Methyl acrylate polymerization tacticity

The same type of addition—as shown by X-ray analysis—occurs in the cationic polymerization of alkenyl ethers R—CH=CH—OR and of 8-chlorovinyl ethers (395). However, NMR analysis showed the presence of some configurational disorder (396). The stereochemistry of acrylate polymerization, determined by the use of deuterated monomers, was found to be strongly dependent on the reaction environment and, in particular, on the solvation of the growing-chain-catalyst system at both the a and jS carbon atoms (390, 397-399). Non-solvated contact ion pairs such as those existing in the presence of lithium catalysts in toluene at low temperature, are responsible for the formation of threo isotactic sequences from cis monomers and, therefore, involve a trans addition in contrast, solvent separated ion pairs (fluorenyllithium in THF) give rise to a predominantly syndiotactic polymer. Finally, in mixed ether-hydrocarbon solvents where there are probably peripherally solvated ion pairs, a predominantly isotactic polymer with nonconstant stereochemistry in the jS position is obtained. It seems evident fiom this complexity of situations that the micro-tacticity of anionic poly(methyl methacrylate) cannot be interpreted by a simple Bernoulli distribution, as has already been discussed in Sect. III-A. 

Another pioneer in the Diels-Alder reactions of vinylpyrroles was Noland, who also developed the reactions of vinylindoles to yield carbazoles. Some examples of the former are shown in Scheme 2 (equations 1 and 2) [4-7], Jones and his colleagues were equally active in this cycloaddition chemistry of vinylpyrroles (equations 3 and 4) [8-12], These workers measured the rates of the reaction between 1-methyl-2-vinylpyrrole and seven dienophiles, with maleic anhydride being 4800 to 50,000 times more reactive than the other dienophiles (DMAD, maleonitrile, fumaronitrile, dimethyl maleate, methyl acrylate, and acrylonitrile) [8], In a clever tactic to thwart the formation of dihydroindoles, Jones used an excess of methyl propio-late to convert the initial adduct to a second Diels-Alder cycloadduct that subsequently loses ethene by a retro-Diels-Alder reaction to afford the dimethyl 1-methyl (phenyl)-4,7-dicarboxylates (equation 4). The reactions are concerted and were consistent with FMO calculations (HOMO[vinylpyrrole]-LUMO[alkene]). The yields are 54% to 81%, but attempts to dehydrogenate the tetrahydroindole products to indoles were unsuccessful. 2-Vinylpyrrole itself undergoes Michael additions and polymerization with these dienophiles. Domingo, Jones, and coworkers subsequently... 

One of the main challenges in the use of metal catalysts is the suppression of undesirable termination reactions, which, for reasons described below, tend to be more prevalent for acrylate systems. Most of the recent developments have thus been seen in the polymerization of methacrylate monomers, especially commercially significant methyl methacrylate (MMA), which is polymerized to the commodity material poly(methyl methacrylate) (PMMA), known by its trademark names Perspex , Plexiglass , andLucite (Scheme 23.1). Much of this chapter, therefore, focuses on tacticity control in the production of PMMA using coordination polymerization catalysts. Though little has been reported on stereocontrolled acrylate polymerization, the basic principles established... 

Table III lists calculated MA-centered triad fractions, F, Fg and Fq values used in this determination. Figure 6 shows plots of the left-hand parts (L.H.P.) of Eqs. 1-3 vs. (F ms+ SHM)/ SMS The plots are linear and their slopes and intercepts define a O g value of 0.47. This suggests that MS and SM placements in the copolymers have nearly equal probabilities of being coisotactic or cosyndio-tactic. Since poly(methyl acrylate)and poly(a-fluorostyrene) have been shown to have random stereosequence distributions when prepared by free radical initiated polymerizations, the copolymers may be considered to have atactic stereosequence structures.

As mentioned already in the polymerization of meth of-phenylacrylate a steri-cally random pdymer was obtained. However, the fraction of heterotactic triad in the polymer did not exceed 50 % under any polymerization conditions with BuLi Initiator (Table 10). On the other hand, methyl a-(p-bromophenyl)acrylate and methyl ce-(p-chlorophenyl)acrylate gave the polymers whose heterotactic contents were 59 and 61 %, respectively, in THF by BuLi at -78 (Table 10). The tacticity was determined by the C-NMR spectra of poly(2-phenylallyI acetate)s derived from the original polymers via pdy(2-phenylallyl alcohol)s. The bulkiness of the o-substituent seems to be important for the heterotactic propagation in these cases, as pointed out by Nozakuia et al. in the formation of heterotactic poty(vinyl alcohol) derived from poly(vinyl trimethylsilyl ether). However, method o-phenylacrylate formed a heterotactic pdymer whose heterotactic content was 66 %, by octylpotassium in THF (Table 10),... 

The first attempts to synthesize poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMAA) were the hydrolysis of poly(acid derivatives) such as esters, acylchlorides, nitriles, or amides. The hydrolysis has to be quantitative otherwise, one obtains a copolymer of acid and derivative [472]. On the other hand, hydrolysis in boiling alkaline solution can diminish the molar masses [473]. One possibility is to polymerize methyl methacrylic ester and to hydrolyze the resulting PMMA in acetic acid by the addition of a small amount of -toluenesulfonic acid as a catalyst. The solution is kept at 120 °C for 18 h and the methylacetate fonned is removed by distillation [474]. The degree of hydrolysis depends strongly on the tacticity of the original polymer. Syndiotactic PMMA is hydrolyzed slowly, but isotactic polymer is hydrolyzed very rapidly [475]. The polymers examined had molar masses up to 125,000. 

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