Phosphorus flame retardants from isosorbide bis-acrylate

Abstract

The increasing concern about the potential negative health effects of traditional organohalogen flame retardants have placed these compounds under increasing regulatory pressure around the world. There is a growing need to develop new, nontoxic, biocompatible or biodegradable flame retardant agents. Phosphorus compounds derived from renewable biosources offer great potential to meet this need. Isosorbide is a dihydroxy ether available from starch. It may be readily converted to the corresponding bis-acrylate ester. This compound undergoes Michael addition of phosphites to provide a number of phosphorus compounds which display good flame retardancy in DGEBA epoxy.

Introduction

The utilization of phosphorus flame retardants as replacements for certain types of organobromine compounds which are coming under increasing regulatory pressure worldwide is gaining attention [[1], [2], [3], [4]]. In particular, organophosphorus compounds generated from renewable biosources are attractive as flame retardants [[5], [6], [7], [8]]. Their manufacture is independent of fluctuations in the petroleum market. They tend to be less toxic than their organohalogen counterparts and often are biodegradable to innocuous products in the environment [9,10]. In addition, “green” additives are viewed positively by the consuming public. Many biobased phosphorus flame retardants are phosphonates or phosphates. These are suitable for many applications. However, they may lack sufficient thermal stability to be useful in polymeric materials that undergo degradation at relatively high temperature. For these materials, a compound in which the phosphorus moiety is incorporated via a P-C bond may be more suitable than those containing a P-O-C linkage [11].

There are various methods for introducing a phosphorus-containing group into an organic substrate. One involves P-H addition to unsaturation [[12], [13], [14], [15], [16], [17]]. This may be accomplished in a variety of ways often involving a basic catalyst. A particularly effective approach is Michael addition to an α,β-unsaturated carbonyl compound [[14], [15], [16], [17]]. In this case this technique has been used to generate a family of phosphorus compounds which display good flame-retarding properties in epoxy resin. First isosorbide, a glucose product, was converted to the bis-acrylate. Michael addition of various phosphites to the unsaturated ester produced a series of compounds with flame-retarding properties.