Facile polycyclotrimerization of "simple" arylene bipropiolates: A metal-free, regioselective route to functional hyperbranched polymers with high optical transparency, tunable refractive index, low chromatic aberration, and photoresponsive patternability

A facile synthetic route to functional hyperbranched polymers is developed. Arylene bipropiolates (HC≡C - CO₂ - Ar - O₂C - C≡CH; 1-4) are readily prepared from a one-step esterification reaction between commercially available propiolic acid and arylene diols. Polycyclotrimerizations of 1-4 proceed regioselectively in reflux dimethylformamide (DMF), giving hyperbranched poly[l, 3,5-tri(aroxy-carbonyl) phenylene]s (hb-P1 - hb-P4) of high molecular weights (M_w up to ∼8.3 × 10⁵) in high yields (up to 82%). The polymers possess perfect 1,3,5-regiostructures and high degrees of branching (DB ∼ 88%). Little weights are lost when the polymers are heated to 390 °C under nitrogen or 380 °C in air. The polymers are highly transparent, allowing almost all light in the entire visible spectral region to transmit through. Thin solid film of hb-P1 shows high refractive indices (RI = 1.6255-1.681) in the wavelength region of 400-1700 nm, extremely high modified Abbé number (v_D′ = 1030.7), and very low optical dispersion (D′ = 0.00097). Its RI values can be modulated and its thin films can be cross-linked by UV irradiation, enabling ready generation of negative photoresist patterns.