Study On Preparation And Properties Of Self-healing Polyurethane Based On Diels-Alder Reaction

Polyurethane materials are widely used in automotive,aerospace and marine fields due to their excellent wear resistance,hardness,flexibility and processing.However,when the material is impacted by external force or irradiated by strong light,it is prone to generate small cracks,which causing irreversible physical damage.In order to solve this problem,based on the Diels-Alder(DA)reaction,this thesis designed and prepared a series of polyurethane materials with high mechanical properties,superior self-healing efficiency and excellent recovery performance,And the thesis explored the influence of components on mechanical properties and self-healing efficiency.The main contents are as follows:(1)Firstly,the new small molecule chain extender(FA-BGE)containing furan groups were prepared by using butyl glycidyl' ether and furfuryl amine,and on this basis,the polyurethane with furan rings as the side groups was further prepared.Furthermore,N,N'-(4,4'-methylenediphenyl)bismaleimide was used as a crosslinking agent to synthesize a self-healing polyurethane with the thermally reversible bonds as the cross-linking point.Finally,the mechanical properties of polyurethane before and after healed were compared,and the self-healing efficiency was measured to reach 90.32%.(2)In order to further improve the mechanical strength of the materials,carbodiimide-modified diphenylmethane diisocyanate(liquified MDI)with a small amount of trifunctional isocyanate groups was used as the hard segment.The carbamate groups were the cross-linking point in the micro-crosslinking system,and then DA reactive groups were added to prepare a network with double cross-linking point constructed by carbamate groups and thermally reversible bonds.The molar ratio of soft segment and FA-BGE was adjusted to prepare a series of liquified MDI-based self-healing polyurethanes.The mechanical properties of polyurethane were tested and we founded that when the molar ratio of soft segment to chain extender was 1:2,the tensile strength was as high as 16.49 MPa,which was 9 times higher than HDI-based self-healing polyurethane with single cross-linking point,and the self-healing efficiency and recycling efficiency were as high as 88.42%and 80.84%,respectively.A series of liquified MDI-based self-healing polyurethanes/carbon nanofiber composite materials were prepared.When 0.1 wt%of carbon nanofiber was added,the mechanical strength was as high as 18.75 MPa,and the self-healing efficiency was 81.81%.(3)In order to further improve the self-healing performance and recycling efficiency of the materials,the types of soft segments were changed,and self-healing polyurethanes with different soft segments were prepared.When polypropylene glycol with a molecular weight of 1500 g/mol was used as the soft,segment of the materials,the self-healing efficiency was 88.65%,.and the recycling efficiency was as high as 87.82%.