Study On Preparation, Structure And Properties Of Poly(Trifluoropropylmethyl)Siloxanes-B-Polyurethane (Urea) Elastomers

Based on the study on synthesis ofα,ω-bis(3-aminopropyldiethoxylsilane) poly(trifluoropropylmethyl)siloxanes (APFS), several series of poly(trifluoropropylmethyl)siloxane-b-polyurethane (urea) (PUFS)/(FS-b-PUU or PUUFS) copolymer elastomers were prepared by reacting between polyurethane materials of changed reactant ratios, and then chain-extending with the obtained APFS of well defined molecular weights. The elastomeric films were formed in TEFLON pans through moisture curing, and then characterized by FTIR, DSC, DMTA, TEM or SEM, TGA, mechanical testing and water contact angle. Moreover, the crosslink density of the films was obtained by swelling experiments.The APFSs of different molecular weights were synthesized by the ring-opening polymerization of 1,3,5-tris(trifluoropropylmethyl)cyclotrisiloxane (F3) in the presence of water and 3-aminopropyltriethoxysilane (APTES) via a one-step process. A reaction mechanism was investigated using 1H NMR and GPC, the results indicated that both the amino group and water catalyzed the polymerization of F3, and the APTESs capped the polymer chains.A series of PUFS elastomeric films with PFS soft segment of different contents were prepared via a two-step process: A prepolymer was made from poly(tetramethylene oxide) (PTMO) and toluenediisocyanate (TDI), and then chain-extended with APFS. The results indicated that the properties of PUFS films were related to their extents of microphase separation and the crosslink structure including both chemical bonds and hydrogen bondings. As the amount of PFS increased in PUFS films, the extent of microphase separation was enhanced, hence the mechanical properties decreased. On the other hand, the increasing crosslink structure caused by the elevated TDI contents could improve the mechanical properties of the films. In a word, the good mechanical properties, for PUFS elastomers with higher contents of PFS, can be achieved by elevating the TDI contents.Two series of FS-b-PUU elastomers were prepared via a three-step process: A prepolymer was made from PTMO and TDI, and then chain-extended with APFS, subsequently, with 3,3'-dicholoride-4,4'-diamino-diphenylmethylene (MOCA).The first series of low modulus FS-b-PUU elastomers consisted of PFS soft segment of different contents and the other segments of unchanged content. It was found that the mechanical properties of FS-b-PUU elastomers were significantly influenced by the content of APFS. The elastomers with the APFS of 15 wt % showed the tensile strength of 9.22 MPa, whereas the elastomers with 22-27 wt % displayed the poor tensile strength of 2.3 MPa. Interestingly, the materials with the 35-45 wt % of APFS exhibited better tensile strengths, and for the elastomer with 45 wt % of APFS, its tensile strength reached 15.2 MPa. The material with APFS of 15 wt % showed the proper extent of phase separation, but the material with 22-27 wt % of APFS showed the increased extent of phase separation. However, the material showed the lower extent of phase separation when the contents of APFS were elevated to 35-45 wt %. It would be conjectured that the high content of APFS dispersing in the material played a role in increasing the cohesive force for different phases. In addition, IR results showed that the elastomers with the APFS of 15 wt % showed the stronger hydrogen bonding.The second series of high tensile PUUFS elastomers consisted of PTMO and APFS of unchanged molar content as well as MOCA and TDI of different contents, all elastomers contained about 30 wt % of PFS. It was found that the mechanical properties of elastomers increased firstly, then decreased with the increasing concentration of hard segments. When the content ratio between hard segments and soft segments (CHS/CSS) reached 3.01, the material owned optimal extent of phase separation leading to the best mechanical properties. The extent of phase separation of materials will increase when the value of CHS/CSS was lower or higher than 3.01, so the mechanical properties of materials will decrease. The primary influencing factor for the mechanical properties of materials was the extent of phase separation, though the crosslink density and the extent of hydrogen bonding increased with the increased concentration of hard segments. The thermal stability somewhat decreased as the increased content of hard segments. The migration of PFS at high temperature became difficult as the hard segments increased because of the increased crosslink density and hydrogen bonding caused by high contents of hard segments.A novel PFS-b-PU copolymer elastomer was synthesized through the copolymerization of diisocyanated PTMO polyurethane with the synthesized PFS polyurethane diol. The analysis results indicated that the crosslink density of elastomers will increase with the increased content of APFS because the APFS with a low molecular weight contained silicon alkoxy groups producing the crosslink structure. Therefore, the materials with higher contents of APFS displayed better mechanical properties. Although TDI increased the concentration of amino groups and hydrogen bonding, the small amount of TDI affected a little for the mechanical properties of materials. Moreover, DSC results indicated that the equivalent reactant ratio gave rise to the complete chain-extending, and the highest molecular weight and tensile strength of the copolymer was present. The migration of PFS became difficult as the crosslink density increased. In addition, the thermal stability of materials increased as the concentration of APFS increased.The results showed that the crosslink density, the extent of phase separation and hydrogen bonding were the primary influencing factors for the properties of FS-b-PUU copolymers. The optimal properties for the copolymers could be achieved by changing the reactant ratio and polymerization process.In addition, the poly(vinylidene fluoride)s (PVDF) were synthesized in the supercritical carbon dioxide (sc-CO2). The sc-CO2 polymerization influenced morphology, molecular weights, polydispersities and H-H defect concentrations of the obtained PVDFs. During polymerization, the great pressure and good solubility of sc-CO2 improved the crystalline complete degree, crystallinity, and affect crystalline phases of PVDFs, which showed a unique effect of sc-CO2 polymerization on PVDF's crystallization. The sc-CO2 polymerization promises well for obtaining the PVDF with better physical properties and application.