ABSTRACT
Pyrolysis of monodisperse poly-α-methylstyrene of wide molecular weight range (M:25,000-5,000,000) was studied isothermally under vacuum in the temperature range 240-280 °C. Thermogravimetric analysis was used for measuring the rate of degradation, and gel permeation chromatography for analyzing the molecular weight and molecular weight distribution as a function of conversion. The initial rate of monodisperse poly-α-methylstyrenes, and the deuterated samples (poly-α-trideuteromethyl-ß, ß-dideuterostyrene) increases with increasing molecular weight. At molecular weight higher than 1 × 106, the initial rate continues to increase almost linearly instead of being constant as concluded from earlier work. The molecular weight distribution ratio, M w /M n , increases as a function of conversion and approaches the most probable distribution. The results conform to a degradation mechanism with random initiation. The curves of initial rate as a function of molecular weight lead to higher zip lengths than previous estimates. Attempts at simultaneous estimation of zip length and transfer constant from the rate and molecular weight data led to inconsistent results. If the variation of termination rate with molecular weight plays a role, this variation must be less than that derived naively from melt viscosity. Bimodal molecular weight distributions were not found.
ABSTRACT
Glass transition measurements on monodispersed polystyrenes of different molecular weight and their binary mixtures result in the following conclusions: (a) the effect of molecular weight on the glass transitions of monodispersed samples satisfies the Fox and Flory equation written as T g = T g∞ - A/M n , with constant A = 0.84 × 10-5; (b) polymers of the same number average molecular weight with a broad distribution show lower glass transitions than the monodispersed; (c) the binary mixtures follow the Gordon-Taylor equation derived for copolymers, with constant k (experimental) 0.5.
