title: AxBAx-type block-graft polymers with soft methacrylate middle segments and hard styrene outer grafts: synthesis, morphology, and mechanical properties.
abstract: Novel copolymers with controlled architectures can function as new building blocks for well-defined nanostructures on the basis of microphase separation, unlike conventional ABA triblock copolymers. A series of well-defined A(x)BA(x)-type block-graft copolymers consisting of soft middle segments (dodecyl methacrylate (DMA)) and hard outer graft chains (styrene (St)) were synthesized by ruthenium-catalyzed living radical block and graft polymerization. NMR spectroscopy and size-exclusion chromatography combined with multiangle laser light scattering confirmed the well-defined structure of the A(x)BA(x) block-graft copolymers with backbones and graft chains of controlled lengths. Transmission electron microscopy and transmission electron microtomography revealed a series of morphologies for the copolymers. Morphological changes were observed from PSt "honeycomb" cylinders to lamellae and poly(DMA) cylinders with increasing PSt-graft content, whereby the phase diagram was shifted significantly to lower volume fractions of the larger-number component (St) relative to those of the corresponding ABA triblock copolymers. More specifically, poly(DMA) cylinders were observed even before the St content reached 50 wt %. The A(x)BA(x) and ABA copolymers with 17-30 wt % of St exhibited characteristics of a thermoplastic elastomer with tensile strengths of 1-6 MPa and elongations at break of 70-300 %. These mechanical properties can be related well to the microphase structures of the A(x)BA(x) and ABA copolymers.
authors: Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
authors: Yu
authors: Y
authors: Miura
authors: Takeshi
authors: T
authors: Kaneko
authors: Kotaro
authors: K
authors: Satoh
authors: Masami
authors: M
authors: Kamigaito
authors: Hiroshi
authors: H
authors: Jinnai
authors: Yoshio
authors: Y
authors: Okamoto