Amino Polysaccharide-Chitosan Mimics Via Ring-opening Metathesis Polymerization

As the only basic polysaccharide in nature,chitosan has been a hotspot of research in polymeric material field due to its excellent performance,such as biocompatibility,multi-function reaction activity,cationic polyelectrolyte and antibacterial activity.However,as a natural polysaccharide,the complexties of structure and conformation make it extremely difficult to control the relationship between structure and property.In order to precisely analyze the relationship between structure and property,to accurately control the the relative molecular weight and distribution,the synthetic polysaccharide has been an effective research tools.Up to now,varieties of polysaccharide mimics that with similar structures and properties to nature polysaccharide had been prepared by many methods,in which,the ring-opening metathesis polymerization(ROMP)has been an important method because of the rapid development of catalyst,special reaction mechanism and moderate reaction condition.The polysaccharide with similar structure to chitosan was prepared via ROMP.The ROMP of 5-norbornene-2-methylimine-t-butyloxycarboryl(NIB)was catalyzed by Hoveyda-Grubbs 2nd catalyst to afford poly(5-norbornene-2-methylimine-t-butyloxycarboryl)(PNIB).Then the chitosan mimics,poly(5,6-dihydroxynorbornene-2-methylimine)(PHNI),was synthesized after the asymmetric dihydroxylation and deprotected of amino of PNIB.The result of Fourier transform infrared spectroscopy(FTIR)and ¹H nuclear magnetic resonance(¹H-NMR)of products were showed the mimic,PHNI,was successfully prepared.The ROMP system of different molar ratio of monomer and catalyst were measured by gel permeation chromatography(GPC),the result showed the ROMP of NIB was a“living”polymerization.The differential scanning calorimetry(DSC),thermogravimetry(TG)and X-ray diffraction(XRD)datas of polymers in each step showed the thermal stabilities,crystallinities and solubilities were significantly changed.The PHNI has excellent thermal stability,low crystallinity and excellent solubility in water.The contents of acetamide group in chitosan were different due to the different degree of deacetylation of chitin.The 5-norbornene-2-methylimine-acetyl(NIA)was added into the ROMP system of NIB to afford block polymer PNIB-PNIA.Then the chitosan mimic with different content of acetamide group,poly(5,6-dihydroxynorbornene-2-methylimine)-poly(5,6-dihydroxynorbornene-2-methylimine-acetyl)(PHNI-PHNIA)were synthesized after the asymmetric dihydroxylation and deprotected of amino of PNIB-PNIA.The result of FTIR,¹H-NMR and ¹³C-NMR of products were showed the mimics,PHNI-PHNIA,was successfully prepared.The block-ROMP system of different ratio of NIB and NIA were measured by GPC,the result showed the block-ROMP of NIB and NIA was also a“living”polymerization.The DSC,TG and XRD datas of block polymers in each step showed the thermal stabilities,crystallinities and solubilities were significantly changed.The PHNI-PHNIA has excellent thermal stability,low crystallinity and excellent solubility in water.