Research progress on construction and properties of polymer gradient materials

Polymer gradient materials are functional heterogeneous polymer-based materials, where their compositions or structures change continuously or quasi continuously in one or multi-dimensional direction. The gradient structure endows the material with unique advantages, such as adjustable spatial distribution of components, avoidance of interfacial stress and compatibility with a variety of properties. Polymer gradient materials have a wide range of applications in aerospace, biomedicines, electronic information, mechanical engineering and other fields. In this paper, they are divided into one-dimensional, two-dimensional and three-dimensional polymer gradient materials according to the variation dimension of gradient. The preparation methods, performance advantages and application fields of the three materials are introduced respectively. The gradient refractive index of one-dimensional polymer gradient fiber improves the speed and distance of optical fiber transmission and contributes to the development of optical communication field. Two-dimensional polymer gradient materials can be divided into the coating and thin film materials. Gradient structures can be prepared by surface modification and field gradient methods. The resulting gradient surface can provide a high-throughput platform to study and optimize the interaction between materials and organisms. Three-dimensional polymer gradient materials include gradient crosslinking network polymer materials, gradient filled polymer composites and gradient crystallization polymer materials. The gradient structure can improve their mechanical properties and stress concentration, and expand the applications of polymers in mechanical engineering and biomedical fields. Finally, the challenges in the preparation, characterization and application of polymer gradient materials are prospected.