Selection of monomers

POROUS HOLLOW-FIBER CONVECTIVE MASS TRANSPORT 

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The selection of monomers for preparation of copolyesters is based on applying established structure/property principles and is usually driven by new market needs and applications with specific end-use properties in mind. Thus, attempts to develop amorphous or semicrystalline CHDM-based polyester compositions for applications requiring greater heat resistance or higher heat deflection temperatures have generally followed the theme of incorporating bulky or rigid constituents to further enhance the desirable thermal properties of CHDM-based... 

They are, as currently practiced, nearly always directed by chemoinformatics, i.e., the application of drug-like product information in library design and selection of monomers. 

Pools 2,3 inactive pool 1 active selection of monomer C1... 

Pools 1,3 inactive pool 2 active selection of monomer B2... 

Compounds 1,2 inactive compound 3 active selection of monomer A3... 

To be useful as a catalyst support, the gelular polymers must be swellable, the propensity of which can be controlled by the degree of cross-linking. Polymers can be tailor-made to swell in a particular solvent by appropriate selection of monomer and cross-linking agent. 

When the library individuals are filtered with physicochemical parameters, the nature of the scaffold becomes fundamental. As an example, if a maximum accepted value of log P (partition coefficient between n-octanol and water) of 4 is set as a limit, the use of a functionalized scaffold with log P = 6 will enormously limit the selection of monomers to highly hydrophilic structures, while the selection of a more appropriate scaffold would allow a higher degree of diversity while respecting the imposed filter. The same is true for monomers. For example, if an upper hmit of 600 is imposed for the molecular weight (MW) of the final library components, the use of monomers with an MW higher than 250-300 will not be acceptable. 

Another important class of targeted libraries is aimed at specific families of targets. Examples are kinases (125, 126), proteases (127-129), and G-protein coupled receptors (130, 131). These libraries are driven by generic structural information on the family of proteins, and the correct use of this information (creation of a loose pharmacophore, selection of monomers/products on the basis of the similarity fit into the pharmacophoric model) is similar to the process observed for focused library design. 

R =M6, CH2C7F 5 Figure 4.11 Selection of monomers polymerized in SCCO2... 

This phenomenon is in remarkable contrast to the cases of alanine NCA and 7-glutamate NCA, where a selection of monomer antipodes by a-helical polymer chain is observed. The lack of selectivity of the growing poiy(valine) chains cannot be attributed to the heterogeneity of the reaction mixture due to the insolubility of the polymer, since the polymerization of alanine NCA in tetrahydrofuran does demonstrate the selectivity, as mentioned previously, despite the heterogeneous reaction observed. The determining factor seems to be the different conformation acquired by the growing poly(valine) as compared to the a-helices of poly(7-benzyl glutamate) and poly(alanine), both in solution and solid state. 

Fig. 4 Relationship between structure and properties of hydrogels. The selection of monomers and cross-linking agent determines hydrogel properties. On the other hand, a hydrogel with specific properties must be synthesized using specific monomers and cross-linking agent.

Selection of monomers for synthesis of MIPs based on the interaction energies Study of correlation between molecular volumes and pKa of templates and the retention factors... 

An alternative approach uses reversible addition-fragmentation chain transfer (RAFT), which has fewer limitations in the selection of monomers (Chong et al, 1999) so that monomers with hydroxyl, t-amino and acid functionality may be polymerized into narrow-polydispersity block copolymers. The RAFT agent is a dithioester of the general formula S=C(Z)S-R, where Z is usually -Ph (phenyl) and R is chosen from a group of alkyl phenyls (e.g. -C(CH3)2Ph). 

Table I summarizes, in a very simplistic way, the uses of different types of monomers for different graft applications. Obviously, a more diverse selection of monomers and a large number of substrates can be considered for various well defined product needs. EB grafting is but a tool to meet a large plurality of product opportunities. 

Because of the instability of the anhydride bond in the presence of water, special properties are required for stable polyanhydride devices. A critical element in the development of polyanhydride biomaterials is controlling hydrolysis within a polymeric device. To obtain implants where hydrolysis is confined to the surface of the polymer, hydrophobic monomers can be polymerized via anhydride linkages to produce a polymer that resists water penetration, yet degrades into low molecular weight oligomers at the poly-mer/water interface. By modulating the relative hydrophobicity of the matrix, which can be achieved by appropriate selection of monomers, the rate of degradation can then be adjusted. For example, copolymers of sebacic acid, a hydrophilic monomer, with carboxyphenoxypropane, a hydrophobic monomer, yield ... 

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