Polymerization microwave

The choice of an appropriate solvent is essential. The coupling with microwave irradiation increases with the dielectric constant. The use of a small amount of a polar solvent, which is heated when irradiated in a microwave oven, acts as  

It was found that for the condensation of anhydrides with amines, o-cresol is a particularly good additive.  

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Polymerization of epoxides (3,4-epoxycyclohexylmethyl, 3,4-epoxycyclohexylcar-boxylate) initiated by diaryliodonium or triarylsulfonium salts under microwave conditions was investigated by Stoffer et al. (Scheme 14.18) [46]. The reactions were conducted in 20 mL vials in which 4 g samples were placed and irradiated in a multimode microwave reactor. Temperature during microwave polymerizations was measured with a thermocouple immediately after the reaction vessel was removed from the microwave reactor. The extent of polymerization was determined by means of DSC and FTIR and compared with that for samples cured under conventional conditions. 

Vogel, B.M., Mallapragada, S.K., Narasimhan, B., 2004. Rapid synthesis of polyanhydrides by microwave polymerization. Macromolecular Rapid Communications 25, 330—333. 

Fig. 4. Thermal profiles and conversions for conventional and microwave polymerization ol methyl methacrylate (MMA). Reprinted from (1995) J Mat Proc Techn 48 445 [35] with permission...

Under similar conditions, polymerization of methyl acrylate (MA) with AIBN as an initiator under microwave irradiation was carried out by Chia et al. [36]. To prepare samples for polymerization, 4.1 mg of AIBN (0.85 wt%) was taken in a 4-ml sample vial of 15 mm diameter together with 0.5 ml (478 mg) of MA. The reaction rate enhancement of microwave polymerization compared to thermal method was found to be as follows 500 W, 275% 300 W, 220% and 200 W 138%. Even though the comparable temperature at variable power was the same, 52 °C, the reaction rate enhancement increased with increase in microwave power indicating a significant correlation between the reaction rate enhancements and the level of microwave power used [36]. 

The bulk polymerization of styrene at two different power levels - 300 and 500 W - conducted in a multimode microwave cavity was investigated by Chia et al. [38]. The reactions were run in 2-ml sample vials of 10 mm diameter, in which 23.0 mg of AIBN was placed together with 455 mg of styrene. The conversion profiles of the microwave polymerization were significantly different from that of the thermal cure at the same temperature of 80 °C. The thermal cure was characteristic of a gradual gel effect at 30-50% conversion while, with the microwave cure at 300 W and 500 W, a sharp and large gel effect was recorded at conversions 20-69% and 20-65%, respectively (Fig. 5). Moreover, the comparison of thermal and microwave polymerization under similar conditions showed a reaction rate enhancement of 190% for 500 W and 120% for 300 W. Similar to the microwave polymerization of MMA [35], the limiting conversion of styrene decreased from 72% for conventional thermal conditions down to 69 % at 300 W and 65 % at 500 W of microwave irradiation power. Finally, it was stated that comparison of kinetic results of microwave induced reactions should consider the temperature as well as the power of micro-wave irradiation due to different energy supplied to the reaction system [38]. 

More recently, using a bench-scale microwave polymerization reactor (Fig. 7), Correa et al. reported that emulsion polymerization of styrene could be carried out more rapidly with significant saving of energy and time when compared to conventional methods [40]. For all the experiments, the concentration range of mate-... 

J. Jacob, L. H. L. Chia and R Y. C. Boey, Microwave polymerization of poly(methyl acrylate) Conversion studies at variable power. Journal of applied polymer science, 63, 787-797 (1997). 

Solution polymerization of VDE in fluorinated and fluorochlorinated hydrocarbons such as CEC-113 and initiated with organic peroxides (99), especially bis(perfluoropropionyl) peroxide (100), has been claimed. Radiation-induced polymerization of VDE has also been investigated (101,102). Alkylboron compounds activated by oxygen initiate VDE polymerization in water or organic solvents (103,104). Microwave-stimulated, low pressure plasma polymerization of VDE gives polymer film that is <10 pm thick (105). Highly regular PVDE polymer with minimized defect stmcture was synthesized and claimed (106). Perdeuterated PVDE has also been prepared and described (107). 

Another illustrative example of the application of FTIR spectroscopy to problems of interest in adhesion science is provided by the work of Taylor and Boerio on plasma polymerized silica-like films as primers for structural adhesive bonding [15]. Mostly these films have been deposited in a microwave reactor using hexamethyldisiloxane (HMDSO) as monomer and oxygen as the carrier gas. Transmission FTIR spectra of HMDSO monomer were characterized by strong... 

Electrochemical cells for microwave conductivity measurements, 445 Electrochemical measurements with microwave frequencies, diagrammated, 448, 449 with microwaves, 478 Electrochemical polymerization... 

Scan rate involving polymerization, cyclic voltammograms as a function of, 559 Schlichthrol, contributions to microwave conductivity, 441... 

During the past decade, MALDI-TOF MS has proven to be an effective tool for the analysis of oligo- and polymeric mannoglucans (for extensive reviews see [222,223]). SEC/MALDI mass spectrometry was employed in the analysis of hemicelluloses isolated by microwave heat-fractionation from spruce and aspen wood [94]. These methods allowed the separation and characterization of the oligo- and polysaccharide fractions derived from the xylan and mannan components of both woods [224]. 

The different interactions of the microwave radiation with the solvent and with the polymeric support might also cause interesting effects. Many authors... 

Soluble polymers have also been used as support. These exploit the combined advantage of homogeneous with those of soHd-phase chemistry [36]. PEG linked 5-bromothiophene-2-carboxyUc acid was cross-coupled with several arylboronic acids under microwave irradiation (constant power of 75 W) using water as the solvent (Scheme 17). Interestingly, microwave irradiation gave less ester cleavage than classical heating (70 °C). The polymeric support remained stable under both conditions. 

Swager et al. prepared conjugated polymers with tethered rotaxane groups [76]. As a substrate, a rotaxane containing a diiodobiphenyl unit was synthesized for this purpose. Polymerization via microwave-assisted Sono-... 

Microwave curing of polymeric materials requires the presence of dipolar materials for effective modification to occur through dielectric heating [45]. This is not an essence in the case of EB modification of polymers which requires the presence of only labile reactive site, e.g., hydrogen in the polymeric stmcture. 

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]. 

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