The influence of composition on the overall rate of isothermal crystallization of isotactic random propylene/1‐butene copolymers is investigated. At a constant crystallization temperature a small fraction of 1‐butene co‐units inserted along a polypropylene chain causes a drastic reduction in the overall rate of crystallization. Further it is found that for a given rate of crystallization it is possible to crystallize the isotactic polypropylene at lower crystallization temperature by adding along the chain a small amount of 1‐butene as comonomer. The equilibrium melting temperature, the surface free energy of folding, the enthalpy and the entropy of fusion decrease with increasing the contents of 1‐butene in the copolymer samples.
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Crispino et al. (1980) studied this question.