Synthesis And Properties Of Ionic Liquid Oligomers With Specific Structures

Three ionic liquid oligomers with specific structures were synthesized in this article. Firstly, an imidazolium based ionic liquid oligomer with one PEG arm (ILO-1) was prepared by imidazole, Poly(ethylene glycol) monomethyl ether (mPEG1000, Mn=1000 g/mol), p-toluenesulfonyl chloride (TsCl) and Methyl iodide (CH3I). Secondly, a 1,2,3-triazolium-based ionic liquid oligomer containing two PEG arms (ILO-2) was obtained using click reaction by mPEG1000, TsCl, sodium azide (NaNa), propargyl bromide and CH3I. Finally, a 1,2,3-triazolium-based ionic liquid diblock copolymer containing PEG and PCL (ILO-3) was synthesized by combination of ring opening polymerization (ROP) and "click" reaction, using ε-caprolactone (ε-CL), mPEG1000, TsCl, NaN3, propargyl alcohol (PGA) and CH3I as the raw materials. All the three ionic liquid oligomers were characterized by 1H NMR, FT-IR, and Gel Permeation Chromatography (GPC). We found that ILO-1 and ILO-2 can miscible in most of the organic solvents we used, but the miscibility of ILO-3 is little worse than ILO-1 and ILO-2 for the presence of PCL chain. The thermal stability of the three ionic liquid oligomers were evaluated by thermogravimetric analysis (TGA), the results indicated that the thermal stability of ILO-1, ILO-2 and ILO-3 decreased compared with their precursors. The possible reason was that the iodine anions have strong nucleophilicity, giving them greater ability to participate in dealkylation which will promote the degradation of the cations. Differential scanning calorimetry (DSC) was further employed to investigate the thermal performance of the three ionic liquid oligomers, indicating that the electrostatic interaction between the cations and anions may restrict aligning the ionic liquid oligomers to form an ordered way, which caused a decrease in melting crystallization temperature. Moreover, ILO-3 showed excellent thermal stability with the T5% of 366℃. The much higher stability will beneficial to the further blending and machining process, which ILO-3 was used as additive in mixed bio-polyester resin, such as PLA/PCL etc.The prepared mPEG-b-PCL and ILO-3 were adopted to modify poly(lactic acid) (PLA) and poly(s-caprolactone)(PCL) by melt blending. The influences of both mPEG-b-PCL and ILO-3 on the mechanical properties of PLA/PCL blends were investigated. The results are as follows:(1) Because the mPEG-b-PCL and ILO-3 containing both of PEG segment and PCL segment, the chains of molecules can tangle more easily at the interface of PLA/PCL blends. But as the weight content of mPEG-b-PCL or ILO-3 increased, the results became worse because they would form micel.(2) The addition of mPEG-b-PCL played an important role on the mechanical properties of PLA/PCL blends. It can improve the elongation at break of the blends significantly without decreasing the modulus and the tensile strength.(3) The addition of ILO-3 also played an important role on the mechanical properties of PLA/PCL blends. It can also improve the elongation at break of the blends significantly.