2,6-Dimethylphenol (2,6-DMP) polymerization with a catalytic complex of Cu2O/HBr/ N,N’-di-tert-butylethylene diamine (DBEDA)/N,N-dimethyl-n-butylamine (DMBA)/di-butylamine (DBA) was studied, in which DMBA was prepared in situ from the methylation of n-butylamine over four different solid acid catalysts (two different gamma-alumina, one silica-alumina, and one zeolite). The effectiveness of the unpurified methylation product solutions for promoting the 2,6-DMP polymerization was strongly dependent on the type of solid acid catalysts used. The performance of the best one (untreated product solution from the methylation reactor with Condea gamma-alumina catalyst) was very similiar to that of the reagent grade DMBA. Infrared spectrum studies showed that DMBA acted as the external base for the 2,6-DMP polymerization catalyst system to neutralize the excess hydrobromic acid and to increase the polymerization rate.