Strategies for degradable dendrimers: Fragmenting o-nitrobenzyl ether dendrimers and disassembling oligomers of model dendritic systems

Two dendrimer cores that contain o-nitrobenzyl photolabile moieties have been synthesized from piperonal. Methylated core analogs undergo clean photocleavage as indicated by the evolution of isosbestic points in the UV spectra during photolysis and the observation of degradation products by ¹H NMR. These dendrimer cores serve as precursors to dendrimer-based photodegradable materials. Second generation benzyl aryl ether dendrimers have been synthesized and undergo clean photocleavage as indicated by the evolution of isosbestic points in the UV spectra during photolysis and the observation of degradation products by ¹H NMR. Two oligomeric models of disassembling dendrimers have been synthesized from vanillin and o-vanillin. The first system tests the para cleavage vector while the latter test cleavage through the ortho vector of dendrimer disassembly. These systems are used to test potential trigger groups prior to dendrimer synthesis due to their ease of synthesis. Each system shows clean cleavage when triggered by an allyloxy or o-nitrobenzyloxy trigger group as indicated by the evolution of isosbestic points in the UV spectra during disassembly and the observation of disassembly products by ¹H NMR. Dendrimers with a 2,4-branching motif have been synthesized. These dendritic systems have been triggered with and allyloxy group and undergo disassembly via both the ortho and para cleavage vectors simultaneously. Cleavage was noted by the evolution of an isosbestic point in the UV spectra during disassembly

Geometric Disassembly of Dendrimers: Dendritic Amplification

Geometric disassembly of dendritic structures was realized by a cascade cleavage reaction triggered by an initially stimulated group at the dendrimer core. Release of an exponential number of dendrimer fragments was a result of the branching nature of the cleavage pathway. Evidence for the completion of the disassembly process was provided by the absorbance peak of the p-nitrophenoxide ion that was covalently installed at the periphery of the dendrons for this purpose. The release by dendrimer disassembly of an exponential number of dendrimer fragments that serve to alter the properties of a system is termed dendritic amplification

Performance Evaluation of Thermally-Activated Polymers for Conformance Correction Applications

AbstractA comprehensive laboratory study was performed to look at a thermally activated polymer (TAP) for conformance correction applications. The focus of study was to see if BrightWater® (a TAP polymer) could perform in high permeability porous media by creating flow resistance to injected fluid, hence enhancing the sweep efficiency. Furthermore, the possibility of enhancing the TAP performance by increasing the solution concentration was investigated. A set of 20-inch long slimtubes packed with acid-washed quartz sand were used to evaluate the performance of two TAP grades at 85°C in a range of 1 to 5 Darcy. Additionally, another set of short slimtubes were used to examine the performance of two low-temperature activation TAP grades at 30°C in the range of 200 to 1300 md.Results showed that residual resistance factor (RRF) values of 2 to 12 could be achieved at 5000 ppm active concentration for the range of permeability tested here. RRF values increased by increasing the concentration to 10,000 ppm active polymer. Low-temperature activation polymers showed RRF values of 10 to 50 depending on the permeability of the short sandpacks tested at 30°C. TAP simulation approaches are also described.</jats:p

Dendrimer Disassembly by Benzyl Ether Depolymerization

The disassembly of dendritic structures was realized by a cascade cleavage reaction triggered by an initially stimulated group in the dendrimer periphery. A depolymerizable backbone was engineered into prototypical dendritic structures. Evidence for the completion of the disassembly process is provided by the absorbance peak of the p-nitrophenoxide ion that was intentionally installed at the focal point of the dendrons. Observation of the UV spectra during the disassembly process supports a stepwise cascade cleavage proceeding from the periphery into the core