High-strain-induced deformation mechanisms in block-graft and multigraft copolymers
Hölzer, Stefan M.
Schneider, Konrad M.
Uhrig, David W.
Mays, Jimmy Wayne
KAUST DepartmentBiological and Environmental Sciences and Engineering (BESE) Division
Physical Sciences and Engineering (PSE) Division
Chemical Science Program
KAUST Catalysis Center (KCC)
Polymer Synthesis Laboratory
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AbstractThe molecular orientation behavior and structural changes of morphology at high strains for multigraft and block-graft copolymers based on polystyrene (PS) and polyisoprene (PI) were investigated during uniaxial monotonic loading via FT-IR and synchrotron SAXS. Results from FT-IR revealed specific orientations of PS and PI segments depending on molecular architecture and on the morphology, while structural investigations revealed a typical decrease in long-range order with increasing strain. This decrease was interpreted as strain-induced dissolution of the glassy blocks in the soft matrix, which is assumed to affect an additional enthalpic contribution (strain-induced mixing of polymer chains) and stronger retracting forces of the network chains during elongation. Our interpretation is supported by FT-IR measurements showing similar orientation of rubbery and glassy segments up to high strains. It also points to highly deformable PS domains. By synchrotron SAXS, we observed in the neo-Hookean region an approach of glassy domains, while at higher elongations the intensity of the primary reflection peak was significantly decreasing. The latter clearly verifies the assumption that the glassy chains are pulled out from the domains and are partly mixed in the PI matrix. Results obtained by applying models of rubber elasticity to stress-strain and hysteresis data revealed similar correlations between the softening behavior and molecular and morphological parameters. Further, an influence of the network modality was observed (random grafted branches). For sphere forming multigraft copolymers the domain functionality was found to be less important to achieve improved mechanical properties but rather size and distribution of the domains. © 2011 American Chemical Society.
SponsorsThe authors thank for financial support of this work within the framework of the German Science Foundation (DFG) and Fraunhofer IWM Halle. A portion of this research at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy (enabled through User Project # 2003-028), and supported in part by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy (DE- ACO5-00OR22725). Y. X. Duan thanks the support from Shang dong Province Science Fund (ZR2009AL011). We thank DESY for beamtime within the project II-20060086.
PublisherAmerican Chemical Society (ACS)