Novel Multiblock Poly(ε-caprolactone) Copolyesters Containing D-Glucose Derivatives with Different Bicyclic Structures

For improving the thermal stability, glass transition temperature (Tg), stiffness, and hydrophilicity of poly(ε-caprolactone) (PCL), two glucose-based bicyclic rigid structures, namely 1,4:3,6-dianhydrohexitols-D-glucidol (isosorbide, Is) and dimethyl 2,4:3,5-di-O-methylene-D-glucarate (glu-diester) have been introduced into PCL via chain extension. The two series of multiblock copolyesters obtained, PCL-b-PIS and PCL-b-PBG, have high number-average molecular weights in the range of 9.6 × 104 to 12.4 × 104 g mol–1 and small PDI values. The thermal and crystallization behaviors, hydrophilicity, as well as the mechanical properties of PCL-b-PIS and PCL-b-PBG have been well investigated. In comparison, the improved effect on thermal stability and Tg of PCL is more pronounced for PCL-b-PBG than for PCL-b-PIS. Both glucose-based units retard the crystallinity of PCL. However, the crystal structure and melting temperature of PCL remain unchanged. The rigidness of PCL is enhanced when glucose-based bicyclic units are introduced as reflected by the increasing storage modulus over all of the studied temperatures. The mechanical properties of PCL-b-PIS are better than those of PCL-b-PBG, especially for the samples containing 30 wt % sugar units. This can be due to the good compatibility of PIS with the PCL block. Although both Is and glu-diester enhance the hydrophilicity of PCL, the PCL-b-PBG copolyester always shows higher hydrophilicity than that of PCL-b-PIS in the whole composition.