Hyperbranched And Tetrafunctional Phenols/Epoxies:Synthesis And Properties

Due to the various advantages,including low cure shrinkage,good adhesion,and excellent chemical resistance,epoxy resins have found wide applications in various fields,such as coatings,composites,electrical and electronic materials,adhesives,and dental materials etc.However,the inadequate performance in some aspects limits its wider applications.For example,although epoxy resins have lower cure shrinkage and toxicity than traditional dental resins,its mechanical strength is lower,and the cure shrinkage as well as cytotoxicity still need to be reduced further;Due to the brittleness,cured epoxies have to be toughened when used as electrical encapsulation.Addition of rubbers,thermoplastics,nanoparticles,and other modifiers can toughen cured epoxies;however,other important properties are compromised;Tetrafunctional epoxy,N,N,N',N'-tetraglycidyl-4,4'-diamino-diphenylmethane(TGDDM),which is the dominant matrix for high-temperature composites,suffers from inadequate toughness and hydrothermal resistance,whereas the Tg of the difunctional epoxy,diglycidyl ether of bisphenol A(DGEBA),which is the most popular epoxy,is not high enough.In addition,epoxy resins are mostly used in traditional applications rather than as functional materials,especially fluorescent materials.With the goal of achieving high-performance and/or imparting functionalities to epoxy resins and in order to address the aforementioned issues,novel multifunctional molecules,hyperbranched polymers and tetrafunctional epoxy resins,were synthesized,and their applications were explored.The main contents of this dissertation are as follows.1.A hydroxyl-containing hyperbranched polyether(HBP-OH),which has terminal phenolic hydroxyl groups and internal aliphatic hydroxyl groups,was synthesized using A2+B3 proton transfer polymerization,via one-pot,two-step procedures and then characterized.The readily available reagents and mild reaction conditions make this synthetic route advantageous.HBP-OH was used as a modifier for cationically-cured cycloaliphatic epoxy systems.Addition of 5 wt%HBP-OH simultaneously reduces the cure shrinkage(reduced from 3.46%to 2.76%),improves the bending strength(increased by 14.8%),and reduces the cytotoxicity.In addition,HBP-OH modified epoxy shows lower cure shrinkage,higher hardness(increased by 31.3%)and lower cytotoxicity compared with dimethacrylate dental resins,which have a cure shrinkage of 7.64%.Those improvements could be related to the increased crosslinking density and changes in network composition due to HBP-OH addition.Results show that HBP-OH is an effective modifier for cycloaliphatic epoxy resins,which broaden its application in dental materials.2.A series of dichlorophthalimides with different spacers were designed and synthesized.Three kinds of hyperbranched polyetherimides with phenolic terminal groups(HBPEI)were prepared using A2+B3 approach via the nucleophilic aromatic substitution reaction between dichlorophthalimides and trihydroxyltriphenylmethane.The reactivity of A2 monomers,and the effects of monomer concentration,reaction time,the molar ratio of A2 to B3 as well as reaction size on the molecular weights of HBPEI were investigated.HBPEIs were then added as modifiers for DGEBA/1MI homopolymerization system.Results show that addition of HBPEI can simultaneously improve the impact strength,tensile strength and hydrothermal resistance of cured epoxies,without forming phase separation and reducing Tg(sometimes even improves Tg).Compared with the unmodified system,the impact strength and tensile strength of 5 wt%HBPEI3 modified system increase 28.8%and 17.2%,respectively,without reducing Tg:the impact strength,tensile strength,and Tg of 7 wt%HBPEI3 modified system increase 23.2%,14.6%and 7?,respectively.The excellent improvements due to HBPEI3 addition are attributed to increased crosslinking density,reduced free volume,and semirigid semiflexible backbone structure,indicating the importance of the designs in the terminal group and backbone structure.3.A fluorine-containing glycidyl ether-type tetrafunctional epoxy resin(FCTE)was synthesized through a three-step procedure.Addition of FCTE into DGEBA/DDS can not only improve Tg and impact strength but also reduce the water absorption and dielectric constant.The best overall performance is achieved at 20 wt%FCTE loading:Tg is 238?,Td5%is 410.3?,the tensile strength is 82.5 MPa,the impact strength is 30.5 kJ.m-2,the saturated water absorption at 95? is 3.64%,dielectric constant at 1 MHz is 4.21,and interlaminar shear strength with polyimide fibers is 63.1 MPa.All properties,except Tg,outperform those of TGDDM/DDS system;the Tg value is,however,still high enough for many high-temperature applications,suggesting that FCTE/DGEBA hybrid epoxy could be a replacement for TGDDM in some applications.The good properties of FCTE/DGEBA not only show the effectiveness of tetrafunctional epoxy resins in improving the Tg of cured difunctional epoxy resins,but also demonstrate that the rational design of spacer is an effective strategy for achieving better performance of tetrafunctional epoxy.4.Epoxide-terminated hyperbranched polyetherimides(EHBPI)were obtained by epoxidation of the phenol-terminated hyperbranched polyetherimide(HBPI).Although fully-aromatic hyperbranched polyetherimide cannot emit fluorescence,the semialiphatic semiaromatic hyperbranched polyetherimide is fluorescent because it can suppress the CT interactions after incorporation of aliphatic segments.Effects of backbone structures,terminal groups,and topology of hyperbranched polymers on the fluorescence emission were investigated.EHBPI3,which has terminal epoxide groups and the most flexible backbone shows the highest fluorescence intensity.Effects of solvent polarity,aggregation state,temperature,and metal ions on the solution fluorescence of EHBPI3 were studied.Results indicate that the solution fluorescence of EHBPI3 agrees with ACQ mechanism.Both Fe and Cu ions can quench its fluorescence,and Fe ion being more effective.EHBPI3 can be used as a fluorescence probe for Fe3+detection,with a detection limit of 6.06×1 0-5 mol.L-1.The EHBPI3 solution emits bluish green fluorescence with a quantum yield of 0.28,whereas bulk solid-state EHBPI3 emits white light with a quantum yield of 0.06.A white-light emitting film(quantum yield is 0.05)was prepared by blending EHBPI3 with PVA.The white emission of EHBPI3 in bulk solid state not only offers a new facile approach for achieving white emission in single-component polymer system,but also enriches the applications of functional epoxy.Results show that the terminal groups and backbone structures not only have strong influences on the fluorescent properties,but also provide more possibilities for the molecular design of hyperbranched molecules.