Simple NMR Experiments Reveal the Influence of Chain Length and Chain Architecture on the Crystalline/Amorphous Interface in Polyethylenes

摘要

The distribution of polyethylene (PE) chain segments between the crystalline) noncrystalline, and interfacial morphological regions is an old question that continues to intrigue the polymer science community. Simple solid state NMR experiments described here reveal that even in:the case of linear PE, four, distinct chain components may be resolved and reliably quantified. The amounts of rigid crystalline chains, in all-trans conformations, amorphous, chains with, increased equilibrium,gauche conformer content, undergoing essentially isotropic reorientation, mobile all chains (termed mobile trans), and less Mobile noncrystalline Chains (termed constrained amorphous) can be quantified by simple C-13 NMR. experiments On polymer samples. A version of the EASY background. suppression pulse :sequence [Jaeger and. Hemmann Solid State Nucl. Magn. Reson. 2014, 57-58; 22], modified to eliminate transient Overhauser effects) is used to obtain all of the data in a-single experimental acquisition. Using a broad range of well characterized linear metallocene PE's, the Method reveals that the constrained amorphous and the mobile all trans fractions, i.e, the total interface content, :increases essentially linearly with increasing M-w. Topologically modified PE's, at similar Mw's, that contain short-chain branches (SCB), long-chain branches (LCB), or long-chain branches with SCB's (LCB + SCB) have significantly larger interfacial content per unit molecular weight and most significantly so for the LCB + SCB polymers.