Dicyclopentadiene reacts with excess sulphur in the melt at 140°C to give initially cyclic tri‐ and pentathianes which then copolymerise with further sulphur to give initially chain polymers and then finally cross‐linked species, Styrene reacts under the same conditions to give rapid initial formation of relatively high molecular weight polymeric polysulphides which then depolymerise to give a mixture of short chain species and 2,4‐diphenylthiophene.

Materials prepared by modifying sulfur with dicyclopentadiene or styrene consist of unreacted sulfur and polysulfides. Dicyclopentadiene reacts with sulfur to give, initially, low -molecular-weight polysulfides (e.g., a pentasulfide) which convert to high-molecular-weight polymers at 140°C. Sty rene initially gives high-molecular-weight polymers which depolymerize. With dicyclopentadiene Ν,Ν,Ν',Ν'-tetramethylethylenediamine catalyzes the formation of low-and inhibits the formation of high-molecular-weight material and therefore offers promise as a viscosity control agent. The mechanical properties of modified sulfur vary with time after preparation. Modifiers can stop or reduce the embrittlement of elemental sulfur. The tensile strength of polypropylene and glass-fiber fabrics may be increased by up to 87 and 104%, respectively, on impregnation with sul fur materials."elemental sulfur has been proposed (1,2) for a wide range of applications in the civil engineering field. In virtually all of these appli cations it has been necessary to modify the sulfur with additives designed to stop the embrittlement which occurs with pure elemental sulfur. Thus if pure elemental sulfur is heated to 140 °C and then cooled to ambient temperature, monoclinic sulfur (S^) is instantaneously formed (3), fol lowed by a reversion to orthorhombic sulfur ( S« ) which is almost com plete in about 20 hr ( Figure 1 ). Many additives have been proposed to modify elemental sulfur, nearly all of which fall under the heading of polymeric polysulfides or, alternatively, substances which may react with elemental sulfur to give in situ formation of polymeric polysulfides. In a previous paper (3), we reviewed the various substances used as addi-0-8412-0391-l/78/33-165-013$05.00/0 Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 15, 2014 |

Liquid sulfur–olefinic reactions at 140°C forming crosslinked polysulfide polymers have been investigated. A systematic approach to the characterization and some structure–property studies on these new polymeric materials has been presented. The olefinic systems of interest are endo‐and exo‐dicyclopentadiene and an oligomeric alkenyl polysulfide. Equimolar S8–olefinic system copolymers are amorphous and they show no tendency for sulfur crystallization. A correlation has been drawn between chemical structure and glass transition temperature of the copolymers and terpolymers. Mechanical properties and, in particular, chemical stress relaxation of the crosslinked polysulfide polymers have been investigated.

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