title: Co-crystallization phase transformations in all π-conjugated block copolymers with different main-chain moieties.
abstract: Driven by molecular affinity and balance in the crystallization kinetics, the ability to co-crystallize dissimilar yet self-crystallizable blocks of a block copolymer (BCP) into a uniform domain may strongly affect its phase diagram. In this study, we synthesize a new series of crystalline and monodisperse all-π-conjugated poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-(2-ethylhexyl)thiophene) (PPP-P3EHT) BCPs and investigate this multi-crystallization effect. Despite vastly different side-chain and main-chain structures, PPP and P3EHT blocks are able to co-crystallize into a single uniform domain comprising PPP and P3EHT main-chains with mutually interdigitated side-chains spaced in-between. With increasing P3EHT fraction, PPP-P3EHTs undergo sequential phase transitions and form hierarchical superstructures including predominately PPP nanofibrils, co-crystalline nanofibrils, a bilayer co-crystalline/pure P3EHT lamellar structure, a microphase-separated bilayer PPP-P3EHT lamellar structure, and finally P3EHT nanofibrils. In particular, the presence of the new co-crystalline lamellar structure is the manifestation of the interaction balance between self-crystallization and co-crystallization of the dissimilar polymers on the resulting nanostructure of the BCP. The current study demonstrates the co-crystallization nature of all-conjugated BCPs with different main-chain moieties and may provide new guidelines for the organization of π-conjugated BCPs for future optoelectronic applications.
authors.affiliation: Department of Chemical Engineering and Institute of Polymer Science and Engineering, National Taiwan University, No. 1 Roosevelt Rd Sec. 4, Taipei 10617, Taiwan. polymer@ntu.edu.tw.
authors.forename: Yi-Huan
authors.initials: YH
authors.lastname: Lee
authors.forename: Wei-Chih
authors.initials: WC
authors.lastname: Chen
authors.forename: Yi-Lung
authors.initials: YL
authors.lastname: Yang
authors.forename: Chi-Ju
authors.initials: CJ
authors.lastname: Chiang
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Yokozawa
authors.forename: Chi-An
authors.initials: CA
authors.lastname: Dai