Modeling the effect of precise short-chain branch placement in ethylene-co-propylene and ethylene-co-butylene materials: Synthesis, thermal behavior, and morphological characterization

By far, ethylene-based materials (homo and copolymers) constitute the highest volume of synthetically produced macromolecules in the world today. Although such factors as mode of polymerization (radical, Ziegler-Natta, etc.), choice of catalyst, temperature of reaction, and molecular weight are of extreme importance, the distribution and amount of the short-chain branching (SCB) content are the most influential factors for determining the final materials properties for ethylene/α-olefin copolymers.; Chapter 2 describes the first synthetic approach to attain precisely controlled methyl branching in ethylene-co-propylene (EP) materials created via acyclic diene metathesis (ADMET) chemistry. In Chapters 2 and 3, differential scanning calorimetry (DSC) was employed to examine the thermal behavior of five model EP copolymers wherein a methyl branch was placed on each and every 9th, 11th, 15th, 19th, and 21st carbon along the backbone.; Chapter 4 details the first secondary structural data for these model EP copolymers via a variety of techniques including wide-angle x-ray diffraction (WARD), small-angle x-ray scattering (SAXS), optical microscopy (OM), transmission electron microscopy (TEM), electron diffraction, infrared (IR) spectroscopy, and Raman scattering. The crystalline regions in these systems were found to be pseudo-hexagonal and consist of parallel-packed arrays of conformationally disordered (Condis) hydrocarbon chains. This is the first verified existence of the pseudo-hexagonal phase for an ethylene-based material without having initially applied high pressures/temperatures to the sample and/or stretching the material prior to analysis.; Chapter 5 presents the synthetic methodology used to create the first ADMET model ethylene-co-butylene (EB) materials in which the ethyl branches are set into a precise methylene sequence length (MSL). In particular, details are provided in regard to monomer/polymer syntheses, characterization, and initial thermal behavior findings for a single model EB copolymer in which the ethyl branch has been placed on each and every 9th carbon along the polymer backbone.; Comparisons of these model polymers with industrial polyethylene samples demonstrate that this polycondensation approach provides a significant opportunity to better understand the morphology, crystalline structure, and thermodynamics of the crystallization process for the most abundant synthetic macromolecule in the world, polyethylene.