The volume contraction of CBFS-1, -2, and -3 after thermal treatment is respectively 27.1, 29.8, and 25.9%, while the linear shrinkage is 10.0, 11.1, and 9.5%.Apparently, the thermal shrinkage of such nanospheres is independent of their size.
This proves the excellent structural homogeneity and great thermal stability of such polybenzoxazine-based nanospheres.
To show the excellent homogeneity of the carbon sample, a typical SEM image recorded on a large area of CBFS-2 is provided in SI Figure S7.