Degradation, Cyclopentadienylation, and Grafting of Vinyl Chloride/2-Chloropropene Copolymers

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Abstract
Poly(vinyl chloride)s containing relatively high concentrations of tertiary chlorines (∼0.8–6.5 mol%) have been synthetized by heterogeneous free radical copolymerization of vinyl chloride with 2-chloropropene (VC/2-CP). Copolymerization rates and M n′s of VC/2-CP decreased with increasing initial 2-CP concentration in the monomer feed, which indicates that 2-CP is a retarder in VC polymerization. Initial dehydrochlorination rates of thermal and thermo-oxidative degradation of VC/2-CP copolymers have been found to be proportional with the concentration of 2-CP in the copolymer. However, other type of irregularities, e.g., unsaturations and/or random initiation of HCl loss from stable -CH2-CHCl- structures, also influence these processes. A linear relationship exists between the rates of initial thermal and thermo-oxidative dehydrochlorination processes. VC/2-CP containing pendant cyclopentadienyl (Cp) groups (VC/2-CP-Cp) has been prepared by treating the co-polymer with dimethylcyclopentadienylalwninum (Me2CpAl). VC/2-CP-Cp gelled on drying, however dissolved in the presence of strong dienophiles, e.g., maleic anhydride or dimethyl acetylenedicarboxylate. Evidently gelation is due to Diels-Alder addition of pendant Cp groups and may lead to thermally reversible networks. While the introduction of oxidizable Cp groups into VC/2-Cp decreases the thermo-oxidative stability, it increases the thermal stability of the copolymer because thermally unstable tertiary chlorines are replaced by Cp and/or Me groups. Grafting of isobutylene from VC/2-CP with Et2AlCl coinitiator yielded poly(vinyl chloride-co-2-chloropropene-g-isobutylene) (VC/2-CP-g-PIB), graft copolymers with relatively high PIB content (60–90%) but low branching frequency (∼1.27). Grafting of isobutylene increased both thermal and thermo-oxidative stability of the copolymer because of the replacement of unstable tertiary chlorines by PIB branches.