Summary: We developed a facile approach to hyperbranched polymers by applying a superelectrophilic reaction within an A2 + B3 strategy. A significant reactivity difference between the intermediate and the starting material was utilized to avoid gelation in the A2 + B3 polymerization. A number of hyperbranched poly(arylene oxindole)s were achieved in a one‐step polymerization and characterized by NMR spectroscopy and gel permeation chromatography. Moreover, further modifications at the interior and exterior of the resulting polymers were explored as well.
Structure of the hyperbranched polymers produced using the A2 + B3 approach. 相似文献
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.
Large scale of well‐ordered macroporous π‐conjugated polymer monoliths have been successfully prepared through a new approach using micrometer‐sized naphthalene crystals as templates. The macroporous monoliths of poly(p‐phenylenevinylene) (PPV) and poly(p‐phenyleneethynylene) (PPE) grew along the unidirectional freezing direction inside the template naphthalene crystals which lead to the formation of controlling morphologies and homogeneous diameters. The polymer monoliths show straight and lamella macroporous structures. The diameters of pores and the thickness of pore walls can be controlled by tuning the freezing temperature.
A cationic water‐soluble polyfluorene (P2) containing a high density of tetraalkylammonium side chains in polymer backbone was synthesized and characterized. The polymer shows excellent water solubility up to 100 mg · mL−1 as well as high photoluminescence (PL) quantum yield of 44% in water. The relatively high cationic density and appropriate side chain length of the polymer are the key factors to achieve such high water solubility. The reduction potential of P2 is decreased as compared with its neutral polymer, reflecting the enhanced electron injection abilities. The standard NPB/Alq3 device using such a polymer as the electron injection layer shows nearly three‐fold enhancement in the electroluminescence (EL) efficiency.
The effect of PAMAM dendrimers (generations G3, G4 and G5) on the fibrillation of α‐synuclein was examined by fluorescence and CD spectroscopy, TEM and SANS. PAMAM dendrimers inhibited fibrillation of α‐synuclein and this effect increased both with generation number and PAMAM concentration. SANS showed structural changes in the formed aggregates of α‐synuclein – from cylindrical to dense three‐dimensional ones – as the PAMAM concentration increased, on account of the inhibitory effect. PAMAM also effectively promoted the breaking down of pre‐existing fibrils of α‐synuclein. In both processes – that is, inhibition and disassociation of fibrils – PAMAM redirected α‐synuclein to an amorphous aggregation pathway.
Poly(N‐isopropylacrylamide) (PNIPAM) oligomer containing one adamantyl (AD) and two β‐cyclodextrin (β‐CD) moieties at the chain terminals, AD‐PNIPAM‐(β‐CD)2, was synthesized by atom transfer radical polymerization (ATRP) and successive click reactions. In aqueous solution, AD‐PNIPAM‐(β‐CD)2 spontaneously forms supramolecular thermoresponsive hyperbranched polymers via molecular recognition between AD and β‐CD moieties. To the best of our knowledge, this work represents the first report of the construction of supramolecular thermoresponsive hyperbranched polymers from well‐defined polymeric AB2 building units.
An experimental investigation of the kinetics of cationic polymerization of β‐pinene was performed using two different initiator systems under two different operating conditions (shot additions of initiator, and continuous feeding of monomer). The experiments were done using calorimetric measurements under isoperibolic conditions. The heat of polymerization of β‐pinene was found to be ?30.6 kcal · mol?1. A simple kinetic model was tentatively proposed, and the model fit reasonably well to the different experimental runs. Different values of the fitting parameters were obtained for runs carried out under different conditions, which can probably be ascribed to the presence of adventitious impurities in the commercial‐grade monomer used.
Two novel monovinyl β‐cyclodextrin (β‐CD) monomers are synthesized. Their chemical compositions are characterized by means of element analysis, NMR and FT‐IR spectroscopy. The results show that the synthesis techniques used are convenient and efficient. Using N‐isopropylacrylamide as a comonomer, two novel linear copolymers can also be synthesized.
A novel α,ω‐heterofunctional poly(ethylene oxide) (PEO) macromonomer possessing methacryloyl and thienyl end groups was prepared by ring‐opening polymerization of ethylene oxide initiated by potassium thienylethoxide and termination of the living PEO ends with methacryloyl chloride. Incorporation of methacryloyl and thienyl groups was confirmed by free‐radical and oxidative polymerization processes, respectively, and by means of 1H NMR analysis.
