Normal Linear Grades or General Purpose Grades
General-purpose grades are mostly produced with n-dodecyl mercaptan as the chain transfer agent and occasionally with xanthogen disulfides. If xanthogen disulfides are used, the elastomers are more readily processible and give vulcanizates with improved mechanical properties.
Precrosslinked grades consist of a blend of soluble polychloroprene and crosslinked polychloroprene. They show less swelling after extrusion (die swell) and better calenderability. Precrosslinked grades are particularly suitable for the extrusion of profiled parts.
Sulfur-modified grades are copolymers of chloroprene and elemental sulfur. The viscosity is adjusted – in contrast to general-purpose grades - mostly after polymerization by “peptization” of the polysulfide bonds by e.g. thiuramdisulfides as peptization agents. Sulfur modification improves the breakdown of the rubber during mastication (lowering of viscosity). Sulfur-modified grades are used in particular for parts exposed to dynamic stress, such as driving belts, timing belts or conveyor belts because of their excellent mechanical properties. But the polymers are less stable during storage and the vulcanizates less resistant to aging.
Slow Crystallising Grades
Slow crystallising grades are polymerized with 2,3-dichloro-1,3-butadiene as a comonomer. This comonomer reduces the degree of crystallisation by introducing irregularities into the polymer chain. High polymerization temperatures also make structural irregularities, if this comonomer is not available. Crystallisation resistant grades are used to produce rubber articles, which have to retain their rubbery properties at very low temperatures.