Free radical polymerization of methyl methacrylate up to the glassy state. Rates of propagation and termination

Abstract

The free radical polymerization of methyl methacrylate in bulk at 0 °C initiated by photochemical decay of azobis(cyclohexanenitrile) (ACN) is tested over the full range of conversion up to the glassy state. Rate constants of propagation, kp, and termination, kt, are evaluated by the rotating sector technique and after effect. Instantaneous degree of polymerization and efficiencies, /, are given for all conversions. The conversion dependence of f can be expressed by the self-diffusion of small molecules in a polymer matrix.Both rate constants depend on the conversion; kt for conversions near and beyond the onset of entanglement also depends on the chain length of the polymer radicals but becomes independent of this length at about 45% conversion. The diffusion processes describing the different stages of conversion are discussed.

Polymerization kinetics of acrylic bone cements by differential scanning calorimetry

“…The rate constant of termination decreases in correspondence to the onset of autoacceleration by 3 orders of magnitude, as reported by Sack et al [10]. On the other hand, the rate of initiation, depending essentially on the concentration of initiator and its efficiency, presents a much lower decrease, at least at the beginning of the reaction.…”

“…The glass transition temperature, continuously increasing during cure, may approach the isothermal cure temperature, strongly reducing the molecular mobility. At this stage of the reaction, the transition to a glassy state (vitrification) strongly affects the polymerization kinetics by reducing the mobility of monomers and radicals whose efficiency goes to zero [10]. When the vitrification occurs, the reaction becomes diffusion controlled and the termination step of the polymerization is governed by this strong reduction in molecular mobility.…”

“…Although the bulk polymerization of MMA has been widely studied [3,[6][7][8][9][10], the polymerization kinetics of bone cements is characterised by unique features as a consequence of the diffusion effects induced by the high fraction of polymeric filler. The addition of a solid polymer to the reactive medium enhances the rate of reaction acting on the onset of the so-called 'autoacceleration effect' or 'gel effect' [2,3,8,10].…”

“…The addition of a solid polymer to the reactive medium enhances the rate of reaction acting on the onset of the so-called 'autoacceleration effect' or 'gel effect' [2,3,8,10]. The autoacceleration effect is related to the viscosity of the reactive medium and can be observed at higher degrees of reaction when a non-reactive solvent is added to the monomer [2].…”

Real-time kinetic study of the polymerization activity of the photoinitiator system p-nitroaniline/N,N-dimethylaniline by real time IR spectroscopy

“…9) reflects the importance of gelation as the polymerization reaction progresses. When the segmental mobility is reduced, as a consequence of the increased viscosity with the monomer conversion, it prevents the polymer chain from further growing, leading to the trapping of the reactive radicals in the polymer formed 22) .…”