Fast‐degrading, salicylate‐based poly(anhydride‐esters) were designed to degrade and release the active component, salicylic acid (SA), within 1 week. The polymer degradation was enhanced by using shorter or oxygen‐containing aliphatic chains. A copolymer of diglycolic acid was also made with a salicylate‐based diacid for comparison of polymer properties, including SA release. Both methods resulted in polyanhydrides with molecular weights ranging from 14 500 to 27 800 Da and displayed glass transition temperatures near physiological conditions, namely 33–40 °C. The homo‐ and copolymers completely degraded within one week releasing the chemically incorporated SA.
Spherical single‐chain‐particles of poly(N‐isopropylacrylamide) were prepared in aqueous solution above the lower critical solution temperature upon the addition of sodium dodecyl sulfate. The size of the single‐chain‐particles was investigated by means of transmission electron microscopy and viscosity measurements of the corresponding solutions, indicating the absence of inter‐chain entanglements among the single‐chain‐particles.
Schematic of the preparation of PNIPAM single‐chain‐globules in solution. 相似文献
Summary: Commercial hydroxy‐terminated poly(ethylene glycol) monomethacrylates (PEG‐MAs) contain poly(ethylene glycol) dimethacrylate, which leads to unfavorable gel formation on polymerization. Here, hydroxy‐terminated PEG‐MA is readily isolated using a dimethylsilyl resin chlorinated with 1,3‐dichloro‐5,5‐dimethylhydantoin. Solution polymerization of the isolated PEG‐MA by free radical routes gives a high‐molecular‐weight amphiphilic graft copolymer without cross‐linking. The resulting polymer is stable for long periods in ambient conditions with preservation of the hydroxy end groups of PEG.
Commercial hydroxy‐terminated PEG‐MA can be separated readily and completely from PEG dimethacrylate contaminant with chlorinated dimethylsilyl resin. 相似文献
The synthesis of a rapidly forming redox responsive poly(ferrocenylsilane)‐poly(ethylene glycol) (PFS‐PEG)‐based hydrogel is described, achieved by a thiol‐Michael addition click reaction. PFS bearing acrylate side groups (PFS‐acryl) was synthesized by side group modification of poly(ferrocenyl(3‐iodopropyl)methylsilane) (PFS‐I) and characterized by 1H NMR, 13C NMR, and FT‐IR spectroscopy. The equilibrium swelling ratio, morphology, rheology, and redox responsive properties of the PFS‐PEG‐based hydrogel are reported.
Oxygen is shown to act as an efficient molar‐mass regulating agent in Gilch syntheses of PPV. As a scavenger, it undergoes instantaneous recombination with the initiating diradicals as soon as they appear in the system. Regular polymer formation can only start when all oxygen has been used, proceeding predominantly as chain‐growth polymerization of the p‐quinodimethane monomers. Since all radical species involved in this Gilch process are diradicals, some polyrecombination events occur in parallel. Therefore the initially formed peroxy diradicals are also incorporated into the resulting chains. Later, they break under very mild conditions, thereby causing a systematic decrease of the final molar mass of PPV.
Poly(amido‐amine)s carrying primary amino groups as side substituents have been obtained by polyaddition of N‐triphenylmethyl‐monosubstituted 1,2‐diaminoethane (TPHMAE) to 2,2‐bisacrylamido acetic acid or 1,4‐bisacryloylpiperazine and subsequent removal of the protecting triphenylmethyl group by treating the resultant polymers with aqueous hydrochloric acid. Soluble polymers can be also obtained directly by the polyaddition of monoprotonated 1,2‐diaminoethane to 2,2‐bisacrylamido acetic acid in the presence of a limited amount of added acetic or hydrochloric acid. The resultant polymers are of a higher molecular weight than the corresponding ones prepared from TPHMAE. By adding a limited amount of N‐triphenylmethyl‐monosubstituted 1,2‐diaminoethane to the monomer mixtures leading to poly(amido‐amine)s with a recognised potential as nonviral vectors, such as ISA 23 and ISA 1, a controlled number of pendant primary amino groups have been introduced. By this procedure, ISA 23 and ISA 1 become suitable as polymer carriers for carboxylated drugs as well as amenable to the labelling techniques by fluorescent probes commonly employed for proteins.
A simple method to fabricate polymer nanocomposites with single‐walled carbon nanotubes is reported, in which the nanotubes were reacted with poly(L ‐lysine) by using high‐speed vibration milling. The nanocomposites obtained were characterized by Fourier transform infrared (FT‐IR), UV–Vis spectroscopy, and thermogravimetric methods. The morphology as well as the dispersion of the carbon nanotubes were determined by scanning and transmission electron microscopy.
A long alkylsilyl group was attached to a thiophene ring system to overcome the instability of 2,5‐bis(halomethyl)thiophene monomers, by imparting steric hindrance and electronic delocalization. The resulting stable monomer could be used directly to prepare low‐band‐gap poly(thienylenevinylene) (1.57 eV) through heteroaromatic dehydrohalogenation polymerization.
Summary: New polymer gelators consisting of poly(propylene glycol) or poly(ethylene glycol) and L ‐lysine‐based low‐molecular‐weight gelators have been developed. These polymer gelators were synthesized according to a simple procedure with high reaction yield, and formed organogels in many organic solvents. The organogelation mechanism was proposed from the transmission electron microscopy and FTIR spectroscopy studies.
Structures of the polymer gelators synthesized here. 相似文献
Carbon black (CB) nanoparticles were encapsulated by poly(vinyl alcohol) (PVA) by a simple method of coacervation. Transmission electron microscopy (TEM) images clearly demonstrated that the successful encapsulation of PVA happened at the surfaces of CB nanoparticles. The particle‐size distribution measurements indicated that the diameters of the obtained PVA‐encapsulated CB (CB@PVA) nanoparticles were distributed within the nanoscale dimension. This strategy avoids the complicated polymerization process involved in the counterpart of polymer‐coating approaches.
