Vinyl acrylate photopolymerization

Vinyl acrylate (VA) is an intriguing compound capable of self-initiation under UV irradiation. Photopolymerization of VA proceeds faster when PI is added, with other conditions being the same. The question is which double bond is attacked by r of PI (Scheme 12.9). 

The expectation that HABls could be used to initiate photo-polymerization was not realized for a long time. Photopolymerization was a field in which the DuPont Photo Products Department was active and we assumed that they would assist us in expanding the HABI chemistry in that area. Some cursory work—adding HABls to vinyl acrylate monomers gave no evidence of photopolymerization. 

Polymers in Schemes 12 and 13 were the first examples of the preparation of pyridinium and iminopyridinium ylide polymers. One of the more recent contributions of Kondo and his colleagues [16] deals with the sensitization effect of l-ethoxycarbonyliminopyridinium ylide (IPYY) (Scheme 14) on the photopolymerization of vinyl monomers. Only acrylic monomers such as MMA and methyl acrylate (MA) were photoinitiated by IPYY, while vinylacetate (VA), acrylonitrile (AN), and styrene were unaffected by the initiator used. A free radical mechanism was confirmed by a kinetic study. The complex of IPYY and MMA was defined as an exciplex that served as a precursor of the initiating radical. This ylide is unique in being stabilized by the participation of a... 

The objective of the present work was to determine the influence of the light intensity on the polymerization kinetics and on the temperature profile of acrylate and vinyl ether monomers exposed to UV radiation as thin films, as well as the effect of the sample initial temperature on the polymerization rate and final degree of cure. For this purpose, a new method has been developed, based on real-time infrared (RTIR) spectroscopy 14, which permits to monitor in-situ the temperature of thin films undergoing high-speed photopolymerization, without introducing any additive in the UV-curable formulation 15. This technique proved particularly well suited to addressing the issue of thermal runaway which was recently considered to occur in laser-induced polymerization of divinyl ethers 13>16. 

Other monomers (for example acrylamide, styrene, vinylpyrrolidone, vinylcar-bazole, vinyl ether, allyl ether, etc.) can be likely studied by carefully selecting other initiating radicals. Cross-polymerization might also be investigated, for example, the addition of TEA-M to vinyl ether since TEA does not react with vinyl ether. The results obtained with this procedure can also be extended to the behavior of different acrylate structures in photopolymerization experiments carried out in bulk. 

Thiol-Ene Photopolymerization The thiol-ene polymerization of suitable systems (10.84) in film is insensitive to oxygen. The reaction refers to the addition of a thiol to a double bond (e.g., vinyl, allyl, acrylate, and methacrylate) [310] and has led in these past years to a new revival of interest [311,312]. Thiol-vinyl ether or -allyl ether polymerization shows some following interesting features very fast process, low or even no oxygen inhibition effect and formation of highly cross-linked networks with good adhesion, and physical and mechanical properties. 

Photopolymerization in the vapour phase has been observed on surfaces exposed to u.v. radiation in the presence of six fluorocarbon monomers.34 Ionic polymerization of vinyl halides in the vapour phase has been initiated by photoionization using photons with energies near the ionization threshold,35 and the photochemical initiation of polymerization of gaseous ethyl acrylate35 and MM A, butyl acrylate, and methacrylates under high pressures37 has been reported. The last study utilized l,r-azocyclohexane carbonitrile as photosensitizer. 

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