Characterization of polysiloxane-block-polyimides with silicate group in the polysiloxane segments

Abstract

A new class of polysiloxane-block-polyimides having silicate in the polysiloxane segments were successfully synthesized and the thermal and mechanical properties of their crosslinking investigated using cast films. The silicate-containing copolyimides were easily derived by hydrosilylation of polysiloxane-block-polyimides having vinyl groups in the polysiloxane segments prepared from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 2,2-bis[4-(3-aminophenoxy)phenyl]sulfone (BAPSM) and several kinds of copolyimides with vinyl functionalized diamino-(poly)siloxanes accompanied by solution imidization. During hydrosilylation a small excess of diethoxy(methyl)silane was reacted using hydrogen hexachloroplatinate (H₂PtCl₆·5H₂O) as the catalyst. The copolyimides finally obtained were soluble in various organic solvents and easily hydrolysed to form crosslinked copolyimides during solution casting of films for investigation. The resulting materials have various potential applications as organic–inorganic hybrid materials.

Introduction

Recently, several kinds of polyimides terminated by silicate groups have been developed and utilized for designing a new class of inorganic–organic hybrid material [1]. The importance of these new materials has recently been recognized because of an increasing demand for high-performance polymers that cannot be produced by conventional methods [2], [3], [4], [5], [6], [7], [8], [9], [10]. Organic–inorganic hybrid materials has the potential to realize desired thermal and mechanical properties with the additional benefits of good creep and durability characteristics. The interaction between the organic and inorganic compositions through physical force and chemical bond is important as a method for controlling the structure and properties of the hybrid materials. A standard technique for formation of hybrid material is to use sol–gel chemistry by which inorganic particles with nanometer-to-micrometer scale can be formed in the polymer matrix and vice versa. The process may induce either physical blending of inorganic and organic components or chemical grafting among them [9], [10]. In general, alkoxysilane derivatives have been most frequently used for preparing hybrid materials because they undergo hydrolytic polycondensation to result in the sol–gel process.

On the other hand, polysiloxane-block-polyimides have been developed and applied in the advanced microelectronics, aerospace and printed circuit industries, mainly for their high thermal stability and excellent electrical and mechanical properties [11], [12], [13], [14], [15], [16], [17]. These copolyimides are known to possess additional characteristic properties such as oxidative stability, low surface energy, high gas permeability, good adhesion, and specific dielectric properties [18]. We have shown that these properties depend mainly on the composition and chain length of the polysiloxane segments [19], [20]. Reactive polyimides, thermosetting-type polyimides containing reactive end groups have been developed for use as the matrix resin for carbon fibre-matrix composites [21], [22], [23], [24]. More recently, polysiloxane-block-polyimides functionalized by the vinyl group in the polysiloxane segments have been synthesized [25]. These copolyimides, consisting of both flexible segments and reactive side chains, are melt-processible and possess excellent thermal properties and resistance to various organic reagents after thermosetting. These properties should be attractive for use in electrical applications. In the present study, based on this background, polysiloxane-block-polyimides (SxPI) functionalized with silicate are prepared, to develop a new class of thermosetting copolyimides and to construct inorganic–organic hybrid materials.