Microwave polymerization process

Chauveau E, Marestin C, Martin V et al (2008) Microwave-assisted polymerization process a way to design new, high molecular weight poly(arylimidazole)s. Polymer 49 5209-5214... 

F. Paeodi, Microwave Heating and the Acceleration of Polymerization Processes. In Polymers and Liquid Crystals, Wlochowicz (Ed.) Proceedings of SPIE - The International Society for Optical Engineering, 1999, 4017, 2. 

FIGURE 54.27 Macro-CTAs and schematic representation of the RAFT precipitation polymerization process. (Reprinted with permission from J. Am. Chem. Soc., 129(46), An, Z., Shi, Q., Tang, W., Tsung, C.K., Hawker, C.J., and Stucky, G.D., Facile RAFT precipitation polymerization for the microwave-assisted synthesis of well-defined, double hydrophilic block copolymers and nanostructured hydrogels, 14493. Copyright 2007 American Chemical Society.)... 

Rolla et ah, used microwave dielectric measurements to monitor the polymerization process of mono functional n-butyl acrylate as well as 50/50 w/w blends with a difunctional hexane-diol diacrylate that gave highly cross-linked networks. In these real time cure experiments the decreasing acrylate monomer concentration was studied via a linear correlation with the dielectric loss index at microwave frequencies. This correlation is a result of the largely different time scales for dipolar polarization in the monomer on one hand and in the polymerized reaction product on the other hand. 

The influence of microwave irradiation on the polymerization process of silicone rubber denture soft lining material to PMMA, and its properties were studied by Wright et al. [65]. Three groups of specimens were polymerized under micro-wave irradiation at 650 W for 3, 5, and 10 min in a household microwave oven. The fourth group of specimens was polymerized using conventional thermal methods, i.e., by boiling in a water bath for 2 h. The study demonstrated that mi-... 

Parodi F (1999) Microwave heating and the acceleration of polymerization processes. In ... 

The rubber industries use alkanolamines as secondary vulcanization accelerators to give improved mechanical properties and better heat resistance. Alkanolamines help stabilize rubber dispersions and may also act as an antioxidant for some rubbers. Alkanolamines are activators for the dielectric heating and microwave vulcanization processes. The various alkanolamines are used in the cold cure of certain rubbers and can act as chain termination agents in the chloroprene polymerization. 

Another basic aspect related to the microwave heating process in polymeric systems is the choice of an adequate microwave heating system. As mentioned before, it is crucial to select the best microwave methodology for each specific application and component size. 

Polyhydroxy acids are another group of biopolymers. Since polylactic acids, polyglycolic acid, and poly(citric acid) are classified as thermoplastic polyesters (saturated), they lack reactive functional groups for surface reactions. Moreover, any chemical manipulation to create activation sites results in hydrolysis of the ester bonds. The only reported successful methods for functionalization of polyhydroxy acids are blending them with ECPs, or using a plasma polymerization process [29]. Prior to the plasma polymerization process, surface activation or ionization of these biopolymers must be carried out, which is acquired by means of vapor phase deposition, laser deposition, microwave or synchrotron radiation [30], pulsed arc, pulsed combustion, spark, or friction induction [30], electron beams, plasma induction, corona, photons, ion beams, and X-rays [25]. 

The effect of microwave power on the polymerization process under microwave irradiation (domestic microwave oven) was studied by Zhang et al. (2004). They found that molecular weight of the polymer was increased and reached a maximum, when 90% conversion was reached up to 255 W. When a higher microwave energy (510 W) was applied, the molecular weight first increased and subsequently decreased in time due to transesterification reactions. 

Bogdal, D., Penczek, E, Pielichowski, J. and Prociak, A. Microwave Assisted Synthesis, Crosslinking, and Processing of Polymeric Materials. Vol. 163, pp. 193-263. 

Aryl vinyl ketones are produced thermally from the corresponding quaternary ammonium salts via Hofmann elimination. However, the conjugated ketones are heat-sensitive and polymerization is difficult to avoid. Traditional preparations afforded only moderate yields. Microwave conditions were established for Hofmann eliminations, performed essentially quantitatively, by batch or continuous processes. 

Being microwave-transparent, the reaction vessels will be no hotter than their contents. As mentioned above, they usually are made from insulating polymeric materials like polytetrafluoroethylene (PTFE), which have inherent advantages for cleaner processing. In contrast with other materials, PTFE is resistant to attack by strong bases or HF and is not corroded by halide ions. 

Numerous other uses of microwaves have appeared in the recent years - essentially drying of different types of material (paper, rubber, tobacco, leather. ..), treatment of elastomers and vulcanization, extraction, polymerization, and many applications in the food-processing industry. 

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