From synthesis to 3D printing: a journey into stereochemistry and its impact on polymer networks

Khalfa, Anissa L. (2024). From synthesis to 3D printing: a journey into stereochemistry and its impact on polymer networks. University of Birmingham. Ph.D.

Preview

Khalfa2024PhD.pdf
Text - Accepted Version
Available under License All rights reserved.
Download (24MB) | Preview

Abstract

Photo-active polymeric materials are valuable to a myriad of industries from paints and inks to binders in rocket propellers and even in healthcare and 3D printing. Changing the thermomechanical properties relies mostly on changing the functionality of monomer units, which limits the choice of possible candidate owing to restriction resulting from a need for biocompatibility or printability. For this reason, it is of high relevance to manipulate the mechanical properties without a change in the chemical functionality. An emerging technique in the field of thermoplastic polymers is now devoted to tuning the mechanical properties via the rational control of the backbone stereochemistry. More specifically, the thiol-ene step growth addition between a dithiol and a diacrylate proved to be a valuable advance for the implementation of cis/trans chemistry for high molecular weight thermoplastic. In addition to be mild enough to preclude the occurrence of unwanted crosslinking or isomerisation, the technique revealed itself to be versatile since the diacrylates are prepared from stereopure diols, enabling the preparation of cis or trans unsaturated or the isohexides ring-based units. In this thesis manuscript, efforts made towards the translation of this unique system to photo-active polymeric materials using 2 kinds of stereopure diacrylate monomers, namely cis and trans 1,4-but-2-ene diol and isohexides will be described. In parallel, the synthesis of a glucose-derived diacrylate and dithiol will be explored in the aim at synthesising a synthetic polysaccharide via nucleophile catalysed thiol-Michael addition. The first chapter will present the state of the art and impact of stereochemistry in polymers. The second chapter will present the synthesis and further functionalisation of the stereopure diols selected for this study with a commercially available isocyanate-acrylate and also the synthesis of a glucose derived dithiol. Chapter three will discuss the work made towards controlling the molecular weight and end groups of diacrylate telechelic oligomers via Michael step-growth polymerisation of the commercially available 1,6-hexanedithiol and the cis/trans unsaturated and isohexides-based diacrylate monomer. In addition, the attempt at producing a high molecular weight polysaccharide mimic using the same polymerisation technique will be presented. Finally, the fourth chapter will focus on the formulation of cis and trans unsaturated prepolymers into photo-active resins to produce films suitable for thermomechanical testing. It was found that for low curing time (< 1 min) the radical initiated crosslinking only occurred at the acrylate end groups and isomerisation of the internal double bonds was mitigated. Furthermore, for films prepared from prepolymers with low molecular weight (4.0 kDa) a significant difference in the thermomechanical properties between cis and trans films was observed as a consequence of the different degree of crystallinity between the two materials. However, at higher molecular weights (8-10 kDa), the cis polymer gains progressive crystallinity and its thermomechanical behaviour becomes comparable to the trans polymer network. Finally, the prepolymers were formulated into resins suitable for 3D printing which displayed both thermomechanical and degradation properties dependent on the backbone stereochemistry.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):