Synthesis Of Functional Hyperbranched Macromolecule And Its Application As Modifier Of Epoxy Thermoset

Because of its excellent mechanical properties,good electrical and thermal properties,epoxy resin is used as one of the most versatile thermosetting polymers with a wide range of applications.However,its high cross-linking density leads to a relatively low impact resistance,which limits its use in many applications.Thus,epoxy toughening has been a long focus in both academic and industrial fields.Up to now,many kinds of tougheners such as liquid rubber,thermoplastic,nanomaterial,core-shell polymer particles,and block copolymers have been developed and used to improve the toughness of epoxy resins.But many of them would affect the glass-transition temperature?T_g?and modulus of the cured resins to some degree,and/or sacrifice the processability due to the increase in viscosity.Especially with the development of microelectronics,aircraft and aerospace,construction and communication,a higher performance is required for epoxy thermosets.Thus toughening epoxy resins with enhancing other properties is still a big challenge.Since first reported in 1996,toughening epoxy thermoset with hyperbranched polymer has given rise to a great attention among scientists in the world.Recently,it has been proved that the incorporation of the hyperbranched polymer?HBP?designed backbone structures and terminal groups into epoxy resins can improve the toughness of epoxy resins without much affecting other properties,such as T_g and modulus.In the meantime,the synthetic approach,intrinsic viscosity and reactable terminal groups of HBP also is beneficial to its application in epoxy toughening.Usually,when HBP is used to toughen epoxy resins,it can form a phase-separated or non-phase-separated mechanism.What should be pointed out is that the key issue for this approache is to toughen an epoxy resin with simultaneous enhancement in its modulus,mechanical strength,and thermal properties.In addition,in order to meet the demands of industrialization,cheap and available raw materials and simple preparation process also need to be considered.In recent years,the fast depletion of petroleum reserves and increasing environmental problems,in addition to the global political toward the principles of sustainable development,have led to a growing interest in the use of biobased sustainable feedstock in the synthesis of biobased chemicals and products.In this regard,some researches had focused on the synthesis and utilization of renewable material as efficient epoxy resin and epoxy hardener.For example,some vegetable oils such as castor oil,colza oil,tung oil and soybean oil have been utilized to prepare the epoxy resins successfully.Then they were used to replace the petroleum based epoxy resin to prepare biobased epoxy thermoset.As we known,epoxy additives are the vital components for the epoxy thermosets in practical application.However,the study on biobased epoxy additives is scanty.So,developing high performance biobased additives is a key problem which would be handled in this paper.Considering the above aspects,this thesis would focus on those two areas mentioned above.We have synthesized two synthetic and biobased hyperbrached tougheners,in which the backbone structures and terminal groups have been designed according to the relationship between the structure of HBP and properties of final thermosets.Both synthetic and biobased hyperbrached tougheners were used as tougheners of epoxy thermosets.The effect and mechanism of all the tougheners modified epoxy systems were realized.So the main framework of this thesis are:Cheap and available raw materials are utilized to synthesis two synthetic HBPs with a simple approach.Then they were used as tougheners of epoxy thermosets.The effect of HBP on the properties of HBP modified epoxy thermosets is studied detailed and toughening mechanism is also demonstrated.Moreover,two tannic acid based hyperbranched epoxy tougheners were also prepared according to the results obtained from the case of synthetic HBP.Finally,the properties and mechanism of biobased tougheners modified thermosets were investigated.The main contents of this thesis are as follows:1.Synthesis and application of carboxyl-terminated hyperbranched polyester as an efficient toughener for epoxy/anhydrideA series of carboxyl group-terminated hyperbranched polyesters?HBPE-COOHs?with different backbone structures are synthesized using a simple one-pot A₂+B₃ approach,and subsequently incorporated into epoxy/anhydride curing system.It is found that the terminal