Phase behavior of poly(2-vinylpyridine)-block-poly(4-vinylpyridine) copolymers

P2VP-b-P4VP copolymers with various molecular weights and block length ratios using anionic polymerization were synthesized. The temperature-dependent interaction parameters (Α) for P2VP/P4VP pair were also determined by obtaining SAXS profiles of a low-molecular-weight P2VP-b-P4VP copolymer at various temperatures and curve fitting to the random phase approximation (RPA) theory. The observation indicates that the repulsive force between P2VP and P4VP becomes significant enough to induce microphase separation in relatively low molecular weights (~6,000) of symmetric P2VP-b-P4VP copolymer even when the only difference between P2VP and P4VP is the position of nitrogen in the pyridine ring (ortho vs para positions). The results show that the values of Α for P2VP/P4VP pair lie between those of PS/P4VP and PS/P2VP pairs.