Acrylates, alkyl polymerization

The activity of transition metal allyl compounds for the polymerization of vinyl monomers has been studied by Ballard, Janes, and Medinger (10) and their results are summarized in Table II. Monomers that polymerize readily with anionic initiators, such as sodium or lithium alkyls, polymerize vigorously with allyl compounds typical of these are acrylonitrile, methyl methacrylate, and the diene isoprene. Vinyl acetate, vinyl chloride, ethyl acrylate, and allylic monomers do not respond to these initiators under the conditions given in Table II. 

Ferguson, R, Sherrington, D.C. and Gough, A. (1993) Preparation, characterization and use in emulsion polymerization of acrylated alkyl ethoxylate surface-active monomers. Polymer, 34, 3281-92. 

It is not necessary to carry out synthesis, if the triggering photochromic compound has good affinity to the polymer matrix. A mixture of the polyacrylate with BMAB which exhibits an excellent function as trigger is equally photoresponsive. While the monomer model compound (i.e. the acrylate before polymerization) does not provide a liquid crystalline phase, the polymer shows a clear nematic - isotropic transition at ca. 61 °C and the glass transition temperature at 24 °C as shown in Fig. 4. Tj j depends very much on the length of the alkyl spacer. In comparison with the... 

A dramatic development in the anionic polymerization of acrylate and methacrylate monomers was the discovery that by addition of lithium chloride it was possible to effect the controlled polymerization of f-butyl acrylate (86). Thus, using oligomeric (o -methylstyryl)lithium as initiator in THF at —78°C, the molecular weight distribution (M /Mn) of the polymer was 3.61 in the absence of lithium chloride but 1.2 in the presence of lithium chloride ([LiCl]/[RLi] = 5). In the presence of 10 equiv of LiCl, f-butyl acrylate was polymerized with 100% conversion and 95% initiator efficiency to provide a polymer with a quite narrow molecular weight distribution (My,/Mn = 1.05). More controlled anionic polymerizations of alkyl methacrylates are also obtained in the presence of lithium chloride. Other additives, which promote controlled pol5unerization of acylates and methacrylates, include lithium f-butoxide, lithium (2-methoxy)ethoxide, and crown ethers (47,48). The addition of lithium chloride also promotes the controlled anionic polymerization of 2-vinylpyridine. 

The amide group is readily hydrolyzed to acrylic acid, and this reaction is kinetically faster in base than in acid solutions (5,32,33). However, hydrolysis of N-alkyl derivatives proceeds at slower rates. The presence of an electron-with-drawing group on nitrogen not only facilitates hydrolysis but also affects the polymerization behavior of these derivatives (34,35). With concentrated sulfuric acid, acrylamide forms acrylamide sulfate salt, the intermediate of the former sulfuric acid process for producing acrylamide commercially. Further reaction of the salt with alcohols produces acrylate esters (5). In strongly alkaline anhydrous solutions a potassium salt can be formed by reaction with potassium / /-butoxide in tert-huty alcohol at room temperature (36). 

The earliest study describing vulcanised polymers of esters of acryUc acid was carried out in Germany by Rohm (2) before World War I. The first commercial acryUc elastomers were produced in the United States in the 1940s (3—5). They were homopolymers and copolymers of ethyl acrylate and other alkyl acrylates, with a preference for poly(ethyl acrylate) [9003-32-17, due to its superior balance of properties. The main drawback of these products was the vulcanisation. The fully saturated chemical stmcture of the polymeric backbone in fact is inactive toward the classical accelerators and curing systems. As a consequence they requited the use of aggressive and not versatile compounds such as strong bases, eg, sodium metasiUcate pentahydrate. To overcome this limitation, monomers containing a reactive moiety were incorporated in the polymer backbone by copolymerisation with the usual alkyl acrylates. 

Because they are acrylic monomers, alkyl cyanoacrylate esters still require the addition of radical polymerization inhibitors, such as hydroquinone or hindered phenols, to prevent radically induced polymerization over time [3j. Since basic initiation of alkyl cyanoacrylate monomers is the predominant polymerization mechanism, large quantities of free radical inhibitors can be added, with little or no effect on adhesive performance. 

Alkyl cyanoacrylate monomers have been copolymerized with a variety of monomers, both by radical and anionic initiation. The radical-initiated copolymerization with acrylic monomers was performed with a sufficient amount of an acid stabilizer present to suppress polymerization by anionic means [19]. This investigation has been covered extensively elsewhere. 

