Influence Of Short-chain Branching Research Articles

The influence of short-chain branching on the morphology and structure of polyethylene single crystals

The influence of short-chain branching on the formation of single crystals at constant supercooling is systematically studied in a series of metallocene catalyzed high-molecular-weight polyethylene samples. A strong effect of short-chain branching on the morphology and structure of single crystals is reported. An increase of the axial ratio with short-chain branching content, together with a characteristic curvature of the (110) crystal faces are observed. To the best of our knowledge, this is the first time that this observation is reported in high-molecular-weight polyethylene. The curvature can be explained by a continuous increase in the step initiationstep propagation rates ratio with short-chain branching, that is, nucleation events are favored against stem propagation by the presence of chain defects. Micro-diffraction and WAXS results clearly indicate that all samples crystallize in the orthorhombic form. An increase of the unit cell parameter a(0) is detected, an effect that is more pronounced than in the case of single crystals with ethyl and propyl branches. The changes observed are compatible with an expanded lattice due to the presence of branches at the surface folding. A decrease in crystal thickness with branching content is observed as determined from shadow measurements by TEM. The results are in agreement with additional SAXS results performed in single crystal mats and with indirect calorimetry measurements. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1751-1762

Rheological Investigation of the Influence of Short Chain Branching and Mw of LDPE on the Melt Miscibility of LDPE/PP Blends

The influences of short chain branching (SCB) and molecular weight (Mw) of low density polyethylene (LDPE) on its melt miscibility with polypropylene (PP) were investigated by rheological techniques. Rheological meas- urement and different data-treatment techniques as well as rheological models suggest that blends of PP with LDPE of high SCB (22 CH3/1000 C) are miscible at all compositions. However, blends of LDPE with low SCB (8.3 CH3/1000 C) are immiscible in the LDPE-rich and miscible in PP-rich regimes. It was suggested that matching the conformations of PP and LDPE and matching the Mw of LDPE and PP is a key to the melt miscibility of PP/LDPE blends. The experimental results are in agreement with theoretical predictions on the miscibility of polyolefin blends.

Impact of Short Chain Branching on Conformations of Metallocene LLDPE Melts: NMR, Light Scattering and MD Simulation Study

AbstractSummary: The influence of short chain branching on molecular conformations of melts and solutions of metallocene linear Low‐density polyethylene (m‐LLDPE) was studied by nuclear magnetic resonance (NMR) spectroscopy, light scattering, and Molecular Dynamics (MD) simulation techniques. Both T2 relaxation measurements by NMR and MD simulations suggest the loss of molecular order in m‐LLDPE at temperatures >135°C. Similar trends were observed for the radius of gyration as measured by light scattering and calculated from MD simulations vs. branch content (BC) and type. At high BC (>40 branches/1000 C) m‐LLDPE tends towards self assembly. Neither the branch type nor the BC has significant effect on the intermolecular orientation correlation function. This might be attributed to the fact that the high temperature of the melt results in loss of order in the chains. This lack of order is independent of BC or type. This result is in agreement with the results of the dihedral distribution analysis. Also, it is in agreement with our NMR T2 measurements. The radial distribution functions are nearly identical indicating no effect of branch type at low branch density on the correlation between branches and backbone segments. However, increasing the BC to 80 branches/1000C resulted in a change in the correlation between the branches and backbone segments.

Influence of Short Chain Branching on the Miscibility of Binary Polymer Blends: Application to Polyolefin Mixtures

The lattice cluster theory (LCT) is used to study the influence of monomer structure, i.e., short chain branching, on the miscibility of binary polymer blends. The systems are chosen as correspondi...