Propene−Norbornene Copolymers:  Synthesis and Analysis of Polymer Structure by ¹³C NMR Spectroscopy and ab Initio Chemical Shift Computations

Abstract

A series of propene−norbornene (P−N) copolymers were synthesized in the presence of rac-Et(indeny)2ZrCl2/MAO in toluene at 30 °C. P−N copolymers were characterized by 13C NMR spectroscopy, SEC, and DSC. Results were compared with those of a series of P−N copolymers synthesized in the presence of rac-Me2Si(Indenyl)2ZrCl2/MAO under the same experimental conditions. Polymerization activity appears to be quite low in comparison with ethene−norbornene (E−N) copolymerization. A first assignment of the main 13C NMR signals of P−N copolymers containing isolated N units was obtained on the basis of distortionless enhancement by polarization transfer (DEPT) 13C spectra and by comparison with isotactic polypropene (i-PP) and E−N copolymer spectra. Ab initio theoretical 13C NMR chemical shifts, computed for the most relevant conformers of a rather simple model compound and averaged using the RIS conformer populations estimated for an isotactic chain (P4−N) x , gave important detailed indications for the assignment of the complex 13C spectra of P−N copolymers with N content up to 35 mol %. Such assignments were used to estimate the N copolymer content. The discrepancy between the values obtained from the areas of methyl signals and from the areas of the signals assigned to norbornene carbons was found to be partially due to the presence of 1,3-propene misinsertions, which are formed in significant amount when increasing the [N]/[P] ratio of the feed. Our results confirm that, despite the relatively lower polymerization activity, at low norbornene/olefin ratio it is possible to obtain P−N copolymers that are relatively richer in norbornene than the E−N copolymers prepared in similar conditions. However, at higher norbornene/olefin feed ratios the great amount of 1,3-propene misinsertions clearly reveals that the steric hindrance of the Mt−tertiary carbon bond when N is the last inserted unit makes difficult the next propene insertion, causing low polymerization activities, molecular masses, and T g.

Design of Efficient Molecular Catalysts for Synthesis of Cyclic Olefin Copolymers (COC) by Copolymerization of Ethylene and α-Olefins with Norbornene or Tetracyclododecene

“…As described in the introduction, reported examples for copolymerization of NBE with α-olefin have been limited [54][55][56][57][58][59][60][61][62][63][64], probably due to the difficulty of α-olefin insertion after NBE incorporation by linked-metallocene catalysts, as pointed out in a previous review by Tritto et al [5]. In fact, both the catalytic activity and the M n values decreased upon increasing the α-olefin content in the NBE/1-octene copolymerization using [H 2 C(Me 2 C 5 H 2 ) 2 ]ZrCl 2 [58].…”

Living polymerization of olefins with ansa-dimethylsilylene(fluorenyl)(amido)dimethyltitanium-based catalysts

“…However, the number of catalysts that copolymerize norbornene with propene or higher 1-alkene is very limited, and their activity and/or the molecular weight of the produced polymers is not sufficient. [58][59][60][61][62][63] Ansa-dimethylsilylene(fluorenyl)(amido)dimethyltitanium-based catalysts were found to be active not only for 1-alkene polymerization but also for norbornene polymerization. We therefore applied these catalysts for copolymerization.…”

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

“…Then, ab initio theoretical 13 C NMR chemical shifts, combined with R.I.S. statistics of the P-co-N polymer chain, gave detailed indications for the final 13 C NMR assignment spectra of copolymers with N isolated units [35][36][37]. In detail, C6 and C5 methylenes resonate at 30.10 and 27.34 ppm, respectively, while the C7 methylene appears at 31.91 ppm.…”

“…On the basis of previous works on P-co-N copolymerization [36], it was assumed that units P 13 and P 21 may be inserted only after N and that N can be inserted only after P 12 . Therefore, only nine diads (P 12 P 12, P 12 N , NP 12 , NN, NP 13 , NP 21 , P 13 P 12 , P 13 N and P 21 P 12 ) and 23 triads, depicted in Chart 1, are possible.…”