Preparation And Properties Of Polymer-based Mechanoflurochromic Materials

Recently,with the rapid development of science and technology,people's requirements for materials have rapidly developed from traditional materials to intelligent materials.As one of the intelligent materials,mechanofluorochromic(MFC)materials have been found to become a research hotspot in the field of intelligent materials due to their excellent optical properties and unique fluorescence effect.Polymer materials have many advantages,such as abundant sources,good optical transparency,excellent mechanical and processing properties.Therefore,the effective combination of polymer materials and MFC materials will provide great convenience for the device-based fluorescent materials and promote the rapid development of this field.In this paper,the recent development of MFC materials was summarized and analyzed from the aspects of molecular structures,preparation methods,process routes and main properties of MFC materials.On this basis,five kinds of carboxylic ester tetraphenylethenyl complexes(TPE-COORn,n=1-5)with different alkyl chain lengths were designed and synthesized.The obtained complexes were characterized by IR,¹H NMR,¹³C NMR,UV and XRD.At the same time,the effects of the molecular structures of these complexes on the MFC properties were systematically studied.The experimental results showed that the complexes TPE-COOR1,TPE-COOR3 and TPE-COOR5 were found to have obvious MFC effect,while the complexes TPE-COOR2 and TPE-COOR4had no MFC effect.Moreover,it was also interesting to find that the fluorescence emission of the ground samples of TPE-COOR1 and TPE-COOR5 could be spontaneously recovered at room temperature without the need for external stimulates.A series of PCL/TPE-COORn blend films were prepared by blending the carboxylic ester tetraphenylethenyl complex with polycaprolactone(PCL)by solution blending method,and their MFC properties were also investigated.The results showed that only PCL/TPE-COOR5 blend film was found to exhibit MFC characteristics at room temperature.Moreover,for PCL blend films with different TPE-COOR5 contents(0.5 wt%,0.8 wt%,1.0 wt%,3.0 wt%,5.0 wt%and 7.0 wt%),when the TPE-COOR5 contents were0.5 wt%and 0.8 wt%,the maximum fluorescence emission wavelength of the blend films was found not to shift obviously before and after stretching,and the color of the blend films did not change appreciably after stretching.When the TPE-COOR5 content reached1.0 wt%,the maximum fluorescence emission wavelength of PCL blend film was found to show an obvious blue shift compared with that before stretching.Moreover,the color of the stretching part of the blend film began to change from yellow to green.In addition,it was also found that the blue shift of the maximum fluorescence emission wavelength of PCL/TPE-COOR5 blend films prepared by different polarity solvents was obviously different after stretching.The stronger the polarity of solvents was,the greater the blue shift of the maximum fluorescence emission wavelength of the blend films after stretching.A series of LLDPE/TPE-COOR5 blends with different TPE-COOR5 contents(0.012wt%,0.03 wt%,0.06 wt%,0.1 wt%,0.2 wt%)were prepared by blending TPE-COOR5with linear low-density polyethylene(LLDPE)by melt blending.The results of fluorescence emission spectrum showed that when the TPE-COOR5 content was 0.012wt%and 0.03 wt%,the maximum fluorescence emission wavelength of the blends had no obvious shift before and after stretching,and the color of the blends had almost no change.When the amount of TPE-COOR5 increased to 0.06 wt%,the maximum fluorescence emission wavelength of the stretched sample was found to shift to red,and the color of the stretched part changed from green to yellow.The XRD results showed that some diffraction peaks of LLDPE/TPE-COOR5 blend after stretching were found to be weakened to some extent or disappeared compared with those before stretching.This is mainly due to the destruction of the crystal structure in the crystalline region by stretching,which leads to the decrease of crystallinity or the formation of amorphous structure in the crystalline region.This is also the main reason for the red shift and color change of the fluorescence spectrum of the stretched part of the blends.