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Graft block polymers are defined by several architectural parameters, including backbone flexibility, graft density, backbone length, side-chain composition, and side-chain length. In this work we probe the impacts of each of these parameters on the phase behavior, rheological properties, and mechanical performance of these materials. Specifically, we examine two sets of materials prepared from backbones of different inherent flexibility. One set was prepared from poly[(n-butyl acrylate)-co-(2-hydroxyethyl acrylate)] (BxEy) copolymers; the other was prepared from hydroxypropyl methyl cellulose (HPMC) samples. Sequential ring-opening transesterification polymerization from these hydroxyl-functionalized macroinitiatiors yielded a diblock graft architecture containing a rubbery interior block and semicrystalline exterior blocks tethered to a flexible (BxEy) or rigid (HPMC) backbone. Good control over side-chain molar mass and composition and judicious choice of the graft block segments enabled the preparation of materials that were either ordered or disordered in the melt state. In the former case, crystallization destroys existing order in the material; in the latter case crystallization induces new microphase separation in the bulk. Many of the structure-mechanical property relationships observed for graft block copolymers with rigid backbones are maintained for graft block polymers with semiflexible backbones, including the tendency for samples to remain transparent when stretched. However, interestingly, the effects of graft density and backbone length are quite different depending on the rigidity of the backbone.
Bibliographical noteFunding Information:
The Center for Sustainable Polymers at the University of Minnesota, a National Science Foundation (NSF)-supported Center for Chemical Innovation (CHE-1413862). Partial funding was also provided by National Science Foundation through the University of Minnesota MRSEC under Award DM R- 1420013 and the National Natural Science Foundation of China (Grant 21504013). SAXS data were obtained at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) Synchrotron Research Center located at Sector 5 of the APS. DND-CAT is supported by the E.I. DuPont de Nemours andCo. and The Dow Chemical Company. Use of the APS was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DEAC02- 06CH11357.
© 2016 American Chemical Society.
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