This review article describes the preparation of polymer brushes by nitroxide‐mediated radical polymerization using either the ‘grafting to’ or the ‘grafting from’ approach. The use of TEMPO as a classical initiator is intensively described. More sophisticated nitroxides are also included in the discussion. Brush formation on flat surfaces such as wafers and also on particles is reported. Finally, some applications of polymer brushes are presented.
A pathway for marking of polymer chains with radical spin traps during pulsed laser polymerization in free radical polymerization is presented. By introducing a so‐called marker that forms a non‐propagating radical at (or shortly after) the incidence of a laser pulse, a polymer subdistribution is generated by specifically terminating propagating radicals via combination with such a marker radical. The generated polymer subdistribution can subsequently be imaged by modern soft‐ionization mass spectrometry. Herein, the general methodology of the method in which such marker is generated via reaction of an initiating radical with a nitrone is demonstrated on the examples of BA and VAc.
Summary: Nitroxide‐mediated polymerization of styrene in a continuous tubular reactor has been demonstrated for the first time. The polymerization kinetics in the tubular reactor are similar to those in a batch reactor. The number average molecular weight increases linearly with conversion, and chain extension experiments were successful, indicating that the living nature of the polymerization is maintained in the tubular reactor.
Evolution of molecular weight as measured by GPC for chain‐extended latex in continuous tubular reactor. 相似文献
Summary: A new approach to the preparation of water soluble polymer in inverse miniemulsions is proposed. A redox initiation system consisting of ceric ions and carbohydrate‐based surfactant Span 60 as a reducing agent is successfully used for the polymerization of AAm. This initiation system provides chain nucleation and growth near interfacial boundaries. As a result, stable uniform latex with particle radius of about 50–70 nm is obtained. The prepared PAAm has a rather high of up to about 2 × 106 Da.
A novel method is described for transforming an anionic polymerization process into a cationic polymerization process assisted by organosilyl groups. The reaction of the p‐tolyldimethylsilyl end group of polystyrene and trifluoromethanesulfonic acid produced a silyl triflate end group that served as a macroinitiator for the living cationic polymerization of isobutyl vinyl ether. The Si O linkage in the block copolymers underwent specific cleavage by reaction with tetrabutylammonium fluoride.
Summary: Plasma‐initiated controlled/living radical polymerization of methyl methacrylate (MMA) was carried out in the presence of 2‐cyanoprop‐2‐yl 1‐dithionaphthalate. Well‐defined poly(methyl methacrylate) (PMMA), with a narrow polydispersity, could be synthesized. The polymerization is proposed to occur via a RAFT mechanism. Chain‐extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA‐block‐PSt copolymer.
Dependence of ln([M]0/[M]) on post‐polymerization time (above), and \overline M _{\rm n} and PDI against conversion (below) for plasma initiated RAFT polymerization of MMA at 25 °C. 相似文献
A methacrylate‐functionalized phosphorescent Ir(III)‐complex has been synthesized, characterized, and applied as a monomer in radical copolymerizations. Together with methyl methacrylate, the complex has been copolymerized under free radical polymerization conditions. Aiming for host‐guest‐systems, applicable e.g. in organic light emitting devices (OLEDs), the complex was further copolymerized with a methacrylate‐functionalized carbazole derivative using the atom transfer radical polymerization technique. Applying gel permeation chromatography, in combination with a photodiode array detector, could clearly prove the formation of the copolymers. The optical properties of the photoactive monomers as well as the copolymers were investigated by absorption and emission spectroscopy (in solution). For the carbazole‐copolymer, the emission originates almost exclusively from the complex. This provides evidence of an efficient intrachain energy transfer, which makes the system an interesting candidate for potential OLED applications.
Summary: A novel experimental set‐up has been devised to measure simultaneously, in real time, the conversion and shrinkage of multi‐acrylates during photopolymerization. The data show that the current practice of assigning the excess volume entirely as excess free volume is inappropriate as this leads to an increasing fractional free volume with conversion. We propose to partition the excess volume into free and occupied volume components. The new model produces satisfactory results.
Experimental set‐up for the simultaneous collection of shrinkage and conversion data. 相似文献
A novel phenylacetylene ( 1 ) having two hydroxyl groups and a chiral pinanyl group together with the other three related phenylacetylenes has been synthesized and (co)polymerized by using an achiral catalytic system. Among the four monomers, only 1 is suitable to the asymmetric‐induced polymerization ( AIP ). Chiral amplification phenomenon is only observed in the copolymerization of 1 with an achiral phenylacetylene having two hydroxyl groups ( 3 ). The tight helical cis‐cisoidal main chain formed by making intramolecular hydrogen bonds between the hydroxyl groups in the copoly( 1 / 3 ) enhances the efficiency of chiral induction and as a result chiral amplification phenomenon is observed during the copolymerization.
