C-13 NMR Spectra and Spin-Lattice Relaxation Times of Poly(alkyl vinyl ether)s

Abstract

13 C NMR spectra of isotactic-rich poly(alkyl vinyl ether)s were measured in toluene-d8 at ll0°C, with some improvements on peak separation. The 13 C spin-lattice relaxation times (T1 's) for syndiotactic sequences were consistently longer than those for isotactic ones, in contrast to the case of polypropylene and polymethacrylates, in which the T1 's for isotactic sequences are longer than those for syndiotactic sequences. The nuclear Overhauser enhancement factors for the polymers of methyl and t-butyl vinyl ethers were close to the theoretical maximum. These results indicate higher flexibility of the syndiotactic sequences in poly(alkyl vinyl ether)s.

Polymerization of vinyl ethers with transition‐metal catalysts: An examination of the stereoregularity of the formed polymers

“…1). 18 We did not employ the data of the triad tacticity determined from the pendant methylene carbon signals [O C H 2 CH(CH 3 ) 2 ] around 76–77 ppm or from the methine carbon signals [OCH 2 C H(CH 3 ) 2 ] around 29–30 ppm17 because the split due to steric structures was insufficient. The isotactic dyad ( m ) sequence of the PIBVEs reported in Table 1 ranged from 63 to 68%.…”

“…The triad tacticity of PTBVE was determined from the 13 C NMR integration ratio of the signals of the quaternary carbon atom at the polymer side chain around 73–74 ppm according to the literature (Fig. 2)17 and was converted into dyad data by the following equations, as summarized in Table 1:18 The dyad m sequence of PTBVE ranged from 46 to 56% (triad mm = 21–28%) in the presence of MAO (runs 9–14), which was certainly lower than that of PIBVE obtained under the same conditions (runs 2–7). This trend implies that the pendant group affects the tacticity.…”

“…It was separated from the supernatant by filtration and dried under reduced pressure. The dyad tacticity of PIBVE was determined from the 13 C NMR peak ratio of the methylene carbon atom on the polymer main chain, and the triad tacticity of PTBVE was determined from the 13 C NMR peak ratio of the quaternary carbon atom on the polymer side chain according to the literature 17…”

Vinyl Ether Monomers and Polymers

“…A variety of soluble initiators can produce isotactic polymers, but there are some initiators, eg, SnCl 4 , that produce atactic polymers under isotactic conditions (26). The nature of the pendant group can influence tacticity; for example, large, bulky groups are somewhat sensitive to solvent polarity and can promote more crystallinity (14,27).…”

Living cationic polymerization of vinyl ethers with carboxylic acid/tin tetrahalide initiating systems. II. Effects of steric hindrance of carboxylate counteranions

“…17 were meso-rich and very similar to each other irrespective of the initiators used (meso ϭ 66 -69%). Therefore, the steric crowding of the carboxylate anions did not change the interaction mode of the counteranion with the growing carbocation and the incoming monomer.…”