Alternating multiblock amphiphilic copolymers of PEG and tyrosine-derived diphenols. 1. Synthesis and characterization

We describe the synthesis and characterization of a new family of strictly alternating multiblock polyethers based on poly(ethylene glycol) (PEG) and the tyrosine-derived diphenols, desaminotyrosyl-tyrosine alkyl ester (DTR). These polymers are referred to as poly(DTR-PEG ether)s. The PEG and DTR units are linked through a hydrolytically stable ether bond, combining an extremely hydrophilic with an extremely hydrophobic unit within the polymer backbone. The resulting copolymers are amphiphilic in nature. Interfacial and solution polymerization methods were evaluated for this synthesis. Interfacial reaction failed to yield multiblock polymers, while solution polymerization afforded poly(DTR-PEG ether)s containing approximately 4-8 repeat units. PEG blocks of molecular weights ranging from 1000 to 8000 and alkyl pendent chains (R) ranging from ethyl (C2) to dodecyl (C12) were used to vary the molecular structure of the multiblock copolymers. The melting behavior of the poly(DTR-PEG ether)s was studied by modulated differential scanning calorimetry in the heat-only mode. Results indicate that the PEG units in the copolymers melt independently and that the DTR units act as impurities, causing melting point depression and reduced crystallinity. The surfactant properties of poly(DTR-PEG ether)s are described in part 2 of this series of reports.