Cascade aza-Michael Addition-Cyclizations; Toward Renewable and Multifunctional Carboxylic Acids for Melt-Polycondensation.

Geert J Noordzij,Carolus H R M Wilsens

doi:10.3389/fchem.2019.00729

Geert J Noordzij, Carolus H R M Wilsens

Open Access

https://doi.org/10.3389/fchem.2019.00729

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Journal: Frontiers in chemistry	Publication Date: Nov 14, 2019
Citations: 31	License type: CC BY 4.0

Affiliation: Maastricht University

Abstract

Although the aza-Michael addition reaction on various unsaturated (di-)carboxylic acids and esters of, for example, itaconic acid, is well-known, the consecutive cyclization reaction has not received much attention in literature. The products of this aza-Michael cascade reaction, being mono- or di-carboxylic acid or ester functionalized N-alkyl-pyrrolidone structures, prove interesting for melt-polycondensation reactions as they exhibit excellent stability at elevated temperatures. In other words, this reaction is a toolbox for the generation of renewable monomers and, in turn, polymers with tunable physiological properties. Therefore, this work provides an overview of the state-of-the-art of the cascade aza-Michael addition-cyclization reactions on biobased unsaturated acids and esters, and their use in polymerization reactions. Furthermore, we extend this overview with the cascade aza-Michael addition-cyclization reaction of trans-trimethyl aconitate with di-amines to form a tetra-functional N-alkyl-bis-(pyrrolidone dimethylcarboxylate), which exhibits excellent thermal stability and could effectively be used as monomer in polycondensation reactions. Importantly, the aza-Michael addition reaction between primary amines and trans-trimethyl aconitate can be considered a click-reaction; it proceeds quantitatively within minutes under ambient conditions and follows the principles of green chemistry.

Highlights

Polymeric materials are increasinglyevaluated in academia, industry, and society as they are reportedly causing pollution and negatively impact the environment (Mülhaupt, 2013)
In contrast to aconitic acid itself, the isolated para-xylylene-bis-(pyrrolidone methyldicarboxylate) (p-XyBPTA, Scheme 11) exhibits excellent thermal stability which allowed for its use as cross-linker in melt-polycondensation reactions of amorphous BPDA-based polyesters reported in our recent work (Noordzij et al, 2019)
Though the GPC traces reflect only the soluble fraction of the synthesized polymers, they clearly indicate a broadening of dispersity by the increase in high molecular weight fractions (Figure 2, bottom), as is typical for branched and crosslinked polymers. These findings demonstrate that the aza-Michael cascade reaction can readily be employed to generate multi-functional methylcarboxylates with the thermal stability required for melt-polycondensation reactions

Summary

Introduction

Polymeric materials are increasingly (re-)evaluated in academia, industry, and society as they are reportedly causing pollution and negatively impact the environment (Mülhaupt, 2013). In this work we provide an overview of the current research activities on renewable unsaturated acids and esters for monomer synthesis via both the aza-Michael addition and the cascade cyclization reaction, and elaborate on their use in melt-polycondensation reactions. SCHEME 3 | Schematic overview of the cascade reaction of the aza-Michael addition of ammonia or a primary amine to an unsaturated monomer with an ester in the γ-position (left).

Results

Conclusion