Polymer pendant sensitizer

The immobilization of the sensitizer and catalyst is especially effective, because contamination of the materials (NBD and QC) with a sensitizer or catalyst markedly lower the efficiency of this system. 4-(N,N-dimethylamino)benzophenone was immobilized on poly(styrene) (30) and silica gel to use it as insoluble sensitizer 101 The polymer pendant sensitizer (30) was much more active than the monomeric compound when used in acetonitrile. Usually, the sensitizing activity of the sensitizer remained almost unchanged through immobilization, but sometimes decreased depending on their structure. As a catalyst of back reaction to release heat, Co(II)-tetraphenylporphyrine was anchored on polystyrene) beads (31), and showed good activity in its immobilized form10Z>. Activity decrease was observed- after several times recyclings of the catalyst. 

A flow type model utilizing a polymer pendant sensitizer and catalyst (Fig. 32) was constructed and operated. 

Treatment of a number of covalent polymers substituted with molecular recognition capability with suitable guests leads to chiral induction. The same crown ether-amino acid complementary pair described for the rosettes above was employed in the form of crown-ether pendant cis-transoidai poly(phenylacetylene). When the achiral polymer is treated with amino acids (in the form of their hydroperchlorate salts in acetonitdle) a large induced CD signal is observed in the backbone of the polymer. The polymer is sensitive to small enantiomeric excesses in the amino acid, as little as 0.005% enantiomeric excess of alanine can be detected. In a similar vein, c/5-transoidal poly(carboxyphenylacetylene) shows induced circular dichroism when treated with nonracemic chiral amines In addition, the system displays chiral memory, in that treatment of the complex with achiral amino alcohols results in retention of the chiral polymer backbone. 

Polymer pendant MtPcs (M Fe, Co, Np, Cu +) were used as films to produce a photoresponse. MV present in the solution was not effective as an acceptor, but Fe EDTA worked as an acceptor to enhance the photocurrent about 10 times A polymer bilayer coated electrode consisting of an electron-mediator film in the inner layer 49) and a sensitizer film (50) in the outer layer produced a rectified photocurrent In the presence of a sacrificial reductant (triethanolamine) in the solution, the bilayer coated electrode gave exclusively anodic photocurrent independent of the applied potential between —0.2 and —0.3 V vs SCE. 

In order to generate stereoregular (usually isotactic) polymers, the polymerization is conducted at low temperatures ia nonpolar solvents. A variety of soluble initiators can produce isotactic polymers, but there are some initiators, eg, SnCl, that produce atactic polymers under isotactic conditions (26). The nature of the pendant group can influence tacticity for example, large, bulky groups are somewhat sensitive to solvent polarity and can promote more crystallinity (14,27). 

Ozonc-rcsjstant elastomers which have no unsaturation are an exceUent choice when their physical properties suit the appHcation, for example, polyacrylates, polysulfides, siHcones, polyesters, and chlorosulfonated polyethylene (38). Such polymers are also used where high ozone concentrations are encountered. Elastomers with pendant, but not backbone, unsaturation are likewise ozone-resistant. Elastomers of this type are the ethylene—propylene—diene (EPDM) mbbers, which possess a weathering resistance that is not dependent on environmentally sensitive stabilizers. Other elastomers, such as butyl mbber (HR) with low double-bond content, are fairly resistant to ozone. As unsaturation increases, ozone resistance decreases. Chloroprene mbber (CR) is also quite ozone-resistant. 

The same group recently reported that the TBB defects can be brought below the nuclear magnetic resonance (NMR) detection limit by employing similar polymerization conditions (i-BuOK in THF at room temperature) in the synthesis of naphthyl-substituted PPVs 51-53 [112]. Although the absorption and PL spectra of all three polymers are similar, the EL can be finely tuned between 486 nm (for 52) and 542 nm (for 53). The external QE (studied for ITO/PEDOT/polymer/Ba/Al device) is also sensitive to the substituents pattern in the naphthyl pendant group 0.08% for 51, 0.02% for 52, and 0.54% for 53. 

