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  • 1990-1994  (5)
  • 1985-1989  (2)
  • Polymer and Materials Science  (7)
  • 1
    Digitale Medien
    Digitale Medien
    Acid photogeneration from sulfonium salts in solid polymer matrices (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 3927-3935 
    Details
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The major photoproduct from irradiation of triphenylsulfonium salts is a Brönsted acid. This photochemical process has been used in several polymer film applications where the acid is used for crosslinking of films or other acid catalyzed reactions. Despite the widespread application of these materials, very little is known about the efficiency of acid generation in polymer films or the extent of the catalytic chain. This paper describes the use of a merocyanine dye technique to analyze for acid production in polymer films. The amount of acid produced on irradiation can be determined by this method and the extent of the catalytic chain then be determined.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1989.080271205
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  • 2
    Digitale Medien
    Digitale Medien
    The effect of polymer structure on the efficiency of acid generation from triarylsulfonium salts (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 309-316 
    Details
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The irradiation of triarylsulfonium salts produces Brönsted acid along with diarylsulfide products. This photochemical conversion has been applied in several areas of polymer film technology including imaging and curing of films. This paper discusses the dependency of acid generation in polymer films on the structures of both polymer and sulfonium salt. The results suggest that the structures of both polymer and sulfonium salt. The results suggest that the efficiency of acid generation is dependent on the interaction between polymer structure and the charged sulfonium salt. Studies have been carried out for both deep-UV and electron beam irradiation of polymer films. The variation of acid generation with sulfonium salt loading has been determined. Finally the effect of accelerating voltage on the amount of acid generation following electron beam irradiation is discussed. ESR spectroscopy has been done on films after uv irradiation to determine the nature of the radicals which are formed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1991.080290303
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  • 3
    Digitale Medien
    Digitale Medien
    Customized neonatal incubator for measurement of platelet-artificial microvascular graft interactions under controlled flow, temperature, and transmural pressure (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Biomaterials 3 (1992), S. 1-7 
    Details
    ISSN: 1045-4861
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: A neonatal incubator has been custom modified to enable measurement of initial platelet retention on biomaterials in vitro under clinically relevant hemodynamic conditions. To calibrate this device, platelet retention on several materials having microconduit geometry (0.7-1.0 mm i.d.) has been measured after perfusion with citrated whole blood (containing 111 Indium-labelled platelets) at a shear rate of 312 s-1, 37°C, and 80 cm H2O transmural pressure. The relative reactivity of these materials toward platelets was: glass 〈 Fibrinogen(Fg)-coatedglass 〈 Fg-coated polyethylene 〈 polyethylene ∼ = Expanded polytetrafluoroethylene. Interindividual variation is relatively large (coefficient of variation = 35.5 ± 9.3%), but comparison to intraindividual controls reduces the variability to 14.8 ± 10.3%, a level which is suitable for economical testing of platelet retention to biomaterials in the presence or absence of drugs. This approach may have particular value in the study of the mechanism of platelet interactions with artificial microvascular grafts under perfusion conditions which are relevant to the first moments of flow, when initial platelet deposition occurs.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jab.770030102
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  • 4
    Digitale Medien
    Digitale Medien
    Spatial and temporal changes in compliance following implantation of bioresorbable vascular grafts (1992)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 26 (1992), S. 1449-1461 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: Compliance matching between the host vessel and vascular grafts used for smalldiameter arterial replacements is thought to be important for longterm patency. However, currently available grafts elicit fibroplastic reactions, resulting in decreasing compliance with time after implantation. Bioresorbable prostheses elicit ingrowth of myofibroblasts containing abundant contractile elements. This led us to investigate whether compliance of implanted bioresorbable prostheses decreased as a function of time and if the kinetics of change correlated with the progession of tissue ingrowth. Woven polyglactin 910 prostheses (10 mm × 4 mm i.d.) were implanted into adult NZW rabbit infrarenal aortas and replicates were harvested serially through 8 months. Control grafts were implanted, and immediately resected. Dynamic compliance was measured a t 1-mm axial increments along each explant using a pulse duplicator apparatus which exposed the harvested samples to realistic pulsatile hemodynamics. Compliance was calculated for proximal, mid, and distal segments of each graft and averaged at each time point by grouping into control (zero time, n =3), early (1-4 weeks, n = 13), and late (6-36 weeks, n = 9) explant periods. At late explant periods both proximal and distal compliance were significantly greater than mid graft compliance (p ≤ .02 and p ≤ .03, respectively). There was a significant increase in proximal compliance between early and late explant times (p ≤ .01). Measured increases in mid and distal segment compliance over time did not reach statistical significance. Myofibroblast laden tissue ingrowth into the inner capsule followed macrophage phagocytosis and was nearly complete prior to the time that an increase in compliance was demonstrated. Thus since the major histologic episodes precede the change in compliance, these are not likely initiated by this biomechanical change. We hypothesize the graft resorption coupled with the ingrowth of more compliant tissue likely leads to the increased compliance of the graft material. © 1992 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820261105
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  • 5
    Digitale Medien
    Digitale Medien
    The effects of pore size and endothelial cell seeding upon the performance of small-diameter e-PTFE vascular grafts under controlled flow conditions (1988)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 163-177 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The purpose of this study was to determine the effects of endothelial cell seeding and graft internodal distance upon the performance of 4-mm-ID e-PTFE grafts during acute reduced blood flow conditions. PTFE grafts especially manufactured with three different mean internodal distances (28, 40, and 52 μm) were evaluated. Fifteen dogs (n = 5 for each design of PTFE graft) underwent bilateral carotid artery replacements with 6 cm lengths of 4-mm-ID PTFE grafts. In each dog one graft was seeded with enzymatically derived endothelial cells; the contralateral graft was nonseeded. All grafts were evaluated 5 weeks postoperatively. Dogs with bilaterally patent grafts were subsequently subjected to flow conditions through the graft that were maintained at 30% of the initial flow rates for 4 hr. Following controlled low flows the grafts were excised and assessed for patency, thrombus-free surface area, inner capsule thickness and prostacyclin production. Endothelial cell seeding of these small-diameter e-PTFE vascular grafts improved patency and thrombus-free surface areas in grafts of all pore sizes, with these parameters being greatest in the 40-μm grafts. Inner-capsule healing in these grafts was controlled and related to the pore size. PGI2 production was improved in endothelial cell seeded grafts of all pore sizes. However, neither endothelial cell seeding nor graft pore size affected the performance of these e-PTFE grafts under conditions of reduced blood flows.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820220302
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  • 6
    Digitale Medien
    Digitale Medien
    Deuterium Isotope Effects during RDX Combustion: Mechanistic burn rate-controlling step determination (1991)
    Weinheim : Wiley-Blackwell
    Propellants, Explosives, Pyrotechnics 16 (1991), S. 279-286 
    Details
    ISSN: 0721-3115
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: High pressure (500 psig/3.55 MPa and 1000 psigl6.99 MPa) burn rate comparisons from the combustion of solid RDX (hexahydro- 1.3,.5-trinitro-1,3,5-triazine) and perdeuterio-labeled RDX-dh cylindrical pressed pellets reveals a large kinetic deuterium isotope cffect (KDIE). This experimental KDIE confirms that chemical reaction kinetics are a significant mechanistic factor in controlling the inherent RDX burn rate and further shows the six-membered RDX hcterocycle's rate-controlling mechanistic step during com- bustion is the same as that previously reported for its larger eight-membered HMX (octahydro-l.3,5,7-tetranitro-l.3.5,7 tetrazocine) homologuc. As with HMX. This experimental KDTE approach also demonstrates a direct mechanistic relationship between RDX's higher order cornbustion regime and its ambient pressure thermochemical decomposition process.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/prep.19910160605
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  • 7
    Digitale Medien
    Digitale Medien
    Kinetic Deuterium Isotope Effects in the combustion of formulated nitramine propellants (1994)
    Weinheim : Wiley-Blackwell
    Propellants, Explosives, Pyrotechnics 19 (1994), S. 42-58 
    Details
    ISSN: 0721-3115
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The kinetic deuterium isotope effect was used to investigate the rate-limiting process in the combustion of formulated nitramine propellants. Model propellant formulations containing either octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), or their deuteriated analogues were pressed into pellets and burned under nitrogen pressure in a window bomb. The magnitudes of the observed deuterium isotope effects indicate that the HMX and RDX exert significant control over the combustion phenomenon of the propellants studied. Furthermore, assuming a consistent mechanism between decomposition and combustion, the observed isotope effects suggest that a carbon-hydrogen bond rupture in HMX or RDX is the rate-controlling step in the combustion of the model nitramine propellants. Observed isotope effect values for HMX-CW5 and RDX-CW5 formulated propellants at 1000 psig (6.99 MPa) pressure were 1.29 ± 0.09 and 1.24 ± 0.07, respectively, compared to a theoretical estimate of 1.29 for a primary effect due to C—H bond rupture at 673 K.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/prep.19940190108
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