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Theses

Préparation et caractérisation de poly(phénylquinoxaline)s poreux

Samuel Merlet 1
1 LMOPS - Matériaux organiques à propriétés spécifiques
LEPMI - Laboratoire d'Electrochimie et de Physico-chimie des Matériaux et des Interfaces
Abstract : The aim of this thesis is to develop new high performance polymeric materials with closed submicron porosity. The adopted strategy is an original foaming process based on the in-situ gas generation from pendant thermolabile group decomposition.
A thermostable polymer matrix poly(phenylquinoxaline)s (PPQ) has been chosen, as well as the thermolabile group tertbutylcarbonate (Boc). A preliminary model study was performed to precisely define the adapted strategy. Grafting the Boc structure on phenol group was shown to be efficient and the thermal decomposition provides carbon dioxide and isobutene in a very clean and quantitative way, which should lead to a good control of the foaming process of the system PPQ + CO2/isobutene.
Different monomers bis(Α-diketone)s were synthesized and polymerized with a commercial bis(o-diamine), leading to PPQ with pendant phenol groups. Depending on the experimental conditions are prepared several structures having various phenol contents and specific repartitions depending on the monomer or "statistic"/"sequenced" architecture. The functionalisation of these phenol groups into Boc thermolabile groups could lead to a gas concentration from 150 to 654 mg/g and a repartition derived from the phenol ones.
Three key parameters enable a good control of the porous materials morphology. They are the gas concentration, the glass transition (Tg) of the polymer and the foaming temperature.
Using high foaming temperatures lead to macroporous PPQ foams (ultra and microcellular foams) whose morphologies are similar with ones obtained after a conventional CO2 foaming process. Parameters of this macroporosity can be controlled by playing on the gas concentration and the Tg of the polymer.
Moreover foaming of "sequenced" architecture (bloc copolymers) lead to the formation of ultra and microcellular foams with a double distribution of pores. This bimodal distribution is probably due to microscopic phase segregations.
All studied polymers associated with moderated foaming temperatures enable the formation of nanocellular foams with closed porosity. This results show that it is possible to form and stabilize nano-cells (8-40 nm) from a nucleation and growth mechanism in a polymer matrix. The production of such very small sizes and high cell densities requires a high nucleation rate (elevated gas concentration) and a limited growth of nucleated nano-cells (elevated system viscosity). Among the studied structures, the PPQ-OH foams show the best compromise between a high gas concentration (345 mg/g) and a high Tg (370 °C) and lead to very interesting nanocellular materials (taille: 8-11 nm – Nc: 4 1016 cells/cm3 – P: 14-16 %vol).
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Contributor : Samuel Merlet <>
Submitted on : Wednesday, December 13, 2006 - 2:24:21 PM
Last modification on : Thursday, November 19, 2020 - 1:50:07 PM

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Samuel Merlet. Préparation et caractérisation de poly(phénylquinoxaline)s poreux. Matériaux. Université de Savoie, 2006. Français. ⟨tel-00120147⟩

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