Project

Discipline

Lead
Lay summary
The first two sub-projects deal with the development of new synthetic methods that allow the synthesis of polymer chains with precisely defined end-groups. The ends of long polymer chains often need to be chemically different to the rest of the polymer chain in order to allow their attachment to surfaces or to synthesize more complex polymer architectures. The ring opening metathesis polymerization (ROMP) using ruthenium carbene initiators developed recently by Grubbs (Nobel Prize in Chemistry 2005) allows the synthesis of well-defined polymers. However, only few methods were reported until recently that addressed the functionalization of the polymer chain ends. The work proposed here deals with the development of new synthetic procedures that allow control over the nature of the polymer chain ends in ROMP polymers. The third sub-project deals with the synthesis of diblock copolymers, i.e. linear polymer chains that consist of two chemically different strands covalently linked via their chain ends. Such polymers often adopt interesting solid state phases because the two chemically linked strands try to separate from each other. As they cannot fully separate due to their chemical linkage, they form periodic patterns in the solid state in which regions of different chemical composition alternate. Some of these patterned solid state structures (for example the so called gyroid phase) are envisaged to be of great interest for the fabrication of solar cells and other electronic devices. However, the synthesis of these more interesting phases is often difficult to achieve in a controlled manner. In our sub-project we propose the synthesis of new polymers that can be altered after the polymerization in such a way as to target these interesting solid state phases with high confidence.

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Last update: 21.02.2013

Title	Year

Number	Title	Start	Funding scheme

One of the fundamental requirements in polymer chemistry today is the control of functionality and functionality placement on various size scales ranging from individual polymer chains to micellar aggregates to self-organised phases in the solid state. The three research projects (subproject A, B, C) described below address different aspects of this requirement, dealing with the placement of functional polymer end-groups in the first two projects and control over the self assembled solid state phases via post polymerisation functionalisation of block copolymers in the third.The first research project deals with the development of methods for introducing end-groups for living olefin metathesis polymers. Since the recent development of very stable and functional group tolerant ruthenium carbene complexes by Grubbs et al., the ring opening metathesis polymerisation (ROMP) has received increased attention. Several techniques for introducing end groups to olefin metathesis polymers via acyclic diene metathesis (ADMET) or ROMP using chain transfer agents have been reported. However, these methods typically give broader molecular weight distributions and carry two functional groups, one at either chain end. The ring opening metathesis polymerization (ROMP) using chain transfer agents is not a living polymerization technique and hence gives less control over the molecular weight distribution and at best homo-telechelic polymers carrying two identical chain-end groups.One major drawback of the living metathesis polymerisation technique, i.e. in the absence of chain transfer, compared to most others was, that it didn‘t offer a straightforward synthetic method for introducing functional end-groups. We recently developed several ways to overcome this limitation and hydroxyl, thiol, aldehyde and carboxylic acid groups are now readily available as living ROMP end-groups. In this proposal we focus on the introduction of amine or protected amine end-groups via the so-called Sacrificial Synthesis. This technique makes use of cyclic olefins that can later on be cleaved to yield the required functionality at the polymer chain end. Amines are very useful nucleophiles that can readily be further functionalised by reductive alkylation or amide formation. More complex polymeric architectures or polymer conjugates with functional molecules, oligomers or biomolecules are thus readily accessible.Secondly, the synthesis of a universal end-capping reagent is proposed based on functionally substituted vinyl esters or vinyl halides. Very recent reports indicate that such compounds are likely to act as living ROMP terminating agents and can easily be synthesised and derivatised. As they carry a readily functionalisable group in addition to a group that forms a non-metathesis active carbene, such compounds will be particularly useful for the attachment to macroscopic surfaces, nanoparticles or functional solid supports. Solid surfaces derivatised in this way will readily react with the polymeric ruthenium carbene such that the polymer block will be transferred onto the surface. In the case of solid supports, the result will be a polymer conjugate with a sequence-controlled oligomer prepared on the solid support, for example a peptide.Making use of this functional group tolerance, we propose a third project dealing with the synthesis of post-polymerization functionalisable di- and multiblock copolymers via ROMP. The block copolymers will undergo a microphase separation adopting different solid-state phases depending on the volume fraction of the individual polymer blocks. At least one of the blocks will, however, carry functionalities that allow a post polymerisation volume fraction alteration and hence the possibility to change the position within the solid-state phase diagram. This will be particularly useful for targeting „difficult phases“ such as the gyroid phase, a bicontinuous phase of two interpenetrating polymer blocks, which takes up only a small area in the phase diagram. Additionally, this approach can be of great use in the examination of polymer phase diagrams as one functionalisable block copolymer can be used to sample a range of positions within the solid-state phase diagram by altering the volume fraction of one or more blocks after the polymerisation.