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42 Ralf Steudel · Bodo Eckert Table 18 Nomenclature of polymeric sulfur as found in the literature. The most frequent while ambiguous terms low) Designation Amorphous, vitreous, glassy or plastic sulfur Polymeric or insoluble sulfur Fibrous sulfur Sw Sm Crystex sulfur S1 are quoted (high-pressure allotropes are omitted; see Section 3 be- Description, nter-relation between forms Quenched product from the melt above 160 C; contains chains and rings of different size depending on the procedure Product after extraction of quenched liquid sulfur with CS2; synonyms are Sm (after Smith [109]) and—sometimes—Sw Stretching the quenched product (with or without extraction of rings), drawing filaments directly from the melt; synonym for the crystallized solid was f-sulfur, which consists of oriented helices (y-sulfur, Sy) and g-S8 [31,110]; actually, y-S is the solid allotrope of fibrous sulfur after extraction of the rings with CS2 Amorphous sulfur not stretched before extraction with CS2, synonyms are "white sulfur of Das" [111, 112] and supersublimated sulfur; actually a mixture of two independent allotropes Sw1 (=Sy0=2nd fibrous sulfur) and Sw2 (=Sc=laminar sulfur) [54, 113– 115]; sometimes also called Sm, plastic, fibrous, or polymeric sulfur Synonym for polymeric or insoluble sulfur; also used for the mole- cule catenapolysulfur in the solid and—sometimes—in the liquid phase (S1)a A mixture of polymeric chains and little S8 rings containing organ- ic stabilizers; also called supersublimated sulfur. Polymer fraction consists of Sw1 and mainly of Sw2 [116, 117]. Generally used for the catenapolysulfur molecule, e.g., the biradi- calic chain (·Sn·) in sulfur melts [43, 106]; also used for the free or hypothetical helix molecule and for the polymeric chain in the sol- id state if the polymeric nature is to be stressed; further synonyms are polymeric sulfur, Sn chain, and Sa a See the recommendations in the text S ignores details in the actual molecular (and solid state) conformation, al- though it is clear that the molecular structure is a three-dimensional helical- like chain even if there is a certain disorder on the molecular and crystalline level. Hence, S should be understood as a generic term. The many efforts to determine the structure of polymeric sulfur al- lotropes have been critically reviewed by Donohue in 1974 [8]. Since that time, only a few experimental results have been reported which, however, did not introduce new structural details. Most of the more recent studies on polymeric sulfur are focused on the unique polymerization transition in the liquid. Experimental structure studies therefore often deal with quenched sulfur melts (see for example [118, 119] and literature cited therein). On the other hand, the polymerization mechanism has attracted increased interest for theoretical studies (see for example [120–123] as well as the literature cit- ed therein).PDF Image | Topics in Current Chemistry
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