Dielectric relaxation of polysiloxanes and kerr effect of p-phenylene vinylene oligomers

The dielectric relaxation behaviour of a series of cyclic and linear poly(dimethylsiloxanes) with overline nn in the range 28 to 99 has been studied, as a function of temperature (142.0K-157.5K) and frequency (12-105Hz). Activation energies for the -relaxation process, Davidson-Cole empirical distribution factors, , and mean-square dipole moments per repeat unit, < 2> , have been calculated. Differences in values of H_act reflected restricted dipolar rotation for the cyclic structures, compared to the linear structures, over the range of molecular weights studied. The dielectric relaxation behaviour of a series of linear oligomers of methyl phenyl siloxane, with n in the range 4 to 10, a series of linear fractions of poly(methyl phenyl siloxane), with overline n_n in the range 31 to 1370, and a cyclic oligomer of mehyl phenyl siloxane, with n = 10, has been studied as a function of temperature (155.5K-264.0K) and frequency (12-105Hz). Activation energies for the -relaxation process, Davidson-Cole and Cole-Cole empirical distribution factors, and , respectively, and mean-square dipole moments per repeat unit have been calculated. The reduced flexibility of short methyl phenyl siloxane chains, compared to dimethyl siloxane chains, was apparent from a comparison of dipole moment ratios. The dilectric relaxation behaviour of poly(methyl hydrogen siloxane) and poly(n-hexyl methyl siloxane) has been studied as a function of temperature and frequency. A polysiloxane liquid crystal has been synthesised and its dielectric relaxation behaviour has been studied, as a function of temperature and frequency, in the liquid crystalline phase and below T_g. Poly(p-phenylene vinylene) and related oligomers have been synthesised and characterised by a variety of experimental techniques. The Kerr effect of two oligomeric fractions, in solution in PPG 2025, has been measured. The electrical conductivities of the undoped and I_2-doped polymer and oligomers have been measured.

New hybrid system:poly (ethylene glycol) hydrogel with covalently bonded pegylated nanotubes

Hydrogels containing carbon nanotubes (CNTs) are expected to be promising conjugates because they might show a synergic combination of properties from both materials. Most of the hybrid materials containing CNTs only entrap them physically, and the covalent attachment has not been properly addressed yet. In this study, single-walled carbon nanotubes (SWNTs) were successfully incorporated into a poly(ethylene glycol) (PEG) hydrogel by covalent bonds to form a hybrid material. For this purpose, SWNTs were functionalized with poly(ethylene glycol) methacrylate (PEGMA) to obtain water-soluble pegylated SWNTs (SWNT–PEGMA). These functionalized SWNTs were covalently bonded through their PEG moieties to a PEG hydrogel. The hybrid network was obtained from the crosslinking reaction of poly(ethylene glycol) diacrylate prepolymer and the SWNT–PEGMA by dual photo-UV and thermal initiations. The mechanical and swelling properties of the new hybrid material were studied. In addition, the material and lixiviates were analyzed to elucidate any kind of SWNT release and to evaluate a possible in vitro cytotoxic effect. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Synthesis, self-assembly and (absence of) protein interactions of poly(glycerol methacrylate)-silicone macro-amphiphiles

The present study focuses on the synthesis of amphiphilic block copolymers containing poly(glycerol monomethacrylate) (PGMMA), showing the advantages of a protection/deprotection strategy based on silyl groups. PGMMA blocks were synthesized via ATRP started by a double functional poly(dimethyl siloxane) (PDMS) macroinitiator of molecular weight ≈7000 g mol-1. The resulting triblock copolymers were characterized by low polydispersity (generally ≤1.1) and their aggregation concentration in water was essentially dominated by the PDMS block length (critical aggregation concentration substantially invariant for GMMA degree of polymerization ≥30). For GMMA blocks with DP > 50, the self-assembly in water produced 35-50 nm spherical micelles, while shorter hydrophilic chains produced larger aggregates apparently displaying worm-like morphologies. Block copolymers with long GMMA chains (DP ≈ 200) produced particularly stable micellar aggregates, which were then selected for a preliminary assessment of the possibility of adsorption of plasma proteins (albumin and fibrinogen); using diffusion NMR as an analytical technique, no significant adsorption was recorded both on micelles and on soluble PGMMA employed as a control, indicating the possibility of a "stealth" behaviour. This journal is © 2013 The Royal Society of Chemistry.

Controlled synthesis of poly(neopentyl p-styrene sulfonate) via reversible addition-fragmentation chain transfer polymerisation

The controlled synthesis of poly(neopentyl p-styrene sulfonate) (PNSS) using RAFT polymerisation has been studied. Selected experimental conditions led to the production of PNSS with variable molecular weights and low dispersities (D{stroke}≤1.50). The controlled synthesis of poly(neopentyl p-styrene sulfonate) (PNSS) using reversible addition-fragmentation chain transfer polymerisation has been studied under a wide range of experimental conditions. PNSS can be used as an organic-soluble, thermally labile precursor for industrially valuable poly(p-styrene sulfonate), widely employed in technologies such as ionic exchange membranes and organic electronics. The suitability of two different chain transfer agents, three solvents, three different monomer concentrations and two different temperatures for the polymerisation of neopentyl p-styrene sulfonate is discussed in terms of the kinetics of the process and characteristics of the final polymer. Production of PNSS with systematically variable molecular weights and low dispersities (D{stroke} ≤1.50 in all cases) has been achieved using 2-azidoethyl 2-(dodecylthiocarbonothioylthio)-2-methylpropionate in anisole at 75°C, with an initial monomer concentration of 4.0molL-1. Finally, a poly(neopentyl p-styrene sulfonate)-b-polybutadiene-b-poly(neopentyl p-styrene sulfonate) (PNSS-b-PBD-b-PNSS) triblock copolymer has been synthesised via azide-alkyne click chemistry. Moreover, subsequent thermolysis of the PNSS moieties generated poly(p-styrene sulfonate) end blocks. This strategy allows the fabrication of amphiphilic copolymer films from single organic solvents without the need for post-deposition chemical treatment.