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The catalytic potential of tin(II)acetate, tin(IV)acetate, dibutyltin-bis-acetate and dioctyl tin-bis-acetate was compared based on polymerizations of L-lactide conducted in bulk at 160 or 130C. With SnAc2 low-Lac/Cat ratios (15/1–50/1) were studied and linear chains having one acetate and one carboxyl end group almost free of cyclics were obtained. Higher monomer/catalyst ratios and lower temperatures favored formation of cycles that reached weight average molecular weights (Mw's) between 100,000 and 2,500,000. SnAc4 yielded mixtures of cycles and linear species under all reaction conditions. Dibutyltin- and dioctyl tin bis-acetate yielded cyclic polylactides under most reaction conditions with Mw's in the range of 20,000–80,000. Ring-opening polymerizations performed with ε-caprolactone showed similar trends, but the formation of COOH-terminated linear chains was significantly more favored compared to analogous experiments with lactide. The reactivity of the acetate catalysts decreased in the following order: SnAc2> SnAc4>Bu2SnAc2 Oct2SnAc2.
The catalytic potential of tin(II)acetate, tin(IV)acetate, dibutyltin-bis-acetate and dioctyl tin-bis-acetate was compared based on polymerizations of L-lactide conducted in bulk at 160 or 130°C. With SnAc2 low-Lac/Cat ratios (15/1–50/1) were studied and linear chains having one acetate and one carboxyl end group almost free of cyclics were obtained. Higher monomer/catalyst ratios and lower temperatures favored formation of cycles that reached weight average molecular weights (Mw's) between 100,000 and 2,500,000. SnAc4 yielded mixtures of cycles and linear species under all reaction conditions. Dibutyltin- and dioctyl tin bis-acetate yielded cyclic polylactides under most reaction conditions with Mw's in the range of 20,000–80,000. Ring-opening polymerizations performed with ε-caprolactone showed similar trends, but the formation of COOH-terminated linear chains was significantly more favored compared to analogous experiments with lactide. The reactivity of the acetate catalysts decreased in the following order: SnAc2> SnAc4>Bu2SnAc2~Oct2SnAc2
The definition of the term “conversion” is discussed for a variety of polymer syntheses. It is demonstrated that in contrast to organic and inorganic chemistry several different definitions are needed in polymer science. The influence of increasing conversion on structure and topology of homo- and Copolymers is illustrated. Chain-growth polymerizations, such as radical polymerization or living anionic polymerizations of vinyl monomers, condensative chain polymerization, two and three-dimensional step-growth polymerizations, ring–ring or chain–chain equilibration and chemical modification of polymers are considered.
One series of BiSub-catalyzed ring-opening polymerizations (ROPs) is per-formed at 160 °C for 3 days with addition of difunctional cocatalysts to find out, if poly(l-lactide) crystallizes directly from the reaction mixture. An analogous series is performed with monofunctional cocatalysts. High Tm crystal-lites (Tm > 190 °C) are obtained from all bifunctional cocatalysts, but not from all monofunctional ones. It is shown by means of SAXS measurements that the high Tm values are mainly a consequence of a transesterification–homogenization process across the lamellar surfaces resulting in thickness and smoothing of the surfaces. An unusual enthalpy-driven modification of the molecular weight distribution is found for samples that have crystallized during the polymerization. A third series of ROPs is performed at 170 °C for 2 h followed by annealing at 120 °C (2 h) to induce crystallization. Complete transformation of the resulting low Tm crystallites (Tm < 180 °C) into the high Tm crystallites by annealing at 170 °C for 1 d is not achieved, despite variation of the cocatalyst.
The main objective of this work was to design new advanced sorbent phases, alternating copolymers, derived from isosorbide and 2,6-difluorpyridine, to be used for the removal of aromatic organic pollutants present in water at low concentrations. Six different monomers, dianhydrohexitols isomers and bisphenol derivatives, weresynthesized in order to make it possible to study their hydrophilic and hydrophobiceffect on the sorption efficiency of the resulting polymeric phases. Before this study, we have confirmed the chemicals structures, molecular weights, and thermal properties of the obtained polymeric phases. Sorption results show a higher adsorption efficiency of P6 co-poly(ether-pyridine) based on bisphenol substituted with pyridineunits, for all tested pollutants, hydrophobic and hydrophilic ones, due to its less compact structure. Two aromatic organic pollutants, p-hydroxybenzoic acid and toluicacid, were selected as sorbates to study the adsorption characteristic, kinetics and isotherms of the copoly(ether pyridine) P6. Langmuir model led to a better fitting of the sorption isotherms; the sorption of toluic acid is easier than of that p-hydroxybenzoic acid. Comparing 1/n values for benzoic acid was two time lower for P6 compared to that for biochar and for crosslinked methacrylate resin, showing a higher efficiency
A set of strained aromatic macrocycles based on [n]cyclo2,7-(4,5,9,10-tetrahydro)pyrenylenes is presented with size dependent photophysical properties. The K-region of pyrene was functionalized with ethylene glycol groups to decorate the outer rim and thereby confine the space inside the macrocycle. This confined space is especially pronounced for n = 5, which leads to an internal binding of up to 8.0×104 M–1 between the ether-decorated [5]cyclo-2,7-pyrenylene and shape complementary crown ether–cation complexes.
Both, the ether-decorated [n]cyclo-pyrenylenes as well as one of their host–guest complexes have been structurally characterized by single crystal X-ray analysis. In combination with computational methods the structural and thermodynamic reasons for the exceptionally strong binding have been elucidated. The presented rim confinement strategy makes cycloparaphenylenes an attractive supramolecular host family with a favorable, size-independent read-out signature and binding capabilities extending beyond fullerene guests.