We report the synthesis of a new polythiophene (PT)-based molecular brush (PT-g-PDMA) by growing poly(N,N-dimethylaminoethyl methacrylate) (PDMA) chains from the PT backbone by ATRP. The polymer shows a reversible pH response in aqueous solution. A combination of AFM, light scattering, and 1 H NMR measurements indicated that the polymer brush forms a more extended conformation with a decrease in pH from 8 to 2 due to the protonation of the Me 2 N-groups and increased repulsive interactions among the PDMA side chains, which drives the red shift of the absorption and PL spectra of the PT backbone. The good solubility of this polythiophene-based brush in a wide range of solvents is attractive for the fabrication of functional polymer composites.
We describe polymer diffusion measurements in poly(butyl acrylate-co-methyl methacrylate) [P(BA-MMA)] copolymer latex films by fluorescence resonance energy transfer (FRET). Four sets of copolymers were prepared from various weight ratios of butyl acrylate and methyl methacrylate by semicontinuous emulsion polymerization. Their glass transition temperatures range from 4 to 28 °C. Latex particles were labeled with phenanthrene (Phe) as the donor dye and with 4-(N,N-dimethylamino)benzophenone (NBen) as the acceptor dye. Latex films were cast from a 1:1 mixture of Phe-and NBen-labeled latex samples. Polymer diffusion was monitored as a function of annealing temperature, and apparent diffusion coefficients (D app ) were calculated from the energy transfer data using a simple diffusion model. These values increased with annealing temperature and decreased with T g . Rheology measurements recorded the response of the dynamic moduli (G′, G′′) with respect to oscillatory shear frequency (ω) over a range of temperature close to that of the diffusion experiments. The temperature dependence of polymer dynamics extracted by the rheology experiments is in good agreement with the temperature dependence of D app . Increasing the BA copolymer content leads to an apparent increase in long-chain branching, which is reflected in both the time dependence of D app and in the dynamic moduli measurements. A greater degree of branching leads to a broader distribution of polymer diffusion coefficients and a stronger time dependence of D app .
Experimental SectionMaterials. Potassium persulfate (KPS), sodium carbonate (Na 2 -CO 3 ), and 1-dodecanethiol (C 12 -SH) were used as received from Aldrich. Polystep A-16 (22% solution of dodecylbenzene and tridecylbenzenesulfonates, 1 Stepan Co., Maywood, NJ) and methylβ-cyclodextrin were kindly supplied by Rohm and Haas Co. and used as received. Methyl methacrylate (MMA, Aldrich), butyl acrylate (BA, Aldrich), and methacrylic acid (MAA, Aldrich) were distilled at reduced pressure, and the purified monomers were stored at 0 °C until use. Water was purified by a Milli-Q ion-exchange filtration system. Phenanthrylmethyl methacrylate (PheMMA) was used as received from Toronto Research Chemicals Inc. 4′-Dimethylamino-2-methacryloxy-5-methylbenzophenone (NBenMA) was synthesized as described elsewhere. 4,5 Latex Preparation. All latex dispersions were prepared by semicontinuous emulsion polymerization reactions. A typical recipe for the synthesis of nonlabeled P(BA-MMA) (BA:MMA weight ratio 60:39) latex is shown in Table 1. In the first stage, a dispersion of seed particles was prepared by batch emulsion polymerization
Latex particles comprised of branched poly(butyl methacrylate) (PBMA) were prepared via semicontinuous emulsion polymerization. The extent of branching was controlled by adding various amounts of bisphenol A dimethacrylate (BPDM) as a branching agent, and 1-dodecanethiol (C 12 SH) was used as a chain transfer agent to prevent cross-linking and to control molecular weight. All PBMA samples have relatively high molecular weights with molecular weight distributions similar to that of the polymers synthesized by regular free radical polymerization in the presence of a chain transfer agent. The degrees of branching were determined using 1 H NMR. G′ and G′′ measurements indicated no significant entanglement contributions to the rheological properties. The latex particles containing branched PBMAs are monodisperse, and the particle sizes are well controlled.
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