X-ray scattering and thermal analysis study of the effects of molecular weight on phase structure in blends of poly(butylene terephthalate) with polycarbonate

Abstract

Blends of Poly(butylene terephthalate), PBT, with Polycarbonate, PC, were studied for a range of molecular weights and blend compositions. Blends were available in PBT/PC compositions 80/20 and 40/60, and with Mw designated by H (high) or L (low). Samples were prepared by melt crystallization, or by cold crystallization following a rapid quench from the melt. Addition of PC reduces the crystallization kinetics of PBT so that the resulting crystals are more perfect than those which form in the homopolymer. Degree of crystallinity of the blends followed the rank ordering: L/L > L/H > H/L = H/H. The glass transition behavior was investigated using dynamic mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC). All blends exhibited two glass transitions at intermediate temperatures between the Tgs of the homopolymers, indicating existence of a PBT‐rich phase and a PC‐rich phase. Blends L/L were most, and H/H the least, miscible. Small‐angle X‐ray scattering was performed at room temperature on cold crystallized blends, or at elevated temperature during melt crystallization. The long period was consistently larger, and the linear stack crystallinity was consistently smaller, in blends L/L or H/L. These results indicate that in blends containing low Mw PC, there is more PC located within the PBT‐rich phase. The long period was consistently smaller in cold crystallized samples, while the linear stack crystallinity was nearly the same, regardless of melt or cold crystallization treatment. Reduction of the average long period in cold crystallized samples could result from crystallization of PBT within the PC‐rich phase. This is consistent with thermal analysis results, which indicate that cold crystallized samples have greater overall crystallinity than melt crystallized samples. A hypothetical liquid phase diagram is presented to explain the differences between melt and cold crystallized blends. © 1996 John Wiley & Sons, Inc.

Analysis of interactions in multicomponent polymeric systems: The key-role of inverse gas chromatography

“…Considerable attention has been given to the origins of miscibility and to binary polymer-polymer phase diagrams. It is usually observed that high molar mass polymer pairs, showing partial miscibility, exhibit phase diagrams that indicate a lower critical solution temperature (LCST) [2,[45][46][47]. In a polymer blend that exhibits LCST behaviour, the miscibility is higher at low temperatures.…”

“…Other approaches exist to determine x for polymer blends. These include the use of the glass transition temperature (T g ) [59] and the use of melting temperature (T m ) [13,46], based on the effect of miscibility on these characteristic temperatures.…”

“…However, several remarks must be made regarding the use of the interaction parameters that is represented by Eqs. (44)- (46). Firstly, the parameters I sp 1 and I sp 2 do not take into account the Lewis base-base repulsion forces and the Lewis acid-acid repulsion forces.…”

Polymer blends: the PC–PBT case

“…These include phosphates and phosphoruscontaining acids. 30,40 Stabiliser systems based on phosphoric acid can lead to a decrease of the hydrolytic stability of the blend. Di-n-octadecyl 44 and triphenyl phospite 35 are widely used as efficient transesterification inhibitors.…”

“…The crystallisation temperature of PBT is approximately 180 uC. 19 The crystallinity of the PBT in PC-PBT blends has been determined by Hanrahan et al 30 and by Cheng et al 30 to be 26 to 38%. A maximum degree of PBT crystallisation of 40% in these blends was observed by Ratzsch et al 28 The overall degree of crystallinity is greater in cold-crystallised blends than in melt crystallised blends.…”