Highly Ordered Structure Formation in RAFT-Synthesized PtBOS-b-P4VP Diblock Copolymers

Linear poly(4-tert-butoxystyrene)-b-poly(4-vinylpyridine) (PtBOS-b-P4VP) diblock copolymers are synthesized using reversible addition-fragmentation chain transfer polymerization. The self-assembly of four different PtBOS-b-P4VP diblock copolymers is studied using small-angle X-ray scattering and transmission electron microscopy and a number of interesting observations are made. A tBOS(62)-b-4VP(28) diblock copolymer with a weight fraction P4VP of 0.21 shows a disordered morphology of P4VP spheres with liquid-like short-range order despite an estimated value of chi(N) of the order of 50. Increasing the length of the 4VP block to tBOS(62)-b-4VP(199) results in a diblock copolymer with a weight fraction P4VP of 0.66. It forms a remarkably well-ordered lamellar structure. Likewise, a tBOS(146)-b-4VP(120) diblock copolymer with a weight fraction P4VP of 0.33 forms an extremely well-ordered hexagonal structure of P4VP cylinders. Increasing the P4VP block of this block copolymer to tBOS(146)-b-4VP(190) with a weight fraction P4VP of 0.44 results in a bicontinuous gyroid morphology despite the estimated strong segregation of chi N congruent to 150. These results are discussed in terms of the architectural dissimilarity of the two monomers, characterized by the presence of the large side group of PtBOS, and the previously reported value of the interaction parameter, chi congruent to 0.39, for this polymer pair.