Endcap group

The R group methyl, ethyl, propyl, butyl, pentyl, vinyl, or phenyl (Scheme 1) influences the hydrolysis rate of the silane endcapping group. The size and the inductive effect of the substituents R, acetyl, methyl, ethyl, or imine modify the reactivity as well. 

Efficient energy transfer was also obtained from a copolymer 31 in which the perylene was attached as an endcapping group (Scheme 11) [47]. By using a ratio of fluorene to monobromo-dye of 18 1 in a Yamamoto polycondensation, a polymer with Mn = 21000 and a polydispersity of 2.1 was obtained, corresponding to about a degree of polymerisation of about 40. As with... 

Endcap groups are then identified as those that provide lateral hydrophobic features that consist of three atoms (e.g., isopropyl) and are abstracted as a single atom. Due to the size of the sulfur atom, thioethers are handled similarly although they contain only two atoms. These features are important for the overall size and shape of a molecule. 

A typical reaction procedure is desoibed in the following (see Scheme 6.3). The step growth polymerization of SPTES copolymers with endcapping group was carried out in a 250 ml three-neck round-bottom flask equipped with a mechanical stirrer and a nitrogen inlet-outlet. 3,3 -Disulfonate-4,4 -difluorodiphenylsulfone (4.5833 g. 

The synthesized SPTES polymers with the endcapping group could be readily cast into membranes of both salt form and acid form. The physical properties of the SPTES polymers are listed in Table 6.2,... 

An implication of the kinetic analysis presented in Sec. IV.A is that the rate of chain scission of polyesters can be retarded by endcapping to reduce the initial carboxylic acid end-group concentration. Alternatively, the rate may be increased by acidic additives that supplement the effect of the carboxy end groups. The first expectation was confirmed by partial ethanolysis of high molecular weight... 

Although the reaction scheme shows a complete hydrolysis before condensation begins, this is likely not correct as stated earlier. The relative rates and extents of these two reactions will particularly depend on the amount of water added and the acidity of the system (10,11). The high functionality of the triethoxysilane endcapped PTMO oligomer should enhance the incorporation of PTMO molecules into the TEOS network. It was also assumed that the reactivities would be the same between silanol groups from silicic acid and endcapped PTMO. Therefore, no preferential condensation was expected and the deciding factors for which type of condensation (self- or co-) took place would be the diffusivities and local concentrations. 

V) If the C-18 bonded phase contained un-reacted silanol groups, how would the retention of the solutes be affected by endcapping the stationary phase ... 

Successive multiple insertions of an aryl isocyanide (ArNC) into the S-S bond of a diaryl disulfide (ArS)2 occurs in the presence of Pd(PPh3)4 to produce the corresponding poly(imino)alkane endcapped with an arylthio group (Equation (65)).167 Products of higher molecular weights are formed when isolated poly(imino)alkanes are again subjected to the conditions of the insertion reaction (up to n — 9). 

Heterotrimetallic sandwiches involving all three cobalt group metals 71-73 have been prepared and isolated 6 3 other tetradecker types synthesized recently include bent,76 arene-endcapped,74 and C2B3-endcapped7S sandwiches... 

The relationship of the selectivity to the polarity of the analytes can be understood from the differences in the retention factors of homologous alkanols (Figure 3.12). The polar alkanols are relatively more retained on the non-endcapped bonded phases (LOC-ODS-NE and HIC-ODS-NE) because smaller-size alkanols can reach the unreacted silanol groups on the surface of silica gels. 

FIGURE 6.1 Groups present on the surface of a typical endcapped alkyl bonded phase (C8). 

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