ROMP-CT/NMP Synthesis of Multiblock Copolymers Containing Linear Poly(ethylene) Segments

Linear Block Copolymer Synthesis

Block copolymers form the basis of the most ubiquitous materials such as thermoplastic elastomers, bridge interphases in polymer blends, and are fundamental for the development of high-performance materials. The driving force to further advance these materials is the accessibility of block copolymers, which have a wide variety in composition, functional group content, and precision of their structure. To advance and broaden the application of block copolymers will depend on the nature of combined segmented blocks, guided through the combination of polymerization techniques to reach a high versatility in block copolymer architecture and function. This review provides the most comprehensive overview of techniques to prepare linear block copolymers and is intended to serve as a guideline on how polymerization techniques can work together to result in desired block combinations. As the review will give an account of the relevant procedures and access areas, the sections will include orthogonal approaches or sequentially combined polymerization techniques, which increases the synthetic options for these materials.

Synthetic approaches for multiblock copolymers

Multiblock copolymers (MBCs) are an emerging class of synthetic polymers that exhibit different macromolecular architectures and behaviours to those of homopolymers or di/triblock copolymers.

Catalytic Living Ring Opening Metathesis Polymerisation: The Importance of Ring Strain in Chain Transfer Agents

A recently developed catalytic living ring opening metathesis polymerisation (ROMP) was investigated using a series of reversible chain transfer agents (CTA) carrying either cyclopentene or cyclohexene rings, differing only in ring strain. All cyclopentene derivatives examined showed significantly faster reaction rates than the corresponding cyclohexene derivatives. This resulted in lower molecular weight dispersities and better control of the molecular weight for the cyclopentene compared to the cyclohexene CTAs. Both Grubbs' second and third generation catalysts could be employed in catalytic living ROMP using cyclopentene CTA derivatives. The kinetics of different CTAs were studied, block copolymers were synthesised and residual ruthenium quantified by ICP-OES. All polymers were fully characterised by NMR, GPC and MALDI-ToF mass spectrometry. The new cyclopentene CTAs are readily synthesised in a few straightforward steps and provide faster reaction kinetics than all previously reported reversible CTAs.

Olefin metathesis in multiblock copolymer synthesis

Multiblock copolymers constitute a basis for an emerging class of nanomaterials that combine various functional properties with durability and enhanced mechanical characteristics. Our mini-review addresses synthetic approaches to the design of multiblock copolymers from unsaturated monomers and polymers using olefin metathesis reactions and other ways of chemical modification across double C=C bonds. The main techniques, actively developed during the last decade and discussed here, are the coupling of end-functionalized blocks, sequential ring-opening metathesis polymerization, and cross metathesis between unsaturated polymers, or macromolecular cross metathesis. The last topic attracts special interest due to its relative simplicity and broad opportunities to tailor the structure and hence the properties of the copolymer products. Whenever possible, we analyze the structure-property relations for multiblock copolymers and point to their possible practical applications.

Sequential ROMP of cyclooctenes as a route to linear polyethylene block copolymers

AB diblock copolymers were prepared by sequential ring-opening metathesis polymerization of cyclooctenes catalyzed by a Ru-based Grubbs catalyst. The relatively slow polymerization of cis-3-phenylcyclooct-1-ene (3PC) or cis-cyclooct-2-en-1-yl acetate (3AC) was first carried out and then followed by the faster polymerization of unsubstituted cis-cyclooctene (COE) from the active Ru-alkylidene chain ends. In contrast, simultaneous polymerization of the two monomers provides copolymers with a statistical monomer distribution owing to extensive chain transfer. The resulting poly(3PC-b-COE) and poly(3AC-b-COE) diblock copolymers were subjected to hydrogenation to selectively saturate the backbone alkenes. The consequences of architectural variance between the materials from simultaneous vs. sequential polymerizations are reflected by the contrasting thermal characteristics.