Polymer aggregates solvation

The mode of action of plasticizers can be explained using the Gel theory [35 ]. According to this theory, the deformation resistance of amorphous polymers can be ascribed to the cross-links between active centres which are continuously formed and destroyed. The cross-links are constituted by micro-aggregates or crystallites of small size. When a plasticizer is added, its molecules also participate in the breaking down and re-forming of these cross-links. As a consequence, a proportion of the active centres of the polymer are solvated and do not become available for polymer-to-polymer links, the polymer structure being correspondingly loosened. 

Even if all blocks of a block polymer are solvated in solution, that is, by using a nonselective solvent, phase segregation of the solvated blocks may occur at high concentration. The result is a supermolecular ordering in solution comparable to that in liquid crystals. In certain cases the aggregates are sufficiently large to diffract visible light, and, as has been mentioned earlier, block polymer solutions that are irridescent above a critical concentration have been observed (81). 

Rgure 1. Scenarios depicting the possible solvation or aggregation states of a polymer-bound peptide sequence, (a) Peptide and polymer chains (bold) are fully solvated, (b) Peptide chains are intramolecularly aggregated whilst polymer is solvated, (c) Peptide chains are well solvated whilst the polymer backbone is poorly solvated, (d) Peptide chains are intermolecularly aggregated whilst polymer is solvated, effectively increasing the overall level of cross-linking in the matrix. (Reproduced from ref. 7 with permission.)... 

Parameters Affecting Self-Assembly and Functionalization When amphiphilic block copolymers are exposed to a solution that solvates only one of the blocks, the polymers self-assemble into micelles [126]. For applications in which bioactive polymers compose the micelle, particle size determines the maximum drug loading, blood-serum half-life, and bio distribution [127,128]. Block copolymer chain length and composition, as well as the method of self-assembly, were found to influence the final size of these particles [80, 129-131]. By varying these parameters, the size of the polymer aggregates could be controlled in the range from 30 nm to 1 pm [129,130]. 

In the work discussed above, the polymers PPTA, BBL, BBB and PBO were in solution in some strong acid (e.g., methane sulfonic acid, chlorosulfonic acid, etc.). Solubility of these pol3nners in a strong acid involves protonation of the polymer, and solvation of the consequent polyelectrolyte. The introduction of a small (e.g., 1%) amount of water can cause deprotonation and aggregation of the polymer. This aggregation can, for example, prevent the order-disorder phase transition that might be expected for an anhydrous solution in the case of rodlike polymers. If the aggregation is not too... 

The dependence of the fluorescence quantum yields and lifetimes of these stabilizers on the nature of the solvent suggests that the excited-state, non-radiative processes are affected by solvation. In polar, hydroxylic solvents, values of the fluorescence quantum yield for the non proton-transferred form are significantly lower, and the fluorescence lifetimes are shorter, than those calculated for aprotic solvents. This supports the proposal of the formation, in alcoholic solvents, of an excited-state encounter complex which facilitates ESIPT. The observed concentration dependence of the fluorescence lifetime and intensity of the blue emission from TIN in polymer films provides evidence for a non-radiative, self-quenching process, possibly due to aggregation of the stabilizer molecules. 

Polymerization of acrylonitrile adsorbed on polyacrylonitrile" An intimate mixture of polyacrylonitrile solvated by its monomer is obtained if one melts acrylonitrile crystals which have been subjected to high energy radiation at low temperatures. The polymer forms under irradiation within the crystal lattice and upon melting, a gel-like phase is obtained in which the individual polymer molecules do not aggregate, presumably because most of the CN groups are then associated in pairs with the -CN groups of the monomer. Such a polyacrylonitrile solvated by its monomer should indeed be an ideal medium for the matrix effect to operate. 

To date, the crystal structures of several a-lithiated ethers have been determined" . Despite the aggregation, i.e. polymers, dimers or monomers, depending on the solvation. 

The unconventional applications of SEC usually produce estimated values of various characteristics, which are valuable for further analyses. These embrace assessment of theta conditions for given polymer (mixed solvent-eluent composition and temperature Section 16.2.2), second virial coefficients A2 [109], coefficients of preferential solvation of macromolecules in mixed solvents (eluents) [40], as well as estimation of pore size distribution within porous bodies (inverse SEC) [136-140] and rates of diffusion of macromolecules within porous bodies. Some semiquantitative information on polymer samples can be obtained from the SEC results indirectly, for example, the assessment of the polymer stereoregularity from the stability of macromolecular aggregates (PVC [140]), of the segment lengths in polymer crystallites after their controlled partial degradation [141], and of the enthalpic interactions between unlike polymers in solution (in eluent) [142], as well as between polymer and column packing [123,143]. 

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