The use of m-ethynylphenol (m-EP) and p-t-butylphenol (PTBP) as coterminators for bisphenol A polycarbonates (BA PCs) provided long-chain-branched PCs, partially crosslinked PCs, or both after the thermal reaction of the terminal m-EP groups, depending on the molar ratio of the chain terminators. Linear m-EP/PTBP PCs were prepared by solution phosgenation of BA and the two coterminators. Differential scanning calorimetry showed the onset of the m-EP-end-group reaction at about 250 °C by the appearance of a reaction exotherm. The enthalpy (⌬H) of this reaction was roughly proportional to the amount of m-EP in the PC and to an extent could be used to monitor the progress of the reaction and estimate its kinetics. A complete m-EP-endgroup reaction was evident from gel permeation chromatography analysis upon heating under N 2 to 380 °C for 10 min or 360 °C for 60 min. The amount, if any, of gel formed after the m-EP-end-group reaction depended on ⌾ EP ; those PCs with a ⌾ EP value less than or equal to 0.33 had little or no gel. The maximum ⌾ EP that precluded the formation of gels after branching was estimated to be about 0.45-0.48. The molecular weight of m-EP/PTBP PCs increased after branching, as evidenced by gel permeation chromatography analysis. Assuming that the terminal m-EP groups had a statistical distribution on the polymer chain ends and that they underwent only homopolymerization, the average reacted m-EP-group functionality according to estimated gel-point composition was about 2.8 -3.0.