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

Abstract

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 initiation—step 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 a0 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. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1751–1762

Effects of Branch Content and Branch Length on Polyethylene Crystallization: Molecular Dynamics Simulation

“…In this simulation of branched polyethylene crystallization, the crystal configuration was lamellae crystal for MSL of 50 CH 2 and bundle crystal for that of 34 CH 2 . Vega et al observed the single crystal in orthorhombic form of metallocene catalyzed butyl branched polyethylene with BC from 0 to 10/1000 C. The crystal configuration was also single lamellae crystal form for BC below 10/1000 C in this simulation. The critical MSL mentioned above for lamellae thickness was 50 CH 2 (20/1000 C) in the butyl branching polyethylene crystallization .…”

New habits in branched polyethylene single crystals

“…The solutions were then recrystallised to obtain single crystals at four temperatures (T c = 73 °C, 68 °C, 63 °C and 58 °C) below T s during 24 hours. At this degree of supercooling almost the whole material crystallizes in 1,2,4trichlorobenzene during the CRYSTAF experiments (2-3 hours) at a cooling rate of 0.1 °C•min -1 [13]. Then, it is expected that the isothermal crystallization experiments performed in p-xylene during 24 hours avoided fractionation of the sample and depleted almost the whole dissolved material.…”

“…The molecular and physical properties were obtained by 13 C-Nuclear Magnetic Resonance, Size Exclusion Chromatography and CRYSTAF-TREF analysis. Please refer to previous works for details about molecular and physical characterization [13,[17][18][19][20][21][22].…”

“…As far as the authors are aware, curved {110} faces in high molecular weight PE have not been observed until recently. In a previous work, the effect of short chain branching (SCB) on the lateral habits of PE single crystals at a constant T = 30 ºC were explored [13]. It was shown that SCB causes a strong effect in both the morphology and the structure of single crystals.…”

Preparation, Characterization, and Rheological Behaviors of Polysiloxanes Presenting Densely Simple and Well‐Defined Short‐Branched Chains

“…In the recent years, many studies have established that physical properties of polymers are governed by the chemical structure and the molecular architecture, especially the influence of short chain branching (SCB). [1][2][3][4][5][6][7][8][9][10] By "short," it is here referred as a branch with a molecular weight far lower than the entanglement molecular weight, M e that is usually more than 1 kg mol −1 . [11] In a number of (2 of 11) 1700005 density and the rheological properties of polymers.…”