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We measured the response of BAS-TR imaging plate (IP) to energetic aluminum ions up to 222 MeV, and compared it with predictions from a Monte Carlo simulation code using two different IP response models. Energetic aluminum ions were produced with an intense laser pulse, and the response was evaluated from cross-calibration between CR-39 track detector and IP energy spectrometer. For the first time, we obtained the response function of the BAS-TR IP for aluminum ions with a kinetic energy as high as 222 MeV. On close examination of the two IP response models, we confirm that the exponential model fits our experimental data better. Moreover, we find that the IP sensitivity in the exponential model is nearly constant in this energy range, suggesting that the response function can be determined even with little experimental data.

The significant progress observed in ogranocatalytic ring-opening polymerization methods and orgranocatalysts for the controlled synthesis of complex polymer structures are reviewed.

Surface pressure-area (PI-A) isotherms and interfacial shear rheology experiments were performed to better understand the effects of two modifications, namely, varying the temperature between 5 and 40 degrees Celsius and introducing small amounts of carboxylic acid groups by partially hydrolyzing the polymer. Results reveal that both of these modifications can change the interactions that govern the shape of the surface pressure-area isotherm and interfacial rheological properties.

The zwitterionic ring-opening polymerization of lactide initiated by N-heterocyclic carbenes has generated cyclic polylactides with well-defined molecular weights with narrow polydispersities. The kinetic model has rationalized the unique features of zwitterionic ring-opening polymerization and has provided a mechanistic framework for optimizing the polymerizations as a strategy to generate well-defined cyclic polyesters.

Background: Telbivudine has been suggested to induce hepatitis B surface antigen (HBsAg) decline to the similar degree as pegylated interferon. We aimed to investigate whether telbivudine could further decrease HBsAg titer in patients who maintain undetectable serum hepatitis B virus (HBV) DNA after initial entecavir treatment. Methods: In this open-label trial, patients who had serum HBsAg and HBV DNA levels ≥1,000 IU/mL and <60 IU/mL, respectively, following entecavir (0.5 mg/day) treatment for HBeAg-positive chronic hepatitis B were randomized to either switch treatment to telbivudine (600 mg/day, n = 47) or continue entecavir (n = 50) for 48 weeks. Results: The baseline characteristics were comparable between groups including HBsAg levels (median, 3.41 log10 IU/mL). All patients had undetectable HBV DNA and normal alanine aminotransferase level. At week 48, the mean change in serum HBsAg levels was not significantly different between the telbivudine and entecavir groups (-0.03 log10 IU/mL vs. -0.05 log10 IU/mL; P = 0.57). No patient experienced HBsAg seroclearance or HBsAg decline >0.5 log10 IU/mL. Eleven patients (23.4%) in the telbivudine group, but none in the entecavir group, experienced virologic breakthrough (P < 0.001). Seven patients (14.9%) exhibited genotypic resistance mutations (M204I +/- L180M) during the virologic breakthrough. Conclusion: Sequential therapy with entecavir followed by telbivudine resulted in a high rate of virologic breakthrough and drug-resistance without any beneficial effect on HBsAg decline. These results do not support the use of low genetic barrier drugs as a switch treatment strategy in patients who achieve virologic response with high genetic barrier drugs. Trial Registration: NCT01595685 (date of trial registration: May 8, 2012). [ABSTRACT FROM AUTHOR]

High molecular weight poly(ε-caprolactone)s (PCL) were synthesized via zwitterionic polymerization of ε-caprolactone initiated with N-heterocyclic carbenes. Ring-opening polymerization of ε-caprolactone (1 M) with carbenes 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (1) or 1,3,4,5-tetramethylimidazol-2-ylidene (3) affords cyclic PCL with molecular weights up to Mn= 114 000 g/mol. Crystallization of the cyclic PCL was investigated by synchrotron small-angle X-ray scattering experiments and differential scanning calorimetry. High molecular weight cyclic poly(ε-caprolactone) crystallizes with a similar lamellar thickness and long period spacing as linear poly(ε-caprolactone), but the crystallization of cyclic poly(ε-caprolactone) is faster than that of linear poly(ε-caprolactone) for molecular weights greater than 75 000 g/mol. These results imply that the polymer topology does not have a significant influence on the crystal structure or morphology but can have a significant influence on the rate of crystallization from the melt. [ABSTRACT FROM AUTHOR]

The article discusses the ring-opening polymerization (ROP) of lactones using organometallic catalysts. According to the authors, the living of ROP of lactide yields a linear relationship between monomer conversion and molecular weight and poly(lactide) with a narrow polydispersity (PDI). They add that the benefits of living ROP have enabled the controlled synthesis of block, graft and star polymers. They also mention the characteristics of a living chain-growth polymerization.

The article discusses a study that reveals that saturated carbene 1,3-dimesitylimidazol-2-ylidene mediates the ring-opening polymerization of four-membered lactones to give cyclic polyesters through a novel mechanism involving the reversible collapse of zwitterionic intermediates to neutral imidazolidine spirocycles. Further efforts are directed toward expanding the synthetic utility of spirocycles and synthesizing macrocycles with functional groups and topology.