Enhanced Self-Assembly and Mechanical Properties of Cellulose-Based Triblock Copolymers: Comparisons with Amylose-Based Triblock Copolymers
Satoshi Katsuhara, Yasuko Takagi, Naoki Sunagawa, Kiyohiko Igarashi, Takuya Yamamoto, Kenji Tajima, Takuya Isono, Toshifumi Satoh
Abstract
Herein, we compared the microphase-separation behavior and mechanical properties of cellulose- and amylose-based block copolymers (BCPs). Various cellooligosaccharide triacetate-b-poly(δ-decanolactone)-b-cellooligosaccharide triacetates (AcCeln-b-PDL-b-AcCelns), 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 α,ω-diazido-end-functionalized PDLs and propargyl-end-functionalized cellooligosaccharide triacetates via click chemistry. We adopted the cellodextrin-phosphorylase-mediated oligomerization of α-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(δ-decanolactone)-b-maltooligosaccharide triacetate (AcMaln-b-PDL-b-AcMalns) amylose counterparts were also synthesized in a similar manner. Small-angle X-ray scattering experiments and atomic force microscopy revealed that AcCeln-b-PDL-b-AcCelns are more likely to microphase-separate into ordered nanostructures compared to AcMaln-b-PDL-b-AcMalns, despite their comparable chemical compositions and molecular weights. Furthermore, AcCeln-b-PDL-b-AcCelns exhibited significantly superior mechanical performance compared to their amylose counterparts under tensile testing, with Young’s modulus and stress at break of AcCeln-b-PDL10k-b-AcCeln being 2.3 and 1.8 times higher, respectively, than those of AcMaln-b-PDL10k-b-AcMaln. The enhanced microphase-separation and mechanical properties of AcCeln-b-PDL-b-AcCelns were found to be attributable to the stiffness and crystalline nature of the AcCeln segments. These results demonstrate the advantages of using cellulose derivatives to synthesize novel biofunctional materials.