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

摘要

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 ~(13)C-NMR. Thermal properties of polymers were investigated using DSC and TGA analysis. The obtained polymers were thermoplastic, having moderate T_g values in the range of 26-78°C and good thermal stability up to 350°C in N_2 and O_2 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.