Helical polyguanidines: Influences and consequences of a biased helix.

摘要

We have been interested in polymers that adopt extended chain helical conformations. The polyguanidines are helical polymers that can be induced to form a biased helical sense by incorporation of enantiomerically pure chiral groups in the side chains of the polymer. We have shown that polyguanidines can show amplification in their optical properties compared to their chiral monomers, but this is not true in all cases. We have shown evidence of both cooperative and non-cooperative polyguanidine systems. We have shown that the inversion barrier of a copolymer is dependent upon the ratio of comonomers. Because the ratio of comonomers is something we have some control over, we can influence a polymer's inversion barrier to some extent.; For some applications external control of the helical conformation is desirable. This control is possible if, in addition to chiral groups, the side chains of the polymer contain switching elements such as azobenzene units. We have prepared several new carbodiimide monomers for the polymerization of polyguanidines. Among these are monomers bearing chiral substituents, azobenzene groups, or both. Initial studies of polyguanidines from these monomers proved difficult due to solubility problems. After trying unsuccessfully to overcome these problems by annealing and protonating the polymers, we developed a new approach to molecular switching in helical polymers. We ran into significant problems in relation to the thermal stability of the isomeric forms of our switching element, azobenzene. We have determined that for future work towards molecular switching new switching elements that are not thermally sensitive should be explored.