Synthesis and Characterization of ABC Triblock Copolymers with Two Different Crystalline End Blocks: Influence of Confinement on Crystallization Behavior and Morphology

Abstract

The preparation of polyethylene-block-poly(ethylene-alt-propylene)-block-poly(ethylene oxide) (PE-b-PEP-b-PEO) triblock copolymers by homogeneous catalytic hydrogenation of the precursor poly(1,4-butadiene)-block-poly(1,4-isoprene)-block-poly(ethylene oxide) (PB-b-PI-b-PEO) triblock copolymers, which were synthesized by sequential anionic polymerization, is described. Thermal analysis using differential scanning calorimetry (DSC) reveals differences in the crystallization behavior of the PEO and PE blocks arising from different morphological confinements active during crystallization. If the PEO block is confined into isolated spherical or cylindrical microdomains, crystallization can only be induced by high supercoolings resulting from the vast number of microdomains (spheres or cylinders) compared to the number of available heterogeneities. In contrast, crystallization of PE proceeds via heterogeneous nucleation regardless of the composition, which can be attributed to the miscibility of PEP and PE segments in the melt. Transmission electron microscopy (TEM) and scanning force microscopy (SFM) have been used to investigate the influence of different confinements, active in PE-b-PEP-b-PEO triblock copolymers, on the formed morphology. In addition, temperature-dependent imaging by hot-stage SFM measurements following the melting of PEO blocks and annealing of PE crystallites within a PE-b-PEP-b-PEO triblock copolymer will be presented.