Pavla Meakin

Degradation Studies of Polyolefins Incorporating Transparent Nanoparticulate Zinc Oxide UV Stabilizers

Coated and dispersed nanoparticulate zinc oxide is shown to improve ultra violet (UV) stability of polypropylene and high-density polyethylene without changing its characteristic absorption spectrum in the visible region (400–800-nm). The performance of these nanoparticulate UV stabilizers is compared to conventional hindered amine light stabilizers (HALS). QUV accelerated weathering is used to simulate long-term exposure. Positron annihilation lifetime spectroscopy (PALS) is used to provide an indication of physical and chemical changes due to accelerated weathering and is shown to have potential for detecting changes well before other techniques. Visual observation, optical microscopy, carbonyl index, yellowness index and PALS indicate that nanoparticulate zinc oxide gives superior resistance to UV degradation compared to organic HALS at appropriate loading levels.

Microstructural and molecular level characterisation of plastic crystal phases of pyrrolidinium trifluoromethanesulfonyl salts

Ambient temperature conductive plastic crystal phases of alkylmethylpyrrolidinium trifluoromethanesulfonyl amide (TFSA) salts are studied using positron annihilation lifetime spectroscopy (PALS) to examine the role of vacancy size and concentration in conductivity. The ethyl methylpyrrolidinium TFSA salt (P12 TFSA) has larger vacancies and a greater concentration of vacancies than the dimethylpyrrolidinium TFSA salt (P11 TFSA) over the temperature range investigated. The relative vacancy size and concentration vary with temperature and reflect the solid–solid transitions as measured by differential scanning calorimetry (DSC). P12 TFSA has greater conductivity than P11 TFSA and has furthermore been observed to exhibit slip planes at room temperature. P12 TFSA has greater entropy changes associated with solid–solid phase transitions below the melting point than P11 TFSA possibly indicating greater rotational freedom in P12 TFSA. These results support the notion that the diffusion, conduction, and plastic flow properties of the pyrrolidinium TFSA salts are derived from the lattice vacancies.

13 C NMR spin–lattice relaxation times as a probeof local polymer dynamics in plasticized polyethers

13 C NMR spin–lattice relaxation times T 1 are used to investigate the effect of low molecular weight diluents, including N,N-dimethylformamide, N-methylformamide, propylene carbonate, γ-butyrolactone, triglyme and tetraglyme, on the local polymer segmental motion in polyether–urethane networks. In all cases, an increase in the local mobility is deduced from the increasing T 1 measurements consistent with a decreasing glass transition temperature. The extent of plasticization, however, is dependent on the nature of the small molecules. Those molecules which can either form strong polymer-diluent interactions (for example through dipolar interactions) or are themselves rigid, give the least enhancement of polymer mobility and the greatest deviation from the Fox equation for T g . In the presence of alkali metal salts, N,N-dimethylformamide and propylene carbonate are shown to have opposite effects on the local polymer motion, as seen from the T 1 measurements. In both cases, addition of the plasticizers increases the 13 C T 1 relaxation times for the plasticizer. However, propylene carbonate decreases the polymer 13 C T 1 whilst N,N-dimethylformamide results in the expected increase in polymer 13 C T 1 .

Materials chemistry communications. 13C Nuclear magnetic resonance spectroscopic study of plasticization in solid polymer electrolytes

Preliminary results are presented on the correlation between enhanced solvent mobility and ionic conductivity in plasticized polyether–urethane solid polymer electrolytes using 13C nuclear magnetic resonance spectroscopic spin–lattice relaxation time measurements to probe polymer mobility.

Characterization of plasticized polyether-urethane solid polymer electrolytes

The effect of plasticizer addition on the density, conductivity, glass transition, and free volume behavior of salt containing polyether-urethanes has been examined. The addition of up to 1.5 molal LiC1O 4 salt results in an effective crosslinking of the polyether-urethane chains due to the Li + coordination with the oxygens of the host polymer. This crosslinking decreases inter- and intrachain separation and reduces polymer chain mobility as illustrated by increased density and T g , decreased free volume, and, at salt concentrations greater than 0.6 molal, decreased conductivity. The addition of approximately 30 wt % tetraglyme plasticizer to the 1 molal LiC1O 4 /host polymer complex is shown to counter the effective crosslinking resulting in a decreased T g to a value equal to that of the pure host polymer, increased conductivity, and increased average free volume cavity size to a value equal to that of the pure host polymer. However, the relative number of free volume cavities in the plasticized host polymer/salt complex remains fewer than that of the pure host polymer over the concentration range of plasticizer studied, and in a similar manner the density remains greater than that of the pure host polymer. The room temperature conductivity, free volume, and density behavior in conjunction with the Tg results suggest that the plasticizer addition leads to Li + coordination with the oxygens of the plasticizer chains as well as increased mobility of the host polymer chains.