Monomer sequence distributions in ethylene-1-hexene copolymers

Abstract

A 13C NMR method is presented for a quantitative determination of the respective comonomer distributions, the triad distributions, average sequence lengths, and run numbers in ethylene-l-hexene copolymers. Complete 13C NMR chemical shift assignments were formulated after observation of two reference systems, a poly(l-hexene) and an ethylene-l-hexene copolymer containing only 1.9 mol % 1-hexene. A second copolymer having 17.3 mol % 1-hexene allowed an observation of all the intermediate connecting sequences between the extremes of the two reference systems. A subsequent quantitative procedure, which avoids errors from peak overlap and uncertainties in configurational assignments, was developed by using relative areas from well-spaced 13C NMR spectral regions, defined uniquely in terms of contributing triad sequences. The method is designed to obtain a triad distribution with the highest possible accuracy, after which, structural information meaningful to the polymer chemist is extracted.

Metallocene-catalyzed ethylene−α-olefin isomeric copolymerization: A perspective from hydrodynamic boundary layer mass transfer and design of MAO anion

“…13 literature supports this finding [36,[69][70][71][72]. The remaining triad mole fractions of the as-synthesized copolymers differ among themselves (see Table 2).…”

“…<r E r C > ≈ r E r C confirms terminal model statistical copolymerization mechanism. The E−1-H average copolymer compositions and microstructural parameters were calculated following the well-known publications of Hsieh and Randall [36], and Seger and Maciel [37]. According to these references, first the mole fractions of the copolymer triad sequences were calculated by using the reported peak assignment procedures (involving the associated collective peak assignment regions) and the Seger-Maciel algorithm.…”

A Comprehensive Review on Controlled Synthesis of Long‐Chain Branched Polyolefins: Part 3, Characterization of Long‐Chain Branched Polymers

“…[8,15,16] In other words, a set of unique signal peaks for the carbons in branch chain with a length of only up to six carbons can be clearly identified in the 13 C NMR characterization. [17][18][19] Therefore, those branches longer than six carbons in length (B 6+ ) are all treated as "long-chain branches" in NMR studies and these "long-chain branches" cannot be differentiated from the real long-chain branches, which have chain lengths adequate for chain entanglement. This is acceptable for metallocene-catalyzed ethylene homopolymerization, because the most likely mechanistic route for hexyl-plus LCB formation is through in-situ copolymerization of maromonomers, which have similar chain lengths as the backbones.…”

Copolymerization of 4-methyl-1-pentene with α,ω-alkenols

“…It means that the structure of the copolymer is still random. Another parameter RMD (Relative Monomer Dispersity) [34], developed on the base of Hsieh and Randall's work [35], was also calculated. All RMD for the three copolymer samples were obtained as 100% or thereabouts, indicating that the comonomer, 4P1O, is uniformly distributed in the polymer chain.…”