Phase behavior of ternary PBT–PC/phenoxy blends

Abstract

SYNOPSISTernary polymer blends were obtained by melt mixing, mixing up to 30% poly (butylene terephthalate) ( P B T ) with polycarbonate ( P C ) and phenoxy in a n attempt to improve the miscibility of the PC/phenoxy binary blend. Although most of the blends with a P B T content higher than 10% appear as transparent, two Tgfs appeared at all the blend compositions. These Tg's correspond to PC-rich and phenoxy-rich phases where a low amount of the main component of the other phase and all P B T are dissolved in amounts that are a function of the PC/phenoxy ratio of the blend. Increasing the P B T contents in the blends closes to linearity the torque versus composition plot, so that a relationship between miscibility level and viscosity exists in these blends. I NTRO DUCT1 0 NThe development of new materials based on polymer blends is becoming one of the most active areas of plastics research thanks to the increasing need for new polymers with improved properties for many different applications. Among polymer blends, binary blends are to date the most often studied and commercialized. Many polymer blends have rubbery materials as a second component, but great attention has also been paid to blends whose components are polyesters or other engineering materials. It is known that miscibility level plays a definitive role in the solid state and mechanical properties of polymers. As a consequence, various attempts have been made to improve the miscibility level of immiscible or partially miscible polymer blends. One such attempt is to add a third component, miscible'-' or at least partially miscibleg-" with the two components of the immiscible blend. This method usually occasions more difficulties in control and optimization of processing and composition of polymer blends, but it seems the natural direction for polymer research to take as seen from the historical development of other materials.Among condensation polymers both bisphenol A polycarbonate ( PC ) 12-25 and poly ( hydroxy ether of * To whom correspondence should be addressed. bisphenol A) ( p h e n~x y )~~-~~ have been widely studied as components of binary polymer blends. However, despite the potential miscibility of phenoxy with polyesters or related materials, the PC /phenoxy blend is not fully miscible,34 although a favorable balance of properties can be produced in this blend through interchange reactions in the melt state. 35736 If we look at the possibility of combining PC/ phenoxy blends with a third component, we realize, first, that PBT is fully miscible with phenoxy, second, that a partially miscible PC/PBT blend with a PBT content of 44% l 3 (Xenoy CL General Electric) has been commercialized, and, finally, that studies have been done of the binary blends PC/ PBT, [12][13][14][15][16][17][18][19][20]33,37,38 P B T / p h e n~x y ,~~,~~ and PC/phenoxy.34-36 Moreover, PC, in spite of its high ductility, stability, and outstanding impact resistance, has a high melt viscosity and poor hydrolysis resistance.PBT is unstable at high temperature^'^,^^ bu...

Phenoxy/Hytrel blends. I. Miscibility and melt-state reactions

“…All these torque increases are probably due to the onset of interchange reactions. A similar torque behavior was also seen in the case of blends of Ph with other polyesters 39,40 or with related polymers [47][48][49][50][51] and was attributed to an alcoholysis reaction. Such a reaction between the ester and hydroxy groups of the blend components is likely to take place in these blends, as will be seen later.…”

“…The maximum torque value increases as the Ph content of the blend increases up to a Ph content double than that of the other component. The fact that the maximum torque values take place at a Ph/second component ratio of 2 : 1 has been also seen in Ph/PBT, 39 Ph/PC, 47,50 and Ph/PMMA blends, 55 where it is assumed that the same reaction takes place. No distinct reason can be stated for this common ratio.…”

“…This may be because Hy can crystallize in contact with THF 24,40 and may lead to some Ph being occluded in Hy, avoiding Ph dissolution. However, the possibility of some reaction even after this short mixing time cannot be excluded; the produced copolymer would be partially responsible 50 for the observed solubility decrease.…”

“…In the first, which at 240°C extends up to roughly 55 min, the torque increases are important with a shoulder that appears after a mixing time of 35 min. In the second region, at mixing times longer than 55 min, the torque increases accelerate and then reach a maximum where a highly crosslinked and powderlike material 39,40,47,50,51 appears.…”

“…As is known, 24,39,40,[47][48][49][50][51] when the chemical nature of melt blends changes through chemical reactions, the viscosity and, consequently, the torque of blending may change. This is mainly true when, as a consequence of the reaction between the components of the blend, either branched or crosslinked products appear, as often happens in polyesters blends like those presented here.…”