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The recent advances in accelerated polymerization of N-carboxyanhydrides (NCAs) enriched the toolbox to prepare well-defined polypeptide materials. Herein we report the use of crown ether (CE) to catalyze the polymerization of NCA initiated by conventional primary amine initiators in solvents with low polarity and low hydrogen-bonding ability. The cyclic structure of the CE played a crucial role in the catalysis, with 18-crown-6 enabling the fastest polymerization kinetics. The fast polymerization kinetics outpaced common side reactions, enabling the preparation of well-defined polypeptides using an α-helical macroinitiator. Experimental results as well as the simulation methods suggested that CE changed the binding geometry between NCA and propagating amino chain-end, which promoted the molecular interactions and lowered the activation energy for ring-opening reactions of NCAs. This work not only provides an efficient strategy to prepare well-defined polypeptides with functionalized C-termini, but also guides the design of catalysts for NCA polymerization. The recent advances in accelerated polymerization of N-carboxyanhydrides (NCAs) enrich the toolbox to prepare well-defined polypeptide materials. Here the authors use crown ethers to catalyze the polymerization of NCA initiated by conventional primary amine initiators in solvents with low polarity and low hydrogen-bonding ability. [ABSTRACT FROM AUTHOR]

This study assesses the use of immobilized lipase catalyst N435 during reactive extrusion (REX) versus magnetically stirred bulk and solution reaction conditions for the copolymerization of ε‐caprolactone with ω‐pentadecalactone (CL/PDL 1:1 molar). N435‐catalyzed REX for reaction times from 1 to 3 h results in total %‐monomer conversion, Mn, and Đ values increase from 92.7% to 98.8%, 36.1 to 51.3 kDa, and 1.85 to 1.96, respectively. Diad fraction analysis by quantitative 13C NMR reveals that, after just 1 h, rapid N435‐catalyzed transesterification reactions occur that give random copolyesters. In contrast, for bulk polymerization with magnetic stirring in round bottom flasks, reaction times from 1 to 3 h result in the following: Mn increases from 12.4 to 25.6 kDa, Đ decreases from 2.98 to 1.87, and the randomness index increases from 0.74 and 0.86 as PDL*–PDL diads are dominant. These results highlight that REX avoids problems associated with internal batch mixing that are encountered in bulk polymerizations. In sharp contrast to a previous study of 1:1 molar PDL/δ‐valerolactone (VL) copolymerizations by N435‐catalyzed REX, VL %‐conversion increases to just 40.1% in 1 h whereas CL reaches 94.7%. [ABSTRACT FROM AUTHOR]

Photo-responsive block copolymer mPEG-b-poly(Tyr)-g-NB was prepared by introduction of o-nitrobenzyl ester group into the side chain of amphiphilic poly(ethylene glycol)-b-poly( α-hydroxy acids) (mPEG-b-poly(Tyr)) containing pendent alkynyl group via copper-catalyzed azide-alkyne cycloaddition reaction. The amphiphilic mPEG-b-poly(Tyr) was synthesized via the ring-opening polymerization of O-carboxyanhydrides, with monomethoxy poly(ethylene glycol) (mPEG) as macroinitiator. The molecular structure, self-assembly, and photo-controlled release of the obtained mPEG-b-poly(Tyr)-g-NB were thoroughly investigated. mPEG-b-poly(Tyr)-g-NB could self-assemble into spherical micelles in water and showed disassembly under UV light irradiation, which was demonstrated by means of UV-vis spectroscopy, scan electron microscopes, and dynamic light scattering measurement. Fluorescence emission measurements demonstrated that Nile red, encapsulated by micelles, can be released upon UV irradiation. This study provides a convenient way to construct smart poly( α-hydroxy acids)-based nanocarriers for controlled release of hydrophobic drugs. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Reversibly light-responsive micelles are constructed from an amphiphilic azobenzene-containing diblock copolymer AZO-mPEG-poly(5)25. The copolymer is synthesized via ring-opening polymerization of O-carboxyanhydrides bearing alkyne group, followed by azide-alkyne click chemistry with an azide-containing azobenzene derivative. AZO-mPEG-poly(5)25 can self-assemble to spherical micelles. Light response of the polymeric micelles is demonstrated by UV-vis spectroscopy and scanning electron micro­scopy (SEM). SEM images show that after UV irradiation, the micelles are partly dissociated, which is ascribed to swelling of the hydrophobic chain because of hydrophobicity change during the trans-cis isomerization of the azobenzene group. After subsequent visible-light irradiation, the morphology returns back to micelles. [ABSTRACT FROM AUTHOR]

The copolymerization of N-phenylmaleimide (NPMI) with styrene (St) was studied with a rare earth coordination catalyst Nd(naph)3–AlEt3 in toluene at 50 °C. The compositions of the two monomers in copolymers were close to 1:1 even at a high monomer conversion of about 60%, and did not change as the NPMI feed mole fraction varied from 10% to 90%. The copolymer was characterized by 13C nuclear magnetic resonance spectroscopy, showing that the copolymer possessed a nearly alternating structure. The thermal properties of the copolymers were also investigated. It was presumed that a charge transfer complex of NPMI and St participated in the polymerization process. [Copyright &y& Elsevier]

Abstract: A novel benzoxazine monomer containing maleimide functional group, namely 1-[3-(4-methyl-phenyl)-3,4-dihydro-2H-benzo[e][1,3]-oxazine-6-yl]maleimide (HPM-Bz-Me), was synthesized. Its copolymerization with styrene was also investigated. The structures of the monomer and the resulting copolymer were identified by NMR and FTIR. Results showed that a nearly alternating copolymer poly(HPM-Bz-Me-co-St) was obtained. The mechanism of alternate complex and the effect of solvent polarity on the copolymer stereochemistry, which further affected the thermal performance of the copolymers, were discussed. TGA results showed that the copolymer emerged good thermal properties. The 10% weight loss temperature was about 441 °C and char yield was 48% at 600 °C, which showed that the copolymers could be used as high thermal resistance materials. The curing kinetics of poly(HPM-Bz-Me-co-St) was investigated via non-isothermal DSC at different heating rates by Kissinger, Ozawa, Flynn-Wall-Ozawa and Friedman methods. The autocatalytic kinetic model was found to be the best description of the investigated curing reactions. [Copyright &y& Elsevier]