Chain consequences

As a class the aliphatic polyalkenamers have low values due to a combination of low chain stiffness and low interchain attraction. The presence of double bonds has the effect of increasing the flexibility of adjacent single bonds (see Chapter 4) and overall this leads to a reduction in. Thus in the sequence from polydecenamer down to polypentenamer an increase in the double bond concentration leads to a lowering of Tg. On the other hand the Tg of polybutenamer, i.e. poly butadiene, is somewhat higher than that of polypentenamer, presumably because the proportion of stiff links, i.e. double bonds, becomes sufficiently high to override the flexibilising effect on adjacent chains. Consequently the polypentenamers have the lowest Tg values known for hydrocarbon polymers (cis- -114°C, trans- -97°C). 

The above spectral densities can be modified for the occurence of chain flexibility, and for the director being oriented at dLD w.r.t. the external BQ field in the L frame. For CD bonds located in the flexible chain, the effect of DF is reduced due to an additional averaging of the time dependent factor (/f g) by conformational transitions in the chain. Consequently, the spectral densities given in Eqs. (60)-(62) are modified by replacing Soc%0(Pm,q) by the segmental order parameter YCD of the C-D bond at a particular carbon site on the chain.146,147 As observed experimentally,148,149 the spectral densities in a flexible chain show a SqD dependence when DF dominate the relaxation rates. The general expression of Jm(co 0LD) due to DF in uniaxial nematic phases is given by... 

The Krebs cycle will only operate when the hydrogen atoms and electrons produced in the cycle enter the electron transfer chain, ultimately to react with oxygen that is, the two processes must take place simultaneously. A metabolic pathway is defined as a sequence of reactions that is initiated by a flux-generating step. In the cycle, citrate synthase catalyses the flux-generating reaction (Table 9.2) but there is no such reaction in the electron-transfer chain. Consequently, the cycle can be considered to be the first part of a longer pathway, which includes the electron transfer chain (Figure 9.3). 

In all these cases and in contrast to starting a polymerization by initiators, there are no fragments of the starting molecule incorporated in the polymer chain. Consequently, the mechanisms are different to those of radical, anionic, or cationic polymerizations. 

It is worth noting that the OCH3 groups project out of the core of the chain and are thus surrounded by atoms of other chains. Consequently, the environment of each side group is significantly asymmetric. 

C X chains). Consequently, the mobile phases need to be more polar (e.g., CH3CN—H20, MeOH—H20) than the coated surface. During elution, separation of constituents of an applied sample mainly relies upon the differences in distribution coefficients between the mobile phase and the hydrocarbon coatings of the stationary phase. For all these reasons, the more polar constituents of a mixture in reversed phase chromatography are eluted before nonpolar components. Note also that although water is more polar than acetonitrile or methanol, it is a poorer eluent in reversed phase chromatography because of the alkyl surface character of the stationary phase. 

Gd2Cl (15, 16), Sc5Cl (]J), and Y r (18). It is not by accident that the halide examples are found among the metals with fewer valence electrons and larger metallic radii. In these structures the M-M and X-X distances must be equal along the chain, consequently the larger spacing required by Cl-Cl or Br-Br nonbonded contacts dictate lower M-M bond+orders. 

But, for large polydispersities, the Rouse process (B) of the long chains overlaps the reptation process of the short chains. Consequently, the most general expression of the relaxation function (or relaxation modulus) must include all the relaxation processes described in part 3.2. 

It is noteworthy that RNA polymerase lacks nuclease activity. Thus, in contrast with DNA polymerase, RNA polymerase does not correct the nascent polynucleotide chain. Consequently, the fidelity of transcription is much lower than that of replication. The error rate of RNA synthesis is of the order of one mistake per 10 or lO nucleotides, about 10 times as high as that of DNA synthesis. The much lower fidelity of RNA synthesis can be tolerated because mistakes are not transmitted to progeny. For most genes, many RNA transcripts are synthesized a few defective transcripts are unlikely to be harmful. 

---