Solvent-Selective Reactions of Alkyl Iodide with Sodium Azide for Radical Generation and Azide Substitution and Their Application to One-Pot Synthesis of Chain-End-Functionalized Polymers

Herein, a new reaction of an alkyl iodide (R–I) with an azide anion (N₃^–) to reversibly generate the corresponding alkyl radical (R^•) is reported. Via this new reaction, N₃^– was used as an efficient catalyst in living radical polymerization, yielding a well-defined polymer–iodide. A particularly interesting finding was the solvent selectivity of this reaction; namely, R–I and N₃^– generated R^• in nonpolar solvents, while the substitution product R–N₃ was generated in polar solvents. Exploiting this unique solvent selectivity, a one-pot synthesis of polymer–N₃ was attained. N₃^– was first used as a catalyst for living radical polymerization in a nonpolar solvent to produce a polymer–iodide and was subsequently used as a substitution agent in a polar solvent by simply adding the polar solvent, thereby transforming the polymer–iodide to polymer–N₃ in one pot. This one-pot synthesis was further applied to obtain N₃-chain-end-functionalized polymer brushes on the surface, uniquely controlling the N₃ coverage (number density). Using the chain-end N₃, the obtained linear and brush polymers were connected to functional molecules via an azide–alkyne click reaction. The attractive features of this system include facile operation, access to unique polymer designs, and no requirement for using excess NaN₃. In addition to N₃^–, thiocyanate (⁻SCN) and cyanate (⁻OCN) anions were also studied

Comprehensive Study on Chain-End Transformation of Polymer–Iodides with Amines for Synthesizing Various Chain-End Functionalized Polymers

Chain-end functionalized polymers (polymer–NHR) were successfully synthesized through the reaction of a polymer–iodide (polymer–I) with a primary amine (NH₂R), where the R moiety contains a functional group. This reaction was comprehensively studied for three different polymers, i.e., poly­(butyl acrylate), polystyrene, and poly­(methyl methacrylate), and six different functional amines with phenyl, alkyl, triethoxysilyl, SH, OH, and NH₂ functionalities, and the detailed reaction mechanisms were probed by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI–TOF–MS). This chain-end transformation reaction is easy to perform, amenable to various polymers and functional amines, and also quantitative and selective in many cases. This synthetic technique may serve as a useful platform method for synthesizing various chain-end functionalized polymers

Forest plots of diabetes incidence rate.

<p>CI indicates confidence interval.Dots indicate diabetes incidence rates. Horizontal lines indicate 95% CIs for incidence rates. The diamonds represent the pooled incidence rate estimates with 95% CIs.</p

Literature search.

<p>Literature search.</p

Bubble plots of diabetes incidence rate against the year of study initiation.

<p>A bubble shows a study, and the size of the bubble is proportional to the inverse of the variance of the log-transformed incidence rate. Diabetes incidence rate was calculated by dividing the number of new-onset diabetes cases by the duration of follow-up. When the mean follow-up duration was not available, the median was used.</p

Living Radical Polymerization with Alkali and Alkaline Earth Metal Iodides as Catalysts

The generation of an alkyl radical (R^•) from an alkyl iodide (R–I) with NaI playing a catalytic role was experimentally demonstrated. This catalytic reaction was exploited as an activation process for living radical polymerization. Alkali metal iodides, NaI, KI, and CsI, and alkaline earth metal iodides, MgI₂ and CaI₂, were systematically studied as catalysts. 18-<i>crown</i>-6-Ether and a polyether, that is, diethylene glycol dimethyl ether (diglyme), were utilized to solvate these catalysts in hydrophobic monomers. Among the five catalysts, NaI exhibited a particularly high reactivity. The polymer molecular weight and its distribution (<i>M</i>_w/<i>M</i>_n = 1.2−1.4) were well controlled with high conversions (e.g., 80–90%) in reasonably short periods of time (3–6 h) at mild temperatures (60–70 °C) in the polymerizations of methyl methacrylate. NaI is also amenable to styrene, acrylonitrile, and functional methacrylates. In addition to homopolymers, NaI also afforded well-defined block copolymers, chain-end functional polymers, and a star polymer. The high monomer versatility and accessibility to a wide range of polymer architectural designs are desirable features of this polymerization system

