MOLDED POLYMER HAVING ESSENTIALLY LOW BIREFRINGENCE

摘要

Intrinsically low birefringent molding polymers have a molten stress optic coefficient that is greater than or equal to -1000 Brewsters and less than or equal to +1000 Brewsters, a glass transition temperature of at least 140 DEG C, and a water absorption according to ASTM D570-81 after 24 hours immersion in water at 23 DEG C) of less than 0.25 percent and comprise in polymerized form at least one structural component providing a positive melt homopolymer stress optic coefficient and at least one other structural component providing a negative melt homopolymer stress optic coefficient. They are particularly useful as substrates for optical storage discs.