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Macromolecular Chemistry

M. w. =. PI. M. n. Macromolecular Chemistry. Lecture 6. Molecular Weight Distribution in Polymeric Materials. Polymer %. Molecular weight. Radical Chain Growth Polymerization.

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Macromolecular Chemistry

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  1. M w = PI M n Macromolecular Chemistry Lecture 6

  2. Molecular Weight Distribution in Polymeric Materials Polymer % Molecular weight

  3. Radical Chain Growth Polymerization • Among the initiators used for radical chain-growth polymerization are diacyl peroxides, which decompose as shown on mild heating

  4. Initiation

  5. Propagation

  6. Termination Coupling + Disproportionation

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

  8. Thermolysis of peroxides -O-O- Thermal decomposition of peroxides Benzoylperoxide (BPO) di-tert-butylperoxide sodium persulfate

  9. Photolysis Photolysis of benzoin (R=R’=H).

  10. Redox Initiators Redox decomposition of cumyl hydroperoxide Redox decomposition of persulfate

  11. Self initiation of monomer

  12. k k I → 2 R· d d d [ I ] ln 2 = t 1 / 2 k d = - dt e -E/kT k= k max [I] = 0.693/kd [Time] For efficient polymerization rate - need sufficient radicals. Too few - slow, poor conversion with t Too many - exothermic, low mol. wt AIBN 64 10 hrs 82 1 hr 100 6 mins 120 1 min ) Optimum = 75-90 C o --> Reaction Time ~ 2-3 (t 1/2

  13. k d [ ] d R • [ ] = = I R 2 f k dt i d Decomposition of Thermal Initiator I → 2 R· Efficiency factor ( f ): di-tert-butylperoxide AIBN di-tert-butylperoxalate f = 0.65 f = 0.75 f=0.95

  14. Temperature of 1 hr t1/2

  15. Where kt = ktc+ ktd Ri= =2 kt [M·]2 dt -d[M] = kp[M][M·] Rp= dt fk fk [ [ I I ] ] d d k k t t Kinetics of free radical polymerization Ri = Rt  Steady state assumption: -d[M·] = × 2 fk [ I ] 2 k [ M ] 2 So… [M·]= d t What is the Propagation rate ( Rp ) -d[M] = kp[M] Rp= dt

  16. Kinetics of free radical polymerization Average kinetic chain length(Ӯ) R R p p = = Ӯ R R i t k [ M ] k [ M ] × [ M ][ M ] p p Ӯ = = = 2 K p × 2 × 2 2 k [ M ] ( fk k [ I ] k [ M ] t d t t Ӯ  Disproportionation : Combination : DP = 2Ӯ DP =

  17. 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.

  18. I I O N O N + M o n o m e r P o l y m e r O N P o l y m e r O N + TEMPO Controlled Polymerization (2,2,6,6-tetramethylpiperidinyl-1-oxy) TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy) TEMPO

  19. Controlled Free Radical Polymerization

  20. Control of polymer Architecture

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