Polymerization reaction with sunlight as energy resource is considered more green and sustainable than that under microwave irradiation and the ring-opening polymerization of e-caprolactone is selected as the model of sunlight-heated polymerization. Natural sunlight can not be directly used as the energy resource for the polymerization of e-caprolactone as its power is too weak. Our strategy is to focus natural sunlight by a Fresnel lens that is designed to concentrate the intensity of sunlight by ten thousand times and the solar power increased from below 1 kw/m2 to over 500 kw/m2 at the focal spot in this way. However, the focused sunlight is not absorbed directly by transparent e-caprolactone and should be converted to heat that supplies the energy for the polymerization. With ferroferric oxide as the medium of light-heat conversion the temperature of the wall of reaction vessel ranged from 300 to 330oC when the solar power was from 721 to 849 W/m2, which is a quite efficient system for the flash-heating polymerization of e-caprolactone based on our previous work. The ring-opening polymerization of e-caprolactone proceeded quickly and smoothly with stannous octoate as the catalyst heated by sunlight-absorbed ferroferric oxide. Experimentally, the molar ratio of e-caprolactone and stannous octoate is 1000 to 1 and the reaction time is twenty minutes. The monomer conversions increased from 78% to 96% with solar power and temperature of ferroferric oxide. The weight-average molar mass (Mw) of obtained polycaprolactone ranged from 80.7x103 to 120.3x103 g/mol and the highest one came from the polymerization with solar power at 744 W/m2, but with higher solar power Mw decreased (Figure 1). The results indicate that light-heat conversion is a potential approach to utilize sunlight as the energy resource for polymerization reactions and is an energy-saving method for chemical synthesis.Figure 1 Results of ring-opening polymerization of e-caprolactone by sunlight-absorbed ferroferric oxide

Ring-opening polymerization of e-caprolactone by sunlight heating

247th National Meeting (2014)

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