Recyclable Organocatalyzed Poly(Thiourethane) Covalent Adaptable Networks.

Angels Serra,Sara Muñoz,Xavier Ramis,Francesco Gamardella,Silvia De La Flor

doi:10.3390/polym12122913

Angels Serra, Sara Muñoz + Show 3 more

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https://doi.org/10.3390/polym12122913

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Abstract

A new type of tetraphenylborate salts derived from highly basic and nucleophilic amines, namely 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) and triazabicyclodecene (TBD), was applied to the preparation of networked poly(thiourethane)s (PTUs), which showed a vitrimer-like behavior, with higher stress-relaxation rates than PTUs prepared by using dibutyl thin dilaurate (DBTDL) as the catalyst. The use of these salts, which release the amines when heated, instead of the pure amines, allows the formulation to be easily manipulated to prepare any type of samples. The materials prepared from stoichiometric mixtures of hexamethylene diisocyanate (HDI), trithiol (S3) and with a 10% of molar excess of isocyanate or thiol were characterized by FTIR, thermomechanical analysis, thermogravimetry, stress-relaxation tests and tensile tests, thus obtaining a complete thermal and mechanical characterization of the materials. The recycled materials obtained by grinding the original PTUs and hot-pressing the small pieces in the optimized time and temperature conditions were fully characterized by mechanical, thermomechanical and FTIR studies. This allowed us to confirm their recyclability, without appreciable changes in the network structure and performance. From several observations, the dissociative interchange trans-thiocarbamoylation mechanism was evidenced as the main responsible of the topological rearrangements at high temperature, resulting in a vitrimeric-like behavior.

Highlights

Thermosetting polymers, thanks to their permanent covalent bonds in the network structure, show outstanding mechanical and thermal properties
In a previous paper [19], we investigated the advantages of using a thermally triggered base generator (1-methylimidazolium tetraphenylborate, BGMI), an organocatalyst, which liberates the corresponding amine at a defined temperature, allowing a good temporary control of the thiol-isocyanate reaction
The relaxation rate of the PTUs prepared with the abovementioned catalysts is faster than the one prepared with dibutyltin dilaurate (DBTDL)

Summary

Introduction

Thermosetting polymers, thanks to their permanent covalent bonds in the network structure, show outstanding mechanical and thermal properties. Their permanent three-dimensional structure hindered this material to be melted or dissolved in any solvents, making it impossible to reprocess and recycle them. The development of covalent adaptable networks (CANs), covalently crosslinked polymers with the ability to be reshaped, to flow and to self-repair, represents a promising approach to improve the lifetime and recyclability of the thermosetting polymers [1,2,3,4]. Networked poly(thiourethane)s (PTUs) have been reported as a new class of CANs thanks to the presence of thiourethane groups that can undergo exchange reactions at moderate temperatures [5,6,7,8]. PTUs are formed by the very efficient coupling reaction between thiols and Polymers 2020, 12, 2913; doi:10.3390/polym12122913 www.mdpi.com/journal/polymers

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