t 1/2 ) [I][I] k = k max max e -E/kT e -E/kT [Time] dtId][kd I → 2 R· kd k t d 2ln 2/1 

Chemistry 367L/392N Decomposition of Thermal Initiator di-tert-butylperoxideAIBNdi-tert-butylperoxalate f = 0.65f = 0.75f=0.95   I kf dt Rd d 2 R i  Efficiency factor ( f ): k d I → 2 R·

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

Chemistry 367L/392N - d[M·] Ri=Ri=Ri=Ri= dt = 2 k t [M·] 2 Where k t = k tc + k td Rp=Rp=Rp=Rp= dt -[M]-d[M]-[M]-d[M] = k p [M][M·] = k p [M][M·] [M·]= Kinetics of free radical polymerization  Steady state assumption: What is the Propagation rate ( Rp ) 2 ][2][2  MkIfk td t d kIfk][ Rp=Rp=Rp=Rp= dt -d[M] = k p [M] = k p [M] t d kIfk][So… Ri = Rt

Chemistry 367L/392N Average kinetic chain length ( Ӯ ) Disproportionation : Disproportionation : Combination : Combination : Kinetics of free radical polymerization Ӯ R R R R t p i p  Ӯ ][( ][ 2 ][2 ][ ][ 2 ]][[ 2 Ikfk Mk Mk Mk Mk MM K dt p t p t p       DP = 2Ӯ2Ӯ2Ӯ2Ӯ Ӯ

Chemistry 367L/392N 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, 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 367L/392N TEMPO Controlled Polymerization (2,2,6,6-tetramethylpiperidinyl-1-oxy) TEMPO 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." (2,2,6,6-tetramethylpiperidinyl-1-oxy) TEMPO

Chemistry 367L/392N Controlled Free Radical Polymerization

Chemistry 367L/392N Control of polymer Architecture

Chemistry 367L/392N