By C. H. Bamford
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Additional info for Comprehensive Chemical Kinetics Degradation of Polymers
The results are given in Fig. 23. They are in good agreement with a mechanism of degradation involving random scission and transfer. References p p . p I s ‘Y zs 1 p-u T I N t Z’ ' y-u 7 Scheme 1. The thermal decomposition of polypropylene [ 50 1. 41 The broad initial distribution characterized by a high value of M , / M n tends to become random [(M, / M n ) = 21 as the degradation proceeds. Analysis of the volatile degradation products has been performed by Moiseev , Bailey and Lieske  and van Schooten and Evenhuis  .
From eqn. (72) one can readily derive T2 T2 j l n R,TXdTT, In RiTX dT TI 1 T* = n [ r In WTX dTTI j In W'TX dT TI The temperature limits T, and T, are identical for both thermograms, and x is an arbitrary constant. If x is taken as zero, n= T, (1nWdT- =,[ l n W ' d T -- (79) AW A R and A are obtained by measuring the shaded areas in Figs. 16 and 17, respectively. Once n is known, A and E are calculated from eqn. (76) by plotting In R, - n In W against 1/T. rt' C i I 1 825 I 850 wo 875 Temperature I 925 (OK) Fig.
Pyrolysis temperature ("C) . 22. Decomposition products of polyethylene [ 4 4 ] . The formation of products is explained on the basis of a free radical mechanism. Initiation consists of preferential scission of weak bonds or ordinary C-C bonds. The weak bonds may include oxygen atoms; carbon-carbon bonds in the 0 position to double bonds or adjacent to tertiary carbons may also be involved. The mechanism proposed is Initiation R-R __+ - 2FC Propagation R R,. + CH,=CH, 37 Intramolecular transfer followed by a decomposition reaction Ri -----* R24H-CH2-R3 R; + CH2=CH-CH2-R, R2-CH=CH2 + R; (87) (88) Intermolecular transfer followed by a decomposition reaction R4-CH2-RS R,* + R; R;+R, + - R4--C'H-RS Termination +R' R4-6H-R5 +RH R4-CH=CH2 + R i (89) (90) R-CH=CH2 + R,H (91) R,-R, (92) Propagation competes with transfer and their relative importance depends on temperature.
Comprehensive Chemical Kinetics Degradation of Polymers by C. H. Bamford