Difference in propagation rate constants between photo-and thermal-initiated polymerization of styrene – effects of light irradiation
✍ Scribed by Mikiharu Kamachi; Atsushi Kajiwara
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 404 KB
- Volume
- 198
- Category
- Article
- ISSN
- 1022-1352
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✦ Synopsis
Abstract
Propagation rate constants (k~p~) for photo‐ and thermal‐initiated radical polymerizations of styrene were determined by electron spin resonance (ESR) spectroscopy. The k~p~ value for the former at 70°C ((420 ± 30) M^−1^ · S^−1^) was more than twice as large as that for the latter ((190 ± 10) M^−1^ · s^−1^) although the former value was almost the same as that obtained with the pulsed‐laser polymerization method. To evaluate the origin of the difference in the k~p~ values between photo‐ and thermal‐initiated polymerization the absorption spectrum of a model of the propagating radical was measured and both the influence of the wavelength of the irradiation light on k~p~ values and the activation energy of the photo‐initiated radical polymerization of styrene were determined. k~p~ decreases for wave‐lengths shorter than 370 nm and is in agreement with the k~p~ value for thermal‐initiated polymerization. No wavelength dependence of k~p~ was obtained for dienes whose propagating radical does not absorb above 300 nm. The difference in k~p~ values for photo‐ and thermal‐initiated polymerizations is considered to be due to the photoactivation (photoinduced excitation) of the propagating radical of styrene.