Abstract
The rate of a decrease of mean molecular weight and molecular weight distribution of polyvinylpyrrolidone (PVP) powders changed by ball-milling in nitrogen, air or oxygen were investigated, and influence of a ball-milling atmosphere on the probability in which a PVP molecule was broken in a unit time and molecular size distribution of the polymers formed by the break of a PVP molecule in a unit time was discussed. If the function representing the probability in which a PVP molecule was cut off in a unit time, S (M), was proportional to (M-M∞)α, α was considered to be between 1.0 and 1.5, and to be 1.0 for the case of ball-milling in nitrogen of air and to be larger than 1.0 for the case of ball-milling in oxygen. It was considered to be much probable that a PVP molecule with molecular weight of 1.6×106 was broken both at the center and at the molecular weight between 6×103 and 1.1×104 from the end of a main chain by ball-milling in nitrogen, and at the molecular weight of 3.6×104 from the end by ball-milling in air or oxygen. It seemed to be possible that a PVP molecule with molecular weight of 1.6×106 was broken at the molecular weight between 5.0×104 and 3.7×105 from the end by ball-milling in oxygen.
