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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 4106-4113 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0887-624X
    Keywords: copolycarbonate ; bisphenol A ; tetrabromobisphenol A ; end group ; analysis ; properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The types and concentrations of end groups present in bisphenol A-tetrabromobisphenol A copolycarbonates (BA-TBBA coPCs) have major effects on the copolymer solution washability and thermal stability. Six types of coPC end groups are possible: two by monophenol capping of each comonomer, two phenolics (BA-OH and TBBA-OH), and two carbamates (one from each comonomer). BA-TBBA coPCs were prepared by typical solution and interfacial methods and their phenolic and carbamate end group concentrations were correlated with their solution washability and thermal discoloration. Both phenolic and carbamate end groups proved deleterious to these two copolymer properties. An improved interfacial process that employs 4-N,N-dimethylaminopyridine as the coupling catalyst provides coPCs having low concentrations of phenolic and carbamate end groups and that, therefore, wash without emulsification and are thermally stable. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0887-624X
    Keywords: polycarbonate ; maleimide terminated ; synthesis ; crosslinking ; stability ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenylmaleimide (PMI)- and phenylnadimide (PNI)-terminated bisphenol A polycarbonates (PCs) were prepared by solution or interfacial phosgenation processes, and their thermal crosslinking, both with and without a free radical initiator, and the thermal stability of the resultant network polymers were investigated. m-PMI PCs were prepared by interfacial phosgenation of bisphenol A and m-hydroxyphenylmaleimide, but p-hydroxyphenylmaleimide caused rapid phosgene hydrolysis under interfacial conditions and PCs from it could only be made by solution phosgenation. The degree of crosslinking of PMI PCs, as measured by their gel fraction, heated in the absence of a free radical initiator was generally higher at 250°C than at 300°C and increased with the concentration of PMI end groups. m- and p-PMI PCs form thermosets having nearly complete gel fractions by radical initiated curing at 150-200°C. The gel fraction of these thermosets decreases with exposure to higher temperatures (300°C). This behavior is attributed to BA PC chain degradation induced by nitrogen-containing maleimide reaction products. p-PNI PC was prepared by solution phosgenation and the thermal reaction of it in the presence of the initiator produced only a small increase in molecular weight. © 1997 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-2072
    Keywords: Nicotine ; Genetics ; Self-administration ; Reinforcement ; Seizures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Inbred mouse strains differ in sensitivity to a first dose of nicotine and in the development of tolerance to nicotine. The experiments reported here used six inbred mouse strains (A, BUB, C3H, C57BL/6, DBA/2, ST/b) that differ in sensitivity to an acute challenge dose of nicotine to determine whether differences in oral self-selection of nicotine exist. Animals were presented with solutions containing nicotine or vehicle (water or 0.2% saccharin) and their daily intake of the two fluids was measured for 4 days starting with a 10 µg/ml nicotine solution. This was followed by sequential 4-day testing with 20, 35, 50, 65, 80, 100, 125, 160, and 200 µg/ml nicotine solutions. The strains differed dramatically in their self-selection of nicotine and in maximal daily dose (mg/kg); the rank order of the strains was C57BL/6〉DBA〉BUB〉A≥C3H≥ST/b for both the tap water and 0.2% saccharin choice experiments. Correlations between nicotine consumption and sensitivity to nicotine, as measured by a battery of behavioral and physiological responses, were also calculated. Strain differences in nicotine intake were highly correlated with senstivity to nicotine-induced seizures. As senstivity to nicotine-in-duced seizures increases, oral self-selection of nicotine decreases. This finding may suggest that this toxic action of nicotine serves to limit intake.
    Type of Medium: Electronic Resource
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  • 6
    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 chain sequence architecture of bisphenol A-tetrabromobisphenol A copolycarbonates depends on the process employed to prepare them. An interfacial process involving a single-step phosgenation produces a segmented block copolymer, contrary to previous assumptions. An interfacial two-step phosgenation process allows the preparation of random copolycarbonates. In each process the control of the pH of the acqueous phase of the two phase reaction mixture is required to achieve complete comonomer conversion to copolymer and to obtain the desired sequence architecture. The chain sequence architecture of these copolycarbonates can be estimated by examination of their Fourier transform infrared spectra. The relative bandwidth of the carbonate stretching band is roughly proportional to the copolycarbonate number average sequence length, allowing the facile distinction between block and random copolymers. The number average sequence lengths of these copolycarbonates were quantified by carbon-13 NMR spectroscopy. These analyses showed that the one-step phosgenation process yields segmented block copolycarbonates having number average sequence lengths from about 4 to 9, and the two-step phosgenation process produces random copolycarbonates having sequence lengths from 1.6 to 2. The distribution of the aromatic carbon triads of these random copolymers shows them to have an alternate-segmented block architecture, which is consistent with the synthesis conditions, rather than a statistically random distribution of comonomer segments. Dynamic mechanical analysis of two of these copolycarbonates shows a dependence of their low temperature secondary transitions on the copolymer sequence structure. A segmented block copolycarbonate, having a number average sequence length of about 4, displays two distinct peaks in its tan δ curve at temperatures corresponding to those transitions observed in the respective homopolymers. The tan δ curve of a random copolycarbonate shows a single low temperature secondary transition midway between those of the homopolymer. © 1994 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 7
    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 physical, thermomechanical, and rheological properties of bisphenol A-tetrabromobisphenol A copolycarbonates (BA-TBBA coPCs) were studied as a function of copolymer composition. TBBA carbonate segments in the copolymer induce proportionally increased glass transition temperatures, heat distortion temperatures, ignition resistance, tensile and flexural moduli, and density. Properties that do not change proportionately with copolymer composition are coefficient of linear thermal expansion, ambient notched Izod and dart puncture impact strengths, and refractive index. Many properties of BA-TBBA coPCs, including glass transition temperature, heat distortion temperature under load, and modulus, approach those of amorphous high-performance thermoplastics such as polyetherimide and polyethersulfone. However, these copolymers have the possible advantage of melt blending with bisphenol A polycarbonate to form homogeneous alloys with variable and controllable properties. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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