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  • Column liquid chromatography  (7)
  • Polymer and Materials Science  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Sample size and retention values in gradient liquid chromatography of synthetic polymers (1996)
    Springer
    Chromatographia 42 (1996), S. 185-190 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gradient elution of synthetic polymers ; Polystyrene and various styrene copolymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention times in gradient liquid chromatography of synthetic polymers are often dependent on sample size. They increase with column load if the separation mechanism is governed by a solution process but decrease with increasing load if the mechanism is governed by adsorption. Since retention times independent of sample size are a prerequisite for peak identification as well as for the correct measurement of elution bands of samples with a broad distribution, measures to counteract sample-size effects deserve attention. Usually both solubility and adsorption are effective in gradient liquid chromatography of synthetic polymers. An appropriate balance of both effects is suitable for diminishing the influence of sample size on retention time of synthetic polymers. Ternary gradients allowing independent control of solubility and adsorption are promising.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269651
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  • 2
    Electronic Resource
    Electronic Resource
    Control of adsorption and solubility in gradient high-performance liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 557-563 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Copoly(styrene/methyl methacrylate) ; Gradient elution ; Precipitation chromatography of polymers ; Solubility of polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Copolymers from styrene and methyl methacrylate (MMA) were separated by both normal and reversedphase gradient chromatography. Both modes could be performed by sudden-transition gradients where the polymers were injected into a non-solvent whose polarity was either rather low (e.g.,n-heptane) or high (e.g., acetonitrile). Then the solvent strength of the starting eluent was rapidly increased to a given level by addition of dichloromethane. Under properly defined conditions, the sample components still remained on the column. Elution could be triggered off by the steady addition of another non-solvent whose polarity was opposite of that of the starting non-solvent. Thus, the mixture of five copolymers with MMA content ranging from 14 to 84% could be separated on a polar cyanopropyl column by injection inton-heptane and elution through acetonitrile (normal phase mode) and on a RP C18 column by injection into acetonitrile and elution throughn-heptane (reversed-phase mode), provided that in both modes about 30% dichloromethane was added to the starting non-solvent. The elution sequence in the reversed-phase mode was opposite to that in the normal-phase mode, obeying the approved polarity rules of chromatography in both cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02268279
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  • 3
    Electronic Resource
    Electronic Resource
    Control of adsorption and solubility in gradient high performance liquid chromatography. Part 4. Sudden-transition gradient elution of styrene/ethyl methacrylate copolymers in reversed phase mode (1994)
    Springer
    Chromatographia 39 (1994), S. 170-174 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Copoly(styrene/ethyl methacrylate) ; Gradient elution ; Precipitation chromatography of polymers ; Solubility of polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Copolymers from styrene and ethyl methacrylate have been separated according to composition byn-heptane gradients on a C18 bonded phase after injection into acetonitrile and subsequent sudden transition to a concentration of either dichloromethane or tetrahydrofuran between 30 and 50% or 20 and 50%, respectively. Acetonitrile is a polar non-solvent for the copolymers under investigation and ensures proper retention of the samples on a non-polar stationary phase. Dichloromethane and tetrahydrofuran are good solvents of moderate polarity. The addition of, e.g., 30 vol% of one of these solvents increased the dissolution power of the starting eluent but not to the extent necessary for elution. The latter was achieved by the addition ofn-heptane, which is a non-solvent for the polymers investigated. Thus, its eluting power must be understood as the consequence of its modifying effect on the polarity of the eluent mixture. The higher the content of copolymer in ethyl methacrylate the earlier it was eluted. Since acetonitrile andn-heptane are only partly miscible, phase diagrams were measured after the addition of either tetrahydrofuran or dichloromethane as a third component. Homogeneous mixtures were obtained on addition of about 30% solvent (one of both of the latter).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274496
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  • 4
    Electronic Resource
    Electronic Resource
    Die Technik der oscillopolarographischen Messungen. R. Kalvoda, aus dem Tschechischen in die deutsche Sprache übersetzt von Ch. Stockmann, Verlag Theodor Steinkopff, Dresden und Leipzig 1965, 187 S., 90 Abb. und 4 Tab. geb. DM 29,30 (1965)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 16 (1965), S. 922-923 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19650161018
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  • 5
    Electronic Resource
    Electronic Resource
    Separation of copoly(styrene/acrylonitrile) samples according to composition under reversed phase conditions (1991)
