A series of polyethylene with precise branch are synthesized by acyclic diene metathesis(ADMET) polymerization to investigated the effect of branch volume on the crystallization behavior using thermal fractionation technique. Branches such as F, Cl, Br, methyl, ethyl, and pentyl are placed on every 21th backbone carbon (Fig.1, Fig.2). After stepwise isothermal crystallization, the melting curves display a varieties of melting range. The PE21F, which has the smallest branch volume, has one melting peak corresponding to a much greater crystalline ethylene sequence length (CESL) than 21. The PE21P with pentyl branch, which has the largest branch volume among these samples, has one melting peak well below the melting point of typical polyethylene, indicating a short CESL of 21. It suggests that F branch can be entirely accommodated in the crystal because of small atomic radius, while pentyl branch is entirely excluded from a crystalline phase, due to large volume of the pentyl group. With increasing volume of the branch from Cl to ethyl, multiple melting peaks move to lower temperature, indicating more and more influence from the branch volume.Figure 1. Molecular structure of ADMET polyolefinsFigure 2.   DSC heating curves of ADMET polyolefins after thermal fractionation (PE21X represents ADMET polyolefins with branches F, Cl, Br, methyl, ethyl, pentyl placed on every 21th backbone carbon)

Crystallization behavior of ADMET polyolefins with precise branching

248th National Meeting (2014)

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