Narrowly dispersed, temperature-responsive BAB block copolymers capable of forming physical gels under physiological conditions were synthesized via aqueous reversible addition fragmentation chain transfer (RAFT) polymerization. The use of a difunctional trithiocarbonate facilitates the two-step synthesis of BAB copolymers with symmetrical outer blocks. The outer B blocks of the triblock copolymers consist of poly(N-isopropylacrylamide) (PNIPAM) and the inner A block consists of poly(N,N-dimethylacrylamide). The copolymers form reversible physical gels above the phase transition temperature of PNIPAM at concentrations as low as 7.5 wt % copolymer. Mechanical properties similar to collagen, a naturally occurring polypeptide used as a three-dimensional in vitro cell growth scaffold, have been achieved. Herein, we report the mechanical properties of the gels as a function of solvent, polymer concentration, and inner block length. Structural information about the gels was obtained through pulsed field gradient NMR experiments and confocal microscopy.

Introduction.Recently, clay-polymer nanocomposites obtained from surface-treated montmorillonite have attracted enormous interest because of unexpectedly high property enhancements at low clay content (1-5 wt %). For instance, improved heat distortion temperatures, moduli, tensile strengths, and yield stresses have been reported for nanocomposites with <5 wt % clay in nylon 6, 1-7 poly(N-vinylcarbazole), 8 polypropylene, 9 polyester, 10-13 polyimide, [14][15][16][17] poly-(methyl methacrylate), 18 poly(ethylene oxide), [19][20][21] poly-(ether-amine), 22,23 polystyrene, 24 and polyurethane. 25,26 The improved properties are believed to result from synergistic interactions between high surface area clay particles and the polymer. The nature, origin, and strength of these interactions are not well understood. Spectroscopic efforts to evaluate the effects of clay on the polymer have combined infrared spectroscopy (IR), 6,11 thermal analysis, and X-ray diffraction (XRD). These techniques have shown that clay induces the γ crystal phase in nylon 6 while maintaining about the same percent crystallinity. However, no determination has been made of whether this phase exists alone or whether it is a kinetically formed component that slowly relaxes to the more stable R-crystal form.We previously reported the observation of R, γ, and amorphous phases in nylon 6 using solid-state 15 N CP/ MAS NMR. 27 Because of speed, simplicity, and accuracy, this method has been used by us and others for characterization of crystallinity in a variety of homoand copolyamides. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] In an attempt to better understand the interaction between exfoliated clay and nylon, we have applied solid-state 15 N CP/MAS NMR methods to characterization of typical nylon 6-clay nanocomposites. We report our initial results here.Experimental Section. 12-Aminolauric acid treated montmorillonite was used as received from Nanocor, Inc. 34 The cation exchange capacity (CEC) was ca. 119 mequiv/100 g of montmorillonite as reported on the MSDS. 34 Solid-state 15 N CP/MAS NMR spectra were collected on a Bruker MSL-400 MHz NMR operating at 40.57 MHz spectral frequency. A routine 15 N CP/MAS pulse program was used with a 7.8 µs, 90°pulse width and a 1 ms contact time. The average number of scans was 30 000 for the nanocomposite and 21 000 for the commercial nylon 6. Chemical shifts are reported relative to 15 N-labeled glycine at 0 ppm.Nylon 6 and nanocomposite samples for solution 13 C NMR were prepared by dissolving in trifluoroethanol (TFE) with heating and then adding CDCl 3 to the cooled solution to give a sample with 10 wt % polymer in a

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The synthesis of nanostructured polymer gels via polymerization of hydrophilic monomers in lyotropic liquid crystal (LLC) phases has recently been of great interest. This work describes the effects of monomer organization on the photopolymerization kinetics of acrylamide in various LLC phases of surfactant/water systems. Resulting polymer morphology is reported as well. The polymerization rate of acrylamide is significantly enhanced when performed in the presence of various LLC phases. An unprecedented 10-fold increase in polymerization rate is observed in bicontinuous cubic and hexagonal phases as compared to polymerizations in water. This significant increase in polymerization rate is a result of diffusional limitations on the propagating polymer as well as segregation and ordering phenomena induced by the LLC phase. 13C T 1 relaxation times and 14N NMR spectra show that the monomer strongly associates with the interface of the surfactant/water assemblies and assumes the orientational order of the LLC phases to some degree. When formed using photopolymerization, the resulting polymer morphology appears to be a direct template of the parent LLC phase.

