Fabrication And Investigation Of Sulfonated Aromatic Polymers Containing POSS In The Chain For Proton Exchange Membranes

Polyhedral oligomeric silsesquioxane(POSS) has attracted considerable interest because of the unique organic/inorganic hybrid structure. The eight organic substituents could be designed as reactive or unreactive, which allows a synthetic“bottom-up” fabrication of many different high performance nano-materials for improving the bulk properties such as increased thermal stability, mechanical properties and oxidative resistance. The POSS hybrid materials are also potential candidates as proton exchange membranes(PEMs) in proton exchange membrane fuel cell(PEMFC) applications. The POSS particles dispersed in a polymer matrix can produce a nanoscale organic-inorganic interface which influences the hydrophilic channels for proton exchange. Although these works could improve the comprehensive properties of membranes for PEMFC application, the polymer fabricated by direct blending of POSS with high content always leads to poor dispersion of POSS, which affects the lower proton conductivity and mechanical strength due to the high surface area and surface energy of POSS. Convalently incorporating POSS into the polymer chain could efficiently improve the properities of sulfonated polymers as PEMs. Firstly, the more stable convalent bond between functional POSS and polymer could made the POSS stably dispersed in a polymer film and improve the long-term stability of the material; Secondly, the introduction of POSS in the polymer could improve the thermal stability, and promote the sulfonated polymer backbone and POSS to form an ordered organic-inorganic micro-phase separation structure. Moreover, the POSS of large free volume(1-3 nm)can improve the nano-phase separated hydrophilic and hydrophobic of the material,which can promote the formation of ion channels, improve proton conductivity,reduce the swelling ratio and methanol permeability, enhance the hydrolysis resistance and mechanical properties. Thirdly, the chemical and physical propertiesof proton exchange membrane could be directly adjust by changing the content of POSS monomers in the PEM preparation process, and the method is more simple and easy to use. In this study, a series of sulfonated aromatic polymer with different content of POSS in the chain were synthesized and characterized. The morphologies,thermal and mechanical properties, chemical resistance, proton conductivity and methanol permeability of the hybrid membranes were investigated. The specific work are shown below:1. A series of linear sulfonated polyimides containing POSS in the main chain were successfully synthesized and characterized. Compared with other POSS hybrid membranes fabricated by direct blending or cross-linking methods, the ultrafine POSS aggregates showed more uniform distribution and the obtained SPI-POSS co-polymers exhibited dramatically enhanced comprehensive properties as proton exchange membranes. The results revealed that the POSS in the SPI main chain facilitates the dispersion of POSS as a nano-filler and increases the confined bound water molecules within the formation of continuous proton transformation channel.2. A series of novel comb-like poly(arylene ether sulfone) with multi-sulfonated polyhedral oligosilsesquioxane(sPOSS) pendants(PAES-sPOSS-x) were synthesized.The large free volume of sPOSS improved the nano-phase hydrophilic and hydrophobic separation of the material, which greatly enhanced the proton conductivity while ensuring good heat resistance and chemical stability.3. To address the problems of the comb polymer containing the sulfonic acid group in the side chain leading to the increased swelling ratio, a series of cross-linked sulfonated poly(ether ether ketone)s containing multi-sulfonated polyhedral oligosilsesquioxane(sPOSS) in the side chain were successfully synthesized by introducing the sodium 4-hydroxybenzenesulfonate and eight epoxy POSS into poly(ether ether ketone)s containing hydroxyl group in the main chain. The crosslinked structure and sulfonated POSS side chain were introduced to poly(ether ether ketone)s by one-step strategy. Moreover, directly introducing the sulfonic acid groups into the polymer by the hydroxyl group dissolved the problems of polymer in traditional sulfonation progress, such as degradation and unsure sulfonation degree control. The results showed that the obtained material not only had a high proton conductivity, but also exhibited low swelling ratio, excellent strength performance and low methanol permeability.