Flexible Epoxy Resins Formed by Blending with the Diblock Copolymer PEO-<i>b</i>-PCL and Using a Hydrogen-Bonding Benzoxazine as the Curing Agent

• Main Authors: Wei-Chen Su, Fang-Chang Tsai, Chih-Feng Huang, Lizong Dai, Shiao-Wei Kuo
• Format: Article
• Language: English
• Published: MDPI AG 2019-01-01
• Series: Polymers
• Subjects: hydrogen bonding; epoxy; benzoxazine; block copolymer; toughness
• Online Access: https://www.mdpi.com/2073-4360/11/2/201
• ISSN: 2073-4360

In this study, we enhanced the toughness of epoxy resin by blending it with the diblock copolymer poly(ethylene oxide&#8315;<i>b</i>&#8315;&#949;-caprolactone) (PEO-<i>b</i>-PCL) with a benzoxazine monomer (PA-OH) as the thermal curing agent. After thermal curing, Fourier transform infrared spectroscopy revealed that intermolecular hydrogen bonding existed between the OH units of the epoxy&#8315;benzoxazine copolymer and the C&#8315;O&#8315;C (C=O) units of the PEO (PCL) segment. Differential scanning calorimetry and dynamic mechanical analysis revealed that the glass transition temperature and storage modulus of the epoxy&#8315;benzoxazine matrix decreased significantly upon increasing the concentration of PEO-<i>b</i>-PCL. The Kwei equation predicted a positive value of <i>q</i>, consistent with intermolecular hydrogen bonding in this epoxy&#8315;benzoxazine/PEO-<i>b</i>-PCL blend system. Scanning electron microscopy revealed a wormlike structure with a high aspect ratio for PEO-<i>b</i>-PCL as the dispersed phase in the epoxy&#8315;benzoxazine matrix; this structure was responsible for the improved toughness.