New main-chain hyperbranched polymers: Facile synthesis, structural control, and second-order nonlinear optical properties

In this paper, two new series of hyperbranched main-chain polymers, P1–P6, with chromophore moieties as the core were successfully prepared through “A3+B2” approach via simple Sonogashira coupling reaction. By changing the bulky size of comonomers, the structure-property relationship has been investigated according to the concept of “suitable isolation group”. The second harmonic generation (SHG) experiments demonstrated that the hyperbranched structure might be very good architecture for the development of NLO materials with high performance. The benzene ring (Bz) could act as suitable isolation groups in these polymers, while the d33 values of the corresponding polymers P1 and P4, were 152.6 and 86.2 pm/V, respectively, much higher than their linear analog polymers bearing the same chromophore moieties. In addition, these hyperbranched main-chain polymers could combine the large nonlinearities of hyperbranched polymers and high stability of main-chain polymers, providing a new solution to solve the “nonlinearity-stability” trade off existing in the main-chain polymers to some degree.