Glassy core, effect

Precirol was successf ully used as a retardant in matrix tablet formulations [8]. The effect of Precirol incorporation into the hydroxypropylmethylcellulose matrix tablets was therefore investigated. Precirol drug ratios of 1 3, 1 2 and 1 1 were used (tablets KET-R A, B, and C). No significant differences in the volume decrease profiles of glassy cores and in ketoprofen release profiles (Fig. 4) in comparison with original core were obtained, even with increased Precirol. 

A crosslinked rubber may be synthesized at the surface of the glass beads to produce a core-shell structure (glassy core and rubbery shell). Thermosets modified with these particles showed a strong toughening effect for an optimum thickness of the rubbery shell (Amdouni et al., 1992). 

The effect of the glassy core in three-layer particles is further demonstrated by the data for the 3LA and 3LE materials. These materials contain particles with essentially identical rubbery-layer outer diameters (284 and 290 nm, respectively), but with glassy-core diameters of 200 and 244 nm, respectively. The values of GIc for these materials are similar when plotted against Vp, but,... 

Finally, comparison of GIc. values for the 3LA materials with those for the equivalent 4L materials demonstrates that, contrary to patent claims (5), the introduction of a 100 nm diameter rubbery core into the glassy core of the 3LA particle has no significant effect on fracture resistance. 

Another way to functionalize the surface of microlatex particles is to incorporate amphiphilic block copolymers (for example, polystyrene/polyvinylpyridine) as cosurfactants together with the classical surfactants used in the formulation [86,87]. The protruding polyvinylpyridinium chains are anchored to the glassy core through the polystyrene blocks. These blocks copolymers were shown to stabilize the oil/water interface and to effectively bind ions of transition and heavy metals via complexation. 

In 2001, Chen and coworkers prepared another interesting series of tetra-phenylmethane-based tetrahedral compounds. The initial step of the synthetic scheme involves the preparation of the tetrazole derivative 8 from the corresponding tetranitrile and its subsequent condensation with various benzoyl chlorides to give the cruciforms 9-11 depicted in Scheme 3.6. A modified procedure was developed to obtain the bipolar tetramers 16 and 17, as shown in Scheme 3.7. The acyl chloride functional group was this time attached to the tetrahedral core unit and the tetrazole function was attached to the triphenylamine component. Once again DSC measurements illustrated the effectiveness of this architecture in inducing a stable glassy state in these cruciform materials. 

For electrostatic and steric stabilization, the particles can be viewed effectively as colloids consisting of a soft and deformable corona surrounding a rigid core. Colloidal particles with bulk elastomeric properties are also available. These particles, which are generally of submicron size, are developed and used as reinforcement additives to improve the Impact resistance of various polymer matrices [28-30]. The rubber of choice is often a styrene/butadiene copolymer. The presence of chemical groups at the matrix-filler interface leads to improved adhesion between them. Typically, the addition of about 30% by volume of these elastomeric particles increases the impact strength of a brittle glassy polymer like polystyrene by up to a factor of 10. For some applications, particles with more complex architecture have been... 

Hydrogen absorption was reported to induce a surface segregation of Pd on glassy Pd-Zr alloys (Oelhafen et al, 1982). However, the reproducibility of the effect was very limited and possibly effects of the sputter yield 7ere stronger than segregation (Oelhafen, 1985). XPS core level analysis of Fe Zr and 24 76 160 ratios of 4,2 and... 

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