Crystallization, Nucleation and Kinetics of TPI in SSBR/TPI Blends

Crystallization behavior including polymorphic behavior , nucleation density , crystal growth rate , kinetics of isothermal and non-isothermal crystallization in the immiscible solution polymerized styrenebutadiene rubber ( SSBR )/trans-1, 4-polyisoprene ( TPI ) blends were investigated by polarized optical microscopy ( POM ) , wide angel X-ray diffraction ( WAXD ) and differential scanning calorimeter ( DSC ) . The results show that less than 40% ( mass fraction ) of SSBR admixing with TPI brings about the suppressed nucleation and crystal growth rate of TPI. The overall crystallinity declines with the addition and increase of amorphous SSBR content, the normalized crystallinity of TPI, however, increases due to the decreased crystallization rate, resulted from the dilution of SSBR components, in turns the reduced equilibrium melting points and the lower undercooling. Additionally, the amorphous component SSBR depresses the formation of a-TPI crystal while enables the formation of beta-TPI crystal. Both the reduced crystallization rate of TPI during the isothermal crystallization and the lower crystallization temperature of TPI during non-isothermal crystallization were observed with the increase of SSBR content. All these results are in line with the crystallization behavior of the miscible amorphous/crystalline polymer blends because of the neglectable phase separation arising from the high viscosity of both rubber components leading to the slow dynamic of molecules. However, as the content of SSBR reached a high level, the nucleation density of the system increased with SSBR content increasing due to the phase separation exerting its influence on TPI crystallization.