Diblock copolymers copolymer solutions

In another study,BorsaU and Benmouna discussed the static and dynamic scattering properties of ring diblock copolymers in solution [289]. They focused their attention on the semi-dilute region and the case of compositionally symmetric ring diblock copolymers. Differences in the scattering profiles were predicted, the main reason being the presence of connection between the two ends of the chain in the case of ring copolymers. Due to this connectivity effect, different con-... 

The lattice model, as put forth by Flory [84, 85], has been proved successful in the treatments of the liquid crystallinity in polymeric systems, despite its artificiality. In our series of work, the lattice model has been extended to the treatment of biopolypeptide systems. The relationship between the polypeptide ordering nature and the LC phase structure is well established. Recently, by taking advantage of the lattice model, we formulated a lattice theory of polypeptide-based diblock copolymer in solution [86]. The polypeptide-based diblock copolymer exhibits lyotropic phases with lamellar, cylindrical, and spherical structures when the copolymer concentration is above a critical value. The tendency of the rodlike block (polypeptide block) to form orientational order plays an important role in the formation of lyotropic phases. This theory is applicable for examining the ordering nature of polypeptide blocks in polypeptide block copolymer solutions. More work on polypeptide ordering and microstructure based on the Flory lattice model is expected. 

Kim, S.Y. et al, 2007. Reverse thermal gelling PEG-PTMC diblock copolymer aqueous solution. Macromolecules, 40(15), 5519-5525. 

Thermogelling aqueous solutions of poly(ethylene glycol)-poly(ethyl-2-cyanoaerylate) (PEG-PEC) were reported (Fig. 13.10). Polycyanoacrylate is degraded by esterases to cyanoacryUc acid. The PEG-PEC diblock copolymer aqueous solution showed a sol-to-gel-to-sol transition as the temperature increased as well as the concentration increased, thus, forming a closed-loop gel domain in the phase diagram. 

Hg. 21a. Schematic sketch of model used in calculation of scattering law for styrene-methyl methacrylate diblock copolymer in solution b Comparison of rotational isomeric state calculation (-----)... 

Ito, H., Imae, T., Nakamura, T., Sugiura, M. and Oshibe, Y. (2004) Self-association of water-soluble fluorinated diblock copolymers in solutions. /. Colloid. Interf. Sci, 276,290-298. 

Mortensen K, Brown W, Almdal K, Alami E, Jada A (1997) Structure of PS-PEO diblock copolymers in solution and the bulk state probed using dynamic light-scattering and small-angle neutron-scattering and dynamic mechanical measurements. Langmuir 13 3635-3645... 

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. 

Figure 3. Dependence of T evaluated at shear stresses of 10 ( ) and 10 (O) dyn/cm on composition in the SI diblock copolymer/MO solutions presented in Fig. 2. The solid and dashed lines are exponential fits to the two data sets.

Block and graft copolymers with incompatible sequences exhibit characteristic morphological behavior and interesting properties, owing to micelle formation in a selective solvent and microdomain formation in the solid state. Many types of micelles formed by diblock copolymers in solution were reported. Spherical self-assembly formed in the solvent for one sequence and not for the other forms a so-called polymer micelle with core-corona morphology. 

AB diblock copolymers in the presence of a selective surface can form an adsorbed layer, which is a planar form of aggregation or self-assembly. This is very useful in the manipulation of the surface properties of solid surfaces, especially those that are employed in liquid media. Several situations have been studied both theoretically and experimentally, among them the case of a selective surface but a nonselective solvent [75] which results in swelling of both the anchor and the buoy layers. However, we concentrate on the situation most closely related to the micelle conditions just discussed, namely, adsorption from a selective solvent. Our theoretical discussion is adapted and abbreviated from that of Marques et al. [76], who considered many features not discussed here. They began their analysis from the grand canonical free energy of a block copolymer layer in equilibrium with a reservoir containing soluble block copolymer at chemical potential peK. They also considered the possible effects of micellization in solution on the adsorption process [61]. We assume in this presentation that the anchor layer is in a solvent-free, melt state above Tg. The anchor layer is assumed to be thin and smooth, with a sharp interface between it and the solvent swollen buoy layer. 

A very specific surface structure is observed after the annealing of a PS/polybuta-diene (PB) diblock copolymer, PS-b-PB, shown in Fig. 7 b. The surface is very smooth directly after preparation of the film from solution (similar to Fig. 7 a). By annealing at 120 °C the surface structure shown in Fig. 7 b evolves, which we believe is due to the formation of layers of PS and PB parallel to the surface. The outermost layer might not be completely filled due to lack of material leading to steps at the surface. Similar behavior is observed with other diblock copolymers such as PS-b-PMMA [61]. Enrichment of one component is also observed at the surface of a polymer solution [115,116] by X-ray fluorescene and evanescent wave techniques. 

The best insight into the relaxation behavior of star polymers in dilute solution can be expected if, in addition to the whole star system, different parts of the star are considered separately. This can be achieved easily by neutron scattering techniques on systems where not only the entity of arms, but also single arms, the core or shell parts are labelled by proton deuterium exchange. With respect to the core-shell labelling it is convenient to build up the arms as diblock copolymers of A-B type with protonated or deuterated but otherwise chemically identical A and B blocks. 

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... 

Figure 69 presents typical NSE spectra of such a system [174]. They were obtained from a 2% diblock copolymer (perdeuterated PS and protonated PI blocks) d-n-decane solution. The molecular masses Mw of PS and PI were 10000 and 7500 g/mol, respectively. The solvent selectively dissolves PI but not PS. In... 

Fig. 51 Phase diagram for PS-PI diblock copolymer (Mn = 33 kg/mol, 31vol% PS) as function of temperature, T, and polymer volume fraction, cp, for solutions in dioctyl ph-thalate (DOP), di-n-butyl phthalate (DBP), diethyl phthalate (DEP) and M-tetradecane (C14). ( ) ODT (o) OOT ( ) dilute solution critical micelle temperature, cmt. Subscript 1 identifies phase as normal (PS chains reside in minor domains) subscript 2 indicates inverted phases (PS chains located in major domains). Phase boundaries are drawn as guide to eye, except for DOP in which OOT and ODT phase boundaries (solid lines) show previously determined scaling of PS-PI interaction parameter (xodt

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

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