EFFICIENCY OF β-NUCLEATING AGENTS IN PROPYLENE/α-OLEFIN COPOLYMERS

Crystallization and melting behavior of β-nucleated propylene/1-pentene random copolymers were studied. Samples with different comonomer content were nucleated with the calcium salt of suberic acid. The WAXS, differential scanning calorimetry (DSC), and polarized light microscopy (PLM) measurements showed that morphological behavior of the β-nucleated copolymers is similar to that of the homopolymer, but the rate of crystallization and the characteristic temperatures decrease with increasing pentene content. Crystallization at low temperatures and lower chain regularity lead to the formation of imperfect crystal structures with high instability, which enables the study of structural perfection processes like ββ′- or βα-recrystallization during partial melting. The PLM studies proved that the critical crossover temperature T(βα) decreases with increasing pentene content. The effect of comonomer content on the critical recooling temperature ( T R * ), as well as on the equilibrium melting point of the β-form ( T m 0) was also investigated. However, in our case, the linear Hoffman–Weeks method proved to be unsuitable for the accurate determination of T m 0.