Crystallization resistant grades

Crystallization-resistant grades of polychloroprene are available for low temperature use but fast-crystallizing grades of polymer are used for quick-grab adhesives. 

Reduced stereoregularity using comonomers leads to reduced crystallization tendency and level, thus the so called crystallization resistant grades. ... 

Neoprene AC (1947). This polychloroprene was developed to provide better viscosity stability and resistance to discolouration, but it cures much more slowly at room temperature. It is a fast crystallizing grade and contains about 90% trans-, 4 structure. 

There are 16 grades of DuPont neoprene alone. They vary in crystallization rate and potential, viscosity, molecular weight, additive content, and other properties ([216], pp. 284-306). Selection of the right materials requires sophisticated knowledge of both the neoprenes and the phenolic additives. Guggenberger provides a good overview of this situation and some basic formulation information ([216], pp. 284-306). She also provides a prototype formula for a heat-resistant contact cement as shown in the Table 18 ([216], source Table 10, p. 293). 

We varied the gel-forming parameters, the content of Kaolin clay, the crystal size, and the thickness-to-diameter ratio in a series of experiments. A dual structure began to appear at about 35-40% Kaolin. If the clay content was increased to too high a level, the microspheres became too weak and began to have poor attrition resistance. The cost of the various grades also affected our choice. Figure 9 shows a comparison of pore volume distribution for a typical synthetic versus a clay modified catalyst. 

Copolymers show chemical resistance generally similar to that of polystyrene and terpolvmers similar to that of ABS (acrylonitrile-butadiene-styrene). Neither type is recommended for use in strongly alkaline environments. All impact versions have good natural color and products are available in a wide range of colors. Copolymer crystal grades have good clarity and gloss. 

As can be seen in Table 30 Co-, Ni-, Ti- and Nd-based catalyst systems yield BR with cis- 1,4-contents >90%. A direct consequence of high cis-1,4-contents is strain-induced crystallization of raw rubbers as well as of the respective vulcanizates. As the cis- 1,4-content is extraordinary high in Nd-BR, strain-induced crystallization is particularly pronounced for this BR-grade. As strain-induced crystallization beneficially influences the tack of raw rubbers as well as tensile strength and resistance of vulcanizates to abrasion and fatigue the high cis- 1,4-content makes Nd-BR particularly useful for tire applications. 

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