Modification of the polymer

Another approach involves the synthesis of a poly mer with a structure able to interact with the CNTs. The mutual interaction between the CNT surface and a polymer can be achieved by using conjugated polymers, which can associate with the CNTs by means of electronic 7t-u interactions with the CNT lattice. These ti-ti interactions lead to substantial modification of the optical and vibrational spectroscopic properties of the conjugated polymers. The results of a microscopic and spectroscopic study of this kind of composites [study carried out 

Long et al. ° focused on the study of MWCNT/PPy nanocomposites. First, they exfoliated as-produced MWCNTs prepared by CVD in water, using a surfactant (cetyltrimethylammonium bromide, CTAB], under sonication. The resulting mixture was then mixed with pyrrole monomer in the presence of an initiator, viz., ammonium persulfate. The in situ polymerization was finally carried out under 

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The third approach employs modifications of the polymer s physical properties and/or resist processing to minimize contaminant absorption, and is described in the section, "Polymer Properties and Lithographic Performance". 

Figure 2. Cyclic voltammograms of a poly(2,2 -bithiophene)-coated electrode in acetonitrile containing 0.1 M Bu4NC 04.34 (Reprinted from G. Zotti, C. Schiavon, and S. Zecchin, Irreversible processes in the electrochemical reduction of polythiophenes. Chemical modifications of the polymer and charge-trapping phenomena, Synth. Met. 72 (3) 275-281, 1995, with kind permission from Elsevier Sciences S.A.)...

A3. The end-to-end distance of the free strands is practically unchanged by the cross-linking process, i.e., the extent of chemical modification of the polymer chains produced by high energy radiation should be small. 

Unsaturated groups are very interesting for application development because this specific functionality opens up a broad range of possibilities for further (chemical) modification of the polymer structure, and therefore its physical and material properties. The direct microbial incorporation of other functional substituents to the polymer side chains, e.g. epoxy-, hydroxy-, aromatic-, and halogen functional groups, influences the physical and material properties of poly(HAMCL) even further [28,33,35,39-41]. This features many possibilities to produce tailor-made polymers, depending on the essential material properties that are needed for the development of a specific application. 

The thermal stability and lightfastness of polyesters is particularly necessary for technical and high-performance applications. The modification of the polymer causes disorder and affects the stability as well as some other properties. PET modified by DEG suffers particularly from photo-oxidative reactions due to the presence of the sensitive ether bonds. These copolymers need special stabilization depending on the kind and degree of modification. The UV stability can also be influenced by the technology of the process, whereby slight improvements of DMT-based polymer are observed [29],... 

Modification of the polymer backbone by the incorporation of trifluoropropyl groups leads to substantial decreases in swelling. In vulcanized systems reinforced with hydrophilic silica (30 phr) the swelling decreased with increasing CH2CH2CF3 content as shown in Table III. 

Most recently, significant research efforts have been focused on materials compatibility and adhesion at the zeoHte/polymer interface of the mixed-matrix membranes in order to achieve enhanced separation property relative to their corresponding polymer membranes. Modification of the surface of the zeolite particles or modification of the polymer chains to improve the interfacial adhesion provide new opportunity for making successful zeolite/polymer mixed-matrix membranes with significantly improved separation performance. 

The possibility of making monomers from F and HMF and of studying their polymerization and copolymerization behaviour, as well as the properties of the ensuing materials, is an attractive proposition considering (i) the ubiquitous and non-depletive character of the sources of F and HMF and (ii) the unique and useful chemical properties of the furan heterocycle with a view to possible structural modifications of the polymers. 

Modification of the polymers in order to better match their polarity with the other compound components... 

In order to metallize a polymer surface, electroless plating can be applied. This process typically consists of a pretreatment process in order to improve the adhesion. In the second step a surface seeding of the electroless catalyst is done. Wet chemical methods of pretreatment are using strong acids such as chromic acid, sulfuric acid and acidified potassium permanganate in order to achieve a surface modification of the polymers (96). 

Chemical modifications of the polymers were performed on films or in toluene solutions. 

Subsequent modifications of the polymers involve extensive formation of O-sulfate esters,1903 193 197 N-deacetylation and N-sulfation,198/199 and epimerization at C5.10 In some tissues almost all GluA is epimer-ized.200 The modifications are especially extensive in dermatan, heparan sulfates, and heparin (see also p. 177).196 201 203b The modifications are not random and follow a defined order. N-Deacetylation must precede N-sulfation, and O-sulfation is initiated only after N-sulfation of the entire chain is complete. The modifications occur within the Golgi (see Fig. 20-7) but not all... 

TDFRS allows for experiments on a micro- to mesoscopic length scale with short subsecond diffusion time constants, which eliminate almost all convection problems. There is no permanent bleaching of the dye as in related forced Rayleigh scattering experiments with photochromic markers [29, 30] and no chemical modification of the polymer. Furthermore, the perturbations are extremely weak, and the solution stays close to thermal equilibrium. 

The labeling must be specific, that is, directed to a specific site in the RNA to yield meaningful results pertaining to specific nucleotides. This is commonly referred to as site-directed spin-labeling (SDSL) (Altenbach et ah, 1989 Barhate et ah, 2007 Edwards et ah, 2001 Kim et ah, 2004 Qin et ah, 2001, 2003 Schiemann et ah, 2004). Therefore, incorporation of multiple labels through enzymatic RNA synthesis (e.g., triphosphate polymerization with polymerases Keyes et ah, 1997) is of limited value. Instead, labels are generally introduced chemically, either during chemical synthesis of the nucleic acid or by postsynthetic modification of the polymer. 

Block copolymerization is one method of mixing chemically different polymers. The block copolymers have received much attention, since the different homopolymer properties are maintained in the block copolymer, and this allows easy modification of the polymer characteristics [63,72,86,87,108]. 

Copolymerization of TMC with e-CL or L-lactide has been reported to be useful for modifications of the polymer properties [144,218,280,283]. The molecular architecture presents a powerful tool for obtaining new materials with interesting properties. For instance, a star-shaped rubbery poly(TMC-co-CL) was synthesized. d,L-LA/GA polymerization was then initiated from the hydroxy terminated arms to yield a poly(TMC-co-CL)-block-PLGA [284]. 

One argument for the selection of dextran as a drug carrier has often been its susceptibility to degradation. However chemical modification of the polymer may impair the biodegradability. Therefore we have studied the biodegradation of dextran and a number of dextran derivatives by dextranase. For this study model derivatives were prepared using the activation procedures discussed before. 

These degradation studies of dextran derivatives, mutually differing in the nature and the degree of modification, clearly demonstrate that the biodegradability of dextran is significantly reduced upon chemical modification of the polymer backbone. This phenomenon should be beared in mind when using dextran as a carrier molecule for the preparation of macromolecular drug derivatives. 

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