ABSTRACT
Chemical behavior of polymers is generally defined by the structural-physical inhomogeneity: homogeneity of a polymer system, its state (solution, solid), presence of association/complexes of macromolecules and supermolecular formations, etc. In the case of the degradation of PVC and its mixtures with other polymers, it was shown that the factors defming the stability of the macromolecules; chemical structure of the polymer chains, existence of low-molecular additives, solvent1.2 induced association in solution and complexity of the kinetic control of the polymer chain degradation. Association of macromolecules occurs in dilute solutions of polymers and is accompanied by solvent substitution in the macromolecular coil volume by monomeric chains of neighbour macromolecules with corresponding increase of local density of chains in the coil. Such structural transitions, when the system transforms from a homogeneously distributed macromolecular coils to a system of associated polymer molecules, is accompanied by a jump-like change of visrosity? For PVC solutions in cyclohexanone (CHN) and 1,2,3-trichloropropane (TCP), it was shown4 that the beginning of association corresponds to PVC concentrations of 0.9 mass% in CHN and 0.6 mass% in TCP. This is accompanied by a coqesponding change in the rate of PVC decomposition (Figure 1, curves 1, 2). If the rate of dehydrochlorination remains constant in the concentration ranges, in which PVC exists as an isolated macromolecule, then increase of the concentration up to a value corresponding to the beginning of macromolecule association, the rate of PVC degradation begins to change, decreasing in CHN and increasing in TCP (Fiture 1, curves 3, 4). The difference in the rates of PVC degradation in the different solvents is connected with the different values of the basicity index B for CHN and TCP.2 However, the observed behavior of the decomposition notes in the absence of a solvent testifies the effects of local structure and is associated with the formation of
a fluctuating network consisting of dense aggregates, the permolecular structure of which is similar to that of PVC structure in the block-copolymer.
