| The epoxy resins toughened with acrylate polymers have the excellent performance of thermal oxygen aging resistance because there are not any double bonds in the main chain structure.The toughened epoxy resins can own the good toughness retention at the high temperature,be easier for the molecular structure design and be prepared by diverse polymerization methods.The acrylate polymers which are used to toughen epoxy resins have the prominent role in improving the bonding strength of epoxy resins,especially the peel strength.In this paper,the epoxy resins toughened with acrylate polymers were studied in details from the aspects of the molecular structure design,synthesis methods,and the structure and morphology of polymers and so on.The mechanical properties,adhesive properties,dynamic thermal mechanical properties and microstructure of polymers with different structures were discussed and the relationship between the structure and properties is discussed.The specific contents are as follows.1.The acrylate oligomers containing carboxyl groups in the side chains were synthesized by the solution polymerization method.It is found that the toughness of modified epoxy resins obtained by the prereaction of the acrylate oligomers containing carboxyl groups and epoxy resins is better than that of modified epoxy resins obtained by the directly mixing of the acrylate oligomers and epoxy resins.The peel strength of modified epoxy resins and the compatibility between epoxy resins and acrylate oligomers increase with the increase of AA contents in the oligomers.The mechanical and adhesive properties of modified epoxy resins’become worse with excess amounts of AA in the oligomers because the compatibility between epoxy resins and oligomers increases,the system becomes much more transparent,and it is difficult for phase separation.When the 10 wt.%oligomer containing BA and AN and AA in the ratio of 75/20/5 is used to modify epoxy resins,the increase in the impact strength of the modified epoxy resin is 290%over the nmodified epoxy resin.And when the 15 wt.%oligomer is used to modify epoxy resins,the peel strength increases from 0.8 kN/m to 6.9kN/m.With the increase of oligomer contents,dispersed particles become concentrated and some particles agglomerate which is easy to form defects and the toughening properties of modified epoxy resins become poor.The results of DMA show that with the increase of oligomer contents,Tg increases and then decreases.Both Tg and shear strength at the high temperature are higher than these of the unmodified epoxy resin when the oligomer content is not more than 5 wt.%.The phase separation is serious and the curing system of epoxy resins is damaged when the oligomer content is 30 wt.%.2.The acrylate oligomers containing epoxy groups in the side chains were synthesized by the in situ polymerization method.Compared with the solution polymerization,the oligomers with the same structure and toughness properties can be obtained by the in situ polymerization method,while the in situ polymerization process is more convenient.When the 10 wt.%oligomer containing BA and AN and GMA in the ratio of 70/20/10 is used to modify epoxy resins,the increase in impact strength of the modified epoxy resin is 219%over the unmodified epoxy resin and the peel strength increases to 7.1kN/m.The results of SEM show that when the oligomer content is lower,spaced holes caused by the removal of rubber particles on the fracture surface are uniformly distributed throughout the matrix and their size is uniform in the range of 0.5～1μm.With the increase of oligomer contents,the size of holes increases obviously with the particle size in the range of 1～2μm,dispersed particles become concentrated and some particles agglomerate,and the toughening properties of the modified epoxy resins become poor because the agglomeration of particles destroys the impact properties.The results of DMA show that with the increase of oligomer contents,Tg increases and then decreases.Tg is higher than that of the unmodified epoxy resin when the oligomer content is not more than 5wt.%.3.The isocyanate acrylate oligomers containing epoxy groups were synthesized by the in situ polymerization method.The influence of the molecular structure on mechanical and adhesive properties was studied.It is found that the molecular weight of epoxy resins and the isocyanate structure of oligomers have the great influence on mechanical and adhesive properties.Especially the introduction of the isocyanate segments can improve the peel strength effectively.The peel strength of the modified epoxy resin with 2-IEMA isocyanate segments reaches 9.0 kN/m.The toughening performance is poor when the mutual solubility between the soft monomer and the curing system of epoxy resins is bad.When the 20 wt%oligomer containing BA and AN and E-03-T-HPMA in the ratio of 70/20/10 is used to modify epoxy resins,the increase in impact strength of the modified epoxy resin is 103.1%over the unmodified epoxy and the peel strength is 7.5 kN/m.The results of SEM show that when the oligomer content is lower,the oligomer particles are uniformly distributed throughout the epoxy resin matrix.When the oligomer content is 30 wt%,the phase separation is serious which results in the decrease of mechanical and adhesive properties.The results of DMA show that with the increase of oligomer contents,Tg increases and then decreases.Tg is higher than that of the unmodified epoxy resin when the oligomer content is not more than 5wt%.4.The acrylate polymer with the core-shell structure were synthesized by the seed emulsion polymerization method.The core-shell particles with the particle size of 60-120nm show the excellent toughness performance.The introduction of nanoparticles with the appropriate amount of GMA can obviously improve the mechanical and adhesive properties of the system.The results of TEM show that the interface between core-shell particles containing GMA and the epoxy resin matrix is vague and their mutual solubility is good which shows the reaction between GMA and the curing system of epoxy resins.When the 10 wt%core-shell particles containing BA and MMA and GMA in the ratio of 70/20/10 is used to modify epoxy resins,the increase in impact strength of the modified epoxy resin is 183%over the unmodified epoxy resin and the peel strength is 7.5 kN/m.The study on the mixing methods shows that with the mixing method I,core-shell particles show the inhomogeneous dispersion in a"spherical" particle cluster with a size range of 2-10μm and with the increase of core-shell particle contents the "spherical" particle cluster becomes big.The results of TEM show that the "spherical" particle cluster is the agglomeration of many core-shell particles.With the mixing method II,the small amounts of core-shell particles can be dispersed in the epoxy resin matrix uniformly and the particles agglomerate when the particle content is 10 wt.%.The "spherical" particle cluster and agglomeration are easy to cause the fracture.So when a certain amount of core-shell particles are used,the modified epoxy resins obtained by the mixing method II have better mechanical and adhesive properties than these obtained by the mixing method I.The results of DMA show that with the increase of core-shell contents Tg increases and then decreases.Tg is higher than that of the unmodified epoxy resin when the oligomer content is in the range of 15 wt.%. |
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