Effect of phase separation on spherulitic growth rate of PP/EPR in‐reactor alloys

In this work, the effect of phase separation on the spherulitic growth rate of a polypropylene/ethylene–propylene random (PP/EPR) copolymer in‐reactor alloy was investigated. The PP/EPR in‐reactor alloy was either directly quenched from homogeneous melt to crystallization temperature or held at various temperatures for phase separation prior to crystallization. It is found that at lower crystallization temperatures previous phase separation in the melt retards the crystallization rate. The higher the phase separation rate, the smaller the spherulitic growth rate. This can be attributed to faster crystallization rate than the rate of secondary phase separation. The composition of the PP‐rich phase and corresponding depression of the equilibrium melting temperature of PP vary with phase separation temperature. On the other hand, at higher crystallization temperature, previous phase separation in the melt has little effect on the spherulitic growth rate because secondary phase separation can take place prior to crystallization. The transition temperature from regime II to regime III also shifts to lower temperature as the phase separation temperature increases. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011