Quantitative contribution of each component to secondary nucleation in the blends of homopolymer and its random copolymers

Abstract

In homopolymer/random copolymer blends, it is still unclear how the two crystallizable components contribute to secondary nucleation and the radial growth rate of spherulites. There are two highly possible nucleation pathways in the blends of homopolymer and the random copolymer with a low content of amorphous co-monomers. One, similar to regime II, the spherulitic growth rate G of the blends is affected by both secondary nucleation and tertiary nucleation, with the former contributed by homopolymers and the latter by random copolymers. The other, similar to regime I and III, the growth rate G of the blends is mainly determined by secondary nucleation, which is involved by both homopolymer and random copolymer. For the two cases, quantitative equations are established to correlate the spherulitic radial growth rate with the volume fraction of the homopolymer and the volume percentage of the crystallizable repeating units in the random copolymer. By analyzing the radial growth rate of the spherulites of poly(butylene succinate)/poly(butylene succinate-co-butylene 2-methylsuccinate) blends, we reveal the microscopic mechanism for the nucleation of homopolymer and random copolymer chains in the blends. Fitting of the experimental results with the theoretical equations precludes the first regime II like possibility that the homopolymer and the random copolymer contribute to secondary nucleation and tertiary nucleation, respectively. It is shown that both the homopolymer and the random copolymer contribute to secondary nucleation in the blends. Namely, a critical secondary nucleus of the blends consists of the crystallizable units from both homopolymer and random copolymer chains. The higher the homopolymer content, the more crystallizable units in a critical nucleus are derived from the homopolymer. In contrast, when the concentration of crystallizable units in the random copolymer becomes larger, more crystallizable units in a critical nucleus come from the random copolymer. Combining theory and experiments, we could determine the quantitative contribution of each crystallizable component to the secondary nucleation in the blends.