Study On Preparation And Properties Of Siloxane Modified Benzoxazine

As a new phenolic resin material,benzoxazine has the advantages of curing without catalyst,almost zero volume shrinkage before and after curing,low humidity,excellent mechanical properties,high carbon residue rate and so on.Scientists think that benzoxazine has replaced the traditional phenolic resin to some extent,but with the further study of benzoxazine,It is found that polybenzoxazine has some disadvantages,such as low cross-linking density,high ring-opening curing temperature,high brittleness,difficult to form film and so on.In order to further broaden the application field of benzoxazine,it is an inevitable trend for the development of benzoxazine materials to overcome these shortcomings and obtain benzoxazine materials with good comprehensive properties.This paper mainly studies the aspects of improving the toughness of benzoxazine,reducing the ring-opening curing temperature of benzoxazine and improving the thermal stability.The specific work is as follows:(1)Two kinds of benzoxazine adhesives(named BOZ-248 and BOZ-1000)with different siloxane content were synthesized by using 1,3-bis(3-aminopropyl)-l,1,3,3,-tetramethyldisiloxane or ?,?-bis(3-aminopropyl)polydimethylsiloxane,catechol and 37%formaldehyde aqueous solution as raw materials,and their chemical structures were characterized by FT-IR and NMR.At the same time,the open-loop curing temperature and bonding properties of BOZ-248 and BOZ-1000 were investigated.The results of FT-IR and differential scanning calorimetry showed that BOZ-248 and BOZ-1000 had lower open-ring curing temperatures of 124?and 138?,respectively.Then,under the condition of no special sandblasting treatment on the substrate,the adhesive properties of the synthesized benzoxazine were tested after thermal curing polymerization at medium and low temperature at 90?.The maximum single tensile shear strength was as high as 7.29MPa and 12.34 MPa,respectively.(2)Taking advantage of the flexible design of the molecular formula of benzoxazine,polysiloxane bisphenol fluorene was introduced into it at the same time,and a material with good flexibility and thermal stability was obtained.In this chapter,two kinds of benzoxazines(named BF-APTMDS and BF-APPDMS)with different siloxane contents were synthesized from 1,3-bis(3-aminopropyl)-1,1,3,3,-tetramethyldisiloxane or ?,?-bis(3-aminopropyl)polydimethylsiloxane,bisphenol fluorene and paraformaldehyde.The products were successfully synthesized by IR and NMR characterization.Thermogravimetric analysis(TGA),dynamic mechanical(DMA)and tensile stress and strain tests were carried out.The thermal stability index(Tc)of PBF-APTMDS and PBF-APPDMS was 190? and 214?,respectively.And the glass transition temperature(Tg)was 270? and-110?,respectively.The test results of tensile stress and strain show that the elongation at break of PBF-APPDMS is 36%and the tensile strength is 1.02 MPa.From the data results,it can be concluded that the benzoxazine modified by polysiloxane has certain toughness and thermal stability.(3)In order to further improve the thermal stability of the benzoxa reactor,we further introduced diphenylmethane diisocyanate on the basis of BF-APPDMS.Then thermogravimetric and tensile stress-strain tests were carried out,and the results showed that compared with PBF-APPDMS,Td5 increased from 382? to 427?,the carbon residue rate at 800? increased from 7.66%to 25.24%,the thermal stability index increased by 160?,and the tensile strength increased from 1.02 MPa to 1.38 MPa.A kind of benzoxazine material with good comprehensive properties was obtained.