Description: 521 synthetic resins or natural rubbers -- part of the class 520 series / 521 synthetic resins or natural rubbers -- part of the class 520 series/() synthetic resins (class 520, subclass 1) (50) cellular products or processes of preparing a cellular product, e.g., foams, pores, channels, etc. (155) cellular product derived from a -n=c=x containing reactant wherein x is a chalcogen atom (156) with three-membered heterocyclic reactant containing two carbon atoms and a hetero atom (i.e., nitrogen or a chalcogen atom)
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