Ethylene−Norbornene Copolymer Microstructure. Assessment and Advances Based on Assignments of ¹³C NMR Spectra

Abstract

A best-fitting procedure for the quantitative determination of the molar fractions of the stereosequences that define the microstructure of an ethylene−norbornene (E−N) copolymer from 13C NMR spectra has been set up. The quantitative determination of copolymer microstructure will allow one to clarify the E−N copolymerization mechanism. This method utilizes the observed peak areas of the 13C signals and takes into account the consistency between peak areas and the stoichiometry of the copolymer chain. Thus, a further extension of signal assignments is made possible by guessing assignments of unknown signals and by discarding inconsistent hypotheses. This procedure has been applied to the analysis of the 13C NMR spectra of a large number of E−N copolymers, prepared with catalyst precursors rac-Et(indenyl)2ZrCl2 (1), rac-Me2Si(2-Me-benz[e]indenyl)2ZrCl2 (2), Me2Si(Me4Cp)(N t Bu)TiCl2 (3), and Me2C(Flu)(Cp)ZrCl2 (4). An estimate of the molar fractions of the various stereosequences with a standard deviation on the order of 1−2% has been obtained. The comparison between controversial assignments existing in the literature for a number of ethylene signals has confirmed our previous assignments. New signals such as those of the C2/C3 carbons of EENNEE meso sequences (M) and of the external carbons C5 of MM and MR triads in ENNNE sequences have been assigned.

Molecular Dynamics in Cyclic Olefin Copolymer

“…The structure of these copolymers has been extensively studied using 13 C high resolution in solution [5][6][7]. It was found that in copolymer with low NB content the close vicinity of two or more NB groups is rather rare.…”

Microstructure of Copolymers of Norbornene Based on Assignments of 13C NMR Spectra: Evolution of a Methodology

“…The thorough microstructure investigation of E-co-N copolymers has taken several years [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. A number of groups dedicated great efforts to assign the 13 C NMR spectra of E-co-N copolymers.…”

“…Progress in chemical shift assignments of these copolymer spectra has included the discrimination of meso/racemic relationships between norbornene units in alternating NEN and in ENNE sequences. In Figure 5, the 13 C NMR spectra of a poly(E-co-N) with 58 mol % of norbornene produced by catalyst i-Pr[(Cp)(Flu)]ZrCl 2 (3) (a) and a poly(E-co-N) with 33 mol % of norbornene produced by catalyst rac-Et(Indenyl) 2 ZrCl 2 (1) (b) are shown [25].…”

“…In Figure 5, the 13 C NMR spectra of a poly(E-co-N) with 58 mol % of norbornene produced by catalyst i-Pr[(Cp)(Flu)]ZrCl2 (3) (a) and a poly(E-co-N) with 33 mol % of norbornene produced by catalyst rac-Et(Indenyl)2ZrCl2 (1) (b) are shown [25]. …”

Phosphine-Thiophenolate Half-Titanocene Chlorides: Synthesis, Structure, and Their Application in Ethylene (Co-)Polymerization

“…[44][45][46][47][48][49][50][51][52][53][54][55][56] Figure 3A showed that the microstructures of the COCs formed using 2a under low NBE concentration of 0.3 mol/L possessed alternating ethylene-NBE sequences and isolated NBE units. In contrast, resonances ascribed to NBE diads or triads were observed for the copolymers prepared at high NBE concentration of 0.5-1.0 mol/L (Figures 3B-C), and the microstructures thus possessed a mixture of NBE repeat units in addition to the alternating, isolated NBE sequences.…”