3.6. Thermal properties of CS-g-PBT copolymers The DSC thermograms of CS, CS-g-PBT and PBT were shown in Fig. 5. PBT is a semicrystalline polymer with a glass tran-sition temperature (Tg) around 25.2◦C. In contrast, no obvious glass transition attributing to CS could be observed in Fig. 5. It was due to the high crystallinity of CS, originating from strongintra/intermolecular hydrogen bonds between OH and NH2. Consequently, the variation of heat capacity, resulting from the change in specific volume around T g, was too small to be detected byDSC. However, upon grafting by PBT, the resultant modified CS samples exhibited a glass transition temperature in the thermograms and the T g increased gradually from 20◦C to 24.7◦C, approaching to the pure PBT.