Study On Preparation, Structure, Properties And Kinetics Of Polysilane/Polyurethane Copolymer

Polyurethane (PU) is an important and versatile class of polymer materials. It is attracting significant attention and becoming more and more important as an engineering material, because of its excellent properties such as good mechanical properties, high abrasive resistance, wearability, chemical resistance and high impact strength. However, conventional PU exhibits poor thermal stability, water resistance, surface and dielectric properties, which limits their application in some fields. Silicon polymer is an important novel material owing to its peculiar properties, such as excellent heat resistance, cold resistance, weather resistance, aging resistance, electricity insulation, ozone resistance, water-proof, fire resistance, physiologically inert et. al. However, its mechanical properties and surface adhesive strength are poor, and its cost is high, which limits its application. Recently, the study of modifying PU by silicon attracts abroad interest and attention of researchers. It is expected to improve the thermal stability, water resistance, surface property and dielectric property without substantially damaging PU mechanical properties. However, the compatibility between PU and silicon is poor due to the great difference of their solubility parameters, and the bonding force is not strong because of the narrow interfacial minor region of hard segments. It brings great difficulty to the preparation of this modified PU and the properties of resulted material are not good. The previous studies focused on the modification of thermoplastic or thermoset PU by silicon. And few studies were on the modification of moisture-curing PU by sol-gel method. However, moisture-curing PU possesses many advantages such as its simple technique and field molding. It has extensive applications in reactive hot melts, sealants, adhesives and field molding materials.In this paper, the hard and soft segments of PU were modified by silane coupling agents and polysiloxane (PDMS), respectively. Moisture-curing polysiloxane/polyurethane (PUSR) copolymers were prepared by sol-gel method. The preparation, structure and properties of PUSR copolymers were investigated in detail, and the kinetics of PUSR sol-gel process was studied. The PUSR copolymer was cured by the hydrolysis and condensation of alkoxysilane to form cross-linking network. During the whole curing process, only little water and alcohol was produced. Comparing with the conventional NCO moisture-curing, the curing of PUSR copolymer is environmental friendly. Therefore, it can be used as novel environmental friendly adhesives, sealants, coatings and field molding materials. The main contents were listed below:1. The preparation of PUSR copolymers by a sol-gel methodThe silicon-polyurethane hyrid materials were prepared by a sol-gel method. Firstly, NCO-capping prepolymer was prepared by the reaction between 4, 4′-Diphenlymethane diisocyanate (MDI) and the mixed soft segments made byα,ω-bis (γ-aminopropyl) poly (dimethylsiloxane) (ATPS) and polyester glycols. Then the prepolymer was end-capped by silane coupling agents to get alkoxysilane-terminated PUSR prepolymer. Finally, the PUSR copolymer was achieved by sol-gel reactions of the alkoxysilane-terminated PUSR prepolymer in Teflon molds under 25℃and 50% relative humidity (R. H). Mixed solvents of 1, 4-dioxane and toluene were employed in the reaction system. Homogenous PUSR copolymer can be obtained by this method, which possesses good thermal stability, hydrophobicity and excellent dielectric properties.2. The effects of silicon on the structure and properties of PUSR copolymers The effects of end-capping agents, the structure and content of PDMS on the morphology and properties of PUSR copolymers were investigated.The structure of end-capping agents has a great influence on the structure and properties of PUSR copolymers, because it determines the kinetics process of moisture-curing process. The results showed that the thermal stability, mechanical properties and crystallinity were affected by the structure of eng-capping agents. If the end-capping agents based on the mixed alkoxysilanes with primary amine and secondary amine other than single alkoxysilane, PUSR copolymer possesses better comprehensive properties. In this study, mixed aniline-methyl-triethoxysilane/aminopropyl-triethoxysilane (KH550/ND-42) was as the enc-capping agents. When the ratio of KH550/ND-42 was 1/1, the PUSR copolymer has better comprehensive properties.Hydroxoalkyl-polysiloxane (HO-PDMS),α,ω-bis (γ-aminopropyl) poly (dimethylsiloxane) (ATPS), fluorine-polysiloxane (F-PDMS) and side chain amido-polysiloxane (NH2-PDMS) were employed in this study. The effects of the four polysiloxanes on the structure and properties of PUSR copolymers were investigated. The morphology of PUSR copolymers was investigated by Transmission Electron Microscopy (TEM) and Atomic Force Microscope (AFM). The thermal stability was studied by Dynamic Machine Analysis (DMTA) and thermogravimetry analysis (TGA). The surface properties was characterized by contact angle analysis, the properties of aging resistance were also investigated. The results indicated that the PUSR copolymer based on ATPS showed better comprehensive properties.The content of ATPS in PUSR copolymers would affect the degree of micro-phase separation; consequently has an influence on the morphology and properties. The results indicated when the content of ATPS was 8～10%, the PUSR copolymers showed a proper degree of micro-phase separation and the mechanical properties and thermal stability were better. While the content of ATPS was larger than 10%, the increasing micro-phase separation would result in the sharp decrease in the mechanical properties. When the content of ATPS was further increased to larger than 14%, the macro-phase separation of PUSR copolymers would be too serious to become a homogeneous material.3. The effects of PU on the structure and properties of PUSR copolymersThe PUSR copolymers were prepared based on the mixed soft segment of ATPS and polyester glycol. The effects of the structure of polyester diol and the ratio of NCO/OH on the morphology and properties of PUSR copolymers were discussed. The results showed that PU structure had a great influence on thermal stability, waterproofing, dielectric properties and morphology of PUSR copolymers. This is not only because of the different structure of PU itself, but the changing compatibility of PU and polysiloxane.4. The preparation of PUSR copolymers on polyether diol and silicon oligomer diol (HO-PDMS)A serial of PUSR copolymers were prepared by bulk polymerization and silicon oligomer diol and polyether diol as the mixed segments. During the whole process, no solvent was used. Therefore, the environmental protection was better and the cost would decrease. The effects of HO-PDMS content on the morphology and properties of PUSR copolymers were investigated. The dielectric properties and surface properties were obviously improved with the increase of HO-PDMS content. The tensile strength decreased and elongation at break of PUSR copolymers increased with the increase of HO-PDMS content. The TGA results showed that the thermal stability enhanced with the increase of HO-PDMS content. The TEM photographs showed that polysiloxane in elliptic particles well dispersed in PU matrix.5. The moisture-curing kinetics of PUSR copolymerFirst, the kinetics of sol-gel process of alkoxysilane was studied. The alkoxysilanes with different functional groups were investigated and a set of simple and convenient method to study the kinetics was built. Then, the moisture-curing kinetics of PUSR prepolymers was studied. The hydrolysis and condensation kinetics of PTMG and PBA systems were followed by FTIR, and the mechanism of moisture-curing were investigated. The structure change and enthalpy of PBA system was followed by DSC. The results showed that the hydrolysis reaction was second-order reaction. The reaction of hydrolysis of PTMG system was obviously faster than PTMG system. The hydrolysis rate constants were 1.60×10-2 (mol/L)-1.min-1, 9.28×10-4 (mol/L)-1.(min)-1 for PTMG and PBA systems, respectively。...