Photoinitiated polymerization monomer

In the case of photoinitiated polymerization, an oxygen-free aqueous solution of acrylamide with a concentration of about 50% mixed with a photosensibilizer and other required additives is passed through a column-type apparatus with exterior water-cooling. A thin layer of the solution is exposed to a mercury lamp, acquires the consistency of a plastic film, which then can be passed through a second exposure zone, and is crushed and dried. Acrylamide polymers produced by this method are easily soluble and have a low residual monomer content. 

The radiolysis of olefinic monomers results in the formation of cations, anions, and free radicals as described above. It is then possible for these species to initiate chain polymerizations. Whether a polymerization is initiated by the radicals, cations, or anions depends on the monomer and reaction conditions. Most radiation polymerizations are radical polymerizations, especially at higher temperatures where ionic species are not stable and dissociate to yield radicals. Radiolytic initiation can also be achieved using initiators, like those used in thermally initiated and photoinitiated polymerizations, which undergo decomposition on irradiation. 

In stereolithography the positions of polymerization x and y are controlled by a mirrored scanner which reflects the laser onto the surface of the to-be-polymerized monomer at a point x,y and the z dimension is determined by the position of the elevator, as shown in Figure 5. During the polymerization z, the depth to which reaction occurs, is held constant through the use of a UV photoinitiator that bleaches either not at all or very slowly, relative to the rate of polymerization. 

If a swelling agent is added to the reaction mixture, a maximum rate is usually noted for some fairly low agent-to-monomer ratio. DMF, which is merely a swelling agent when mixed with monomer, gives a maximum rate at 10 mol-% in photoinitiated polymerization, at about 25 mol-% in polymerization catalyzed by benzoyl peroxide (9), and at about 30 mol-% with gamma rays (114), all near room temperature. On the other hand, as little as 10 mol-% of DMF reduces the rate at 60° by a factor of about 15. It decreases also the ratio of the fast reaction at 60° to the 25° rate. 

Photoinitiated polymerization and crosslinking of monomers, oligomers, and polymers constitute the basis of important commercial processes with broad applicability, including photoimaging and UV curing of coatings and inks. 

The nematic LC is the original eutectic mixture of 35% (weight %) 4 (m-octyl oxy)-4-cyanobiphenyl (80CB) and 65% 4/-(n-pentyl)-4-cyanobiphenyl (5CB). The sample is doped with perylene and 2% (mol %) of NIAC, which is acrylate monomer containing the easily reduced l,4 5,8-naphthalenediimide moiety (see Scheme 3). Finally, 0.5% (mol %) of benzoin methyl ether (BME) is added to photoinitiate polymerization of the NIAC. 

Different techniques have been used to study the products of photoreactions of organometallic compounds for example, irradiation of the arene complexes [CpFe() -arene)]+ resulted in the substitution of the arene by solvent or other potential ligands present in solution. In solutions containing an epoxide monomer, this photochemical reaction generated a species that initiated polymerization. Ion cyclotron resonance Fourier transform mass spectrometry and electrospray ionization mass spectrometry were used to elucidate the mechanism of these photoinitiated polymerizations. 

The effect of pulsed discharge on plasma polymerization may be viewed as the analogue of the rotating sector in photoinitiated polymerization. The ratio r of off time 2 to on time ti, r = l2lti, is expected to influence the polymerization rate depending on the relative time scale of t2 to the lifetime of free radicals in free radical addition polymerization of a monomer. This technique was used to estimate the average lifetime of free radicals in the polymerization. 

In the first detailed study of benzoin photoinitiated polymerization of vinyl monomers (styrene, butyl acrylate, methyl acrylate and methyl... 

In the benzophenone-photoinitiated polymerization of methyl methacrylate, interpretation (i) would tend to increase the order of reaction with respect to monomer concentration, whereas interpretation (ii) would tend to decrease this, assuming that the species formed as the result of quenching initiated polymerization less efficiently than the solvent-derived radicals. The data of Block et al. (46) give a value of 0.84 for the order in monomer, and it could be argued that this is significantly lower than the value of unity predicted by the suggested... 

Solvent effectiveness in the benzophenone-photoinitiated polymerization of methyl methacrylate was in the order tetrahydrofuran > isopropanol > toluene > benzene (46). In the case of TCMB, isopropanol gaw slightly higher polymerization rates than tetrahydrofuran, but both wore again considerably more effective than toluene and benzene. As might be expected, monomers which thonselves contain ether grouj , e.g. diethylene glycol diacrylate (7), do not require addition of a separate hydrogen-donor solvent for efficient photoinitiation by benzophenone. 

In the photopolymerization of methacrylamide by benzoin methyl ether, chain-transfer to monomer has been found to be important, and benzalde-hyde is reported to be an inefficient photoinitiator of methyl methacrylate polymerization unless benzophenone and triethylamine are present. Acetophenone has been found to sensitize the cycloaddition of maleic anhydride to 7-oxabicyclo[2.2.1]heptan-5-one-2,3-dicarboxylic anhydride, , a-hydroxy-acetophenone derivatives have been found to be non-yellowing initiators, and h.p.l.c. has been used to determine residual carbonyl photoinitiators in u.v.-cured resins. In the emulsion-polymerization of methyl methacrylate using an aromatic ketone and a continuous or intermittent laser, the former conditions were found to be similar to those under continuous u.v. irradiation. The dependence of the polymerization rate and average chain-length on the absorbance of the initiator used in the photoinitiated polymerization of vinyl monomers has been studied. Interestingly, irrespective of all conditions, maximum conversion is observed when initiator absorbance is 2.51. "... 

When the photoinitiated polymerization process occurs under the same experimental conditions, in terms of c, /, Iq and type of monomers mixture, and is assumed to be equal for each photoinitiator based on the benzophenone moiety, Ri results proportional to and hence Rp to according to Eqs. (1) and (2). 

Whereas in the MMA photoinitiated polymerization by quinoline-bromine CT complex the formation of radicals is preceded by an instantaneous complexation reaction between the CT complex initiator and the monomer [68], no evidence of this occurrence is observed in the case of the poly(NVC)-Br2 CT complex, probably due to the steric hindrance provided by the polymeric chain. The behaviour of the above system should however be compared with that of the corresponding low-molecular-weight A-alkyl carbazole-Bra CT complex in order to clarify this point. 

TaWe 13. Photoinitiated polymerization rate (Rp) of various monomers in the presence of high- and low-molecular-weight aliphatic ketone initiators [83]... 

Figure 35. Rate of polymerization as a function of free energy change (-AGet) for photoinitiated CQ-NPG systems. Polymerizing monomer mixture 2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate (TMPTA) and ethylated bisphenol-A dimethacrylate (bis-EMA) (1 1). Polymerization was initiated by an argon-ion laser beam. Data from Ref. [175].

For evaluating the influence of CD on the photoinitiated polymerization process, the polymerization of a water soluble monomer, AMsopropylacrylamide (NIPAAM), using complex of Me-P-CD and 2-hydroxy-2-methyl-1-phenylpropan-l-one (13) as... 

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