Polystyrene and poly[(tert-butyl acrylate)-b-styrene] with well-defined molecular weights and polydispersities were prepared by nitroxide-mediated free-radical polymerization. The homopolymers and block copolymers were used to functionalize shortened single-walled carbon nanotubes (SWNTs) through a radical coupling reaction involving polymer-centered radicals generated at 125 °C via loss of the stable free-radical nitroxide capping agent. The resulting polymer−SWNT composites were fully characterized and were found to be highly soluble in a variety of organic solvents. This solubility could also be altered through chemical modification of the appended polymers. The tert-butyl groups of appended poly[(tert-butyl acrylate)-b-styrene] could be removed to produce poly[(acrylic acid)-b-styrene]-functionalized carbon nanotubes. The resulting composite was found to form aggregates in a mixture of chloroform/methanol (v/v:  1/1) as determined by dynamic light scattering.

The development of activatable photodynamic therapy (PDT) has demonstrated a utility for effective photosensitizer quenchers. However, little is known quantitatively about Forster resonance energy transfer (FRET) quenching of photosensitizers, even though these quenchers are versatile and readily available. To characterize FRET deactivation of singlet oxygen generation, we attached various quenchers to the photosensitizer pyropheophorbide-alpha (Pyro) using a lysine linker. The linker did not induce major changes in the properties of the photosensitizer. Absorbance and emission wavelength maxima of the quenched constructs remained constant, suggesting that quenching by ground-state complex formation was minimal. All quenchers sharing moderate spectral overlap with the fluorescence emission of Pyro (J > or = 5.1 x 10(13) M(-1) cm(-1) nm4) quenched over 90% of the singlet oxygen, and quenchers with weaker spectral overlap displayed minimal quenching. A self-quenched double Pyro construct exhibited intermediate quenching. Consistent with a FRET deactivation mechanism, extension of the linker to a 10 residue polyproline peptide resulted in only the quenchers with spectral overlap almost 2 orders of magnitude higher (J > or = 3.7 x 10(15) M(-1) cm(-1) nm4) maintaining high quenching efficiency. Overall, there was good correlation (0.98) between fluorescence quenching and singlet oxygen quenching, implying that fluorescence intensity can be a convenient indicator for the singlet oxygen production status of activatable photosensitizers. Uniform singlet oxygen luminescence lifetimes of the compounds, along with minimal triplet state transient absorption were consistent with quenchers primarily deactivating the photosensitizer excited singlet state. In vitro, cells treated with well-quenched constructs demonstrated greatly reduced PDT induced toxicity, indicating that FRET-based quenchers can provide a level of quenching useful for future biological applications. The presented findings show that FRET-based quenchers can potently decrease singlet oxygen production and therefore be used to facilitate the rational design of activatable photosensitizers.

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Single-walled carbon nanotubes were oxidatively shortened and functionalized with ruthenium-based olefin metathesis catalysts. These catalyst-functionalized nanotubes were shown to be effective in the ring-opening metathesis polymerization of norbornene, resulting in rapid polymerization from the catalyst sites on the nanotube. It was found that high polymer molecular weights could be reached, and the molecular weight increased linearly with polymerization time. The resulting polynorbornene-functionalized nanotubes were found to exhibit solubility in organic solvents, whereas the starting materials and catalyst-functionalized nanotubes were completely insoluble. The polymerized materials were characterized by NMR, IR, DSC, AFM, and TEM.

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

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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.

Summary: Solketal acrylate (SA) was homopolymerized by atom transfer radical polymerization (ATRP) using CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the catalyst and cyclohexanone as the solvent with controlled molecular weights and low polydispersities. The prepared bromine‐terminated homopolymers, PSA, were used as macroinitiators to initiate polymerization of tert‐butyl acrylate (tBA) under similar ATRP conditions to produce diblock copolymers, PSA‐b‐PtBA, with controlled molecular weights and low polydispersities. ATRP of SA using bromine‐terminated PtBA as the macroinitiator was also carried out and diblock copolymers, PtBA‐b‐PSA, were obtained. The PSA block was selectively hydrolyzed by stirring for 3 h in 6 N HCl/THF (1/9, v/v) at room temperature to form a poly(glycerol monoacrylate) block. Both blocks of PSA and PtBA were hydrolyzed by stirring in anhydrous trifluoroacetic acid (TFA)/dichloromethane for 4 h, then adding water to the system and stirring for another 3 h to form corresponding diblock copolymers of glycerol monoacrylate and acrylic acid.Kinetic plot for the atom transfer radical polymerization of solketal acrylate at 90 °C.magnified imageKinetic plot for the atom transfer radical polymerization of solketal acrylate at 90 °C.