Cell opening agents

The dimensional stability of low density, water blown rigid PU foams for pour-in-place thermal insulation applications was improved by the use of a phthalic anhydride based polyester polyol containing a dispersed cell opening agent. The foam systems obtained allowed some of the carbon dioxide to be released through the cell windows immediately after filling of the cavity, and to be rapidly replaced by air. Studies were made of the flowability, density, open cell content, dimensional stability, mechanical properties, thermal conductivity and adhesion (particularly to flame treated PE) of these foams. These properties were examined in comparison with those of HCFC-141b blown foams. 21 refs. 

Paracellular transport Enhancement is achieved by modulating the tight junctions between the cells. Chelating agents such as ethylenediamine tetraacetic acid can chelate calcium ions and transiently open the tight junctions for drug... 

Cell wall agents, such as glycopeptides, have concentration-independent bactericidal activity, and the time over which the antibiotic serum concentration persists over the minimal inhibitory concentration of the pathogen is a main pharmacodynamic determination of the outcome. In a two-way, randomized, open, two-period, crossover study in 10 healthy adults, teicoplanin given in two 200 mg doses intramuscularly produced steady-state trough concentrations even higher than those after once-daily intravenous administration of 400 mg (3). Conversion from intravenous to intramuscular administration may therefore allow better compliance with preserved efficacy. Intramuscular teicoplanin was well tolerated. Adverse effects reported were mild local pain for 2-3 hours, headache, and backache. 

Other methods are able to produce the cell opening without pressing the foams. For example, several patents propose to invert the relationships between the decomposition temperature of the crosslinking agent and the decomposition temperature of the blowing agent [52,53], which results in an open-cell material with a similar structure to that shown in Fig. 4, but without plastic deformation of the polymeric matrix. 

A typical phenohc foam system consists of hquid phenohc resia, blowiag agent, catalyst, surface-active agent, and modifiers. Various formulations and composite systems (65—67) can be used to improve one or more properties of the foam ia specific apphcations such as iasulation properties (63,68—71), flammabihty (72—74), and open cell (76—78) (quahty). 

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