Miscibility of a nematic liquid crystalline polymer pair Tsung-Tang Hsieh a , Carlos Tiu b , George P. Simon c, * a UMC, Advanced Technology Development, Hsin-Chu 30077, Taiwan, ROC b Department of Chemical Engineering, Monash University, Clayton, Vic. 3800, Australia c School of Physics and Materials Engineering, Monash University, Clayton, Vic. 3800, Australia Received 26 January 2001; received in revised form 30 March 2001; accepted 7 May 2001 Abstract ThisworkinvestigatesthemiscibilityoftwocommerciallyimportantthermotropicmainchainliquidcrystallinepolymersLCPs),Vectra A950 and Vectra B950, using dynamic mechanical analysis DMA), differential scanning calorimetry DSC) and positron annihilation lifetime spectroscopy PALS). Although previously reported to be either miscible or show a compositional-dependent miscibility, they are shown here to be immiscible based on DMA, DSC and PALS results. The latter technique is somewhat more novel in its use to assess miscibility,byprobingthefreevolumeoftheblendsandcomparingthistorule-of-mixturesvaluesofthetwocomponents. q 2001Elsevier Science Ltd. All rights reserved. Keywords: Thermotropic liquid crystalline polymer; Miscibility; Blend 1. Introduction Miscibility between different liquid crystalline polymers LCPs)canbeaninterestingissuegiventhedualpolymeric and liquid crystalline nature of these materials. For exam- ple,thebehaviourobservedforlowmolecularweightliquid crystals LMWLCs) is that those of the same class e.g. nematic) are generally miscible [1], whereas blends of different polymers without strong interactions between different macromolecules tend to be immiscible [2]. The relatedliteraturetodateshowsthatthepolymericcharacter- istics of LCPs often dominate as far as miscibility is concerned, since many nematic LCPs have been found to be immiscible [3±6] and, occasionally, miscibility of LCPs of the different classes e.g. nematic and smectic [7]) has been reported. Miscibility of polymer pairs is often determined by ther- mal and/or mechanical methods, such as differential scan- ning calorimetry DSC) or dynamic mechanical analysis DMA). For miscible systems, a single glass transition temperatureT g )isobservedandmovesintemperatureloca- tion in proportion to concentrations of the constituents, as well as often varying likewise in intensity. For immiscible blends, two distinct T g s belonging to the pure components occur, remaining constant in temperature location, the peak size varying in magnitude according to the component concentration. Morphological observation such as by electron microscopy can also serve as complementary evidence to con®rm the conclusion drawn from above- mentioned techniques, provided the electron densities of the various phases differ suf®ciently. Whilst this may be enhanced by staining, for example, not all polymers are so amenable to this technique Ð LCPs with low solvent uptake being an example of this. Total miscibility between two widely used and commer- cially important LCPs, Vectra A950 and Vectra B950, was reported recently [8], although an earlier study by Kenig et al. [9] on the same materials indicated a more complicated scenario, composition-dependent miscibility. Our research laboratory has reported results on a number of LCP blends in recent times [6,10±12] in terms of their rheology, misci- bility and free volume. The aim of this paper is to investi- gate this system and attempt to clarify the difference in miscibilities reported by both groups [8,9] using similar techniques.Inaddition,amorenovelsub-atomictechnique, positron annihilation lifetime spectroscopy PALS), which probes excluded or free volume in the blends is used to assess the miscibility or otherwise of these polymers. Given that synergies are often observed in the blending of two LCP phases [10] such as lower viscosity or higher modulus) and that the components of this blend series are readily available albeit often in a ®lled form) it is a blend worthy of further investigation. Polymer 42 2001) 8007±8011 0032-3861/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII:S0032-386101)00331-7 www.elsevier.nl/locate/polymer * Corresponding author. Fax: 161-3-9905-4940. E-mail address: george.simon@spme.monash.edu.au G.P. Simon).