Well-defined polymer brushes grafted onto silica nanoparticles were prepared by reversible addition−fragmentation chain transfer polymerization (RAFT). A versatile RAFT agent, 4-cyanopentanoic acid dithiobenzoate (CPDB), was attached to amino-functionalized colloidal silica nanoparticles by direct condensation of the mercaptothiazoline-activated CPDB with the surface amino groups. RAFT polymerizations were then conducted from the particle surface to graft polymer brushes to the particles. The kinetics of methyl methacrylate and styrene surface RAFT polymerizations were investigated and compared with model polymerizations mediated by free CPDB. The MMA surface graft polymerization was more controlled than the solution polymerization mediated by free RAFT agent, indicated by the faster polymerization rate and narrower polydispersity. High-performance liquid chromatography techniques were used to quantitatively estimate the amount of ungrafted free polymer which was minimal compared with the grafted polymer.

Interaction chromatography has been employed to validate that adsorption of poly[styrene-co-(4-bromostyrene)] (PBr(x) S) random copolymers, where x denotes the mole fraction of 4-bromostyrene (4-BrS) in PBr(x) S in solution depends on the average number of adsorptive segments, the type of adsorbing substrate, and on the co-monomer sequence distribution in PBr(x) S.

Dendronized polyferrocenylsilanes were synthesized by a substitution reaction of reactive poly-(ferrocenylchloromethylsilane) with monodendrons with a focal hydroxy group. The resulting dendronized polymers were studied by 1 H NMR, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). To facilitate the direct visualization of single polymer chains by atomic force microscopy (AFM), an interaction chromatography technique (IC) was used to fractionate the polydisperse polymers to separate the high molecular weight dendronized PFSs. AFM studies of the fractionated high molecular weight PFSs revealed a spherical cocoon for the single chains of the dendronized polymer as well as elongated single-chain structures. The cocoon of the dendronized PFS could be interesting as a unimolecular micelle with the transition-metal-rich core which is isolated by the dense outer layer of the dendrons.

The cyclolinear polycarbosilane, (poly(1-hexyl-1,3-ditolyl-1,3-disilacyclobutane) poly(HDTDSCB)), which has tolyl groups attached to the main chain Si atoms, was prepared by ADMET polymerization with the second-generation Grubbs catalyst, and 10%, 5%, and 2% of the tolyl groups were brominated by reactions with N-bromosuccinimide. A series of well-controlled poly(methyl methacrylate) (PMMA) anions of 2.5K, 5K, and 10K molecular weight were introduced via the "grafting onto" strategy at low temperature to the randomly 10%, 5%, and 2% brominated poly(HDTDSCB), respectively, without any lithiation or ring opening of the disilacyclobutane in the main chain. Because of side reactions initiated by the PS anion under similar conditions, a "grafting from" strategy by ATRP was employed to yield the corresponding poly(HDTDSCB)-g-PS random copolymers. The product poly(HDTDSCB)-g-(PMMA or PS) random copolymers were purified by using total adsorption-desorption interaction chromatography, which involves selective adsorption of the polycarbosilane on a C18 HPLC column from a CH 2 Cl 2 /CH 3 CN (50/50) eluent, while the excess PMMA or PS homopolymer eluted. This method was also successfully applied to the separation of larger quantities of the copolymers by using multiple injections onto the C18 column.

The crazing and fracture behaviors of glassy-glassy block copolymers were investigated for polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymers that had similar overall molecular weights but different poly (methyl methacrylate) (PMMA) molar fractions. A liquid chromatography technique was applied to separate as-synthesized PS-b-PMMA [(1) weight-average molecular weight (M w ) ¼ 94,000 g/mol and PMMA molar fraction ¼ 0.35 and (2) M w ¼ 65,000 g/ mol and PMMA molar fraction ¼ 0.28] into three fractions with different chemical compositions. With a copper-grid technique, the fracture behaviors of 0.5-lm-thick PS-b-PMMA films were studied as a function of the applied strain. For the higher M w PS-b-PMMA samples, the median strains at crazing and fibril breakdown increased with an increase in the PMMA molar fraction from 0.24 to 0.46, corresponding to an increase in the chain entanglements in the PMMA domains. In contrast, for the lower M w samples, the two values were not significantly changed even when the PMMA molar fraction was varied from 0.16 to 0.35. M w of the minor component in PS-b-PMMA played a critical role in controlling the fracture behaviors of the block copolymers. Specifically, M w /M e of the minor component (where M e is the molecular weight between entanglements) had to be roughly larger than 2 for the block copolymers to sustain sufficient strains before fracture.