Kinetics of microwave‐assisted polymerization of ϵ‐caprolactone

Abstract

ABSTRACT:The kinetics of polymerization of ⑀-caprolactone (CL) in bulk was studied by irradiating with microwave of 350 W and frequency of 2.45 GHz with different cycle-heating periods (30 -50 s). The molecular weight distributions were determined as a function of reaction time by gel permeation chromatography. Because the temperature of the system continuously varied with reaction time, a model based on continuous distribution kinetics with time/temperature-dependent rate coefficients was proposed. To quantify the effect of microwave on polymerization, experiments were conducted under thermal heating. The polymerization was also investigated with thermal and microwave heating in the presence of zinc catalyst. The activation energies determined from temperature-dependent rate coefficients for pure thermal heating, thermally aided catalytic polymerization, and microwave-aided catalytic polymerization were 24.3, 13.4, and 5.7 kcal/mol, respectively. This indicates that microwaves increase the polymerization rate by lowering the activation energy.

Synthesis and processing of biodegradable and bio-based polymers by microwave irradiation

“…The kinetics of pure and zinc catalyzed ring opening polymerization of ε-caprolactone was also investigated in comparison to conventional heating syntheses and a model based on continuous distribution kinetics with time/temperature-dependent rate coefficients was proposed. From these coefficients the activation energies were calculated: while for pure thermal heating and catalyzed thermal heating the values were respectively 24.3 and 23.4 kcal/mol, the value found for catalyzed microwave heating was 5.7 kcal/mol, reflecting the observed increment in the polymerization rate (Sivalingam et al, 2004). Kinetic investigations were also performed comparing the rate constant for the stannous octoate catalyzed ROP of ε-CL under microwave conditions and conventional heating.…”

Microwave‐Assisted Polymer Synthesis: State‐of‐the‐Art and Future Perspectives

“…Zinccatalyzed polymerizations of e-caprolactone were reported by both Zhuo and co-workers [81] and by Madras and coworkers. [93] The latter used a multimodal microwave oven without controlling devices for temperature or pressure. To prevent overheating, the microwave irradiation was supplied in cycles of 40 or 50 s as it is commonly done with multimodal (domestic) microwaves ovens.…”

Understanding the microwave annealing of silicon

“…28 This indicates so-called nonthermal effects, that the regrowth rate is increased with the assistance of the microwave field. Indeed, Sivalingam et al 29 and Fang et al 30 both found that the activation energy required for the bonding reaction by the microwave process is less than the thermal process, which leads to the recombination process being realized at lower temperature.…”