Synthesis of dendritic–linear block copolymers by living ring-opening polymerization of lactones and lactides using dendritic initiators

Polyether dendrons have been successfully used as macroinitiators for the living ring-opening polymerization (ROP) of lactones and lactides. A hydroxyl group located at the focal point of dendrimers of different generations was transformed into diethyl aluminum alkoxides by reaction with triethyl aluminum. The dendritic aluminum alkoxides proved to be efficient macroinitiators for the living ROP of ε-caprolactone (εCL), 1,4,8-trioxa(4,6)spiro[9]undecanone (TOSUO), D ,L - and L ,L -lactide. Formation of these block copolymers of unusual macromolecular architecture was supported by size exclusion chromatography and spectroscopy. The versatility of this synthetic approach allowed ω-functional dendrimer block-polyesters, such as macromonomer, and macromolecules with novel architectures, to be prepared. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1923–1930, 1999     

Poly(aryl ether phenylquinoxalines) via anionic ring opening polymerization of macrocycles

A cyclic poly(aryl ether phenylquinoxaline) was prepared via the self-polymerization of 1 in an N-methyl-2-pyrrolidone (NMP) solution containing base using a pseudo-high dilution polymerization condition. The macrocycle formation of 1 was carried out in the presence of potassium carbonate in a NMP/toluene solvent mixture at a solids content of 1%. The water generated by phenoxide formation was removed as an azeotrope with toluene 170 °C. A concentrated solution of the macrocycle was added to the reaction mixture over an 8 hour period. The reaction was allowed to proceed for an additional 24h to ensure quantitative reaction. A number of characterization techniques were used to study the cyclization of 1 including GPC, HPLC, H NMR and matrix-assisted laser desorption ionization (MALDI) mass spectroscopy. The MALDI-TOF mass spectrum of the cyclization of 1 clearly showed that a mixture of macrocycles is obtained, with the expected distribution of molecular weights. Facile ring opening polymerization of the cyclic poly(aryl ether phenylquinoxaline) oligomers was accomplished with a nucleophilic initiator. High polymer was obtained for each polymerization temperature (η = 0.4–0.5 dl/g in NMP), however, prolonged reaction time resulted in significant gel formation. The Tg's were high and commensurate with the high molecular weight linear analog (250 °C).     

Toward biodegradable nanogel star polymers via organocatalytic ROP

Organocatalytic ring opening polymerization (OROP) is used to effect the rapid, scalable, room temperature formation of size-controlled, highly uniform, polyvalent, nanogel star polymer nanoparticles of biodegradable composition.     

A simple, high-resolution method for establishing DNA binding affinity and sequence selectivity.

Full details of the development of a simple, nondestructive, and high-throughput method for establishing DNA binding affinity and sequence selectivity are described. The method is based on the loss of fluorescence derived from the displacement of ethidium bromide or thiazole orange from the DNA of interest or, in selected instances, the change in intrinsic fluorescence of a DNA binding agent itself and is applicable for assessing relative or absolute DNA binding affinities. Enlisting a library of hairpin deoxyoligonucleotides containing all five base pair (512 hairpins) or four base pair (136 hairpins) sequences displayed in a 96-well format, a compound's rank order binding to all possible sequences is generated, resulting in a high-resolution definition of its sequence selectivity using this fluorescent intercalator displacement (FID) assay. As such, the technique complements the use of footprinting or affinity cleavage for the establishment of DNA binding selectivity and provides the information at a higher resolution. The merged bar graphs generated by this rank order binding provide a qualitative way to compare, or profile, DNA binding affinity and selectivity. The 96-well format assay (512 hairpins) can be conducted at a minimal cost (presently ca. $100 for hairpin deoxyoligonucleotides/assay with ethiduim bromide or less with thiazole orange), with a rapid readout using a fluorescent plate reader (15 min), and is adaptable to automation (Tecan Genesis Workstation 100 robotic system). Its use in generating a profile of DNA binding selectivity for several agents including distamycin A, netropsin, DAPI, Hoechst 33258, and berenil is described. Techniques for establishing binding constants from quantitative titrations are compared, and recommendations are made for use of a Scatchard or curve fitting analysis of the titration binding curves as a reliable means to quantitate the binding affinity.