Phase Behavior of poly(2-vinyl pyridine)-\textit{block}-poly(4-vinyl pridine) Copolymers

Phase behavior of a block copolymer depends on the volume fraction ($f)$ of one block, total degree of polymerization (N), and the segmental interaction parameter ($\chi )$. Recently, we found that the order-to-disorder transition temperature (T$_{ODT})$ of polystyrene-\textit{block}-poly(2-vinylpridine) copolymer (PS-P2VP) was much lower than that of PS-\textit{block}-poly(4-vinylpridine) copolymer (PS-P4VP) at similar values of $f$ and N. The only difference between PS-P2VP and PS-P4VP is the different location of the nitrogen group in phenyl ring (2 versus 4-position). In this study, we studied, via small angle X-ray scattering (SAXS), rheometry, and birefringence, the phase behavior P2VP-\textit{block-}P4VP copolymers (P2VP-P4VP) with various $f$ and N. We determined the temperature dependence of $\chi $ between P2VP and P4VP from SAXS profiles in the disordered states with the aid of the random phase approximation. We found that the value of $\chi $ between P2VP and P4VP was relatively large. For instance, it is larger than $\chi $ between PS and P2VP. Thus, even when the molecular weight of symmetric P2VP-P4VP is ca. 12000, the T$_{ODT}$ is larger than 280 $^{o}$C. This work was supported by Creative Research Initiative Program supported by KOSEF