Syntheses of Acetophenone Eno1 Ester Polymers and Their Conversion to Poly(phenylacetylenes)

α-Acetoxystyrene (ACOST), 4-methylene-4H-1,3-benzodioxin-2-one (MBDOON), and 3-methylenephthalide (MP) readily undergo radical polymerization although they are α-substituted styrene derivatives. While poly(α-acetoxystyrene) (PACOST) is syndiotactic-rich due to the severe steric hindrance, the α,α-cyclic analogues are almost perfectly atactic (heterotactic-rich), indicating that the cyclization reduces the steric hindrance. PACOST and poly(4-methylene-4H-1,3-benzodioxin-2-one) (PMBDOON) release acetic acid and carbon dioxide upon heating to 200°C, being converted to poly(phenylacetylene) (PPA) and poly((o-hydroxyphenyl)acetylene) (PHOPA), respectively. PPA thus obtained has a trans structure. The thermolysis temperature can be lowered to ca. 100°C by generating a strong acid in the PACOST film through photolysis of a sulfonium salt cationic photoinitiator. PPA produced by acidolysis at the lower temperature contains a significant amount of cis sequences. PMBDOON can be also converted to PHOPA by heating the polymer powder with an acid at ca. 100°C. However, thermolysis and acidolysis of PACOST and PMBDOON are accompanied by depolymerization. In contrast, poly(3-methylenephthalide) (PMP) is very stable toward thermolysis and acidolysis. © 1990, American Chemical Society. All rights reserved.