Polymer-grafted nanocomposites consisting of nanoparticles decorated with covalently-attached polymer chains in a polymer matrix are of particular interest because of their ability to combine the properties of hard and soft matter while suppressing the tendency of nanoparticles to aggregate. While athermal "symmetric" systems in which graft and matrix polymers are of the same chemical type are widely investigated, here the focus in on "asymmetric" systems where graft and matrix chains are chemically different. Specifically, controlled radical polymerization methods are used to generate random copolymers that subsequently are end-grafted to functionalized silica nanoparticles. The dispersion behavior of two different asymmetric systems containing copolymer-grafted nanoparticles (CPGNs) will be described. In the first, the composition of random copolymers of poly(cyclohexyl methacrylate-<i>ran</i>-methyl methacrylate) is used to mediate miscibility in polystyrene, displaying phase behavior in complete accord with bulk systems. In the second, "Tg-tuned" random poly(alkyl methacrylate)s end-grafted to silica nanoparticles are examined in dissimilar matrices of poly(methyl methacrylate) (PMMA). Across all choices of comonomer type and copolymer composition, these CPGNs remain dispersed and an increase in glass transition temperature, Tg, of the resultant nanocomposite is observed, even when matrix chains are of higher molecular weight. Broadband dielectric spectroscopy is used to probe temperature-dependent dynamic relaxation processes and make connections between copolymer design, loading level, and enhancements in thermomechanical properties. In view of the ability to widely manipulate the properties of polymeric materials through the integration of different monomers, these lines of investigation point to the potential of copolymer design as a generally useful handle that can be used to tailor nanocomposite properties.

Organization and dynamics of compositionally-tuned polymer grafted nanocomposites

255th National Meeting (2018)

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