Macromolecular Chemistry

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Jerzy Wilk
5 lat temu
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1 Macromolecular Chemistry Mn = MiNi Ni Mw = WiMi = Wi NiMi 2 NiMi PI = M M w n Lecture 6

2 Molecular Weight Distribution in Polymeric Materials Polymer% Molecular weight

3 adical Chain Growth Polymerization Among the initiators used for radical chain-growth polymerization are diacyl peroxides, which decompose as shown on mild heating Dibenzoyl peroxide C 2 A benzoyloxy radical A phenyl radical

4 Initiation CH H 2 C CH 2 CH

5 Propagation CH 2 CH H 2 C CH CH 2 CH H 2 C CH

6 Termination Coupling Ph * n n Ph * 2 Ph * n 2 Ph * n + H 3C n Ph Disproportionation

7 adical Generation Thermolysis N N ' N N + ' + N 2 + ' Thermal decomposition of azo-compounds NC N N CN CN N N CN 2,2 -azobis(2 azobis(2-methylpropanenitrile) 1,1 -azobis(1 azobis(1-cyclohexanenitrile) (AIBN)

8 Thermolysis of peroxides --- ' ' + Thermal decomposition of peroxides Na + S S Na + Benzoylperoxide (BP) di-tert tert-butylperoxide sodium persulfate

9 Photolysis ' hν C + ' C Photolysis of benzoin (= =H). =H).

10 edox Initiators H + Fe 2+ + Fe 3+ + H _ edox decomposition of cumyl hydroperoxide - 3 S S Fe(II) S 4 S * Fe(III) edox decomposition of persulfate

11 Self initiation of monomer H + Diels-Alder dimerization molecular-assisted homolysis

12 [I] kd I 2 kd d [ I] = dt k = k max max e -E/ E/kT [Time] For efficient polymerization rate - need sufficient radicals. Too few - slow, poor conversion with t Too many - exothermic, low mol. wt AIBN hrs 82 1 hr mins min t = 1 /2 ln 2 k d = 0.693/k d ptimum = o C --> > eaction Time ~ (t 1/2 1/2 )

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

14 Temperature of 1 hr t1/2

15 i = Kinetics of free radical polymerization i = t - d[m ] dt Steady state assumption: = 2 k t [M ] 2 Where k t = k tc + k td 2 fk [ I ] = 2k [ M d t What is the Propagation rate ( p ) ] 2 So [M ]= fk d[ I ] fk k t p = -d[m] = kp [M][M ] dt p = -d[m] = kp [M] dt fk d[ I] fk k t

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

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, 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. ecipients are selected by an anonymous panel of judges appointed by the Chairman of the Doolittle Award Committee.

18 TEMP Controlled Polymerization 1993 M. K. Georges,. P. N. Veregin,, P. M. Kazmaier and G. K. Hamer (Xerox Corporation), "Narrow Molecular Weight esin by Free adical Process." I I N + N (2,2,6,6-tetramethylpiperidinyl-1-oxy) TEMP Monomer Polymer + N Polymer N DP = [monomer] [Initiator]

19 Controlled Free adical Polymerization

20 Control of polymer Architecture N + CH 3 AIBN CH 3 CH 3 CH 3 TEMP TEMP

21 CH 3 CH 3 CH 3 TEMP TEMP CH 3 CH 3 CH 3 Ph Ph Ph Ph

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