Chain collapses

In self-nucleation, the extended oligomer chain collapses upon itself to nucleate a particle. 

There diould be another explanation of plateau region a chain collapsed and strongly adsorbed on the substrate. In this case, the detachment of monomer one by one fix)m the substrate corresponded to the observation. Further studies are required to elucidate the point. However, this example was probably not the case because the substrate was repulsive wall for PS chains. 

These observations can be qualitatively explained in terms of the constrained-junction theory. If a network is cross-linked in solution and the solvent then removed, the chains collapse in such a way that there is reduced overlap in their configurational domains. It is primarily in this regard, namely reduced chain-junction entangling, that solution-cross-linked samples have simpler topologies, and these diminished constraints give correspondingly simpler elastomeric behavior. 

Fig. 5. Protein folding. The unfolded polypeptide chain collapses and assembles to form simple structural motifs such as p-sheets and a-helices by nucleation-condensation mechanisms involving the formation of hydrogen bonds and van der Waal s interactions. Small proteins (eg, chymotrypsin inhibitor 2) attain their final (tertiary) structure in this way. Larger proteins and multiple protein assemblies aggregate by recognition and docking of multiple domains (eg, p-barrels, a-helix bundles), often displaying positive cooperativity. Many noncovalent interactions, including hydrogen bonding, van der Waal s and electrostatic interactions, and the hydrophobic effect are exploited to create the final, compact protein assembly. Further structural...

When using high dichloroethane ratios or 1% TDM, precipitation occurs when BD-AN chains collapse—i.e.y at high values of n owing to their more linear macromolecular structure. From the shape of the fractionation curve it is possible to conclude that all PVC chains are grafted in these samples Examination of Figure 13 leads to the conclusion that such copolymer may contain only small quantities of PVC. 

The effect of copolymer sequence on coil-to-globule transition was also studied using Langevin molecular dynamics [103]. The method for estimation of the quality of reconstruction of core-shell globular structure after chain collapse was proposed. It was found that protein-like sequences exhibit better reconstruction of initial globular structure after the cooling procedure, as compared to purely random sequences. 

We have studied the dispersibility of several pure PVAc-styrene graft copolymers with one PS branch in various selective solvents mainly at room temperature5. The experiment was done with two kinds of dried samples one was recovered from a tetrahydrofuran solution by pouring it into water and the other from a benzene solution which was poured into n-hexane. Let us refer to the former sample as A and the latter sample as B. Due to the difference in solubility of each polymer sequence in those solvents, sample A is supposed to have approximately such a microstructure that PVAc chains are extended and PS chains collapsed, while sample B has the inverse structure. A similar tendency was also pointed out by Merrett12. The results are summarized in Table 2. 

Fig. 16 A/S>c>eq vs./s>eq for PEO (A), PTHF (B), PM A (C) and PVAc (D) are plotted from es,max the chain collapse, and the data shown in Fig. 14A are represented by solid curves for clarity, that are drawn from Limit I to eSjITiax. In each case P increases clockwise from indicated es>max to 77 10 for PEO (A), 77 17 for PTHF (B), 77 20 for PM A (C), and...

The dispersion polymerization of lipophilic monomers in CO2 is initiated homogeneously with chain collapse into a discrete polymer particle at a critical molecular... 

Fig. 5 Synthesis of PVME particles by irradiation of phase-separated solutions. Above the phase transition temperature Tc, the polymer chains collapse to globular aggregates. The collapsed structures are fixed by electron beam irradiation to yield temperature-sensitive microgel particles...

Phosphorescence studies in isobutylene-methyl methacrylate-1-naphthyl-methyl methacrylate co-polymer provided evidence to show that in very dilute solution the chain collapses into more compact structures, and intramolecular excimer formation in poly-(2-vinylnaphthalene) has been shown to exhibit non-Stokes-Einstein behaviour. Laser photolysis of polymers containing phenanthryl groups, such as poly-(9-vinylphenanthrene), indicates the presence of plural dimer sites having different geometries owing to the stacking effect of phenanthrene chromophores. In poly-(2-naphthyl methacrylate). 

A question may be whether the three-body or the two-body screened interactions are more effective in resisting chain collapse. An analysis based on Eqn. (2.2.22) shows that the screened interactions predominate for lower molecular weights whereas the three-body repulsions prevail for longer chains [52]. The number of chain atoms for which the two components have equal weight in the collapsed state just after transition is... 

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