Precisely controlled methyl branching in polyethylene via acyclic diene metathesis (ADMET) polymerization

A synthetic approach to attain precisely controlled methyl branching in pol yethylene is described. Model polymers based on polyethylene have been crea ted using acyclic diene metathesis (ADMET) chemistry as the mode of polymer ization. Differential scanning calorimetry (DSC) was employed to examine th e thermal behavior (melting point, heat of fusion, glass transition tempera ture) of five model polyethylene polymers wherein a methyl branch was place d on each 9th, 11th, 15th, 19th, and 21st carbon respectively along the bac kbone. Melting points and heats of fusion decrease as the frequency of prec ise methyl branching increases. On the other hand, the beta glass transitio n and its change in specific heat are independent of branch frequency. Comp arisons of these model polymers with industrial polyethylene samples demons trate that this polycondensation approach will provide the basis for a bett er understanding of the morphology, crystalline structure, and thermodynami cs of the crystallization process of the most abundant synthetic macromolec ule in the world, polyethylene.