METMED-CRP

Toward new polymeric materials by metal-mediated controlled radical polymerization

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 Obiettivo del progetto (Objective)

'Controlled radical polymerization has revolutionized polymer research and has already started to revolutionize the polymer industry as previously unthinkable and complex polymer architectures are becoming available. However, access to a wider variety of polymer material is limited by the inability (so far) to control the radical polymerization of nucleophilic monomers. The host team is a world leader in the understanding and application of transition metal one-electron processes (homolytic bond breaking, atom transfer) to controlled radical polymerization and has recently obtained an important breakthrough in this area, by showing how the strength of metal-carbon bonds in organometallic complexes can be tuned to control the polymerization of vinyl acetate by the organometallic radical polymerization (OMRP) mechanism. The post-doctoral candidate has received outstanding training in precision polymer synthesis by ATRP from one of the leading polymer groups in Korea, and he has also familiarity with simple coordination compounds of a few metals commonly used for ATRP. Thus, he has the perfect background to give a strong contribution to this area. This fellowship represents an opportunity for the researcher to receive high quality training in the research area that is not yet highly developed in his own Country (China). Therefore, the training experience and the acquired know-how will be most valuable for a future reintegration of the researcher in his own Country either in an academic or in an industrial environment and for the development of a fruitful continuing collaboration with the host group.'

Introduzione (Teaser)

The organic monomer vinyl acetate (VAc) is the precursor to polyvinyl acetate, an important industrial polymer. Controlled polymerisation of Vac is set to produce an explosion in production of previously impossible to engineer compounds.

Descrizione progetto (Article)

The advent of controlled radical polymerisation has led to the development of complex polymer architectures that were once impossible to produce. VAc is a very high-profile monomer or building block due to its application in coatings, textiles and pharmaceutical industries.

A disadvantage attached to VAc is that the monomer can only undergo radical polymerisation and is nucleophilic. Complete success in gaining a wide variety of polymer materials has so far been hindered by the resulting inability to control the radical polymerisation process.

The 'Toward new polymeric materials by metal-mediated controlled radical polymerization' (Metmed-CRP) project aimed to overcome this limitation. By tuning the strength of metal-carbon bonds in organometallic complexes, they aimed to modulate and control the organometallic radical polymerisation (OMRP) process.

To achieve this, metals that do not form very strong metal-carbon bonds are required and iron (Fe) (II) and copper (Cu) (I) therefore fit the bill. Fe-based catalysts seem particularly attractive due to their low cost and toxicity as well as their use in other polymerisation processes.

Using Fe in the system, VAc polymerisation is controlled, albeit weakly; additional control was achieved by the addition of phosphines as they slowed down the process. One further problem was higher molecular weights compared to the theoretical proportion. However, results showed relatively low polydispersity (range of size). Use of dimethylphenylphosphine in particular gave the smallest differential between the observed and calculated polydispersity index (PDI).

Metmed-CRP scientists have also isolated a metal-capped short oligomer for future use. The team characterised the fragment using nuclear magnetic resonance (NMR) spectroscopy, electron paramagnetic resonance (EPR) and chemical derivatisation and they proved reversible radical release from the oligomer. During the OMRP process, there has to be reversible release of the PVAc chains from the acetylacetonate (acac) 2Fe-PVAc species.

Being able to manipulate molecular weights and structures of derived polymers will help to realise the full industrial potential of VAc.