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.
In this paper, a new nonlinear optical (NLO) hyperbranched polymer P1 is designed and synthesized successfully through one‐pot “A3+B2” approach via a simple Sonogashira coupling reaction, in which isolation chromophore is introduced to improve its comprehensive performance such as NLO activity, optical transparency, and stability. For comparison, its analogs, P2 and P3 , just containing one type of chromophore, are also prepared. Although P1 cannot be well poled under our test conditions, its NLO coefficient is still much higher than its analogs P2 , P3, and the linear polyaryleneethynylene P4 , which also contains isolation chromophore, indicating the advantages of isolation chromophore and the three‐dimensional (3D) spatial isolation from the highly branched structure in the NLO field.
Porous polymeric monoliths were prepared via electron beam triggered free radical polymerization of (meth)acrylates. Post‐synthesis functionalization of these supports was accomplished via electron beam initiated free radical graft polymerization of methacryloyl‐substituted NHC precursors. The grafted precursors were converted into the corresponding copper complexes. Cu‐loadings were between 1.3 mg · g−1 and 1.5 mg · g−1. These supported catalysts were used in selected CO hydrosilylation and cyanosilylation reactions using a continuous flow setup.
Biodegradable polymeric nanocylinders were fabricated by segmental degradation of electrospun nanofibers. Poly(L ‐lactic acid) (PLA) was electrospun to produce non‐crystalline nanofibers that were immediately treated with amino group‐containing strong bases to fabricate semi‐crystalline PLA nanocylinders with tunable aspect ratio. The formation of PLA nanocylinders was attributed to two concurrent events occurring during the aminolysis reaction: (i) development of stacked lamellae and (ii) transversely oriented degradation and fragmentation of the amorphous gaps between lamellae, both responsible for the fragmentation of PLA nanofibers into uniformly shaped nanocylinders. The aspect ratio of PLA nanocylinders was tunable by varying aminolysis time and controlling nanofiber diameter.
A new strategy for the self‐polymerization of chromophores is investigated to develop a 2,7‐carbazole‐based nonlinear optical (NLO) conjugated polymer with an increasing conjugation length of chromophores. Elongation of the conjugation‐path length in chromophores has established engineering guidelines to enhance optical nonlinearity. Compared with the traditional synthesis of an NLO polymer, the chromophores should be well‐designed at a limited conjugation spacer, and then incorporated into a polymer matrix. In this research, the π‐conjugation spacer of chromophores extended perpendicularly to the dipole of chromophores during the polymerization process. Furthermore, this study marks the first research of integrating the π‐electrons of chromophores and conjugated polymers. These conjugated backbones promote a bulk‐polarization response, leading to large NLO coefficients.
Polyaniline nanostructures (nanosheets, nanofibers, and nanoparticles) can be assembled at the organic/aqueous interface or in solution by controlling the diffusion rate and the polymerization induction time of aniline. The quality of polyaniline nanostructures is determined by the polymerization solution conditions. Polyaniline nanosheets formation mechanism was proposed. Under certain polymerization conditions, polyaniline nanofibers or/and nanoparticles were obtained.
Perfectly alternating copolymers can be synthesised by reacting diacrylates with terminal dienes using alternating diene metathesis polycondensation (ALTMET). This novel method is very versatile and allows preparation of diverse structures of polymers, including main‐chain liquid crystalline polymers.
Main‐chain liquid crystalline polymer obtained by ALTMET. 相似文献
Different theoretical models for the computation of multiphoton absorption response are described and reviewed. The influences of intrinsic molecular structure parameters on the multiphoton absorption properties for organic conjugated molecules are discussed in terms of: i) the donor/acceptor substitutions; ii) the π conjugation length; iii) the ground‐state polarization mimicking structural character such as bond‐length alternation; iv) the molecular dimensionality; and, v) some other possible factors, such as vibronic coupling and the solvent, as well as aggregation effects. Some theoretical designing strategies for organic materials with large multiphoton cross‐sections are then proposed.
The present features review article discusses the crystallisation of the polymer matrix when containing silicate layers. The accent is put on nylons (polyamides) and poly(ethylene oxide) as typical hydrophilic polymers and, poly(propylene) from the hydrophobic group. The effects of the clay, either intercalated or exfoliated, on the crystallisation behaviour of the matrix are highlighted. In addition, the crucial aspects of the semicrystalline morphology of the matrix in the presence of the clay platelets are also debated. The overall crystallisation rate is reported to slow down for most of the crystallisable polymer matrices on account of a retarding growth effect exerted by the clay platelets. As far as the location of the exfoliated clay platelets in the polymer matrix is concerned, they are assumed to be rejected from the crystalline phase in the interspherulitic space.
Two poly(p‐phenylenevinylene) derivative alternating copolymers ( P1‐I and P2‐I ) have been prepared featuring iodo substituents and m‐phenylene units to periodically disrupt conjugation. P1‐I was derivatized with various chromophores to yield P1a‐f . In P1a‐f , the chromophores were positioned within a sterically protected pocket shielding them from interchain interactions so that intrachain interactions between polymer segments could be observed. Solution and film properties of polymers have been examined. Post‐polymerization chromophore modification leads to new photophysical properties such as intramolecular charge transfer and fluorescent resonance energy transfer processes in some cases.
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.
The stability and reactivity of mono‐ and multi‐protonatred N‐substituted isatin derivatives were studied at PBE0/aug‐cc‐pvtz//PBE0/6‐31+G** level of theory in triflic acid (TFSA) solution. Calculations showed that the monocationic intermediates are the principal reactive species in the reaction of hydroxyalkylation of isatin derivatives in TFSA media. Electron‐withdrawing substituents on the nitrogen atom increase the reactivity of isatin‐containing electrophiles towards aromatic hydrocarbons, in accordance with their expected electronic influence. Steric factors also play an important role in the reactivity of isatin‐containing electrophiles, especially in the second reaction step, due to their more sterically hindered reactive center.
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
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.
The helical mechanoclinic deformation of a main‐chain chiral smectic elastomer, which is prepared by a crosslinking reaction under twist deformation, is investigated. The twist deformation induces a layer tilt angle that depends on the handedness of twist. The layer tilt angle in the right‐handedly twisted elastomer, of which the handedness is consistent with that of the helix in the SmC* phase of the non‐crosslinked backbone polymer, is estimated to be up to 16° at room temperature, although that in the left‐handedly twisted elastomer is less than several degrees. The experiments provide evidence of chiral coupling between tilt and twist for helical mechanoclinic deformation in the chiral smectic system.
Organic π‐conjugated polymers have emerged as one of the most fascinating classes of materials as they have found utility in a host of plastic electronics technologies. The distance between π‐systems and their relative orientation dictate energy/charge transfer, conductivity, and photophysical properties of these materials in bulk. This Feature Article discusses π‐conjugated polymers and model compounds in which specific inter‐π‐system interactions are covalently enforced and the effect that the scaffolding has on optoelectronic properties.
The synthesis and polymerization of novel diallyldimethylammonium ionic liquid monomers is described. A free‐radical polymerization follows a ring‐closing cyclopolymerization mechanism similar to the one observed previously for diallyldimethylammonium halides that leads to pyrrolidinium functional polymers. As previously observed in other families of polymeric ionic liquids, their physico‐chemical properties are seriously affected by the nature of the counter‐anion. As an example, the thermal stability increases following the trend SCN− < < < bis(trifluoromethane)sulfonamide. Interestingly, this polymerization route may lead to the synthesis of a new family of random copolymers that have a similar poly(diallyldimethylammonium) backbone and a mixture of counter‐anions determined by the comonomer selection.
