Hydrogenation of High Molecular Weight Bisphenol A Type Epoxy Resin BE503 in a Functional and Greener Solvent Mixture Using a Rh Catalyst Supported on Carbon Black.

Bo-Xin Lai,Ping-Chieh Wang,Yi-Hao Huang,An-Bang Duh,Saurav Bhattacharjee,Chung-Sung Tan

doi:10.3390/polym12112513

Abstract

A functional greener solvent mixture containing water, isopropyl alcohol (IPA) and ethyl acetate with the ratio 10:20:70 (wt%) was found to accelerate hydrogenation of bisphenol A type epoxy resin BE503 with a molecular weight of 1500 through an on-water mechanism, and led to an increased H2 availability, due to high solubility of H2 in IPA. Different carbon-based supports were tested and VulcanXC72 was found as the best support among the tested carbon-based ones as it possessed the highest amount of electron deficient promoter, RhOx. The catalyst, Rh5/VulcanXC72-polyol, synthesized by the microwave assisted polyol method, yielded a 100% hydrogenation of aromatic rings with an epoxy ring opening below 20.0% at 50 °C and a H2 pressure of 1000 psi in 2.25 h. Intrinsic activation energies for the hydrogenation of aromatic rings and epoxy ring opening were experimentally estimated and a mechanism for the hydrogenation of BE503 was proposed, wherein the hydrogenation of aromatic rings and epoxy ring opening in BE503 proceeded simultaneously in parallel and in-series with parallel being the major pathway.

Highlights

With the light emitting diode (LED) industry reported to have a current value of USD 15 billion and explosive growth predicted, research on light emitting diode (LED) packaging materials that can withstand yellowing at temperatures higher than 200 ◦ C are in great demand
The results showed that, though the bimetallic Rh-Pt catalyst exhibited higher catalytic activity than the monometallic Rh catalyst for the hydrogenation of aromatic rings in BE186, due to enhanced hydrogen (H2 ) spillover on the surface of Rh-Pt alloys, a higher epoxy loss was observed owing to the cleavage of C-O bond by Pt and Rh/VulcanXC72-polyol was preferred
A greener solvent mixture of if wt% H2O, 20 wt% isopropyl alcohol (IPA) and 70 wt% ethyl acetate (EA) denoted as Solvent 8 was most effective for the hydrogenation of BE186 and BE503 using Rh5/VulcanXC72-polyol through on-water mechanism and higher solubilities of Bisphenol A type epoxy resins (BPAERs) and H2 because of the presence of IPA in the liquid mixture

Summary

Introduction

With the light emitting diode (LED) industry reported to have a current value of USD 15 billion and explosive growth predicted, research on light emitting diode (LED) packaging materials that can withstand yellowing at temperatures higher than 200 ◦ C are in great demand. Three proposed variants of BPAERs for a reduction in yellowing include the use of polysiloxane resins [1], BPAERs doped with UV-resistant additives and hydrogenated BPAERs (HBPAERs) [2,3,4]. While synthesizing silicone-based epoxy resins is complicated and involves expensive starting materials, BPAERs doped with UV-resistant additives are still susceptible to Polymers 2020, 12, 2513; doi:10.3390/polym12112513 www.mdpi.com/journal/polymers. HBPAERs with easier synthesis and comparatively higher resistance to yellowing due to complete hydrogenation of aromatic rings are being investigated with the purpose of being LED packaging materials [4]. The cost of HBPAERs is about 100 USD/kg, 30–50 times that of BPAERs. the epoxy rings in BPAERs are highly reactive during hydrogenation of aromatic rings, leading to severe epoxy loss by C-O bond cleavage that needs to be avoided [5]. Preserving epoxy rings in HBPAERs is imperative as subsequent hardening of HBPAERs takes place by cross-linking of epoxy rings with hardeners

Methods

Results

Conclusion