Two kinds of representative polymers, poly(N‐isopropylacrylamide) (PNIPAAm) and β‐cyclodextrin (β‐CD) were selected and modified with azide and alkyne fucntional groups, respectively. When the solutions of these two modified polymers were mixed together, a cross‐linking reaction, a type of Huisgen's 1,3‐dipolar azide‐alkyne cycloaddition, occurred in the presence of Cu(I) catalyst. The strategy described here provides several advantages for the hydrogel formation including mild reaction conditions and controllable gelation rate. The resulted hydrogels were studied in terms of scanning electric microscopy (SEM), equilibrium swelling ratio and swelling/shrinking kinetics. The data obtained demonstrated the hydrogels had a porous structure as well as favorable thermosensitivity.
The mixed Langmuir monolayers and Langmuir–Blodgett (LB) films of homo‐polystyrene (h‐PS) and the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) have been characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. When the content of h‐PS is below 80 wt.‐%, the mixed LB films of h‐PS/PS‐b‐P2VP mainly exhibit isolated circular nanoaggregates. With a further increase of the h‐PS content (80–95%), however, highly uniform and stable necklace‐network structures are observed in the mixed LB films.
A new concept to build shape memory polymers (SMP) combining outstanding fixity and recovery ratios (both above 99% after only one training cycle) typical of chemically crosslinked SMPs with reprocessability restricted to physically crosslinked SMPs is demonstrated by covalently bonding, through thermoreversible Diels–Alder (DA) adducts, star‐shaped poly(ε‐caprolactones) (PCL) end‐functionalized by furan and maleimide moieties. A PCL network is easily prepared by melt‐blending complementary end‐functional star polymers in retro DA regime, then by curing at lower temperature to favour the DA cycloaddition. Such covalent network can be reprocessed when heated again at the retro DA temperature. The resulting SMP shows still excellent shape memory properties attesting for its good recyclability.
Summary: A water‐soluble gold nanoparticle aggregate 2 was prepared by chloroauric acid and a polypseudorotaxane 1 of mono‐6‐thio‐β‐cyclodextrin with poly(propylene glycol) bis(2‐aminopropyl ether) ( ≈ 2 000) in the presence of sodium borohydride in N,N‐dimethylformamide (DMF) solution. The investigative results indicated that the gold nanoparticle aggregate 2 might act as an efficient DNA‐cleavage reagent.
A typical TEM image of gold nanoparticle aggregate 2 . 相似文献
Summary: The vapor‐based synthesis and characterization of a reactive polymer, poly[(4‐formyl‐p‐xylylene)‐co‐(p‐xylylene)] ( 1 ), have been reported. The reactive polymer coating enables the immobilization of oligosaccharides via the chemoselective aldehyde‐hydrazide coupling reaction.
A novel supramolecular network has been prepared based on the formation of inclusion complexes between γ‐cyclodextrin and poly(ethylene glycol), in which the PEG chains are interlocked by γ‐CD rings. This PEG/γ‐CD network exhibits good shape memory behavior because of the crosslinked structure. The crosslinked PEG/γ‐CD inclusion complexes and PEG crystallites account for the fixing phase and reversible phase, respectively. The characteristics of the materials have been investigated by 1H NMR spectroscopy, XRD, DSC, DMA, viscosity tests, and swelling measurements.
A novel synthetic method combining chemo and enzymatic synthesis strategies was employed to prepare a vinyl acetate type monomer, 6‐(4‐methoxybiphenyl‐4′‐oxy)hexyl vinyl hexanedioate (VA‐LC). Homo‐ and copolymers of VA‐LC with maleic anhydride (MAn) were prepared by conventional free radical polymerization using 2,2′‐azobisisobutyronitrile (AIBN) and 1,1′‐azobis (cyclohexane carbonitrile) (AHCN) as an initiator at 95 and 60 °C, respectively. The thermal properties of the generated polymeric material were investigated by differential scanning calorimetry (DSC), and the optical texture was inspected by polarizing optical microscopy (POM). While the monomer VA‐LC does not exhibit liquid‐crystalline properties, poly(VA‐LC), and the alternating copolymer of VA‐LC with maleic anhydride both displayed such properties.
Hyperbranched polythiophenes were prepared via a simple one‐pot synthesis approach based on oxidative coupling of branched conjugated monomers. Only small variations in the building unit and architecture lead to large differences of absorption and photoluminescence properties. Interestingly, soluble hyperbranched polythiophenes with relatively small molecular weights show enhanced absorption at low and high wavelengths compared to linear analogues, such as poly(3‐hexyl thiophenes) with high molecular weights. With this versatile approach we present a method to design tailor made, functional materials with potential applications in optoelectronics.
