Study on thermal degradation of polystyrenes by pyrolysis-gas chromatography and pyrolysis-field ionization mass spectrometry

Thermolysis of polystyrene

“…They obtained evidence to suggest that dimers and trimers are possibly formed by monomer recombination, occurring within the molten polystyrene and in the vapour phase above it. In support of this, Ostani et al [34] have shown that the hydrogen 1,3-transfer of the normal polystyryl radical (R2) followed by ~-scission is not the main pathway to the dimers.…”

“…This is true at ail reaction temperatures and at ail time throughout a reaction. Il has been shown previously that the dimer is formed, in the reactlon zone, by combination of the newly formed monomer units [34]. Therefore, a longer residence time should cause a decrease in the amount of monomer, because il is converted to dimer.…”

Mechanisms of thermal degradation of polystyrene, polymethacrylonitrile, and their copolymers on flash pyrolysis

“…19,20 Contrarily, it has been reported that in the flash pyrolysis of poly(styrene) monomer units of 60 -80% were generated as monomer molecules and the remaining monomer units of 20 -40% were produced as dimer and trimer molecules. 21,22 The yields of monomer molecules regenerated from the copolymers of styrene-acrylonitrile and styrene-methylmethacrylate in flash pyrolysis differed from those of monomers produced by the pyrolysis of corresponding homopolymers under the same conditions. 3,23,24 As a first approximation, it was considered that, in the pyrolysis of the A-B copolymer, the regeneration probability of A monomer unit at the boundary of A and B sequences, P AB , differed from that in A sequence, P AA , and also the same situation was expected for B monomer units; i.e., P BA was different from P BB .…”

“…As shown in Scheme 1, which presents the thermal degradation mechanisms of polystyrene according to the previous works, 22,25 as a typical example, in flash pyrolysis at a high temperature radical chain ends are formed first by the scission of a main chain and then followed by a depolymerization or an intramolecular hydrogen abstraction, i.e., the so-called back-biting reaction. Monomer molecules are regenerated mainly by a depolymerization, but oligomers such as dimers and trimers are formed by a back-biting reaction followed by ␤-scission.…”

Role of back-biting for generation of hybrid dimers and trimers on flash pyrolysis of poly(styrene-co-methacrylonitrile)

“…It has been reported that from the blend of homopolymers, hybrid dimers and trimers were produced as the product of pyrolysis; that is, as the result of the second reaction in the vapor products of thermal degradation, the hybrid dimers and trimers were generated. 7,8 So we examined the generation mechanisms of hybrid dimers and trimers and considered whether it was the result of the back-biting reaction or the result of the second reaction in the volatile products of flash pyrolysis. In our measurement of the blend of homopolymers, peaks corresponding to the hybrid dimers and trimers did not appear, as shown in Figure 6, in agreement with the results of Bate and Lehrle.…”