Environmentally Responsive “Hairy” Nanoparticles:  Mixed Homopolymer Brushes on Silica Nanoparticles Synthesized by Living Radical Polymerization Techniques

Abstract

This article reports on the preparation of environmentally responsive "hairy" nanoparticles by growth of mixed poly(tert-butyl acrylate) (PtBA)/polystyrene (PS) brushes from silica particles using living radical polymerization techniques and subsequent hydrolysis of PtBA to produce amphiphilic mixed poly(acrylic acid) (PAA)/PS brushes. Silica particles were synthesized by the Stober process and were functionalized with an asymmetric difunctional initiator-terminated monolayer. Surface-initiated atom transfer radical polymerization of tBA was carried out in the presence of a free initiator. Kinetics study showed that the polymerization was well controlled. By cleaving PtBA off the particles, the molecular weights of the grafted and free polymers were found to be essentially identical. Mixed PtBA/PS brushes were obtained by the nitroxide-mediated radical polymerization of styrene from PtBA particles. The M(n) of the grafted PS was found to be the same as that of the free PS formed in the solution from the free initiator. Amphiphilic mixed PAA/PS brush-coated nanoparticles were synthesized from mixed PtBA/PS particles by hydrolysis of PtBA with iodotrimethylsilane. Tyndall scattering experiments and (1)H NMR study showed that the mixed PAA/PS particles can be dispersed and form a stable suspension in CHCl(3), a selective solvent for PS, and also in CH(3)OH, a selective solvent for PAA, demonstrating the capability of these hairy nanoparticles to undergo chain reorganization in response to environmental changes.

Hierarchically Ordered Montmorillonite Block Copolymer Brushes

“…The use of BCPs in surface chemistry has been further varied by attaching Y-branched initiators and that produce BCP that are pinned at the BCP interface. 57,58 The formation of pinned micelles via Y-branched initiation has been demonstrated by Boyes et al using a combination of ATRP and NMRP synthesis. 54 The grafting of CRP initiators, targeting specific molecular weight, and the minimization of brush PDI are all techniques developed for surface modification that have now been directly applied to grafted BCP nanocomposites.…”

“…Recently work has focused on confinement effects of BCP assemblies in lithographic patterned channels [123][124][125][126][127] , oil-in-water emulsions, 128,129 and surface grafted nanoparticles. [130][131][132] Each of these phenomena can be viewed independently as specialized applications for self-assembled BCPs or collectively as the tools for hierarchically engineered materials. 133 Of primary concern to this work is the application of BCP selfassembly to nanoparticle alignment; due to the sparse amount of literature about BCP grafted nanoparticles it is 1 Graduate student and Assistant Professor, respectively, Department of Chemical and Biological Engineering, Iowa State University.…”

“…Li et al produced silica particles with a difunctional initiator-terminated monolayer to produce spherical brushes. 131 These "hairy" nanoparticles were produced by a combination of atom transfer radical polymerization (ATRP) and nitroxide mediated radical polymerization (NMRP). The resulting environmentally responsive nanoparticles formed colloidal suspensions in solvents as diverse as chloroform and methanol.…”

Hybrid metal–polymer composites from functional block copolymers

“…For example, inorganic species incorporated within stimulus-responsive polymer systems might serve as simple sensors or as components of more complex devices. [119][120][121] At longer length scales (hundreds of nanometers to micrometers), the integration of these materials with larger systems, especially through the formation of regular arrays of metal-containing domains, becomes a seemingly attainable target, and several successes toward this end have been reported. 100,[122][123][124] Because of the structurally rich nature of their bulk selfassembly, block copolymers hold great promise, not only for two-dimensional pattern formation but also for organization of metal-containing domains in three dimensions.…”

Quartz crystal microbalance study of the kinetics of surface initiated polymerization

“…For example, polymer brushes via SIP rendered stability to dispersed nano-particles and colloids [4][5][6][7][8][9] , minimized nonspecific protein adsorption, improved biocompatibility [10][11][12][13][14][15] , and acted as matrix for biosensors [16][17][18] and separation applications [19][20][21][22] . SIP also opened new ways for nano/micro-fabrication [23][24][25][26][27][28] , altered fluid behavior in nano/micro-fluidic devices [29][30][31] , and was found in other exotic applications [32][33][34][35] .…”