Radically polymerizable monomers

Low-molecular weight azo compounds have frequently been used in cationic polymerizations producing azo-containing polymers. Thus, the combination of ionically and radically polymerizable monomers into block copolymers has been achieved. Azo compounds were used in all steps of cationic polymerization without any loss of azo function as initiators, as monomers and, finally, as terminating agents. 

Moreover, block copolymers with two radically polymerizable monomers can be synthesized with a combination of thermal and photochemical polymerizations. Regarding their utilization in block copolymer synthesis, azocompounds with photoactive benzoin [103,109-111] and azyloximester groups [112] have been described. Two low-molecular weight azo benzoin initiators of the general formula (Scheme 32) were synthe-... 

Ceresa (80) demonstrated the possibility of synthetizing block copolymer by subjecting a starch emulsion with free radical polymerizable monomers to repeated freezing at — 200° C and subsequent thawing to room temperature. He used acrylonitrile owing to the case of separating the insoluble block copolymer fraction, see Table 22. 

Unsaturated tetrahydropyran derivatives have received only cursory attention in the literature as heterocyclic monomers. 2,3-Dihydropyran and several of its substituted derivatives apparently undergo cationic polymerization in a manner typical of vinyl ethers (72MI11103), while tetrahydropyranyl esters of methacrylic acid (123) are fairly typical free radically polymerizable monomers (Scheme 35) (74MI11105). The THP group was used in this study as a protecting group for the acid functionality, and it was found that deprotection of polymers (124) could be accomplished under extremely mild conditions. 

All acrylic structural adhesives consist basically of a solution or a mixture of polymers and unsaturated, low-molecular-weight, free-radical-polymerizable monomers with other materials added as needed for the particular intended use. In addition, some precursor of the polymerization initiator will be present. 

Ethenyl acetate (vinyl acetate, Vac) is polymerizable only by radical species. Until recently, the polymerization of any monomer was out of control because of the unavoidable occurrence of irreversible termination reactions. In 1995, Matyjaszewski and Sawamoto and coworkers reported that the deleterious impact of these irreversible reactions could be minimized by acting on the kinetics of both the propagation and the termination reactions. Indeed, a decrease in the instantaneous concentration of radicals ([M ]) decreases much more importantly the termination rate (proportional to [M ] ) than the propagation rate (proportional to [M ]). A scheme proposed consists in converting reversibly radicals into unstable covalent species ( dormant species). The last radically polymerizable monomer to fall under this type of kinetic control was vinyl acetate. Indeed, very recently Debuigne and coworkers proposed to polymerize Vac by 2.2 -azobis-(4-methoxy-2,4-dimethyl)valeronitrile (V-70) in the presence of cobalt(II) acetyl acetonate [Co(acac)2]. Under these conditions, a linear relationship is observed between... 

Controlled free-radical polymerization (CFRP) has been used successfully to produce block, graft, and other controlled architecture copolymers within the last decade for a variety of free radically polymerizable monomers. The main techniques include reversible addition fragmentation and transfer (RAFT) polymerization, stable free-radical polymerization (SFRP) mediated by nitroxide/alkoxyamine based radicals, atom transfer radical polymerization (ATRP), diphenyl ethylene (DPE) mediated polymerization, and novel precipitation/emulsion polymerization based methods like free-radical retrograde precipitation polymerization (FRRPP). ... 

The larger portion of the current literature on photochemistry of onium salts deals either with fundamental mechanisms of onium salt photodecomposition (see above) or application of this chemistry to generation of catalysts for cationic polymerizations (see below). Application to the photoinitiation of radically polymerizable monomer systems developed in parallel with applications to cationic polymerizations [17,96, 111]. 

Coating compositions for this process can contain cyclic ethers, vinyl ether monomers, organosilicone monomers, and a wide variety of mono-, di-, and polyepoxy functional materials. Further modifications to this process include the addition of free radical polymerizable monomers in combination with the cationic polymerizable monomers so that both curing processes may take place at the same time. The photoinitiator systems that generate acid catalyst intermediates also generate free radical intermediates or can be combined with other photosensitizer materials such that both... 

Emulsion polymerization requires free-radical polymerizable monomers which form the structure of the polymer. The major monomers used in emulsion polymerization include butadiene, styrene, acrylonitrile, acrylate ester and methacrylate ester monomers, vinyl acetate, acrylic acid and methacrylic acid, and vinyl chloride. All these monomers have a different stmcture and, chemical and physical properties which can be considerable influence on the course of emulsion polymerization. The first classification of emulsion polymerization process is done with respect to the nature of monomers studied up to that time. This classification is based on data for the different solubilities of monomers in water and for the different initial rates of polymerization caused by the monomer solubilities in water. According to this classification, monomers are divided into three groups. The first group includes monomers which have good solubility in water such as acrylonitrile (solubility in water 8%). The second group includes monomers having 1-3 % solubility in water (methyl methacrylate and other acrylates). The third group includes monomers practically insoluble in water (butadiene, isoprene, styrene, vinyl chloride, etc.) [12]. 

