Photopolymerization agents

C.C. Chappelow etal, US Patent 6,653,486 (November 25, 2003) Assignee Curators of the University of Missouri Utility Photopolymerization Agents... 

The photopolymerization process taking place within a representative mixture of sensitizer, initiator, chain-transfer agent, and monomer, typical of positive Cromalin, has been studied in detail (41,42). The exact mechanism is still controversial, but a generalized reaction scheme can be postulated as follows, where L2 = biimidazole dimer, S = sensitizer, RH = chain-transfer agent, L2 = excited biimidazole dimer, L = biimidazole radical,... 

Fig. 20 Phosphorylcholine-containing iniferter derivatized on glass through silane coupling agent (upper) and graft chain photopolymerized with poly(dimethylacrylamide) (lower)...

Oster [174] proposed the second hypothesis to explain his results on the photopolymerization of acrylonitrile in aqueous solution, buffered at pH 7.0, and sensitized by xanthene dyes and riboflavin using ascorbic acid as the reducing agent. Whereas the monomer is efficiently polymerized when the solution is illuminated in the presence of oxygen, irradiation in its absence leads to photoreduction of the dye to its leuco form but no polymer is formed. Therefore, the author suggests that the leuco dye reacts with atmospheric... 

A more conventional mechanism appears to be operative in the photopolymerization of ethyl acrylate [178] and methyl methacrylate [179] in aqueous solution, sensitized by fluorescein and Erythrosin, respectively. Ascorbic acid is the reducing agent in both cases and it is observed that the reaction does not proceed in the absence of buffer, usually phosphate buffer pH 6. Polymer formation starts after an induction period but its dependence on light intensity and ascorbic acid concentration has not been determined. The rate of photopolymerization is proportional to the monomer concentration and to the square root of the light intensity, dye, and ascorbic acid concentration. The authors report the order with respect to the monomer as 3/2. However, from our analysis of the data for fluorescein, which are more... 

Photooxidation of Eosin with periodate ion has been used to initiate the polymerization of acrylonitrile in aqueous solution [187]. Addition of acrylonitrile to a periodate solution shifts the absorption maximum from 220 to 280 nm. This spectral change is interpreted as being due to complex formation between the monomer and oxidizing agent. The rate of photopolymerization increases linearly with the absorbed light intensity and monomer concentration. The observed intensity dependence indicates the main chain terminator is not produced photochemically. Polymer is not formed when the concentration of periodate ion is lower than 0.5 mM and the rate of polymerization is independent of its concentration for higher values. 

Other than beads, porous polymer monoliths, which were photopolymerized in a COC chip, were used for solid-phase extraction. It is known that priming polymeric surfaces is not as simple as priming silica surfaces, which use a common surface primer agent, TMPM. Therefore, the grafting method as initiated by UV should be used to attach the polymer monoliths [588]. A similar strategy was used for sample pre-concentration of PAHs (e.g., pyrene). Pyrene (900 nM) was first concentrated by 400-fold in 24% ACN before switching to 56% ACN for CEC separation (see Figure 5.5) [148]. 

The Inifer technique enables us to fulfil some requirements of polymer architecture even in some radical processes. An amplified form may be applied, the Iniferter variant, where the radical initiator simultaneously acts as a transfer and terminating agent. Otsu et al. used sulphides and disulphides (tetraethylthiuram disulphide, PhSSPh, Ph2S, PhCH2SSCH2Ph) [96] and carbamates (benzyl-A,A-diethyldithiocarbamate, p-xylylene-A,7V-diethyl-dithiocarbamate) [97] in the photopolymerization of methyl methacrylate and styrene, and phenylazotriphenylmethane in the polymerization of methyl methacrylate [98]. Living radical polymerizations yield polymers with defined end groups or the required block copolymers. 

Two trifunctional benzophenone derivatives have been synthesized that are UV photoactive at 254 nm and photolytically incorporated into poly(s-caprolactone) and poly(vinylpyrrolidone). These agents are designed to be used in photopolymerization... 

Air interface orientation controlling agent, (11), 0.2 parts (unspecified) Photopolymerization initiator HJ-1, (HI), 2.0 parts by mass Lucirin TPO-L, 2.0 parts Methyl ethyl ketone, 300 parts... 

Unlike other photosensitive polyimides (2), the use of N-phenylmaleImide (10% to polymer weight) as crosslinking agent did not improve the photopolymerization of PSiPI. 

Photoinitiators as Iniferters The availability of iniferters that behave as an initiator, a transfer agent and a terminator is rather limited [98,99]. A renewal of interest is noted for the development of efficient compounds usable in controlled radical photopolymerization reactions [100-104]. Examples of cleavable photoiniferters are shown in (10.42) the particular tetrazole derivative shown here is noticeably attractive due the generation of a tetrazoyl radical that presents a low selectivity and a high efficiency for the addition to acrylate double bonds [105],... 

The use of dye-sensitized initiation in polymerization dates to 1949 when Bamford and Dewar observed that some vat dyes could sensitize the photopolymerization of styrene. This was quickly followed up hy Gerald Oster s discovery " in 1954 that the polymerization of acrylonitrile and of acrylamide could be photoinitiated by fluorescein, rose bengal, and similar dyes, in the presence of reducing agents (such as phenylhydrazine, ascorbic acid) and oxygen. Remarkably, the amount of dye required for the photoinitiation event was extremely small ( 0.1% of the weight of monomer), and the quantum yield of monomer consumption was in excess of 4000 monomer units per photon. " ... 

Peroxide (254) was developed as a cross-linking and vulcanization agent and also serves as a vinyl polymerization initiator <90JAP(K)02i 17670). Pseudoester (255) is a photopolymerization initiator <89JAP(K)01180857). 

Uses Curing agent for flexible substrates, photopolymeric printing plates, and no-wax vinyl tile coatings ManuUDistrib. CPS Monomer-Polymer Dajac Labs Trade Names SR 272... 

Hazardous Decomp. Prods. Heated to decomp., emits acrid smoke and irritating fumes Uses Curing agent for flexible substrates, photopolymeric printing plates, and no-wax vinyl tile coatings Manuf./Distrib. CPS Hunan Xinyu http //WWW. hunanxinyu. com-, M onomer-Polymer Dajac Labs PEG-4 diacrylate CAS 17831-71-9... 

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