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Hypromellose, formerly known as hydroxypropylmethylcellulose (HPMC), is by far the most commonly employed cellulose ether used in the fabrication of hydrophilic matrices. Hypromellose provides the release of a drug in a controlled manner, effectively increasing the duration of release of a drug to prolong its therapeutic effect. This review provides a current insight into hypromellose and its applicability to hydrophilic matrices in order to highlight the basic parameters that affect its performance. Topics covered include the chemical, thermal and mechanical properties of hypromellose, hydration of the polymer matrices, the mechanism of drug release and the influence of tablet geometry on drug-release rate. The inclusion of drug-release modifiers within hypromellose matrices, the effects of dissolution media and the influence of both the external environment and microenvironment pH within the gel matrix on the properties of the polymer are also discussed.

Four diblock copolymers of styrene oxide and ethylene oxide were prepared by oxyanionic polymerization:  E45S10, S15E63, S17E65, and S20E67. Surface tension measurements were used to determine critical micelle concentrations of copolymer E45S10 in aqueous solution at several temperatures and thereby its standard enthalpy of micellization. A compilation of known results for copolymers with hydrophobic blocks formed from either styrene oxide or 1,2-butylene oxide shows a discontinuity at S5 or B10 in the block length dependence of the Gibbs energy of micellization which is assigned to lengthy hydrophobic blocks being tightly coiled in the molecular state in water. Light scattering was used to determine micellar association numbers and radii, and scaling exponents were established for the dependence of these parameters on S-block length. Phase diagrams defining regions of hard and soft gel were determined by tube inversion and Couette rheometry.

Nine triblock copolymers of ethylene oxide and styrene oxide (type EmSnEm, E ) oxyethylene, S ) oxyphenylethylene, n and m ) number-average block lengths) were prepared by sequential oxyanionic polymerization. Surface tensiometry was used to determine critical micelle concentrations (cmc's) and standard enthalpies of micellization, and isothermal titration calorimetry was used to confirm the enthalpy of micellization. Light scattering was used to determine micellar association numbers and hydrodynamic radii. Phase diagrams defining regions of hard and soft gel were determined by tube inversion and Couette rheometry. Comparison is made with reported results for diblock copolymers of ethylene oxide and styrene oxide and, so far as possible, with results for triblock copolymers of ethylene oxide and styrene. Compilation of values of the cmc for three series of triblock copoly(oxyalkylene)s, EmSnEm, EmBnEm (B ) oxybutylene), and EmPnEm (P ) oxypropylene), reveals a discontinuity in the block length dependence of log(cmc) at S6 and B12.