Morphological partitioning of ethyl branches in polyethylene by carbon-13 NMR

Abstract

A combination of 13C and magnetic resonance experiments has been performed on a model ethylene copolymer (hydrogenated polybutadiene) of about 100000 molecular weight and 17 ethyl branches per 1000 total carbons. The fraction of ethyl branches found in the crystal in this 41 % crystalline sample was 0.06 ± 0.02, and the ratio of concentrations between the crystalline and noncrystalline regions was correspondingly about 1:10. For reasons of best integrability, the methyl resonance of the ethyl branches was used to deduce the concentrations in each morphological phase. This same resonance is rather ill-behaved in cross-polarization experiments, so several auxiliary experiments were undertaken to deduce the true concentrations attributed to each phase. The experimental technique utilizes cross-polarization as a probe of proton polarization levels; moreover, the success of the method relies on local proton spin diffusion. Results are discussed in terms of other experimental findings regarding the question of partitioning. Also, these results are used to interpret more accurately the data in a previous report on partitioning in an ethylene-l-butene copolymer having a branch concentration about 7 times smaller. Finally, in an appendix, some supplemental data are presented on the effects of magic-angle spinning on the spin dynamics of the noncrystalline region and the influence of this spinning on the validity of the results deduced from cross-polarization experiments.

Effect of Short Chain Branching on the Interlamellar Structure of Semicrystalline Polyethylene

“…It has been observed that the methyl and, to a lesser extent, ethyl branches can be included in the crystallites, due to their small sizes, while propyl and longer branches are completely excluded. [5][6][7][8] Using solid state NMR, White and co-workers 9 also reported an increase in the interfacial content (i.e. "constrained amorphous" plus "mobile all-trans" fractions) with increasing co-monomer content.…”

Thermal and mechanical analysis of metallocene‐catalyzed ethene–α‐olefin copolymers: The influence of the length and number of the crystallizing side chains

“…2 It is generally agreed that these side groups are concentrated in amorphous regions, and at most, only a small proportion of the ethyl groups are located inside crystallites. 3,4 Metallocene catalysts enable the production of a new family of materials, which are eliminating the differences between commodity and engineering polymers and between thermoplastics and elastomers. Consequently the mechanical and physical properties of polyethylene (PE) are drastically changed by copolymerization with small amounts of a-olefins.…”

“…The masses were calculated with the universal method and both detectors. 32 A Fontune TP 400 table press and a special mold were used for the compression molding of the DMA specimens and plates with the dimensions of 2 Â 80 Â 80 mm 3 . From these plates, the tensile test specimens according to ISO 527-2:1993 (type 5A) were made with a stamping press.…”

Metallocene-catalyzed ethylene−α-olefin isomeric copolymerization: A perspective from hydrodynamic boundary layer mass transfer and design of MAO anion

“…This means that the structural/enchainment defects due to 4M1P or 1-hexene were excluded from the pure polyethylene-phase crystal lattice. The [ECC] and [CCC] values (where C = H or 4M1P) of Table 2 as well as the relevant literature support this conclusion [41,[78][79][80][81][82]. The 4M1P or 1-hexene homosequence was not long enough to arrange in a crystal lattice.…”