Polymerizations of Acrylic and Methacrylic Esters

Polymerizations of acrylic and methacrylic esters are highly exothermic (e.g., A//polymeriZation of ethyl acrylate is 13.8 kcal/mol [2]). Generally, the heats of polymerization of acrylates are greater than those of methacrylates. 

The experimental difficulties involved with the controlled use of Grignard initiators were recognized early on. The exact nature of the species present in the reaction media is often unclear. In many instances, it is difficult to obtain reproducible kinetic data. The polymerizations are very sensitive to the presence of small concentrations of impurities. Finally, the polymerization of acrylic and methacrylic esters is further complicated by side reactions involving the carbonyl group. Consequently, it is not uncommon for two workers in the same laboratory to prepare different products using the same procedure [9,10]. 

Methyl methacrylate polymerizations, initiated by oiganomagnesium compounds, also yield abnormal products. Here, the active centers are unusually persistent and stabile. In addition, the a-carbon atoms of the monomers were found to assume tetrahedral configurations.This suggests that the active centers contain covalent magnesium carbon bonds. Also, gel permeation chromatography curves of the products show that more than one active center operates independently. A pseudoanionic mechanism was therefore postulated for polymerizations of acrylic and methacrylic esters by Grignard reagents. 

Coordinated anionic polymerizations of methyl methacrylate with diethyliron-bipyridyl complex in nonpolar solvents like benzene or toluene yield stereoblock polymers. In polar solvents, however, like dimethylformamide or acetonitrile, the products are rich in isotactic placement. There are many reports in the literature on polymerizations of acrylic and methacrylic esters with Ziegler-Natta catalysts. " The molecular weights of the products, the microstructures, and the rates of the polymerizations depend upon the metal alkyl and the transition metal salt used. The ratios of the catalyst components to each other are also important. ... 

Discuss the chemistry of free-radical polymerization of acrylic and methacrylic esters. 

Free-radical polymerizations of acrylic and methacrylic esters in the presence of the above backbones result in high yield of graft copolymers. ... 

Lithium ester enolates are extremely important in polymer chemistry as initiators and active centers of the anionic polymerization of acrylic and methacrylic monomers in polar solvents. Thus, HF-SCF studies, comparable to those mentioned above, were undertaken on monomeric methyl isobutyrate (MIB) enolate210,211. The overall conclusions on the aggregation and solvation trends are exactly the same, the bent rj3-0,C mode being preferred over the rj1-O planar one by ca 3.3 kcalmol-1. While the dimeric MIB enolate solvated by four molecules of THF was found to be the enthalpically most stable aggregate, the prismatic S6 unsolvated MIB hexamer was computed as the preferred structure in non-polar solvents (Scheme 55)212. In the latter case, the supplementary oxygen of the ester acting as a side-chain ligand for the lithium seems to explain this remarkable stability. 

Ester enolates can be used as molecular models of the active centers in the anionic polymerization of acrylates and methacrylates. Thus, knowledge of the structure of these models in polar and nonpolar solvents is important for the understanding of the polymerization processes. Earlier C and Li NMR smdies by Wang and coworkers of methyl... 

Prepared by the polymerization of acrylic and methacrylic acids or their esters, e.g. butyl ester or dimethylaminoethyl ester. 

Flame retardants are usually halogen-containing materials. 2,4,6-Tribromophenyl, pentabromopheuyl, and 2,3-dibromopropyl derivatives of acrylate and methacrylate esters can be readily polymerized or copolymerized with styrene, methyl methacrylate, and acrylonitrile to produce polymers with improved flame retardancy (Equation 5.20). 

GTP of acrylate and methacrylate esters using group 4 metallocene initiators dates back to the early work of Hertler and Farnham at DuPont where neutral enolate complexes of Zr and Ti were found to initiate polymerization of It is unclear that this early report actually involves metal-mediated GTP, since subsequent work has... 

These thermoplastic resins are obtained by the polymerization or copolymerization of acrylic and methacrylic esters. Acrylic resins may be combined with melamine, epoxy, alkyd, acrylamide, etc., to produce systems that bake to a film with excellent resistance to water, acids, alkalies, chemicals, and other corrosives. Acrylic resins are used in coatings for all types of appliances, cans, and automotive parts and for all types of metals. 

The furfuryl esters of acrylic and methacrylic acid polymerize via a free-radical mechanism without apparent retardation problems arising from the presence of the furan ring. Early reports on these systems described hard insoluble polymers formed in bulk polymerizations and the cross-linking ability of as little as 2% of furfuryl acrylate in the solution polymerization of methylacrylate121. ... 

