Photopolymerizations acrylic monomers

Clarke and Shanks have examined the influence of sample thickness on the benzoin photoinitiated polymerization of butyl acrylate. They found that as the photoinitiator concentration increases so the extent of polymerization become less susceptible to changes in sample thickness. Grauchak et al. have successfully photopolymerized acrylic monomers in polyamide matrices with aromatic carbonyl compounds. In the photocycloaddition of olefins to poly(4,-vinylbenzo-phenone) and its copolymers with styrene, the rate of addition was found to be independent of the glass transition temperature suggesting that large-scale molecular motion is unimportant in this photoreaction. 

The well-known photopolymerization of acrylic monomers usually involves a charge transfer system with carbonyl compound as an acceptor and aliphatic tertiary amine, triethylamine (TEA), as a donor. Instead of tertiary amine such as TEA or DMT, Li et al. [89] investigated the photopolymerization of AN in the presence of benzophenone (BP) and aniline (A) or N-methylaniline (NMA) and found that the BP-A or BP-NMA system will give a higher rate of polymerization than that of the well-known system BP-TEA. Still, we know that secondary aromatic amine would be deprotonated of the H-atom mostly on the N-atom so we proposed the mechanism as follows ... 

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 chapters in this book are organized into three sections. A majority of the commercial photopolymerization systems are based on acrylate monomers therefore, the first several chapters focus on fundamental characterization of... 

General Electric Co.) were added to the acrylic and epoxy monomers, respectively, to initiate photopolymerization. The acrylic monomers that polymerized by a free-radical mechanism were irradiated under nitrogen. The output of the lamp measured at the substrate was about 4 mW/cm2 at 260 nm and about 11 mW/cm2 at 310 nm. 

Conventionally, solutions of acrylamide or other acrylic monomers, or mixtures of them, can be photopolymerized onto flat glass surfaces which have previously been derivatized with acrylic groups to promote covalent and robust binding of the gel (e.g. by reaction with 3-(triethoxysilylpropyl)acryla-mide) [59]. Irradiation of the substrate occurs through a mask, so that poly-... 

The DnPont photopolymeric system consists of polymeric binder resins, e.g. PVA, PMMA, cellnlose acetates and styrene-acrylates, reactive acrylic monomers, e.g. aryloxy or alkoxy acrylates, a dye sensitiser and a radical or charge transfer photoinitiator, e.g. DEAW and HABI respectively (see Chapter 4, section 4.5.2), and plasticisers. The process for producing the refractive index structures is as follows ... 

We have also used the Eosin-triethanolamine system to design a two-photon system based on visible laser-induced photopolymerization followed by UV-induced crosslinking as a means of building a three-dimensional network structure aimed at three-dimensional imaging. The key to our design, shown in Scheme 4 below, is incorporation of an acrylate monomer... 

Other carboxylate-dye interactions have been reported. Ethylenediamine tetracarboxylic acid (EDTA) and its salts are well known reductants for a variety of dyes (54,55). The amino-acid N-phenylglycine can be photooxidized and induce polymer formation (26,56,57). Studies of the efficiency of photopolymerization of acrylate monomers by MB/N-phenylglycine combinations as a function of the pH of the medium suggest that either the amino group or the free carboxylate can act as an electron donor for the dye excited state, but that the amine functional-lity is the more efficient coinitiator (10). Davidson and coworkers (58) have shown that ketocarboxylic acids are photode-carboxylated by electron transfer quenching of dye triplet states under anaerobic conditions. Superoxide formation can occur when oxygen is present. 

Anisotropic polymer filaments could be produced by in-situ photopolymerization of oriented acrylate monomers. Ordering of the monomers was achieved by an elongational flow prior to the polymerization process. The produced polymers showed a high elastic modulus and a low thermal expansion coefficient in the direction of the orientation. 

The investigation on oriented polymeric networks obtained by the photopolymerization of oriented low molecular weight species, as presented in this paper, has been carried out with a more or less conventional acrylate monomer. Already with this material an anisotropy in properties could be demonstrated. It is to be expected that even more pronounced effects can be obtained with monomers which have a strong tendency to alignment. Based on this idea we are now investigating liquid crystalline monomers in our laboratory. 