A TEM image of PVA‐encapsulated carbon black. 相似文献
A polymeric film of a biodegradable poly(p‐dioxanone) was grown from 490 nm silica particles by monolayer formation via self‐assembly of hydroxy‐terminated triethoxysilane and subsequent surface‐initiated ring‐opening polymerization of p‐dioxanone. The resulting silica/poly(p‐dioxanone) hybrid particles were characterized by means of 1H NMR spectroscopy, IR spectroscopy, thermogravimetric analysis, field‐emission scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy.
Poly(ethersulfone) membranes were surface modified in a one‐step procedure. For this purpose, the membranes were soaked with aqueous solutions of different low‐molecular weight molecules bearing diverse hydrophilic functionalities and subject to electron beam treatment. No catalysts, photoinitiators, organic solvents or other toxic reagents were used, and no additional synthetic or purification steps were required.
Summary: A novel method for the tailoring of unique three‐phase crystalline systems in isotactic poly(propylene) has been proven. It is based on a synergistic application of a specific β‐nucleating agent and high pressure during crystallization. The formation of a γ phase was supported by elevated pressure and high temperature during crystallization; under these conditions the growth of both β and α phases was significantly suppressed. Nevertheless, during the course of crystallization at lower pressure and/or lower temperatures, strong β‐nucleation efficiency favored the formation of a β phase.
Summary: Octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane (OpePOSS) was used as the crosslinking agent to prepare the nanocrosslinked poly(4‐vinylpyridine) (P4VP) with POSS content up to 55.2 wt.‐%. The formation of the crosslinked structure is ascribed to the macromolecular reaction between pyridine rings of P4VP and epoxide groups of OpePOSS. The POSS‐crosslinked P4VP displayed enhanced glass transition temperatures (Tgs) and an improved thermal stability in terms of the results of thermal analysis.
Crosslinking of poly(4‐vinylpyridine) with octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane. 相似文献
A new soluble conjugated copolymer based on 2,7‐dibenzosilole and 4,7‐dithien‐2‐yl‐2,1,3‐benzothiadiazole units has been synthesized (PBSDTBT). Bulk heterojunction solar cell devices are fabricated using this material as the donor and [6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM) as the acceptor. The power conversion efficiency is 1.6% under AM1.5 illumination. This material also shows a good VOC (0.97 V). The results are quite promising considering the relatively large bandgap (1.9 eV) of this polymer.
Grafted conjugated polyelectrolytes were synthesized for the first time and characterized. The polymers demonstrated properties of a convenient and efficient protocol for creating Hg2+ sensors. The unique character of the new material comes from an anionic counterion nature with no external cofactors, and imparts high selectivity and fast detection for mercury ion in a fluorescence probe. The concept may be potentially applied to create new sensors for monitoring other ions.
Regioregular poly(3‐hexylthiophene) has been successfully incorporated into a novel amphiphilic block copolymer. The amphiphilic nature of poly(3‐hexylthiophene)‐block‐poly(acrylic acid) has been investigated using spectroscopic methods and has yielded solvatochromic behavior in several solvents of varying polarity. Evidence suggests that a supramolecular, long range ordering of block copolymer occurs in polar solvents, resulting in the formation of aggregates. Despite relatively large amounts of non‐conductive blocks, the poly(3‐hexylthiophene) diblock copolymer yields a high conductivity of 1 S · cm−1, and atomic force microscopy shows the formation of a highly organized nanofibrilar morphology in the solid state.
4‐Vinylbenzoyl azide was synthesized from p‐vinylbenzoic acid and polymerized by free radical polymerization. The obtained polymer contained acyl azide groups which were thermally transformed to the corresponding isocyanato groups. Reactions on these polymers with ethanol, hydroxyethyl methacrylate and 1‐pyrenebutanol proceeded quantitatively. Time‐resolved FT‐IR studies of the reactions with ethanol were carried out by varying the concentration and temperature. The effect of the solvent polarity on the Curtius rearrangement was investigated.
A series of novel temperature and pH responsive block copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly(L ‐lysine) (PLL) were synthesized. The effect of pH and the length of PLL on the lower critical solution temperature (LCST) of PNIPAM, and the self‐assembly of these PLL‐based copolymers induced by temperature and pH changes were investigated by the cloud point method, dynamic light scattering (DLS) and environmental scanning electron microscopy (ESEM). These PNIPAM‐b‐PLL copolymers can self‐assemble into micelle‐like aggregates with PNIPAM as the hydrophobic block at acidic pH and high temperatures; and at alkaline pH and low temperatures, they can self‐assemble into particles with PLL as the hydrophobic block. The copolymers may have potential applications in biotechnological and biomedical areas as drug release carriers.
Summary: Poly(dimethylsiloxane) (PDMS) star polymers having a nanosized silica particle as a core were prepared by reacting silica nanoparticles with monoglycidylether‐terminated poly(dimethylsiloxane). This star polymer was a hybrid material having an extremely high content of silica. The PDMS arms formed an organic domain to separate the silica particles and to prevent particle aggregation. The star polymers exhibited good thermal stability and high activation energy of their degradation reaction, in comparison to the linear PDMS polymer and the PDMS/silica blending materials. This star polymer can be used as a flame retardant for polymeric materials and this preparation technique can be applied to prepare other star polymers.
An SEM image of poly(dimethylsiloxane) star polymers having nanosized silica particles as a core. 相似文献
