Methacrylates polar solvents

Although the low temperature polymerization of methyl methacrylate in polar solvents such as THF was believed to proceed without termination, a more exhaustive investigation55) revealed some slow termination processes resulting from the formation of a, not yet specified agent, supposedly produced in the initiation step. Since the nature of the terminating agent is still unknown it is premature to discuss here the proposed schemes of this termination process. 

Methyl and ethyl methacrylate polymers, although extensively used in Industry, do not possess the solubility characteristics (low polarity) that would make them appropriate for use over traditional oil paintings and other organic-based museum objects that might be sensitive to polar solvents such as alcohols, ketones and esters. Poly(n-butyl methacrylate), offered as an artists varnish in the late 1930 s, did not become widely accepted in the war-disrupted decade that followed. Accordingly, early in 1951, our laboratory began a detailed study of the higher alkyl methacrylate polymers for potential use as picture varnishes (1). 

The transition state of this reaction has a polar structure and therefore this reaction occurs more rapidly in polar solvents (compare rate constants in chlorobenzene and /V,/V-dimethylforma-mide for reactions of styrene and butyl methacrylate in Table 4.4). The effect of multidipole interaction was observed for reactions of polyatomic esters [47 49],... 

A bulky methacrylate, triphenylmethyl methacrylate (TrMA), is a unique monomer which gives an almost 100% isotactic polymer in anionic polymerization with n-butyllithium both in nonpolar and polar solvents. Moreover, even free-radical polymerization affords a highly isotactic polymer from this monomer.23 The isotactic specificity of TrMA polymerization is ascribed to the helical formation of the main chain. When TrMA is polymerized in toluene at —78°C... 

For example, a proline-based chiral ligand was attached to a vinyl-substituted monomer (Fig. 42.15) by reacting vinylbenzoyl chloride with the amine functionality of the ligand [106]. As mentioned previously, the apolar Merrifield resin as a support is not swollen in polar solvents. Hence, in order to match the polarity of the resin with that of the typically used substrates in enantioselective hydrogenation, the functionalized monomer was copolymerized with polar units of methacrylic acid 2-hydroxyethyl ester. 

Ganushchak et al. (1972, 1984) proposed to perform the Meerwein chloroarylation of ethylenic compounds using the preliminarily prepared aryldiazonium tetrachlorocuprates. They found that methyl, ethyl, butyl acrylate, methyl methacrylate, and acrylonitrile in the polar solvent reacted with tetrachlorocuprate. Chloroarylation products were obtained with better yields than when using the traditional Meerwein reaction conditions. 

The need for solvation in anionic polymerization manifests itself in some instances by other deviations from the normal reaction rate expressions. Thus the butyllithium polymerization of methyl methacrylate in toluene at — 60°C shows a second-order dependence of Rp on monomer concentration [L Abbe and Smets, 1967]. In the nonpolar toulene, monomer is involved in solvating the propagating species [Busson and Van Beylen, 1978]. When polymerization is carried out in the mixed solvent dioxane-toluene (a more polar solvent than toluene), the normal first-order dependence of Rp on [M] is observed. The lithium diethylamide, LiN(C2H5)2, polymerization of styrene at 25°C in THF-benzene similarly shows an increased order of dependence of Rp on [M] as the amount of tetrahydrofuran is decreased [Hurley and Tait, 1976]. 

The stereoselective polymerization of various acrylates and methacrylates has been studied using initiators such as atkyllithium [Bywater, 1989 Pasquon et al., 1989 Quirk, 1995, 2002]. Table 8-12 illustrates the effects of counterion, solvent, and temperature on the stereochemistry of the anionic polymerization of methyl methacrylate (MMA). In polar solvents (pyridine and THF versus toluene), the counterion is removed from the vicinity of the propagating center and does not exert an influence on entry of the next monomer unit. The tendency is toward syndiotactic placement via chain end control. The extent of syndiotacticity... 

Many radical polymerization systems were examined hy Challa at a/. A number of papers were devoted to polymerization of methyl methacrylate, MM, in the presence of poly(methyl methacrylate). The role of tacticity of template was stressed. Isotactic PMM forms stereocomplex with syndiotactic PMM. Polymerizations of MM in the presence of isotactic PMM were carried out and the product (template + daughter polymer) was analyzed by NMR. When MM is polymerized in the polar solvent in the presence... 

PAN has a solubility parameter of about 11 H and is soluble only in polar solvents, such as dimethylacetamide (DMAc). Because of PAN s high polarity, its fibers are difficult to dye. This difficulty has been overcome by producing copolymers of acrylonitrile with small amounts (4%) of more-hydrophilic monomers, such as jV-vinyl-2-pyrrolidone (left), methacrylic acid (center), or 2-vinylpyridine (right), which have the following structures ... 

Present View of the Anionic Polymerization of Methyl Methacrylate and Related Esters in Polar Solvents... 

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. 

In Sect. 1.3, photoinitiation by means of donor—acceptor complexes was described. In some cases, these complexes may play an important role even without the contribution of light energy. In the presence of aliphatic amines and CCI4, methyl methacrylate is polymerized at temperatures 300 K. In polar solvents (7V,7V-dimethy formamide, dimethylsulphoxide, chloroform), interaction of aliphatic amines as donors with methyl methacrylate as acceptor produces complexes [91] which yield initiating radicals with CC14 [92]... 

The radiation degradation of poly(2-octyne) occurs only in the presence of oxygen. Its degradation products contain carbonyl and hydroxyl groups, and so dissolve in polar solvents (e.g., acetone). Such solubility change is essential to resist materials. The Gs value (number of main-chain scission per 100 eV of absorbed dose) of poly(2-octyne) is ca. 12. It is noteworthy that this value is higher than that of poly-(methyl methacrylate) (Gs ca. 2)118) which is being used as electron-beam resists. 

The template, the functional monomers and the cross-linking monomers are dissolved in a non-polar solvent. The functional monomers and the template form complexes and the strength of these are reflected in the selectivity of the imprinted polymer. The choice of functional monomer is based on the template structure. Functional monomers are chosen for their ability to interact non-covalently with the template molecule. The most frequently used functional monomer so far is methacrylic acid (MAA). Also vinylpyridines have been frequently used. As cross-linking monomers, ethyleneglycol dimethacrylate (EDMA) or trimethylolpropane trimethacrylate (TRIM) are widely used. Several other types of functional and cross-linking monomers have been used in molecular imprinting experiments using the non-covalent approach. The choice of monomers is of course important to the... 

Table 9. Relaxation times (ns) for comb-like polymers in polar solvents at 25 °C (rjredO-38 cP) PMA poly(aIkyl methacrylates), n is the number of C-atoms in the alkyl chain...

In polar solvents such as THF anionic polymerization of methyl methacrylate at low temperature is classically assumed to proceed via free anions and the products are syndiotactic. Indeed the structure of such polymers has been confirmed recently and tactic addition shown to conform to Bernoullian... 

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