On the miscibility of liquid crystalline polymers (original) (raw)
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Macromolecules, 1994
ABSTRACT The miscibility behavior of blends of high molecular weight isotactic poly(propylene) (it-PP) and isotactic poly(1-butene) (it-P1B) has been investigated by a combination of optical and scanning electron microscopies, differential scanning calorimetry, and dynamic mechanical analysis. The results of these investigations demonstrate that for the molecular weights investigated, it-PP and it-P1B form blends that are partially miscible in the liquid state. Liquid-liquid demixing is observed by optical microscopy at temperatures above the melting temperature of the it-PP component and is also inferred from scanning electron micrographs of the freeze fracture surface of quenched blends after extraction of the it-P1B component with cyclohexane. It-PP spherulites grow through both liquid phases at relative rates that depend markedly on the crystallization temperature. The complex multiple-melting behavior of the isotactic poly(propylene) component in the blend is explained in terms of a bimodal distribution of it-PP lamellar crystals which results from crystal growth in the phase-separated liquid. The heterogeneous nature of the mixed liquid is consistent with the upper critical solution temperature behavior observed in our previous study of blends of atactic poly(propylene) and atactic poly(1-butene). Finally, the dynamic mechanical analysis data are explained in terms of a liquid-liquid demixing process that results in a significant degree of phase mixing.
Polymer, 1997
The miscibility of liquid crystalline poly(p-oxybenzoate-cop -phenyleneisophthalate) (HIQ) and polycarbonate (PC) was investigated with differential scanning calorimetry (d.s.c.). It was found that blends of liquid crystalline HIQ and PC showed a single glass transition temperature across the whole composition range. Annealing these blends at temperatures slightly above the melting point of HIQ, ester exchange occurred as confirmed both by i.r. and n.m.r. spectroscopy. The apparent miscibility of HIQ and PC was caused by this reaction. The blends retained liquid crystalline characteristics in the first few reaction minutes. As the transesterification continued, the bisphenol-A segment in PC reacted with both isophthalate and oxybenzoate segments in HIQ. This resulted in amorphous polymers. These amorphous polymers exhibited a single glass transition temperature higher than that for both pure polymers. Q 1997 Elsevier Science Ltd.
Journal of Applied Polymer Science, 2003
The phase behavior and the crystallization kinetics of blends composed of isotactic polypropylene (iPP) and linear low-density polyethylene (LLDPE) were investigated by differential scanning calorimetry. The phase behavior indicates the formation of separate crystals of iPP and LLDPE at each investigated blend composition. The crystallization trace reveals that iPP crystallizes in its normal range of temperatures (i.e., at temperatures higher than that of LLDPE), when its content in the blend is higher than 25% by weight. In the blend whose iPP content is as high as 25%, at least a portion of iPP crystallizes at temperatures lower than that of LLDPE. This behavior has been proposed by Bassett to be attributed to a change in the kind of nucleation from heterogeneous to homogeneous. From the Avrami analysis of the isothermal crystallization of iPP in the presence of molten LLDPE, n values close to 2 are always obtained. According to our previously proposed interpretation of the Avrami coefficient, it can be related to the crystallite fractal dimension, through d ϭ n ϩ 1, which gives values close to 3, according to the spherulitic observed morphology. The kinetics parameter, i.e., the half-time of crystallization, and the kinetic constant k show that a decrease in the overall rate of crystallization of iPP occurs on blending. Optical microscopy photographs, taken during the cooling of the samples from the melt, confirm the above results and show increasingly less resolved spherulite texture on increasing LLDPE content in the blend. The diffusion parameters evaluated for the neat polymers and for the blends in dichloromethane, which give information on the miscibility in the amorphous state, show that the diffusional behavior of the blends is governed by iPP, suggesting a two-phase amorphous state.
Miscibility of a nematic liquid crystalline polymer pair
Polymer, 2001
This work investigates the miscibility of two commercially important thermotropic main chain liquid crystalline polymers (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, by probing the free volume of the blends and comparing this to rule-of-mixtures values of the two components. q
X-ray microscopy of novel thermoplastic/liquid crystalline polymer blends by mechanical alloying
Macromolecular Rapid Communications, 1998
Incorporation of liquid crystalline polymers (LCPs) into commodity polymers remains a challenge in the design of high-performance, low-cost polymeric blends. Blends of a thermoplastic polymer and a nematic LCP are produced here by mechanical alloying. Functionality sensitive X-ray microscopy reveals LCP dispersions as small as 100 nm in diameter. Intimate mixing remains upon subsequent melt processing, indicating that mechanical alloying is suited for applications such as recycling.
Science and Engineering of Composite Materials, 1989
Blends based on two different thermoplastic polymers (Polycarbonate and the Polyetherimide Ultem) have been studied to verify the effect of the inclusion of a low amount of two different types of thermotropic liquid crystalline polymers (the copolyesters PET-PHB60 by Kodak and K161 by Bayer) on the rheological and mechanical properties of the matrices. Moreover, the morphological analysis of the polymers and of the blends was performed and related to their mechanical behavior.
Morphology and properties of blends of polyethylene with a semiflexible liquid crystalline polymer
Journal of Applied Polymer Science, 1995
Blends of three polyethylene (PE) samples (two HDPE grades and LLDPE) with an experimental sample of a semiflexible liquid crystalline polymer (SBH 1:1:2 by Eniricerche) have been prepared in a Brabender compounder. The processing‐aid effect of the LCP has been demonstrated by the decreased energy required for extruding the blends, as compared to that needed for neat PE. The thermal properties, as studied by differential scanning calorimetry (DSC), have shown that the two components of the blends are immiscible. However, the dispersed SBH phase has been found to act as a nucleating agent for the crystallization of LLDPE, whereas no such effect was observed for HDPE. This has been taken as an indication that the phase interactions of SBH with LLDPE are more pronounced than with HDPE. The morphological study of the blends, done by scanning electron microscopy (SEM), has confirmed this conclusion. In fact, the SBH particles show a much better dispersion and a narrower size distribution...