Synthesis Of Flexible Chain Blocking Hyperbranched Polyester And Its' Modification On Epoxy Resin

Hyperbranched polymers commenly contain highly branched structure and a large number of functional end groups.It can be used to modify the dielectric and mechanical properties of the epoxy resin,by utilizing its'huge free volume and flexible chain segments which introduced by the highly branched structure and modification end groups of hyperbranched polymers.In this paper,a novel flexible chain blocking hyperbranched polyester(FCBHBP)was synthesized by using pentaerythrite and dimethylolpropionic acid as raw materials,and blocking by butyric acid,hexanoic acid or capric acid as blocking agents,respectively.The FCBHBP and its cured modified epoxy resins were characterized by FT-IR.Results showed the occurrence of the ester group and alkane chain segments in FCBHBP resins.Moreover,results also indicated that the FCBHBP was not involved in the curing reaction of epoxy resin.The branched degree of the hyperbranched polyester resin was characterized by ¹³C-NMR,and results showed that the branched degree of the obtained polyester resin was 0.609,0.603and 0.530,respectively,when used butyric acid,hexanoic acid and capric acid as the blocking agents.The mechanical and dielectric properties of the epoxy resins which modified by three blocked hyperbranched polyester were characterized.Results showed that when the weight content of the FCBHBP which blocked by butyric acid was20 wt.%for epoxy resin,the dielectric constant of the modified epoxy resin was3.87,and the impact strength and bending strength were 26.334 k J/m²and147.912MPa,respectively.In case of the same mass percentage of hyperbranched polyesters,the dielectric constant of epoxy resin modified by hyperbranched polyesters which blocked by hexanoic acid was 3.35,and the impact strength and bending strength was 29.920 k J/m²and 151.377 MPa.Moreover,the dielectric constant,impact strength and bending strength of epoxy resin modified by FCBHBP which blocked by capric acid was 3.53,22.634 k J/m²and 134.059 MPa.Microstructures of impact sections of cured epoxy resins were characterized by SEM and a typical ductile fracture characteristic was found.Broadband dielectric spectroscopy testing results showed that the epoxy resin modified by FCBHBP which blocked by butyric acid had a rather low dielectric loss in the testing frequency range from 10⁰to 10³Hz.While the epoxy resin modified by FCBHBP which blocked by hexanoic acid had a low dielectric constant and loss at the frequency from 10⁴to 10⁶Hz,and the epoxy resin modified by FCBHBP which blocked by capric acid had a low dielectric constant and loss at the frequency from 10³to 10⁴Hz.All these results indicated that one could choose different kinds of end blocking agent modified hyperbranched polyester to modify epoxy resin according to the different requirements in application,which has potential application value in the field of modified epoxy resin.