Synthesis and Characterization of Sequence-Controlled Semicrystalline Comb Copolymers: Influence of Primary Structure on Materials Properties

Sequence-controlled semicrystalline copolymers were prepared by nitroxide-mediated copolymerization of a large excess of octadecylstyrene with small amounts of functional N-substituted maleimides (i.e., N-(n-propyl)maleimide, N-benzylmaleimide, pentafluorophenyl 4-maleimidobenzoate, 4-(N-maleimido)azobenzene, N-(1-pyrenyl)maleimide, and N-(2-(amino-BOC)ethylene)maleimide). These copolymers were prepared in bulk at 110 degrees C using the commercial alkoxyamine BlocBuilder MA as initiator and control agent. Time-controlled additions protocols were used to place the N-substituted maleimides at precise chain location along the poly(octadecylstyrene) backbones. Size exclusion chromatography and H-1 NMR studies indicated that well-defined copolymers with controlled monomer sequences, composition, chain length, and molecular weight distribution were formed in all cases. Although possessing an atactic backbone, these polymers exhibit a semicrystalline behavior. The electron diffraction method indicated that the octadecyl side chains form lamellar phases. Moreover, differential scanning calorimetry studies evidenced a melting temperature in the range 40-45 degrees C and a crystallization temperature around 30-35 degrees C. It was observed that melting is influenced by the composition and sequence distribution of the copolymers. Thus, small microstructural variations allow a precise control over order disorder transitions.