    Springer
    Chromatographia 32 (1991), S. 107-112 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Styrene/acrylonitrile polymers ; Gradient elution ; Solubility effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Copoly(styrene/acrylonitrile) samples (S/AN) have been repeatedly separated according to composition by gradient HPLC with alkane hydrocarbons as a starting eluent A and dichloromethane (DCM) or tetrahydrofuran (THF) as a solvent B. In these systems, retention increased with AN content of the copolymers. The chemical nature of the column packings used had almost no influence on the retention of S/AN samples. The present paper shows thatn-pentane andn-heptane, when used in a given volumetric gradient with DCM+20% methanol as a solvent B, lead to identical solution characteristics of S/AN on silica columns. A similar result was obtained on C18 columns withn-heptane or cyclohexane, whereas gradient elution with toluene as a starting eluent caused insufficient resolution. Reversed phase separation of S/AN copolymers could be achieved on polystyrene gel columns through gradients with methanol as a starting eluent and DCM or THF as a solvent B. In both systems, retention decreased with increasing AN content of the copolymers. The elution characteristics were almost linear in the range 0–20 wt% AN. This behaviour can be understood in the context of polymer solubility: in both systems, the solubility borderline of S/AN has a distinct maximum at about 25 wt% AN. Reversed phase separation was achieved at the lefthand slope of these curves where the dissolution of a sample with a higher AN content requires less DCM or THF solvent than the dissolution of copolymers which are poorer in AN. This idea predicts that samples with more than 25 wt% AN should elute later than S/AN whose composition is near to the solubility maximum. This indeed was found with a copolymer containing 36.2 wt% AN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02325011
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  • 6
    Electronic Resource
    Electronic Resource
    Gradient high performance liquid chromatography of block copolymers of styrene andt-butyl methacrylate II. Association phenomena in mixtures of block copolymer with polystyrene (1992)
    Springer
    Chromatographia 34 (1992), S. 363-368 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Precipitation chromatography of polymers ; Block copolymers of styrene-butyl methacrylate ; Association phenomena
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Block copolymers of styrene andt-butyl methacrylate can be analysed by methanol/tetrahydrofuran gradients on C18 or phenyl bonded phase columns. On both of these columns, retention increases with styrene content of the samples. At 50°C, the retention of PS or a block copolymer containing 45% styrene was longer on the phenyl than the C18 columns. This indicates the contribution of adsorption to retention on phenyl bonded phase columns. Lowering the temperature from 50 to 30°C caused earlier elution of part of the sample from the phenyl phase. On a C18 phase the same drop in temperature improved the shape of the peak, which also started later than at 50°C. This effect of temperature is generally observed in polymer retention due to an adsorption mechanism, whereas increasing retention with decrease in temperature is characteristic of a precipitation mechanism. The block copolymer investigated contained 15% free polystyrene precursor which could not be separated from the block copolymer under the conditions employed. The addition of 20% PS homopolymer with a molecular weight similar to that of the styrene block in the copolymer showed that the polystyrene eluted together with the block copolymer, whereas the addition of PS homopolymer with a much higher molecular weight caused an extra peak at the expected elution time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02268369
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  • 7
    Electronic Resource
    Electronic Resource
    Control of adsorption and solubility in gradient high-performance liquid chromatography. Part 2: Sudden-transition gradient elution of styrene/ethyl methacrylate copolymers (1994)
    Springer
    Chromatographia 38 (1994), S. 559-565 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Copoly(styrene/ethyl methacrylate) ; Gradient elution, sudden transition ; Precipitation chromatography of polymers ; Solubility of polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Copolymers from styrene and ethyl methacrylate have been separated according to composition by methanol gradients on a cyanopropyl column after injection inton-heptane and a subsequent rapid increase of dichloromethane (DCM) concentration from zero to a constant value in the range from 10 to 40%. Retention and resolution in sudden-transition gradients increased with decreasing DCM concentration. The gradient rate was varied between 2.5 and 7.5%/min with optimum resolution at 2.5% min. At a level of 20% DCM and a gradient rate of 5%/min, the separation of a mixture of five copolymers in a sudden-transition gradient was the same as with the corresponding common gradient, i.e., with injection into a mixture ofn-heptane and 20% DCM. Elution was also achieved at a level of 20% DCM by continuous addition of tetrahydrofuran (THF) instead of methanol. With THF, the peaks appeared later than with methanol in spite of the fact that methanol is a non-solvent and THF a good solvent for the polymers investigated. This indicates that elution was, in the first instance, caused by the polarity of the eluent. The elution characteristics of the copolymers in the system heptane/methanol at constant DCM concentration were basically similar to the already known characteristics iniso-octane/methanol at constant THF concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277154
