Thermal properties, adhesive strength, and optical transparency of cyclolinear poly(aryloxycyclotriphosphazenes)

Four cyclolinear poly(aryloxycyclotriphosphazenes) derived from poly[4,4′-(isopropoylidene)diphenoxytetrachlorocyclotriphosphazene] and poly[4,4′-(hexafluoroisopropylidene)diphenoxytetrachlorocyclotriphosphazene] were synthesized from the reaction of hexachlorocyclotriphosphazene (HCP) with 4,4′-(isopropylidene)diphenol (bisphenol A) or 4,4′-(hexafluoroisopropylidene)diphenol (bisphenol AF) in molar ratio 1 : 1 via a one-step condensation polymerization. Subsequent reaction of the resulted chlorine-bound polymers with adequate amount of the sodium salts of 4-methoxycarbonylphenoxide or 4-propoxycarbonylphenoxide yielded the corresponding chlorine-free polymers, [poly(tetra-4-methoxycarbonylphenoxy)-4,4′-(isopropoylidene)diphenoxy cyclotriphosphazene] (MBACP), [poly(tetra-4-propoxycarbonylphenoxy)-4,4′-(isopropoylidene)diphenoxycyclotriphosphazene] (PBACP), [poly(tetra-4-methoxycarbonylphenoxy)-4,4′-(hexafluoroisopropylidene)diphenoxycyclotriphosphazene] (MBAFCP), [poly(tetra-4-propoxycarbonylphenoxy)-4,4′-(hexafluoroisopropylidene)diphenoxycyclotriphosphazene] (PBAFCP), respectively. The chemical structures were characterized by Fourier transformer infrared, 1H, and 13C-NMR. Thermal properties of polymers were investigated using DSC and TGA analysis. The obtained polymers were thermoplastic, having moderate Tg values in the range of 26–78°C and good thermal stability up to 350°C in N2 and O2 gases. The thermal decomposition of the isopropylidene-containing polymers is a one-step process, while that of hexafluoroisopropylidene-containing polymers is a two-step process. However, presence of the latter group in the polymers backbone showed negligible effects on the thermo-oxidative stability. The adhesive strength was measured by lap-shear strength test on glass–glass bonded joint and found to be in the range of 1.78–2.62 MPa, this property may be attributed to the physical interactions between glass–glass interfaces and the polar-pendant units present at the polymers backbone. The products showed high optical transparency when they applied between two glass surfaces, the adhesive layers were colorless, with the UV cut-off wavelength of 300–302 nm, and the maximum transparency of about 90% was observed within the wavelengths range of 400–700 nm. Because of their properties, the cyclolinear poly(aryloxycyclotriphosphazenes) synthesized in this study are recommended as potential candidates for high thermally stable, transparent adhesives required in industrial applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.