Junheng Zhang

The effect of molecular weight of hyperbranched epoxy resins with a silicone skeleton on performance

Hyperbranched epoxy resins with a silicone skeleton (HERSS) obtained by us through an environmentally-friendly synthetic method have shown a prominent comprehensive performance in modifying the diglycidyl ether of bisphenol-A (DGEBA). However, controlling the performance of the HERSS is still a challenge. In this paper, we report the preparation of three other kinds of HERSS with various molecular weights via hydrosilylation, in order to study the effect of the molecular weights of the HERSS on the degree of branching (DB), the viscosity and the mechanical performance, the thermal properties and the micro-phase separation behavior of cured HERSS–DGEBA composites, which contain the HERSS prepared recently. The degree of branching and viscosities of the HERSS are 0.71–0.84 and 103.5–697.4 mPa s, respectively. An increase in the molecular weight of the HERSS results in a decrease in the DB and an appearance of a maximum viscosity. Accordingly, the mechanical properties of the cured HERSS–DGEBA composites, including the tensile, flexural and impact strength, increase first and then decrease, and their glass transition temperatures decrease weakly. Both the average diameters of 3.62–4.75 μm and the distribution of the islands in the “sea–island” structure of all the cured composites show an increase. Compared with those of DGEBA, the tensile, flexural and impact strength could be increased by about 76.4–88.6%, 25.3–36.0% and 78.4–92.1%, respectively, but their glass transition temperature was impaired only by about 6.3–6.8%.

Environment-friendly synthesis and performance of a novel hyperbranched epoxy resin with a silicone skeleton

Hyperbranched epoxy resins have attracted increasing attention for their excellent comprehensive performance in toughening and reinforcing the diglycidyl ether of bisphenol-A (DGEBA). However, the tedious synthetic procedure, high cost, and the use of large amounts of organic solvents have hampered their industrial application. This paper presents an environment-friendly method to synthesize a novel hyperbranched epoxy resin with a silicone skeleton (HERSS) through a hydrosilylation reaction catalyzed by a heterogeneous halloysite-supported platinum catalyst. The reaction involves only one solvent and affords a high yield (>90%). The chemical structure, molecular weight, and degree of branching of the HERSS were characterized by FT-IR, GPC and NMR. The resulting HERSS was used to modify a DGEBA based epoxy resin and showed excellent performance. With the incorporation of 9 wt% HERSS, the impact, flexural and tensile strength of DGEBA are increased by about 92.5%, 36.0% and 88.6%, respectively. The toughening and reinforcing mechanism was attributed to the “sea-island” structure of the cure composite, as shown by the SEM micrographs of the fractured surfaces. An initial thermal decomposition temperature of about 380.0 °C of the cured HERSS/methyl nadic anhydride resin also indicates promising applications with regard to high-temperature-resistance.

Surface Hybrid Self-Assembly, Mechanism, and Crystalline Behavior of a Carboxyl-Ended Hyperbranched Polyester/Platinum Complex

The self-assembly of hyperbranched polymers has attracted much attention because of their wide application. In this article, we report a new facile surface self-assembly method for a carboxyl-ended hyperbranched polyester/platinum complex (HTD-3-Pt) and obtain ordered structural microrods with a length of 10-20 μm and a width of 1 μm. The length and diameter of the self-assembled microrods could be increased to 300-600 μm and 4-5 μm, respectively, by hierarchical self-assembly. The main factors affecting the morphology of the self-assemblies, including temperature, time, solvent and solubility parameter, and relative humidity were discussed by transmission/reflection polarizing optical microscopy (TRPOM), SEM, and HRSEM. The indications for the coordination bond (-COOPt) included the appearance of a new peak at 1606 cm(-1) and its shifting to 1634 cm(-1) in the FT-IR spectra, the disappearance of the C 1s peak at about 288.6 eV, and the increase in the O 1s electron binding energy in the XPS spectra. Furthermore, an interesting crystal property of the HTD-3-Pt self-assemblies was discovered and confirmed by XRD. The study results from the surface self-assembly mechanism suggest that the coordination induction of the platinum ion play a key role in driving microphase separation between the intermolecular chains and end groups of the HTD-3-Pt to form the microrod self-assemblies. Another interesting finding was that HTD-3-Pt showed a higher catalytic activity for hydrosilylation than did a traditional homogeneous catalyst.

2D Self-assembly of an amido-ended hyperbranched polyester induced by platinum ion coordination effect

Compared with amphiphilic hyperbranched polymers (HBPs), the self-assembly of hydrophilic HBPs remains a challenging area. In this article, we report the self-assembly of an amido-ended, hydrophilic hyperbranched polyester (HTDA-2), by taking advantage of the induction effect of the platinum ion. Self-assembled HTDA-2-Pt polymers are composed of ordered 2D tree-like structures with a diameter of about 500 μm and a trunk-width of approx. 1–2 μm, as shown by transmission/reflection polarizing optical microscopy (TRPOM), scanning electron microscopy (SEM) and dynamic light scattering (DLS). Factors such as temperature, time, solvent, concentration and humidity which influence the morphology of the self-assemblies were investigated using XPS, XRD, SEM, and FT-IR techniques. It is proposed that the coordination between the platinum and oxygen atoms in the amido groups together with hydrogen bonding may induce individual aggregation of core chains and peripheral chains, resulting in micro-phase separation and formation of micelles. These micelles then aggregate and self-assemble into perfect tree-like structures on the surface of a glass substrate in a limited region. The dimension (Df) of about 1.59 for the fractal tree-like morphology suggests perfect fractal behavior of the self-assemblies. Another interesting finding is the appearance of crystal behavior of the tree-like self-assemblies as revealed by XRD analysis.

Influence of vinyl-terminated hyperbranched polyester on performance of films obtained by UV-initiated thiol–ene click reaction of A 2 + B 3 system

UV curing technology has become an efficient method to fabricate films with desirable properties, although it is susceptible to oxygen inhibition, resulting in low conversion of double bonds and poor mechanical performance. Thiol–ene click reaction can overcome the shortcomings of common UV curing techniques. In this paper, the vinyl-terminated hyperbranched polyester (VTDP) was incorporated into the curing system of di-ene (A2) and trithiol (B3). Trithiols, including 1,3,5-tris(2-hydroxyethyl)isocyanurate tris(3-mercaptopropionate) (THMP) and trimethylolpropane tris(3-mercaptopropionate) (TMMP), were synthesized by an esterification between 3-mercaptopropionic acid and 1,3,5-tris(2-hydroxyethyl) isocyanurate, and tri(hydroxymethyl)propane, respectively. The UV-initiated thiol–ene click reaction between 1,4-butanediol diacrylate (BDDA) and trithiols (TMMP and THMP) was researched by adjusting different VTDP content. FTIR spectral analysis showed that the thiol–ene reactions proceeded smoothly and the conversion degree of acrylic groups was higher than that of thiol groups. The pencil hardness and abrasion resistance of the cured film increased first and then decreased with the increase in VTDP content, but both their flexibility and adhesion had little change. Their glass transition temperatures increased slightly with the increase in VTDP content. THMP has better positive effect than TMMP on the pencil hardness, abrasion resistance and thermal performance of the cured film.