Summary: Laser‐induced fluorescence spectroscopy of the optical probe Nile Blue A in polymer clay nanocomposites is described. Concentration quenching of the fluorescence dominates the probe behavior until the clay platelets are physically separated by polymer intercalation. Further separation into an exfoliated structure results in an intense increase in probe fluorescence. Preliminary results indicate the ability to discriminate between intercalated and exfoliated structures in nanocomposites formed by melt processing.
Summary: The polymerization of ε‐caprolactone (CL) in the presence of HCl · Et2O by an activated monomer mechanism was performed to synthesize diblock or triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε‐caprolactone) (PCL). The obtained PCLs had molecular weights close to the theoretical values calculated from the CL to PEG molar ratios and exibited monomodal GPC curves. We successfully prepared PEG and PCL block copolymers by a metal‐free method.
The non‐metal catalyzed living ring‐opening polymerisation of ε‐caprolactone by PEG. 相似文献
Chromophore‐containing dendritic structures (G1, G2) are utilized to intercalate layered silicates, which results in a large d‐spacing up to 126 Å. An exfoliated morphology is obtained by mixing the dendritic structure intercalated layered silicates with polyimide in N,N‐dimethylacetamide solution. The dendritic structures attached on the clay template would arrange in a non‐centrosymmetric manner. This self‐assembled arrangement brought about the electro‐optical coefficients of 5–6 pm · V−1 for these relatively low chromophore‐containing organic/inorganic nanocomposites without resorting to poling. Excellent temporal stability (100 °C) is also achieved.
L,L ‐lactide (LA) and ε‐caprolactone (CL) block copolymers have been prepared by initiating the poly(ε‐caprolactone) (PCL) block growth with living poly(L,L ‐lactide) (PLA*). In the previous attempts to prepare block copolymers this way only random copolyesters were obtained because the PLA* + CL cross‐propagation rate was lower than that of the PLA–CL* + PLA transesterification. The present paper shows that application of Al‐alkoxide active centers that bear bulky diphenolate ligands results in efficient suppression of the transesterification. Thus, the corresponding well‐defined di‐ and triblock copolymers could be prepared.
Summary: Microwave‐assisted ring‐opening polymerization of ε‐caprolactone in the presence of 1‐butyl‐3‐methylimidazolium tetrafluoroborate ionic liquid using zinc oxide as a catalyst is investigated. By adding 30 wt.‐% ionic liquid, poly(ε‐caprolactone) with a weight‐average molar mass of 28 500 g · mol−1 is obtained at 85 W for 30 min. The results indicate that the polymerization could be efficiently enhanced in the presence of ionic liquids under microwave irradiation because ionic liquids can effectively absorb microwave energy.
Well‐defined amphiphilic PCL‐b‐PDMAEMA block copolymers were successfully synthesized by a combination of ATRP and “click” chemistry following either a commutative two‐step procedure or a straightforward one‐pot process using CuBr · 3Bpy as the sole catalyst. Compared to the traditional coupling method, combining ATRP and click chemistry even in a “one‐pot” process allows the preparation of PCL‐b‐PDMAEMA diblock copolymers characterized by a narrow molecular weight distribution and quantitative conversion of azides and alkynes into triazole functions. Moreover, the amphiphilic character of these copolymers was demonstrated by surface tension measurements and critical micellization concentration was calculated.
Summary: Three kinds of organoclay, i.e., Cloisite15A® (C15A), Cloisite20A® (C20A), and Cloisite30B® (C30B) were modified with silane to prepare twice functionalized organoclay (TFC). The pristine Cloisite® clays and the TFC were melt compounded with poly(L ‐lactide) (PLLA) and morphology of the composites was observed to elucidate the effects of the d001 gallery distance, the epoxy content of TFC, and the compatibility between the organic ammonium surfactant and PLLA on the degree of exfoliation of the clay layers.
Plots of ITFC/ICloisite versus epoxy content for PLLA composites with (a) Cloisite15A® (C15A), (b) Cloisite20A® (C20A), (c) Cloisite30B® (C30B). 相似文献
2,5‐Bis(chloromethyl)‐1,3,4‐oxadiazole was synthesized and dehydrohalogenation of this model compound was investigated under various base conditions. The formation of an intermediate with quinodimethane‐type structure is suggested for reaction in EtONa/EtOH. Polymerization of this intermediate proceeds via an anionic mechanism to form poly(1,3,4‐oxadiazole‐2,5‐diyl‐1,2‐vinylene). Polymerization at a toluene/water interface results in shorter polymerization times, milder conditions, higher molecular weights, higher yields and fewer defects in the polymer as compared to the corresponding polycondensation route.
Films of an α‐cyclodextrin/poly(ε‐caprolactone) inclusion complex have been successfully prepared and show high transparency and heat resistance in comparison to the pure polymer film. The physical properties, such as transparency, mechanical properties, and thermal stability, of the α‐CD‐PCL‐IC films are found to depend on the α‐cyclodextrin‐to‐polymer stoichiometry.
This communication reports a strategy for scale‐up of an in situ polymerization technique for polyolefin‐based nanocomposites preparation, taking layered silicate (clay) and multi‐walled carbon nanotubes (MWCNTs) as examples of nanofillers. The strategy is realized by transforming the nanofillers into granular “nanosupports” for Ziegler‐Natta catalysts. With a catalyst to polymer replication effect on particle morphology, the in situ prepared nanocomposites are of controlled granular particle morphology. With the polymer particle morphology controlled, the in situ polymerization technique becomes suitable for industrial olefin polymerization processes for mass production of polyolefin nanocomposites.
