Molecular weight microwave polymerization

MAE of additives from polymeric matrices has clearly established good records. Some additional studies may be needed in order to validate this approach for analytical sample preparation. Microwave heating has also been applied to dissolve polymers for molecular weight determination [446]. 

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... 

Free-radical polymerization reactions have recently been studied for different monomers, for example mono and disubstituted vinyl monomers and dienes. The bulk polymerization of vinyl monomers (e.g. vinyl acetate, styrene, methyl methacrylate, and acrylonitrile) has been investigated by Amorim et al. [10]. The reactions were conducted in the presence of catalytic amounts of AIBN (or benzoyl peroxide). It was found that the rate of polymerization depends on the structure of the monomers and the power and time of microwave irradiation. In a typical experiment 10.0 mL of each monomer and 50 mg AIBN was irradiated in a domestic microwave oven for 1 to 20 min to afford the polymers polystyrene, poly(vinyl acetate), and poly(methyl methacrylate) with weight-average molecular weights 48 400, 150 200, 176700 g mol, respectively (Scheme 14.1). The experiments were performed without temperature control. 

The results obtained under microwave irradiation were compared with those from conventional experiments. Under the action of microwaves the amount of initiator needed to achieve constant conversion was reduced by 50% at the same polymerization rate if the same initiator concentration was used (0.15 and 0.20% wjw) the rate of polymerization increased by factors of 131 and 163%, respectively. The molecular weights of the polymers were 1.1 to 2.0 times higher than those obtained by use of conventional conditions. The glass transition temperatures (Tg), polydispersity index, and regularity of the polymers obtained by use of the two processes (microwave and conventional) were similar, indicating an analogous mechanism of polymerization. 

Scheme 14.13). The procedure was similar to that in their two previous papers. It was stated that polymerization of D,L-lactide proceeded quickly, but no comparison with a conventional procedure was performed. Under optimum conditions, poly(D,L-lactide) (weight-average molecular weight 400000 g mol ) was obtained with 90% yield after 10 min. It was stated, however, that degradation of the product was much affected by microwave irradiation. 

Synthesis of conjugated p-phenylene ladder polymers by means of a microwave-assisted reaction has been achieved by Scherf et al. (Scheme 14.35) [72]. The polymerization reactions were performed in THE solution at 130 °C in the presence of palladium catalyst with phosphine ligands with irradiation in a single-mode micro-wave reactor for 11 min. Compared with conventional thermal procedures, the reaction time was reduced from days to a couple of minutes and molecular weight distributions ( PDI ca 1.8) of the polymers were changed substantially. 

A limited number of reports have appeared in the literature showing the use of water as a solvent for the microwave-promoted synthesis of thermoplastics. An example is the synthesis of water-borne polyimides using the standard polycondensation reaction of a dianhydride with a diamine (Seheme 3.1). In a scientific microwave unit, polymers with high molecular weights (Af up to 35.460 g/mol) were obtained within 22 min of heating using a one-pot two-step procedure. The dianhydride was first hydrolyzed in water to obtain the corresponding tetracarboxylic acid. This was then condensed with the diamine. The obtained polymers were completely comparable in their chemical and thermal properties to those obtained by conventional polymerization in m-cresol as solvent. 

The ring-opening polymerization (ROP) of p-dioxanone using triethylaluminum or tin powder as catalysts has also been performed solvent free using a scientific microwave unit (Scheme 3.6). Increased-molecular-weight products were obtained in shorter reaction times as compared with conventional heating. 

Dependence of the monomer conversion and the peak molecular weight (MW-peak) on the AIBN concentration and the temperature profile obtained in styrene miniemulsion polymerization with microwave heating. 

On the other hand, by free radical suspension polymerization of MMA in n-heptane solution in the presence of poly(styrene)-Wocfc-poly(ethene-aZt-propene) (SEP) as a dispersing agent, PMMA samples were prepared with similar molecular weights and polydispersity under both conventional and microwave conditions [37]. The reactions were run for 1 h at 70 °C with different monomer (9.0-28.3vol.%), SEP (21.7-5.4 wt%), and AIBN (1.0-0.27 wt%) concentrations (Table 1). In a typical experiment, 30 ml of the reaction mixture was fed into a 50-... 

In order to reach a conversion of styrene of 70 %, constant heating in an oil bath for as long as 6 h was required in comparison with only 8.3 min in the microwave oven. Calculated values of Rp (mol/Js) for both processes showed that the rate of microwave-assisted emulsion polymerization of styrene was higher by a factor of 26 than the reaction activated by conventional heating (Fig. 6) [39]. Molecular weight distribution and polydispersities of the polystyrene samples obtained under microwave and conventional conditions were similar for both activation methods and depended on the initiator concentration. 

More recently, Al Doori et al. studied microwave and conventional polymerization of denture base acrylic materials in respect of their molecular weights, conversion of monomer and porosity [54]. For this purpose, four commercially available resins that contained benzoyl peroxide as an initiator were compared while a household microwave oven was applied as a microwave source. It was found that molecular weight values of polymerized materials cured under microwave irradiation and in a water bath were essentially the same. Moreover, the conversion of monomer under microwave conditions was substantial, but minimum residue... 

Recently, Seyler et al. reported a continuous-flow methodology for Suzuki coupling polymerization. poly(9,9-dioctylfluorene) (PFO) using this method shows a quite high molecular weight of 62 000 within only 30 min. This reaction time is comparable to that of microwave-assisted polymerization. 

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