Branching by reactive end groups. III. Synthesis, branching, and analysis of m-ethynylphenol/p-t-butylphenol-coterminated bisphenol A polycarbonates

The use of m-ethynylphenol (m-EP) and p-t-butylphenol (PTBP) as coterminato rs for bisphenol A polycarbonates (BA PCs) provided long-chain-branched PCs , partially crosslinked PCs, or both after the thermal reaction of the term inal m-EP groups, depending on the molar ratio of the chain terminators. Li near 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 degrees C by the appearance of a reacti on exotherm. The enthalpy (Delta H) of this reaction was roughly proportion al to the amount of m-EP in the PC and to an extent could be used to monito r the progress of the reaction and estimate its kinetics. A complete m-EP-e nd-group reaction was evident from gel permeation chromatography analysis u pon heating under N-2 to 380 degrees C for 10 min or 360 degrees C for 60 m in. The amount, if any, of gel formed after the m-EP-end-group reaction dep ended on X-EP; those PCs with a X-EP value less than or equal to 0.33 had l ittle or no gel. The maximum X-EP that precluded the formation of gels afte r 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 chrom atography analysis. Assuming that the terminal m-EP groups had a statistica l distribution on the polymer chain ends and that they underwent only homop olymerization, the average reacted m-EP-group functionality according to es timated gel-point composition was about 2.8-3.0. (C) 2000 John Wiley & Sons , Inc.