Synthesis And Properties Of Functionalized Oligomeric Silsesquioxanes And Their Application In Hybrid Materials

Organic-inorganic hybrid materials represent a new class of materials with scientific and technological potential.Polyhedral Oligomeric Silsesquioxanes(POSS)are considered as well-defined nanosized molecules and can be used as inorganic building blocks incorporated into polymeric materials.Unlike traditional nano-fillers,POSS possess a silsesquioxane cage cental core surrounded by an organic periphery,which enables the ease of design at molecular level and makes POSS compatible with polymers.The incorporation of POSS endows polymer systems with unique chemical and physical properties and thus attracted widening interests to researchers.This thesis centered on three projects:(1)optimizing the synthetic routes for a large-scale preparation of some functionalized POSS,and synthesizing new functional POSS;(2)studying the structure-property relationship of POSS;(3)developing new POSS-based polymer nanocomposite;(4)exploring new POSS-based hybrids.The main contents are as follows:(1)A series of functional POSS with different functionalities were prepared via direct hydrolysis method,corner-capping method or conversion of side groups.The synthetic routes of some existing POSS and monomers were optimized,and four types of epoxy-containing POSS with novel structures were synthesized.(2)The structure-property relationship of bi-,tetra-and octa-functionalized POSS were studied.The melting,crystallization and thermal degradation behavior were investigated.(3)Four new types of POSS-containing epoxy nanocomposites were prepared and investigated in-depth.The curing kinetic analysis of these polymer systems with the M(?)lek method ascertained that the SB(m,n)model was able to well simulate the reaction rates.Using the advanced iso-conversional method(AICM),the relationship between effective activation energy and fractional conversion during curing was studied,revealing the complex reaction mechanisms.The Vyazovkin method was used to predict the curing systems in wider temperature and time ranges beyond the experimental observation scale,providing guidance for the storage,operation and curing cycle of precuring systems.The morphology and composition study of the cured composites showed that POSS could achieve a molecular-level uniform dispersion in the epoxy resin matrix.Performance evaluation demonstrated that the incorporation of POSS significantly improved the water resistance,thermal stability and impact resistance of epoxy resin.(4)A novel layered double hydroxide modified by octa-substituted carboxy-terminated POSS was prepared via a one-step method.Results showed that this new kind of hybrid was characterized with excellent thermal stability and low flammability.(5)Epoxy nanocomposites with different loading of POSS-LDH hybrid were prepared via a multi-step blending method.The influence of POSS-LDH addition on the curing kinetics and mechanism of epoxy resin were studied.The microstructure,morphology and performance of the cured resins were also investigated.Results showed that POSS-LDHs were highly exfoliated and uniformly dispersed in the epoxy matrix,with particle sizes ranging from 20 to 150 nm.These nanocomposites showed potential in flame retardancy and impact resistance.