Читать книгу Poly(lactic acid) - Группа авторов - Страница 115

Click chemistry [56] has evolved as an efficient and simple approach to develop HMW sb‐PLA with controlled block lengths and chain architecture. The combination of ROP and click chemistry has been shown by Han et al. to prepare HMW sb‐PLA (PLLA–PDLA) with controlled composition and block length [57]. The sc‐crystallinity was found to increase when the PLLA/PDLA block ratio approached 50/50, which also increased the storage modulus of HMW sb‐PLA. In another study, Isono et al. applied the combination of sb and star polymer approaches and succeeded in synthesizing stereo‐miktoarm star‐shaped PLAs by a click coupling method [58]. This approach led to the preferential sc formation in the solution cast samples, without any homo‐crystallite formation. The variation in the arm number also led to the variation in T _m of the stereo‐miktoarm star polymers, thereby providing a mechanism to tailor the physical properties of sc‐type PLAs. Besides these approaches, the synthesis of cyclic stereoblock copolymers of PLLA and PDLA with head‐to‐head and head‐to‐tail configurations has been carried out by implementing the click chemistry and ring closing metathesis approaches [59]. The orientation of PLLA and PDLA segments in the cyclic structure may be controlled in a facile way by using this approach, along with modulated thermal properties.