Design And Sythesis Of Functionalized Hyperbranched Polyethylene And Its Application In Liquid Phase Exfoliation Of Graphene

Flexible conductive membrane is a kind of material with good conductivity,bending,stretching and other deformation ability.It is widely used in medical and health care fields because of its electric heating,sensing and other properties.Due to its special conductive structure,deposited flexible conductive film is one of the hot spots in current research,and various materials with excellent properties have been reported in the literature.In practice,the stability of materials is an important property.For the deposited conductive film,it is easy to be damaged due to the interface action between the conductive layers,between the conductive layer and the substrate under the action of external force.How to improve the stability of the conductive film is a meaningful research.Graphene is a kind of packing with excellent electrical conductivity.The application of graphene prepared by liquid phase exfoliation is the most easy to deposit flexible conductive film.At the same time,assistant exfoliation is an effective way to improve the exfoliantion efficiency,which is the main strategy for the preparation of graphene.Whether to synthesize a kind of assistant can effectively improve the efficiency of liquid phase exfoliation.Further more,graphene can be used in the flexible conductive film,which can help to improve the stability of the conductive film.Based on the above ideas,a kind of functional hyperbranched polyethylene（HBPE@A@P）with both acryloyl and pyrene groups at the end of chain was synthesized in this paper,which was used as an assistant to prepare graphene by liquid phase stripping.Then the graphene was pumped into the filter membrane to obtain the conductive membrane,and finally solidified under UV irradiation to obtain a highly stable and flexible conductive membrane.The specific research contents are as follows（1）Through the"chain walking"mechanism of Pd-diimine catalyst,ethylene,BDA and pyrene monomers were copolymerized to obtain functional hyperbranched polyethylene HBPE@A@P with acryloyl and pyrene groups.The chemical composition,molecular weight and structure were characterized by ¹H-NMR,GPC and rheology respectively.The results of ¹H-NMR showed that the grafting ratio of acryloyl group and pyrene group was 2.4 and 0.3/100-CH₂-CH₂-respectively,and the degree of branching was 87/1000C.GPC showed that the number-average molecular weight of the polymer was 16.4 k D and the molecular weight distribution index was 5.05.Through rheological analysis,it was found that the polymer had spherical structure and non-entanglement between molecular chains.The results of UV curing and FTIR indicate that the double bond at the end of the chain can be initiated under UV light,and the polymer can be cured and crosslinked.（2）HBPE@A@P was used as assistant in liquid phase stripping to prepare graphene.The effects of stripping process on the concentration of graphene were studied:different solvents,different polymer feed ratio,different graphite feed ratio,different ultrasonic time.The results show that the best exfoliation process is that the ratio of polymer to graphite is 0.5,the concentration of graphite is 8 mg·m L^-1,and the sonication time is 48 hours.The large-scale preparation of graphene under the above process and indirectly proves the?-?effect role of pyrenyl and graphene.The structure defects of graphene nanoflakes were characterized:The Raman results show that the defects of graphene are large and the number of layers is less than 5.AFM spectrum shows that the thickness is concentrated between 2～3 layers,and the transverse dimension is mainly 100～400 nm.The transverse dimension of graphene is mainly100～400 nm,and the electron diffraction structure of graphene monolayer is observed by TEM and The hexagonal lattice of graphene was obtained by FFT of graphene monolayer.Through XPS characterization,we know that graphene surface contains more polymers,and there is oxidation or adsorption of oxygen-containing gases.（3）The flexible conducting membrane was obtained by pumping and filtering the large-scale graphene onto the membrane.The relationship between the construction of conducting network and the surface density of graphene was studied.It was found that when the surface density was 92.8?g·cm^-2,the threshold value of permeability was reached.The relationship between the working voltage and the steady-state temperature is studied.When the working voltage is 10～25 V,the corresponding steady-state temperature is 34～87℃.The high stability flexible conductive film was obtained by UV curing,and its stability was studied:bending,scraping,solvent resistance.It is reflected by the change of sheet resistance,electric heating performance and SEM characterization of surface morphology.The results show that the polymer in the conductive layer reacts to form a cross-linked grid structure due to curing treatment,which firmly"locks"the graphene nanosheets,leading to a significant increase in its stability.