Sizes of long‐chain branches in a high‐pressure low‐density polyethylene as a function of molecular weight

Abstract

SYNOPSISThe mean length and the indices of long-chain branches (LCBs) of a high-pressure lowdensity polyethylene (HPLDPE) as a function of molecular weight have been determined for its molecular-weight-fractionated parts by the I3C-NMR analysis and the viscosity measurements. The mean LCB length of the fractions was of the order of 200-300 carbons in length. The size of LCBs increases with increasing molecular weight, but the size of LCBs relative to the overall macromolecular size decreases with increasing molecular weight. The LCB sizes as a function of molecular weight determined for the fractions of one parent HPLDPE are in good agreement with those previously reported for HPLDPE whole polymers.

Characterization and microstructure study of low‐density polyethylene by Fourier transform infrared spectroscopy and temperature rising elution fractionation

“…For vinyl groups at 910 cm −1 , an independent determination exists that gives vinyls per 1000 carbon atoms as follows:25 where A 910 and t are the absorption at 910 cm −1 and the film thickness (cm), respectively. According to this equation, the number of vinyl groups in the LDPE (grade LF0200) sample was 0.03561 per 1000 carbon atoms.…”

Trace levels of mechanochemical effects in pulverized polyolefins

“…These characteristics are affected by changes in the branching architecture of the polymer chain, which may occur as a result of mechanochemistry. Short‐chain branches influence the morphology and solid‐state properties of semicrystalline polymers,19–29 whereas long‐chain branches affect the melt rheology 30–41. Based on this differentiation, the results are discussed in three categories: First is a discussion of the rheological changes as obtained from MI and oscillatory shear measurements, followed by a discussion on the MW distribution data obtained from the GPC experiments, and then a discussion of the crystallization and thermal property data obtained from DSC results.…”

“…The difference in the extent of viscosity change between the two LLDPEs could be due to the heterogeneous Ziegler–Natta catalyst used to make each polymer. Such catalysts create chains with a random distribution of branches and branch content 31, 34, 42. Based on the extent of viscosity changes, it appears that the LLDPE‐NG sample, having a greater viscosity increase upon high shear S 3 P processing, has more branch points (and, therefore, more tie molecules), and it therefore undergoes greater mechanochemically induced structural changes upon pulverization.…”

Development of an Integrated On‐Line 2D Analytical TREF‐High Throughput SEC Technique for Polyolefins Characterization

“…Traditionally, this second dimensional information described by Equations () and () can only be obtained by the tedious and costly proparative cross‐fractionation () followed by off‐line SEC analysis. [ 2,5,6,16,31,32,33 ]…”

“…The traditional ways to acquire both MWD and CCD information were via the conventional preparative cross‐fractionation, that is, a solvent gradient fractionation (SGF) fractionation of the full polymer followed by TREF fractionation of each of the SGF fractions before all these cross‐fractions were characterized by off‐line techniques, or via preparative TREF fractionation followed by off‐line MWD analysis of each TREF fraction via SEC. [ 2,5,6,16,31–33 ] However, these off‐line techniques are generally tedious—usually taking weeks or months per sample, labor‐intensive, and wasteful in terms of solvents consumption and waste disposal costs. On the top of these, the resolution of each fraction is usually poor because only limited cuts can be made within a given time.…”