Block and Graft Copolymers Containing Carboxylate or Phosphonate Anions
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This dissertation focuses on synthesis and characterization of graft and block copolymers containing carboxylate or phosphonate anions that are potential candidates for biomedical applications such as drug delivery and dental adhesives. Ammonium bisdiethylphosphonate (meth)acrylate and acrylamide phosphonate monomers were synthesized based on aza-Michael addition reactions. Free radical copolymerizations of these monomers with an acrylate-functional poly(ethylene oxide) (PEO) macromonomer produced graft copolymers. Quantitative deprotection of the alkylphosphonate groups afforded graft copolymers with zwitterionic ammonium bisphosphonate or anionic phosphonate backbones and PEO grafts. The zwitterionic copolymers spontaneously assembled into aggregates in aqueous media. The anionic copolymers formed aggregates in DMF and DMSO, while only small amounts of aggregates were present in copolymer/methanol or copolymer/water solutions. Binding capabilities of the acrylamide phosphonic acids were investigated through interactions with hydroxyapatite. Previously our group has prepared poly(ethylene oxide)-b-poly(acrylic acid) (PEO-b-PAA) copolymers and used these polymers as carriers for both MRI imaging agents and cationic drugs. To enhance the capabilities of those carriers in tracking and crosslinking, we have designed, synthesized and characterized amine functionalized PEO-b-PAA copolymers. First, heterobifunctional poly(ethylene oxide) (PEO) with three different molecular weights were synthesized. Modification on one of these afforded a PEO macroinitiator with a bromide on one end and a protected amine on the other end. ATRP polymerization of tert-butyl acrylate (tBuA) in the presence of this initiator and a copper (I) bromide (CuBr) catalyst yielded a diblock copolymer. The copolymer was deprotected by reaction with trifluoroacetic acid (TFA) and formed an amine terminated H2N-PEO-b-PAA. Recently our group has utilized the novel ammonium bisdiethylphosphonate (meth)acrylate and acrylamide phosphonate copolymers to incorporate Carboplatin. The resulting complexes exhibited excellent anticancer activity against MCF-7 breast cancer cells which might be related to ligand exchange of the dicarboxylate group of Carboplatin with the phosphonic acid moieties in the copolymer. Hence, complexation of small-molecule phosphonic acids with Carboplatin was investigated. Three compounds, vinylphosphonic acid, 3-hydroxypropyl ammonium bisphosphonic acid and 2-hydroxyethyl ammonium phosphonic acid were complexed with Carboplatin under acidic and neutral conditions. Covalent bonding of these acids to carboplatin was only observed under acidic pH. The covalently bonded percentage was 17%, 37% and 34%, respectively. More in-depth investigation was of great importance to further understand this complexation behavior.
- Doctoral Dissertations