Common good solvent

As an extension of this work viscometry was used to study the conformation of A3B stars (A=PI and B=PS) in the common good solvent toluene [65]. In this case the experimental data, together with the ones obtained from the previous work, were used to extract the dimensionless ratio gg. This ratio expresses quantitatively the effects of heterointeractions between unlike segments on the conformational properties of the copolymers. The oG values for the A3B case were higher than for the A2B case it seems that this is due to the increased segment density of A units in the vicinity of B units for A3B. The experimental values compared rather well with the ones obtained from renormalization group theory and Monte Carlo calculations taking into account the uncertainty in the asymmetry correction coefficient used in the calculations (see Table 2). 

The versatility of the crosslinked structures opens a new broad avenue for their application in several areas. As mentioned above, corona-crosslinked PFS assemblies demonstrate excellent shape retention upon pyrolysis and permit the formation of ceramic replicas. We have also recently shown that in a common good solvent, the PFS chains in the microgel interior of xPMVS can serve as a microreactor forthe localized production of metal nanoparticles [25], We are also about to begin light scattering studies of PMVS micelles, before and after corona crosslinking, and hope to use these experiments to learn more about the self-assembled structures formed in dilute solution. 

Then in section III, we analyze the liquid-liquid phase separation of polymer blends in solvents of various quality. Particular emphasis is put on the case of a common good solvent and on the discussion of the critical properties of demixing which are very unusual as the critical behavior is not of the mean-field type (except for very long chains and low incompatibility degrees) and is als very different from that of low molecular weight ternary mixtures. We also focus on well- demixed systems and consider the interfacial properties following the work of Broseta et al. ... 

We now present briefly more explicit calculations of the mutual virial coefficients obtained with the use of des Cloizeaux direct renormalization method for blends of linear flexible polymers in a common good solvent, a common 0-solvent and a selective solvent and for blends of rodlike polymers and flexible polymers in a 0-solvent (marginal behavior). These calculations enable one to find (universal) prefactors relating the mutual virial coefficient to the chain volume (in Eq. 7) in the asymptotic limit. Moreover they give the corrections to the scaling behavior which explicitly depend on the interactions between unlike monomers and are actually responsible for the phase separation of flexible polymer blends in a good solvent. 

In a common good solvent, we expect polymers to interact as hard spheres, we thus introduce dimensionless virial coefficients by ... 

We now apply these results for the values of the virial coefficient calculated in the previous section in a common 0-solvent, a selective solvent and a common good solvent. 

We discuss here two examples of aggregation of diblock copolymers in solution, the formation of spherical micelles in a highly selective solvent, good for one block and poor for the other block, and the formation of ordered mesophases in a common good solvent for both blocks. 

In a dilute solution in a common good solvent for both blocks, the interactions between. different copolymers may be studied using the same direct renormalization procedures as the interactions between two homopolymers A and B equivalent to the two blocks.As for blends, in the asymptotic limit of infinite molecular masses, the chemical difference between the two blocks is irrelevant and the dimensionless virial coefficient gc between block copolymers defined by Eq. (10) is equal to the same value g as for homopolymers. The interactions which may provoke the formation of mesophases are here again due to the corrections to the scaling behavior ... 

In a dilute solution, blends of homopolymers A and B equivalent to the two blocks of the copolymers are compatible in a common good solvent contrary to what happens in a highly selective solvent, we do not expect mesophases to form in a dilute solution but only in semidilute and concentrated solutions. Mesophases formed by block copolymers in nonselective solvents have been studied many experimental groups, perhaps most recently bv Hashimoto et al. and Williams et al. The usual interpretation of experiments is based on the "dilution approximation" in which the phase diagram of a solution can be obtained from the corresponding pure copolymer phase diagram by replacing Xab AB where is the monomer volume fraction. We have seen in section... 

In a common good solvent, chains of equal radius behave as hard spheres due to the excluded volume effects. In the asymptotic limit of very long chains, different polymers cannot tell each other apart a polymer A cannot distinguish between a polymer A and a polymer B. Interactions between unlike... 

In a more concentrated solution the interactions between unlike polymers provoke a demixing phase transition. In a common 0 solvent, the critical concentration scales as the overlap concentration c (in the symmetric case). In a common good solvent the critical concentration ck lies well in the semidilute regime and is governed by interactions related to corrections to the... 

The critical behavior has been studied in details for polymer blends in a common good solvent. The composition fluctuations play an important role and the critical behavior is not of the mean field type except in the limit of... 

In a common good solvent in a semidilute solution, the interactions between unlike chemical species may provoke phase separation into a solvent rich disordered (homogeneous) phase and a solvent poor ordered phase (mesophase). The two-phase regions are extremely narrow and in a good approximation the phase diagram of copolymer solutions has a topology similar to that of a pure molten copolymer the symmetry of the mesophases... 

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