Study On The Structure And Properties Of Photosensitive Polyurethane Based On Hexaarylbiimidazole

Polyurethane is a widely used polymer material,which is simple to synthesize and mature in technology.The material has excellent mechanical properties and processing properties,and is easy to be modified and optimized.Hexaarylimidazole(HABI)is a new photochromic molecule,which can be introduced into the polyurethane system to prepare photosensitive polyurethane.The rapid light response property of the HABI molecule was used to regulate the crosslinking degree of the polymer network,so as to achieve macroscopic regulation of the photosensitivity of polyurethane.However,the photosensitivity mechanism of hexaarylbiimidazole-based polyurethane needs further study.In this paper,a series of photosensitive polyurethanes were synthesized by using diisocyanates with different structures,and the differences of photosensitive properties of polyurethanes were studied in depth.The content is as follows:(1)A hexaaryl biimidazole monomer(4OH-HABI)containing tetrahydroxy modification was prepared with a yield of 75%.When the tetrahydrofuran solution of the molecule was irradiated by 405 nm laser,the solution quickly changed to dark blue,the color returned to yellow quickly after removing the light,and the fading half-life was 60 s,which proved that the molecule had good photoresponse.(2)The crosslinked polyurethane(PPU)containing five different diisocyanate structures were synthesized by one-step polymerization.The maximum fracture stress of polyurethane MDI-PPU with hard segment of diphenylmethane diisocyanate(MDI)was only 0.1MPa,while that of polyurethane HDI-PPU with hard segment of 1,6-hexyl diisocyanate(HDI)was as high as 14 MPa.The other three polyurethanes,The maximum fracture stress of 4,4'-dicyclohexylmethane diisocyanate(HMDI),isopharone diisocyanate(IPDI)and 2,4-toluene diisocyanate(TDI)hard segment polyurethane HMDI-PPU,IPDIPPU and TDI-PPU was about 10 MPa.In MDI-PPU,because MDI and HABI molecules were connected to form hard segments with strong steric hindrances,resulting in sparse accumulation between molecular chains,the maximum fracture stress of MDI-PPU was far less than that of the other four types.In HDI-PPU,HDI was a straight-chain molecule with small steric hindrance and compact accumulation of polymer molecular chains,so the mechanical properties of HDI-PPU polyurethane are the strongest.(3)The difference of photosensitivity of five kinds of polyurethane was deeply studied from three aspects: photorheological properties,photo-induced self-healing and photochromism.Before and after illumination,the internal stress attenuation of MDI-PPU was larger,while that of HDI-PPU was smaller.After the cutting fracture of HDI-PPU,MDIPPU and IPDI-PPU and illumination for a period of time,the mechanical properties of the materials could be restored to more than 95% of the original samples.When the surface of polyurethane film wass irradiated by 405 nm laser,the discoloration time of polyurethane film was different.After discoloration,MDI-PPU and TDI-PPU faded quickly within 30 seconds,which proved that HABI molecules in polyurethane have good photoresponse.