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

Abstract

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[1,3,5-tri(aroxycarbonyl)phenylene]s (hb-P1−hb-P4) of high molecular weights (Mw 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 (νD′ = 1030.7), and very low optical dispersion (D′ = 0.000 97). Its RI values can be modulated and its thin films can be cross-linked by UV irradiation, enabling ready generation of negative photoresist patterns.