Polyimide/silica hybrids via the sol-gel route: High performance materials for the new technological challenges

Abstract

Abstract. The present review article describes in detail the state-of-the-art of organic-inorganic hybrid materials based on polyimide/silica components. The article is divided in three parts. In the first the basic processing route for the preparation of these systems is described, i.e. the sol-gel technique, along with the strategies developed to control the final morphology. In the second part the curing characteristics, the dynamic-mechanical and the mechanical and fracture properties of hybrids with different morphologies are reviewed. Finally, the more technologically relevant applications devised for these high performance materials are discussed. : nanocomposites, hybrid materials, polyimide, silica, sol-gel eXPRESS Polymer Letters Vol.3, No.7 (2009) [413][414][415][416][417][418][419][420][421][422][423][424][425][426][427][428] Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2009.51 or as functional materials [14] such as catalyst supports [15] and microelectronic devices [16]. The sol-gel route represents the preferred way for the synthesis of polyimide based hybrids. The classical sol-gel process consists in a two step hydrolysis-condensation reaction, starting with a metal alkoxides M(OR) 4 , typically tetraethoxisilane Si(OCH 2 CH 3 ) 4 or titanium isopropoxide Ti[OCH(CH 3 ) 2 ] 4 , to produce hydroxyl groups followed by the polycondensation of the hydroxyl groups and residual alkoxy groups to form a three-dimensional network [5,[17][18][19][20][21]. Polyimides are particularly suited for this type of process because they can be obtained from polyamic acid precursors, which are soluble in hygroscopic solvents and can, therefore, tolerate the addition of water necessary to bring about the hydrolysis of the metal alkoxide. Moreover, the outstanding thermal stability of polyimides allows the hybrids to be post-cured at very high temperatures (300-350°C) making it possible the development of a very dense inorganic network without inducing appreciable degradation of the organic phase. Polyimide/silica hybrids made by the sol-gel technique are the subject of this review, in which the approaches used for a close control of their final morphology, the effects of the silica phase on the curing process of polyimide precursors, the dynamic-mechanical and the mechanical and fracture properties that these materials can display, and their possible applications will be presented and discussed. Keywords Processing and morphologyA typical procedure for the preparation of PI/silica hybrids via the sol-gel route, involves the following steps: i) The polyamic acid (PAA) (PI precursor) is formed by a polyaddition reaction of a dianhydride [e.g., pyromellitic anhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), or 2,2-bis(3,4-dicarboxy-phenyl)-hexafluoropropane dianhydride (6FDA)] with a diamine [e.g., 4,4′-oxydianiline (ODA), or p-phenylen diamine (PPA)] in a common solvent [e.g., dimethylacetamide (DMAc), or N-methyl pyrolidone (NMP)]. The reaction and chemical str...

Structure-gas Transport Property Relationship of Hyperbranched Polyimide-silica Hybrid Membranes

“…The synthesis of polyimide-silica hybrid materials and the investigation of their physical and gas transport properties have also received much attention. [9][10][11]. In previous researches, we found that the gas permeability and CO 2 /CH 4 selectivity of these membranes prepared via sol-gel reaction using tetramethoxysilane (TMOS) increased with increasing silica content, suggesting the characteristic distribution and interconnectivity of free volume holes created by the incorporation of silica [12][13][14][15][16][17][18].…”

Thermo-stabilized, porous polyimide microspheres prepared from nanosized SiO2 templating via in situ polymerization

“…Herein, an excellent porous polymer matrix should satisfy a variety of requirements, such as desirable thermal stability, chemical resistance and high modulus to support the void structure. Polyimide (PI) is considered as the most promising candidates that could satisfy the above requirements with high thermal stability, good mechanical properties, excellent adhesion properties and outstanding dimensional stability [5][6][7]. Up to now, several studies have been contributed to the preparation of well-defined porous PIs, such as PI membranes and PI foams; however, few reports have focused on preparing porous PI microspheres.…”

Effect of nanosilica on the dielectric properties and thermal stability of polyimide/SiO2nanohybrid

“…In particular, an important advantage of the sol-gel synthesis route for polyimide/silica hybrid is that the poly(amic acid) organic matrix acts to prevent agglomeration of the silica, which can induce to nanometer scale silica clusters in the hybrids [18][19][20][21].…”