Flame-retardant epoxy resins (EPs) with superior optical, mechanical and dielectric properties are highly desired in high-tech industries. In this work, a multifunctional hyperbranched additive (BDHDP) was synthesized for EPs. Our results showed that BDHDP catalyzed the curing of epoxy resin because of its tertiary amine and hydroxyl groups. At a low addition level (<3.0 wt%), BDHDP increased the glass-transition temperature and maintained the optical transmittance of epoxy thermoset. Meanwhile, BDHDP improved the mechanical strength and toughness, and reduced the dielectric constant and loss of EP because of the rigid phosphaphenanthrene groups and intra-molecular cavities. Moreover, BDHDP reduced the heat release and smoke generation during the EP combustion. Adding 1.5 wt% of BDHDP led to a UL-94 V-0 rating, and reduced the total smoke production by 16.4%. Hence, this study offers an effective method to create transparent EP thermosets with outstanding mechanical, dielectric and fire-retardant properties via incorporating a P/N/B-containing hyperbranched oligomer. 

A hyperbranched P/N/B-containing oligomer as multifunctional flame retardant for epoxy resins

Green and Facile Synthesis of Bio-Based, Flame-Retardant, Latent Imidazole Curing Agent for Single-Component Epoxy Resin

The fabrication of fire-safe, robust yet tough polymeric materials represents a challenge for both academia and industry. In this work, a novel hyperbranched polymer (TP) based on trihydroxymethylphosphine oxide and phenylboronic acid for epoxy resin is described. The presence of 2 wt% TP afforded epoxy blend with a high limiting oxygen index of 33.2%, a UL-94 V-0 rating, 36.3% and 13.7% reductions in peak heat release rate and total smoke production, making it superior to previously described counterparts. The high efficiency of TP may be mainly attributed to its promotion of carbonization. Notably, an epoxy thermoset is strengthened and toughened due to the introduction of TP. The presence of 4 wt% of this additive increased the tensile strength, elongation at break, impact strength, and flexural strength by 54.0%, 32.8%, 32.0% and 36.9%, respectively. In addition, the high transparency of the epoxy thermoset is maintained in the presence of TP. Thus, this approach offers an integrated design for the preparation of transparent, fire-safe, strong but tough epoxy thermoset via the introduction of a hyperbranched polymer. It may be expected that this technique will find wide application in different industrial fields.

A novel hyperbranched phosphorus-boron polymer for transparent, flame-retardant, smoke-suppressive, robust yet tough epoxy resins

The aggregation and plasticizing of most 9,10-dihydro-9-oxa-10-phosphaphenanthrene −10-oxide (DOPO) derived additives often result in deteriorating the glass transition temperature and mechanical properties of epoxy resins (EP). To address this issue, an imide-DOPO derivative (BMP) with bulky aromatic structure was successfully synthesized. Benefitting from the space hindering and intermolecular interaction (π-π stacking) of BMP, it does not lead to the loss of glass transition temperature, and only a minor damage of tensile and impact strengths is caused. Additionally, with only 0.78 wt% loading of phosphorus (10 wt% BMP), the EP/BMP10% achieves UL-94 V-0 and high LOI value of 35%. Simultaneously, both the heat release rate and total smoke production are markedly reduced. More excitingly, BMP exhibits aggregation-induced emission enhancement of fluorescence in the N, N-dimethylformamide/water mixed solution as well as epoxy resin. This work provides a new insight in simultaneously imparting flame retardancy and fluorescence to epoxy resins without losing glass transition temperature. 

Zhongxiao Zhou

Papers

Flame-retardant, transparent, mechanically-strong and tough epoxy resin enabled by high-efficiency multifunctional boron-based polyphosphonamide