Poly(γ‐alkyl glutamates). I

Abstract

AbstractGood yields of some crystalline γ‐alkyl esters of L‐glutamic acid were obtained by carrying out the esterfication with a small (20–50 mole‐%) excess of alcohol in aqueous hydrochloric acid or 60–80% sulfuric acid followed by neutralization with an alkaline solution. This new method made it possible to synthesize various γ‐alkyl L‐glutamates, including those higher than ethyl, and consequently, various poly(γ‐alkyl L‐glutamates) such as methyl, ethyl, n‐propyl, n‐butyl, isobutyl, and isoamyl. The conformation of these poly‐L‐glutamates in the solid state was determined by the infrared absorption method. The molecular motions of the polymers of γ‐methyl, ‐ethyl, ‐n‐propyl, ‐n‐butyl, and‐isoamyl L‐glutamates and poly(γ‐methyl‐D‐glutamate) in the solid state were studied by NMR, and dielectric and mechanical measurements. At temperatures up to 400°K., the NMR spectra of poly(γ‐methyl D‐glutamate) can be explained only by rotational motion of the side chain. Also, from NMR results, rotational motion of CO groups in the side chain of poly(γ‐methyl D‐glutamate) is expected near room temperature, and such a motion was examined by dielectric measurements. Rotation of CO groups in the side chains of polymers of γ‐methyl, γ‐ethyl, γ‐n‐propyl, γ‐n‐butyl, and γ‐isoamyl L‐glutamate was also observed near room temperature by dielectric measurements in the frequency range from 102 to 106 cps. Activation energies obtained by dielectric and mechanical measurements were similar to those for the side chain motions of the corresponding esters of poly(methacrylic acid). Although it has been noted that the molecular motion of poly(γ‐benzyl L‐glutamate) in the solid state at room temperature may be related to the motion of its back bone, the molecular motion in these poly‐L‐glutamates at these temperatures can be explained only in terms of side‐chain rotation.