The Synthesis Of Monofunctional Polyhedral Oligomeric Silsesquioxane And The Preparation And Characterization Of POSS/Epoxy Composites

Polyhedral oligomeric silsesquioxane(POSS) has been widely researched during these years.The molecular consists of Si-O-Si framework with some organic groups around,so it is relatively easy to be designed.Some functional and reactive organic groups could be incorporated,and then it could be incorporated into polymer to prepare organic/inorganic hybrid materials.In this paper,through proper chemical methods,monofunctional-anhydride polyhedral oligomeric silsesquioxane(i-C₄H₉)₇Si₈O₁₂OSi(CH₃)₂(C₈H₉O₃) (AH-POSS) was synthesized with T₇(OH)₃ as raw material and was characterized by FTIR,NMR and element analysis.It was incorporated into epoxy system either pre-reacted or non-reacted using hexahydrophthalic anhydride(HHPA) as curing agent to obtain POSS-epoxy organic/inorganic hybrid materials. Pre-reacted POSS-epoxy hybrid materials were obtained by two-step preparation. First,AH-POSS reacted with diglycidyl ether of bisphenol A(DGEBA) to form AH-POSS-epoxy precursor in DGEBA,then cured with HHPA.Non-reacted POSS-epoxy hybrid materials were prepared by directly mixing AH-POSS, HHPA and DGEBA together and cured afterwards.Morphologies of hybrid materials were observed by SEM and TEM. Non-reacted system led to a dispersion of spherical particles with sizes in the range of micrometers.For pre-reacted system,polymerization-induce phase separation took place with POSS content lower than 30 wt%and some irregular clusters were formed.The magnifications of the irregular clusters were some "vesicle" structure after curing with a diameter of 20 nm.Some POSS aggregated and some epoxy chains were enwraped inside.A typical macro-phase separation happened with POSS content up to 40 wt%before and after curing.For non-reacted system,A typical macro-phase separation happened with POSS content only up to 5 wt%before and after curing. The glass transition temperatures(Tg's) and the storage modulus(E') were measured by dynamic mechanical analysis(DMTA).For pre-reacted system, Tg's and modulus displayed irregularly decreasing.However,the E' increased with AH-POSS content of 40 wt%.Non-reacted system led to a decreasing trend of Tg and E'.The changes of Tg and E' were closely effected by the morphologies and the structure of hybrid materials and also effected by several factors.The initial thermal decomposition temperatures(T_d's) characterized by thermogravimetry analysis(TGA).T_d's were decreasing with the AH-POSS content up to 30 wt%.T_d with 40 wt%AH-POSS content was closed to that of control epoxy.Non-reacted system led to a decreasing trend of T_d's with the increasing of AH-POSS content.However,T_d's were higher than those of epoxy composites when using amine as curing agent.