Abstract
Variation in the molecular weight distribution of polyvinylpyrrolidone (PVP) by ball-milling in various kinds of atmosphere in the absence and in the presence of various kinds of organic and inorganic additives was investigated. A line broken at several points was obtained by the logarithmic plot of -log R versus the molecular weight of PVP, Mu, and equation (1) was applied in the limited range of Mu, respectively, where R was the ratio of the weight of the polymers of molecular weight above Mu to the total weight of the polymers, and k and n were parameters dependent on the experimental conditions and so on. R=exp (-kMnu) (1) The existence of the critical molecular weight, Mc, was observed, at the region of Mu below which n was larger than 1.0 and formation of the polymers of Mu below Mc was considered to become more difficult with a decrease of Mu. The value of Mc was below 4×105 and varied remarkably by the kind of the additive and by the ball-milling atmosphere. Theoretical consideration was made on the molecular weight distribution of the polymers formed by chain scission of polymers by application of the mechanical stress, by assuming that chain scission was produced by activation of the bonds between atoms of the main chain by the mechanical stress and that these activated bonds were distributed at random and obeyed to Poisson's distribution law. It was suggested from the consideration mentioned above and from the investigation of the value of n in equation (1) and of the variation of R with the ball-milling time that, in many cases, random chain scission was most probable and that the density of the activated bonds over a polymer of low molecular weight was approximately equal to or higher than the density over a polymer of high molecular weight.
