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Coote, Jonathan P.,Kim, Jin-Seong,Lee, Byeongdu,Han, Junghun,Kim, Bumjoon J.,Stein, Gila E. American Chemical Society 2018 Macromolecules Vol.51 No.22
<P>Conjugated block copolymers (BCPs) can self-assemble into highly ordered nanostructures in a melt state. However, when cooled below the melting temperature, crystal growth can disrupt the self-assembled structure and produce a poorly ordered fibrillar texture. We demonstrate that crystallization modes of conjugated BCPs based on poly(3-dodecylthiophene) (P3DDT) and poly(2-vinylpyridine) (P2VP) can be tuned through P3DDT regioregularity (RR), as this attribute controls the melting temperature and crystallization rates of P3DDT. When RR is low (70-80%), crystallization is observed at temperatures near or below the glass transition of P2VP, so crystal growth is largely confined by the glassy cylindrical or lamellar BCP structure. When RR is high (94%), crystallization occurs at 40 K above the glass transition of P2VP, so there is no longer a restriction of glassy domains. Importantly, crystal growth remains confined by the rubbery P2VP lamellae, but breaks through the rubbery P2VP cylinders. This morphology-dependent behavior is attributed to geometric compatibility of P3DDT crystal growth and the self-assembled symmetry. In a lamellar phase, the P3DDT chain orientations at the P3DDT-<I>block</I>-P2VP interface are compatible with crystal growth, and both the alkyl-stacking and π-π growth directions are unrestricted within a lamellar sheet. In a cylindrical phase, the radial orientation of P3DDT chains at the P3DDT-<I>block</I>-P2VP interface is not compatible with crystal growth, and the hexagonal close-packed symmetry only allows for one direction of unrestricted crystal growth. Significantly, these studies demonstrate that tuning RR of polyalkylthiophenes can open up multiple crystallization modes with the same monomer chemistries and block lengths, thereby decoupling the parameters that govern classical BCP self-assembly and crystal growth.</P> [FIG OMISSION]</BR>
Domain Structures of Poly(3-dodecylthiophene)-Based Block Copolymers Depend on Regioregularity
Kim, Jin-Seong,Han, Junghun,Kim, Youngkwon,Park, Hyeonjung,Coote, Jonathan P.,Stein, Gila E.,Kim, Bumjoon J. American Chemical Society 2018 Macromolecules Vol.51 No.11
<P>Microphase-separation behavior of conjugated-amorphous block copolymers (BCPs) is driven by a complex interplay between Flory-Huggins interaction (χ), liquid crystalline (LC) interaction, and crystallization. Herein, in order to elucidate the influence of LC interaction on the morphology of the BCPs, we report the effects of regioregularity (RR) on the microphase separation and molecular packing structures of poly(3-dodecylthiophene)-<I>block</I>-poly(2-vinylpyridine) (P3DDT-<I>b</I>-P2VP). To decouple the effect of LC interactions from crystallization kinetics, we investigate the morphological behavior of the P3DDT-<I>b</I>-P2VP at above the melting temperature of P3DDT (∼160 °C). Both electron microscopy and X-ray scattering show an abrupt reduction in the domain spacing of both lamellar and cylindrical phases as the RR of P3DDT block increases. Specifically, lower RR (i.e., 85, 79, and 70%) BCPs have larger domain spacings than high RR (94%) by 50% (lamellar) or 80% (cylindrical), even though the overall molecular weights and P2VP volume fractions were similar for each RR. We propose that the RR-driven transition in domain spacing is caused by a change in P3DDT conformations and interchain interactions. When RR is low, the system assembles into a typical bilayer structure like other semiflexible and flexible block copolymer systems. When RR is high, the less flexible P3DDT chains are extended, driving their assembly into an LC monolayer. Significantly, this study demonstrates that tunable RR provides a simple route to manipulate melt state self-assembly of conjugated-amorphous materials.</P> [FIG OMISSION]</BR>