Preparation And Characterization Of Multi-hydroxyl POSS And Polymer/POSS Hybrid Fibers

Polyhedral Oligomeric Silsesquioxane (POSS) is a nanohybrid molecule with eight organic groups radiating from one cubic Si-O-Si inorganic core. Peripheral groups facilitate its compatibility with numerous polymers, while rigid inner framework can effectively improve composites’mechanical and thermal properties. Developing novel functional POSS monomers and POSS-based polymer hybrid materials is of great research and application significance.In this thesis, a novel multi-hydroxyl POSS was synthesized through facile thiol-ene click reaction. This POSS derivative was introduced into polymer (PMMA, PVA) matrix via solution mixing and sequentially the blends were electrospun into hybrid fibers. The influences of POSS on the structure, morphology and properties of electrospun polymer fibers were well investigated. This thesis achieved some results as follows:1. Multi-hydroxyl POSS (POSS-OH16) was successfully synthesized via thiol-ene click reaction between octavinyl POSS (OVPOSS) and1-thioglycerol (TG) in the presence of2,2’-azobisisobutyronitrile (AIBN) as initiator. When the thiol/alkene molar ratio was2.5, AIBN amount was1mol%and the reactant was refluxed in dry tetrahydrofuran (THF) for6hours, the yield of desired product could reach88～93%after the crude was precipitated in diethyl ether for several times. The structure as well as the high purity of POSS-OH16was confirmed by FTIR, NMR, MALDI-Tof MS, Elemental Analysis, etc. TGA results indicated that the thermal stability of POSS-OH16was improved.2. Poly(vinyl alcohol)(PVA)/POSS-OH16hybrid fiber mats were fabricated via the combination of solution mixing and static electrospinning technique. XRD revealed that when POSS-OH16content was low, the crystalline structures of POSS-OH16disappeared in the corresponding hybrid fibers which indicated POSS-OH16homogeneously dispersed in the PVA matrix via hydrogen bonding. When POSS-OH16content was as high as50wt%, the responsible peaks for POSS-OH16became stronger because of the crystallization and aggregation of POSS-OH16molecules in the PVA matrix. SEM showed that when the total concentration of blends was kept at8%(w/v), the number of beads-on-string structures increased with POSS-OH16content; but when PVA concentration was kept at8%(w/v), bead-free fibers could be observed even with a POSS-OH16content as high as PVA content. Both the average diameter and surface roughness of electrospun fibers increased with POSS-OH16content. The addition of POSS-OH16also enhanc the hydrophobicity of PVA fiber mats. For instance,37.5wt%of POSS-OH16could increase the water contact angle of electrospun PVA fiber mats from57°to95°. DSC showed that when POSS-OH16content was low, the glass-transition temperature (Tg) of the PVA/POSS-OH16hybrid fibers increased with POSS-OH16content.33.33wt%of POSS-OH16could increase Tg of PVA fiber mats from72.6℃to114.3℃.3. Three kinds of hybrid fibers-PMMA/POSS-OH16, PMMA/OVPOSS and PMMA/Methacrylisobutyl POSS (MIPOSS)-were prepared by solution mixing-electrospinning technique. When POSS-OH16content was low, POSS-OH16dispersed well in the PMMA matrix and no POSS-OH16crystals were observed. The crystalline structures always existed in the PMMA/OVPOSS and PMMA/MIPOSS hybrid fibers even when the content of OVPOSS or MIPOSS was low. PMMA/POSS-OH16electrospun fibers were observed as smooth fibers without any observable bead structures. OVPOSS was likely to show regular cubic crystals with dimensions ranging from100-200nm on the surface of PMMA beads or fibers. MIPOSS hybrid fibers showed no obvious phase separation but a rougher surface than POSS-OH16hybrid fibers. Comparing the structures and morphologies of these three kinds of fibers, it can be known that POSS-OH16has better compatibility with PMMA matrix. Moreover, the addition of POSS-OH16could obviously improve the thermal stability of PMMA hybrid fibers while it was not the case for OVPOSS.