ORIGIN OF CHARACTERISTIC PROPERTIES OF NATURAL-RUBBER - SYNERGISTIC EFFECT OF FATTY-ACIDS ON CRYSTALLIZATION OF CIS-1,4-POLYISOPRENE .1. SATURATED AND UNSATURATED FATTY-ACIDS

The influence of stearic acid, linoleic acid and their methylesters on crystallization or synthetic cis-1,4-polyisoprene was investigated at the isothermal crystallization temperature of -25 degrees C by means of differential scanning calorimetry and dilatometry. The overall crys tallization rate of cis-1,4-polyisoprene increased in step with increa sing stearic acid content, while the glass transition temperature of c is-1,4-polyisoprene did not change with the additive level. The additi on of 1 wt% stearic acid or methyl stearate showed an acceleration eff ect on the initial crystallization of the polymer, while 1 wt% linolei c acid or methyl linoleate suppressed the initial crystallization. Coe xistence 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 pr operties of natural rubber were revealed to be related to the specific ratio of miscible fatty acids to immiscible fatty acids in natural ru bber.