Design and synthesis of isosorbide‐based copolycarbonates with high transparency and low hygroscopicity for optical applications

Poly(isosorbide carbonate) (PIC) is an example of the shift from fossil to bio‐based feedstocks in polymeric materials. However, the naturally high hygroscopicity of isosorbide may lead to the bad dimensional stability of its polymers, limiting its application. This work aims to develop a series of isosorbide‐based copolycarbonates by introducing hydrophobic groups, such as alkane chains and aromatic rings, into the polymer backbone via one‐pot melt polycondensation. As expected, the molecular structure and steric hindrance of the comonomer have a remarkable effect on the water absorption of the copolycarbonates. Among the comonomers, tricyclo[5.2.1.0(2,6)]decanedimethanol with an alkane skeleton bridge effectively reduces the saturation water absorption by 61% compared to PIC. The water absorption mechanism and kinetics of the copolycarbonates are investigated. Moreover, the incorporation of comonomers in PIC not only exhibits stronger hydrophobicity, but also significantly improves its optical properties. Copolycarbonates obtained have a light transmittance of 92% and a refractive index of 1.5394, which are higher than those of PIC, along with better thermal stability, flexibility, and lower glass transition temperature. This work provides a new strategy for the design of isosorbide‐based polycarbonates for use in optics. In this paper, a series of novel poly(diol‐co‐isosorbide) carbonates (PDICs) have been designed and developed through the melt polymerization of ISB and seven hydrophobic comonomers catalyzed with the ionic liquid catalyst 1‐ethyl‐3‐methylimidazole lysine ([Emim][Lys]). The poly (tricyclo[5.2.1.0(2,6)]decanedimethanol‐co‐isosorbide carbonate) (PTIC) effectively reduced the saturation water absorption by 61% compared to poly(isosorbide carbonate) and exhibited excellent optical properties, thermal and mechanical properties.