Preparation And Thermoresponsive Properties Of Glycopolypeptides

Glycopolymers are a type of functional polymers containing mono- or oligosaccharide moieties. They have shown many attractive properties, including biocompatibility, chemical diversity and chirality of saccharide moieties, which make them gained significant attention as attractive materials for a variety of applications, such as matrices for controlled cell culture, drug release carriers, and scaffolds for tissue engineering. Thermoresponsive polymers can undergo solution phase transitions regarding to the changes of temperature which makes it has potential applications as biomedical materials. However, most thermoresponsive polymers are non-biodegradable which will limit their use in a wide range of applications, especially as biomedical materials. Synthetic polypeptides are mimics of natural peptides, they have shown excellent biocompatibility and unique secondary structures（e.g., α-helix and β-sheet）. When polypeptides conjugated with mono- or oligosaccharides, they are glycopolypeptides. Thermoresponsive polymers have been widely studied but glycopolypeptides with thermoresponsive properties have been less reported.In this thesis, a series of glycopolypeptides homopolymers and random copolymers with different main-chain length, component units and contents was prepared by the combination of ring-opening polymerization and copper-mediated [2+3] alkyne-azide 1,3-dipolar cycloadditions. The effects of the polymer structures, type of fatty alcohols, and polymer concentration on the thermoresponsive properties of the resulting glycopolypeptides have been systematically studied.A series of polypeptides with constant main-chain lengths and various compositions of mannose moieties and biphenyl pendants were synthesized. ¹H NMR, FTIR, and GPC results confirmed the molecular structures of the resulting polypeptides. FTIR analysis characterized their molar contents of the mannose pendants（x） and α-helical conformations in the solid state. Glycopolypeptides conjugated with tetra-O-acetyl-D-（+）-mannopyranoside（x ≥ 78%） showed a reversible UCST-type transition in Et OH and Me OH which was analysis by variable-temperature UV-vis spectroscopy. The UCST-type transition temperature(T_pt) decreased as the concentration decreased and increased by incorporation of biphenyl groups.A series of glycopolypeptides with different contents of tetra-O-acetyl-D-（+）-mannopyranoside and tetra-O-hydroxyl-D-（+）-mannopyranoside pendants were prepared. The chemical structures of the intermediates and target products were confirmed by ¹H NMR as well as FTIR. GPC determined the molecular weights and molecular weight distributions of the polymers. Aggregate sizes of the glycopolypeptides in solution were determined by DLS in room temperature. FTIR results revealed that the mechanism of the UCST-type phase behavior originated from the hydrophobic interaction and H-bonding between the polymers and the H-bonding between the polymer and solvent. Variable-temperature UV-vis spectroscopy analysis show that glycopolypeptides with high contents of tetra-O-acetyl-D-（+）-mannopyranoside（x ≥ 44%） exhibited a reversible UCST-type phase behavior in both Me OH and Et OH and the T_pt decreased as the polymer concentration or main-chain length decreased. Moreover, incorporation of proton donating groups（i.e., tetra-O-hydroxyl-D-（+）-mannopyranoside） or increasing the number of carbons of aliphatic alcohols led an increase of T_pt.