Optimizing filler network formation in poly(hexahydrotriazine) for realizing high thermal conductivity and low oxygen permeation

Shape, size, and orientation of fillers within polymer matrix are important factors for realizing various composite functionalities. Here, we describe an industrially scalable approach to preparing composites bearing highly aligned model hexagonal boron nitride filler (hBN) by simple melt-pressing. This outcome is achieved by using a malleable but thermal stiffening polymer matrix. The matrix maintains or even increases its stiffness during processing at elevated temperatures, producing the composites with highly aligned hBN and consequently a high thermal conductivity (28 W/mK). Furthermore, the composite bearing aligned hBN exhibits a 62% reduction in oxygen permeation with only 2.7 vol% of hBN. Since the matrix can be chemically depolymerized with an aid of acid, it is also possible to recover the hBN from the composite without physical/chemical denaturation of the filler, thus the recovered filler can be re-used in the future.