3.2. Solid state 13C NMR analysis of PUF resin
The chemical structure of synthesized PUF resin copolymers was illustrated by 13C NMR. The chemical shifts assignments of carbons in LMWPF and PUF prepolymer is summarized in Table 2 according to published literature [4], [7], [8], [33], [34] and [35] to assist in the interpretation and identification of peaks in regions from 20 to 200 ppm.