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Acyclic diene metathesis (ADMET) is a flexible approach for the production of diverse polymeric materials. The advent of well‐defined catalysts and the simplification of laboratory techniques has made the ADMET reaction useful for many applications, such as polyolefin model studies and the synthesis of organic/inorganic hybrid polymers, telechelics, copolymers, conjugated polymers, liquid crystalline polymers, and amino acid‐based chiral polymers. Many of the polymer architectures that have been produced using ADMET cannot be made by other means.

Amorphous, hydrophobic telechelic hydrocarbon diols were synthesized using acyclic diene metathesis (ADMET) polymerization. These diols can be used in hydrolysis and UV resistant polyurethanes. The hydrocarbon backbone is based on a mimic of an ethylene/isobutylene polymer, made by the ADMET polymerization of a gem‐dimethyl substituted α,ω‐diene followed by hydrogenation of the polymer's repeat unit unsaturation. Chain termination reactants (CTR's) having one, three, and nine methylene “spacers,” respectively, between their olefin and alcohol precursor group were used to cap the polymer chain ends to yield 2.0 functional telechelics. Use of the medium length CTR in a polymerization–depolymerization scheme, resulted in amorphous (Tg = −56 °C) telechelic diols with good molecular weight control.magnified image

Summary: Polyethylene can be rendered completely amorphous via the insertion of regularly spaced gem‐dimethyl defects along its backbone, where frequency of insertion is the deciding factor in achieving the totally amorphous state. Accurate placement of defects along polyethylene's backbone is achieved with step polymerization metathesis chemistry (the ADMET reaction) rather than using chain polymerization techniques. These gem‐dimethyl polyethylene macromolecules, when compared with other ADMET ethylene‐based model materials, demonstrate that steric bulk, frequency, and distribution of the defect along the polymer backbone are more important than stereoregularity (tacticity) when the defects are spaced nine carbon atoms or more apart. Comparisons are made between gem‐dimethyl “defects” and methyl “defects” in a polyethylene backbone.

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The synthesis, characterization, and thermal behavior of ADMET models of ethylene/methyl methacrylate (EMMA) and ethylene/methacrylic acid (EMAA) copolymers are described. These model copolymers exhibit sharper melting transitions and lower melting points relative to random copolymers made using chain-growth polymerization methods. The EMMA and EMAA model copolymers are compared with ADMET ethylene-based model copolymers reported previously, comparisons which support the earlier finding that melting points decrease with an increase in the steric bulk of the pendant group.

Back Cover: Polyethylene can be rendered completely amorphous by inserting regularly spaced gem‐dimethyl defects along the polymer backbone. Frequency of insertion is the deciding factor. For example, placing a gem‐dimethyl defect at each and every 9th carbon (8 carbon run length) yields amorphous polyethylene, whereas the polymer possessing an equivalent defect at each and every 15th carbon (14 carbon run length) crystallizes. Precise placement of these gem‐dimethyl defects along the polymer backbone is accomplished by employing step polymerization chemistry (the ADMET reaction) rather than using traditional chain polymerization techniques. Further details can be found in the Full Paper by J. E. Schwendeman and K. B. Wagener* on page 1461.