Enhanced Performance of Polybutadiene/Polyisoprene (PB/PI) Blend with Asymmetric PB-b-PI Diblock Copolymers

Symmetric block copolymers (BCPs) are widely reportedas the mosteffective BCPs for compatibilizing polymer blends via one-pot mixing.However, many BCPs may not be optimally distributed at the interfacedue to both thermodynamic and kinetic factors. Here, a series of well-definedpolybutadiene-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 orderto explore the impact of the compositional symmetry of BCPs on compatibilizingPB/PI blends under various kinetic pathways. By a combination of microscopicobservation and rheological and mechanical measurements, it is shownthat the addition of BCPs in PB/PI blends reduces the dispersed domainsize (PB phase) and simultaneously enhances their processability andmechanical performance. Surprisingly, compatibilized blends with asymmetricBCPs could achieve better performance than the blend with symmetricBCPs via sequential mixing. Their properties are even better thanthe one-pot mixed blend with symmetric BCPs. A mechanism is proposedto explain how these asymmetric BCPs could be more easily distributedat the interface than symmetric ones, thus enhancing the mechanicalproperties of PB/PI blends. These intriguing results demonstrate thatthe asymmetric BCP could achieve better compatibilization efficiencythan the symmetric BCP by the synergy between molecular symmetry andkinetic pathways.