As expected, the incorporation of pendant unsaturation in the resists greatly enhances sensitivity as demonstrated by a comparison of the contrast curves for poly(N-aiiyl maleimide-VBC) and the structurally similar poiy(N-ethyl maleimide-VBC) (Figure 4). Both polymers have similar molecular weights and nearly identical mass absorption coefficients but the allyl-containing copolymer is 5X faster. 

Zhang Y, Murphy CB, Jones WE Jr (2002) Poly[p-(phenyleneethynylene)-alt-(thienyle-neethynylene)] polymers with oligopyridine pendant groups highly sensitive chemosensors for transition metal ions. Macromolecules 35 630-636... 

The parent polymer by itself is not a useful material owing to the extreme hydrolytic sensitivity of the P-Cl bond. However, this feature has been turned around and used as an advantage. Nucleophilic substitution of the chlorines in the polymer results in substituted polyphosphazenes which are hydrolytically stable. Also, using this method the polymer architecture and properties are readily fine-tuned by a subtle variation of the substituent. Over three hundred types of polyphosphazenes have been synthesised by this method. Assembly of organic polymers containing cyclo-phosphazenes as pendant groups is another approach that is gaining importance [6]. 

Polymers with other pendant photosensitive moieties such as 0-furylacrylic ester (2) or / -styrylacrylic ester (5) are highly photosensitive and have even higher photosensitivity after the addition of photosensitizers. However, the thermal stability of these polymers is inferior to that of the polymer with pendant cinnamic esters (4). Polymers with pendant benzalacetophenone (5), styrylpyridinium (6), a-cyanocinnamic ester (7) or a-phenylmaleimide (8) have high photosensitivity but they can not be sensitized. In addition, the photosensitive moieties that are used in the syntheses of these polymers are not commercially available, in contrast to cinnamic acid. 

Syntheses of Self-Sensitized Polymers by Cationic Copolymerizations. The cationic polymerizations of several vinyl ethers containing pendant ester groups such as cinnamic ester 12), methacrylic ester 16), acrylic ester (77), and crotonic ester 18) have been reported. Based on these reports, cationic copolymerizations of CEVE with photosensitizer monomers such as NPVE, NNVE, VNP and NPEVE were carried out using TFB as a catalyst in toluene at — 65 °C. Each copolymer was obtained with high yield except in the case of copolymerization of CEVE with VNP as summarized in Table I. 

The relationship between the thickness of polymer films containing about 10 mol-% of pendant photosensitizer groups and the conversions of the —C bonds after 10 min. irradiation is shown in Figure 5. The photochemical reactivity of PCEVE-NNVE decreased slightly with increasing thickness of the film. Interestingly, the reactivity of PCEVE-NPVE was not influenced by the thickness of the film in contrast to the self-sensitized polymers previously... 

The efficiency of energy conversion in the polymers, i.e. how much the change in shape of the chain is induced by a photon, is, however, rather low. They need many photons and a high content of pendant photochromic chromophores to induce a large conformation change. To make a sensitive photo-responsive polymer, i.e. one which responds more efficiently to fewer photons, it is necessary to introduce an amplification mechanism to the system. One possible way of achieving this is to utilize the phase transition of polymers [7,8]. 

The rate of electron transfer of the polymer-bound Co(III) complex, cis-[Co(en)2 PVP(N3)]2+ (PVP = poly-4-vinylpyridine, en = ethylenediamine) (15), with [Ru (NH ]2 is very sensitive to the type of dissolved innert anions at a given ionic strength73). In the domain, partial dehydration of the pendant Co III) and, probably, [Ru(NH3)6]2+ ions proceeds successively with an increase in the perchlorate ion concentration, leading to enhancement of the rate. The lower activation enthalpy observed in the perchlorate solution, relative to the chloride ion solution, is attributable to the rate enhancement in the former solution. 

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