Polymer liquid-crystalline blends with

A number of liquid crystalline polyphosphazenes with mesogenic side groups have been prepared (48—50). Polymers with nonlinear optical activity have also been reported (51). Polyphosphazene membranes have been examined for gas, liquid, and metal ion separation, and for filtration (52—54). There is interest in phosphazene—organic copolymers, blends, and interpenetrating polymer networks (IPNs) (55—61) to take advantage of some of the special characteristics of phosphazenes such as flame retardance and low temperature flexibility. A large number of organic polymers with cydophosphazene substituents have been made (62). 

Specific blends, which could offer an interesting combination of properties with proper com-patibilization, include PPS/PSE, PEl/PPS, PA/PSE, PA/PEI, and PC/PPS. Patent activity has been noted for most of these blend combinations as well as other selected blends involving engineering polymers as noted in Table 17.3. A number of recent patent and published papers have discussed blends of engineering polymers with various specialty polymers including high temperature polymers, liquid crystalline polymers (LCP s), conductive polymers, and as matrix materials for molecular composites. These will be discussed in the following sections. 

W. Grasser, H.-W. Schmidt, and R. Giesa. Fibers spun from poly(ethyl-ene terephthalate) blended with a thermotropic liquid crystalline copolyester with non-coplanar biphenylene units. Polymer, 42(21) 8517-8527, October 2001. 

Blizard, K. G. and Baird, D. G., Rheology and polymer processing. The morphology of polymer blends of a liquid crystalline copolyester with polycarbonate, Poiym. News I2.A4 (1986). 

Isayev AI, Modic M (1987) Self-reinfOTced melt processible polymer composites extrusion, compression, and injection molding. Polym Compos 8 158 James SG, Donald AM, MacDonald WA (1987) Blends of a liquid crystalline copolyester with polyethersulphone. Mol Cryst Liq Cryst 153 491 Jerman RE, Baird DG (1981) Rheological properties of copolyester liquid crystalline melts. I. Capillary rheometry. J Rheol 25 275... 

As Carfagna et al. [61] suggested, the addition of a mesophasic polymer to an amorphous matrix can lead to different results depending on the properties of the liquid crystalline polymer and its amount. If a small amount of the filler compatible with the matrix is added, only plasticization effect can be expected and the dimensional stability of the blend would be reduced. Addition of PET-PHB60 to polycarbonate reduced the dimensionality of the composite, i.e., it increased the shrinkage [42]. This behavior was ascribed to the very low... 

Blends of polypropylene (PP) and liquid crystalline polymer (LCP) processed without melting the LCP were compared with conventional melt processed blends. In a first stage, PP was blended with 20 wt% of LCP in a twin-screw extruder with the take-up speed varied to achieve blends with different LCP fiber dimensions. In the second stage, these blends were processed both below and above the Tm of the LCP by extrusion and injection molding. 

Block copolymers, polymer blends, polymers at interfaces, liquid crystalline polymers, polymers with novel optical and electronic properties, cross-linked polymers (including elastomers and thermosets), and biocompatible polymers are all areas of active research that are beyond the scope of this chapter. 

Novel Composites from Blends of Amorphous and Semicrystalline Engineering Thermoplastics with Liquid-Crystalline Polymers... 

The objective of this work has been to generate films, tapes or ribbons which might serve as a prepreg from blends of either an Ultem or a PEEK or a high molecular weight PPS with various liquid crystalline polymers, to identify the parameters that control the formation of reinforcing microfibrils of LCP phase, and to study the mechanical properties of the composite films. 

The concentration of Vectra in the blend also shows a pronounced effect on the drawability and the modulus of the Ultem/Vectra blend sheets. Under the same extrusion conditions, the drawability, as characterized by the maximum draw ratio, decreased with increasing content of the liquid crystalline polymer in the blend. However, when the draw ratio is similar the higher the content of the reinforcing phase, the higher the torsional modulus. The highest value of the torsional modulus was obtained for the materials with only 10 X Vectra because of the higher drawability of the system. 

By analogy with small molecule liquid crystals, where the type of liquid crystal formed is used as a test for miscibility, it is expected that all polymer molecules that form the same type of liquid crystalline phase will be miscible (4). This is in contrast to more traditional polymers where miscibility is the exception rather than the rule. The present work will suggest which of these concepts is applicable to liquid crystal polymer blend systems. 

The purpose of the present work is to extend the above studies to blend systems consisting of two components, each of which is capable of forming a liquid crystalline phase in the melt. Such blends become of increasing importance with the recently reported finding (6) that it is possible to observe synergisms in mechanical properties in these systems. Our previous studies in this area have suggested that the theories of traditional polymer blend systems (7.8) are applicable to these blends. This paper is a further study of the applicability of these concepts. 

Very little work has appeared in the literature which deals with blends in which the component materials can cocrystallize. It is generally believed (16.17) that a requirement for cocrystallization is that there must be a close matching of the polymer chain conformations and of crystalline dimensions. Also, some level of miscibility should exist between the two polymers and the crstallization kinetics cannot be very different. Certainly, in the case of liquid crystalline polymers, in general, these requirements would be expected to be met. Some of our recent work (8) has suggested, however, that not all liquid crystal polymers do cocrystallize. The present work suggests that in certain cases it may be possible to achieve this effect. 

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