The kinetics of polysulphone formation II. The formation of 1-butene polysulphone in the region of the ceiling temperature

Abstract

The effect of temperature on the rate of formation of 1-butene polysulphone from mixtures of liquid sulphur dioxide and 1-butene has been investigated dilatometrically. Three methods of initiation were used: photochemical, silver nitrate and benzoyl peroxide, and the temperature range covered was 0 to 70° C. For appreciable rates of reaction, the photochemical rate may be expressed in the form: rate = k 1 [ B ] [ S ] — k 2 , where [ B ] [ S ] denotes the monomer concentration product and k 1 and k 2 are temperature-dependent constants. For each reaction mixture there is a critical temperature defined as the ceiling temperature T c above which the reaction rate and molecular weight of polymer formed are very small. This temperature is independent of the method and rate of initiation. Previous explanations of the ceiling temperature phenomenon are shown to be unsound. The present results may be interpreted on the assumption that the reverse of the propaga­tion reaction, here designated the depropagation reaction, becomes important as the ceiling temperature is approached. The kinetic data permit the evaluation of both the heat and entropy of polymerization, and for the reaction (l - C 4 H 8 + SO 2 ) liq. mixt → 1/ n (C 4 H 8 SO 2 ) n (solution in monomer mixture), — Δ H = 20.7 ± 1.4 kcal mole -1 , — Δ S ° = 68.2 cal mole -1 ° K -1 (standard state 1 mole l. -1 each reactant). The heat change determined by adiabatic calorimetry is 22.0 ± 0.7 kcal mole -1 . In principle, all polymerization systems should exhibit the ceiling temperature effect under suitable conditions. Possible systems for investigation are suggested. The ceiling temperature is the temperature at which the free energy of formation of long-chain polymer is zero. Above the ceiling temperature the polymer is thermodynamically unstable. Depolymerization experiments on I-butene polysulphone indicate that below 130° C the degradation is random in character, whether effected by light or by heat.