Web Release Date: March 22,
Nanoscale Phase Separation in Mixed Poly(tert-butyl acrylate)/Polystyrene Brushes on Silica Nanoparticles under Equilibrium Melt Conditions
and
Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, and Polymer Program, Institute of Materials Science and Department of Chemical Engineering, University of Connecticut, Storrs, Connecticut 06269
Received December 17, 2005
Abstract:
This communication reports on the study of microphase separation of well-defined mixed poly(tert-butyl acrylate) (PtBA)/polystyrene (PS) brushes on silica nanoparticles under equilibrium melt conditions. Mixed PtBA/PS brushes were synthesized from an asymmetric, difunctional initiator-terminated self-assembled monolayer by combining atom transfer radical polymerization and nitroxide-mediated radical polymerization. Two symmetric PtBA/PS mixed brush samples with different molecular weights were used in this study and were thermally annealed in vacuum at 150 
C. For the mixed brushes with number average molecular weights (Mn) of 24 200 g/mol for PtBA and 23 000 g/mol for PS, two glass transitions were observed in the differential scanning calorimetry analysis. Transmission electron microscopy study showed that the two grafted polymers underwent a lateral microphase separation, forming a random worm-like pattern with a feature size of ~10 nm on the silica particle surfaces. In contrast, the mixed brushes with a Mn of 10 400 g/mol for PtBA and 11 900 g/mol for PS did not microphase separate. Although the mixed brushes are on curved substrates, this work provides results consistent with the theoretical prediction that symmetric mixed homopolymer brushes undergo lateral rather than vertical phase separation under equilibrium melt conditions.
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