Attaching one or more amorphous blocks to a crystallizable chain can strongly modify its crystallization behavior and semicrystalline morphology, whether the blocks are mixed or microphase-separated in the melt.  By employing an amorphous block which is itself a random copolymer—creating a so-called random copolymer—the interblock interaction strength in the melt can be continuously tuned through the random block composition, independent of block copolymer molecular weight.  We have examined the miscibility in a wide range of diblock-random copolymers prepared from styrene, isoprene, and butadiene, followed by catalytic hydrogenation; low-vinyl polybutadiene becomes a crystallizable polyethylene (PE) upon hydrogenation.   We find strong positive deviations from regular mixing of PE with polymers containing styrene, and substantial negative deviations from regular mixing in polymers containing vinylcylohexane.  Using these measured segregation strengths, we then design and synthesize nonfrustrated A-B-C triblock copolymers, wherein the A block is PE.  Though the amorphous B and C blocks are sufficiently compatible that they would not be microphase-separated if they were connected as a diblock, attachment of the A block, and consequent localization of the A-B block junction to the A-B lamellar interface, induces extensive separation between the B and C blocks.  Crystallization of the A (PE) block further sharpens the extent of B-C microphase separation, demonstrating that both macromolecular architecture and crystallization can be used to generate spatial separation between components that would otherwise mix homogeneously.

Miscibility and crystallization in hydrocarbon block and block-random copolymers

249th National Meeting (2015)

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