Microwave-assisted cationic ring-opening polymerization of 2-oxazolines.

In this study microwave-assisted anionic ring opening polymerization (ROP) of alkylene oxides is reported. Low molar mass polymers of propylene oxide (PO), butylene oxide (BO) and hexylene oxide (HO) are synthesized by anionic ring opening using various monohydric alcohols as initiators. The monohydric alcohols and lower molar masses allowed for monitoring of different types of possible unwanted by-products and their sources. Liquid chromatography at critical conditions (LCCC) and liquid adsorption chromatography (LAC) are used to determine the presence of oligomers other than targeted. Finally, MALDI-TOF MS of the products have clearly shown the trends and extents of different types of side reactions that are possible in anionic ring opening of alkylene oxides. Propylene oxide is most vulnerable to chain transfer reactions compared to higher alkylene oxide.

Microwaves in Organic Synthesis

In this work, microwave-assisted ring opening polymerization (ROP) of lactide (LA) and glycolide (GA) initiated by magnesium lactate was investigated. The influence of microwave power, temperature, and reaction time on homopolymers and copolymer’s structure and thermal properties is discussed. Polymerization of L-lactide (LLA) initiated by the magnesium compound resulted in yields up to 78% and poly(L-lactic acid) (PLLA) with average molar mass of up to 30,600 g mol-1. Homopolymerization of glycolide generate poly(glycolic acid) (PGA) in yields up to 90% and in L-lactide/glycolide copolymerizations yields between 34-82%. PLLA prepared with the initiator presented microstructure with significant amount of stereo errors as the result of a racemization process during polymerization as well as low glass transition temperature (Tg) and melting temperature (Tm), while the PGAs presented high Tg, due to high crystallinity, and Tm in accordance with the literature. LLA and GA copolymerization result in poly(lactic acid-co-glycolic acid) (PLGA) with composition close to polymerization feed composition.

Functional polyhedral oligomeric silsesquioxane reinforced poly(lactic acid) nanocomposites for biomedical applications

Summary form only given. During the last decades microwave technology gathered growing industrial interest for thermal processing of various kinds of materials. Many industrial processes using microwave technology, such as for example food processing, drying, rubber vulcanization or polymer curing, were already successfully realized by use of microwave technology. Here the benefit of microwave volumetric heating can be exploited to significantly shorten processing times, especially if large volumes of materials with low thermal conductivity have to be processed. The use of microwaves for sintering of ceramics has been proposed and investigated by several research groups, because a direct energy transfer into the material's volume allows much higher heating rates compared to conventional heating. Furthermore, the densification process of ceramic bodies has been reported to be enhanced by sintering in a microwave field due to non-thermal microwave effects. Non-thermal effects are the usual explanation for phenomenological observations like reduced sintering temperature and soaking time or the evolution of more fine-grained microstructures in case of microwave sintering compared to conventional sintering. Since such non-thermal effects are always superimposed to thermal effects especially in case of ceramics sintering, a direct access for experimental verification of existing theoretical models on such non-thermal microwave effects is difficult. Based on the theory of the so called ponderomotive driving forces which specifies an enhanced diffusion in ionic solids under the influence of the microwave field, the influence, of the microwave field orientation on the diffusion in a faceted pore has been described by Boosky et al. Because of this, a non-isotropic pore closure can be expected during sintering of ceramics in a linearly polarized microwave field. Therefore, systematic investigations of the pore structure evolution in yttria-stabilized zirconia have been started in a single mode 2.45 GHz waveguide applicator. For the first time, strong experimental evidence for the existence of a non-isotropic pore closure due to a non-thermal microwave-effect was found with an adequate statistic evaluation of the pore aspect ratios after sintering

Master equation is a successful model to describe the conventional heating reaction, it is expanded to capture the "microwave effect" in this work. The work equation of "microwave effect" included master equation presents the direct heating, indirect heating, and nonthermal effect about the microwave field. The modified master equation provides a clear physics picture to the nonthermal microwave effect: (1) The absorption and the emission of the microwave, which is dominated by the transition dipole moment between two corresponding states and the intensity of the microwave field, provides a new path to change the reaction rate constants. (2) In the strong microwave field, the distribution of internal states of the molecules will deviate from the equilibrium distribution, and the system temperature defined in the conventional heating reaction is no longer available. According to the general form of "microwave effect" included master equation, a two states model for unimolecular dissociation is proposed and is used to discuss the microwave nonthermal effect particularly. The average rate constants can be increased up to 2400 times for some given cases without the temperature changed in the two states model. Additionally, the simulation of a model system was executed using our State Specified Master Equation package. Three important conclusions can be obtained in present work: (1) A reasonable definition of the nonthermal microwave effect is given in the work equation of "microwave effect" included master equation. (2) Nonthermal microwave effect possibly exists theoretically. (3) The reaction rate constants perhaps can be changed obviously by the microwave field for the non-RRKM and the mode-specified reactions.

