Abstract
The phenomenon of exciton coupling, which is very well known from circular dichroism (c.d.) spectroscopy studies of biopolymers, has now also been found for syndiotactic vinyl polymers in solution. The syndiotactic polymers were prepared by reacting poly(methacrylic acid hydrazide) with the N-protected amino acids l-(+)-serine and l-(+)-alanine, yielding poly[methacrylic acid-N β(N( t-butyloxycarbonyl) l-seryl) hydrazide ] and poly[methacrylic acid-N β(N( t-butyloxycarbonyl) l-alanyl) hydrazide ] . On removal of the N-t-butyloxycarbonyl group, the corresponding deprotected polymers were also obtained. All four polymers possess functional and optically active lateral chains which are capable of mutual interactions by hydrogen bonding, dipolar and electrostatic forces. At strongly alkaline pH, the diacyl hydrazide moiety is deprotonated to confer polyelectrolyte character to the macromolecule. The interactions between lateral chains lead in the deprotonated state to spatial and conformational order between the side chains, causing sizeable excition effects in the c.d. spectra. The presence of exciton effects was supported by the c.d. spectroscopic behaviour of the polymers at different pH and by that of copolymers, the latter being obtained by different degrees of conversion of the poly(methacrylic acid hydrazide). The degree of order is strongly influenced by changing temperature and the addition of methanol and salts. By comparison with previously studied polymers derived from syndiotactic poly(methacrylic acid hydrazide) and l-(+)-lactic acid or d-(−)-lactic acid, the structural features necessary for exciton coupling are discussed. A model for the main-chain conformation which was proposed earlier was found to be compatible also with the results obtained for the present polymers.
Published Version
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