Nuclear Magnetic Resonance Detection of Two Distinctly Different Chains in the Orthorhombic Crystalline Phase of Polyethylenes

Abstract

Several commercial and noncommercial, high- and low-density and ultraoriented polyethylene samples, as well as polyethylene samples with inorganic fillers, have been investigated by inversion-recovery cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (NMR). In all these samples two types of all-trans chains in orthorhombic crystalline domains are detected, which give two overlapping carbon-13 lines with different line widths and different relaxation times. From the NMR relaxation parameters we conclude that one type of the crystalline chains, which composes 60-90% of the crystalline fraction in all samples, can execute at room temperature 180 degrees flips with a frequency in the kilohertz domain. The other crystalline chains are more rigid and probably are found in more perfect structures in which such chain flips do not occur or occur on a much slower time scale. Adding kaoline filler particles to polyethylene enhances the contribution of the more mobile crystalline chains. The presence of the two distinctly different types of crystalline environments is found in all polyethylene samples investigated so far (more than 25 samples).

Partitioning of Main and Side-Chain Units between Different Phases: A Solid-State 13C NMR Inversion-Recovery Cross-Polarization Study on a Homogeneous, Metallocene-Based, Ethylene-1-Octene Copolymer

“…This third phase is usually thought to be a transitional region located in between the crystals and the mobile amorphous regions. This region has been named an interfacial or interphase region [20][21][22][23][24][25][26][27][28][29]40]. However, the techniques used so far, DSC, WAXD, SAXS, do not give clear information on this matter.…”

“…This experiment shows an improved selectivity to different phases compared to standard CPMAS experiment [21,37]. Because of the overlapping resonances in 13 C NMR spectra of semi-crystalline m-PE, partitioning into crystalline and amorphous phases of major fractions of the main-and side-chain groups will be considered.…”

“…Up to now, numerous 1 H; 2 H and 13 C solid-state NMR studies on polyethylenes have provided detailed information down to the nano-scale level on phase structure and morphology, especially with respect to crystalline polymorphs, phase composition, chain conformation and molecular motions [20][21][22][23][24][25][26][27][28][29]. A 13 C CPMAS spectrum of linear PE (LPE) consists of a peak at 33:1 ppm due to the all-trans polymer chains within the orthorhombic crystal structure and a broader peak at about 31 ppm due to the non-crystalline phase.…”

“…5. The interpretation of the dependence of the peak areas on t in with respect to chain mobility is complicated because several NMR relaxation processes and complex spin dynamics determine the signal evolution against t in [21,37]. However, it was shown in several studies (see e.g.…”

Morphology and Phase Characteristics of High‐Density Polyethylene Probed by NMR Spin Diffusion and Second Moment Analysis

“…[4,7,8] It is well known that polyethylene (PE) can build polymorphic crystals with both orthorhombic and monoclinic structures. [9] The nature of the boundary between the crystalline and the amorphous phase has also been the subject of many investigations. Kitamaru et al [10] measured three different carbon T 1 values for the orthorhombic crystalline phase, which means that this region behaves heterogeneously with respect to motions in the MHz frequency range.…”