Preparation And Properties Of Vanillyl Alcohol-based Thermosetting Polyurethane

Polyurethane（PU）is widely used in protective coatings,elastomers,foams,adhesives,composites and other fields due to its good mechanical properties,thermal properties and chemical resistance.Traditional polyurethanes are mostly prepared from non-renewable petroleum resources.With the shortage of petroleum resources,it is of great significance to develop bio-based polyurethanes with excellent comprehensive properties from renewable biomass resources.In addition,most of the polyurethanes are difficult to degrade after the service period,causing serious pollution problems;and degradable polyurethanes usually do not have excellent mechanical and thermal properties.Therefore,it is extremely challenging to design polyurethanes that can combine high performance and degradability.At the same time,flammability is another key problem of polyurethane.Generally,the flame retardant properties of polyurethane are improved by using flame retardants.For the consideration of environmental protection,the development of green and environmentally friendly flame retardants is also a hot spot today.In this paper,bio-based vanillyl alcohol is used as the monomer to prepare polyurethane,in which the benzene ring provides rigidity and strength,and the hydroxyl group further reacts to form an ester bond to provide a degradable group,which solves the contradiction between the high performance and degradability of bio-based polyurethane;and phenylphosphonic dichloride improves the flame retardancy of polyurethane.The main research contents and main achievements of this paper are as follows:（1）Using vanillyl alcohol（VA）and three acid chlorides,including succinyl chloride,adipoyl chloride,and suberoyl chloride,through a one-step reaction in the aqueous phase,three kinds of vanillyl alcohol-based diols with flexible chain differences were synthesized,which named VA4,VA6 and VA8.The synthesized structure was confirmed to be consistent with the designed structure by FTIR,NMR and MS.The three diols were cured with hexamethylene diisocyanate trimer（HDI Trimer）to prepare three thermosetting polyurethane films,which named PU4,PU6 and PU8 with tunable high performance.The existence of ester bond inherent in the PU can be rapidly degraded within hours in alkaline solution.The thermal properties,thermomechanical properties,mechanical properties and degradability of polyurethane films were systematically studied.The results show that:PU4shows the best comprehensive properties,with T_{g DMA}of 79.95℃,tensile strength of 79.4 MPa,and Young’s modulus of 1.5 GPa;PU8 has better toughness（elongation at break 68.9%）while reaching comparable mechanical strength（63.7 MPa）;thus,the properties of the material can be tuned by controlling the length of the flexible segment in the diol.（2）A novel vanillyl alcohol-based phosphorus-containing diol（PPDVA）was synthesized by reacting vanillyl alcohol with phenylphosphonic dichloride.The chemical structure of the monomer was characterized by FTIR,NMR and MS.Then it was cured with HDI Trimer to prepare bio-based flame retardant thermosetting polyurethane PU-C,which was compared with polyurethane PU-A prepared from commercially available polypropylene glycol 400（PPG400）,and its thermal properties,thermal stability,The mechanical properties and flame retardancy were systematically studied.It was found that compared with the PU-A system,the performance of PU-C was significantly improved in all aspects:T_{g DMA}increased from-5.35℃to72.58℃;tensile strength increased from 1.2 MPa to 62.7 MPa;the limiting oxygen index increased from 17.9%to 28.9%;the residual carbon content increased from 2.58%to 19.09%;the total heat release decreased by 26.55%;After testing,the PU-C system reaches the HB level combustion level.In summary,a series of vanillyl alcohol-based thermosetting polyurethanes were successfully prepared in this paper,and all of them achieved high performance levels and tunable performance.