Polymer Chemistry
(University of Helsinki )
Heikki Tenhu
Professor, PhD
Controlled syntheses of 'smart' polymers are in the focus of our research. The polymers under study are water soluble or amphiphilic (i.e. contain both water soluble and insoluble structural units), polyelectrolytes (electrically charged polymers) and thermally responsive polymers. Thermally responsive polymers are ones which dissolve in water around room temperature but phase separate upon increasing (or decreasing) temperature. With these polymers it is possible to construct various materials from nanosized particles to macroscopic gels which compress upon increasing temperature and swell when temperature is lowered again. On the other hand, polyelectrolytes are used when materials are needed that respond to changes in pH or ionic strength.
Metallic nanoparticles (gold, silver, copper) stabilised with polymers are also prepared in the laboratory. Using e.g. thermoresponsive polymers it has been possible to prepare gold nanoparticles, which either disperses in water or precipitate. Nanosized metal particles have optical and electric properties which strongly differ from those of bulk metals.
Modern controlled polymerisation reactions make it possible to adjust the molar mass and molar mass distribution in radical polymerisation. These reaction types can also be used in constructing complex polymer architectures like block, graft, or star polymers. One example of such polymers is star block copolymers synthesised in the laboratory. A star polymer is one where several chains are grown from one point. Recently, stars with six arms have been synthesised where the inner parts of the arms are insoluble in water but the outer parts comprise of extremely soluble polyelectrolyte chains. These kinds of polymers show very complex self-assembling behaviour in water. Micelles formed by these polymers can also be used in the complexation and transfection of plasmid DNA.
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