Enhancement of Epoxy Thermosets with Hyperbranched and Multiarm Star Polymers: A Review

Hyperbranched polymers and multiarm star polymers are a type of dendritic polymers which have attracted substantial interest during the last 30 years because of their unique properties. They can be used to modify epoxy thermosets to increase their toughness and flexibility but without adversely affecting other properties such as reactivity or thermal properties. In addition, the final properties of materials can be tailored by modifying the structure, molecular weight, or type of functional end-groups of the hyperbranched and multiarm star polymers. In this review, we focus on the modification of epoxy-based thermosets with hyperbranched and multiarm star polymers in terms of the effect on the curing process of epoxy formulations, thermal, mechanical, and rheological properties, and their advantages in fire retardancy on the final thermosets.

Simultaneous reinforcement and toughness improvement of an epoxy–phenolic network with a hyperbranched polysiloxane modifier

An epoxy–phenolic network is modified with hyperbranched polysiloxane (HBPSi). The addition of HBPSi-2, which has medium molecular weight, can significantly decrease the viscosity of the uncured epoxy–phenolic system and increase the crosslinking density and homogeneity of the cured crosslinking network. With 10% HBPSi-2, the mechanical properties of the samples are improved comprehensively: tensile modulus and maximum strength increase by 11.4% and 36.2%, respectively, while elongation at break and impact strength increase by 153.8% and 186.7%, respectively. The comprehensive improvements in the mechanical properties are attributed to combined effects of crosslinking density, network rigidity, cohesive density and the matrix-modifier compatibility. What is more, HBPSi-2 also significantly increases the char yield of the material and decreases the thermal weight loss rate, indicating an improved thermal stability. All these results may provide a new strategy for toughness and strength improvement of the epoxy–phenolic network.

An epoxy–phenolic network is modified with hyperbranched polysiloxane (HBPSi).

Improved epoxy thermosets by the use of poly(ethyleneimine) derivatives

Epoxy resins are commonly used as thermosetting materials due to their excellent mechanical properties, high adhesion to many substrates and good heat and chemical resistances. This type of thermosets is intensively used in a wide range of fields, where they act as fiber-reinforced materials, general-purpose adhesives, high-performance coatings and encapsulating materials. These materials are formed by the chemical reaction of multifunctional epoxy monomers forming a polymer network produced through an irreversible way. In this article the improvement of the characteristics of epoxy thermosets using different hyperbranched poly(ethyleneimine) (PEI) derivatives will be explained.

Transparent luminescent hyperbranched epoxy/carbon oxide dot nanocomposites with outstanding toughness and ductility

A luminescent transparent hyperbranched epoxy nanocomposite with previously unachieved outstanding toughness and elasticity has been created by incorporation of a very small amount of carbon oxide nanodots. The nanocomposites of the hyperbranched epoxy with carbon oxide dots at different dose levels (0.1, 0.5, and 1.0 wt %) have been prepared by an ex situ solution technique followed by curing with poly(amido-amine) at 100 °C. Different characterizations and evaluations of mechanical and optical properties of the nanocomposites have been performed. The toughness (area under the stress-strain curve) of the pristine system has been improved dramatically by 750% with only 0.5 wt % carbon oxide dots. The tensile strength has been enhanced from 38 to 46 MPa, whereas the elongation at break improved noticeably from 15 to 45%. Excellent adhesive strength combined with transparency and photoluminescent behavior renders these materials highly interesting as functional films in optical devices like light-emitting diodes and UV light detection systems as well as in anticounterfeiting applications.