Modification Of Unsaturated Polyester By High Cis-1,4 Hydroxyl-terminated Polybutadiene

Unsaturated polyester resin(UPR)has become one of the most commonly used thermosetting resins due to its excellent mechanical and electrical properties,good corrosion resistance and simple processing technology.Its composite materials are widely used as structural materials,adhesives,coatings and insulation materials in the automotive,aviation,electronics,construction and packaging industries.However,it is hard and brittle after curing and has poor impact performance,which limits their application in more fields.It is important to improve the impact property,and meanwhile keep or even increase the stiffness of unsaturated polyester.High cis-1,4 content hydroxyl-terminated polybutadiene(HTPB)was used as modifier for UPR.The cis polybutadiene oligomers was introduced into UPR prepolymer chain by co-condensation polymerization between hydroxyl groups of HTPB and carboxyl groups of UPR.Mechanical and thermal properties of cured product at room temperature and low temperature were investigated.UPR modified by HTPB with three diffent molecular weight of 1000?3000 g/mol were synthesized to explore the influence of HTPB molecular weight on the modification effect.It has been found that the elongation at break,tensile strength and impact strength of all the modified UPR were higher than the corresponding values of pure UPR.The modification effect of UPR modified by HTPB with molecular weight of 2000 g/mol is best.In order to figure out the influence of HTPB content on modification effect,a series of modified UPR prepolymer by HTPB with molecular weight of 2000 g/mol were prepared through solution co-condensation polymerization method.It has been found that the elongation at break,the tensile strength and the impact strength of all the modified UPR were superior to those of pure UPR whether at room or low temperature(-20?).When the mass fraction of HTPB is 5 wt%,the three mechanical properties of modified UPR at room temperature are increased with 124%,94%and 84%than those of pure UPR respectively.At low temperature,the three properties of modified UPR are increased with 220%,186%and 167%than those of pure UPR respectively,indicating that the modification effect is more obvious at low temperature.Results of DMA shows that Tg of the modified UPR is 19? lower than that of pure UPR.And the modified UPR has significant improvement of curing shrinkage.When the mass fraction of HTPB is 5 wt%,the shrinkage of UPR-HTPB is 2.1%.The analysis of the impact section morphology shows that agglomeration of rubber and formation of large elastomer particles can be effectively prevented by insertion of HTPB in UPR prepolymer chain and by its participation in the cross-linking reaction,and the microphase separation regions are obviously increased,which induce microcrack and shear zone,so that both toughening and strengthening effects are given.Furtherly,HTPB maleate ester was prepared and introduced into the main chain of UPR prepolymer through the copolycondensation polymerization,and a series of UPR with different HTPB contents were synthesized.It has been found that the modified UPR has higher elongation at break,tensile strength,elastic modulus and impact strength than those of pure UPR.When the mass fraction of HTPB is 5 wt%,the four properties of modified UPR are increased with 118%,60%,7%and 130%than those of pure UPR,respectively.The impact fracture surface of modified UPR shows smaller and less rubber holes than that of UPR-HTPB.DMA shows that there are two glass transition temperatures of modified UPR,indicating that microphase separation occurred in the polyester matrix.The toughness,strength and rigidity of the cured products can be improved simultaneously by this method,and the toughening modification effect is similar to that of UPR-HTPB,while the improvement effect of modulus,Rockwell hardness and heat deformation temperature are far better than that of UPR-HTPB.It is because that the synthesis of HTPB maleate ester converts the terminated hydroxy1 group of HTPB into the more active terminated carboxyl group,which improves the structure regularity of the modified UPR and increases the binding force between HTPB and UPR matrix.