фотополимеризация

[Evgeni]

Может есть у кого-нибудь информация о фотополимеризации метилметакрилата? Спасибо!

[eukar]

Например:

The polymerization of MMA photoinitiated by the dye thionine (ThH+) in the presence of triethylamine as co-initiator, has been studied in methanol. Polymerization rates increase with amine concentration up to a maximum at ~0.1M, after which they decrease. A general mechanism for the photoinitiating process is proposed which leads to an equation relating the yield of initiating radicals to the concentration of amine. When using the rate constants and other data determined for the elemental photochemical steps involved in the photoinitiating mechanism, the behaviour of the yield of initiating radicals as a function of amine concentration is similar to that of the polymerization conversion. In agreement with that mechanism, no polymerization products were observed in the absence of amine, or in the presence of oxygen.

MMA photopolymerization initiated by thionine/triethylamine
F. Catalina, M.R. Rodrigues, M.G. Neumann
Journal of Photochemistry and Photobiology A: Chemistry, 127 (1999), 1-3 (октябрь), 147-152

The kinetics of radical polymerization and copolymerization of alkyl(meth)acrylates with and without polyoxyethylene macromonomers in fine emulsions photoinitiated by a UV light was investigated. The fine monomer emulsions were formed in the presence of high amount of emulsifier without any homogenization. The rate of polymerization with ethyl acrylate was larger than that with methyl methacrylate or nonyl methacrylate. The addition of PEO-MA macromonomer decreases the rate of polymerization and the molecular weight as well. The rate-conversion curve showed four regions with two rate maxima ca. at 5-20% and 50-70% conversion in which the first maximum was much more pronounced than the second one. The results were discussed in terms of polymerization within fine microdroplets. The particle number increased with increasing alkyl group of monomer. The particle size distribution was observed to increase from NMA, via EA to MMA. The polymer molecular weights were inversely proportional to the particle size.

Photopolymerization of alkyl(meth)acrylates and polyoxyethylene macromonomers in fine emulsions
I. Capek
European Polymer Journal, 36 (2000), 2 (февраль), 255-263

Photopolymerization of the vinyl monomer (M) methyl methacrylate (MMA) was studied at 40oC using pyridinium chlorochromate (PCC) as the photoinitiator. Observed dependence of rate of polymerization, Rp, on concentrations of PCC and MMA may be expressed as Rp # [PCC]0.21.[M]1.0. PCC-induced photopolymerisation of MMA proceeds via instantaneous complexation between the initiator (PCC) and the monomer (MMA). Chain initiation actually takes place by radicals derived from photodecomposition of the said complex and the PCC-MMA complex is believed to be the actual initiating species. The polymers formed tested positive to the sensitive dye-partition test for the presence of halogen (chlorine) atom end groups in polymers. Nonideality in the polymerization kinetics in respect of initiator exponent < 0.5 is explained on the basis of significant termination by degradative initiator transfer over and above the normal bimolecular mode of termination. Monomer exponent of unity precludes consideration of primary radical termination as the cause of kinetic nonideality.

Photopolymerization of methyl methacrylate using pyridinium chlorochromate (PCC) as the photoinitiator
P. Ghosh, G. Pal
European Polymer Journal, 33 (1997), 10-12 (октябрь), 1695-1700

Photoinitiated free-radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate has been investigated in toluene at a monomer concentration of 35w/v%. The photoinitiators used were benzoin, benzoin methyl ether, benzoin ethyl ether and 2,2-dimethoxy-2-phenyl-acetophenone. Conversion of monomer and pendant vinyl groups and the size of the pregel polymers were measured as a function of the reaction time up to the onset of macrogelation. Approximately 30% of the pendant vinyl groups were found to be consumed by cyclization reactions. The fraction of units in cycles is independent of the EGDM concentration. As a result of the cyclization reactions, the accessibility of the radical centres and pendant vinyl groups for other polymer molecules is strongly reduced. Consequently, both termination and crosslinking reactions are controlled by the segmental diffusion of the polymer radicals. Calculations indicate a 1-2 orders of magnitude decrease in the average reactivity of pendant vinyls for intermolecular reactions compared to the monomeric vinyls. This drastic decrease in pendant reactivity is mainly responsible for the delay in the gel point. Contrary to gelation theories, the size distribution curves of the pregel polymers change from monomodal to bimodal distributions as polymerization proceeds. This finding confirms the coagulation-type gelation mechanism of compact primary particles and indicates the shape polydispersity of the pregel polymers.

Gel formation by chain-crosslinking photopolymerization of methyl methacrylate and ethylene glycol dimethacrylate
H.J. Naghash, O. Okay, Y. Yagci
Polymer, 38 (1997), 5, 1187-1196

This is a first comprehensive study on the photoinitiating capability of a vinyl polyperoxide. Polymerization of methyl methacrylate photoinitiated by poly(styrene peroxide) (PSP) at 30oC has been shown to follow the usual kinetic behaviour with respect to the initiator, monomer and light intensity for a PSP concentration of 0.0021-0.034 mol-equiv 1-1. At higher concentrations of PSP (0.046-0.31 mol-equiv 1-1 although kinetic order with respect to the monomer and light intensity follows usual kinetics the order with respect to PSP was found to be very low (0.21), which has been attributed to the occurrence of primary radical termination which has been quantified in terms of the primary radical termination parameter (d/S). The initiator efficiency was found to be very low (0.06-0.07), it has been attributed to the competing unimolecular decomposition of alkoxy radicals with primary radical initiation. The presence of PSP segments in the poly(methyl methacrylate) backbone was confirmed by 1H nuclear magnetic resonance.

Kinetics of poly(styrene peroxide) initiated photopolymerization of methyl methacrylate
K. Subramanian, K.S. Murthy, K. Kishore
Polymer, 38 (1997), 3 (февраль), 527-533

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