Synthesis And Photopolymerization Kinetics Of Benzophenone Derivative Photoinitiators

Benzophenone is by far one of the most widely used conventional low molecular weight photoinitiators for UV-curing coatings as it has good surface curing, solubility and been shown to initiate free radical polymerization of (meth)acrylic systems effectively in the presence of amines. Conventional low molecular weight photoinitiators have some disadvantages. For example, benzophenone is known for its relatively strong odour, yellowing and exceptional ability to migrate and be extracted from cured products, it is clear that there is a need for a benzophenone derivative without these disadvantages. The development of difunctional photoinitiators is possible to reduce the risk of migrate because of the rather high molecular weight. The incorporation of both benzophenone moiety and tertiary amine into the same molecule has obvious advantages that the benzophenone moiety is expected to be attached with (meth) acrylate through amine-derived radical during the curing process, which makes the modified benzophenone derivative a potential photoinitiator with low odour, good solubility, and limited tendency to migrate and so can be used in UV formulations as a benzophenone alternative.In this thesis, three different photoinitiators have been synthesized and studied. 1), A benzophenone (BP) derivative difunctional photoinitiator, HMBP-TDI-HQ-TDI-HMBP (HTHTH) was synthesized from 4-hydroxymethylbenzophenone (HMBP), hydroquinone (HQ) and toluene-2,4-diisocyanate (TDI). The absorption ability of HTHTH is over two times higher than that of BP. 2) HBP-TDI-DHBP-TDI-HBP (HTDTH), based on 4-hydroxy benzophenone (HBP), toluene-2,4-diisocyanate (TDI) and 4.4'-dihydroxy benzophenone (DHBP), was synthesized 3) HBP-TDI-DMEA (HTD) bearing in-chain benzophenone and coinitiator tertiary amine, based on 4-hydroxybenzophenone (HBP), toluene-2,4-diisocyanate (TDI) and N,N-Dimethylethanolamine (DMEA), was synthesized. HTD had longer absorption wavelength in the UV-vis absorption spectra than the low molecular counterpart benzophenone (BP). Extract analysis showed that the extractability of HTD was much lower than that of BP/DMEA. When the combination of these photoinitiatos and amine was used to initiate polymerization of tripropylene glycol diacrylate (TPGDA), both rate of polymerization and final conversion increased with the increase of amine concentrations, photoinitiators concentrations and light intensity.