Preparation, characterization, and optical properties of disulfide-comprising oligo[2,5-bis(thiomethyl)-1,4-dithiane] and its poly[S-alkylcarbamate]

Novel poly[S-alkylcarbamate]s were prepared by polyaddition of oligo [2,5-bis(thiomethyl)-1,4-dithiane] (oligo[BMMD]) with isocyanate for optical polymers having high refractive indices (nD) and Abbe's numbers (νD). Oxidation of 2,5-bis(mercaptomethyl)-1,4-dithiane (BMMD) with ferric chloride or methylsulfoxide gave oligo[BMMD] in a mixture of n-mers (typically n = 1−6) by disulfide-forming propagation. The use of the former oxidant giving mainly BMMD dimer appeared to be preferable for the subsequent preparation of transparent poly[S-alkylcarbamate]. With 1,3-bis(isocyanatomethyl)cyclohexane, 1,6-diisocyanatohexane, or 1,3,5-tris(isocyanatomethyl)cyclohexane, nD:νD values of poly[S-alkylcarbamate]s ranging from 1.609:38.0 to 1.659:35.6 were comparable to those of flint glasses. Copoly[S-alkylcarbamate]s were prepared using 2-mercaptoethylsulfide or 2-mercaptoethylether for modification of nD and νD. Contribution of the disulfide bond and the 1,4-dithiane ring in oligo[BMMD] to increase nD is discussed in terms of molar refraction. Suppressed UV absorption of the polymer, which caused high νD, was attributed to the trans-gauche-trans conformation around the disulfide bond. This work shows that oligo[BMMD] serves as a useful material for the preparation of polymers having high nD and high νD and that poly[S-alkylcarbamate]s thus obtained are promising optical materials.