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Synthesis and properties of polyhydroxyacid functionalized metathesis polyacetylenes

Final Activity Report Summary - SYNTBIOPOL (Synthesis and properties of polyhydroxyacid functionalized metathesis polyacetylenes)

The emerging technologies (e.g. in optics, microelectronics, medicine etc.) require availability of synthetic polymers with continuously more sophisticated properties and performances. The best way for production of the multicomponent materials with unusual technologies is to tailor their molecular architectures. Thus, the aim of this project was to synthesise and characterise the biodegradable graft copolymers with a regular non-polar backbone via metathesis polymerisation and the polar, biocompatible side chain via ring opening polymerisation. Because the physical properties of the polymeric material are tied directly to its molecular weight and control of polymer molecular weight is of utmost importance in the synthetic procedure, we decided to use well-defined ruthenium initiators.

Although, to our knowledge there is only few example of polyacetylene derivatives produced in the metathesis polymerisation by well-defined ruthenium catalyst. Thus, in the first year of the project a series of hydroxyacetylenes were subjected to metathesis polymerisation by two well-defined ruthenium initiators, modified second generation Grubbs and Grubbs-Hoveyda complexes, to prepare polyacetylenes with polar groups. Additionally, those polymers were prepared also by using ill-defined molybdenum based initiator to compare the structure with that obtained by ruthenium catalysts. The geometric structure and properties of polyacetylenes prepared with ruthenium catalysts were different from those obtained in the presence of molybdenum initiators. On the basis of NMR and UV-VIS spectra, we assumed that polymers prepared with the Ru and Mo catalysts had different geometric structure of the main chain.

The ruthenium initiators gave polymers of higher stereoselectivity than molybdenum-based one. The rates of polymerisation of hydroxyacetylenes by ruthenium initiators depend on the structure of hydroxyacetylene and the location of hydroxyl group in the substrate. The lack of polymerisation of acetylene with long linear hydroxyalkyl substituent might be due to chelation of the oxygen of hydroxyl group to the ruthenium. To the best of our knowledge, this is the first example of the polymerisation of hydroxyacetylenes by well-defined ruthenium catalysts.

Those alkylidene ruthenium catalysts were also effective in metathesis polymerisation of polylactide macromonomers end-capped with acetylene group. The degree of polymerisation strongly depends on the structure of macromonomers. The more bulky substituents of the macromonomer the lower degree of polymerisation was observed.

We believe these graft copolymers will constitute a new class materials which would attract growing interest for practical applications from packaging to more sophisticated biomedical devices. The tolerance of state-of-the-art ruthenium catalysts to impurities and organic functionality and their activity in metathesis polymerisation of substituted acetylenes allow for synthesis of polyacetylene derivatives with unique properties as well as for preparation of polymers with more complex molecular architecture.