R.P. Chaplin

Solubility of phenylacetic acid and vanillan in supercritical carbon dioxide

Abstract The solubility of phenylacetic acid and vanillan in supercritical carbon dioxide were measured at 308.15 and 318.15 K over a pressure range of 80 to 200 bar. The applicability of several density-based correlations and the Peng-Robinson equation-of-state to the data obtained is examined. The possible effects of both the carboxylic acid and hydroxyl groups on solubility behavior are also discussed.

Use of retention plots of n-alkyl benzenes for determining dead times in liquid and gas chromatography

Abstract The retention behaviour of the homologous series of n -alkylbenzenes from toluene to hexylbenzene has been examined in reversed-phase liquid chromatography (RPLC) and in gas chromatography (GC) using columns of varying polarity. The series was found to be inappropriate for the mathematical estimation of dead time in GC. The series ethylbenzene to hexylbenzene provided a reasonable estimate of system hold-up volume in RPLC when compared with the retention volume for uracil. However, when toluene was included in the estimation procedure erroneous results were obtained and it is therefore suggested that the use of the alkylbenzene series is unwise in dead time determination in both chromatography systems.

Interpenetrating polymer networks of poly(allyl diglycol carbonate) and polyurethane: effect of composition and crosslink density on morphology and mechanical properties

Simultaneous interpenetrating polymer networks (SINs) of poly(allyl diglycol carbonate) (ADC) and a polyurethane (PU) were synthesized. The effects of the network composition and the crosslink density of the PU phase on the morphology, mechanical properties and thermal transition behaviour of the PU/ADC SIN were studied. At 10% composition, dynamic mechanical analysis revealed complete phase miscibility. As the PU content increased, although phase separation occurred, the samples retained their optical transparency. Modulus and tensile strength decreased, whilst elongation increased, as the PU content increased. At 30% PU content, transmission electron micrograph studies revealed a co-continuous phase morphology, and the domain sizes increased as the PU crosslink density increased. Modulus, tensile strength and fracture toughness also increased with increasing crosslink density.

The role of polarity in correlations of solid-supercritical fluid phase systems

Abstract Three complementary correlations capable of modelling binary SCF equilibrium data have been examined. The results of this study have shown that neither the purely empirical semi-log correlation of enhancement factor with solvent density nor the theoretical log-log relationship between the solute concentration and solvent density predicted experimental solubility data satisfactorily over a wide range of SCF conditions. The above mentioned correlations were suitable for nonpolar solutes where distinct “fine splitting” of the solubility isotherms was observed. These simple relationships break down as the solute polarity increases, indicating that the solute-solute and solute-solvent interactions such as hydrogen bonding, acid-base, and dipole-dipole interactions need to be considered. The semi-empirical semi-log correlation of Ziger and Eckert appeared to provide a distinct advance in handling of data for both the nonpolar and polar compounds studied.

An assessment of the copolymerization reaction between styrene and 2-methylene-1,3-dioxepane

The copolymerization behaviour of 2-methylene-1,3-dioxepane (MDO) with styrene has been studied via pulsed-laser polymerization. The average propagation rate coefficients, [k(p)], were determined for a number of feed ratios of MDO ranging from 0 to 0.938 at both 30 and 40 degrees C. Both the [k(p)] and the polymer composition data indicate a complete absence of copolymerization - contrary to a previously published study. The experimental data indicate the homopolymerization of styrene, with the MDO merely acting as a diluent

Radical copolymerisation propagation kinetics of methyl ethacrylate and styrene

AbstractPulsed-laser polymerisation has been used to investigate the radical copolymerisation kinetics of styrene with methyl ethacrylate.Experiments were conducted over the temperature range 30–808C. The results for copolymer composition and the average propagationrate coefficients, kk p l, can be interpreted using terminal model kinetics. It is argued that the primary factor influencing the copolymerisationkk p l data is the sterically hindered methyl ethacrylate radicals and this steric effect swamps any enthalpic penultimate unit effect which maybe expected to play a role in the copolymerisation reaction. The terminal model reactivity ratios are a strong function of temperature and thisreflects the importance of depropagation reactions at higher temperatures and lower concentrations of methyl ethacrylate. q 2000 ElsevierScience Ltd. All rights reserved. Keywords: Copolymerisation; Hindered radical; Pulsed-laser 1. IntroductionThe nature of the a-substituent of a vinyl monomer hasbeen shown to play an important role in the kinetics ofradical polymerisation. This can be illustrated by comparingstyrene (STY), which readily polymerises to high molecularweight, with a-methyl styrene (AMS) which propagatesslowly to low limiting molecular weights. The main sourceof the low propagation rate (k

Fracture of polymer networks based on diethylene glycol bis(allyl carbonate)

Abstract Double torsion tests were used to evaluate the fracture toughness of a brittle organic network, poly[diethylene glycol bis(allyl carbonate)] commonly known as CR-39 resin, and to evaluate the enhancement in fracture toughness due to the incorporation of various additives. These additives were either polymerized to form a second network, an interpenetrating polymer network, or added as a second monomer which was copolymerized with the diethylene glycol bis(allyl carbonate) to form a random copolymer. The additives, which comprised two urethane acrylates, an allyl urethane and an epoxy acrylate, were found to have little effect on toughness at levels of around 2 wt% and 10 wt%. However, the stiffness of the polymer network was reduced by all four additives. Dynamic mechanical analysis revealed that all the additive agents had two competing influences on toughness. Toughening due to the lowering of an upper glass transition was counteracted by an antiplasticization effect, whereby the presence of the second network reduced the available free volume for segmental motion which caused an inherent decrease in toughness. Scanning electron microscopy revealed little evidence to support crazing as being an important mechanism in the deformation of CR-39 resins.

Sampling and high-performance liquid chromatographic analysis of organic compounds in liquified carbon dioxide

Abstract A new technique for the sampling and analysis of solutions of organic compounds in liquified carbon dioxide is described. A high-pressure sample injection valve is incorporated in a commercial high-performance liquid chromatography instrument. Pressurization of the solution diminishes the effects of nucleate boiling and gasification within the liquid phase.

Interpenetrating polymer networks of poly(diethyleneglycol bis(allylcarbonate)) and poly(urethane acrylates)

Abstract Simultaneous full interpenetrating polymer networks of poly(diethyleneglycol bis(allylcarbonate)) and poly(urethane acrylates) have been synthesized and characterized by the measurement of mechanical properties, fracture toughness parameters, and by dynamic mechanical analysis. No evidence of phase segregation was detected in the interpenetrating polymer networks. The networks exhibited a single glass transition temperature at all the compositions studied. Significant enhancement in mechanical properties and fracture toughness was observed in one of the interpenetrating polymer networks which was characterized by high chain intermixing. The high optical transparency of the base resin system was retained in all the interpenetrating polymer network systems studied.

Mechanical and fracture properties of diethylene glycol bis(allyl carbonate) resins

Abstract Mechanical properties and fracture tests were conducted on the thermoset diethylene glycol bis(allyl carbonate). It was found that both σy and E increase as the testing rate increases. Crack propagation which is unstable (stick-slip) at a low loading rate changes to stable propagation as the loading rate is raised. Linear elastic fracture mechanics concepts were employed to analyse the stress intensity factors versus the yield stress. It is suggested that the stick-slip behaviour is due to blunting of the crack, which is controlled by the yield behaviour of the resin. It is shown that a critical stress of the order of five times the yield stress must be achieved at a critical distance ahead of the crack tip. Fracture surfaces were analysed using scanning electron microscopy and optical microscopy. No indication of crazing was detected.