Preparation And Characterization Of Shape Memory And Self-healing Materials Containing POSS

Shape memory polymers have received enormous interest in the past decades due to their low density,ease of processing,biocompatibility and tailorable performance through extensive molecular design.However,synthetic polymers,derived from organic substances,generally suffer from some defects like poor thermal stability,aging and low strength,while the inchorporation of POSS into the polymer matrix on the nanometer scale will endow polymers with the advantages of inorganic materials to improve the thermal properties and mechanical properties and overcome some of its disadvantages.However,there always exists chemical crosslinking in the POSS reinforced shape memory materials,resulting in the poor processibility.Therefore,it is of great significance to introduce POSS with the ability of forming microphase separating structure into the polymer matrix.On the one hand,POSS improves the thermal and mechanical properties of the polymer;on the other hand it forms a physical cross-linking network,imparting shape memory properties to the material while enabling the material to be reprocessed and recycled.In this thesis,POSS-containing polymer materials with different structures were synthesized by ring-opening polymerization,click reaction,ring-opening metathesis polymerization,reversible addition-fragmentation chain transfer polymerization etc.The situations of POSS as the end group or in the backbone of poly(?-caprolactone)were inestigated and further extended to another polybutylacrylate matrix with POSS termini.Their microstructure,phase transition behavior,shape memory behavior and self-healing behavior were discussed.The main research contents are as follows:(1)A Design of Star-Like Shape Memory Networks of Poly(?-caprolactone)s via POSS-POSS Interactions and Its PerformanceA series of PCL stars were synthesized by the polymerization of?-caprolactone initiated by pentaerythritol.After alkyne grouping of PCL,a click reaction with 3-azidopropyl heptaphenyl POSS was carried out to obtain the organic-inorganic POSS-capped PCL satrs.Studies had shown that the POSS-terminated organic-inorganic PCL stars exhibited a microphase-separated structure,and the POSS cage at the end of the PCL chain were demixed into spherical microdomains of 10-20 nm in diameter through POSS-POSS interaction.At the same time,the introduction of POSS reduced the crystallinity of the PCL segment,which improved the crystallization restriction of PCL by POSS.Shape memory cycle tests showed the excellent shape memory properties of this material,and its shape memory performance was derived from the physical cross-linking network formed by POSS-POSS interaction.(2)A Design of Brush-Like Shape Memory Networks of Poly(?-caprolactone)s via POSS-POSS Interactions and Its PerformanceOxygenated norbornene terminated POSS and PCL were first synthesized respectively,followed by the ROMP reaction to afford a series of POSS-containing graft polymers P(ONBPCL-r-ONBPOSS).The results of thermal analysis showed that the thermal stability increased with the increaseing of POSS content,and the introduction of POSS had a significant effect on the crystallization behavior of the polymer.Studies had also shown that the internal POSS-POSS interaction formed nano-domains.It was this physical cross-linking network that provided POSS-containing P(ONBPCL-r-ONBPOSS)samples with elastomeric characteristics above the melting point of the polymer and excellent shape memory performance.(3)Preparation and Characterization of POSS-termi nated Telechelic Polymer with Shape Memory and Self-healing PropertyFirst,a POSS-capped macromolecular chain transfer agent was synthesized to initiate the random copolymerization of n-butyl acrylate(BA)and the monomer with quadruple hydrogen bonding(UPy).Under the condition of controlling the POSS content,a series of telechelic polymer POSS-PBAUPy with different UPy content were obtained.Studies had shown that the POSS-terminated telechelic polymer POSS-PBAUPy exhibited a microphase-separated structure,and POSS cages at the end of the molecular chain were assembled into spherical microdomains with a diameter of 10-20 nm by POSS-POSS interaction.The average distance of the spherical microdomains was 8.78 nm.The microdomains formed by the POSS-POSS interaction and the UPy hydrogen bonding formed a physical cross-linking network inside the polymer,giving the material shape memory properties.At the same time,the supramolecular role of the quadruple hydrogen bonding in UPy also endowed the material with self-healing properties.