Vinyl ethers free radical polymerizations

Tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, perfluoroalkyl vinyl ether Free-radical-initiated chain polymerization Coatings for chemical process equipment, cable insulation, electrical components, nonsticking surfaces for cookware... 

A second type of uv curing chemistry is used, employing cationic curing as opposed to free-radical polymerization. This technology uses vinyl ethers and epoxy resins for the oligomers, reactive resins, and monomers. The initiators form Lewis acids upon absorption of the uv energy and the acid causes cationic polymerization. Although this chemistry has improved adhesion and flexibility and offers lower viscosity compared to the typical acrylate system, the cationic chemistry is very sensitive to humidity conditions and amine contamination. Both chemistries are used commercially. 

Thus, a mixture of simple carbonyls Me(CO)n and halides should behave as a photoinitiator of free radical polymerization. Many such systems have been found to function in this way. Complexes formed by irradiation of Fe(CO)5 in the presence of a vinyl monomer (M) (such as MMA, styrene, vinyl acetate, propylene, and vinyl ether) have been studied by Koerner Von Grustrof and colleagues [12,13] and shown to have the chemical struc-... 

Vinyl Acetate CH3COOCH=CH2 OH compds, HCN, Halides, Halogens, Mer-cap tans, Amine, Silanes Oxygen Vap in Air 2.6 to 13.4% > Ambient > Ambient Inhibitor—Methyl Ether of Hydroquinone or 3-5ppm Diphenylamine. Store in a dry, cool place shield from light impurities 20.9-21.5 402 427 Free-radical polymerization initiated by Benzoyl Peroxide... 

Two pieces of direct evidence support the manifestly plausible view that these polymerizations are propagated through the action of car-bonium ion centers. Eley and Richards have shown that triphenyl-methyl chloride is a catalyst for the polymerization of vinyl ethers in m-cresol, in which the catalyst ionizes to yield the triphenylcarbonium ion (C6H5)3C+. Secondly, A. G. Evans and Hamann showed that l,l -diphenylethylene develops an absorption band at 4340 A in the presence of boron trifluoride (and adventitious moisture) or of stannic chloride and hydrogen chloride. This band is characteristic of both the triphenylcarbonium ion and the diphenylmethylcarbonium ion. While similar observations on polymerizable monomers are precluded by intervention of polymerization before a sufficient concentration may be reached, similar ions should certainly be expected to form under the same conditions in styrene, and in certain other monomers also. In analogy with free radical polymerizations, the essential chain-propagating step may therefore be assumed to consist in the addition of monomer to a carbonium ion... 

Lignin, brown coal polymer of methacrylic acid, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, vinyl acetate, methyl vinyl ether, ethyl vinyl ether, N-methylmeth-acrylamide, N,N-dimethylmethacrylamide, vinyl sulfonate, or 2-acrylamido-N-methylpropane sulfonic acid free radical polymerization of a water-soluble vinyl monomer in an aqueous suspension of coals [705,1847]... 

Finally, we should indicate that we have not ruled out the possibility that there is a contribution to initiating photopolymerization in maleimide/vinyl ether systems from an exciplex type complex between an excited state maleimide and ground state vinyl ether. A biradical formed from such a complex might initiate free radical polymerization in lieu of cyclization to form a 2 + 2 adduct. However, we note that at present we have no evidence for such a reactive exciplex. 

These copolymers are prepared by the solution free radical polymerization of the electron-poor monomer (substituted maleimide) and the electron-rich monomer (substituted styrene or vinyl ether). Predominantly alternating copolymers result from such polymerizations (IQ). We will report on this unique copolymerization that permits the copolymerization of two double bonds in the presence of a third reactive double bond elsewhere. 

Since these reports, a number of new approaches based on vinyl monomers and various initiating systems have been explored to yield hyperbranched polymers such as, poly(4-acetylstyrene) [26], poly(vinyl ether) [27] and polyacrylates [28], In view of the fact that free radical polymerizations are most widely used in industrial polymerization processes the development of these procedures for vinyl monomers has opened a very important area for hyperbranched polymers. 

