Chain interruptions

Operating at low temperature (<80°), ki can be neglected with respect to k Pc st Therefore, the relationship (29) is equal to the ratio between the number of polymeric chains interrupted by the chain transfer processes, depending on the catalyst concentration, and the number of polymeric chains interrupted by the chain transfer with monomer. 

Because the lipid components of membranes must be in a fluid state to function as membranes in living cells, it is reasonable to assume that primitive membranes in the first forms of cellular life must also have had this property. Straight-chain hydrocarbons have relatively high melting points due to the ease with which van der Waals interactions can occur along the chains. Any discontinuity in the chains interrupts these interactions and markedly decreases the melting point. As an example, stearic acid contains 18 carbons in its alkane chain and melts at 68 °C, while oleic acid, with a cis-double bond between carbons 9 and 10, has a melting point near 14 °C. If cellular life today requires fluid membranes, it is reasonable to assume that the earliest cell membranes were also composed of amphiphilic molecules in a fluid state. 

A proline residue in a polypeptide chain interrupts a-helix formation because the amide nitrogen of proline has no hydrogen that can contribute to the hydrogen-bonded structure of an a-helix. 

Pure polyacrylonitrile is difficult to spin because it is insufficiently soluble in those organic solvents which are available on a commercial scale, and also because it is not easy to dye. Commercial fibres are usually copolymers containing small amounts of other monomers which introduce polar groups into the molecule. Amongst the compounds which have been used for copolymerization are methylmethacrylate, vinyl pyridine, and vinyl chloride or acetate. The side chains interrupt the regularity of the acrylonitrile skeleton, thus opening up the structure and improving accessibility to solvents and dyes. Usually the additions are small in amount and, by convention. 

Other theories that have been evolved also consider the action of inhibitors to be through the destruction of active intermediate oxidation products, such as peroxides, and the resultant interruption of a chain of reactions which normally would have involved many molecules of the oxidizable substance. Such theories differ principally in the mechanism through which peroxide destruction and chain interruption are brought about without the total concomitant destruction of the inhibitor.54... 

The materials studied must be carefully made and purified to reduce the effects of breaks and impurities in the conducting chains (interrupted strands). 

When we say a polymer is crystalline, it does not mean the polymer has periodically translational atomic or molecular structure as small molecules. In fact, the crystalline regions in polymer where chains are folded and arranged regularly, mingles with amorphous regions where the randomness of chains interrupts the ordering (Figs. 3.1A and B). 

In this case, the conductivity should increase in proportion to the mean distance between chain interruptions, cross links, sp defects, etc. If the mean defect scattering time, Tdef = (L/vf), becomes sufficiently long, that phonon scattering limits the mean free path,then Eq. 5 becomes valid, and the system is in the clean and intrinsic transport limit. 

When the concentration of chain interruptions is sufficiently high such that the left hand side of equation 1.3 is small, then the wave function will be localised. The possible limits for the conductivity arise from the chain interruptions and/or phonon scattering. All the above factors suggest that in high-quality conducting polymers the electronic mean free path could be much larger than the structural coherence length and real metallic features could be observed. 

Ferdousi R., Rouhi, M., Mohammadi, R., et al. (2013) Evaluation of probiotic survivability in yogurt exposed to cold chain interruption. Iran J Pharm Res 12, 139—144. 

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