Pure copolymer solutions

Figure 67 shows Q QVQ2 vs. Q for both systems. As expected from Eqs. (142) and (143) their behavior is completely different. One can see that a pronounced divergency occurs at small Q-values in the semi-dilute block copolymer solution. If Qi(Q)/Q2 is analyzed in terms of a generalized mobility ji(Q) [see Eq. (94)], Fig. 68 results from the different concentrations of the diblock copolymer solution. Q(Q) varies both with Q and with c. In particular, the Q-dependence is indicative of the non-local character of the mobility and incompatible with the assumption of a pure Rouse type of dynamics. The... 

The plots of h/h vs. copolymer concentration also reveal differences in the micropolarity of the hydrophobic domains created upon association of the various copolymers in water. A qualitative assessment of this property is given by the h/h value determined in the copolymer solutions of highest concentration when the plateau value is attained (Fig. 25). This value depended significantly on the grafting level the solution of the most densely grafted copolymer yielded the lowest h/h value (1.40) and the pure homopolymer the highest. In all cases, this value is higher than the value (1.20) recorded for micellar solutions of the macromonomer. It can be concluded... 

In fact, even in pure block copolymer (say, diblock copolymer) solutions the self-association behavior of blocks of each type leads to very useful microstructures (see Fig. 1.7), analogous to association colloids formed by short-chain surfactants. The optical, electrical, and mechanical properties of such composites can be significantly different from those of conventional polymer blends (usually simple spherical dispersions). Conventional blends are formed by quenching processes and result in coarse composites in contrast, the above materials result from equilibrium structures and reversible phase transitions and therefore could lead to smart materials capable of responding to suitable external stimuli. 

The free-standing films are either formed from aqueous surfactant/poly-electrolyte solutions or from pure aqueous diblock copolymer solutions. 

The (integral) enthalpy of mixing or the (integral) enthalpy of solntion of a binary system is the amount of heat which must be supplied when ha mole of pure solvent A and ub mole of pure copolymer B are combined to form a homogeneous mixture/solution in order to keep the total system at constant temperature and pressure. 

Liu et al. reported the preparation of two types of shell-cross-linked (SCL) micelles with inverted structures via click chemistry starting from a well-defined schizophrenic water-soluble triblock copolymer in purely aqueous solution. They present an efficient synthesis of two types of SCL micelles with either pH- or temperature-sensitive cores from a novel poly(2-(2-methoxyethoxy) ethyl methacrylate)-ft-poly(2-(dimethylamino) ethyl methacrylate)-Z -poly(2-(diethylamino) ethyl methacrylate) [PME02MA-ft-P(DMA-co-QDMA)- -PDEA] triblock copolymer. First, PMEO2MA- -PDMA- -PDEA was prepared and the DMA blocks were partially converted to a quaternized DMA (QDMA) block with click-cross-linkable moieties to form novel schizophrenic water-soluble triblock copolymers. The pH- or temperature-induced micellization and subsequent shell cross-linking of the P(DMA-co-QDMA) inner shell with the tetra-(ethylene glycol) diazide via click chemistry resulted in nanogel networks (Figure 54.14). 

In the case of copolymer solutions, the melting temperature also depends on interactions between the different monomeric imits and the solvent. Considering the case in which the crystalline phase is pure (i.e., only monomeric units of a single type crystallize and no solvent is present in the lattice), the decrease in the melting temperature can be derived in a similar manner as for the homopolymer solution case using the Flory-Huggins theory with an appropriate modification [15]. To take into accoimt the interactions between both comonomers and solvent, the net interaction parameter for binary copolymers should be calculated as follows ... 

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... 

With these approximations, the phase diagram calculated for copolymer solutions can be obtained from previous theoretical calculations for pure copolymer melts by Leibler in the mean-field theory (Fig. 3) or by... 

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... 

There are two different situations for the liquid-liquid equilibrium in copolymer/solvent systems (i) the equilibrium between a dilute copolymer solution (sol) and a copolymer-rich solution (gel) and (ii) the equilibrium between the pure solvent and a swollen copolymer network (gel). Only case (i) is considered here. To understand the results of LLE experiments in copolymer/solvent systems, one has to take into account the strong influence of distribution functions on LLE, because fi actionation occurs during demixing, both with respect to chemical distribution and to molar mass distribution. Fractionation during demixing leads to some effects by which the LLE phase behavior differs fi om that of an ordinary, strictly binary mixture, because a common copolymer solution is a multicomponent system. Cloud-point curves are measured instead of binodals and per each individual feed concentration of the mixture, two parts of a coexistence curve occur below or above (UCST or LCST behavior) the cloud-point curve, i.e., to produce an infinite number of coexistence data. 

The enthalpy effect might be positive (endothermic solution/mixture) or negative (exothermic solution/mixture) depending on the ratio tijns, i.e., the concentration of the total system. Unfortunately, in some of the older literature, the definition of the sign of the so-called (integral) heat of solution is reversed, compared to the enthalpy, occasionally causing some confusion. In principle, the enthalpy effect depends also on pressure. However, in the case of condensed systems this pressure dependence is relatively small. All values in this handbook usually refer to normal pressiue. Hoa and Hog are the molar enthalpies of pure solvent A and pure copolymer B and and Hg the partial molar enthalpies of solvent and copolymer in the solution/mixture. 

The vapor pressure depression of the solvent in a binary copolymer solution, i.e., the difference between the saturation vapor pressure of the pure solvent and the corresponding partial pressure in the solution, AP = Pf -Pa, is expressed as ... 

Figure 7b corresponds to the solution series with < )bC 7 wt% and reveals two very interesting features. The first is that both the pure SI (< >si=7 vi ) and the pure SIS (< )isi=0 wt%) copolymer solutions exhibit comparable magnitudes of T, on the order of about 3 P. In both cases, t is virtually independent of x, as was evident for only the SI solution in Fig. 2. This behavior does not change substantially if is reduced to 6 wt% or increased to 1 wt%. Within these bounds, however, r is seen to increase dramatically, and its shear dependence becomes sensitive to solution composition. Consider the solution wiA 3 wt% SI copolymer. Its steady-shear Tj increases by up to -5 orders of magnitude at low X, and then decreases by 2 orders of magnitude over the range of x shown in Fig. 7b. Comparison of Figs. 7a and 7b reveals that, between 3 and 5 wt% SI, the 11 curves displayed in Fig. 7b resemble the curves for SIS-containing solutions in Fig. 7a. Such similarity suggests that solutions wt%) lying...

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