Rasmussen and co-workers. Chapter 10, have shown that many free-radical polymerizations can be conducted in two-phase systems using potassium persulfate and either crown ethers or quaternary ammonium salts as initiators. When transferred to the organic phase persulfate performs far more efficiently as an initiator than conventional materials such as azobisisobutyronitrile or benzoyl peroxide. In vinyl polymerizations using PTC-persulfate initiation one can exercise precise control over reaction rates, even at low temperatures. Mechanistic aspects of these complicated systems have been worked out for this highly useful and economical method of initiation of free-radical polymerizations. 

A-Vinyl-2-pyrrolidone (1.8 mol), 2,2 -azobis(2-methyl-N-(2-hydroxyethyl)-propio-namide) (0.018 mol), and 2-mercaptoethanol (0.072 mol) were dissolved in 3000 ml of 2-propanol degassed for 1 hour. The free radical polymerization was carried out at reflux while stirring for 44 hours. The mixture was concentrated and then dissolved in 400 ml of 4-methyl-2-pentanone and slowly precipitated into 5000 ml of t-butyl methyl ether. The suspension was filtered and the filter cake washed twice with 200 ml of -butyl methyl ether. The solid was purified by dissolving in 400 ml of... 

Like the vinyl ethers, isopropenyl acetate does not readily form homopolymers by free radical initiation. It does participate in the donor-acceptor mode of polymerization with maleic anhydride and the copolymer was made by free radical polymerization (see Table III). When attempts were made to measure molecular weight by GPC using THF as a solvent on STYRAGEL columns, the polymer did not elute. Therefore, viscosity in acetone at 30"C was used as a measure of molecular size changes on irradiation. The changes on exposure... 

Chiral induction was observed in the cyclopolymerization of optically active dimethacrylate monomer 42 [88], Free-radical polymerization of 42 proceeds via a cycliza-tion mechanism, and the resulting polymer can be converted to PMMA. The PMMA exhibits optical activity ([ct]405 -4.3°) and the tacticity of the polymer (mm/mr/rr =12/49 / 39) is different from that of free-radical polymerization products of MMA. Free-radical polymerization of vinyl ethers with a chiral binaphthyl structure also involved chiral induction [91,92]. Optically active PMMA was also synthesized through the polymerization of methacrylic acid complexed with chitosan and conversion of the resulting polymer into methyl ester [93,94]. 

Vinyl ethers can also be formulated with acrylic and unsaturated polyesters containing maleate or fumarate functionality. Because of their ability to form alternating copolymers by a free-radical polymerization mechanism, such formulations can be cured using free-radical photoinitiators. With acrylic monomers and oligomers, a hybrid approach has been taken using both simultaneous cationic and free-radical initiation. A summary of these approaches can be found in Table 9. 

Iwatsuki and Yamashita (46, 48, 50, 52) have provided evidence for the participation of a charge transfer complex in the formation of alternating copolymers from the free radical copolymerization of p-dioxene or vinyl ethers with maleic anhydride. Terpolymerization of the monomer pairs which form alternating copolymers with a third monomer which had little interaction with either monomer of the pair, indicated that the polymerization was actually a copolymerization of the third monomer with the complex (45, 47, 51, 52). Similarly, copolymerization kinetics have been found to be applicable to the free radical polymerization of ternary mixtures of sulfur dioxide, an electron donor monomer, and an electron acceptor monomer (25, 44, 61, 88), as well as sulfur dioxide and two electron donor monomers (42, 80). 

Use of triphenylmethyl and cycloheptatrienyl cations as initiators for cationic polymerization provides a convenient method for estimating the absolute reactivity of free ions and ion pairs as propagating intermediates. Mechanisms for the polymerization of vinyl alkyl ethers, N-vinylcarbazole, and tetrahydrofuran, initiated by these reagents, are discussed in detail. Free ions are shown to be much more reactive than ion pairs in most cases, but for hydride abstraction from THF, triphenylmethyl cation is less reactive than its ion pair with hexachlorantimonate ion. Propagation rate coefficients (kP/) for free ion polymerization of isobutyl vinyl ether and N-vinylcarbazole have been determined in CH2Cl2, and for the latter monomer the value of kp is 10s times greater than that for the corresponding free radical polymerization. 

