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Abstract Hyperbranched epoxy resins (HERs) is a group of thermoset resins which can be used to improve specifically the toughness and strength of popular diglycidyl ether of bisphenol-A (DGEBA). However, a relationship between the epoxy equivalent weight (EEW) of HERs and the level of property improvement has not been established due to the difficulty to control their EEW. Here we report the synthesis of a series of hyperbranched epoxy resins with different EEW (EHBP-n) through thiol-ene click reaction between thiol-ended hyperbranched polyesters and allylglycidyl ether. The rheological properties of the uncured EHBP-n/DGEBA blends are determined by viscosity and modulus changes, and are directly affected by the EEW of EHBP-n. Moreover, the EEW of EHBP-n also can tune the glass transition temperature and mechanical performances of the cured EHBP-n/DGEBA composites, and these properties first increased and then decreased with a decrease in the EEW of EHBP-n. At 9 wt % of EHBP-6, the improvements on the tensile, flexural, impact and adhesive strengths are 38.9%, 35.3%, 158.6% and 96.2%, respectively, compared with those of cured DGEBA. This result will give a basic guidance for obtaining epoxy resins with various performance. Graphical abstract Image 1 Highlights • Hyperbranched epoxy resins with a controlled epoxy equivalent weight (EHBP-n) were synthesized. • The rheological properties of the uncured EHBP-n/DGEBA blends were also researched. • EHBP-n has an positive effect on mechanical strength on DGEBA. • The paper will give a basic guidance for obtaining epoxy resins with various performance. [ABSTRACT FROM AUTHOR]

ABSTRACT Epoxy-ended hyperbranched polymers (EHPs) have a wide range of applications due to their outstanding performances. Because their microstructures are not positively identified, it is very difficult to ascertain the reinforcing and toughening mechanisms of EHPs and their interface interaction with other matrixes. Controllable synthesis of EHPs with precise degree of branching (DB) remains to be a major challenge. Here, a method for preparing novel nitrogen-phosphor skeleton epoxy-ended hyperbranched polymers (NPEHP) with controllable DB by a thiol-ene Michael addition between thiol-ended hyperbranched polymers (NPHSH) and glycidyl methacrylate have been firstly reported. NPHSH is synthesized by an esterification between hydroxyl-ended hyperbranched polymers (NPHOH) and 3-mercaptopropionic acid. NPHOH is prepared by a thiol-ene Michael addition between methacrylate group of a monomer and thiol group of linear monomer (AB) and/or branched monomer (AB2). The molar ratio between the AB and AB2 monomers controls the DB of the products. The 1H NMR spectra analysis of NPHOH shows that their experimentally determined DBs are very close to their theoretical values, indicating good controllability of their DBs. The narrow molecular weight distributions of NPHOH, NPHSH, and NPEHP suggest high efficiency of the thiol-ene Michael addition. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44277. [ABSTRACT FROM AUTHOR]

• Thiol-epoxy click reaction was used as an energy-saving and high-efficient crosslinking approach. • THBP-n were used to crosslink diglycidyl ether of bisphenol-A (DGEBA) by a thiol-epoxy click reaction. • THBP-n could improve the crosslinking efficiency of DGEBA about 5 times. • THBP-n could increase several times of mechanical strength of DGEBA. • The reinforcement mechanism was attributable to the minimization of internal molecular free volume. Simultaneous improvement on mechanical performance, thermal stability and crosslinking efficiency of epoxy resins is a large challenge. Here, we have synthesized a series of thiol-ended hyperbranched polymers (THBP-n) as curing agents to crosslink bisphenol-A epoxy resins by a thiol-epoxy click reaction. Compared with the common amine curing agent, the THBP-n could improve the crosslinking efficiency of DGEBA about 5 times. Increasing the thiol group number n from 3 to 6, 9 in THBP-n, the tensile strength, flexual strength, impact toughness of cured THBP-n/DGEBA materials increased simultaneously and sharply several times, besides their thermal degradation and glass transition temperatures raised to some extent. This improvement could be attributable to the synergetic effect about the minimization of internal molecular free volume, hyperbranched structure, and high-crosslinking density, substantiated by integrating techniques of dynamic light scattering, dynamic mechanical analysis, positron annihilation lifetime spectroscopy and SEM, and the novel mechanism was proposed. The thiol-epoxy click reaction will supply an energy-saving route for high-efficient crosslinking of thermosetting epoxy resins with excellent comprehensive performance. [ABSTRACT FROM AUTHOR]

