Enhanced Performance of Polybutadiene/Polyisoprene (PB/PI) Blend with Asymmetric PB-<i>b</i>-PI Diblock Copolymers
Yinhu Deng, He Sun, Xinpeng Hu, Keqiang Wang, Chuanjiang Long, Feng Yu, Zhong‐Ren Chen
Abstract
Symmetric block copolymers (BCPs) are widely reported as the most effective BCPs for compatibilizing polymer blends via one-pot mixing. However, many BCPs may not be optimally distributed at the interface due to both thermodynamic and kinetic factors. Here, a series of well-defined polybutadiene- b -polyisoprene (PB- b -PI) diblock copolymers with varied block lengths (asymmetric/symmetric) were studied, while a comparable number-average molecular weight ( M n ) served as a polymer model system in order to explore the impact of the compositional symmetry of BCPs on compatibilizing PB/PI blends under various kinetic pathways. By a combination of microscopic observation and rheological and mechanical measurements, it is shown that the addition of BCPs in PB/PI blends reduces the dispersed domain size (PB phase) and simultaneously enhances their processability and mechanical performance. Surprisingly, compatibilized blends with asymmetric BCPs could achieve better performance than the blend with symmetric BCPs via sequential mixing. Their properties are even better than the one-pot mixed blend with symmetric BCPs. A mechanism is proposed to explain how these asymmetric BCPs could be more easily distributed at the interface than symmetric ones, thus enhancing the mechanical properties of PB/PI blends. These intriguing results demonstrate that the asymmetric BCP could achieve better compatibilization efficiency than the symmetric BCP by the synergy between molecular symmetry and kinetic pathways.