Epimerization and NMR Spectra of Poly(2-vinylpyridine)

Abstract

ABSTRACT:Isotactic poly(2-vinylpyridine) was epimerized by the action of t-BuOK in D MSO solution. The course of the reaction was followed by 300 MHz 1 H NMR as well as 20 and 90 MHz 13 C NMR spectroscopy. It was found that the polymer epimerized until equilibrium was reached had essentially the same microstructure (<T 0.5) as the polymer obtained by radical polymerization. Monte-Carlo simulation was used to calculate n-ad stereosequence distributions for the partially and completely epimerized polymers. Isotactic (mm) contents of the polymers measured from the methine proton and aromatic C2-carbon resonances, were in excellent agreement with those calculated by the Monte-Carlo method. The (mm)-aromatic C2 -carbon resonance patterns were interpreted in terms of heptad stereosequence resonances. CSMP programming, coupled with an optimization routine was used to evaluate rate constants for the epimerization reaction. When studied at 90 MHz all aromatic carbon resonances were sensitive to stereosequence effects. Several of these were interpreted in terms of pentad resonances.

Stereospecific catalytic precision polymerization of 2-vinylpyridine via rare earth metal-mediated group transfer polymerization with 2-methoxyethylamino-bis(phenolate)-yttrium complexes

“…24,25 The group of Natta introduced the anionic polymerization of 2VP with metallorganic compounds in the early 60s. [32][33][34][35][36] In addition Frustrated Lewis pair, 37,38 anionic [39][40][41][42][43][44] and radical [45][46][47][48] polymerizations have been applied to synthesize functional but atactic P2VP based materials. Subsequent mechanistic studies of Soum and Fontanille with organomagnesium compounds revealed that the stereocontrol derives from a Markov-chain end control through a favoured gauche coordination of two monomers to the metal cation.…”

“…[28][29][30][31] Apart from the mentioned examples only few groups investigated the stereospecific polymerization of 2VP. [32][33][34][35][36] In addition Frustrated Lewis pair, 37,38 anionic [39][40][41][42][43][44] and radical [45][46][47][48] polymerizations have been applied to synthesize functional but atactic P2VP based materials. Rare earth metal-mediated group transfer polymerization (REM-GTP) in contrast is a relatively recent polymerization method for 2VP.…”

Rare‐earth‐catalyzed alternating copolymerization of carbon monoxide with styrene

“…Copolymer ST/CO (C) was heated to 60 °C under nitrogen for 24 h in o ‐chlorophenol in the presence of sodium o ‐chlorophenolate for the epimerization of propene and CO copolymer 26–28. The product was precipitated with methanol, and the obtained copolymer, ST/CO (D), had less crystallinity and less stereoregularity.…”

Aromatic Quaternary Carbon Signals in the 13C NMR Spectrum of Poly(2-vinylpyridine) in Methanol-d4

“…However, from a comparison of the and the 13C NMR spectra of the ß,ß-di polymer, Matsuzaki et al concluded25 that the three C-2 resonances could not be directly attributed to triad tacticity. Thus, the relative intensity of the downfield C-2 carbon signal (signal B-I in Figure 2) was found to be considerably larger than the downfield signal in the methine proton spectrum assigned to the mm triad.25 Harwood et al 26 attributed the downfield C-2 absorption (signal B-I in Figure 2) to mm triads on the basis of 13C NMR studies of partially epimerized isotactic P2VP and proposed heptad assignments for its fine structure (Table 1). However, deviations of the observed mr and rr contents from the simulated curves indicated that the other two resonance areas (signals B-II and B-III in Figure 2) may not be solely due to mr and rr triads.…”