Rheological Behavior of Blends of Metallocene Catalyzed Long-Chain Branched Polyethylenes. Part I: Shear Rheological and Thermorheological Behavior

Abstract

Long-chain branched metallocene-catalyzed high-density polyethylenes (LCB-mHDPE) were solution blended to obtain blends with varying degrees of branching. A high molecular LCB-mHDPE was mixed with low molecular LCB-mHDPE at varying concentrations. The rheological behavior of those low molecular LCB-mHDPE is similar but their molar mass and molar mass distribution are significantly different. Those blends were characterized rheologically to study the effects of concentration, molar mass distribution, and long-chain branching level of the low molecular LCB-mHDPE. Owing to the ultra-long relaxation times of the high molecular LCB-mHDPE, the blends exhibited a clearly more long-chain branched behavior than the base materials. The thermorheological complexity analysis showed an apparent increase in the activation energies Ea determined from G′, G″, and especially δ. Ea(δ), which for LCB-mHDPE is a peak function, turned out to produce even more pronounced peaks than observed for LCB-mPE with narrow molar mass distribution and also LCB-mPE with broader molar mass distribution. Thus, it is possible to estimate the molar mass distribution from the details of the thermorheological complexity.

Recent Advances in Controlled Production of Long‐Chain Branched Polyolefins

“…The macromers are then efficiently enchained intra-molecularly at the Ni coordinated by the (SO 2 )FI ligand fragment. Repeating this cycle yields high molar mass LCB polyethylenes up to 11 LCB/1000C, as determined by 13 C NMR analysis. It is interesting that in comparison, the tandem monometallic (CF 3 )FI-Ni + (SO 2 )FI-Ni catalytic system produces a bimodal mixture under the same reaction conditions.…”

“…[74] In a similar study, two nonmetallocene catalysts; difluoro-substituted 2,6-bis(imino) pyridyl Fe/MMAO as the oligomerization catalyst and mono 𝛽-diiminato titanium complex/MMAO as copolymerization catalyst were used to convert ethylene as the sole monomer feed to branched polyethylene. [75] In both studies, which were conducted in a single reactor following a simultaneous approach, 13 C NMR spectra revealed that by increasing the molar ratio of oligomerization/polymerization catalyst, the number of ethyl, butyl, and long (≥6C) branches per 1000 carbon atoms increase and the melt temperature shifts into lower temperatures as measured by DSC, accordingly. Miller and coworkers reported a variation of LCB density in the range of 14-21 LCB/1000C.…”

“…The polybutadienyl chains are terminated by the 𝛽-H process leading to a conjugated diene, which can be reinserted into a polybutadienyl growing chain, as described in Figure 12. In this study, branching was quantified by 13 C NMR analysis after hydrogenation of the polybutadiene. The number of LCB was reported to increase from 0 to 4.7 and 9 LCB/1000C in the case of using AlEt 3 as CTA, upon increasing CTA/Ni from 0 to 2.5 and 5.…”

“…Rheological studies show that melt rheological properties of the Ziegler-Natta-catalyzed propylene/𝛼,𝜔-diene copolymers resemble those of metallocene-catalyzed LCB homopolymers. The number of LCB structures per 1000 carbons, as determined from 13 C NMR spectra, was reported to vary in the range of 0.7-1.15 when 1,9-Decadiene commoner was added between 160 and 320 mmol. More affirmation for LCB formation was obtained from the van Gurp-Palmen (vGP) plot of 𝛿 versus G*, which demonstrated a gradual reduction of 𝛿 at low G* region from 80°t o 20°for linear and LCB PP, respectively.…”

“…[11] These deviations are indirectly used to quantify the LCB content from the various rheological properties like dynamic storage and loss moduli, G′ and G″, and the loss angle, 𝛿. [8,[12][13][14] The alternative direct method of LCB quantification in polyolefins based on NMR spectroscopy, unfortunately, www.advancedsciencenews.com www.mrc-journal.de fails to distinguish between branches longer than six carbons. [15] Another alternative technique is based on coupling size exclusion chromatography with multi-angle laser light scattering, which indirectly determines the LCB content by comparing the radius of gyration of each polymer fraction to that of a linear reference chain having the same molar mass.…”