The major commercial fluoropolymers are made by homopolymerization of tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE),vinyhdene fluoride (VF2), and vinyl fluoride (VF), or by co-polymerization of these monomers with hexafluoropropylene (HFP), perfluoro(propyl vinyl ether) (PPVE), per-fluoro(methyl vinyl ether) (PMVE), or ethylene. The polymers are formed by free-radical polymerization in water or fluorinated solvents. 

Two simple a, P-unsaturated acylsilanes, l-trimethylsilyl-2-propen-l-one (III) and l-trimethylsilyl-2-methyl-2-propen-l-one (IV) were chosen for polymerization studies. The polymerization of the carbon analogues of these a,p-unsaturated acylsilanes, that is, 4,4-dimethyl-2-propen-3-one (vinyl tert-butyl ketone, V) and 2,4,4-trimethyl-2-propen-3-one (isopropenyl tert-hutyl ketone, VI) has been studied by Willson et al. 16, IT), These authors reported that whereas V readily polymerizes under free-radical-polymerization conditions, VI undergoes polymerization only under anionic-initiation conditions in the presence of a crown ether as a complexing reagent. On the basis of UV and NMR spectroscopic data, Willson et al. (i6, 17) ascribed the difference in polymerization behavior to the nonplanar, unconjugated structure of ketone VI brought about by steric hindrance caused by the methyl group at C-2. 

Application of these arguments to those data which are unequivocally free ion values does seem to work, however. For example the radiation induced polymerizations produce pre-exponential factors of 10 —10 1 mole sec , slightly larger than the accepted range for the free radical polymerization of styrene. Similarly the work on iV-vfnylcarbazole [29] produces Ap — 10 1 mole" sec", somewhat larger than the free radical value [106], and presumably affected by solvation contributions. The data for isobutyl vinyl ether [31] indicate a value for Ap of 10 —10 , consistent with the idea that free cations are the main contributors. 

Commercially, PFA is polymerized by free-radical polymerization mechanism usually in an aqueous media via addition polymerization of TFE and perfluoropropyl vinyl ether. The initiator for the polymerization is usually water-soluble peroxide, such as ammonium persulfate. Chain transfer agents such methanol, acetone and others are used to control the molecular weight of the resin. Generally, the polymerization regime resembles that used to produce PTFE by emulsion polymerization. Polymerization temperature and pressure usually range from 15 to 95°C and 0.5 to 3.5 MPa. 

Transition metal catalyzed, ring opening polymerization Dispersion, cationic polymerization Homogeneous/precipitation, cationic polymerization Homogeneous, free radical/cationic polymerization Precipitation, free radical polymerization Dispersion, free radical polymerization Norbornene polymer, polycarbonate Isobutylene polymer Vinyl ether polymer Amorphous fluoropolymers Vinyl polymer, semicrystalline fluoropolymers Polyvinyl acetate and ethylene vinyl acetate copol5Tner... 

In 1982, Crlvello and co-workers published a report on the UV Initiated cationic polymerization of vinyl ether monomers using onlum salt catalysts(14). Vinyl ethers are among the most reactive monomers which polymerize by a cationic mechanism. The radiation Induced cationic curing of vinyl ethers occurs much faster than the cationic curing of epoxy coatings. In fact, cure rates that are at least as fast as the free radical polymerization of acrylates can be achleved(8,14). A recent report Indicates that the cationic polymerization of vinyl ethers can occur even in the presence of certain polar functional groups(15). 

Some special reaction with a particularly designed route can be used to synthesize azo BCs. For instance, a series of poly(vinyl ether)-based azo LCBCs were synthesized by using living cationic polymerization and free-radical polymerization techniques (Serhatli and Serhatli, 1998). As shown in Scheme 12.8, 4.4 -azobis(4-cyano pentanol) (ACP) was used to couple quantitatively two well-defined polymers of LC living poly(vinyl ether), initiated by the methyl trifluor-omethane sulfonate/tetrahydrothiophene system. Then the ACP in the main chain was thermally decomposed to produce polymeric radical, which was used to initiate the polymerization of MMA or styrene to obtain PMMA-based or PS-based azo BCs (AB or ABA types). 

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