Summary: Three‐dimensional polyaniline (PANI) nanowire networks were synthesized in high yield using a “soft template” self‐assembled with hexadecyltrimethylammonium bromide and oxalic acid. The PANI nanowire networks had diameters from 35–100 nm depending on synthesis conditions and/or procedures. The networks and the “cross‐linking points” were clearly observed by field‐emission scanning electron microscopy and transmission electron microscopy. A possible mechanism for the formation of three‐dimensional PANI nanowire networks is discussed.
FESEM image of PANI with three‐dimensional nanowire networks. 相似文献
Mn(salen)Cl was applied as a low‐cost catalyst for the formation of alkoxyamines from nitroxides and substituted styrenes. These “unimolecular initiators” for nitroxide‐mediated radical polymerization (NMRP) were synthesized using 2,2,6,6‐tetramethyl‐1‐piperidine‐1‐oxyl and 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐oxyl. Functionalized alkoxyamines were obtained from 4‐vinylbenzyl chloride and 4‐vinylbenzyl alcohol. The divinyl compound 1,2‐bis(4‐vinylphenyl)ethane was converted to an alkoxyamine monomer and to bisaminooxy compounds, which can be used as “biradical initiators” for NMRP.
Formation of alkoxyamines using Mn(salen)Cl as the catalyst. 相似文献
DUV interferometric lithography and diblock copolymer self‐organization have successfully been combined to provide a simple and highly collective nanopatterning technique enabling the organization of nanoparticles over several orders of magnitude, from nanometre to millimetre. The nanostructural changes at the surface of the polymer film after thermal annealing have been monitored by AFM and the process parameters optimized for obtaining a long‐range organization of the lamellar domains. In particular, the impact of the annealing conditions and geometric parameters of the substrate patterns have been investigated. The nanopatterns resulting from the lamellar demixion of (PS‐b‐MMA) were used for a controlled deposition of nanoparticles. The affinity of the hydrophobic particles for the PS block was demonstrated, opening new doors towards the preparation of high‐density arrays of nanoparticles with potential applications in data storage.
A series of π‐conjugated polymers linked by benzocarborane (1,2‐(buta‐1′,3′‐diene‐1′,4′‐diyl)‐1,2‐dicarbadodecaborane) were synthesized via Sonogashira–Hagihara polycondensation reaction. The opened molecular structure of diiodo monomer containing benzocarborane resulted in fast polymerization and high molecular weights. The obtained polymers were fully characterized by 1H, 13C, and 11B NMR spectroscopies. UV‐vis absorption and photoluminescence studies revealed the acceptor‐profile of benzocarborane. Unlike the polymers linked by o‐carborane, these polymers exhibited strong luminescence in the solution state, presumably because the inductive effect of carborane is dominant, rather than cage‐π interactions.
A novel redox‐induced shape‐memory polymer (SMP) is prepared by crosslinking β‐cyclodextrin modified chitosan (β‐CD‐CS) and ferrocene modified branched ethylene imine polymer (Fc‐PEI). The resulting β‐CD‐CS/Fc‐PEI contains two crosslinks: reversible redox‐sensitive β‐CD‐Fc inclusion complexes serving as reversible phases, and covalent crosslinks serving as fixing phases. It is shown that this material can be processed into temporary shapes as needed in the reduced state and recovers its initial shape after oxidation. The recovery ratio and the fixity ratio are both above 70%. Furthermore, after entrapping glucose oxidase (GOD) in the system, the material shows a shape memory effect in response to glucose. The recovery ratio and the fixity ratio are also above 70%.
It is the general consensus that in Gilch polymerizations the 1,4‐bis(chloromethylene)benzene starting material first changes into p‐quinodimethane intermediates which then act as the real monomers. However, direct observation of these intermediates has not been possible so far. This is because usually the p‐quinodimethane auto‐initiates its rapid radical polymerization instantaneously, keeping its concentration extremely low throughout the whole process. Here it is shown that, when the reaction is carried out at very low temperatures, the formation of p‐quinodimethane still proceeds but chain growth is suppressed. Hence, the concentration of the active monomer reaches a level sufficient for NMR analysis.
Acrylamide and acrylic acid are grafted on graphene by free‐radical polymerization to produce a series of graphene–poly(acrylamide‐co‐acrylic acid) hybrid materials with different contents of graphene. The materials demonstrate shape memory effect and self‐healing ability when the content of graphene is in the range of 10%–30% even though poly(acrylamide‐co‐acrylic acid) itself had poor shape memory ability. The permanent shape of the materials can be recovered well after 20 cycles of cut and self‐healing. The result is attributed to the hard–soft design that can combine nonreversible “cross‐link” by grafting copolymer on graphene and reversible “cross‐link” utilizing the “zipper effect” of poly(acrylamide‐co‐acrylic acid) to form or dissociate the hydrogen‐bond network stimulated by external heating.
