In this study we describe the synthesis of bis(pyrrolidone) based dicarboxylic acids from itaconic acid and their application in 2-oxazoline resins for fully renewable thermoset materials. The monomers are obtained using a bulk aza-Michael addition of a diamine and two itaconic acid molecules using a catalytic amount of water. The monomers can be isolated in high purity after recrystallization, though their yield proved to be highly dependent on the selected diamine spacer length: In general, only the dicarboxylic acids containing diamines with an even number of methylene spacers are isolated in high yields. Through NMR, GPC, and FTIR analysis we demonstrate that these bis(pyrrolidone) based dicarboxylic acids exhibit significantly enhanced curing rates in 2-oxazoline resins compared to resins containing aliphatic dicarboxylic acids such as sebacic acid. Overall, we demonstrate that the rate of 2-oxazoline ring-opening addition with carboxylic acid functionalities is determined by the used dicarboxylic acid, whereas the ring-opening addition of the 2-oxazoline functionality with amide groups is determined by the used bis(2-oxazoline) compound. The thermosets obtained after curing proved to be readily plasticized by water, opening up possibilities for enzymatic degradation.

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.

This paper reports, for the first time, semi-crystalline polymers based on bis-pyrrolidone dicarboxylic acids (BPDA) obtained from the aza-Michael reaction between renewable itaconic acid and various diamines.

A kinetic analysis on the aluminum salen-catalyzed ring-opening polymerization (ROP) of (macro)­lactones is presented, which focuses on how chain transfer agents and the steric hindrance at the α-methylene groups of both the growing chain and the (macro)­lactones affect the polymerization rate. It is shown that for branched macrolactones the choice of initiator does not only influence the initiation rate but surprisingly also the apparent rate of polymerization. The increased polymerization rate, when an unbranched initiator was used, was ascribed to transesterification reactions taking place at the polymer chain end, which effectively results in an unprecedented chain growth at the other end of the polymer chain compared to normal ROP. Furthermore, application of a kinetic model including initiation, propagation, and transesterification led to the ability to accurately quantify the effect of steric hindrance for various alkoxide initiators by determining individual rate constants for initiation. It appeared that secondary alcohols not only have a lower reactivity but also are less likely to be bonded to the metal center than primary alcohols when an excess of the two types of alcohols (i.e., chain transfer agents) is used. For the strained seven-membered lactone it was shown that branching mainly has a retarding effect when present at the metal-bonded alkoxide and not on the monomer, which was ascribed to the cisoid conformation of the ester group of the monomer. On the other hand, the transoid conformation of the ester group in macrolactones resulted in a similar decrease in reactivity for branching on the metal-bonded alkoxide and the monomer. Next to this, it was shown that an excess of alcohol chain transfer agent had a retarding effect on the reaction, which was ascribed to coordination of the alcohol to the metal center.

In this work, we report on the small scale polycondensation and consecutive analysis of novel polyesters based on the potentially renewable 1,3-cyclopentanediol (CPdiol).