1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD), N-methyl-TBD (MTBD), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) are effective organocatalysts for the ring-opening polymerization (ROP) of cyclic esters such as lactide (LA), δ-valerolactone (VL), and ε-caprolactone (CL). TBD is shown to polymerize LA, VL, and CL in a fast and controlled manner, whereas MTBD and DBU polymerized LA and addition of a thiourea cocatalyst led to the ROP of VL and CL being achieved. Each of the catalysts produced polymers displaying high end group fidelity, good correlation between theoretical and observed molecular weight, and linear relationships between conversion and molecular weight. The enhanced activity of TBD relative to MTBD and DBU is attributed to its bifunctionality, enabling the simultaneous activation of both the cyclic ester monomer and the alcohol group of the initiator/propagating species. Temperature-dependent NMR studies generated individual association constants for MTBD with benzyl alcohol and thiourea with VL. In combination with temperature-dependent ROP of VL in the presence of benzyl alcohol, MTBD, and thiourea, these data have led to the derivation of the activation energy for the ROP (49 ± 3 kJ mol-1). The simplicity of the reaction conditions, the ready availability of the catalysts, the variety of polymerizable cyclic ester monomers, and the exquisite control over the polymerization are demonstrated.

A variety of organocatalysts has been surveyed in the ring opening polymerization of trimethylene carbonate. Excellent control was found for several of these catalysts yielding well-defined polycarbonates with molecular weights up to 50 000 g mol-1, polydispersities below 1.08, and high end-group fidelity. Melt or bulk polymerization was accomplished without loss of control of molecular weight or polydispersity, and random ester−carbonate bulk polymerizations were also demonstrated. Furthermore, by combining disparate polymerization techniques using bifunctional initiators, the mild polymerization conditions allow for the preparation of new block copolymers. Hydrogen-bond activation of monomer and initiator/propagating species is proposed as the underlying mechanism, which can be tuned to mitigate adverse side reactions.

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In einer Umgebung, die reich an protonierenden oder oxidierenden Spezies ist (z. B. in Krebszellen), wird die Hauptabsorptionsbande sphärischer, wasserlöslicher Polyanilin‐Nanopartikel in den Nah‐Infrarot(NIR)‐Bereich verschoben. Verursacht wird dies durch die Bildung des Emeraldinsalzes (siehe Bild). Die dotierten Nanopartikel verursachen eine photothermische Ablation von Krebszellen bei NIR‐Laserbestrahlung in vitro und in vivo.

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Hyperbranched poly( -caprolactone)s (HPCLs) were synthesized by moisture-sensitive catalyst-free polycondensation of AB 2 macromonomers, 2,2-bis[ω-hydroxy oligo( -caprolactone)methyl]propionic acids. The HPCLs were designed to incorporate different lengths of linear oligomeric segments consisting of 5, 10, and 20 -caprolactone monomer units on the branched backbone chains, accordingly named as HPCL-5, -10, and -20, respectively. End-group analyses were performed on 1 H NMR spectra of the three HPCLs, which provided information about the average number of -caprolactone units incorporated in the AB2 macromonomers and thus the average number of AB2 macromonomer units incorporated in the resulting hyperbranched polymers. Consequently, the absolute values of molecular weights for the HPCLs were calculated. Size exclusion chromatography equipped with multiangle laser light scattering detector (SEC-MALLS) was employed to measure absolute molecular weights and molecular weight distributions of HPCLs. Then, the results were compared with those obtained from 1 H NMR end-group analyses, indicating that there was a good agreement between them. From small-angle X-ray scattering (SAXS), the radii of gyration of the HPCLs and their linear counterpart, poly(caprolactone) (LPCL), were determined from the initial slope of the reciprocal of scattered intensity, 1/I(q), vs the square of scattering vector, q 2 , curves, fit by the Zimm scattering function. The ratio of meansquare radius of gyration of each HPCL to that of LPCL, termed the branching ratio, resulted in the relative degree of branching for individual HPCLs. As the length of linear oligo( -caprolactone) segments decreased, the more highly branched polymers were obtained, i.e., in the order of HPCL-5, -10, and -20 from higher to lower degree of branching. The melting temperatures of HPCLs were lower than that of LPCL and decreased with increase in the degree of branching. In contrast, the thermal decomposition temperatures of HPCLs were shown to be higher than that of LPCL, becoming higher as the degree of branching increased.

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