Interplay of microphase separation, crystallization and liquid crystalline ordering in crystalline/liquid crystalline block copolymers

A series of liquid crystalline/crystalline block copolymers (BCPs) containing poly(methacrylate) block with liquid crystalline (LC) azobenzene moieties in the side chains (PMMAzo) and crystalline block poly(L-lactide) (PLLA) were prepared. The interplay of microphase separation, crystallization and LC ordering in these BCPs was investigated. It is revealed that microphase separation between two blocks is favorable to the LC ordering, which is attributed to the enhanced local concentration of LC moieties in PMMAzo microdomains. For a similar reason, crystallization of PLLA can intensify microphase separation thus facilitate LC ordering of PMMAzo. PLLA crystallization may also stabilize the LC structure, leading to phase transition temperatures of the BCPs higher than that of PMMAzo homopolymer. On the other hand, the LC ordering can conversely affect crystallization of PLLA. The crystallizability of PLLA is weakened by the chemically linked PMMAzo block. The special PLLA ε-crystals, which are usually formed in the presence of organic solvents, are unexpectedly observed under suitable conditions.