Influence of the catalyst and polymerization conditions on the long-chain branching of metallocene-catalyzed polyethenes

Evidences of Long‐Chain Branching in Ziegler‐Natta Polyethylene Homopolymers as Studied via SEC‐MALS and Rheology

“…Now the question is why LCB in these Z-N homopolymers did not result in a melt viscosity increase as observed in other longchain branched resins such as HDPE-1 and other Cr-resins [13][14][15][16]28] and in some longchain branched metallocene resins. [17][18][19][20][21][22][23][24][25][26] To answer this question, two factors have to be considered: the polymer architecture and concentration of LCB species in the resin. First of all, it is well-known that not all LCB results in elevated melt zeroshear viscosities, h o .…”

“…The parts-per-million level of LCB can cause melt viscosity to increase by several order of magnitudes compared to a linear polymer of the same molecular weight. In more recent years, [17][18][19][20][21][22][23][24][25][26] LCB was found to be a common structural phenomenon in polyethylene catalyzed by various metallocene catalyst systems, even in resins catalyzed by the common bis (cyclopentadienyl)zirconium dichloride/ MAO system. [26] It has become generally accepted that LCBs in HDPE are formed through the reinsertion of macromers formed during the b-hydride elimination process, a chain termination mechanism that forms dead polymers having a vinyl chain end.…”

“…[15] It also seems commonly accepted that LCB formation in mPE involves macromers reinserted into the propagating polyethylene chains. [23,27] The vinyl group of macromers is believed to freely compete with other monomers and comonomers in polymerization, and thus, the LCB levels are proportional to the concentration of the macromers. [27] In some cases, however, LCBs are likely formed through an intramolecular pathway in which the macromers remained coordinated to the same sites that made them.…”

Copolymerization of Ethylene with 1,9‐Decadiene: Part I – Prediction of Average Molecular Weights and Long‐Chain Branching Frequencies

“…[18] Many previous investigations have tried to understand how LCBs are formed in ethylene or propylene homopolymerization. [7,14,[27][28][29][30][31][32][33][34][35][36] Nevertheless, only few publications dealt with polymerization kinetic studies that included LCB generation in copolymerization of olefins and dienes, [19,21,32,37] and even fewer proposed mathematical models to describe the polymerization kinetics and microstructure of olefin-diene branched copolymers. [10] Kokko et al [37] reported that the copolymerization of ethylene and 1,7-octadiene with metallocene catalysts had higher selectivity for branch formation and could make LCBs.…”

Branching degree and rheological response correlation in peroxide-modified linear low-density polyethylene

“…For LCB-PEs, a decrease in activation energy (E a ) with an increase in storage modulus was reported, which is considered as a sign for thermorheological complexity. [26][27][28][29][30][31][32][33][34][35][36][37] In our previous work, [38] we made a correlation between reactive modification conditions and degree of LCB in chemically modified LLDPE using response surface experimental design. By the use of a response surface method and according to a box Behnken statistical design, various contour plots were constructed to establish correlations between the processing parameters and degree of LCB.…”