Methyl methacrylate, deuterated polymerization

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. 

The polymerization mechanism is based on the insertion of a coordinated monomer into a covalent Mg C bond, as in methyl methacrylate. However, different modes of monomer double-bound opening cis, trans, and the 1 1 cis trans mixture) can occur, depending on the polymerization conditions and on the monomer [59]. Several mechanistic studies were performed using partially deuterated monomers, such as methyl a,) ,i/2-acrylate E and Z isomers) [60], or (Z)-ethyl a-methyl-)5-Ji-acrylate [61]. 

Figure 3. NMR spectra of poly(methyl methacrylate-co-methacrylic acid) obtained by (1) plasma-initiated polymerization and (2) thermal polymerization in 0.2% deuterated pyridine.

Table 11. Polymerization rate and elementary rate constants in the free radical polymerization of methyl methacrylate and vinyl acetate in benzene and deuterated benzene at 30 °C17 ...

H NMR spectra were recorded on Briiker ACP 400 or DPX 400 spectrometers using deuterated solvents obtained from CEA or Aldrich. Polymerization kinetics, followed by NMR, were recorded using the Briiker built-in kinetics software. Molecular mass analyses were carried out by gel permeation (size exclusion) chromatography on a Polymer Laboratories system. THF was the eluent at 1.0 mL min with a PL-gel 5 jim (50 X 7.5 mm) guard column, two PL-gel 5 pm (300 x 7.5 mm) mixed-C columns with a refractive index detector. Samples were compared against narrow standards of poly(methyl methacrylate), A/p = 200 to 1.577 x 10 g mol , obtained from Polymer Laboratories, except for methyl methacrylate dimer, trimer, and tetramer which were prepared by catalytic chain transfer polymerization at the University of Warwick. 

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