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  • 8
    Electronic Resource
    Electronic Resource
    Control of adsorption and solubility in gradient high performance liquid chromatography. Part 3. Sudden-transition gradient elution of styrene/ acrylonitrile copolymers (1994)
    Springer
    Chromatographia 38 (1994), S. 749-755 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Copoly(styrene/acrylonitrile) ; Gradient elution ; Precipitation chromatography of polymers ; Solubility of polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Copolymers from styrene and acrylonitrile could be separated according to composition by gradient elution through methanol after injection inton-heptane and sudden addition of 50, 60, or 70 vol% tetrahydrofuran. The peak sequence was the same as with a common binary gradientn-heptane/tetrahydrofuran, i.e., retention increased with acrylonitrile content of the samples. With copolymers containing 37, 31, or 26% acrylonitrile, the elution characteristics in the ternary systems could be logically extrapolated towards the points measured in the corresponding binary gradient system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269631
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  • 9
    Electronic Resource
    Electronic Resource
    Organophosphorus antioxidants action mechanisms and new trendsPaper presented at the “16th International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 14-17, 1994. (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 232 (1995), S. 239-246 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Phosphite and phosphonite esters can act as antioxidants by three basic mechanisms depending on their structure, the nature of the substrate to be stabilized and the reaction conditions. All phosph(on)ites are hydroperoxide-decomposing secondary antioxidants. Their efficiency in hydroperoxide reduction decreases in the order phosphonites 〉 alkylphosphites 〉 arylphosphites 〉 hindered arylphosphites. Five-membered cyclic phosphites are capable of decomposing hydroperoxides catalytically due to the formation of acidic hydrogen phosphates by hydrolysis and peroxidolysis in the course of reaction. Hindered aryl phosphites can act as chain-breaking primary antioxidants being substituted by alkoxyl radicals and releasing hindered aryloxyl radicals which terminate the radical chain oxidation. At ambient temperatures, the chain-breaking antioxidant activity of aryl phosphites is lower than that of hindered phenols, because the rate of their reaction with peroxyl radicals and their stoichiometric inhibition factors are lower than those of phenols. In oxidizing media at medium temperatures, however, hydrolysis of aryl phosph(on)ites takes place giving hydrogen phosph(on)ites and phenols which are effective chain-breaking antioxidants.2,2,6,6-Tetramethyl- and 1,2,2,6,6-Pentamethylpiperidinyl phosphites and phosphonites (HALS-phosph(on)ites) surpass many common phosphites, phenols and HALS compounds as stabilizers in the thermo- and photo-oxidation of polymers. Their superior efficiency is probably due to an intramolecular synergistic action of the HALS and the phosph(on)ite moieties of their molecules.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1995.052320115
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  • 10
    Electronic Resource
    Electronic Resource
    Photochemistry and photopolymerization activity of perester derivatives of benzophenone (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 1169-1178 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The spectroscopic properties and photopolymerization activities of a mono- and tetraperester derivative of benzophenone are examined and compared with those of benzophenone. Their photopolymerization activity in methyl methacrylate (MMA) and an ethoxylated bis-phenol-A diacrylate have been studied using a combination of gel permeation chromatography (GPC), and real time Fourier transform infrared spectroscopy (RTFTIR) as well as the commercial pendulum hardness test. Using GPC analysis on the poly(methyl methacrylate) samples the tetra--t-butyl perester derivative of benzophenone is found to give a higher weight average (Mw) and number average (Mn) molecular weight polymer than that produced using the mono perester. For the two peresters of benzophenone photopolymerization efficiency using real time FTIR increases with increasing initiator concentration, and no self-termination is observed up to 0.75% w/w concentration with the mono perester derivative being the more efficient initiator. Similar results were obtained using the commercial pendulum hardness tester with a triacrylate/epoxyurethane acrylate resin with benzophenone exhibiting the lowest activity. Photopolymerization activities of the initiators correlate well with their spectroscopic properties. The phosphorescence quantum yield is higher for the monoperester than the tetraperester derivative and is consistent with a shorter lifetime and lower photolysis quantum yields in 2-propanol. Compared with benzophenone, phosphorescence analysis indicates that the perester groups impart a degree of charge-transfer content to the molecule which is consistent with the degree of substitution. Ketyl radical formation on microsecond flash photolysis follows the order benzophenone 〉 mono- 〉 tetraperester derivative and is consistent with the phosphorescence quantum yields. On nanosecond laser flash photolysis in nitrogen-saturated acetonitrile, triplettriplet absorption is extremely weak for both the perester derivatives, being stronger for the monoperester.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1991.070420501
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