2,2-Dimethoxy-2-phenyl acetophenone DMPA

Trimethylolpropane triacrylate (TrMPTrA, mw 296.3, Polysciences Inc., Warrington, PA) was mixed with 1 wt% 2,2-dimethoxy-2-phenyl-acetophenone (DMPA, mw 256.3, Aldrich Chemical Co., Milwaukee, WI) as a photoinitiator. For... 

In this work, the kinetics of these reactions are closely examined by monitoring photopolymerizations initiated by a two-component system consisting of a conventional photoinitiator, such as 2,2-dimethoxy-2-phenyl acetophenone (DMPA) and TED. By examining the polymerization kinetics in detail, further understanding of the complex initiation and termination reactions can be achieved. The monomers discussed in this manuscript are 2-hydroxyethyl methacrylate (HEMA), which forms a linear polymer upon polymerization, and diethylene glycol dimethacrylate (DEGDMA), which forms a crosslinked network upon polymerization. 

The monomers studied, 2-hydroxyethyl methacrylate (HEMA) and diethylene glycol dimethacrylate (DEGDMA), were obtained from Aldrich (Milwaukee, WI) and Polysciences, Inc. (Warrington, PA), respectively, and were used after dehibition to remove the hydroquinone inhibitor. 2,2-Dimethoxy-2-phenyl acetophenone (DMPA), the conventional initiator used in this study, was obtained from Ciba-Geigy (Hawthorne, NY) and the tetraethylthiuram disufide (TED) was obtained from Aldrich. 

Oligomeric benzil ketals (DTGPA), prepared by reaction of 2,2-dimethoxy-2-phenyl-acetophenone (DMPA) with triethyleneglycol, in the presence of p-toluen-sulphonic acid, are reported [88] to be efficient in the UV curing of styrene/ unsaturated polyester formulations giving rise to coatings with very low odour. 

Values relative to 2,2-dimethoxy-2-phenyl acetophenone (DMPA), set as equal to one... 

All the MBA/A(,iV-dialkylamino acrylate copolymers behave similarly to poly(MBA-co-MtA)s (Tables 21 and 25), thus suggesting that the replacement of MtA by A,A(-dialkylamino acrylate co-units does not markedly affect the photoinitiation activity of the system. Accordingly, BMI/A,A(-dialkylamino isobutyrates mixtures exhibit substantially the same activity as MBI alone [118]. Similar results have previously been obtained for 2,2-dimethoxy-2-phenyl acetophenone (DMPA), when additioned with diethylmethylamine, in the UV initiated polymerization of -butyl methacrylate [113]. However, a remarkable shortening of the induction period (to) of UV curing is observed for all the polymeric photoinitiators in the presence of tertiary amines as compared with the low-molecular-weight MBl/A,A(-diatkylamino isobutyrates systems, the maximum effect resulting in the case of MBA/A(,iV-dialkylamino acrylate copolymers (Table 25). 

Benzoin Ethers Benzoin ethers were the most widely used photoinitiators for a long time [13-15]. The cleavage process in the triplet state (10.8) is very fast compared to that of some related structures (>1010 s ). The cleavage yield is almost unity for 2,2-dimethoxy—2 phenyl-acetophenone DMPA or 2-methoxy -2 phenyl acetophenone BME. A secondary photochemical cleavage (the possible thermal cleavage is less efficient) can arise in the dimethoxy benzyl radical and leads to a methyl R" radical and an alkyl benzoate. 

All the materials in this study are commercially available and were used as received. The compositions of the mixtures are given in Table I. The components can be described as follows Resin is a proprietary blend of acrylated epoxy resins with an number average molecular weight (Mn) of "4800, based on acrylated diglycidyl bisphenol A, DGEBAcr is the diacrylate derivative of diglycidyl bisphenol A, IBOA is isobomyl acrylate, TMPTA is trimethyloltriacrylate and DMPA is 2,2-dimethoxy-2-phenyl acetophenone. 

Kinetics of the Cleavage Process in Type I Photoinitiators Working now on the picosecond timescale (with a pump-probe laser setup) shows the shortlived transient absorptions observed upon light excitation [250], For example [251], the cleavage process of DMPA (2,2-dimethoxy -2 phenyl-acetophenone) occurs... 

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