Carboxylated viscosity-concentration

In the production of viscose, the workers are exposed to carbon disulfide. In addition to inhalation exposure, absorption through the skin may be important. It is strongly neurotoxic. Its TLV is 10 ppm and the Finnish OEL 5 ppm. Both carry the skin notation. Urinary 2-thiothiazolidine-4-carboxylic acid concentration can be used for biological monitoring of exposure to carbon disulfide. Its ACGIH BEI is 5 mg/g creatinine (4 mmol/mol creatinine) and the BEI given by the FIOH 2.0 mmol/mol creatinine. 

Figure 2. Relative viscosity-concentration plots in toluene at 25 C for poly 06-methylstyrene (Mn 6,000) end -capped with ( ) Mg carboxylate, (A) Mg sulfonate and ( ) dimethyl benzyl ammonium chloride.

During extrusion, an increase of the shear rate in the presence of water intensifies degradation, which is reflected in the increase of the carboxylic groups concentration and the decrease of the viscosity of the final product. 

When equal amounts of solutions of poly(ethylene oxide) and poly(acryhc acid) ate mixed, a precipitate, which appears to be an association product of the two polymers, forms immediately. This association reaction is influenced by hydrogen-ion concentration. Below ca pH 4, the complex precipitates from solution. Above ca pH 12, precipitation also occurs, but probably only poly(ethylene oxide) precipitates. If solution viscosity is used as an indication of the degree of association, it appears that association becomes mote pronounced as the pH is reduced toward a lower limit of about four. The highest yield of insoluble complex usually occurs at an equimolar ratio of ether and carboxyl groups. Studies of the poly(ethylene oxide)—poly(methacryhc acid) complexes indicate a stoichiometric ratio of three monomeric units of ethylene oxide for each methacrylic acid unit. 

Solution Deposition of Thin Films. Chemical methods of preparation may also be used for the fabrication of ceramic thin films (qv). MetaHo-organic precursors, notably metal alkoxides (see Alkoxides, metal) and metal carboxylates, are most frequently used for film preparation by sol-gel or metallo-organic decomposition (MOD) solution deposition processes (see Sol-GEL technology). These methods involve dissolution of the precursors in a mutual solvent control of solution characteristics such as viscosity and concentration, film deposition by spin-casting or dip-coating, and heat treatment to remove volatile organic species and induce crystaHhation of the as-deposited amorphous film into the desired stmcture. 

A different approach to design a self-calibrating dye was proposed [70], in which a viscosity-sensitive molecular rotor (2-cyano-3-(4-dimethylaminophenyl) prop-2-enoic acid) was covalently linked to a reference dye, 7-methoxycoumarin-3-carboxylic acid, which exhibited no viscosity sensitivity (40, Fig. 13). A ratiometric measurement, that is, rotor emission relative to reference emission, was shown to be widely independent of dye concentration [70]. However, the design of such a ratiometric dye poses some challenges because of resonance energy transfer from... 

Generally, two to three preheater sections are used for the product heat-up by using nitrogen, and two to three sections are required to reach the final viscosity. Cooling is carried out either in an additional compartment or with a fluid bed. Typically, for a viscosity increase from 0.60 up to 1.0, the crystallinity increases to ca. 62 vol%, and the carboxyl end group concentration decreases by approximately 10-15 mol/t. This equates to both esterification and transesterification contributing half of the IV increase if side reactions are neglected. 

Figure 5.23 Variation in the concentration of carboxylic end groups and intrinsic viscosity during the postcondensation of PET powder produced from DMT (1) and TPA (2) prepolymers (7, 240 °C) [49]. From Gerking, L., Modifications of fiber properties by polymer and within spinning line, presentation (Paper 52b) given at the 32nd International Man-Made Fibre Congress, 22-24 September, 1993, Dornbirn, Austria, and reproduced with permission of EMS Inventa-Fischer, GmbH Co. KG...

The key to a controlled molecular weight build-up, which leads to the control of product properties such as glass transition temperature and melt viscosity, is the use of a molar excess of diisopropanolamine as a chain stopper. Thus, as a first step in the synthesis process, the cyclic anhydride is dosed slowly to an excess of amine to accommodate the exothermic reaction and prevent unwanted side reactions such as double acylation of diisopropanolamine. HPLC analysis has shown that the reaction mixture after the exothermic reaction is quite complex. Although the main component is the expected acid-diol, unreacted amine and amine salts are still present and small oligomers already formed. In the absence of any catalyst, a further increase of reaction temperature to 140-180°C leads to a rapid polycondensation. The expected amount of water is distilled (under vacuum, if required) from the hot polymer melt in approximately 2-6 h depending on the anhydride used. At the end of the synthesis the concentration of carboxylic acid groups value reaches the desired low level. 

Photon correlation spectroscopy, carried out under very dilute conditions, has unambiguously demonstrated the expansion of carboxylic emulsion polymers at high pH, but it may not always be useful in predicting properties of practical interest. Of special concern is the apparent decrease in the intrinsic ionization constant of surface carboxyls at very low concentration. Since most uses of emulsion polymer occur at high concentrations, the measurement of particle-particle interactions is of great practical importance (21J. It has been found that the sedimentation and viscometric techniques closely reflect viscosity changes in latexes at much higher solids. Extension of the PCS approach to more concentrated systems is underway but not without problems (22). 

These results on viscosity behavior are in good agreement with the results of the latex characterization by conductometric titration (see Figures 5 6), which showed that the carboxyl groups are uniformly distributed within the particle for the semi-continuous latex, whereas in the batch latex the carboxyl groups are concentrated at the water-particle interface. 

The viscosity of anhydrous Nd-carboxylates in organic solvents significantly increases with the concentration of the Nd-salt. At reasonable concentrations (10 wt. %) the viscosities are rather high [223]. A significant reduction of the solution viscosity of, for example, NdV is achieved by the addition of small amounts of aluminum alkyls [154,155]. 

For ternary Nd-carboxylate-based catalyst systems only two studies seem to be available for which M,vi/MNd-ratios were investigated. Wilson compared the two Nd precursors neodecanoate and neodecanoate/neononadecanoate in the ternary catalyst system Nd(carboxylate)3/DIBAH/tBuCl. An increase of mNd/100g(BD) in the range 0.12 to 0.19 resulted in the reduction of Mooney viscosities from 60 to 25 MU [183]. Sylvester et al. also varied the amount of Nd at constant BD concentrations. An increase of mNd/100g(BD) from 0.025 to 0.30 reduced Mv from 750 kg mol-1 to 300 kg mol-1 [88]. 

Contrary to viscosity measurements GPC provides number average molar mass data (Mn). For a few studies on the polymerization of BD with Nd-carboxylate-based catalyst systems GPC was systematically applied for the monitoring of Mn as a function of monomer conversion. In these studies three catalyst systems were used (1) NdV/DIBAH/EASC [178], (2) NdV/TIBA/EASC [179] and (3) NdO/TIBA/DEAC [188]. In the first two studies linear Mn-conversion plots were obtained at various molar ratios Al/ Ndv- In these studies, however, molar mass data at low monomer conversions (<20%) are lacking and positive intercepts on the Mn-axis were found. For the ternary catalyst system NdO/TIBA/DEAC used in the third of these studies the concentrations of Nd and TIBA were varied. A linear increase of Mw and Mn on monomer conversion was found. Deviations from linearity were also observed for low monomer conversions. 

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