Bio-based epoxy functionalized MQ silicone resins: from synthesis to toughened epoxy composites with good mechanical properties, thermal resistance and transparency

Abstract

Conventional epoxy thermosets lack toughness, and conventional methods to toughen them are at the cost of decreasing other properties of the materials, such as the mechanical modulus, strength and transparency. Herein, hydrogenated MQ silicone resins (H–MQ) of various M/Q ratios, where M and Q denote R₃SiO_1/2 and SiO_4/2, respectively, are synthesized from co-hydrolytic condensation of siloxane precursors. Then, these H–MQ resins are bonded with two epoxy monomers, bio-based eugenol glycidyl ether (EG) and allyl glycidyl ether (AG), through hydrosilylation to afford EG–MQ and AG–MQ, respectively, with tailored organic segments and M/Q ratios. The obtained epoxy-functionalized MQ silicone resins will have increased compatibility with the epoxy matrix. Compared with neat DGEBA thermosets, the addition of 20% EG-1.2MQ (M/Q ratio = 1.2 : 1) leads to marked increases in impact, tensile, and flexural strengths by 90%, 3%, and 3%, respectively, as well as increases in tensile and flexural strains by 55% and 100%. The epoxidized organic segments are found to be critical for enhancing the mechanical properties of the obtained epoxy composites. The EG–MQ/epoxy composites show better mechanical properties than AG–MQ/epoxy systems due to the improved compatibility of EG–MQ with DGEBA due to the aromatic EG moieties attached. Furthermore, the thermal stability and residual yield are increased by adding these silicone resins, with an increased water contact angle from 80 to as high as 110°. Our contribution provides a new avenue for integrating such good properties as impact toughness, mechanical properties, thermal stability and water repellance into the obtained epoxy thermosetting materials, without compromising the transparency.