Polyvinylchloride sequences

Besides the use of micromolecular multiinitiators, block copolymers can be obtained from macromolecular initiators. In a first step, a polymeric initiator is generally synthesized by reacting a mono- or difunctional polymer with a functional initiator. Various macromolecular initiators were prepared in this way including quite different sequences polystyrene [13, 18, 19, 25, 26], poly(dimethylsiloxane) [27], polymethylmethacrylate) [13,15,28], polyvinylacetate [28], polyvinylchloride [29, 30], polyesters [30], polycarbonate [31,32], polybutadiene [13, 25, 33], polyamide [34], polyethylene glycol) [35] or polyaromatic [36], An excellent review of the synthesis and uses of such macroinitiators was written by Nuyken and Voit [37]. Thus, only few typical examples are going to be mentioned below. 

Fig. 47. Absorption spectrum of thermally degraded polyvinylchloride (Vestolit SK 55), polyvinylbromide and a copolymer vinyl chloride—isobutene in tetrahydrofuran. The absorption maxima correspond to polyene sequences with n = 4, 5, 6, etc. [ 184 ].

Fig. 48. Frequency of polyene sequences for a polyvinylchloride sample degraded at 170 C in nitrogen and a polyvinylbromide sample degraded at 100°C in nitrogen [184] conversion x 0.16 x 10 2.

The values calculated according to this model for the yield of HC1, and concentration and distribution of polyene sequences are in agreement with the experimental results that Tvidos et al. obtained for the degradation of polyvinylchloride. 

However, this does not result in the formation of sequences of conjugated double bonds as in the photodegradation of polyvinylchloride (see p. 379) or in the radiolysis of poly vinylacetate [13]. 

It is possible for free radicals produced on irradiation of polymers to initiate a sequence of reactions leading to the ultimate loss of the physical or mechanical properties of the sample. Two examples of this may be mentioned here the photo-oxidation of polymers in general and the discolouration of polyvinylchloride in the absence of oxygen. 

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