prov:value
| - Preferred ballasting groups are those represented by the formula: ##STR2## wherein X is an oxygen atom or a sulfur atom, R.sub.2 is abranched or linear alkylene group, R.sub.1 is a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a heterocyclic group, an aralkyl group, an aryloxy group, a hydroxy group, an acyloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group,an alkylthio g
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