Competition and Coupling Between Crystallization and Microphase Separation in a Triblock Copolymer.

Block copolymers (BCPs) can self-assemble into various nanostructures. The introduction of polymers with special properties, such as liquid crystalline (LC) and semicrystalline ones, will affect the self-assembled structures of BCPs. In this work, BCPs containing a coil block polydimethylsiloxane (PDMS), an LC block poly[4'-(methoxy)-2-vinylbiphenyl-4-methyl ether] (PMVBP) that is a mesogen-jacketed LC polymer (MJLCP), and a semicrystalline poly(L-lactic acid) (PLLA) were synthesized. The diblock copolymer PLLA-b-PMVBP does not form ordered nanostructures because the solubility parameters of the two blocks are quite close. The triblock copolymer PDMS-b-PLLA-b-PMVBP forms the lamellar (LAM) structure at ambient temperature and the hexagonally packed cylindrical (HEX) structure at high temperatures. The results of temperature-dependent small-angle x-ray scattering show that the crystallization of PLLA significantly affects the self-assembled structures of the BCPs. Crystallization of PLLA may compete or couple with the microphase separation of the BCP. In addition, a rare type of phase transformation, lower disorder-order transition (LDOT), is observed in the sample D56L19V4.