Fluorine-driven amorphous solid-state polycondensation: phosgene-free synthesis of high-molecular weight polycarbonate from fluorinated carbonate

Abstract

This study presents amorphous solid-state polymerization (SSP) with fluorinated carbonate to realize efficient and facile synthesis of bisphenol-A (BPA) polycarbonate without using highly toxic phosgene gas. Prepolymer prepared from bis(1,1,1,3,3,3-hexafluoro-2-propyl) carbonate and BPA in dichloromethane (CH₂Cl₂) by eliminating hexafluoroisopropyl alcohol undergoes SSP under vacuum when reaction temperature is gradually increased from 43 °C to 180 °C to obtain high-molecular-weight polycarbonate (M_w = 83 000) without discoloration. Differential scanning calorimetry and wide-angle X-ray diffraction measurements indicate that this polymerization proceeds in an amorphous-solid state, whereas conventional SSP of the BPA polycarbonate requires prepolymer crystallization to locally concentrate the terminal groups for propagation. Density functional theory calculations and small-angle X-ray scattering measurements suggest that efficient polymerization, even without a crystalline phase, is driven by both the high reactivity of fluorinated carbonates and fluoroalkyl-terminal aggregation by fluorine mutual affinity. Phenolic terminals join the aggregated area via the dipole–dipole interactions between the fluoroalkoxycarbonyl and phenolic-hydroxyl terminals.