Temperature-and pH-responsive, micelle-forming, amphiphilic block copolymers were prepared from N,N-dimethylacrylamide (DMA), N-isopropylacrylamide (NIPAM), and N-acryloylvaline (AVAL) utilizing aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. A series of block copolymers were synthesized by employing DMA as a macro-chain transfer agent to mediate the statistical copolymerization of NIPAM with AVAL. Structural organization and solution behavior were investigated utilizing dynamic light scattering, two-dimensional NMR spectroscopy, and transmission electron microscopy. It has been demonstrated that the critical micellization temperature for the block polymers can be tuned to range from ≈10 to 36 °C by adjusting the solution pH. Micelles with apparent hydrodynamic diameters from 45 to 86 nm are formed between pH 2 and 5. Above pH 5, a sufficient number of the AVAL units are deprotonated which prevents micellization. The extent of pH and temperature changes on the apparent hydrodynamic diameters have been illustrated via 3-D plots. Significantly, micelles assembled within a specified range of pH and temperature can be "locked" by interpolyelectrolyte complexation of anionic AVAL segments with those of a cationic polymer, in this case a RAFT-generated poly ([ar-vinylbenzyl]trimethylammonium chloride) (PVBTAC). When the temperature is lowered to room temperature, the polymeric micelles remain "locked" in their multimeric structures which remain dispersed in water. Addition of 0.3 M NaCl to the aqueous solution results in dissociation of the complexes into the respective water-soluble components. † Paper no. 129 in a series titled "Water Soluble Polymers".

A simple synthetic method for preparing stable colloidal dispersions that form polymeric films containing fluorinated acrylates is presented. The simultaneous presence of the dual tail anionic fluorosurfactant phosphoric acid bis(tridecafluorooctyl) ester ammonium salt (FSP) and sodium dodecyl sulfate (SDS) surfactants facilitates a suitable environment for the aqueous polymerization of methyl methacrylate/n-butyl acrylate/heptadecafluorodecyl methacrylate (MMA/nBA/FMA) colloidal particles. Polyermerization is achieved by a low-sheer monomer-starved emulsion polymerization process in which the FSP/SDS surfactant mixture significantly reduces the surface tension of the aqueous phase, thus facilitating mobility and subsequent polymerization of FMA along with MMA and nBA momomers. Using this approach, it is possible to obtain stable nonspherical MMA/nBA/FMA colloidal dispersions containing up to a 8.5% (w/w) copolymer content of FMA. These studies illustrate that the incorporation of FMA into MMA/nBA particle morphologies facilitates surface phase separation during coalescence, resulting in F-containing film−air (F−A) interfaces. Thus, surface properties with a significant decrease in the kinetic coefficient of friction as well as high contact angles can be produced.

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[VO(Sal-L-tryp)(H2O)] 1 (where sal-L-tryp = N-salicylidene-L-tryptophanate) was used as a precursor to produce the novel complexes, [VO(Sal-L-tryp)(MeATSC)].1.5C2H5OH 2 (where MeATSC = 9-Anthraldehyde-N(4)-methylthiosemicarbazone), [VO(Sal-L-tryp)(N-Ethhymethohcarbthio)].H2O 3 (where N-Ethhymethohcarbthio = (E)-N-ethyl-2-(4-hydroxy-3-methoxybenzylidene)hydrazinecarbothioamide), and [VO(Sal-L-tryp)(acetylethTSC)].C2H5OH 4 (where acetylethTSC = (E)-N-ethyl-2-(1-(thiazol-2-yl)ethylidene)hydrazinecarbothioamide), by reaction with the respective thiosemicarbazone. The chemical and structural properties of these ligands and complexes were characterised by elemental analysis, ESI MS, FT-IR, UV-visible, ESR, 1H and 13C NMR spectroscopy, and X-ray crystallography. DMSO and DMSO-d6 solutions of compounds 1-4 were oxidised in air to produce vanadium(V) species which were verified by ESI MS and 51V NMR spectroscopy. Anti-cancer properties of compounds 2-4 were examined with three colon cancer cell lines, HTC-116, Caco-2, and HT-29, and also with non-cancerous colonic myofibroblasts, CCD18-Co. Compounds 2-3 exhibited less inhibitory effects in the CCD-18Co cells, indicating a possible cytotoxic selectivity towards colon cancer cells. In general, those compounds which exhibited anti-proliferative activity on cancer cells, but did not affect non-cancerous cells, may have a potential in chemotherapy.