Synthesis And Characterization Of"first Arm After Core" Type Hyperbranched Polyurethane

According to the polymer synthesis theory, hydroxyl-terminatedpolyurethane prepolymer (PPU) was prepared by polymerizationstepwise. On this basis, a large number of branched structure ofhyperbranched polyurethane (HBPU) were obtained by "first arm aftercore" synthesis method. Their synthesis conditions and reaction lawwere deeply discussed through single factor experiments. The molecularstructures of PPU and HBPU were characterized by modern analyticaltechniques. The HBPU composite was prepared and its microscopicstructure was observed and the appropriate compound scheme wasdetermined.The hydroxyl-terminated PPU was prepared by polymerizationstepwise with4，4`-diphenylmethane diisocyanate (MDI) and polyesterP-3020(dibutyl adipate PBA) as raw materials. The synthesisconditions were investigated through single factor experiments and theresults were shown as follows. Melted P-3020was directly added inMDI at80℃for30min with the feed ratio of1.15:1, then addingglycerol (TG), ethylene glycol (EG), MDI in PPU, and HBPU wasobtained by "first arm after core" synthesis method. By the method ofsingle factor experiments, the synthesis conditions were obtained anddescribed as follows. TG, EG were added once and MDI was addedstepwise for three times, the feed ratio was1:1.15. The reaction timeand temperature were30min and80℃respectively. IR, NMR and GPCwere used for detection and characterization of HBPU compound, the results showed that the desired products were synthesized as expect.The GPC tests showed that HBPU had a greater relative molecular masscompare with PU under the same viscosity conditions. It suggested thatHBPU had lower viscosity and good liquidity. TG and DSC testsshowed that HBPU had better thermal performance, and the crystallinityof HBPU increased38%compared with ordinary PU, which can befound in XRD test.A series of HBPU samples were prepared on the basis of theoptimized synthesis conditions of HBPU. It was not difficult to find thatwith the increase of the amount of branched molecules, the elongationcontinued to decline, while tensile strength and tear strength showed thesame trend that increased firstly and then decreased. Compared withordinary PU, the tensile strength and tear strength of HBPU-3150increased41.4%and32.5%, respectively. In different soft and hardsegment proportion trial, as the reduction of soft and hard segmentproportions, the elongation decreased while the tensile strength and tearstrength had improvements. In solvent resistance test, different HBPUmembranes had no great difference in water, while swelling degreeslowly increased with the increase of branching unit in acetone andtoluene solvent. On the contrary, the welling degree slowly decreasedwith the increase of the soft and hard segment proportion. It could beseen that HBPU had a higher reactivity comparing with PU in DSCthermograms.Through observation and analysis of the microstructure whichowned by a series of complex products of HBPU, different performanceand characteristics of HBPU were explored, the different molecularweight and additive amount of polyethylene glycol (PEG) and thedosage of polystyrene acrylonitrile (SAN) were discussed for theirinfluence in wet and dry method on membrane formation.