Insertion of ester bonds in three terpolymerization systems

Nonbiodegradable (co)polymers with all-carbon backbone produced via radical polymerization are used in various applications. For some applications, like for example in skincare and haircare, these polymers are nonrecoverable and therefore would be preferably made biodegradable. Therefore, inserting ester bonds in the backbone via radical ring opening terpolymerization of acrylates and 2-methylene-1,3 dioxepane (MDO) could be a suitable approach to obtain biodegradable terpolymers. This report investigates the influence of batch versus semibatch process on the polymerization of three terpolymerization systems viz. (i) methacrylamide (MAAM)/n-butyl acrylate (nBA)/BMDO (5,6-Benzo-2-Methylene-1,3-Dioxepane), (ii) MAAM/nBA/MDO, and (iii) methyl methacrylate (MMA)/VAc (vinyl acetate) /MDO. We demonstrate the improvement in number of ester groups inserted and the homogeneity of insertion via semibatch polymerization processes. The process is guided via optimal monomer addition feeding profiles generated using the reactivity ratios of comonomers. Such improved insertion was demonstrated by the molecular weight distribution of fragments after alkali degradation in the investigated systems.</p

Radioactive Phosphorylation of Alcohols to Monitor Biocatalytic Diels-Alder Reactions

Nature has efficiently adopted phosphorylation for numerous biological key processes, spanning from cell signaling to energy storage and transmission. For the bioorganic chemist the number of possible ways to attach a single phosphate for radioactive labeling is surprisingly small. Here we describe a very simple and fast one-pot synthesis to phosphorylate an alcohol with phosphoric acid using trichloroacetonitrile as activating agent. Using this procedure, we efficiently attached the radioactive phosphorus isotope 32P to an anthracene diene, which is a substrate for the Diels-Alderase ribozyme—an RNA sequence that catalyzes the eponymous reaction. We used the 32P-substrate for the measurement of RNA-catalyzed reaction kinetics of several dye-labeled ribozyme variants for which precise optical activity determination (UV/vis, fluorescence) failed due to interference of the attached dyes. The reaction kinetics were analyzed by thin-layer chromatographic separation of the 32P-labeled reaction components and densitometric analysis of the substrate and product radioactivities, thereby allowing iterative optimization of the dye positions for future single-molecule studies. The phosphorylation strategy with trichloroacetonitrile may be applicable for labeling numerous other compounds that contain alcoholic hydroxyl groups

Synthesis of transition-metal-free and sulfur-free nanoparticles and nanocapsules via reversible complexation mediated polymerization (RCMP) and polymerization induced self-assembly (PISA)

NaI-catalyzed reversible complexation mediated living radical polymerization (RCMP) was combined with polymerization induced self-assembly (PISA) to generate self-assemblies. Poly(methacrylic acid) (PMAA) and poly(methyl methacrylate) (PMMA) were used as hydrophilic and hydrophobic segments, respectively, to generate self-assemblies. Micelles (nano-particles), worms (nano-cylinders), and vesicles (nano-capsules) were generated in ethanol at 5–9 wt% solid content. The self-assemblies were also fixed (crosslinked) by using a cross-linkable divinyl monomer, i.e., ethylene glycol dimethacrylate (EGDMA), as a comonomer in the hydrophobic segment. NaI-catalyzed RCMP is a heavy-metal-free and sulfur-free synthetic method. The nano-particles, cylinders, and capsules obtained through the RCMP/PISA process are highly attractive for biomedical, healthcare, cosmetics, and agrochemical release applications.ASTAR (Agency for Sci., Tech. and Research, S’pore

Backbone-Degradable Acrylate Latex:Toward Overcoming Hydrolysis Limitations of Cyclic Ketene Acetal Monomers

