Polymorphs Of Hindered Phenol And Preparation Of Polymer/Hindered Phenol Damping Hybrid

Hindered phenol compounds have widely industrial application as antioxidants for polymers. Recently, it was found that a new type of multi-functional hybrid with high damping performance, self-repairing and shape-memory properties could be prepared by blending polar polymer and hindered phenol compound. Although various kinds of polar polymer/hindered phenol compound damping hybrids (abbr. hindered phenol hybrid) with great damping performance have been developed, their damping mechanism is not very clear and there exist some key defects, e.g. weak thermal stability, in the practical application. Therefore, now it is not the time to extensively industrialize and generalize them. This study is aimed at clarifying the damping mechanism of hindered phenol hybrids and at solving some applied problems.In this thesis, first of all, damping and polymorphous properties of amorphous hindered phenol were investigated. In comparison with damping properties and molecular structure of hindered amine and petroleum resin, the mechanism of high damping performance for small molecular compounds was also proposed. Secondly, we paid particular attention to the morphology and crystalline structure of hindered phenol crystals. Thirdly, hydrogenated nitrile butadiene rubber (HNBR)/AO-80 damping hybrids were prepared by mechanical mixing and co-solvent methods, respectively. Also, the miscibility and damping properties of hybrids prepared by the two methods were systematically investigated and compared. Based on the systematical analysis of the HNBR/AO-80 hydrogen bonding system, fourthly, the effect of hydrogen bonding on the properties of hindered phenol hybrids was discussed. Finally, two methods were put forward to improve the weak thermal stability of hindered phenol hybrids.Thermal analysis indicated that hindered phenol and amine were both polymorphous substances. Furthermore, dynamic mechanical analysis showed that hindered phenol compounds and petroleum resins had the best dynamic mechanical property, which may depend on their molecular length and structure.Because the crystallization of amorphous hindered phenol in the polymer matrix can result in the decreasing of damping property of materials, it is necessary to study its crystallizing behavior. In a certain temperature range, different crystals could be obtained from amorphous hindered phenol compounds by isothermal crystallization. As the crystallizing temperature changed, the morphology of crystal surfaces also changed. Amorphous AO-60 and AO-70 could crystallize into hopper crystals. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that there existed three morphological features for hopper crystal:hollow, steps and raisings around the edge. Amorphous AO-80 could isothermally crystallize into spherulites and banded spherulites in the temperature range of 90-70℃, while it generated petal-shaped crystals in the range of 100-90℃. The crystallization power of amorphous AO-70 at room temperature was much stronger than that of AO-60 and AO-80.HNBR/AO-80 damping hybrids were prepared by mechanical mixing and co-solvent methods. Dynamic mechanical analysis showed that the addition of AO-80 could apparently improve the damping property of HNBR matrix. Furthermore, morphological and thermal analyses indicated that AO-80 was completely miscible with HNBR in the case of high AO-80 content; AO-80 dispersed in the matrix as amorphous microspheres in the case of low AO-80 content. For the sample, incorporating low-content AO-80, prepared by co-solvent method, microsphere phase, which was substantially dependent on the thermodynamic property, was still able to be observed.In order to elucidate the miscibility of HNBR/AO-80 hybrids that was in disagreement with our common sense, further Fourier transition infra-red (FT-IR) and ultra-violet (UV) spectroscopic analyses of hydrogen bonding were conducted. The FT-IR and UV results showed that there existed extensive hydrogen bonding in the binary hybriding system of HNBR and AO-80. The ester group of AO-80 was able to form hydrogen bonding with the phenolic hydroxyl of AO-80, i.e. intra-component hydrogen bonding, in any case, while the nitrile group of HNBR hydrogen-bonded with the phenolic hydroxyl of AO-80, i.e. inter-component hydrogen bonding, as the AO-80 content was above 10 phr. The inter-component hydrogen bonding is the key factor for improving the miscibility and damping property of HNBR/AO-80 hybrids. Because of the extensive existence of the intra-component hydrogen bonding, HNBR/AO-80 hybrids were not stable in the thermodynamic sense. The elasticity of AO-80 might be attributed to the small molecular self-assembly that was induced by hydrogen bonding.Taking the HNBR/AO-80 hybrid for example, we tried to improve the weak thermal stability of hindered phenol hybrids. In the case of the low AO-80 content the hybrid was thermally stable, whereas the samples were easy to break up as the AO-80 content was above 10 phr. By means of vulcanization and ternary hybridation, the thermal stability of the HNBR/AO-80 hybrids could be strikingly improved. The vulcanized HNBR/AO-70/AO-80 (100/25/25) hybrid, which was of great practical value, had good damping performance, excellent thermal stability, self-adhesion and adjustable damping temperature range.