2,2-Dimethoxy-2-phenyl acetophenone

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... 

It is interesting to note that among initiators studied, a benzyl ketal type initiator (2,2-dimethoxy-2-phenyl acetophenone) is more active than other initiators of acetophenone type. 2,2-Dimethoxy-2-phenyl acetophenone is more active than BME, probably due to the presence of the extra methoxy group on the -carbon, which gives a more active phenyldimethoxy methyl radical (and it further cleaves to give an even more active methyl radical) than the phenylmethoxy methyl radical from BME (4). It is known that the phenylmethoxy methyl radical dimerizes easily and thus loses some of its role as a radical in a... 

The Effect of Initiator Concentration on the Rate of Polymerization. BME, 2,2-dimethoxy-2-phenyl acetophenone, 2-hydroxy-2,2-dimethyl acetophenone and Darocur-3331 (its structure is not known) were chosen for further evaluation on the effect of initiator concentration on the rate of polymerization. They were chosen because they are the among the most active or the least active initiator in polymerizing HEMA. 

Table II also lists the peak times from these studies. As expected, the rate of polymerization (by peak time) increased as the concentration of initiator was increased until screening effects started to appear (between 0.34 to 0.68 %). In term of rate of polymerization, the relative ranking ofinitiators remained the same and 2,2-dimethoxy-2-phenyl acetophenone was the most active.

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. 

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. 

Ketones 2-butanone, acetophenone, benzophenone, 2,2-dimethoxy-2-phenyl acetophenone... 

In the first study 2,2-dimethoxy-2-phenyl acetophenone was photolysed at 366 ran in n-butylvinyl ether in the presence of di-p-tolyl iodonium hexafluorophosphate as oxidising salt. The free radicals produced in the photolysis were transformed into cationic active species for the polymerisation of the vinyl ether by the electron transfer to the iodonium ion. In the second report, various radical sources were photolysed in the presence of the monomer and silver hexafluorophosphate, the latter acting as one-electron oxidant. 

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. 

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). 

C16H1403 4-methyl benzoic acid anhydride 13222-85-0 561.15 49.789 2 29297 C16H1603 2,2-dimethoxy-2-phenyl acetophenone 24650-42-8 568.48 50.501 2... 

The sulfonium salt was shown to spontaneously oxidize highly stabilized free radicals such as the triphenylmethyl radical to form the corresponding triphenylmethyl carbonium ion.(20) It would also appear that the dimethoxybenzylic free radical (a Norrish Type I photocleavage product of 2,2-dimethoxy-2-phenyl-acetophenone) is similarily oxidized by the arylsulfonium salt ( ). 

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. 

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... 

Phan X.T. (1986) Photochemical a-cleavage of 2,2-dimethoxy-2-phenyl-acetophenone and 1-hydroxy-cyclohexyl-phenyl ketone photoinitiators. Effect of molecular oxygen on free radical reaction in solution. J. Radiation Curing, 13, 18-25. 

Sandner M.R. and Osborn C.L. (1974) Photochemistry of 2,2,-dimethoxy- 2-phenyl-acetophenone-tri-plet detection via spin-memory. Tetrahedron Lett., 415-418. 

Figure 4.4. The kinetic curves of the polymerization under continuous illumination (solid lines) and after the light has been cut off (dashed lines). Diethylene glycol dimethacrylate, Ar, 40 C initiator, 2,2-dimethoxy-2-phenyl acetophenone (Irgacure 651), 0.06 M [30].

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