In addition, the photocurable compositions contain radically polymerizable monomers, such as various acrylics (38). Thus, the photopolymerization initiator will decompose in radicals. 

Controlled/living radical polymerization (CRP) has been successfully applied to many different radically polymerizable monomers. A recent book has summarized this very rapidly developing field, at least till 2001 (87). Because of limited space available, only the most important issues will be discussed here. 

Dental Composite Restoratives. Polymeric restoratives have three major components an organic resin matrix, an inorganic filler modified with a coupling agent, and a suitable polymerization initiator system. The formulation used to produce the organic matrix, or continuous phase, is made up of free-radical polymerizable monomers. The monomer mostly used in the formulations for both anterior and posterior resins is BisGMA (Fig. 7), or alternatively formulated with... 

Most dental sealants are resinous materials derived from free-radical polymerizable monomers, but GI dental cements (discussed earher) also have some use as sealants. Sealing with resinous materials or GIs is part of modem preventive technology, where the sealants used for this piupose are called preventive dental sealants (PDS). Dental caries that occiu- aroimd restorations are called secondary caries. Sealing the microspaces with adhesive resinous materials is effective in controlling secondary caries here we call these adhesive materials the restorative dental sealants. 

Pit and Fissur Sealants. Resin sealants consist of a free-radical polymerizable monomer mixture, having a viscosity low enough to penetrate easily into narrow pits and fissures, capable of being cured to a hard and durable sealing material. BisGMA, urethane dimethacrylate, and other methacrylates are very popular as monomers for resin sealants, along with other monomers, to lower... 

Most of the work reported in the open literature has used Schlenk techniques for the polymerizations but this reflects a desire to obtain reproducible kinetics and the use of monomers stored long term under normal laboratory conditions, rather than indicating a need for excessive purification of commercially available materials. It is expected that in commercial scale operations use of standard industrially available radically polymerizable monomers would not require any pretreatment of the reaction medium prior to initiation of the controlled polymerization. 

In contrast, it is well known that styrene is a useful radical polymerizable monomer, and diacyl peroxide such as benzoyl peroxide and alkanoyl peroxide are widely used as conventional radical initiators. Since the interaction between theLUMO of diacyl peroxide (e.g., butyryl peroxide) and the HOMO of styrene become extremely weak compared to that of perfluorobutyryl peroxide (see Figure 4.3), the interaction of the SOMO of acyloxy radicals, which produce in the radical decomposition of diacyl peroxides, should interact with the HOMO of styrene to afford the radical polymerization of styrene. In contrast, styrene reacted with fluoroalkanoyl peroxides to afford not the radical polymerizable products but 1 1 adducts [PhCH(OCORp)CH2Rp] via... 

Ceresa [114] demonstrated the possibility of synthesizing block copolymer by subjecting a starch emulsion with free radical polymerizable monomers to repeated freezing at — 200°C and subsequent thawing to room temperature. He used acrylonitrile, owing to the ease of separating the insoluble block copolymer fraction (see Table 5.22). Simionescu and co-workers applied the same technique to cellulose and acrylonitrile solutions [167], and Fujii and co-workers to solutions of starch and to the vinyl polymers, for example, polystyrene, poly(methyl methacrylate), poly(vinyl acetate), and poly(acrylic acid) [144]. 

Among all the free-radical polymerizable monomers, highly electron-deficient MA is one of the most reactive in copolymerization with electron-rich... 

Cyclic disulfides are also radically polymerizable monomers. Although they do not have a C-C double bond for accepting radicals, the homolysis of the S-S bond permits the formation of S radicals (Scheme 19). The resulting biradical undergoes polyaddition to afford polydisulfide. 

Most of the SPS-t-B polymer was suspended in benzene and was subjected to the oxidation reaction by oxygen in the presence of free radical polymerizable monomers, that is, MMA and n-butyl methacrylate (BMA). As illustrated in Scheme 19.2, the SPS-t-B was selectively oxidized and transformed to a stable polymeric radical for the polymerization of MMA and BMA. The resulting reaction mixture was carefully fractionated by Soxhlet extraction using boiling THF to remove any PMMA or poly(butyl methacrylate) (PBMA) homopolymers. In most cases, only a very small amount (about 10%) of homopolymer was present, which may have been initiated by the radical in a bicyclic ring... 

The production of polymer dispersions by emulsion polymerization requires deionized water, free-radical-polymerizable monomers, emulsifiers and/or protective colloids and initiators. Further auxiliaries, such as chain transfer agents, buffers, acids, bases, anti-aging agents, biocides, etc., can be used. 

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