Latex particles made with radical emulsion polymerization contain all carbon-backbone polymer chains, which are nonhydrolyzable and nonbiodegradable in the environment and hence pose a huge challenge as persistent pollutants. Radical ring-opening copolymerization (rROP) of cyclic ketene acetals (CKAs) such as 2-methylene-1,3-dioxepane (MDO) with vinyl monomers is an interesting approach being explored intensely for introducing degradable ester groups in the polymer backbones, opening up the potential of synthesizing biodegradable copolymers. However, carrying out such reactions in an aqueous medium to obtain biodegradable dispersions is very challenging due to the hydrolytic instability of CKAs. There are conflicting reports on preparing degradable lattices via rROP of MDO with vinyl acetate (VAc) monomers, but subsequent detailed reaction parameters were published, which show that under the right conditions, successful copolymerizations can be performed. We report that the use of neutral surfactants, high pH, and stabilizing comonomers play a crucial role in the successful incorporation of degradability in the polymer backbone during emulsion copolymerization. This is the first report on the synthesis of acrylate copolymers with the incorporation of hydrolytic degradability (utilizing MDO) under potentially more industrially feasible emulsion polymerization conditions. The findings underscore the potential for further improvement in this area. The results in the current study provide further insight into the breadth of parameters that must be carefully considered to produce biodegradable lattices via the rROP of CKAs.</p

Backbone-Degradable Acrylate Latex:Toward Overcoming Hydrolysis Limitations of Cyclic Ketene Acetal Monomers

Latex particles made with radical emulsion polymerization contain all carbon-backbone polymer chains, which are nonhydrolyzable and nonbiodegradable in the environment and hence pose a huge challenge as persistent pollutants. Radical ring-opening copolymerization (rROP) of cyclic ketene acetals (CKAs) such as 2-methylene-1,3-dioxepane (MDO) with vinyl monomers is an interesting approach being explored intensely for introducing degradable ester groups in the polymer backbones, opening up the potential of synthesizing biodegradable copolymers. However, carrying out such reactions in an aqueous medium to obtain biodegradable dispersions is very challenging due to the hydrolytic instability of CKAs. There are conflicting reports on preparing degradable lattices via rROP of MDO with vinyl acetate (VAc) monomers, but subsequent detailed reaction parameters were published, which show that under the right conditions, successful copolymerizations can be performed. We report that the use of neutral surfactants, high pH, and stabilizing comonomers play a crucial role in the successful incorporation of degradability in the polymer backbone during emulsion copolymerization. This is the first report on the synthesis of acrylate copolymers with the incorporation of hydrolytic degradability (utilizing MDO) under potentially more industrially feasible emulsion polymerization conditions. The findings underscore the potential for further improvement in this area. The results in the current study provide further insight into the breadth of parameters that must be carefully considered to produce biodegradable lattices via the rROP of CKAs.</p

Morphology control of liposome - RAFT oligomer precursors to complex polymer nanostructures

Different types of butyl acrylate (BA)-co-acrylic acid (AA) oligomers were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and mixed with extruded 200 nm dimethyldioctadecylammonium bromide vesicles. The resulting precursor structures form the basis for subsequent vesicle-templated polymerizations. Systematic variations in temperature, pH, oligomer length, and oligomer composition and their effects on precursor morphology were studied. Surprisingly, different morphologies were obtained, including capsules, protruded capsules, solid spheres, and multicompartment structures. For example, capsules and multicompartment structures were found to result from higher AA contents, and protruded capsules and solid particles resulted from lower AA contents. Subsequent chain extension of the RAFT oligomers resulted in polymer nanostructures resembling the precursor morphologies

Synthesis and rheological characterization of latexes stabilized by methacrylic acid containing macromonomers

A range of copolymers of methacrylic acid (MAA) macromonomers prepared by cobalt-catalyzed chain transfer and methyl methacrylate (MMA) and/or butyl acrylate (BA) was synthesized and used as a stabilizer in the emulsion polymerization of MMA. Although clear differences were observed in polymerization rates using the different MAAx-MMAy stabilizers, these differences were not as clearly reflected in the particle sizes nor in the rates per particle. However, a clear difference between these systems and those stabilized by MAAx-BAy was observed. The latter systems were all characterized by much smaller particle sizes and corresponding higher rates of polymerization. In addition, the molar masses in the latter systems were all significantly larger than those obtained in the MAAx-MMAy stabilized system, in which the stabilizers act as "sulfur-free" RAFT agents. Interestingly, the prepared latexes showed a range of appearances varying from "milky" to "gel-like" depending on the used stabilizer. The MAAx-BAy stabilized latexes had, in general, a lower viscosity and a significantly smaller (if any) yield stress than the MAAx-MMAy stabilized latexes, and in the latter case the rheological behavior was found to depend on the block lengths in and concentration of the stabilizer