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Study on Photo Polymerization System of Visible-light Dyes Bearing Benzophenone Fragments

Author: PengHuaYong
Tutor: GaoFang
School: Chongqing University
Course: Polymer Chemistry and Physics
Keywords: Visible light polymerization Benzophenone Chromophore Branching effect Spectra
CLC: O631.3
Type: Master's thesis
Year: 2009
Downloads: 32
Quote: 0
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Abstract


Study on visible light polymerization technology has been developed in recent decades. Visible light polymerization technology possesses lots of advantages: fast curing speed, high curing depth, less pollution, energy-saving and curing products with excellent performance, which meets the development and requirements of modern green industries. So this technology has been used widely in graphic arts, stereo lithography, ink, coating, adhesive, and bio-medical materials, such as dental, orthopedic repair materials and contact lens.A series of benzophenone (BP) derivatives bearing visible-light chromophore prevenient synthesized by our research group has been used for photoinitiators, including p-nitro-stilbene chromophore linked by ether bond, p-(diethylamino)- p’-nitro-stilbene chromophore linked by ether bond, p-(diethylamino)- p’-nitro- azobenzene chromophore linked by ether bond, p-nitro-stilbene chromophore linked by ester bond, and triphenylamine chromophore linked by double bond. The relationship between light-sensitive wavelength and fluorescence emission of the photoinitiators was investigated. Intramolecular charge transfer and spectral response wavelength of the photoinitiators can be controlled and optimized by changing the types of chromophore as well as the linked bond between chromophore and BP segment. BP derivatives containing triphenylamine chromophore linked by double bond with comparatively large intramolecular charge transfer could absorb visible light 400～500 nm, BP derivatives bearing p-(diethylamino)- p’-nitro-stilbene chromophore linked by ether bond could absorb visible light 400～550 nm; BP derivatives bearing p-(diethylamino)- p’-nitro- azobenzene chromophore linked by ether bond with comparatively poor intramolecular charge transfer could absorb visible light 400～600 nm; BP derivatives bearing p-nitro-stilbene chromophore linked by ether bond with weak intramolecular charge transfer could absorb visible light 400～450 nm; BP derivatives bearing p-nitro-stilbene chromophore linked by ester bond with weak intramolecular charge transfer nearly sense visible light.The initiating effect of these initiators induced by visible light were studied, all the polymerization reactions demonstrated typical radical polymerization characteristics. Relationship between the initiating activity and the structure showed that visible light polymerization initiating effect could be controlled and optimized by changing chromophore structures as well as branching number of the BP segment. Radicals induced by intramolecular charge transfer showed better initiating effect in polymerization reactions than those induced by intermolecular charge transfer; BP derivatives bearing p-nitro-stilbene chromophore linked by ether bond owned the best initiating effect, and the initiating effect of those BP derivatives bearing triphenylamine chromophore linked by double bond was the lowest; BP derivatives bearing p-(diethylamino)- p’-nitro-stilbene chromophore showed stronger photo-initiating effect than those BP derivatives bearing p-(diethylamino)- p’-nitro- azobenzene; BP derivatives bearing p-(diethylamino)- p’-nitro-stilbene chromophore linked by ether showed stronger photo-initiating effect than those linked by ester; the shorter the linked bond between chromophore and BP segment was, the stronger the photo-initiating effect demonstrated; initiating effect could be enhanced by increasing the branching number of the BP derivatives, however, increasing the branching number of the BP derivatives bearing p-nitro-stilbene chromophore linked by ether bond could not accelerate photopolymerization reactions.The molecular structure optimization calculation of the photo-initiating intramolecular charge transfer of this series of BP derivatives matched well with the experimental data. Electron cloud distribution of the excited HOMO→LUMO moved from chromophore moiety to BP moiety. The free energy change of C1～C12 charge transfer estimated by Rohm-Weller equation was negative and it showed that the photo-induced electron transfer process was thermodynamics permitted. DTA-TGA analysis demonstrated that these photoinitiators were the heat-stable, weight-loss temperatures were all above 250 degree. The thermal stability of the BP derivatives bearing chromophores with triphenylamine linked by double bond was the best, followed by those linked by ether bond. The thermal stability of those BP linked by ester bond was worse. Photobleaching experiments showed that photolysis rates accelerated through the introduction of ester-BP group; photolysis rates of the compounds with two ether-BP group were significantly lower than the compounds with a single ether-BP group, while the intramolecular charge transfer and energy transfer in two ether-BP compounds were much easier than those in single ether-BP compounds; photobleaching level of the BP derivatives bearing chromophores with triphenylamine linked by double bond decreased as the number of BP groups increased.The mechanism of photo-initiating polymerization of these photoinitiators was speculated through the summarizing results of the molecular structure optimization calculation, the value from estimation of free energy change of charge transfer, the spectral change regularity of the initiating polymerization systems induced by visible light, and nuclear magnetic resonance characteristics peak of semi-benzopinacol obtained after photoinitiators reacts with triethanolamine.

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CLC: > Mathematical sciences and chemical > Chemistry > Polymer chemistry ( polymer ) > Polymer physics and physical chemistry of polymers > The chemical nature of polymers
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