| http://www.w3.org/ns/prov#value | - More preferably A is A, where A is 1,2-ethylene, 1,3-propylene or unsubstituted meta or para phenylene.Preferably R.sub.2 is R'.sub.2, where R'.sub.2 is a group of the formula ##STR13##where the symbols R'.sub.11 and R'.sub.12 are defined below.
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