Pyrene-functionalized Hyperbranched Polythylene: Synthesis And Application In Noncovalent Production And Functionalization Of Graphene Flakes

As a type of unique two-dimensional carbon nanomaterials,graphene possesses wide application prospects in various fileds,such as electric conduction,energy,environment,biomedical,sensor and polymer modification,and so on.It is of significant importance to obtain stable,high-concentration solutions of graphene free of structural defects and functionalized modifications to graphene surface for its researches and various emerging applications.We herein report a strategy for synthesizing hyperbranched polyethylene covalently tethered with multiple pyrene moieties(HBPE@Py)and isobutyryl bromide(HBPE@Py@BIEA)which can trigger the ATRP polymerization,via chain walking ethylene copolymerization with Pd-diimine catalyst.Further more,The characterizations of the structure of copolymer,reveal the regulations of copolymerization reaction and methods of copolymer composition control.On this basis,we investigate the ability of efficient preparation of graphene in low boiling point organic solvent with HBPE@Py.Meanwhile,the rules of non-covalent function between polymer and graphene are studied within the system.The details are summarized as followings:(1)Under ethylene pressure of 1 atm and 25~35 �C,ethylene copolymerization with pyrene monomers were performed via one-step chain walking copolymerization with a Pd-diimine catalyst,giving a series of HBPE@Py copolymers by changing the polymerization time.The structure and composition of the copolymers were characterized with proton nuclear magnetism resonance(1H NMR),gel permeation chromatography(GPC)and dynamic light scattering(DLS)techniques,differential scanning calorimetry(DSC),fourier transformed infrare(FTIR)spectroscopy,UV-Vis spectroscopy and melt rheology measurement,respectively,examining the polymerization activity/controllable characteristics,as well as the polymerization temperature,time and feeding concentration on the influence law of molecular weight,chain form and composition.It is confirmed that pyrene moieties can be successfully introduced into HBPE.More over,pyrene grafting ratio can be controlled by adjusting the polymerization temperature and pyrene monomer feeding concentration.At the same time,molecular weight can be adjusted by the changes of polymerization time.HBPE@Py copolymer with narrow distribution(PDI = 1.16),containing the pyrene rate as high as 7.63 mol %,can be synthesized via one-step chain walking copolymerization with a Pd-diimine catalyst in 24 hours under 1 atm ethylene pressure,35 �C temperature,0.5 M pyrene feeding concentration.(2)Based on the study mentioned above,ethylene copolymerization with pyrene monomers and BIEA(containing acryloyl group and Acyl of butyl bromide group)were performed via one-step chain walking copolymerization with a Pd-diimine catalyst under ethylene pressure of 1 atm and 25~35 �C,giving a series of HBPE@Py@BIEA copolymers.The structures and compositions of the copolymers were characterized as HBPE@Py,examining the influence law of copolymer composition on polymerization temperature and monomer feeding concentration.Researches show that: Multiple pyrene and butyl bromide functional groups are successfully introduced onto the branched chain ends of HBPE(HBPE@Py@BIEA).At the same time,the proportion of pyrene and functional groups of the copolymer can be adjusted by the changes of polymerization temperature and feeding monomer concentration.The HBPE@Py@BIEA copolymer(PDI = 1.23)can be synthesized successfully via one-step chain walking copolymerization with a Pd-diimine catalyst in 24 hours under 1 atm ethylene pressure,35 �C temperature,0.5 M pyrene feeding concentration.(feeding concentration:pyrene monomer 0.3 M,BIEA 0.6M)(3)The resulting HBPE@Py was further used to noncovalently exfoliate graphite under the assistance of ultrasonication in THF/chloroform,leading to a series of stable graphene solutions.The graphene concentrations were characterized and compared with UV-Vis technology,High-resolution transmittance electron microscopy(HRTEM),atom force microscopy(AFM),raman spectroscopy and wide-angle X-ray diffraction(WAXRD),X-ray photon spectrometer(XPS),thermogravimetry analysis(TGA),fourier transformed infrare(FTIR)spectroscopy,investigating the efficiency of ultrasonic time,feeding ratio,pyrene introduction to the preparation of graphene within the system.It is found that the pyrene-functionalized HBPE is found to have improved ability in noncovalently exfoliating graphite into graphene solutions both in THF and chloroform,and also can adjust graphene concentration effectively.Compared with the pure HBPE,we can obtain higher concentration and more stable graphene solution,the graphene thickness is around 3~5 layers with free of defects,and stronger non-covalent impaction between grapheme and polymer.(4)Based on prepared organic solution of graphene above,further,a series composite materials of grapheme/HBPE@Py were made through vacuum filtration,and Characterized by UV-Vis,FTIR and TGA.It turned out that it is more stable non-covalent acting force between graphene surface and HBPE@Py than HBPE,which owe to the help of synergistic effect from ?-? and CH-? stacking of HBPE@Py.With the help of the non-covalent synergy,part of the copolymer can be firmly adsorbed on the surface of grapheme,containning 32,59% in THF and 38.95% in chloroform,respectively.In conclusion,We establish a new method and thought for the synthesis of HBPE@Py and preparation of low defect and surface functionalization graphen with HBPE@Py copolymer.The graphene has important and wide application prospects in the field of high performance polymer/graphene nanocomposites.