Oriented specimens doubly

Because of its ready availability and simple chemical composition this material has been a favoured polymer for structural and mechanical studies. The relative ease with which doubly oriented specimens of overall orthorhombic symmetry can be obtained has intensifi investigations of the relation between physical properties and molecular and supermolecular structure. But these investigations have demonstrated that the structure of this material is in fact exceedingly complex (see Apfiendix). 

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