Origin of Characteristic Properties of Natural Rubber—Synergistic Effect of Fatty Acids on Crystallization of cis-1,4-Polyisoprene: I, Saturated and Unsaturated Fatty Acids

Abstract

Abstract The influence of stearic acid, linoleic acid and their methylesters on crystallization of synthetic cis-1,4-polyisoprene was investigated at the isothermal crystallization temperature of −25°C by means of differential scanning calorimetry and dilatometry. The overall crystallization rate of cis-1,4-polyisoprene increased in step with increasing stearic acid content, while the glass transition temperature of cis-1,4-polyisoprene did not change with the additive level. The addition of 1 wt % stearic acid or methyl stearate showed an acceleration effect on the initial crystallization of the polymer, while 1 wt % linoleic acid or methyl linoleate suppressed the initial crystallization. Coexistence of stearic acid and linoleic acid or stearic acid and methyl linoleate in cis-1,4-polyisoprene gave rise to a dramatic increase in the overall crystallization rate of the polymer. The characteristic properties of natural rubber were revealed to be related to the specific ratio of miscible fatty acids to immiscible fatty acids in natural rubber.