Single-sized, pure arylene ether macrocycles (11-21) ranging from 30 to 60 atom ring sizes were synthesized in good yields (up to 83%) by the two-component method under high dilution conditions. These macrocycles have unsymmetric structures containing sulfone/ketone or sulfone/phosphine oxide functional groups and have relatively low melting points. The melt ROP of the single-sized macrocycles to form poly(arylene ether)s exhibits two-stage characteristics : the first stage is very fast, presumably driven by the large entropy difference between cyclics and linears; the second stage is very slow and is believed to be diffusion controlled due to the high viscosity created in the first stage reaction. The latter stage leads to incomplete polymerization at the low initiator concentrations (1-3 mol%). At high initiator concentrations (5-7 mol%), 100% conversion is reached due to improved initiator distribution in the macrocycles; however, this reduces the molecular weights of the polymers. The molecular weight is found to build up very rapidly, independent of conversion, reaction time, and type of initiator. The ROP is initiated by CsF and alkali phenoxides. The efficiency of the alkali metal counterion is generally in the order Cs+ > K+ > Na+, while a phenoxide initiator is more efficient than a fluoride initiator. It is also found that the Cs counterion leads to the highest degree of crosslinking. The ROP of cyclic oligomeric mixtures (22) is also reported for comparison; the study shows that the molecular weight depends on time and conversion and that the conversion is sensitive to the content of linear impurities and the average ring size of the cyclic mixtures.