Abstract
Protection of intrinsically brittle quartz chromatographic columns (CCs) from breakage or property deterioration in gas chromatography (GC) analysis has become an important research topic regarding high-temperature GC techniques. Polyimide (PI) has proved to be the most suitable protective coating for quartz CCs. In the current research, a series of novel high-temperature-resistant PI coatings for quartz CCs operated over 320 °C have been successfully prepared. For this purpose, the aromatic diamine with a rigid skeleton structure 2-(4-aminophenyl)-5-aminobenzimidazole (APBI) was copolymerized with two aromatic dianhydrides—3,3’,4,4’-benzophenotetracarboxylic acid dianhydride (BTDA) and 4,4’-oxydiphthalic anhydride (ODPA)—and an aromatic diamine with flexible ether linkages—4,4’-oxydianiline (ODA)—by a two-step polymerization procedure via soluble poly(amic acid) (PAA) precursors, followed by thermal imidization at elevated temperatures. The developed PI coatings exhibited good comprehensive properties, including glass transition temperatures (Tg) as high as 346.9 °C, measured by dynamic mechanical analysis (DMA), and coefficients of linear thermal expansion (CTEs) as low as 24.6 × 10−6/K in the range of 50–300 °C. In addition, the PI coatings exhibited good adhesion to the fused quartz capillary columns. No cracking, delamination, warpage, or other failures occurred during the 100-cycle thermal shock test in the range of 25–320 °C.
Highlights
Gas chromatography (GC) analytical techniques have been widely used in modern analysis for more than half a century [1]
PI coatings were obtained by thermally baking the corresponding poly(amic acid) (PAA) varnishes cast onto clean borosilicate glass substrates in nitrogen
It can be clearly observed that the tensile strength and elongation at break of the PI coatings increased first and decreased when the molar ratio of 4-APBI increased from 0% to 60% in the diamine components
Summary
Gas chromatography (GC) analytical techniques have been widely used in modern analysis for more than half a century [1]. CCs usually consist of a quartz capillary that is coated with a polymer layer [4,5,6,7]. The unique characteristics of the quartz capillary have made it the preferred material for GC analysis. A drawback of the quartz capillary is its inherently brittle nature; it needs to be protected by flexible polymer coatings in practical applications [8]. Polymers serving as the protective coating for quartz CCs should meet severe property requirements, including excellent thermal and dimensional stability at elevated temperatures, so as to maintain good adhesion with the inner quartz CCs during thermal shock; good mechanical flexibility and toughness to resist winding; high surface hardness to protect the quartz surface from abrasive damage; and good environmental stability
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