Solo Randriamahefa

Synthesis of new statistical and block co-polyesters by ROP of α,α,β-trisubstituted β-lactones and their characterizations

The preparation of α,α,β-trisubstituted β-lactones has opened the route to living anionic ring-opening polymerization of these monomers. Therefore, transfer reactions due to hydrogen abstraction were limited and it is now possible to strickly control sample molecular weight. Moreover, living end-groups lead to the preparation of block co-polymers with block controlled lenghts. In the same way, high-molecular-weight statistical co-polymers have been synthesized. Hydrolyzable micelles and nanoparticles will be prepared from these co-polymers after chemical modifications to adjust the hydrophilic/hydrophobic balance.

Some aspects of the orientational order distribution of flexible chains in a diblock mesophase

The segmental motions of flexible chains in the lamellar structure of a strongly segregated poly(styrene)-poly(dimethylsiloxane) (PS-PDMS) diblock were investigated over a time scale of a few tens of microseconds. (2)H NMR experiments were performed on the PDMS block, selectively perdeuterated. Transverse relaxation measurements show that the main part of the PDMS repeat units display anisotropic reorientational motions within the diblock lamellae and such a segmental ordering essentially results from interchain steric repulsions. (2)H double quantum-based experiments evidenced a non-uniform local stretching of PDMS chains and enabled the underlying distribution of the orientational order parameter to be determined quantitatively. Besides, a fraction of the PDMS chain segments, about 14%, were found to display isotropic - or nearly isotropic - reorientations, which could be assigned to repeat units located within a thin sublayer (about 1-2 nm) at the lamellae midplane, but also deeper in the lamellae, close to folded parts of the chains. These experimental results were confronted to theoretical descriptions of opposing polymer brushes and, in particular, to the strong-stretching theory (SST) including the entropic contribution of free chain ends.

Polystereoisomers of 2-butyl and 3,3-dimethyl-2-butyl malic acid esters: configurational structures/properties relationship

New poly(β-malic acid alkyl esters) with two stereogenic centers have been synthesized by anionic ring-opening polymerization of racemic and optically active 2-butyl and 3,3-dimethyl-2-butyl malolactonates. The configurational structure of these racemic and optically active polyesters has been determined by 13C NMR analysis. Comparison between polydiastereisomers structures has been possible by using this spectroscopic method. Several main-chain and side-chain carbon atoms were stereosensitive, and polystereoisomers composition has been deduced from 13C NMR spectra. Thermal properties of the different polystereoisomers have been correlated with the configuration of both chiral sites in the macromolecular chains. It has been shown, crystallinity rate was dependent on main-chain configurational structure. The lateral stereogenic center is important to increase the organization of macromolecular chains in crystallites and therefore their regularity. Moreover, the presence of the 3,3-dimethyl-2-butyl group led to a semi-crystalline racemic polymer, that confirms the particular behaviour of this bulky group in a macromolecular architecture. Comparison has been done with poly(benzyl 3-alkylmalates) containing two stereogenic centers in the main-chain.

Natural and Artificial Functionalized Biopolyesters. II. Medium-Chain Length Polyhydroxyoctanoates from Pseudomonas Strains

Sixteen Pseudomonas strains have been tested with a view to developing medium-chain length polyhydroxyalkanoates. Four strains were selected and it is shown that their ability for producing three different polyesters with variable properties was dependent on the strains and substrates. Otherwise, Pseudomonas oleovorans was grown on a mixture of sodium octanoate and undecenoate salts at a 90/10 mol/mol ratio. The corresponding copolymer, bearing lateral double bonds, was chemically modified in the carboxy group. Finally, the ability to tailor-make functional bacterial polyesters aimed at temporary therapeutic applications is demonstrated.