Preparation Of Carbon Nanotubes Grafted With Hyperbranched Polymer And Their Modification For Epoxy Resin

In recent years,the carbon nanotubes(CNTs)have been widely used in the modification of polymer resin due to their excellent properties,including unique small size effects,quantum size effects,surface effects,high mechanical properties and good thermal and electrical conductivity.The introduction of CNTs into the epoxy matrix not only reinforces the matrix,but also improves the thermal and electrical properties of materials.However,the CNTs have a large specific surface area and a high number of surface atoms due to their nanometer size.As a result,they are easily aggregated in the resin matrix,reducing the effect of the carbon nanotubes as reinforcing fillers and leading to the degradation of composites performance.It is necessary to chemically modify the surface of the carbon nanotubes to prevent agglomeration and improve their dispersion stability and compatibility in the resin matrix.In this paper,the hyperbranched polymer was introduced on the surface of carbon nanotubes by the“thiol-yne”click chemistry method to chemical modify the surface of the carbon nanotubes.Compared to the traditional grafting methods,the“thiol-yne”click chemistry method has many advantages,including high selectivity and conversion,rapid reaction speed,environmental friendly and simple experimental condition.Firstly,the hyperbranched monomers(but-3-yn-1-yl 3-mercaptopropanoate)were synthesized via a series of protection and deprotection reactions,then the hyperbranched polymers were introduced on the surface of carbon nanotubes via"thiol-yne"click reaction to obtain hyperbranched polymer-grafted carbon nanotubes(CNTs-HBP).The resulted CNTs-HBP were used as modifiers and mixed with epoxy resin(E-51)to prepare the hyperbranched polymer-grafted carbon nanotube/epoxy resin(CNTs-HBP/EP)composites.The mechanical,thermal and electrical properties of the composites were investigated to study the influence of hyperbranched polymers grafted on the surface of carbon nanotubes on the properties of the composites.The specific completion is as follows:(1)The raw carbon nanotubes(Raw-CNTs)are treated with mixed acid,and then?-mercaptopropionic acid trimethoxysilane(KH590)was introduced onto the surface of CNTs via the hydrolysis condensation reaction to obtain the thiol-functionalized carbon nanotubes(CNTs-KH590).The resulted CNTs-KH590 was characterized by FT-IR and TGA.The experimental results show that KH590 is successfully grafted onto the surface of carbon nanotubes and the grafting rate is about 14%.(2)Because the thiol group is easily oxidized,the hyperbranched monomer(but-3-yn-1-yl 3-mercaptopropanoate)can be prepared by an esterification reaction and a series of protection and deprotection reactions on the thiol group.Based on the"thiol-yne"click reaction,the hyperbranched polymer was grafted onto the surface of the CNTs-KH590 to obtain hyperbranched polymer-grafted carbon nanotubes(CNTs-HBP).The characterization results of FT-IR,TGA,XPS,~1H NMR indicate that the hyperbranched monomer was successfully synthesized and the hyperbranched polymer was successfully grafted onto the carbon nanotubes surface by the“thiol-yne”click reaction and the grafting rate was 17%.TEM results indicate that the hyperbranched polymer forms a flexible coating with about 4-8 nm thickness on the surface of the carbon nanotubes.In addition,the dispersion test results show that the introduction of hyperbranched polymers on the surface of carbon nanotubes can significantly improve the dispersion stability in ethanol.(3)The Raw-CNTs and CNTs-HBP were used as modifier and mixed with epoxy resin(E-51)to prepare CNTs/EP composites.The influence of the carbon nanotubes content and hyperbranched polymers on the composites properties was investigated.The results show that the reinforcing effect of CNTs-HBP on epoxy resin is significantly better than that of Raw-CNTs.When the content of CNTs-HBP is 0.6%,the impact and flexural strength of the CNTs-HBP/EP-0.6 composites reach to the best,which are increased by180%and 72%,respectively compared to pure epoxy resin.The results of SEM showed that a large number of carbon nanotubes were fractured at the fracture surface of CNTs-HBP/EP composites and the composites exhibit the characteristics of ductile fracture.(4)As the content of CNTs-HBP increases,the heat resistance of the composites is increased,and the glass transition temperature moves to a high temperature area.At the same time,the thermal conductivity of the composites is higher than that of the pure epoxy resin.In addition,the volume resistivity of the composites begins to decrease when the Raw-CNTs content increases.However,as the content of CNTs-HBP increases,the volumetric surface resistance of the composite does not decrease significantly,and almost is equivalent to pure epoxy resin.