Highly Efficient Host-Guest Photoinitiators Based On β-Cyclodextrin

UV radiation curing science and technology has been widespread used in coating, adhesives and electronic package due to its enormous advantages, which include rapid cure rate, energy conservation and environmental benefits. UV radiation curing techniques have been rapidly developed from 50's of the last century. All applications require photoinitiators as a key component, which must meet the requirements of the different curing conditions and environmental protection. Compared with traditional photoinitiator systems, host-guest photoinitiator systems attract more attention because of their low odor, toxicity and good storage stability. TypeⅠand typeⅡphotoinitiator can form crystalline inclusion complexes with cyclodextrins (CDs), which are hydrophilic. This dissertation focuses on the preparation and characterization of the new host-guest photoinitiators. Moreover, their photochemical and photophysical properties and photoinitiation properties were studied in detail.A novel water soluble supramolecular-structured host-guest photoinitiator was successfully synthesized by supramolecular self-assembling between methylatedβ-cyclodextrin (MβCD) and hydrophobic typeⅠ2,2-dimethoxy-2-phenylacetophenone (DMPA). FT-IR,XRD,1H NMR and Fluorescence were used to characterize the photoinitiator. The results indicate that MβCD and DMPA had formed 1: 1 crystalline inclusion complex in methanol solution. The binding constant (K) for the complex was 7.51×102 M. The solubility of the product in water is 15.3g / 100mL at 20℃. UV-Vis and EPR results gave that DMPA-MβCD and DMPA possessed the same initiation mechanism. DMPA-MβCD was the more efficient photoinitiator than DMPA for the photopolymerization of acrylamide (AM) in homogeneous aqueous system. The conversion for photopolymerization of trimethylolpropane triacrylate (TMPTA) system initiated by DMPA-MβCD was similar to that initiated by DMPA. Compared with photo-DSC profiles for the photopolymerization of the UV-curable TMPTA systems initiated by DMPA in the range of 20-90℃, DMPA-MβCD showed better thermal stability with high efficiency than DMPA.The kinetics for photopolymerization of AM initiated by DMPA-MβCD was investigated by photo-DSC. The results showed that temperature and light intensity have similar effects on photopolymeization. The increase in them led to the increase in the polymerization rate (Rp) and the final conversion. At low conversion (10%), the Arrhenius plot was linear, and we could get that the apparent activation energy is about 14.66 kJ?mol-1. However, the increase in photoinitiator concentration did not always lead to the increase in the Rp and the final conversion. It exhibited a maximum Rp and the final conversion for 6×10-4 M of DMPA-MβCD. UV-Vis was used to characterize the complex ability of other typeⅠphotoinitiators such as azodiisobutyronitrile (AIBN), acetophenone (AP) and I 907 with MβCD. The results indicate that the complex process of AIBN and AP with MβCD is easier than that of I 907 with MβCD.TypeⅡphotoinitiator benzophenone (BP) could form crystalline inclusion complex with MβCD and hydroxypropyl-β-cyclodextrin (HP-β-CD). 1H NMR and Fluorescence results indicated that the stoichiometries between the cyclodextrins and BP are 2:1. The binding constant (K) for the complexes were 8.66×103 M and 1.15×104 M, respectively. BP-HP-β-CD was much steadier than BP-MβCD. These host-guest typeⅡphotoinitiators exhibited the usual characteristic UV-Vis absorption in comparison with BP. EPR spectra indicated that the supramolecular structure did not affect the photoinitiation mechanism of photoinitiator. Photopolymerization of AM and TMPTA using these host-guest photoinitiators, BP and DMAEMA (as the coinitiator) were studied. The results showed that BP-HP-β-CD is the most efficient for AM; BP-MβCD is the most efficient for TMPTA. The solubility of the products in water is 48.7g / 100mL and >300g /100mL, respectively, at 25℃. UV-Vis was used to characterize the complex ability of other typeⅡphotoinitiators such as Michler's (MK) and 2-epoxypropyloxy-4-hydroxyl thioxanthone (ETX) with HP-β-CD. The results indicate that the complex process of MK with HP-β-CD is easier than that of ETX with HP-β-CD.A BP monomer containing two epoxy group, 2,4-di(2,3-epoxypropyloxy) benzophenone (2,4-DEBP), was synthesized. Through the reaction of 2,4-DEBP and amine monomer, polymeric photoinitiator (PBP-P) containing in-chain coinitiator amine and bearing side-chain BP was synthesized, as well as low weight model compound DAHBP. Compared with BP, their UV-Vis have a significantly red-shifted maximum absorption. The photoefficiency of PBP-P is highest than BP/TEA and DAHBP in the photopolymerization of poly-(propylene glycol) diacrylate (PPGDA) and TMPTA.A series of polymeric photoinitiators (PBP-P, PBP-E and PBP-B) were synthesized from 2,4-DEBP and different amine monomers (N,N'-dimethylethylenediamine, N,N'-diethyl-2-butene-1,4-diamine and piperazine). The UV-Vis spectra of PBP-P, PBP-E and PBP-B are similar with slightly-shifted maximum absorption, and the fluorescence emission are almost the same. Photopolymerization of PPGDA and TMPTA initiated by these photoinitiators were studied. The results showed that PBP-E is the most efficient for PPGDA; PBP-B is the most efficient for TMPTA.Three polymeric photoinitiators could form complexes with HP-β-CD in DMSO. But they could not form complexes with HP-β-CD in CH3OD.The synthesis of host-guest photoinitiators and the study of these photoinitiators photochemical and photophysical behavior pave the way for their academic research in a deeper level and wide range of application. The finding of new photoinitiators promises the fascinating future of this field and enlighten us to discovery more new novel photoinitiators.