Ethylene-1-butene copolymers. 1. Comonomer sequence distribution

Abstract

A carbon-13 NMR method is presented for a quantitative determination of the comonomer distribution, the triad and tetrad sequence distributions, average sequence lengths, and run numbers in ethylenel-butene copolymers. A series of hydrogenated polybutadienes and a poly(1-butene) served as reference systems for establishing chemical shift assignments and for determining optimum conditions for a quantitative development. A dependence of relative spectral areas upon concentrations was noted a t polymer sample weight percents of 30 and higher. The method presented should be free of errors associated with differences in spectral line widths, peak overlap, difficulties in detailed assignments, and complexities introduced through a configurational sensitivity.

Structural Distribution of Linear Low-Density Polyethylenes

“…Tetramethyl silane was used as a chemical shift reference. The conditions for measurement were as follows: pulse interval, 10 s; acquisition time, 3 s; pulse width, 8.5 µs (90°); spectral width, 8000 Hz; number of data points per spectrum, 32 K. Triad sequence distribution, average sequence Jength, and run number in ethylene/butene-1 copolymers were calculated from 13 C NMR spectra using the method proposed by Hsieh et al 18 …”

The interrelationships between microstructure and melting, crystallization and thermal degradation behaviors of fractionated ethylene/1-butene copolymer

“…1-Butene, 1-hexene, and 1-octene are frequently used in ethylene polymerization to control LLDPE density by varying the amounts of comonomer incorporated [4,5]. This maintains polymer chain linearity in an overall configurational sense but leads to short chain branches (SCBs) randomly spaced along the polymer backbone [6].…”

The effect of an unsymmetric branched branch on the13C NMR chemical shifts of main chain carbons in polyethylene

“…[1][2][3] Generally, short chain, linear branches are the most common branches present in polyethylene copolymers, and have traditionally been produced through ␣-olefin incorporation or through spontaneous formation mechanisms in free radical mechanisms. 3,4 Recent work in nickel-and palladium-catalyzed ethylene homopolymerization has resulted polymers containing branches of varying structure through a spontaneous chain walking mechanism.…”

“…1,2,[11][12][13] However, the spectra of polymers are often very complex and the exact structural relationship between branches is unknown, making assignment of resonances difficult. A great help in the assignment of chemical shifts to structural forms comes from the ability to theoretically predict chemical shift values 14 -17 or through the synthesis of model compounds.…”

“…This peak is shifted considerably downfield relative to the analogous 2B methylene of an nbutyl branch, which appears at 23.37 ppm. 1 The downfield shift is likely due to the influence of both the neighboring tertiary carbon 3B and the two ␤-position 1A and 1B carbons. 14 Variable temperature experiments were undertaken to determine the magnitude of temperature effects on the chemical shift differences.…”