Methyl methacrylate (MMA) was polymerized in bulk via atom transfer radical polymerization (ATRP) with azobis(isobutyronitrile) (AIBN) and tert-butyl peroxybenzoate (TBPB) as initiator for continuous activator regeneration (ICAR). The ATRP was first carried out up to high conversion at 70 °C. When the system reached its glass state at about 94%, the polymerization temperature was elevated to 120 °C to maximize the conversion. Livingness of the ICAR ATRP process and control of polymer molecular weight at high conversion were carefully examined to elucidate the mechanisms of diffusioncontrolled reactions. The "gel effect" started at about 50% conversion, and it was accompanied by molecular weight distribution broadening. A dramatic increase in polydispersity was observed at above 90% conversion. The loss of control over molecular weight was caused by diffusion-controlled deactivation, which could be reduced to some extent by increasing deactivator concentration. However, despite the loss of control at high conversion, livingness of the system did not suffer, owing to diffusioncontrolled termination. The polymer chains collected at very high conversion could be easily extended with high efficiency.

Abstract:In high-conversion atom transfer radical polymerization (ATRP), all the reactions, such as radical termination, radical deactivation, dormant chain activation, monomer propagation, etc. could become diffusion controlled sooner or later, depending on relative diffusivities of the involved reacting species. These diffusion-controlled reactions directly affect the rate of polymerization and the control of polymer molecular weight. A model is developed to investigate the influence of diffusion-controlled reactions on the high conversion ATRP kinetics. Model simulation reveals that diffusion-controlled termination slightly increases the rate, but it is the diffusion-controlled deactivation that causes auto-acceleration in the rate ("gel effect") and loss of control. At high conversions, radical chains are "trapped" because of high molecular weight. However, radical centers can still migrate through (1) radical deactivation-activation cycles and (2) monomer propagation, which introduce "residual termination" reactions. It is found that the "residual termination" does not have much influence on the polymerization kinetics. The migration of radical centers through propagation can however facilitate catalytic deactivation of radicals, which improves the control of polymer molecular weight to some extent. Dormant chain activation and monomer propagation also become diffusion controlled and finally stop the polymerization when the system approaches its glass state. OPEN ACCESSPolymers 2015, 7 820

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Controlled radical polymerization (CRP) such as atom transfer radical polymerization (ATRP) is often conducted in solution processes and stopped at medium monomer conversions to yield well controlled polymer samples. A great challenge lies in running bulk CRP up to high conversions but still retaining system livingness and molecular weight control. In this work, we demonstrate the achievement of good living and well controlled high-conversion bulk ATRP by means of design and optimizing polymerization thermal histories. The initiator-for-continuesactivator-regeneration (ICAR) ATRP of methyl methacrylate (MMA) is used as a model system. Employing step functions in temperature, MMA conversions are pushed up to 98% and the PMMA samples possess polydispersities <1.3. Chain extension experiments confirm good livingness of synthesized polymers collected at high conversions.

A permanent anti-graffiti coating based on a polyurethane resin was prepared by incorporating different levels of an OH-functional silicone modified polyacrylate additive. Static contact angle measurements and dynamic mechanical thermal analysis (DMTA) were employed to evaluate surface free energy and mechanical properties of the coating specimens, respectively. Effect of ageing condition on the graffiti properties of the coating samples was evaluated utilizing an accelerated weathering test. Color changes, surface morphology, and variations in the mechanical properties were also examined prior to and after being exposed to UV irradiation for 864 h in a QUV chamber. Results showed that surface free energy of the samples decreased with replacement of polyol with additive up to 5 mol %. A Scanning electron microscope equipped with energy dispersive X-ray detector revealed that for the sam-ples containing more than 5 mol % additive, there was an enrichment of silicone at the interface of films and air. At long exposure times and higher concentrations of additive, depreciation of graffiti properties was seen. DMTA and attenuated total reflectance-fourier transform infra-red studies before and after ageing showed that the silicone additive tended to degrade while it could cause an increase in crosslinking density. Water contact angles and atomic force microscopy images after ageing revealed that the cause of the depletion in anti-graffiti properties was attributed to the deterioration of the silicone additive. EXPERIMENTAL Materials and methodsBYK-SILCLEAN 3700 (a solution of 25 wt % OH-functional silicone modified polyacrylate in methoxypropylacetate), was obtained from BYK Correspondence to: M. Mohseni (mohseni@aut.ac.ir).