Mechanistic implications of the end group structure in radical telechelic polybutadienes as studied by NMR

Abstract

270 MHz 'H NMR spectra were used to study the structure of end groups and terminal monomeric units in polybutadienes produced by radical polymerization, initiated with hydrogen peroxide and a series of substituted benzoyl peroxides. The hydroxyl or aroyl groups were found to be bonded to the methylene end group of the 1,4-cis-, 1.4-frans-or 1,2-butadiene terminal units. The terminal units are richer in 1,2-structures than the backbone due to the influence of hydroxyl or of the aroyl groups on the relative reactivity of carbons 1 and 3 in the allylic radical, formed by initiation. 1,2-Units at the chain ends and in the backbone are predominantly joined to 1 ,4-units; this results in a magnetic nonequivalence of the methylene protons in 1.2-structures. Data are also presented on the extent of radical decarboxylation during initiation by substituted benzoyl peroxides and also on the introduction of solvent fragments in polybutadienes obtained by initiation with hydrogen peroxide in alcoholic media. 4,20 CH=CHl 2 bands, 6 = 3,94 and 3,93 2 bands, 6 = 3,42 and 3.40 Multiplet Doublet, J = 6 Hz 2 bands, 6 = 3,28 and 3.27 2 bands, 6 = 4,21 and 4,19 2 bands, 6 = 4,70 and 4.68 2 bands, 6 = 4,81 and 4,79 2 bands, 6 = 3,29 and 3,27 2 bands, 6 = 4,21 and 4,19 2 bands, 6 = 4,lO and 4,68 2 bands, 6 = 4,79 and 4,77 Multiplet Doublet, J = 7 Hz Triplet, J = 7,3 HZ

Use of controlled radical polymerization of butadiene with AIBN and TEMPO for the determination of the NMR characteristics of hydroxymethyl groups

“…1 summarizes the chemical shifts of the hydroxymethyl end-groups observed by 1 H and 13 C NMR in the corresponding studies. As it can be seen, C OH and T OH groups are ambiguous since they led to different attributions: they have been regarded as equivalent by Fages and Pham 7,8) but slightly different by the other authors (Bresler et al 9,10) , Ramey et al 11) , and Vilar et al 12,13) ). Moreover, Fages and Pham 7,8) have suggested that the peak centred at 4.05 ppm corresponds to the G OH group coming from a transfer reaction.…”

Hydrogenation of low-molar-mass, OH-telechelic polybutadienes. II. Nuclear magnetic resonance and infrared spectrometric determination of hydroxyl end groups before and after hydrogenation by diimide

“…In the 1 H‐NMR spectrum [Fig. 1(b) ], the multiplet at 3.79 ppm can be assigned8, 9 to methine protons of the CH(CH 3 ) OH end groups.…”

Determination of hydroxyl groups in polymers. Review

“…In [204] it was demonstrated that during polymerization of butadiene with hydrogen peroxide in alcohol solution, alcohol end fragments (22% of total HG content) appeared in the polymer. I t was determined from the signals with chemical shifts at 3.67 ppm (methyl protons) and 1.805 ppm (methine protons) which correspond to the signals of the product with the end fragment -CH(OH)CH, specially prepared by anionic polymerization.…”