Study on Crystal Nucleation of Polymers and Molecular Design of Environmentally Benign Polymers

Prof. Dr. Jun Xu, Department of Chemical Engineering, Tsinghua University (China)

Determining the size of critical nuclei of crystals is key to understanding the nucleation mechanism and testing the nucleation theories. However, it has been a great challenge from both experimental and theoretical perspectives. We have proposed a method to determine the size of critical nuclei in polymer lamellar crystals based on the probability of selecting crystallizable units on the chains of random copolymers. The sizes of critical secondary nuclei of poly(butylene succinate) and poly(L-lactide)/poly(D-lactide) stereo-complex have been obtained, which show that a critical secondary nucleus consists of multiple chain stems rather than one stem. The results contest the classical Lauritzen-Hoffman theory. Furthermore, we show that the sizes of critical secondary nuclei, isothermally crystallized from dilute solution, do not vary with supersaturation, which contradicts with the common view.

In the second part, I will show our research on fundamental research and industrial applications of biodegradable polyesters synthesized form diacids and diols. Via molecular design adopting dynamic covalent bonds, we synthesized a series of self-healable and recyclable polyurethanes, which are finding applications in biomedical fields.