The synthesis of end-functionalized hydrogen-bonding polymers and the investigation of their melt phase blend behavior are reported. Monofunctional and telechelic ureidopyrimidinone (UPy)-functionalized poly(styrene)s and poly(methyl methacrylate)s were synthesized using atom transfer radical polymerization (ATRP) followed by atom transfer radical Coupling (ATRC). Aggregation of UPy end-groups in solution was observed using size exclusion chromatography. The effect of UPy end-groups on blend miscibility in the melt state was studied using optical microscopy and differential scanning calorimetry. The incorporation of associating groups Onto one end of either blend component decreases miscibility relative to unfunctionalized parent blends. Lower miscibility was also observed for blends in which both components were monofunctionalized with associating end-groups. The largest decrease in miscibility was observed for blends containing telechelic UPy-functionalized polymers, which were immiscible across the entire composition range.