Influence of copolymer fraction composition in ultrahigh molecular weight polyethylene blends with ethylene/1‐hexene copolymers on material physical and tensile properties

Abstract

The reactor blends (RBs) with bimodal molecular weight distribution on the base of ultrahigh molecular weight polyethylene (UHMWPE) and low molecular weight random ethylene/1-hexene copolymers (CEH) were synthesized by two-step processes including ethylene polymerization followed by ethylene/1-hexene copolymerization over rac-(CH 3 ) 2 Si(Ind) 2 ZrCl 2 /methylaluminoxane catalyst. The four series of blends differed in a composition of copolymer fraction that was varied in a wide range (from 3.0 to 37.0 mol % of 1-hexene). The differential scanning calorimetric study shows the double melting behavior of the net semicrystalline CEHs, which can be attributed to intramolecular heterogeneity in chain branch distribution. The introduction of CEHs leads to the modification of nascent RB crystalline and amorphous phases. Physical and tensile properties as well as melting indexes of the materials depend not only on the percentage of copolymer fraction that varied from 6.9 to 35.8 wt % but also on its composition. The increase of copolymer fraction with high content of 1-hexene (11.0 mol %) in the blends leads to the change of the character of stress-strain curves; the materials behave as elastomers. Controlled regulation of copolymer fraction characteristics in the synthesis yields RBs combining the enough high strength, good plastic properties with enhanced melting indexes as compared with the net UHMWPE.

In‐reactor blends based on ultrahigh molecular weight polyethylene: Effect of microstructure of modifying fraction on the morphology and viscoelastic behavior of blends

“…The introduction of other polymers with increased fluidity (LLDPE, LMWPE) in UHMWPE matrix is one of the ways to modify material morphology and properties, to reduce the melt viscosity and improve its processability 5–8 . Considerable attention is paid to the development of the methods for producing polyolefin blends directly in the synthesis with organometallic catalysts (in‐reactor methods) 9–16 . They are particularly effective for synthesis of UHMWPE‐based materials since homogeneous blends of this polymer with good mechanical properties cannot be obtained by mechanical blending due to its high melt viscosity 17 …”

“…We used homogeneous single‐site zirconocene catalysts to produce a series of new materials (in‐reactor blends RB‐s) on the base of UHMWPE with M w = 1000 kg mol −1 and random ethylene/1‐hexene copolymers (CEH‐s) of different composition (UHMWPE/CEH‐n). For this purpose, two‐stage processes of ethylene homopolymerization followed by copolymerization of ethylene with 1‐hexene over catalyst rac ‐(CH 3 ) 2 Si(Ind) 2 ZrCl 2 /MAO were carried out 15 . In‐reactor blends of UHMWPE and LMWPE with M w = 160 kg mol −1 were also synthesized in two‐stage sequential polymerization of ethylene in the presence of specified metallocene catalyst (UHMWPE/LMWPE) 16 .…”

One pot synthesis of bimodal UHMWPE/HDPE in‐reactor blends with Cr/V bimetallic catalysts

“…Direct synthesis of UHMWPE/LLDPE IRBs by including LLDPE in the catalyst solution before polymerization could be a choice . Multiple‐stage polymerization technique (MSPT) is another choice for the synthesis of UHMWPE/NMWPE IRBs by regulating the polymerization conditions, such as the H 2 partial pressure and the concentration of comonomers . By contrast, multisite catalysis technique (MSCT) aiming at synthesizing IRBs in a single reactor with multisite catalysts is more preferred because it is more cost‐, resource‐, eco‐, and energy‐efficient, and a milestone of polyolefin catalysis.…”

(Co)polymerization of ethylene via nonmetallocene catalysts with diphenyl phosphoroso schiff‐base ligand

“…Mikhail synthesized ethylene/1–hexene copolymers using supported catalysts of different composition. The copolymer of ethylene with 1‐hexene showed excellent properties including stretchability and toughness . Endre prepared copolymers of ethylene with 1‐octene by zirconium and hafnium catalysts with diimine ligands.…”