Enhanced Self-Assembly and Mechanical Properties of Cellulose-Based Triblock Copolymers: Comparisons with Amylose-Based Triblock Copolymers

Herein, we compared the microphase-separation behavior and mechanical properties of cellulose- and amylose-based block copolymers (BCPs). Various cellooligosaccharide triacetate-b-poly(delta-decanolactone)-b-cellooligosaccharide triacetates (AcCel(n)-b-PDL-b-AcCel(n)s), which are cellulose-based ABA-type BCPs, with PDL molecular weights of approximately 5, 10, and 20 kg mol(-1) and PDL volume fractions of 0.65, 0.77, and 0.87, were synthesized from alpha,omega-diazido-end-functionalized PDLs and propargyl-end-functionalized cellooligosaccharide triacetates via click chemistry. We adopted the cellodextrin-phosphorylase-mediated oligomerization of alpha-D-glucose-1-phosphase in the presence of a propargyl-end-functionalized cellobiose primer to synthesize the functional cellooligosaccharide segment. The maltooligosaccharide triacetate-b-poly(delta-decanolactone)-b-maltooligosaccharide triacetate (AcMal(n)-b-PDL-b-AcMal(n)s) amylose counterparts were also synthesized in a similar manner. Small-angle X-ray scattering experiments and atomic force microscopy revealed that AcCel(n)-b-PDL-b-AcCel(n)s are more likely to microphase-separate into ordered nanostructures compared to AcMal(n)-b-PDL-b-AcMal(n)s, despite their comparable chemical compositions and molecular weights. Furthermore, AcCel(n)-b-PDL-b-AcCel(n)s exhibited significantly superior mechanical performance compared to their amylose counterparts under tensile testing, with Young's modulus and stress at break of AcCel(n)-b-PDL10k-b-AcCel(n) being 2.3 and 1.8 times higher, respectively, than those of AcMal(n)-b-PDL10k-b-AcMal(n). The enhanced microphase-separation and mechanical properties of AcCel(n)-b-PDL-b-AcCel(n)s were found to be attributable to the stiffness and crystalline nature of the AcCel(n) segments. These results demonstrate the advantages of using cellulose derivatives to synthesize novel biofunctional materials.