Preparation And Application Of Comb Hyperbranched Molecules

Due to the excellent overall mechanical performance,epoxy resin is the most widely used thermosetting resins and has important industrial applications.Epoxies used in radomes and electronic packaging materials also require good dielectric properties.In this thesis,in order to take advantage of the characteristics of hyperbranched polymers,comb-like hyperbranched molecules was designed and synthesized.Then it is used to modify bisphenol A epoxy resin(DGEBA)in order to improve mechanical and electrical performance.The main work of my thesis is summarized as follows.(1)Using low polarity monomers(styrene and imide),a comb-like hyperbranched polymer(P-HBPE)containing imide structures was synthesized using a three-step procedure.Effects of monomer ratio,temperature,solvents,and reactor size were studied and optimized reaction conditions were determined.(2)P-HBPE was mixed with DGEBA and cured with MNA,optimized cure scheme was determined.When the P-HBPE addition is increased,the glass transition temperature(Tg)of DGEBA/P-HBPE/MNA curing system first increases then decreases,and the tensile and impact strengths are also improved.Because the terminal groups of P-HBPE is not modified and thus non-reactive,the dielectric performance is not improved.(3)Starting from linear poly(4-vinylphenol),comb-like hyperbranched epoxy PVPE without imide structures was synthesized by a two-step procedure.Optimized reaction condition was determined for the first step.Under the optimized condition,the degree of grafting is increased and by-products are reduced,which leads to higher molecular weights and yield.The thermal and rheological properties of PVPE were investigated.DSC results showed that the glass transition temperature(Tg)of PVPE was 79.8?;TGA results showed the initial thermal decomposition temperature is 340.1?and the residual carbon content is 30.2%at 800?,showing good heat resistance.The rheological results showed that the viscosity was higher than 103 Pa s at 190?,and the method of heating the mixture cannot be used.(4)PVPE was mixed into DGEBA and cured with MNA.When PVPE loading was increased,Tg increases and reaches maximum at 10wt%.The initial thermal decomposition temperatures(Td5)of all mixed epoxies are higher than 395?,indicating excellent thermal stability.Compared with unmodified system,the dielectric constant of PVPE modified system is about 0.20 lower in the frequency range of 1-30MHz,and the dielectric loss is lowered by 0.008.Addition of PVPE also improved mechanical properties:at 5wt%PVPE loading,the impact strength reached 29.5kJ/m2,which was 23.9%higher than the pure DGEBA system,Tg and tensile strength are also improved without compromising other properties.(5)DSC dynamic scans were used to study the cure kinetics of PVPE/DGEBA/MNA system,and model-free kinetics were used to analyze the data.Results show that the addition of PVPE lower the onset exothermic temperature,suggesting that the reactivity of the epoxide groups in PVPE was higher than those that in DGEBA,ensuring the complete incorporation of PVPE.Isothermal cure measurements were also performed,and Kamal auto-acceleration model was used to analyze the data.Results show that the total order of reaction in the cure process is approximately two.