Precisely Controlled Methyl Branching in Polyethylene via Acyclic Diene Metathesis (ADMET) Polymerization

Abstract

A synthetic approach to attain precisely controlled methyl branching in polyethylene is described. Model polymers based on polyethylene have been created using acyclic diene metathesis (ADMET) chemistry as the mode of polymerization. Differential scanning calorimetry (DSC) was employed to examine the thermal behavior (melting point, heat of fusion, glass transition temperature) of five model polyethylene polymers wherein a methyl branch was placed on each 9th, 11th, 15th, 19th, and 21st carbon respectively along the backbone. Melting points and heats of fusion decrease as the frequency of precise methyl branching increases. On the other hand, the β glass transition and its change in specific heat are independent of branch frequency. Comparisons of these model polymers with industrial polyethylene samples demonstrate that this polycondensation approach will provide the basis for a better understanding of the morphology, crystalline structure, and thermodynamics of the crystallization process of the most abundant synthetic macromolecule in the world, polyethylene.

Precision Ethylene/Vinyl Bromide Polymers

“…A linear decrease in T m is evident with increasing bromine content. This linear trend has been observed for a series of precise methyl-branched PE derivatives synthesized via ADMET [20] (see Supporting Information); and here, the correlation of the trends is accentuated by the similarity in the size of the bromine atom and the methyl group. The decrease in T m can be explained using the same arguments proposed for PE19Br and similar halogenated ADMET polyolefins, [12] specifically, that increased bromine content in the crystal is the direct consequence of polymer composition and the larger incorporation of defects leads to a proportionally decreasing T m .…”

Synthesis of poly(sulfonate ester)s by ADMET polymerization

“…20,53 A comparison of the literature data suggests that an increase of the fraction of methyl groups has a more significant influence on the melting point of the corresponding polymer than an increase of the ester content. In addition, an increase of the methyl content was found to cause a change of the morphology from an orthorhombic to a hexaganol crystal structure, 53 whereas the orthorhombic structure was maintained in long-chain polyesters.…”

“…18,19 Unlike the related ring-opening metathesis polymerization (ROMP), which is a chain-growth process driven by the release of ring strain, ADMET is driven by the removal of the ethylene gas generated as a by-product. ADMET chemistry has been used recently in the synthesis of both all-carbon polyolefins [20][21][22] as well as polyethylene-like polymers containing heteroatoms [23][24][25][26][27][28][29] or aromatic rings [30][31][32] in the main chain. ADMET offers an interesting alternative for the incorporation of aliphatic sulfonate esters into the polymer backbone, which are rare in the literature.…”

gem‐Dimethyl Effects in the Thermal Behavior of Polyethylene

“…This alternative approach is founded on equilibrium polycondensation chemistry (acyclic diene metathesis (ADMET) reaction) to precisely insert branches within polyethylene. [13,14] The course of this work has led to identifying parameters needed to render polyethylene completely amorphous.…”