Due to its advantages of direct heating, high temperature homogeneity, reaction rate enhancement, as well as energy savings, microwave-assisted polymerization has become a fast-growing field of polymer research. This paper reviews microwave-assisted polymerization, with an emphasis on the microwave-assisted ring-opening polymerization, covering both homopolymerization and copolymerization of the cyclic monomers. The advantages of microwave-assisted ring-opening polymerization over conventional polymerization are discussed briefly.

Microwave-assisted synthesis is considered environmental-friendly and, therefore, in agreement with the principles of green chemistry. This form of energy has been employed extensively and successfully in organic synthesis also in the case of metal-catalyzed synthetic procedures. However, it has been less widely exploited in the synthesis of metal complexes. As microwave irradiation has been proving its utility as both a time-saving procedure and an alternative way to carry on tricky transformations, its use can help inorganic chemists, too. This review focuses on the use of microwave irradiation in the preparation of transition metal complexes and organometallic compounds and also includes new, unpublished results. The syntheses of the compounds are described following the group of the periodic table to which the contained metal belongs. A general overview of the results from over 150 papers points out that microwaves can be a useful synthetic tool for inorganic chemists, reducing dramatically the reaction times with respect to traditional heating. This is often accompanied by a more limited risk of decomposition of reagents or products by an increase in yield, purity, and (sometimes) selectivity. In any case, thermal control is operative, whereas nonthermal or specific microwave effects seem to be absent.

There have been a growing number of articles that report dramatic improvements in the experimental performance of chemical reactions by microwave irradiation compared to that under conventional heating conditions. We theoretically examined whether nonthermal microwave effects on intramolecular reactions exist or not, in particular, on Newman-Kwart rearrangements and intramolecular Diels-Alder reactions. The reaction rates of the former calculated by the transition state theory, which consider only the thermal effects of microwaves, agree quantitatively with experimental data, and thus, the increases in reaction rates can be ascribed to dielectric heating of the solvent by microwaves. In contrast, for the latter, the temperature dependence of reaction rates can be explained qualitatively by thermal effects but the possibility of nonthermal effects still remains regardless of whether competitive processes are present or not. The effective intramolecular potential energy surface in the presence of a microwave field suggests that nonthermal effects arising from potential distortion are vanishingly small in intramolecular reactions. It is useful in the elucidation of the reaction mechanisms of microwave synthesis to apply the present theoretical approach with reference to the experiments where thermal and nonthermal effects are separated by screening microwave fields.

Decoupling thermal effects and possible non-thermal effects of microwaves in vacuum evaporation of glucose solutions

Perturbation of a solid phase separation process by a non-thermal microwave effect

Non-thermal effect of microwave on organic sulfur removal from coal by microwave with peroxyacetic acid

This review describes recent developments in the field of glycopolymer (polymer–carbohydrate conjugate) synthesis. The interest in this class of polymers that have a wide range of biological recognition properties has grown rapidly in the last decade due to their application in the areas of biotechnology and medicinal chemistry. Modern synthetic methodologies such as controlled radical polymerization, ionic polymerization, ring-opening polymerization (ROP), ring-opening metathesis polymerization (ROMP) and Click chemistry have recently been proven to be extremely efficient and versatile tools for building tailor-made functional polymers with different molecular architectures. The use of these synthetic methods to prepare glycopolymer conjugates is outlined and discussed in detail. The self-assembling behavior of these glycopolymer designs and their interactions with their corresponding lectins (cell surface receptor proteins) are also presented in this review.

Development of extended-voyaging anti-oxidant Linked Amphiphilic Polymeric Nanomicelles for Anti-Tuberculosis Drug Delivery

Evaluating the potential nonthermal microwave effects of microwave-assisted proteolytic reactions