title: Double-Gyroid Network Morphology in Tapered Diblock Copolymers.
abstract: We report the formation of a double-gyroid network morphology in normal-tapered poly(isoprene-b-isoprene/styrene-b-styrene) [P(I-IS-S)] and inverse-tapered poly(isoprene-b- styrene/isoprene-b-styrene) [P(I-SI-S)] diblock copolymers. Our tapered diblock copolymers with overall poly(styrene) volume fractions of 0.65 (normal-tapered) and 0.67 (inverse-tapered), and tapered regions comprising 30 volume percent of the total polymer, were shown to self-assemble into the double-gyroid network morphology through a combination of small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The block copolymers were synthesized by anionic polymerization, where the tapered region between the pure poly(isoprene) and poly(styrene) blocks was generated using a semi-batch feed with programmed syringe pumps. The overall composition of these tapered copolymers lies within the expected network-forming region for conventional poly(isoprene-b-styrene) [P(I-S)] diblock copolymers. Dynamic mechanical analysis (DMA) clearly demonstrated that the order-disorder transition temperatures (T(ODT)'s) of the network-forming tapered block copolymers were depressed when compared to the T(ODT) of their non-tapered counterpart, with the P(I-SI-S) showing the greater drop in T(ODT). These results indicate that it is possible to manipulate the copolymer composition profile between blocks in a diblock copolymer, allowing significant control over the T(ODT), while maintaining the ability to form complex network structures.
authors.affiliation: Department of Chemical Engineering, University of Delaware, Newark, DE 19716.
authors.forename: Raghunath
authors.initials: R
authors.lastname: Roy
authors.forename: Jong Keun
authors.initials: JK
authors.lastname: Park
authors.forename: Wen-Shiue
authors.initials: WS
authors.lastname: Young
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Mastroianni
authors.forename: Maëva S
authors.initials: MS
authors.lastname: Tureau
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Epps