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ABO-incompatible red blood cell (RBC) transfusions have rarely been associated with delayed haemolysis. However, we report the case of a 75-year-old man (blood type O) with hepatic disease, who received 5 units of incompatible type B RBCs over 8 days. The patient did not develop symptomatic or biochemical evidence of haemolysis until 7–8 days after the first incompatible RBC unit. The patient had a low anti-B antibody titre (1 : 64) prior to the first transfusion. The onset of haemolysis was temporally associated with an increase in anti-B and the infusion of fresh-frozen plasma. In conclusion, a patient with hepatic failure experienced a delayed haemolytic transfusion reaction after receiving multiple ABO-incompatible RBC transfusions that were initially well-tolerated. We speculate that the delayed haemolysis may have resulted from an anamnestic antibody response to the initial incompatible transfusion, or possibly as a result of the transfusion of fresh-frozen plasma, which might have repleted low complement levels. [ABSTRACT FROM AUTHOR]

Changes in the crystallite size distribution during the isothermal crystallization of linear polyethylene fractions were studied using low frequency Raman spectroscopy (LAM). Increases in the crystallite size and broadening distributions were observed as a function of time for all molecular weights studied. Large increases in size occurred even after most of the isothermal crystallinity had formed. The rate of increase was faster for higher crystallization temperatures, while the process was retarded for the higher molecular weights. Similar results were obtained for an unfractionated polymer except for complications that are likely due to molecular weight fractionation. [ABSTRACT FROM AUTHOR]

Polyurethanes have been widely used as underwater acoustic encapsulants for over 20 years. In an attempt to produce polyurethane encapsulants with improved resistance to seawater exposure, polyurethane systems containing aliphatic isocyanate groups were investigated. Several commercial prepolymers containing aliphatic isocyanate groups were obtained for evaluation. Initially, low-temperature cure systems were developed to cure these prepolymers. It was found that the physical and acoustic properties of the resultant polyurethanes depended significantly on the composition of the cure formulation. The effect of prepolymer composition on the properties of the cured urethanes was then investigated. In particular, the molecular weight and isocyanate content of the prepolymers were varied. Several urethane systems suitable as underwater encapsulants were developed. These urethanes were subjected to long-term aging in seawater. It was found that this exposure to seawater did not significantly affect the dynamic mechanical properties of these polyurethanes. [Work supported by Sonar Transducer Reliability Improvement Program (STRIP).] [ABSTRACT FROM AUTHOR]

A study was performed to determine the relationship between polyurethane composition and viscoelastic properties in a series of model urethane compounds. The compositional variables studied included the nature of the soft segment, amount of hard segment, and cure stochiometry. Model urethanes were prepared using the aliphatic diisocyanate, metatetramethylene diisocyanate (m-TMXDI). This aliphatic isocyanate is less reactive than commonly used aromatic isocyanates and does not undergo the secondary cross-linking reactions commonly observed with aromatic isocyanates. The urethanes chosen for this study contained soft segments based on hydroxy-terminated polybutadiene (HTPBD) or polycaprolactone (PCL), which is a highly polar material in which extensive phase mixing should occur. In contrast, polyurethanes based on HTPBD should undergo more complete phase separation. Prepolymers were prepared with both of these soft segments and with available isocyanate contents varying from 3.7% to 5.7%. Diethyltoluene diamine (DETDA) was used to cure these prepolymers over a range of cure stochiometries. Thermal transitions attributed to the hard and soft segments were observed in these urethanes using a Perkin-Elmer DSC-4. Dynamic mechancial behavior was measured using both a Polymer Labs dynamic mechanical thermal analyzer (DMTA) and a resonance apparatus developed at the NRL-USRD. [Sponsored by ONT.] [ABSTRACT FROM AUTHOR]