Preparation, analysis, and properties of benzocyclobutene-terminated polycarbonate?polycarbonate thermoplastic alloys

Abstract

Thermoplastic alloys of benzocyclobutene-terminated bisphenol A polycarbonates (BCB PC) and t-butylphenol-terminated PC can be prepared by double extrusion of the flake components, as follows: first, at a relatively low temperature at which the BCB PC reacts slowly; and, second, at a higher temperature to complete the BCB PC reaction. These alloys can then be injection-molded using the same conditions as used to mold the base PC. Gel permeation chromatography (GPC) and liquid chromatography (LC) analyses show that the BCB PC forms a very high-molecular-weight branched polymer, which is largely soluble in the base PC. Only minor amounts of insoluble, crosslinked BCB PC are formed under the appropriate melt processing conditions. The melt flow rate (MFR) of BCB PC—PC alloys is much lower than that of the base PC, yet the two materials can be injection-molded under identical conditions. This phenomena indicates that the melt viscosity of these alloys have high shear sensitivity. Therefore, MFR is not an accurate measure of the melt processability of BCB PC—PC alloys. The melt strength of BCB PC—PC alloys is much greater than that of linear or branched PC and is dependent on the amount and type of BCB PC and the MFR of the base PC. Transparent alloys having about a six-fold increase in melt strength over branched PC were prepared. The mechanical properties of these alloys that were examined are largely unchanged compared to standard grades of PC. Alloys retain the high toughness, heat distortion, and flexural modulus typically associated with PC. The surface gloss on injection-molded BCB PC—PC alloys is reduced compared to linear PC and appears to decrease with increasing BCB PC content in the formulation. The melt strength of BCB PC—PC alloys also imparts drip suppressant properties in burning samples. An ignition resistant alloy formulation had a 1/16 in. UL-94 V-0 rating while retaining transparency and normal PC physical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1821–1829, 1997