Poly -modified anionic species

The second part describes the application of this automated potentiostat as an electrochemical detector for various electro-inactive anionic species nitrate (NOg ), nitrite (NOg"), sulfate (SO "), chloride (CD, etc. (1,2). The electrochemical detection involves the use of a conducting poly(3-methylthiophene) (P3MT) polymer modified platinum electrode in a flow injection analysis (FIA) mode. 

One of the first reported uses of a conducting polymer moditied electrode for the detection of anions by flow ipjection analysis (FIA) utilized poly(pyrrole) 13). Low detection limits were achieved. However, poly(pyrrole) is irreversibly oxidized in the presence of oxygen at potentials of around +1.0 volts. Poly(3-methylthiophene) does not exhibit this behavior. Therefore, poly(3-methylthiophene appeared to be a good candidate as an electrochemical detector for anionic species by FIA with electrochemical detection at an poly(3-methylthiophene) modified electrode. Also P3MT does not need to be undoped (cyded between the negative and positive detection potentials) between successive injections as many other polymer systems must. 

SCBs play an important role in the formation of other block copolymers. For example, the relatively less nucleophilic poly(ethylene oxide) oxyanion cannot initiate the polymerization of styrene, which needs a more nucleophilic alkyllithium initiator. To enable the synthesis of multi-block copolymers from various combinations of monomers by anionic mechanisms, it is important to modify the reactivity of the growing anionic chain end of each polymer so as to attack the co-monomer. There have only been a few reports on the polymerization of styrene initiated by an oxyanion (see <2001MM4384> and references cited). Thus, there exists a need for a transitional species that is capable of converting oxyanions into carbanions. In 2000, Kawakami and co-workers came up with the concept of the carbanion pump , in which the ring-strain energy of the SCB is harnessed to convert an oxyanion into a carbanion (Scheme 13) <2000MI527>. 

Sol-gels containing electroactive species have been used in the development of both amperometric and potentiometric electrodes. Films coated with anionic poly-(dimethyldiallylammonium chloride) (PDMDAAC) and cationic poly(vinylsulfonic acid) were used to concentrate Ru(bpy)3 + and the hexacyanoferrate anion, respectively, for use as amperometric electrodes [208a]. The detection limit by square-wave voltammetry improved by up to 50-fold compared with uncovered electrodes. In Figure 41, curve 1 corresponds to a bare graphite electrode, curve 2 to a sol-gel-covered electrode and curve 3 to a sol-gel-PDMDAAC-modified electrode after 10 min of exposure to Fe(CN)g. ... 

LDH-modified electrodes have been also obtained by a layer-by-layer (LbL) deposition technique, by exploiting the net positive charges on the brucite-like layers [47] after delamination of suitably synthesized LDHs [48,49], the positively charged component of the film is thus obtained. The anionic counterpart consists of an organic polymer, such as poly(sodium 4-styrenesulphonate) [48, 49], of negatively charged electroactive species, such as metal porphyrins [50], phthalocya-nines [51], Au NPs surrounded by an anionic cloud [52], or a specific enzyme deposited from buffered solutions at pH values above the isoelectric point [53]. 

Modifying chitosan to become a water soluble species, such as carboxymethylchitosan, is another way to enhance gelation as the structure effectively allows the interaction with water molecules. Pourjavadi et al. (18) and Yu et al (19) demonstrated the grafting of anionic polymers, i.e. poly(acrylonitrile), poly(acrylic acid) onto water soluble chitosan to obtain SAP, and the products showed a swelling of-200 and -500 times, respectively. 

In order to optimize specific anionic functionalization reactions such as carbonation with carbon dioxide, the effect of chain end structure (stability and steric requirements) has often been investigated. The steric and electronic nature of the anionic chain end and the chain-end aggregation can be modified by reaction with 1,1-diphenylethylene as shown in Eq. (13). When the direct carbonation is effected in benzene at room temperature with the diphe-nylalkyllithium species formed by addition of poly(styryl)lithium to 1,1-diphenylethylene (Eq. 31), the carboxylated polymer can be isolated in 98% yield compared to only a 47% yield for poly(styryl)lithium without end-capping under the same conditions [141] ... 

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