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.

Because of its robust nature, Grubbs' ruthenium benzylidene catalyst RuCl2(CHPh)(PCy3)2 promotes the successful acyclic diene metathesis (ADMET) bulk polymerization of alcohol-functionalized dienes, thus providing a method for the direct synthesis of linear polymers containing hydroxy groups. Primary, secondary, and tertiary alcohol functional groups can be placed at precise intervals along an unsaturated hydrocarbon backbone. Exhaustive hydrogenation of the secondary alcohol homologue produces a well-defined ethylene−vinyl alcohol copolymer. Only the unsaturated and saturated secondary alcohol polymers crystallize, a phenomenon likely attributed to the enhanced packing propensity of these macromolecules in comparison with those of their primary and tertiary analogues.

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