Kinetic and Mechanistic Studies of Carboxylic Acid–Bisoxazoline Chain‐Coupling Reactions

Abstract

Kinetic studies of the reactions between a model carboxylic acid and bisoxazoline coupling agents, namely 2,2′‐(1,3‐phenylene)bis(2‐oxazoline) (mbox), 2,2′‐(1,4‐phenylene)bis(2‐oxazoline) (pbox), and 2,2′‐(2,6‐pyridylene)bis(2‐oxazoline) (pybox), were carried out in bulk at 140–220 °C. A second‐order two‐step reaction mechanism was proposed and was verified by the experimental results. The results also indicate that the reactivity of the oxazoline groups is unchanged after the reaction of the other oxazoline group of the same coupling agent moiety, that is, oxazoline groups are equireactive. Rate constants and activation enthalpies and entropies were determined, allowing the comparison of bisoxazoline reactivity. The following reactivity order was found: pybox > mbox > pbox. The formation of a stabilized protonated complex is postulated to explain the much higher reaction rate observed with the new coupling agent pybox.Variation of the experimental concentrations of reactants and reaction products versus time.magnified imageVariation of the experimental concentrations of reactants and reaction products versus time.

Chain Extension of Carboxy‐Terminated Aliphatic Polyamides and Polyesters by Arylene and Pyridylene Bisoxazolines

“…Figure 4 for the case of the reaction of PA12-1 with the three bisoxazolines. At the beginning of reaction, the experimental data perfectly fit the theoretical curves obtained using the rate constant values determined for the model reactions carried out on dodecanoic acid at 200 8C [13] (mbox:…”

“…In a previous study, we have shown using model compounds that the carboxylic acid-oxazoline reactions are second order and that oxazoline groups are equireactive, i.e., oxazoline group reactivity does not change after other oxazoline groups of the same molecule has reacted. [13] Therefore, in the case of a stoichiometric reaction, the variations of carboxylic acid concentration, [COOH], versus time t should follow Equation (1),…”

“…It should be pointed out that no side reactions, such as those reported by Sano [14] and Böhme, [15] were detected in the 1 H NMR spectra of the final polymers. The same samples were also studied by 13 and the appearance of a new peak, C 1bL , at 177.12 ppm corresponding to the ester carbonyl. A signal, C 3Lb , at 169.19 ppm assigned to the amide carbonyl of reacted oxazoline moieties is also present.…”

“…Several chaincoupling or chain-extension reactions have been described, using coupling agents such as diisocyanates [1] or bisoxazolones, [2][3][4][5] in the case of hydroxy-or amine-terminated oligomers, and bisimidazolines, [5] bisoxazines [6] or bisoxazolines [6][7][8][9][10][11][12] in the case of carboxy-terminated oligomers. In a previous article, [13] we studied the kinetics of the bulk chain-coupling reaction of a model carboxylic acid with 2,2 0 -(1,3-phenylene)bis(2-oxazoline) (mbox), 2,2 0 -(1,4-phenylene)bis(2-oxazoline) (pbox), and 2,2 0 -(2,6-pyridylene)bis(2-oxazoline) (pybox). The kinetic studies showed that oxazoline groups are equireactive and that pybox is much more reactive than mbox and pbox.…”

Introduction of a New Coupling Agent for Selective Coupling of Hydroxy and Amino Group‐Containing Polymers

“…In the literature, numerous examples are given that describe the utilization of reactive bifunctional compounds as chain extenders and coupling agents, such as diisocyanates, [1][2][3] bisoxazolines, [4][5][6][7][8][9][10] bisepoxides, [11][12][13][14] bislactamates, [15][16][17] and bisoxazolones. [18,19] In the case of polymers that contain different reactive groups, a combination of coupling agents has been applied.…”