Optical rotatory properties of synthetic polymers. II. Optical rotatory dispersion of poly(propylene sulfide)

Abstract

Optically active propylene sulfide was polymerized in the presence of potassium hydroxide as catalyst to give optically active poly(propylene sulfide). Rotatory dispersion curves of the polymer thus obtained were measured in benzene and chloroform media. In both cases, the curves were anomalous in shape with the same sign, having troughs at 290 and 275 mμ, respectively. (–)‐1,2‐Diethylthiopropane was prepared as an optically active model compound of poly(propylene sulfide) in optical rotatory properties. It was found that the model compound also shows anomalous rotatory dispersion both in benzene and chloroform with the same sign. Thus it may be concluded that the anomalous dispersion of poly(propylene sulfide) must be attributed to an additional Cotton effect caused by the absorption of sulfide bonds, which are generally admitted to have absorptions at 200 and 230 mμ (shoulder).

Properties and methods of synthesis of several optically active polyoxiranes and polythiiranes

“…It seems that the optical inversion is not the result of a conformational change of the polymer in different solvents, but must be ascribable to local solvent effects on the polarizabilities of the groups surrounding the asymmetric center. This is supported by the fact that a polymer model shows the same solvent effect as the high molecular weight product [38].…”

“…Consequently an oxirane of the R configuration produces a thiirane of the S configuration. R(+)-and S(-)-methyl thiirane [24], [38] and S(-)-isopropyl thiirane [30] were prepared using this method. In the case of R(-)-phenyl thiirane racemization seems to occur to some extent [39].…”

“…On the contrary, the optical activity of poly(propy1ene sulfide) has the same sign in alJ solvents and depends little on the concentration [24], [38], [41], [58]. A synthesized model compound showed the same behavior as the high polymer [38].…”

“…On the contrary, the optical activity of poly(propy1ene sulfide) has the same sign in alJ solvents and depends little on the concentration [24], [38], [41], [58]. A synthesized model compound showed the same behavior as the high polymer [38]. S(-)-methyl thiirane and S(-)-isopropyl thiirane give polymers levorotatory in chloroform and in benzene, the optical activity in the latter solvent being slightly lower than in the former ( Table V).…”

“…The synthesis of thiirane from an oxirane by reaction with thiourea or potassium thiocyanate has been supposed to be stereospecific and seems not to introduce any racemization as shown in the example of 2,3epithiopropane [37], [103-1041. This is also probably the case for @)-methyl thiirane [38], [46] but some racemization occurs in the case of (R)-phenyl thiirane [39]. The use of chiral shift reagents in NMR seems to be an attractive method for the determination of the optical purity.…”