Transesterification in blends of poly(butylene terephthalate) and bisphenol‐A‐polycarbonate

Abstract

By means of differential calorimetric and X-ray examinations it was shown that poly(buty1ene terephthalate) (PBT) and bisphenol-A-polycarbonate (PC) are only compatible in the melt if they stay in the melt for a short period of time. During mixing in the melt, transesterification begins and block copolymers are formed. A characteristic glass transition temperature is observed for each individual blend. Butylene terephthalate (BT)-blocks are crystallizable; however, with an increasing share of bisphenol-A-carbonate (BPAC) the specific melting enthalpy of the BT-blocks decreases. Within copolymers with a high BPAC content, the BPAC segments crystallize considerably faster than in pure PC. By means of diffraction measurements with synchrotron radiation, the mechanism of stress-induced a-P-modification change in pure PBT and in block copolymers with high BT-contents could be explored. ZUSAMMENFASSUNG:Differentialkalorimetrische und rdntgenographische Messungen ergeben, dal3Poly(butylenterephtha1at) (PBT) und Bisphenol-A-Polycarbonat (PC), wenn sie aus einer gemeinsamen LZjsung gefallt werden, unvertraglich sind. In der Schmelze beginnt wahrend des Durchmischens der Komponenten Umesterung. Es bilden sich Blockcopolymere, die einen Glasubergang rnit einem fur jede Zusammensetzung charakteristischen T,-Wert zeigen. Die Butylenterephthalat (BT)-Blocke in den Copolymeren sind kristallisierfahig; jedoch wird ihre spezifische Schmelzenthalpie rnit zunehmendem Bisphenol-A-carbonat (BPAC)-Massenanteil kleiner. In den Copolymeren rnit hohen BPAC-Massenanteilen kristallisieren die BPAC-Segmente erheblich schneller als im reinen PC. Mit Hilfe von Rontgenbeugungsuntersuchungen rnit Synchrotronstrahlen konnte der Mechanismus fur die spannungsinduzierte a-P-Modifikationsumwandlung im reinen PBT und in den Blockcopolymeren rnit hohem BT-Gehalt aufgeklart werden.

Copolymer Composition: a Key to the Mechanisms of Exchange in Reactive Polymer Blending

“…The reactions that can occur in this system are summarised in Scheme la-c. The exchange reaction between high MW PBT and PC, ie., containing non-detectable amounts of reactive end-groups, occurs even at 240°C in the presence of an esterification catalyst, by an inner-inner mechanism (Scheme la) [4][5][6][7][8][9][10][11][12][13]401. To explore the dependence of the copolymer composition on the inner-inner exchange mechanism, we have reacted an equimolar mixture of high MW PBT and PC at 240°C in the presence of Ti(OBu)4, in a Brabender mixer for different times [40].…”

Mechanism of Exchange in PBT/PC and PET/PC Blends. Composition of the Copolymer Formed in the Melt Mixing Process

“…In recent years considerable interest has arisen in the study of the exchange reactions which may occur during the melt mixing processes of polymers containing reactive functional groups (ester, carbonate, amide, etc. ). − …”

“…End-group-activated exchange, or catalyst-activated exchange, may occur in such systems below 300 °C, − whereas both thermal activated exchange (i.e., without catalysts) and thermal decomposition occur above 300 °C. ,,, …”

Effects of Trans-Esterification Stabilizers on Mechanical Properties and Structure of Poly(butylene terephthalate)/Polycarbonate Blends

“…It has been reported that PBT/PC blends are immiscible 13,[18][19][20][21] or partially miscible 5,22,23 at the T g level as multiphase materials. More importantly, investigations have shown that PC can hinder PBT crystallization in PBT/PC blends 24,25 .…”