Controlled synthesis and toughening mechanisms of an all-purpose hyperbranched modifier, which can form non-phase-separated networks with simultaneous enhancements inT_g, modulus, impact and tensile strengths.

The strong fluorescence, in both the solution and the bulk state, of a chromophore-free aliphatic hyperbranched polyether which does not contain N and P atoms was reported for the first time. Effects of concentration and solvent solubility were measured. Its ethanol solution shows a strong blue-green fluorescence (Y_u = 0.11–0.39), and its fluorescence shows a strong selective quenching with respect to Fe³⁺.

The synthesis of epoxide-terminated hyperbranched polyethers (EHBPEs) with different backbone stiffness and molecular weight (MW) is obtained using simple one-pot A₂ + B₃ approach. When used as tougheners for DGEBA/TETA system, non-phase-separated cured networks are always obtained. Effects of MW and backbone stiffness on the toughening performance were systematically investigated. Among the EHBPEs studied, EHBPE-4C which has the lowest MW and stiffest backbone and EHBPE-10C which has the highest MW and most flexible backbone can simultaneously improve toughness, tensile strength, and T_g. In contrast, addition of EHBPE-6C and EHBPE-8C, which have medium MW and backbone stiffness, lead to incomplete cure and cannot improve or worsen the toughness and tensile strength. Both stiffness and MW of hyperbranched polyether play important roles in determining the crosslink density and structure of non-phase-separated networks, which dictate the toughness, strength and T_g of toughened epoxy.

A new AB₂ monomer 4-hydroxyl-4′,4′′-difluorotriphenylmethane was successfully synthesized via a Friedel–Crafts alkylation of phenol from 4,4′-difluorodiphenylmethanol. Based on the AB₂ monomer, novel fluoro-terminated hyperbranched poly(phenylene oxide)s (FHPPOs) were synthesized via the S_NAr reaction by self-condensation in one step. The FHPPOs were characterized by various techniques, including NMR, FT-IR, GPC, TGA and DSC. It was found that the molecular weight and polydispersity index of the FHPPOs increased with monomer concentration and reaction time. The degree of branching of the FHPPOs, determined by ¹³C NMR and ¹⁹F NMR with the aid of model compounds, decreased from 0.63 to 0.53 as the molecular weight increased. The glass transition temperature (T_g) of the FHPPOs increased with increasing molecular weight, up to 164 °C when the M_n was over 6, 800. The FHPPOs showed excellent thermal stability up to a T_d5 temperature of 559 °C. Because of the low polarity of the poly(phenyl oxide) (PPO) backbones, abundant fluoro-terminated groups, which have large molar free volume, low polarizability of C–F bonds, and inherent free volume or molecule-scale cavities in hyperbranched structures, the addition of FHPPO into diglycidyl ether of bisphenol A (DGEBA) could effectively lower the relative dielectric constant, the dissipation factor, and moisture absorption of the cured DGEBA/FHPPO composites. The free volume of the composites, which was quantified by positron annihilation lifetime spectroscopy (PALS), increased with increased FHPPO loading. The excellent dielectric and thermal properties make FHPPO a promising low-k modifier for epoxy resins.