Production of large-particle-size monodisperse latexes

The research program achieved two objectives: (1) it has refined and extended the experimental techniques for preparing monodisperse latexes in quantity on the ground up to a particle diameter of 10 microns; and (2) it has demonstrated that a microgravity environment can be used to grow monodisperse latexes to larger sizes, where the limitations in size have yet to be defined. The experimental development of the monodisperse latex reactor (MLR) and the seeded emulsion polymerizations carried out in the laboratory prototype of the flight hardware, as a function of the operational parameters is discussed. The emphasis is directed towards the measurement, interpretation, and modeling of the kinetics of seeded emulsion polymerization and successive seeded emulsion polymerization. The recipe development of seeded emulsion polymerization as a function of particle size is discussed. The equilibrium swelling of latex particles with monomers was investigated both theoretically and experimentally. Extensive studies are reported on both the type and concentration of initiators, surfactants, and inhibitors, which eventually led to the development of the flight recipes. The experimental results of the flight experiments are discussed, as well as the experimental development of inhibition of seeded emulsion polymerization in terms of time of inhibition and the effect of inhibitors on the kinetics of polymerization

The Effect of Relative Pricing on the Fixed-Rate Mortgage Term Decision

This paper analyzes determinants of the fifteen- versus thirty-year fixed-rate mortgage (FRM) loan term decision. Because the thirty-year FRM may be converted (by partial prepayment) to the shorter term, the thirty-year instrument provides the implicit option to extend repayment. Relative rates measure the price (cost) of this option to the consumer. The results indicate that the term decision of consumers is highly sensitive to relative rates: probit estimates using data from a large national lending institution for the 1987 to 1990 period indicate that a 1% increase in the ratio of fifteen- to thirty-year rates lowers the probability of fifteen-year term choice by 20%. The results also indicate that expected housing price appreciation, which measures investment determinants of housing demand, is negatively related to the fifteen-year FRM term choice.

Evolution of a physiological pH 6.8 bicarbonate buffer system: application to the dissolution testing of enteric coated products.

The use of compendial pH 6.8 phosphate buffer to assess dissolution of enteric coated products gives rise to poor in vitro-in vivo correlations because of the inadequacy of the buffer to resemble small intestinal fluids. A more representative and physiological medium, pH 6.8 bicarbonate buffer, was developed to evaluate the dissolution behaviour of enteric coatings. The bicarbonate system was evolved from pH7.4 Hanks balanced salt solution to produce a pH 6.8 bicarbonate buffer (modified Hanks buffer, mHanks), which resembles the ionic composition and buffer capacity of intestinal milieu. Prednisolone tablets were coated with a range of enteric polymers: hypromellose phthalate (HP-50 and HP-55), cellulose acetate phthalate (CAP), hypromellose acetate succinate (HPMCAS-LF and HPMCAS-MF), methacrylic acid copolymers (EUDRAGIT® L100-55, EUDRAGIT® L30D-55 and EUDRAGIT® L100) and polyvinyl acetate phthalate (PVAP). Dissolution of coated tablets was carried out using USP-II apparatus in 0.1M HCl for 2h followed by pH 6.8 phosphate buffer or pH 6.8 mHanks bicarbonate buffer. In pH 6.8 phosphate buffer, the various enteric polymer coated products displayed rapid and comparable dissolution profiles. In pH 6.8 mHanks buffer, drug release was delayed and marked differences were observed between the various coated tablets, which is comparable to the delayed disintegration times reported in the literature for enteric coated products in the human small intestine. In summary, the use of pH 6.8 physiological bicarbonate buffer (mHanks) provides more realistic and discriminative in vitro release assessment of enteric coated formulations compared to compendial phosphate buffer

Adjustable- versus Fixed-Rate Mortgage Choice: The Role of Initial Rate Discounts

This paper investigates relative pricing determinants of the fixed-rate mortgage (FRM) versus adjustable-rate mortgage (ARM) decision. A probit model is estimated using data from a national sample of residential housing transactions for the 1986 and 1988 period. The results suggest that the probability of ARM choice is highly sensitive to ARM initial rate ("teaser") discounts and differences in the ratio of FRM to ARM points. In addition, the findings indicate that the level of local housing prices is an important determinant of ARM choice.