Matthew P. Tonge

Pulsed‐laser radical polymerization and propagation kinetic parameters of some alkyl acrylates

Pulsed-laser photoinitiated polymerization was used to determine, in toluene solution, the propagation kinetic parameters of a series of acrylates with increasing size of the alkyl side group. Transfer to monomer and to toluene did not occur significantly in our PLP conditions and our temperature range since no broadening of the MMD was observed, allowing generally to work with two inflection points. In contrast, depending on the nature of the acrylate and on the PLP conditions, transfer to polymer, and thus long chain branching, can critically interfere. Indeed, the Mark-Houwink-Sakurada parameters, which are used to calculate the absolute molar mass at the inflection point, strongly depend on the polymer structure and thus, should be carefully measured for each PLP sample. Although still preliminary, the results show that the k p s measured in toluene solution present a tendency to continuously decrease when increasing the size of the side group. This observation is conflicting with the reported behaviour for PLP experiments in bulk, revealing a possible solvent effect.

Testing free volume theory for penetrant diffusion in rubbery polymers

Vrentas and Vrentas (Eur Polym J, 34 (1998) 797) have provided a method of evaluating diffusion coefficients using free volume theory, wherein all parameters can be estimated from the available experimental physical data or best estimates from approximate correlations (e.g. from a knowledge of the density, isothermal expansion coefficient, etc.). This method is tested using data for diffusion of methyl methacrylate and butyl methacrylate monomers in mixtures of the monomer and both polymers above the glass transition, over a range of polymer weight fraction and temperature (above T-g) (Macromolecules, 31 (1998) 7835). It was found that the predictions are reasonable for the well-studied MMA/PMMA system (although the predicted effective activation energy was poor), but the a priori predictions were in significant error for the other systems. The Vrentas method can be used reliably for interpolation and extrapolation of limited data, although because the predicted activation energies are too low, care should be taken with extrapolation over a significant temperature range

E.s.r. measurements of the propagation rate coefficient for styrene free radical polymerisation

Electron spin resonance (e.s.r.) spectroscopy should be useful for the measurement of propagation rate coefficients (k(p)) in free radical polymerisations, since the propagating radical concentration can be directly observed. However, in previous studies, k(p) values have generally been inconsistent, and disagreed with data from other accepted experimental techniques, such as pulsed laser polymerisation. This study shows that for styrene, consistency can be obtained, but only when experimental conditions are selected such that polymer of sufficiently high molecular weight is formed; otherwise incorrect rate constants may be measured. The measured Arrhenius parameters were in good agreement with IUPAC accepted data. The values at 343 K for both thermally and photochemically initiated experiments were found to be consistent, suggesting that photoinitiated systems may polymerise in the ground state. Some previously inconsistent data could be explained in terms of selection of experimental conditions

Penetrant diffusion in poly(methyl methacrylate) near Tg: dependence on temperature and polymer weight fraction

Forced Rayleigh scattering was employed to measure diffusion coefficients for a ternary system comprising camphorquinone or diacetyl in poly(methyl methacrylate) with methyl isobutyrate as the diluent. Measurements were made at polymer weight fractions, w(p), over the range 0.78-0.90 and temperature 25-50 degrees C for camphorquinone (which spans the glass transition regime), and at w(p) = 0.9 and 0.95 and at room temperature for diacetyl. Results for camphorquinone show a strong temperature dependence, with diffusion coefficients changing as much as two orders of magnitude between 25 and 50 degrees C, and showing high activation energies for diffusion approximate to 125 kJ mol(-1). No sharp change in the activation energy for diffusion was observed as the glass transition is crossed. The pre-exponential factor for the diffusion coefficient decreased dramatically through the glass transition. The diffusion coefficients of small penetrants in glassy polymers appear strongly dependent on the molecular size

Synthesis and Homopolymerization of the Olefin- Derived Acrylic Monomer, 1-Methyl-1-Propyl-Hexyl Acrylate

Abstract The synthesis of a new olefin-derived acrylate monomer, 1-methyl-1-propylhexyl acrylate (1-MPHA), starting from 1-pentene, is reported. 1-MPHA was found to be polymerizable to high conversion by conventional free radical means. Homopolymerization of the monomer in benzene and toluene progressed faster in toluene than in bulk. Kinetic studies show 1-MPHA to be a relatively slow reacting monomer. The homopolymer of 1-MPHA was found to be thermally stable to about 200 °C, and soft at room temperature, with a Tg of -43 °C.