H NMR Analysis of Chain Unsaturations in Ethene/1-Octene Copolymers Prepared with Metallocene Catalysts at High Temperature

Abstract

In this paper, we report the full resonance assignments in the olefinic region of the 600 MHz 1H NMR spectra of a typical ethene/1-octene copolymer (4.0 mol % of octene units) produced with a metallocene catalyst at high temperature, and of an ethene homopolymer prepared under similar conditions for comparison. The assignments were based on a thorough analysis of 1D (1H, 1H{1H}, 13C) spectra and of 2D 1H−1H (COSY, TOCSY) and 1H−13C (HSQC, DEPT-HSQC) maps. Thirteen different olefinic structures were identified, and their formation explained in terms of plausible mechanistic paths associated with the high polymerization temperature. The fraction of internal chain unsaturations traceable to allylic activation turned out to be comparable to that of terminal ones in both samples. Despite its complexity, the said spectral region is now amenable to deconvolution and full simulation in terms of known and recognizable patterns, and usable for fast (possibly on-line) measurements of chain unsaturation degree, as well as for catalyst “fingerprinting” studies.

Terpolymerization of Substituted Cycloolefin with Ethylene and Norbornene by Transition Metal Catalyst

“…They are similar to those of E-O copolymers reported in the literature [44]. The signals at 4.73 and 4.68 ppm attributed to vinylidene structures O-4 and O-5, related to the β-H elimination after 1-octene insertion, are quite strong, while the broad multiplet centered at 5.09 ppm, which includes internal unsaturation O-1, O-2 and O-3, is rather small.…”

NMR study of the comonomer effect in metallocene poly(propylene‐co‐1‐pentene) copolymers synthesized at low temperature

“…). This feature has been attributed to internal exo vinylidene groups whose signal overlaps with the downfield Vd1 proton . Such a group is thought to come from the allylic activation of Vd1 chain‐ends, which evolve further by inserting new propene molecules (pathway c + d in Scheme ) …”

“…In the case of the metallocene iPP, chain transfer reactions leading to chain‐end double bonds have been thoroughly studied since their control can be used not only to avoid the obtainment of chains with low molecular weights but also, in the opposite way, to produce oligomeric oils derived from propylene . Studies have been very limited for the α‐olefin copolymers, these being mainly focused on polyethylene based grades . There are also some studies that address the termination mechanism in metallocene α‐olefins homopolymerization, but there is not much available information for α‐olefin‐ co ‐propylene copolymers.…”

Alk‐1‐ene Polymerization in the Presence of a Monocyclopentadienyl Zirconium(IV) Acetamidinate Catalyst: Microstructural and Mechanistic Insights

“…In all polymers prepared by us at 25 8C, the 1 H NMR spectra revealed the presence of both vinylidene, CH 2 --C(R)(P), and vinylene, R-CH --CH(P) terminal unsaturations (columns 7 and 8 of Table 1, and Figure S3-S5 in the Supporting Information), traceable to b-H elimination from a last-inserted 1,2 or 2,1 monomeric unit, respectively. [8,19] Notably, in the samples of poly(but-1-ene) and poly(hex-1-ene) the 2,1 units turned out to be strictly confined to the chain ends, whereas for poly(propylene) the 13 C NMR spectra ( Figure 2) revealed a significant amount of internal head-to-head/tail-to-tail enchainments with the stereostructure of Figure 3. The latter indicates that an occasional 2,1 propene insertion, and the 1,2 insertion which immediately follows, occur with opposite enantioface with respect to that preferred in 'normal' 1,2 insertion.…”