Preparation And Post-modification Of A New Bio-based Hyperbranched Polyamide Based On Furfurylamine/Lenvnilic Acid

Polyamide widely used in aviation,medical,military and other fields due to its excellent thermal,mechanic and tensile properties,has become an indispensable material in human life.However,most polyamide monomers are derived from petroleum-based chemicals,which is inconsistent with the concept of sustainable development.In order to reduce dependence on fossil resources and inhibit the generation of environmental pollutants,the design and preparation of bio-based monomers and their polymers by using renewable platform compounds as the main raw materials has become a hot topic in the polymer research.Firstly,a new AB₂type bio-based monomer（FDA-E）with two amino functional groups and one ester functional group was prepared from renewable levulinic acid and furfurylamine by using a three-step reaction.The results of nuclear magnetic resonance（NMR）and mass spectrum（MS）confirmed that the monomer contained two amino groups and one ester group.Then,three new and fully bio-based hyperbranched polyamides with different molecular weights and photoluminescent properties were successfully prepared by controlling the reaction time and step heating for the self-condensation polymerization of FDA-E.The polymerization process was monitored by the changes in the infrared absorption spectra of ester group and amino group.The hyperbranched structure of polyamide was confirmed by fourier transform infrared spectroscopy（FT-IR）and NMR.Due to the coincidence of characteristic peaks,it is difficult to calculate the branching degree,However,the relative ratios of amino group,ester group and amide group can be calculated by NMR results,and the primary amine content in HPA-100is the highest.In addition,the polyamides were characterized by X-ray diffraction（XRD）,gel permeation chromatography（GPC）,autoflex III matrix-assisted laser desorption ionization time-of-flight mass spectrometer（MALDI-TOF-MS）,scanning electron microscope（SEM）,differential scanning calorimetry（DSC）and thermogravimetric Analysis（TGA）.The XRD results indicate that the three hyperbranched polyamides are amorphous,which further prove the existence of hyperbranched structures.GPC and MALDI-TOF-MS were used to determine the molecular weight of the polymer,the result of GPC determination was relatively large due to the aggregation of polyamide by intermolecular hydrogen bond.The polyamides show excellent solubility in strong polar solvent and acid solution.In pure water,the rigid polyamides form a stable elastic gel by absorbing water and are insoluble for a long time（6 months or more）.The porous structure of freeze-dried samples was confirmed by SEM.The thermal properties of three polyamides were analysed by DSC and TGA.Their glass transition temperatures are over 97°C and their char yields at 700°C are greater than 40%.Furthermore,due to sub-fluorophores（C=O）and primary amines in the three hyperbranched polyamides,the polyamides emitted strong fluorescence both in the solid and solution states,and their photoluminescent properties depend on molecular weight,solvent,excitation wavelength,and excitation time,as the molecular weight,irradiation time and acid concentration increase,their fluorescence intensity also increase.Hyperbranched polymers with abundant terminal groups can be endowed with new properties by post-modification.In this paper,the amino-terminated hyperbranched polyamide was modified by the methods of Michael addition and ring opening reaction,with the use of methyl acrylate（MA）,2,3-epoxypropyl trimethylammonium chloride（GTA）andε-caprolactone（CL）.After post-modification,ester groups,quaternary ammonium groups and hydroxyl groups were introduced in HPA-GTA,HPA-MA,and HPA-CL,and their post-modifying group contents in per gram of polyamide were 1.9 mmol,1.3 mmol and 1.6 mmol,respectively.Their structure was confirmed by NMR and FT-IR spectrum.The solubility of hyperbranched polyamide was altered by post-modification.HPA-GTA was easily soluble in water,HPA-MA was easily soluble in low polar solvent,such as dichloromethane and chloroform,and HPA-CL is easily soluble in polar solvents,such as methanol.HPA/PAA polyelectrolyte composites were prepared by mixing hyperbranched polyamide（HPA-120）with polyacrylic acid（PAA）based on the electrostatic interaction between amino group and carboxyl group,and were characterized FT-IR.The SEM results show the pore structure of HPA/PAA polyelectrolyte composites dried by different methods（freeze-drying and ambient natural-drying）is different.In addition,the mechanical properties of HPA/PAA polyelectrolyte composites with different molar ratios were studied by tensile test at room temperature,the HPA₁/PAA₁with a feed ratio of amino to carboxyl of 1:1 had the highest elongation at break（921%）.The self-healing ability of HPA₁/PAA₁depends on treating methods,and salt,acidic and alkaline solution can improve its self-healing ability compared with distilled water alone.In addition,HPA₁/PAA₁polyelectrolyte composite exhibits good recycling properties,after 5 cycles（gel→drying→crushing→water repairing→gel）,the elongation at break（717%）is very close to the original sample（781%）.