Acyclic metathesis polycondensation reaction

Acyclic diene metathesis (ADMET) is a step-growth polycondensation reaction for the polymerization of o -dienes 729 The process is catalyzed by the same metal alkylidene initiators used for ROMP, and is driven by the removal of ethylene from the system (Scheme 13). Both molybdenum and ruthenium-based initiators have been used to prepare a variety of materials including functionalized polyethy-... 

Metathetical polycondensation of acyclic dienes has not been successful with conventional catalysts used for the ring-opening metathesis polymerisation of cycloolefins, which is due to the fact that Lewis acids are usually present, and produce deleterious side reactions [13,16,17]. Only Lewis acid-free, well-defined catalysts have been successfully applied for acyclic diene metathesis polycondensation the key success has been to choose catalysts that obviate other pathways not involving the metathesis mechanism [18-20]. It was Wagener et al. [16,21] who first were able to convert an acyclic a, co-diene (1,9-decadiene), by using an acid-free metal alkylidene catalyst, to a high molecular weight... 

Lewis acid-free catalysts for acyclic diene metathesis obviate the formation of carbocations, which in turn completely eliminates competing reactions, mostly involving cationic oligomerisation via 1-alkene bonds. Thus, metathesis polycondensation occurs quantitatively to yield high molecular weight poly(l-alke-nylenejs with vinyl end groups and ethylene as a byproduct. 

The ruthenium-based catalyst provided by Grubbs et al. [19] also promotes acyclic diene metathesis polycondensation, although with higher concentrations being required to achieve reasonable reaction rates [24,25] ... 

The participation of metallacyclobutane rings in metathesis polycondensation is the reason why the aforementioned sterically encumbered acyclic diene monomers hardly undergo reaction [7-9] in such cases, steric influences at particular positions in the monomer hinder the formation of the necessary metallacyclobutane ring, thus inhibiting polymer formation [1],... 

Telechelic dienes for metathesis polycondensation, containing functional groups such as those in alcohols, esters, carboxylic acids and imides, can be obtained via acyclic diene metathesis depolymerisation [64,65]. They can then be used in further reactions to create hydrophobic polyurethanes and other special-purpose polymers [1]. 

Let us emphasise that the driving force for acyclic diene metathesis, which is a step-growth condensation polymerisation, is the release and removal of a small condensate molecule. The polycondensation is performed preferably under bulk conditions (no solvent used), since acyclic diene metathesis is thermally neutral and there is no need to remove the heat of the reaction, in contrast to exothermic cyclic olefin ring-opening metathesis polymerisation. 

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