Synthesis and Characterization of Water Soluble Block Copolymers for pH-Sensitive Delivery
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Synthesis and Characterization of Water Soluble Block Copolymers for pH-Sensitive Delivery Brian C. Anderson1,3, Paul D. Bloom2,3, Valerie V. Sheares2,3, and Surya K. Mallapragada1,3,* 1 Department of Chemical Engineering, Iowa State University, 2114 Sweeney Hall, Ames, Iowa, 50011 2 Department of Chemistry, Iowa State University, 2760 Gilman Hall, Ames, Iowa, 50011 3 Ames Laboratory, Department of Energy, Iowa State University, Ames, Iowa, 50011 * Corresponding Author
ABSTRACT A novel, water-soluble AB-block copolymer of diethylaminoethyl methacrylate (DEAEM) and poly(ethylene glycol) (PEG) was synthesized by anionic polymerization. Poly(ethylene glycol) methyl ether (PEGME) was converted into the corresponding potassium salt by reacting with potassium metal. The PEG salt was used as a macroinitiator for the polymerization of DEAEM to yield a PEG-b-PDEAEM block copolymer. Carbon dioxide was used to terminate DEAEM polymerization with a carboxylic acid group. This polymer, loaded with dye, was tested for pH sensitivity by release studies into solutions of various pH.
INTRODUCTION One beneficial characteristic that polymeric materials have added to the field of drug delivery is their ability to be responsive to their environment. By modifying the chemical composition of either the backbone or pendant groups, polymers can respond to a wide range of stimuli. One of the stimuli that has been exploited for drug delivery purposes is pH dependence. This dependence can be expressed with polymers containing either anionic or cationic character. Polymers with cationic functionality will tend to swell in low pH aqueous solutions, whereas polymers with anionic functionality tend to swell in high pH solutions. Crosslinked cationic polymer membranes of diethylaminoethyl methacrylate (DEAEM) and dimethylaminoethyl methacrylate (DMAEM) have been synthesized for drug delivery applications [1-5]. With the attachment of glucose oxidase, these polymers were rendered glucose sensitive and have been studied for insulin release. The main disadvantage of these materials was that they were not water-soluble and, if implanted, would remain in the body long after the useful life of the delivery device. Other research efforts have focused on graft and block copolymers comprised of domains with anionic functionality and separate water soluble portions, such as poly(ethylene glycol) (PEG) [6-8]. The use of these polymers was primarily for the release of drugs in the intestines, where a rise in pH would indicate that the device had passed through the stomach and is no longer in the harsh acidic conditions. Once in the intestines, where the pH is higher, the delivery polymer is water-soluble and the polymer-bound drug is released. NN1.8.1
The goal of this research is to develop a water-soluble block copolymer, containing cationic functionality, that could be used for insulin delivery. A block copolymer approach is chosen over other options such as grafting, due to the control over the size and properties available with anionic polymerization o
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