Effect of azoinitiators on nitroxide-mediated photo-living radical polymerization of methyl methacrylate

Thermal hazard investigation and hazardous scenarios identification using thermal analysis coupled with numerical simulation for 2-(1-cyano-1-methylethyl)azocarboxamide

Polymers are salient participants in the current world, and roughly more than 40%-45% of all industrial polymers were produced by free radical polymerization. Azo-initiators now have been the foremost radical initiator with the virtue of low tendency to undergo chain transfer reactions. Nevertheless, azo-initiators are readily to decompose and release an immense amount of heats and gases under elevated ambient temperature. 2-(1-Cyano-1-methylethyl)azocarboxamide (CABN) was deliberately picked as an example for identifying the hazardous scenarios in the application of azo-initiators. Initially, thermal analysis technologies were used to investigate the thermal decomposition characteristics of CABN, and selected decomposition mechanism functions were verified for the best-fitting thermokinetic model. Subsequently, thermokinetic-based numerical simulations were implemented to evaluate the thermal hazards of CABN under the ideal adiabatic scenario. Process safety parameters under adiabatic conditions including time to maximum rate as well as induction period were consequently retrieved. Furthermore, inherent safety recommendations for free-radical polymerization were established to forestall the process accidents in storage and the applications of azo-initiator.

Smart Control of Nitroxide-Mediated Polymerization Initiators' Reactivity by pH, Complexation with Metals, and Chemical Transformations

Because alkoxyamines are employed in a number of important applications, such as nitroxide-mediated polymerization, radical chemistry, redox chemistry, and catalysis, research into their reactivity is especially important. Typically, the rate of alkoxyamine homolysis is strongly dependent on temperature. Nonetheless, thermal regulation of such reactions is not always optimal. This review describes various ways to reversibly change the rate of C–ON bond homolysis of alkoxyamines at constant temperature. The major methods influencing C–ON bond homolysis without alteration of temperature are protonation of functional groups in an alkoxyamine, formation of metal–alkoxyamine complexes, and chemical transformation of alkoxyamines. Depending on the structure of an alkoxyamine, these approaches can have a significant effect on the homolysis rate constant, by a factor of up to 30, and can shorten the half-lifetime from days to seconds. These methods open new prospects for the application of alkoxyamines in biology and increase the safety of (and control over) the nitroxide-mediated polymerization method.

Effects of Illuminance and Heat Rays on Photo-Controlled/Living Radical Polymerization Mediated by 4-Methoxy-2,2,6,6-Tetramethylpiperidine-1-Oxyl

The effects of illuminance and heat rays released from the light source on the photo-controlled/living radical polymerization of methyl methacrylate were investigated with the aim of strict control of molecular weight. The bulk polymerization was performed at room temperature using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator and (2RS,RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate as the accelerator by irradiation with a high-pressure mercury lamp. The polymerization by the direct irradiation from the light source yielded polymers containing an uncontrolled high-molecular-weight polymer and having the molecular weight distribution over 3. On the other hand, the polymerization by the indirect irradiation with reflective light using a mirror produced polymers with controlled molecular weights with comparatively narrow molecular weight distribution at ca. 1.4. Too high an illuminance caused an increase in the molecular weight distribution. During the polymerization, the monomer conversion increased as the illuminance increased. It was found that the elimination of heat rays from the illuminating light was indispensable for the molecular weight control by the photo-controlled/living radical polymerization.