carboxyl groups of HBPE-COOHs can promote the curing process of epoxy/anhydride system,which has a great effect on the final properties of HBPE-COOH modified epoxy thermosets.Owing to the miscible backbone structure and terminal carboxyl groups,HBPE-COOHs can efficiently toughen epoxy/anhydride thermosets with a non-phase-separated morphology.In the meantime,a simultaneous enhancement in tensile strength is achieved.The effects of HBPE-COOH structure and HBPE-COOH loading on the thermal,and thermomechanical properties are investigated.The results show that thermoset modified with HBPE-COOH3,which has the most flexible backbone structure and moderate terminal carboxyl groups,exhibits the highest crosslinking density,T_g and T_5%,which are 6°C and 25°C higher than that of neat epoxy thermoset.2.One-pot synthesis of tetramethyl biphenyl backboned hyperbranched epoxy resin as an efficient toughening modifier of epoxy resinThree tetramethyl biphenyl backboned hyperbranched epoxy resins?BPHBEs?were synthesized through a simple one-pot A₂+B₃ polycondensation reaction.Then,they were incorporated into epoxy/anhydride and epoxy/jeffaimne curing systems,respectively.The curing behavior was investigated by differential scanning calorimetry?DSC?,which reveals that the adding of BPHBE to the formulation would not much affect the curing process.The influence of BPHBE on the mechanical and thermomechanical properties of both epoxy/anhydride and epoxy/jeffaimne systems was studied.The results show that BPHBE can significantly toughen both two systems without much trade-offs in their strength,modulus and Tg.While the initial decomposition temperature of the cured thermosets slightly drops.Owing to the miscible backbone structure and terminal epoxy groups,no phase separation was observed in SEM.3.Modification of epoxy–anhydride thermosets using modified tannic acid:synthsis and curing behaviorIn this part,an approach to toughen epoxy resin with tannic acid,a common polyphenolic compound extracted from plants and microorganisms,is presented.First,dodecane functionalized tannic acid?TA-DD?and carboxylic acid functionalized tannic acid?TA–COOH?were prepared through a simple reaction between TA with epoxydodecane and methylhexahydrophthalic anhydride.Their structures were characterized by NMR and FT-IR.Then,TA-DD and TA–COOH were incorporated into epoxy/anhydride curing system.Because of strong intermolecular interactions,TA is immiscible with epoxy resin and tends to precipitation during curing.However,owing to the chemical modification,both TA-DD and TA-COOH could easily disperse in epoxy resin.The curing behaviors of TA-DD and TA-COOH modified epoxy samples were studied by DSC and FT-IR.The results showed that the hydroxyl groups in TA-DD can activate the anhydride groups and then lower the activation energy of the curing system.For the TA-COOH,its terminal carboxyl groups can act as a hardener and then react with epoxy groups.With such mechanism,both TA-DD and TA-COOH could decrease the activation energy and promote the curing process.4.Modification of epoxy–anhydride thermosets using modified tannic acid:propertiesOwing to the modification of long aliphatic chain,TA-DD can induce epoxy matrix yielding phase separation,forming microscaled separated phases.In the meantime,the terminal hydroxyl groups of TA-DD can participate in the curing process,which offers a good interfacial interaction between TA-DD and epoxy matrix.For the TA-COOH modified epoxy resin,its terminal carboxyl groups can participate in the curing process and then lead to a homogeneous morphology.With such a mechanism,the results show that both TA-DD and TA-COOH could significantly improve the toughness with a great increase in impact strength and T_g under a low loading amount.The toughening and reinforcing mechanism was studied by SEM and AFM.Which should be owned to the micro-phase separation structure with good interface interaction for the TA-DD modified epoxy system and in-sute toughening and strengthening mechanism.In summary,both synthetic and biobased hyperbranched epoxy tougheners were synthesized in this thesis.They can effectively toughen epoxy thermosets with simultaneous increasement in strength,modulus and T_g.What's more,the raw materials is cheap and available,and the synthetic route is simpe.Which makes the hyperbranched epoxy tougheners easy to be industrialized.On the other hand,we believe utilizing the renewable tannic acid as an effective modifier for epoxy resin with good properties has positive effect on developing high performance biobased epoxy thermosets.