The application of automated parallel synthesizer robots for the investigation of polymerization processes is of major interest at present. In this contribution we describe the application of the emulsion polymerization of styrene and vinyl acetate. The preparations of emulsions and latexes were investigated in detail and compared to “conventional” stirred tank reactors. In particular the influence of the vortex mixing as well as the limitations regarding solid content and reactor fouling are addressed.
Disulfide‐functionalized hyperbranched poly(amido amine)s (HPAMAMs) were synthesized by Michael addition polymerization of N,N'‐cystaminebisacrylamide and 1‐(2‐aminoethyl)piperazine. The novel HPAMAMs displayed bright fluorescence, and the emissions bands cover nearly the whole visible wavelength range. When polymer solutions were excited at 330–385, 460–490, and 510–550 nm, blue, green, and red solutions were observed, respectively. The HPAMAMs are biodegradable and they can be easily cleaved by 2‐mercaptoethanol or glutathione, leading to a decrease in the fluorescence intensity. Studies of applications of the biocompatible and biodegradable HPAMAMs in fluorescence imaging technology and biological science are in progress.
The preparation of open‐cell macroporous membranes made by the ring opening metathesis polymerization (ROMP) of a mixture of norbornene and dicyclopentadiene, and their basic applicability as separators in lithium‐ion batteries, is discussed. Cyclic voltammetry (CV) measurements of negative electrodes (graphite) and positive electrodes (LiCoO2) are performed and the results prove the absence of parasitic decomposition reactions within the membrane at high oxidative or reductive potentials. Furthermore, LiCoO2/Li half cell cycling studies of 100 charging/discharging cycles reveal that the newly disclosed separator and conventional commercial polyolefin based separators have similar performance. These results demonstrate that a potential weakness in the newly disclosed separator, namely residual double bonds present in the polymer network, does not limit the use of this material as a separator in lithium‐ion batteries.
Addition polymerization of norbornene was performed with several pyridine bis(imine) cobalt dichloride complexes activated with methylaluminoxane (MAO), first described for ethylene polymerization. For the first time, norbornene was also polymerized with CoCl2 associated to MAO. The influence of several reaction parameters has been investigated. Quite different behavior was observed compared with ethylene polymerization. Moreover, the copolymerization of ethylene and norbornene with these complexes was not possible but led to a mixture of both homopolymers.
The pyridine bis(imine) cobalt dichloride complexes used in this study. 相似文献
POSS‐functionalized polyisobutylenes (PIBs) were synthesized by carbocationic polymerization using an epoxy‐POSS/TiCl4 initiating system in hexane/methyl chloride (60:40 v/v) solvent mixture at −80 °C. 1H NMR spectroscopy verified the incorporation of one epoxy‐POSS per polymer chain. Light scattering and TEM analysis demonstrated the formation of 50–100 nm sized aggregates and micron‐sized clusters.
Photolabile polymer brushes with tailored length containing a photoremovable protecting group (NVOC) are prepared via the SI‐ATRP method. Upon light irradiation, the NVOC group is removed to generate controlled densities of free amine groups (PAMA) randomly distributed along the brush. The presence of the ionizable groups induces a photo‐triggered swelling response. The swelling degree can be tuned by the irradiation dose. A dual (light and pH), tunable response is demonstrated.
The nucleophilic living ring‐opening polymerization of N‐substituted glycine N‐carboxyanhydrides using solid‐phase synthesis resins is reported. By variation of experimental parameters, products with near Poisson distributions are obtained. As opposed to reversible deactivation radical polymerization, the living polymerization is demonstrated to be viable to high monomer conversion and through multiple monomer addition steps. Successful preparation of a multiblock copolypeptoid is proof for a highly living and robust character of the solid‐phase peptoid polymerization.
Binary reactive/inert antifouling polymer brushes were grafted via a two step surface initiated polymerization from printed initiator monolayer and provided robust, effective polymeric surfaces for bioattachment with distinguishably reduced non‐specific adsorption. This synthetic strategy can be harnessed to build complex binary polymeric structures on substrate surfaces and the polymer brush surfaces reported in the present paper can be widely used for versatile biological study.
Addition of commercially available 2‐isocyanatoethyl methacrylate to a water solution of potassium bisulfite unexpectedly yields an anionically charged hydrogel. Structural analysis shows the presence of sulfonato‐blocked isocyanates (with no detectable residual isocyanates), a full polymerization of the vinyl groups, and the appearance of urea functional groups. A mechanism is proposed to explain the gel formation, based on a combination of bisulfite‐initiated free‐radical polymerization, crosslinking by urea bridge formation, and addition of bisulfite ions to isocyanate groups. Some basic physical properties (TGA, swelling) of the gel are presented.
