Controlled Release Agents

The most important of the phosphate bonded cements are the zinc phosphate, dental silicate and magnesium ammonium phosphate cements. The first two are used in dentistry and the last as a building material. Copper(II) oxide forms a good cement, but it is of minor practical value. In addition, certain phosphate cements have been suggested for use as controlled release agents. The various phosphate cements are described in more detail in the remainder of this chapter. 

More recently copper phosphate cements have been suggested for use as controlled-release agents for supplying trace amounts of copper to cattle and sheep over an extended period (Allen et al., 1984 Mansion et al., 1985 Prosser et al., 1986). The cements were prepared with a Cu/P ratio of 1 1 to ensure that the matrix was an add phosphate and so subject to dissolution in aqueous solutions. They released copper at a constant rate for 90 days. 

Glyceryl behenate 0.5 1 Hydrophobic, also used as controlled-release agent... 

A block copolymer effective as a controlled release agents of biologically active materials have been prepared. This agent consisted of ethylene oxide-propylene sulfide-ethylene oxide teipolymer that had been end-capped with a selected cysteine-containing peptide. These materials resist degradation prior to reaching their intended targets because they behave as multilamellar vesicles. 

Controlled-release agents Chien, Y. Encyclopedia of Pharmaceutical Technology, Swarbrick, J., Boylan, J., Eds. Marcel Dekker, Inc. New York, 1990 Vol. 3, 281. 

Major polymer applications nonnietallic conductors, EMI shielding, battery electrodes, sensors, electronic displays, optoelectronic systems, capacitors, controlled release agents for other components... 

The lack of definitive studies is due to a mixture of reasons including 1) wide variety of polymers 2) newness of interest in the area 3) wide variety of applications (both potential and actual) of inorganic and organanetallic polymers not requiring thermal stability or thermal analysis (uses as anchored metal catalysis, control release agents, electrical and photochemical applications, speciality adhesives) 4) insufficient description, identification, of the products 5) wider variety of degradation routes and other thermal behavior in comparison to organic polymers and 6) many products were synthesized and briefly characterized before the advent of modern thermal instrumentation. 

Hydrogenated vegetable oils 1-5 Hydrophobic, used at higher concentrations as controlled release agents. 

Advancements in synthetic polymer chemistry have allowed a remarkable range of new nonlinear block copolymer architectures to be synthesized. The result is a wide variety of new materials with the capacity to form self-assembled phases in bulk and in solution. At present our synthetic capabilities exceed our understanding, both theoretical and experimental, of the properties of such macro-molecular systems. We anticipate that a better understanding of structure-property relationships for these materials will lead to impressive new polymers with applications such as structural plastics, elastomers, membranes, controlled release agents, compatibilizers, and surface active agents. From the synthetic standpoint it seems likely that recent advances in living free radical polymerization will make the syntheses of many non-linear block copolymers more commercially appealing. 

The first symposium on Organometallic Polymers, held at the National Meeting of the American Chemical Society in September 1977> attracted a large number of scientists interested in this field, both established investigators and newcomers. Subsequent symposia in 1977, 1979, 1983, and 1987 have seen the field mature. Hundreds of papers and patents have been published. Applications of these materials as semiconductors and one-dimensional conductors, as radiation shields or as photo-resists, as catalysts, as controlled release agents for drugs and biocides and a wide variety of applications have been studied (see Chapter 1). 

Uses Binder, controlled release agent in pharmaceutical grans., tablets, controlled-release preps. film-former, protectant In pharmaceutical coatings... 

Chem. Descrip. Porous inorg. material encapsulating a biocide Uses Carrier, protectant, controlled release agent for biocides, fungicides and functional additives in paints/coatings, metalworking fluids, water/waste treatment, cosmetics, toiletries, household prods., plastics, paper, wood, textiles... 

PCL has a low glass transition temperature of —62 °C, existing always in a rubbery state at room temperature, and a melting temperature of 57 °C. It has been postulated that these properties lead to a high permeability of PCL for controlled release agents. Other thermal and mechanical properties are listed in Table 55.1. 

Vinyl acetate polymers have long been used as chewing gum bases. They have been studied as controlled release agents for programmed administration of drugs and as a base for antifouling marine paints (168,169). 

Studies by our group have established that most metal-containing polymers undergo hydrolysis when wetted. Polymeric derivatives of cis-DDP in DMSO solution also undergo hydrolysis when added to water. Thus, polymeric derivatives of cis-DDP can act as controlled release agents, releasing therapeutic quantities of the active drug. 

Thus Group 1 VB-containing polymers can effectively act as controlled release agents. 

---