Critical rate of cooling for suppression of crystallization in random copolymers of propylene with ethylene and 1-butene

Fast scanning calorimetry has been employed for evaluation of the critical rate of cooling for complete suppression of non-isothermal melt-crystallization of random copolymers of propylene with low amount of ethylene or 1-butene. While crystallization/mesophase formation of isotactic polypropylene can only be suppressed by cooling the quiescent melt at rates faster than 300 K s−1, in case of random copolymers the critical cooling rate for complete inhibition of crystallization is shifted to lower rate as a function of the concentration of co-units. Preparations with about 10 mol% ethylene or 1-butene do not crystallize if the cooling rate exceeds 100 K s−1. Subsequent cold-crystallization and reorganization of mesomorphic structure, formed by aging of initially fully amorphous samples at ambient temperature, can only be avoided by heating with a rate faster than 5000 K s−1. Fast heating of quenched and at ambient temperature aged specimens, which only contained mesomorphic domains in an amorphous matrix, revealed that the melting temperature of mesomorphic structure is about 350 K.