In the anthraquinone-sensitized photopolymerization of acrylate monomers, the percent conversion depends markedly on the nature of the solvent as well as on the type of monomer. Ethyl and n-butyl methacrylate, for example. 

The study of light-induced polymerization of the new compounds, especially CL 1042, demonstrated the outstanding reactivity of acrylic monomers containing five membered cyclic carbonate function (Ref. 52). Photopolymerization even occurs without any added photoinitiator. 

Photopolymerization of acrylic monomers and related systems is a challenging area for the application of real-time MIR spectroscopy since the reactions are often completed within seconds, so there needs to be an excellent SNR in the spectra if reliable kinetic data are to be generated. The temporal resolution of an FT-IR spectrometer at a resolution of 16 cm is 11 ms, so 100 spectra can be gathered in the time frame of the fastest reaction, but without multiplexing to improve the SNR. Using a diamond ATR element of area 4 mm that could also be heated to 200 C, uniform irradiation was possible and the cure reactions of films of thicknesses ranging from 1 to 20 pm could be followed (Scherzer and Decker, 1999). 

Another interesting case is the self-initiation of some acrylic and styrenic monomers upon UV irradiation. Since this process is quite slow, a photoinitiator is normally required. Recent findings on the self-initiation of maleic anhydride, [ 10] styrene, [11] and anumber of acrylic monomers [12] have demonstrated that photopolymerization and photografting could possibly be achieved without using photoinitiators or sensitizers. 

A critical and most important problem that still remained to be solved was to find an adequate analytical methcxl that would enable us to follow in real time the kinetics of such ultra-fast polymerizations. Different techniques have already been used to study the laser-induced curing of acrylic monomers (DSC, IR spectroscopy, interferometry,...) but none of them provide conversion versus exposure time curves for polymerization that occur in a fraction of a second. The results obtained by some of these techniques are now briefly reported for comparison with those obtained by using real-time infra-red (RTIR) spectroscopy, a powerful method newly developed in our laboratory to investigate the kinetics of ultrafast photopolymerizations (0. 

Keywords photopolymerization, kinetics, acrylate monomers, epoxides... 

It has been possible to fabricate porous monoliths within silicon [16], glass [17], and polymer [18, 19] microchaimels. Within silica and glass channels, porous monoliths can be fabricated by a thermally aided sol-gel reaction. Photopolymerization of acrylate monomers in the presence of porogens (inert organic solvents) has also been used to obtain porous monoliths. By varying the composition of the monomer blend, the composition of the porogen mixture, and the ratio of monomer to porogen, it is possible to control the porosity of the monolith and the modal size of its pores. In addition, if the channels are made out of acrylate... 

Fig. 4 Porous monoliths with different porosities and pore size distributions created by the photopolymerization of a blend of acrylate monomers and porogens...

Free-radical photopolymerizations (see Chap. 10) of multifunctional acrylic monomers result in cross-linked polymeric networks. The kinetic picture of such polymerizations varies from ordinary linear polymerization because the diffusion of free radicals and functional groups becomes severely restricted. This causes growing polymer chains to rapidly cyclize and cross-link into clusters (microgels). The clusters become linked up into networks. Many free radicals become trapped, but terminations take place by combinations and by chain transferring. The cumulative chain length in such polymerizations can be calculated from the following equation [125] ... 

Photopolymerization of phosphorus-based (meth)acrylic monomers was largely investigated for dental applications (Scheme 1.4) 20,21,56 69 monomers bore one or two polymerizable groups and phosphoric acid ester, phosphonate, and phosphonic acid moieties were evaluated. When the phosphorus atom was directly linked to a hydrocarbon chain phosphonate ester), the monomers were more resistant to hydrolysis in comparison with phosphoric acid esters. 

There are also several reports in the literature on use of poly(arylsilanes) as initiators in photopolymerization of acrylic monomers. The photoinitiating efficiency of silane polymers with thioxanthone side groups was found to depend not upon exiplex formation with tertiary amines but rather... 

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