Publication

Synthesis of Functional Polyesters via Baylis-Hillman Polymerization

Sanhao Ji
2011
Thèse EPFL
Résumé

Aliphatic polyesters receive increasing attention over the last years driven by their application as biodegradable substitutes for conventional commodity thermoplastics and applications in the biomedical field, where amongst the family of biodegradable polymers, aliphatic polyesters possess the leading position as a consequence of the ready metabolization of the degradation products in most cases. This has led to a wide spread use of polyester homo- and copolymers in drug delivery, surgical implants, and functional materials in tissue engineering. In general, polyesters have a high level of commercial importance, and a variety of well known processing technologies are available. To tune the properties of these materials, e.g. their degradation behavior and to add further functionality, there is significant interest in synthetic strategies which can be used to prepare side-chain functionalized polyesters with variable architectures. This Thesis explores the feasibility of a novel approach towards functional polyesters that is based on the Baylis-Hillman reaction, which involves the base catalyzed condensation of an aldehyde and an acrylate building block to produce an α-methylene-β-hydroxycarbonyl compound. As the Baylis-Hillman polymerization does not require the use of side chain protected monomers, this route may represent an interesting alternative strategy for the preparation of functional polyesters. An attractive feature of the Baylis-Hillman polymerization is that it generate polymer with reactive hydroxyl and vinyl groups, which can be used in a subsequent step for post-modification or prepare functional crosslinked scaffolds. This Thesis consists of four chapters. The different synthetic strategies that have been used for the preparation of multi-functional polyesters and the Baylis-Hillman reaction are reviewed in Chapter 1. Chapter 2 investigates the feasibility of the Baylis-Hillman polymerization of diacrylates and dialdehydes to prepare side-chain functional polyesters and explores the subsequent post-polymerization modification of these polymers to further enhance their functionality. Using 1,3-butanediol acrylate and 2,6-pyridinecarboxaldehyde as monomers and DABCO as catalyst, polymers with a degree of polymerization of up to 25 were prepared. These polymers are attractive as they contain chemically orthogonal side-chain hydroxyl and vinyl groups that can be further modified. In first experiments, it was demonstrated that the side-chain hydroxyl and vinyl groups can be quantitatively post-modified with phenyl isocyanate, respectively, methyl-3-mercaptopropionate. Chapter 3 explores the feasibility of the Baylis-Hillman reaction for the synthesis of hyperbranched polyesters. This Chapter describes an efficient and novel approach to functional hyperbranched polyesters via an A2 + B3 approach based on the Baylis-Hillman reaction. Using trimethylolpropane triacrylate and 2,6-pyridinedicarboxaldehyde as monomers and 3-quinuclidinol as the catalyst, polymer swith a degree of branching between 0.36 and 0.8, and a molecular weight of up to 28,100 were prepared. The effects of monomer ratio and addition mode on the final molecular weight, polydispersity index and degree of branching were studied. In order to demonstrate the potential of this polyester as a reactive polymer, the hydroxyl, vinyl groups and pyridine residues were post-modified with phenyl isocyanate, methyl-3-mercaptopropionate and methyl iodide. Chapter 4 aims to further explore the scope and versatility of the Baylis-Hillman polymerization and studies the preparation of side-chain functional polyesters by polymerization of 1,3-butanediol diacrylate with meta- and para-phthalaldehyde, which are two commercially available dialdehyde building blocks.

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Concepts associés (41)
Polyester
vignette|Fibres de polyester observées au MEB Un polyester est un polymère dont les motifs de répétition de la chaîne principale contiennent la fonction ester. La méthode de synthèse la plus simple et la plus courante est appelée polycondensation par estérification. Il s'agit de la réaction d'un diacide carboxylique ou de l'un de ses dérivés comme le dianhydride d'acide avec un diol, donnant l'ester et un autre composé (eau, acide carboxylique).
Polymérisation
vignette|Le latex de ce ballon de baudruche est synthétisé par polymérisation. vignette|Structure du UHMWPE, un haut polymère avec n supérieur à . La polymérisation désigne la réaction chimique ou le procédé par lesquels des petites molécules (par exemple des hydrocarbures de deux à dix atomes de carbone) réagissent entre elles pour former des molécules de masses molaires plus élevées. Les molécules initiales peuvent être des monomères ou des pré-polymères ; la synthèse conduit à des polymères.
Polymère
vignette|Fibres de polyester observées au Microscopie électronique à balayage. vignette|La fabrication d'une éolienne fait intervenir le moulage de composites résines/renforts. Les polymères (étymologie : du grec polus, plusieurs, et meros, partie) constituent une classe de matériaux. D'un point de vue chimique, un polymère est une substance composée de macromolécules et issue de molécules de faible masse moléculaire. Un polymère est caractérisé par le degré de polymérisation.
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