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An interface study of zirconium(IV) coupling for the adhesion of polymeric coatings on glass and aluminum

Abstract (Summary)
During the synthesis of zirconium Schiff-base polymers it became apparent that the polymers adhere quite strongly to the silica (glass) vessels in which they were recrystallized from dimethyl sulfoxide solution. This observation inspired the following research: A new soluble linear Schiff-base zirconium-containing coordination polymer poly((N,N$\sp\prime$,N$\sp{\prime\prime}$,N$\sp{\prime\prime\prime}$-tetrasalicylidene-3,3$\sp\prime$-diaminobenzidine)-zirconium(IV)) ((Zr(tsdb)) $\sb{\rm n}$) has been synthesized via the condensation of 3,3$\sp\prime$-diaminobenzidine with tetrakis(salicylaldehydato-O,O$\sp\prime$)zirconium(IV) in dry dimethyl sulfoxide. Molecular weights have been characterized by nuclear magnetic resonance spectroscopy, gel permeation chromatography, and viscosity measurements. A copolymer average degree of polymerization of up to 92 has been obtained by careful stoichiometric control and fractionation. The polymer shows high thermal stability to about 500$\sp\circ$C and has a glass transition temperature of about 74$\sp\circ$C. An electronic charge-transfer transition occurs at about 400 nm with a molar extinction coefficient of 30,000 L(mol Zr)$\sp{-1}$cm$\sp{-1}$. The interface interaction between the polymer and oxides (glass and alumina) has been studied. A series of (Zr(tsdb)) $\sb{\rm n}$ polymers with different end group ratios were used for the surface coverage studies. Polymers with more zirconium end groups obtain higher surface coverage. The interface bonding, Zr-O-Si, is identified from Fourier-transform infrared at 990 cm$\sp{-1}$. Scribe-stripping tests show adhesion vanishes after the polymers are end-capped. (Zr(tsdb)) $\sb{\rm n}$ oligomers couple with ($\pm$)-$\beta$-butyrolactone and stearoyl chloride to produce organic hybrid copolymers. These copolymers have been synthesized for the study of adhesion promotion for polymeric coatings on glass and aluminum substrates. Based on scribe-stripping, indentation debonding, and peel tests, results with films of poly(methyl methacrylate), polybutyrolactone, polythylene, and polypropylene show that adhesion increases when the substrates are pretreated with these hybrid copolymers.
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