On the stereoisomerization in thermal degradation of isotactic poly(propylene)

Abstract

SUMMARY:The terminal microstructure of the hydrogenated a,w-diisopropenyloligo(propy1ene) prepared by thermal degradation of isotactic poly(propy1ene) at 370 "C was determined by means of I3C NMR spectroscopy, and therefrom the stereoisomerization reaction of the reacting polymer segment is discussed in relation to polymer dynamics. With respect to the asterisked carbons of the propyl end group CH3CHfCH2--(n-Pr) and of the isopropyl end group (*CH3)&H-(i-Pr) formed by hydrogenation, the mole fractions of triads ( m rneso, r racemo) F,, = 0.64, F,, = 0.09, F , = 0.15 and F,,. = 0.12 of n-Pr-*CH2 differ from the rnicrotacticity of the main chain of telechelic oligorners, and the mole fraction of i-Pr-*CH3 is as follows:These results clearly show that the stereoisomerization occurs only at the asymmetric carbon near the end group of the telechelic oligomer. The value of the mole fraction of i-Pr-*CH3 is consistent with F, = 0.73 (F,, + F,J and F,. = 0.27 (Frr + F, ) of n-Pr-*CH2 at the outer position of the main chain rather than with F, = 0.79 (F,, + F,) and F, = 0.21 (Frr + Fmr) at the inner position. These results could be consistently traced by a simulation based on a reaction model including stepwise intramolecular hydrogen abstraction of the tertiary on-chain macroradical near the center of the main chain before the successive p-scission. This stepwise back-biting is estimated to occur once (20%) and twice (80%) via a quasi six-membered cyclic structure in a transition state, and occurs in a very limited part of the molecular chain.

Functionalization and Applications of Telechelic Oligopropylenes: Preparation of α,ω-Dihydroxy- and Diaminooligopropylenes

“…The value f TVD is a measure of functionality and is defined as the average number of terminal vinylidene double bonds (TVDs) per molecule. The number of TVDs and saturated termini is determined by quantitative 13 C NMR spectroscopy . Low molecular weight PP-TVD ( M n ≤ 1000) was also obtained by controlling the degradation conditions, but a slight decrease in f TVD value was observed.…”

“…Low molecular weight PP-TVD ( M n ≤ 1000) was also obtained by controlling the degradation conditions, but a slight decrease in f TVD value was observed. This lower microtacticity was due to disorder in the stereoregularity of terminals during degradation 1 Characteristics of PP-TVDs microtacticity (mol %)PP-TVD M n × 10 -3 M w / M n mm mr rr functionality f TVD a iPP-TVD (I) 4.42 1.85 94 4 2 1.84 iPP-TVD (II) 0.90 1.11 78 13 9 1.60 sPP-TVD 5.27 1.78 5 9 86 1.76 aPP-TVD 4.96 1.73 80 12 8 1.66 a Determined by quantitative 13 C NMR spectroscopy …”

“…This lower microtacticity was due to disorder in the stereoregularity of terminals during degradation 1 Characteristics of PP-TVDs microtacticity (mol %)PP-TVD M n × 10 -3 M w / M n mm mr rr functionality f TVD a iPP-TVD (I) 4.42 1.85 94 4 2 1.84 iPP-TVD (II) 0.90 1.11 78 13 9 1.60 sPP-TVD 5.27 1.78 5 9 86 1.76 aPP-TVD 4.96 1.73 80 12 8 1.66 a Determined by quantitative 13 C NMR spectroscopy 2 Hydroxylation of PP-TVDs end group of the product (mol %) b runPP-TVDboranes (equiv) a PP-OH−CH 2 OHCH 2 conversion (%) 1 iPP-TVD (I) 9-BBN (16) iPP-OH (I) 75 14 84 2 iPP-TVD (I) 9-BBN (32) iPP-OH (II) 84 5 94 3 sPP-TVD 9-BBN (16) sPP-OH 79 3 96 4 aPP-TVD 9-BBN (16) aPP-OH 90 3 98 5 iPP-TVD (I) BH 3 ·THF (1) iPP-OH (III) 78 9 90 6 iPP-TVD (III) c BH 3 ·THF (4) iPP-OH (IV) 80 0 100 a Amount of boranes equivalent to the number of terminal double bonds of PP-TVD.…”

“… a Amount of boranes equivalent to the number of terminal double bonds of PP-TVD. b Determined by quantitative 13 C NMR spectroscopy . The others (7−20%) are unreactive saturated termini.…”

“…In an earlier study we found that telechelic propylene oligomers with two terminal vinylidene double bonds (α,ω-bis(2-propenyl)oligopropylene, PP-TVDs) were obtained briefly by controlled thermal degradation from polypropylenes (PPs) . In this paper, we report the preparation of telechelic propylene oligomers with a hydroxyl or amino group at both ends and copolymerization of the difunctional oligomers directed toward the novel recyclable polyolefins.…”