An example of this improvement in toughness can be demonstrated by the addition of Vamac B-124, an ethylene/methyl acrylate copolymer from DuPont, to ethyl cyanoacrylate [24-26]. Three model instant adhesive formulations, a control without any polymeric additive (A), a formulation with poly(methyl methacrylate) (PMMA) (B), and a formulation with Vamac B-124 (C), are shown in Table 4. The formulation with PMMA, a thermoplastic which is added to modify viscosity, was included to determine if the addition of any polymer, not only rubbers, could improve the toughness properties of an alkyl cyanoacrylate instant adhesive. To demonstrate an improvement in toughness, the three formulations were tested for impact strength, 180° peel strength, and lapshear adhesive strength on steel specimens, before and after thermal exposure at 121°C. 

The free radical initiators are more suitable for the monomers having electron-withdrawing substituents directed to the ethylene nucleus. The monomers having electron-supplying groups can be polymerized better with the ionic initiators. The water solubility of the monomer is another important consideration. Highly water-soluble (relatively polar) monomers are not suitable for the emulsion polymerization process since most of the monomer polymerizes within the continuous medium, The detailed emulsion polymerization procedures for various monomers, including styrene [59-64], butadiene [61,63,64], vinyl acetate [62,64], vinyl chloride [62,64,65], alkyl acrylates [61-63,65], alkyl methacrylates [62,64], chloroprene [63], and isoprene [61,63] are available in the literature. 

Thiols react more rapidly with nucleophilic radicals than with electrophilic radicals. They have very large Ctr with S and VAc, but near ideal transfer constants (C - 1.0) with acrylic monomers (Table 6.2). Aromatic thiols have higher C,r than aliphatic thiols but also give more retardation. This is a consequence of the poor reinitiation efficiency shown by the phenylthiyl radical. The substitution pattern of the alkanethiol appears to have only a small (<2-fokl) effect on the transfer constant. Studies on the reactions of small alkyl radicals with thiols indicate that the rate of the transfer reaction is accelerated in polar solvents and, in particular, water.5 Similar trends arc observed for transfer to 1 in S polymerization with Clr = 1.4 in benzene 3.6 in CUT and 6.1 in 5% aqueous CifiCN.1 In copolymerizations, the thiyl radicals react preferentially with electron-rich monomers (Section 3.4.3.2). 

Chain transfer to polymer is reported as a major complication and is thought to be unavoidable in the polymerization of alkyl acrylates.200 202 The mechanism is believed to involve abstraction of a tertiary backbone hydrogen (Scheme 6.32). It has been proposed that this process and the consequent formation of branches may contribute to the early onset of the gel or Norrish-Trommsdorff effect in the polymerization of these monomers. At high temperatures the radicals formed may undergo fragmentation. 

The processes described in this section should be contrasted with RAFT polymerization (Section 9.5.3), which can involve the use of similar thioearbonylthio compounds. A. A -dialkyl dithiocarbamates have very low transfer constants in polymerizations of S and (mctb)acrylatcs and arc not effective in RAFT polymerization of these monomers. However, /V,A -dialkyl dithiocarbamates have been successfully used in RAFT polymerization of VAc. Certain O-alkyl xanthates have been successfully used to control RAFT polymerizations of VAc, acrylates and S. The failure of the earlier experiments using these reagents and monomers to provide narrow molecular weight distributions by a RAFT mechanism can he attributed to the use of non-ideal reaction conditions and reagent choice. A two part photo-initiator system comprising a mixture of a benzyl dithiocarhamate and a dithiuram disulfide has also been described and provides better control (narrower molecular weight distributions).43... 

K. Takahashi et al, The Polymerization and Copolymerization of Nitro Alkyl Acrylates and Nitroalkyl Methacrylates , JApplPolymerSci... 

Polymerization employing Co complexes as catalysts or else polymers incorporating functionality that includes Co ions represent aspects of polymerization reactions of interest here. Cobalt-mediated free-radical polymerization of acrylic monomers has been reviewed.55 Co11 porphyrins act as traps for dialkylcyanomethyl radicals.1098 Alkyl complexes of Co(TMesP)... 

The lanthanocene initiators also polymerize EtMA, PrMA and BuMA in a well-controlled manner, although syndiotacticity decreases as the bulk of alkyl substituent increases. Reactivity also decreases in the order MMA EtMA > PrMA > BuMA. Chain transfer to provide shorter polymer chains is accomplished by addition of ketones and thiols.460 The alkyl complexes (190) and (191) also rapidly polymerize acrylate monomers at 0°C.461,462 Both initiators deliver monodisperse poly(acrylic esters) (Mw/Mn 1.07). An enolate is again believed to be the active propagating species since the model complex (195) was also shown to initiate the polymerization of MA. 

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