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    Ultrastable Glassy Polymer Films with an Ultradense Brush Morphology

    Year: 2021

    Journal: ACS Nano, Volume 15, JUN 22, page 9568–9576

    Authors: Zuo, Biao; Li, Cheng; Xu, Quanyin; Randazzo, Katelyn; Jiang, Naisheng; Wang, Xinping; Priestley, Rodney D.

    Organizations: National Natural Science Foundation of China [21973083, 22011530456, 21674100]; National Science Foundation (NSF) Materials Research Science and Engineering Center Program through the Princeton Center for Complex Materials [DMR-1420541, 2011750, CBET-1706012]; U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0012704]

    Keywords: ultrastable polymer glasses; glass transition; thermal expansion; polymer brushes; thin polymer flims

    Glassy polymer films with extreme stability could enable major advancements in a range of fields that require the use of polymers in confined environments. Yet, from a materials design perspective, we now know that the glass transition temperature (T-g) and thermal expansion of polymer thin films can be dramatically different from those characteristics of the bulk, i.e., exhibiting confinement-induced diminished thermal stability. Here, we demonstrate that polymer brushes with an ultrahigh grafting density, i.e., an ultradense brush morphology, exhibit a significant enhancement in thermal stability, as manifested by an exceptionally high T-g and low expansivity. For instance, a 5 nm thick polystyrene brush film exhibits an similar to 75 K increase in T-g and , similar to 90% reduction in expansivity compared to a spin-cast film of similar thickness. Our results establish how morphology can overcome confinement and interfacial effects in controlling thin-film material properties and how this can be achieved by the dense packing and molecular ordering in the amorphous state of ultradense brushes prepared by surface-initiated atom transfer radical polymerization in combination with a self-assembled monolayer of initiators.
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