Three copolymers that incorporate dithieno[3,2‐b:2′,3′‐d]pyrrole with fluorene, carbazole, or pyridine have been prepared by Suzuki reaction and characterized by NMR spectroscopy and GPC. A new homopolymer of dithieno[3,2‐b:2′,3′‐d]pyrrole was also synthesized for the comparison of their structure–property relationships. Their thermal, optical, and electrochemical properties have been investigated. All the polymers exhibit good thermal stability with decomposition temperatures around 400 °C. The fluorescence quantum efficiencies of all these polymers in solution are in the range of 33.5–55.5%. The copolymers also show high film fluorescence quantum efficiencies of about 20% while the fluorescence of the homopolymer film is almost quenched.
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.
Detection of the adduct radical by ESR spectroscopy and after‐effect ESR measurements of the adduct radical concentrations in the photosensitized polymerization of styrene (St) in the presence of dimers of α‐methylstyrene (MSD) and methyl methacrylate have revealed that the dominant mechanism of adduct radical loss changes from bimolecular termination to fragmentation as the temperature is increased beyond 90 °C for St/MSD.
The morphology transition of polystyrene‐block‐poly(butadiene)‐block‐poly(2‐vinylpyridine) (SBV) triblock thin film induced in benzene vapor showing weak selectivity for PS is investigated. The order‐order transitions (OOT) in the sequence of core‐shell cylinders (C), sphere in ‘diblock gyroid’ (sdG), sphere in lamella (sL) and sphere (S) are observed. The projection along (111) direction in Gyroid phase (sdG(111)) is found to epitaxially grow from C(001) in the film. Instead of sdG(111), sdG(110)0.1875 develops to the phase of sL. Consequently, the film experiences the transition sequence of sdG(111) → sdG(211) → sdG(110)0.25 → sdG(110)0.1875 between C and sL. The mechanism is analyzed from the total surface area of the blocks.
This review covers the literature concerning the modification of polysaccharides through controlled radical polymerizations (NMP, ATRP and RAFT). The different routes to well‐defined polysaccharide‐based macromolecules (block and graft copolymers) and graft‐functionalized polysaccharide surfaces as well as the applications of these polysaccharide‐based hybrids are extensively discussed.
Summary: Transcrystallinity in UHMWPE fiber‐reinforced HDPE composites promotes a significant β transition that is untypical of high‐density polyethylene. Surface profiling by atomic force microscopy identifies two distinct morphologies in the composite without a boundary phase between them, which coincide with the transcrystalline layer and with the bulk spherulitic matrix. As a result, the claim that attributes this transition to loose chain folds at the lamella surface is favored.
Atomic force microscopy scan of the transcrystalline layer above the fiber with the impression of the fiber in the center. 相似文献
A novel strategy to prepare reactively compatibilized polymer blends is reported. An oligomer that consists of AMS (α‐methyl styrene) and GMA (glycidyl methacrylate) is initially synthesized. When this oligomer is melt blended with poly(propylene) (PP), the GMA units in the oligomer are successfully grafted onto the PP chain, which is proven by measuring the FT‐IR spectrum of the blended PP. When the oligomer is added to a blend of PP/Ny66, an in‐situ compatibilization occurs, which leads to an increase in torque values during blending, a decrease in crystallinity degree of Ny66, and is observed by SEM images of the resulting blends. The compatibilizing effects of the oligomer are also observed in PP/Ny6 and polyethylene/Ny6 blends. A relevant compatibilization mechanism is proposed.
A high‐molar‐mass cylindrical brush polymer with a main chain degree of polymerization of Pw = 1047 is synthesized by free‐radical polymerization of a poly‐2‐isopropyloxazoline macromonomer with Pn = 28. The polymerization is conducted above the lower phase transition temperature of the macromonomer, i.e., in the phase‐separated regime, which provides a sufficiently concentrated macromonomer phase mandatory to obtain high‐molar‐mass cylindrical brushes. Upon heating to the phase transition temperature, the hydrodynamic radius is observed to shrink from 34 to 27 nm. Further increase in temperature resulted in aggregated chains which were observed to coexist with single chains until eventually only aggregates of μm size were detectable.
