Abstract
Abstract (英文摘要) Commercially available silicones such as methyl- or phenyl-substituted siloxanes possess unique properties, including thermal stability over a wide range of temperature (-70 °C to 250 °C), resistance to oxidation and chemical reaction,water-repellency,weather-stability, unusual electrical properties, low surface energy and releasing characteristic. Base on these characteristics, silicones have been used in a wide variety of applications. Silicones are immiscible with most organic polymers. It is difficult to modify the properties of silicones by blending them with other polymers. Interfacial adhesion between silicones and organic polymers is usually poor. The preparation of composite materials by laminating silicones with other organic polymers is difficult too. These drawbacks have limited the application fields of silicones. In this thesis, we try to improve the adhesion between silicones and other organic polymers such as polyurethane (PU) rubber by synthesizing different kinds of bifunctional copolymers as adhesion promoters. They are polydimethylsiloxane-b-Hydroxyl terminated polybutadiene (PDMS-b-HTPB), polydimethylsiloxane-polycaprolactone (PCL-b-PDMS), and polydimethylsiloxane-block-hydroxyl graft acrylate prepolymer (PDMS-b- HGAP) copolymers. The surface of the target polymer is modified by blending with aforementioned copolymers where one block interacts favorably with the base matrix and the other block with the target matrix. The polymeric surface can form ordered, oriented layers at the surface during subsequent curing. The part of such copolymers with a low critical surface tension is readily miscible with the silicone base matrix, whereas the other part interacts favorably with the more polar target matrix. Both blocks can anchor the copolymers into the respective substrate which ensures permanency of the surface modification and increases adhesion between two immiscible polymers. This process is called induced surface reconstruction (ISR) For the PDMS-b-HTPB copolymers, ISR of silicone rubber by blending PDMS reactants with bifunctional PDMS-b- HTPB copolymers and curing with appropriate mold material was found to improve the adhesion of chemically-inert silicone rubber to PU. Surface characterization using FTIR-ATR indicated that the surface of the silicone rubber possessed a controlled amount of HTPB. The surface was enriched with HTPB by using mold materials having high critical surface tension such as aluminum. A dynamic surface rearrangement occurred during a 1 hr heating cycle at 70 ℃ changing from a HTPB-enriched surface to a PDMS-enriched surface. The peel strength between the silicone rubber and PU was found to increase with decreased propanol residue and with an increase in critical surface tension of the molding materials. The increased content of surface HTPB was suggested to account for the improved adhesion of silicone rubber to PU. For the PCL-PDMS-PCL-PDMS copolymers, ISR of silicone rubber by blending polymethylphenylsiloxane (PMPS) reactants with bifunctional PCL-PDMS-PCL-PDMS copolymers and curing with appropriate mold material was observed to enhance the adhesion of chemically-inert silicone rubber to PU. The peel strength between the silicon rubber, which was blended with 1.0 % PCL-PDMS-PCL-PDMS copolymers and cured with polyethyleneterephthalate as mold materials, and the PU was 1.2 Kg/cm. Surface characterization using static secondary ion mass spectrometry and Fourier transform infrared-attenuated total reflectance indicated that its surface was enriched with PCL segments. The increased content of surface PCL was suggested to account for the adhesion improvement of silicone rubber/PU joints. For the PDMS-b-HGAP copolymers, the copolymers were characterized using Fourier transform infrared spectroscopy as well as 1H and 13C nuclear magnetic resonance spectroscopy. The hydroxyl groups of the HGAP were reacted with the chlorine terminal in the PDMS to yield a triblock copolymer consisted of two segments of PDMS linked to a HGAP segment. The induced surface reconstruction of silicone rubber by blending polysiloxane reactants with bifunctional PDMS-b-HGAP copolymers and curing using mold materials having high critical surface tension such as polyethyleneterephthalate was attempted to improve the adhesion between chemically-inert silicone rubber and PU. Surface characterization using Fourier transform infrared-attenuated total reflectance indicated that the surface of the silicone rubber was enriched with HGAP. The increased content of surface HGAP was suggested to account for the improved adhesion between silicone rubber and PU. The results indicate the synthesized copolymers in conjunction with the induced surface reconstruction process could enhance the adhesion between the immiscible polymers such as the silicon rubber and PU investigated in this thesis. The ISR process is highly compatible with existing preparation process. This process could extend the application fields of siloxanes.