New polymer syntheses. 103. In situ end group modification of hyperbranched poly(3,5-dihydroxybenzoate)

3,5-Bis(trimethylsiloxy)benzoyl chloride (BTBC) was polycondensed with N,N'-bisitrimethylsilyl)bisaniline-P in hulk with variation of the feed ratio. In this way star-shaped hyperbranched polyesters were prepared, and the average degree of polymerization (DP) was controlled by the monomer/comonomer (M/C) ratio. A star-shaped, hyperbranched polyester having a DP of 50 was treated with an excess of an acid chloride in refluxing 1-chloronaphthalene, and the trimethylsiloxy groups were almost quantitatively transformed into ester groups. The following acid chlorides were used: acetyl, chloroacetyl, undecenoyl, stearoyl, 4-methoxycinnamoyl and perfluorooctanoyl. Due to the low boiling point, the acylation with acetyl chloride required two steps for completion. The solubilities and glass-transition temperatures varied largely with the nature of the end groups. Irradiation with UV light (254 nm) caused rapid cross-linking of films cast from poly(3,5-dihydroxybenzoate) bearing 6-methoxycinnamoyl end groups.