For less polar monomers, the most extensively studied homopolymerizations are vinyl esters (e.g. VAc), acrylate and methacrylate esters and S. Most of these studies have focused wholly on the polymerization kinetics and only a few have examined the mierostructures of the polymers formed. Most of the early rate data in this area should be treated with caution because of the difficulties associated in separating effects of solvent on p, k and initiation rate and efficiency. 

Close to 2 billion pounds of polymeric products based on acrylic and methacrylic esters are produced annually in the United States, about evenly divided between acrylates and methacrylates. A substantial fraction of the methacrylate products are copolymers. Most of the acrylate products are copolymers. The copolymers contain various combinations of acrylate and/or methacrylate monomers, including combinations of ester and acid monomers. Methyl methacrylate (MMA) is by far the most important methacrylate ester monomer, accounting for 90% of the volume of methacrylic ester monomers. Ethyl and n-butyl acrylates account for about 80% of the total volume of acrylate ester monomers. 

Alkyl derivatives of the alkaline-earth metals have also been used to initiate anionic polymerization. Organomagnesium compounds are considerably less active than organolithiums, as a result of the much less polarized metal-carbon bond. They can only initiate polymerization of monomers more reactive than styrene and 1,3-dienes, such as 2- and 4-vinylpyridines, and acrylic and methacrylic esters. Organostrontium and organobarium compounds, possessing more polar metal-carbon bonds, are able to polymerize styrene and 1,3-dienes as well as the more reactive monomers. 

Polymerizations of vinyl ketones such as methyl vinyl ketone are also complicated by nucleophilic attack of the initiator and propagating carbanion at the carbonyl group although few details have been established [Dotcheva and Tsvetanov, 1985 Hrdlovic et al., 1979 Nasrallah and Baylouzian, 1977]. Nucleophilic attack in these polymers results in addition, while that at the ester carbonyl of acrylates and methacrylates yields substitution. The major side reaction is an intramolecular aldol-type condensation. Abstraction of an a-hydrogen from a methyl group of the polymer by either initiator or propagating carbanion yields an a-carbanion that attacks the carbonyl group of the adjacent repeat unit. 

Acrylic Polymers. Although considerable information on the plasticization of acrylic resins is scattered throughout journal and patent literature, the subject is complicated by the fact that acrylic resins constitute a large family of polymers rather than a single polymeric species. An infinite variation in physical properties may be obtained through copolymerization of two or more acrylic monomers selected from the available esters of acrylic and methacrylic acid (30) (see Acrylic esterpolya rs Methacrylic acid and derivatives). 

Optically active acrylic, chloro-acrylic and methacrylic esters of sec. butyl alcohol, 2-methyl-butyl alcohol, 1.3-dimethyl-butyl alcohol, 1-methyl-benzyl alcohol, bomeol and menthol have been polymerized mostly by radical mechanism (Tables 16, 17, 18). 

The methyl, ethyl, and butyl esters of acrylic and methacrylic acids are polymerized under the influence of heat, light, and peroxides. The polymerization reaction is exothermic and may be carried out in bulk for castings, or by emulsion, or in solution. The molecular weight decreases as the temperature and catalyst concentration are increased. The polymers are noncrystalline and thus very clear. Such resins are widely used because of their clarity, brilliance, ease of forming, and light weight. They have excellent optical properties and are used for camera, instrument, and spectacle lenses. 

The USPNF 23 describes methacrylic acid copolymer as a fully polymerized copolymer of methacrylic acid and an acrylic or methacrylic ester. Three types of copolymers, namely Type A, Type B, and Type C, are defined in the monograph. They vary in their methacrylic acid content and solution viscosity. Type C may contain suitable surface-active agents. Two additional polymers, Type A (Eudragit RE) and Type B (Eudragit RS), also referred to as ammonio methacrylate copolymers, consisting of fully polymerized copolymers of acrylic and methacrylic acid esters with a low content of quaternary ammonium groups, are also described in the USPNF 23. A further monograph for an aqueous dispersion of Type C methacrylic acid copolymer is also defined see Section 9. 

The acrylate resinoids are esters of acrylic and methacrylic acid. Methyl methacrylate, CH2 = C(CH3)COOH3, is a liquid ester which polymerizes to a transparent resin of high tensile strength. The polymerization is brought about by catalysts such as peroxides and heat. The polymerization is assumed to take place by addition to form linear molecules ... 

---