N I biphase

In addition to visual observation by polarizing microscopy, the biphase temperature range may be determined by methods such as DSC or broad line NMR (the fraction of nematic component present at any given temperature can be determined from the relative intensity of the narrow line associated with isotropic motion). 

Small isotropic droplets, c, 1 im or smaller in size, are not easily resolved by microscopy. A minor isotropic component is often found to trail at the lower temperature range within the biphase and its presence can be overlooked [25]. Yet a finely dispersed I phase can be expected to influence rheological behavior, order and orientation dynamics in the mesophase, as well as the mechanical properties of the resulting solid phase. In contrast to microscopy or DSC which detect macroscopic behavior, NMR provides a molecular or segment level view of morphology and cannot distinguish between phase and microphase separation. Thus accurate biphase delineation may be delicate to accomplish. We should further note that the customary dynamic scans do not provide the equilibrium value of biphase width but rather an apparent value as determined by thermal history (section 6.5). 

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Influence of chain length and spacer length on Tg, on the heat capacity increment at Tg (ACp), and the shape of the Cp(T) curve win be presented in the first paper (preliminary results can be found in (3)). Subsequently, we will address influence of thermal history in the isotropic phase and N+I biphase, physical aging below Tg and Tg in blends of LCPs. Finally, an interpretation of the macroscopic data in terms of molecular organization in these and other nematic LCP glasses will be attempted. 

The polymers were formed by condensation of 4,4dihydroxy-benzene and 2,2 -dimethyl-4,4 dihydroxyazoxybenzene with various diacid chlorides acting as flexible spacer groups Polydisperse homopolymers and copolymers, sharp fractions of homopolymers and mixtures of polydisperse polymers with a low mass mesogen were investigated. Supercooling at the mesophase-isotropic and solid-mesophase transitions, sharpness of the nematic-isotropic transition (range of N+I biphase), polymer crystallization from the mesophase melt, and enhancement of crystallinity upon addition of a low mass nematic, were studied. 

The extent of correlation between repeating units is dependent on molecular mass entropy of isotropization and nematic order parameter at the l/N transition both increase rapidly with molecular mass, before leveling off. The N/I transition temperature T l also follows a similar trend, leveling off at Mn 10,000. As a result of this molecular mass dependence of Tni> a N+I biphase is observed in polydisperse samples. 

N+I biphase. The nematic-isotropic intervals as observed by microscopy provide a very inadequate representative of the extent of the N+I biphase. This is clearly illustrated on Fig. 1, where the [T2 Tc interval measured by microscopy is considerably smaller than the biphase observed by NMR. Microscopic observation under slow rates of scanning with measurement of the transmitted light intensity by means of a photomultiplier, to eliminate observer subjectivity, gives substantially the same results. Fig. 1 shows that the N+I biphase extends well into what is seemingly a "homogeneous nematic phase. In polymer DDA-9, for example, the shortest chains become isotropic approximately 90 before chains whose mass is Mn> 10,000 and act as isotropic "contaminants of the polydisperse mesophase. 

The N + I biphase finds its origin in polydispersity in chain length coupled with polydispersity in chain flexibility and is observed within a temperature range delineated by and T. Polarizing microscopy observation of the biphase in Pi (n = 10, M = 18 700) is illustrated in Figures 6.5a-c for three different conditions of thermal history [42]. It is apparent that textures and biphase width both depend on sample thermal treatment. 

Veiy recently it was disclosed, that the water-soluble dinuclear complex obtained in the reaction of [ RhCl(COD) 2] and 11-mercaptoundecanoic acid catalyzed the aqueous/organic biphasic hydroformylation of styrene and various arene-substituted styrenes with good activity and useful selectivity to the branched aldehydes (Scheme 4.6) [82], Below pH 4 the acid form of the complex [ Rh(p-S(CH2)ioC02H)(COD) 2] precipitated virtually quantitatively but could be redissolved in water on addition of base. Importantly, higher olefins could also be hydroformylated by this catalyst (for 1-octene TOP = 17.5 h at 55 °C, 35 bar syngas, n/i = 1.0). 

An ionic liquid was fully immobilized, rather than merely supported, on the surface of silica through a multiple-step synthesis as shown in Fig. 15 (97). A ligand tri(m-sulfonyl)triphenyl phosphine tris(l-butyl-3-methyl-imidazolium) salt (tppti) was prepared so that the catalyst, formed from dicarbonylacetylacetonate rhodium and the ligand (P/Rh = 10), could be soluble in both [BMIMJBFq and [BMIM]PF6. The supported ionic liquid-catalyst systems showed nearly three times higher rate of reaction (rate constant = 65 min ) that a biphasic system for the hydroformylation of 1-hexene at 100°C and 1500 psi in a batch reactor, but the n/i selectivity was nearly constant the same for the two ( 2.4). Unfortunately, both the supported and the biphasic ionic liquid systems exhibited similar metal leaching behavior. 

Hydroformylation of Mid Range Olefins - Rhodium/tppts catalysts exhibit low catalytic activity in the hydroformylation of mid range olefins (C5-Cg) in a two phase system due to the much lower solubility of such olefins in water. In the Rh/tppts catalysed biphasic hydroformylation of 1-hexene, for example the conversion is only 11-22% with a n/i ratio of aldehydes of 98/2.353,373 The rate of 1-hexene hydroformylation catalysed by Rh/tppts increased by a factor 2.3 when subjected to ultrasound (35 kHz) and high stirring rates.360,361... 

Kalck et /.96,359,362 studied the biphasic hydroformylation of 1-hexene using water soluble dinuclear species such as Rh2(m-S-lBu)2(CO)2(tppts)2 and C0/H20 where H20 acts both as a solvent and hydrogen source according to the water gas shift reaction (Equation 2). The turnover frequency (TOF) obtained was 40 h 1 and the n/i ratio of the aldehyde 96/4.96 Using RhH(CO)(tppts)3 catalysts lower rates were obtained under the same conditions.96... 

Rh/76 (Table 4 n=l, x=0, R= Me, Bu), which should be able to induce micelle formation, were used as catalysts in the biphasic hydroformylation of 1-dodecene.371 The conversion was 80%, the n/i ratio 60/40 with no carry-over of the rhodium catalyst into the organic phase.371... 

The extension of the biphasic principle to higher olefins may be accomplished by changing the ligand [25] from TPPTS, e.g., to bisphosphines, some of which have already been proven to be valuable tools to increase the specific activity combined with high n/i selectivity [5]. Increasing the specific (better intrinsic) activity of rhodium in the aqueous two-phase system may be coupled with understanding of the relevant mass transport phenomena. In this case the role of the phase boundaries as a potential barrier for the chemical reaction will have to be carefully analyzed. 

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