End group modification of polyamide-6 in supercritical and subcritical fluids. Part 2: Amine and carboxylic acid end group modification with 1,2-epoxybutane

The amine and carboxylic acid end groups of polyamide 6 (PA-6) granules were blocked with 1,2-epoxybutane in supercrit. or subcrit. fluids. The fluids were mixts. of either propane or CO2 with 10 mol% 1,4-dioxane. Temps. of 50-140 DegC and pressures of 70-80 bars were applied. The reactions were followed in time. The modified polyamide samples were analyzed by carboxylic acid end group titrns., by FTIR spectroscopy, by soln. and melt viscosity measurements, by DSC and SEC/DV. End group concns., relative viscosities and mol. wt. distributions (MWD) of modified samples were compared with corresponding values of unmodified PA-6. It was found that better blocking of the end groups was obtained with increasing reaction temp. However, after modification, at higher temps., a decrease in relative viscosity was found. SEC measurements showed that this decrease in relative viscosity not necessarily implies that chain scission had occurred, but that it must be the result of a different interaction of the modified polymer end groups with the solvent. Best results were obtained for PA-6 modified at 100 DegC in propane/1,4-dioxane: an improved melt stability was obtained without discoloration of the PA-6 granules or a change in mol. wt., due to the blocking of the amine end groups but leaving the majority of the carboxylic acid end groups unblocked. [on SciFinder (R)]