of the copolymers. The hydrophilic pendant hydroxyl groups on the grafted PBT formed hydrogen bonds with amino groups and hydroxyl groups of chitosan, and broke the intra/intermolecular hydrogen bonds of chitosan. This significantly improved the water solubility and the products were readily soluble in deionized water, which is promising to expand the application of CS. Generally speaking, the water solubility of CS derivatives increasedwith increasing degree of substitution when CS was grafted with hydrophilic groups [27,21]. As far as a polymer chain was grafted,the rule seems to be different. From Table 3, it is found that the water solubility of the grafted copolymers based on PBT with the same molecular weight just varied slightly with increasing DS,while it improved obviously with increasing molecular weight of PBT. It could be inferred that PBT with longer chain destroys the crystalline structure of CS more effectively due to the larger stereohindrance. Meanwhile, the number of hydrophilic hydroxyl groups on each graft PBT segment is larger for the grafting copolymersbased on longer PBT, which may compensate the loss in the solubility arising from its low substitution degree in some extent.Therefore, it could be concluded that the water solubility of the product is mainly determined by the molecular weight of graft PBT rather than DS.