Biocompatible Choline Iodide Catalysts for Green Living Radical Polymerization of Functional Polymers

Herein, nontoxic and metabolizable choline iodide analogues, including choline iodide, acetylcholine iodide, and butyrylcholine iodide, were successfully utilized as novel catalysts for “green” living radical polymerization (LRP). Through the combination of several green solvents (ethyl lactate, ethanol, and water), this green LRP process yielded low-polydispersity hydrophobic, hydrophilic, zwitterionic, and water-soluble biocompatible polymethacrylates and polyacrylates with high monomer conversions. Well-defined hydrophobic–hydrophilic and hydrophilic–hydrophilic block copolymers were also synthesized. The accessibility to a range of polymer designs is an attractive feature of this polymerization. The use of nontoxic choline iodide catalysts as well as green polymerization conditions can contribute to sustainable polymer chemistry

Theoretical and Experimental Studies on Elementary Reactions in Living Radical Polymerization via Organic Amine Catalysis

The reaction mechanism of living radical polymerization using organic catalysts, a reversible complexation mediated polymerization (RCMP), was studied using both theoretical calculations and experiments. The studied catalysts are tetramethyl­guanidine (TMG), triethyl­amine (TEA), and thiophene. Methyl 2-iodoisobutyrate (MMA-I) was used as the low-molar-mass model of the dormant species (alkyl iodide) of poly­(methyl methacrylate) iodide (PMMA-I). For the reaction of MMA-I with TEA to generate MMA^• and ^•I-TEA radicals (activation process), the Gibbs activation free energy for the inner-sphere electron transfer mechanism was calculated to be 39.7 kcal mol^–1, while the observed one was 25.1 kcal mol^–1. This difference of the energies suggests that the present RCMP proceeds via the outer-sphere electron transfer mechanism, i.e., single-electron transfer (SET) reaction from TEA to MMA-I to generate MMA^• and ^•I-TEA radicals. The mechanism of the deactivation process of MMA^• to generate MMA-I was also theoretically studied. For the studied three catalysts, the theoretical results reasonably elucidated the experimentally observed polymerization behaviors

Flow diagram of study selection.

<p>Flow diagram of study selection.</p

Low-Carbohydrate Diets and All-Cause Mortality: A Systematic Review and Meta-Analysis of Observational Studies

<div><h3>Objective</h3><p>Low-carbohydrate diets and their combination with high-protein diets have been gaining widespread popularity to control weight. In addition to weight loss, they may have favorable short-term effects on the risk factors of cardiovascular disease (CVD). Our objective was to elucidate their long-term effects on mortality and CVD incidence.</p> <h3>Data sources</h3><p>MEDLINE, EMBASE, ISI Web of Science, Cochrane Library, and ClinicalTrials.gov for relevant articles published as of September 2012. Cohort studies of at least one year’s follow-up period were included.</p> <h3>Review methods</h3><p>Identified articles were systematically reviewed and those with pertinent data were selected for meta-analysis. Pooled risk ratios (RRs) with 95% confidence intervals (CIs) for all-cause mortality, CVD mortality and CVD incidence were calculated using the random-effects model with inverse-variance weighting.</p> <h3>Results</h3><p>We included 17 studies for a systematic review, followed by a meta-analysis using pertinent data. Of the 272,216 people in 4 cohort studies using the low-carbohydrate score, 15,981 (5.9%) cases of death from all-cause were reported. The risk of all-cause mortality among those with high low-carbohydrate score was significantly elevated: the pooled RR (95% CI) was 1.31 (1.07–1.59). A total of 3,214 (1.3%) cases of CVD death among 249,272 subjects in 3 cohort studies and 5,081 (2.3%) incident CVD cases among 220,691 people in different 4 cohort studies were reported. The risks of CVD mortality and incidence were not statistically increased: the pooled RRs (95% CIs) were 1.10 (0.98–1.24) and 0.98 (0.78–1.24), respectively. Analyses using low-carbohydrate/high-protein score yielded similar results.</p> <h3>Conclusion</h3><p>Low-carbohydrate diets were associated with a significantly higher risk of all-cause mortality and they were not significantly associated with a risk of CVD mortality and incidence. However, this analysis is based on limited observational studies and large-scale trials on the complex interactions between low-carbohydrate diets and long-term outcomes are needed.</p> </div