• A thiol-ene click reaction was used to functionalize CNTs by thiol-ended hyperbranched polymers. • Thiol-functionalized CNTs showed well dispersion in epoxy resins. • Functionalized CNTs could increase conductivity and mechanical strength of epoxy resins. • The flexible and ellipsoidal hyperbranched polymers could deform and transfer the load. • A reinforcing mechanism was supposed and substantiated by SEM, TEM, XPS and Raman techniques. Carbon nanotubes (CNTs) have been considered as the attractively multifunctional nanomaterials for high conductivity and high strength, but it is still a challenge to prepare CNTs with high dispersion and their nanocomposites with simultaneous high strength and longation. Here, we used thiol-ended hyperbranched polymers to functionalize CNTs and obtain thiol-functionalized CNTs with excellent dispersion and good compatibility with epoxy resins matrix. The grafted thiol-ended hyperbranched polymers can supply a bridging function between epoxy resins and the CNTs to promote their interaction. The thermal conductivity, elongation, tensile, flexural and impact strengthes of thiol-functionalized CNTs/epoxy nanocomposites could be improved simultaneously by 23.33%, 37.46%, 60.74%, 26.72% and 86.71%, respectively. A reinforcing mechanism was supposed and substantiated by combining SEM, TEM, XPS and Raman techniques. The flexible and ellipsoidal hyperbranched polymers chains grafted on CNTs deform and transfer the load to increase mechanical strength and elongation. An efficient and environmentally-friendly route is introduced to functionalize CNTs and fabricate simultaneous high strength and high elongation CNTs/epoxy nanocomposites. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have attracted increasingly interest in preparing CNTs/epoxy nanocomposites for improving thermal and mechanical properties. The well distribution of prime CNTs in epoxy matrix is still a challenge due to the strong interaction among nanotubes and property of self-aggregation. Here, we report a highly efficient approach to functionalize prime CNTs by a thiol-ene click reaction between double bonds of CNTs and thiol groups of mercaptans, and the resulted in thiol-functionalized CNTs with different chemical chains show well dispersion in ethyl acetate and epoxy. The thiol-functionalized CNTs show a positive effect on reinforcing and toughening diglycidyl ether of bisphenol-A (DGEBA). With an increase in the thiol-functionalized CNTs content, the mechanical and thermal properties of the CNTs/DGEBA nanocomposites, including tensile, flexural and impact strengths, and thermal conductivity, increase first and then decrease. The maximum improvements on the tensile, flexural, impact strengths and thermal conductive were 43.75%, 25.11%, 196.44% and 33.81%, respectively. These grafted mercaptans chains play a bridging action between CNTs and epoxy matrix to supply a strong interaction, substantiated by their good rheological property and ductile SEM micrographs. Both the simple method of thiol-functionalized CNTs and preparation of CNTs/DGEBA nanocomposites will supply dependable data for wide application of CNTs. • A highly efficient thiol-ene click reaction was used to functionalize prime CNTs. • Thiol-functionalized CNTs showed well dispersion in ethyl acetate and epoxy. • Thiol-functionalized CNTs could reinforce and toughen diglycidyl ether of bisphenol-A. • A strong interaction between CNTs and epoxy matrix was substantiated by rheological property and SEM. [ABSTRACT FROM AUTHOR]