# Interpenetrating Polymer Network Based on Polyether-Polyester Polyurethane and Epoxy Resin

## TL;DR

This paper presents a new toughened epoxy composite using interpenetrating polymer networks that improve mechanical and adhesive properties for engineering applications.

## Contribution

A novel soft-segment design strategy using polyether-polyester polyurethane and epoxy resin to enhance epoxy toughness and performance.

## Key findings

- At 15 wt% PU prepolymer, IPNs achieved balanced mechanical properties with 59.90 MPa tensile strength and 69.99 MPa compressive strength.
- Adding polyester polyol improved tensile and compressive strengths by 11.4% and 6.07%, respectively.
- The PS-2412/PPG-1000 blend increased dry and wet bond strengths by 12.1% and 36.3%.

## Abstract

Epoxy resins often require toughening to broaden their engineering applications, such as in durable concrete repair. This study addresses this need by developing high-performance polyurethane/epoxy (PU/EP) interpenetrating polymer networks (IPNs). The composites were synthesized via prepolymer and stepwise methods using polyether polyol (PPG-1000), isocyanate (MDI-50), and E51 epoxy. At an optimal PU prepolymer content of 15 wt%, the polyether-based IPNs achieved a balanced mechanical profile (tensile strength: 59.90 MPa; elongation at break: 6.46%; compressive strength: 69.99 MPa). Further tuning of the soft segment by introducing polyester polyol (PS-2412) yielded superior performance at a PS-2412/PPG-1000 ratio of 30/70. This formulation increased tensile and compressive strengths by 11.4% and 6.07% (to 66.74 MPa and 74.24 MPa), and dry and wet bond strengths by 12.1% and 36.3% (to 5.68 MPa and 4.62 MPa), respectively. The enhancement is attributed to the increased crosslinking density and more uniform network structure imparted by PS-2412, which improves stress distribution and interfacial adhesion. This work provides an effective soft-segment design strategy for fabricating toughened epoxy composites with robust mechanical and adhesive properties.