Monofunctional modifiers

All monofunctional modifiers decrease the surface concentration of silanols by 50% (depending on the alkyl ligand) compared to original silica (7.6pmol/m ), while difunctional modifiers only slightly reduces the surface concentration of silanols by 12% and trifunctional modifiers apparently increases the amount of silanols. This reflects actual hydrolysis of nonreacted chlorine groups of the alkyl di- and trifunctional modifiers and their conversion into silanols. 

Fan et al. [56] attached an initiator to MMT via cation-exchange suitable for free radical initiation, investigating monofunctional and bifunctional (48, 49). The initiator-clay was thermally active and the clay rendered adsorptive rather than organophihc as no compatible groups with the matrix had been added to the clay. A comparative study of the monofunctional and bifunctional-modified days used to polymerize styrene found that the monofunctional modified days led to better exfoHated nanocomposites [57, 58]. 

Equation (5.40) also applies to the case when some of the excess B groups present are in the form of monofunctional reagents. In this latter situation the definition of r is modified somewhat (and labeled with a prime) to allow for the fact that some of the B groups are in the BB-type monomers (unprimed) and some are in the monofunctional (primed) molecules ... 

Hydroxy-terminated PDMS, however, has disadvantages. The monofunctional ends limit the number of connections between the polymer (or oligomer) molecule and the glass network to two. This limitation raises the possibility that some PDMS molecules are not tied at both ends to the glass network if the polycondensation does not go to completion i.e. there may be "dangling" or loose PDMS chains in the final sol-gel material. This occurance of free ends would indeed be anticipated since the extent of reaction most likely is not 100%. Hence, the physical properties, specifically the mechanical behavior of the overall material, would be expected to suffer as a result of loose PDMS chains in the system. Disregarding this potential problem, the mechanical behavior of the sol-gel hybrids are, ultimately, influenced by the mechanical behavior of the modifying elastomer ... 

Di- and trifimctional silanes are also used for the preparation of alkyl-modified silicas to be employed as chromatographic sorbents. Under anhydrous reaction conditions, sorbents prepared from these silanes have similar surface coverages and chromatographic behavior to monomeric stationary phases prepared with monofunctional silanes. 

Since quenching the reaction or adding a stoichiometric excess of one reactant is seldom economical, the commercial practice is to add a specific amount of a monofunctional reactant in the synthesis of polyesters, nylons, and other similar polymers. In these cases, a functionality factor / is used that is equal to the average number of functional groups present per reactive molecule. While the value of / in the preceding examples has been 2.0, it may be reduced to lower values and used in the following modified Carothers equation ... 

To the first category belong the homo- and copolymerization of macromonomers. For this purpose, macromolecules with only one polymerizable end group are needed. Such macromonomers are made, for example, by anionic polymerization where the reactive chain end is modified with a reactive vinyl monomer. Also methacrylic acid esters of long-chain aliphatic alcohols or monofunctional polyethylene oxides or polytetrahydrofurane belong to the class of macromonomers. 

The soluble hydroxymethyl compounds can be chemically modified, before crosslinking, by reaction with monofunctional compounds (e.g., by esterification or ether formation). The properties of the starting materials as well as the crosslinked end products can thereby be substantially altered. For example, by partial etherification with butanol the hydroxymethyl compounds, originally soluble only in polar solvents, become soluble also in nonpolar solvents (toluene), without losing their ability to undergo self-crosslinking. 

A similar class is die titanates. Three-dimensional Ti—O chains form pigments and pigment binders for paints and water-proofing compounds for use on cloth. Their properties can be modified by substituting monofunctional groups for some of the oxygen, for example, by forming esters to interrupt the chains. 

Novakova O, Kasparkova J, Bursova V, Hoff C, Vojtiskova M, Chen H, Sadler PJ, Brabec V (2005) Conformation of DNA modified by monofunctional Ru(II) arene complexes recognition by DNA binding proteins and repair. Relationship to cytotoxicity. ChemBiol 12 121-129... 

From these experiments it can be concluded that the closure of the monofunctional adducts depends upon the presence of other adducts in its vicinity. Although a systematic study has not yet been done, the interference between two or more adducts is expected to be a function of several parameters, such as the nature and the number of base pairs between the adducts, the DNA supercoiling, the local environment of the DNA, in addition to the distortions of the DNA double helix induced by the adducts, which are also function of these parameters. DNA has to be platinated at a low drug-to-nucleotide residue ratio when in vitro and in vivo experiments are compared. This holds also for cisplatin-modified DNA, but is masked by the preferential binding of cisplatin to runs of guanine residues and the ability of the monofunctional adducts to react with the adjacent residues. 

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