Block copolymers dynamic properties

To date, the melt state linear dynamic oscillatory shear properties of various kinds of nanocomposites have been examined for a wide range of polymer matrices including Nylon 6 with various matrix molecular weights [34], polystyrene (PS) [35], PS-polyisoprene (PI) block copolymers [36,37], poly(e-caprolactone) (PCL) [38], PLA [39,40], PBS [30,41], and so on [42],... 

Here, we focus on one class ofblock copolymers synthesized by this method polystyrene-6-poly(vinylperfluorooctanic acid ester) block copolymers (Figure 10.33). After describing the synthesis and characterization, we will treat some properties and the potential applications of this new class ofblock copolymers. The amphiphilicity of the polymers is visualized by the ability to form micelles in diverse solvents that are characterized by dynamic light scattering (DLS). Then the use of these macromolecules for dispersion polymerization in very unpolar media is demonstrated by the polymerization of styrene in 1,1,2-trichlorotrifluoroethane (Freon 113). 

These concentration fluctuations are pivotal to the phase transitions in block copolymer melts and are dynamic in nature. They lead to a renormahzation of the relevant interaction parameters and are thought to be responsible for the induction of the first-order nature of the phase transition [264,265]. Such fluctuations are better studied in dynamic experiments. Thus, one can observe an increasing interest in diblock copolymer dynamics. These dynamic properties are being analysed through experimental, theoretical [266,267] and computer simulation approaches [268,269] with the aim of determining the main featirres of diblock copolymer dynamics in comparison to homopolymer dynamics. There are three main issues ... 

By covalent linkage of different types of molecules it is possible to obtain materials with novel properties that are different from those of the parent compounds. Examples of such materials are block-copolymers, soaps, or lipids which can self-assemble into periodic geometries with long-range order. Due to their amphiphilic character, these molecules tend to micellize and to phase-separate on the nanometer scale. By this self-assembly process the fabrication of new na-noscopic devices is possible, such as the micellization of diblock-co-polymers for the organization of nanometer-sized particles of metals or semiconductors [72 - 74]. The micelle formation is a dynamic process, which depends on a number of factors like solvent, temperature, and concentration. Synthesis of micelles which are independent of all of these factors via appropriately functionalized dendrimers which form unimolecular micelles is a straightforward strategy. In... 

The mechanical properties at low strain rates, dynamic mechanical properties, creep-recovery behaviour, thermal expansion and thermal conductivity of foams manufactured from blends of LDPE with an EVA and with an isoprene-styrene block copolymer were studied as a function of the LDPE content in the blends. The experimental results demonstrated important aspects related to the modification of the foam properties by blending. 16 refs. 

Cohen, R.E., Tschoegl,N.W, Dynamic mechanical properties of block copolymer blends—a study of the effects of terminal chains in elastomeric materials. I. Torsion pendulum measurements. Intern. J, Polymeric Mater. 2, 49-69 (1972) II. Forced oscillation measurements. Ibid 2, 205-223 (1973) III. A mechanical model for entanglement slippage. Ibid (in press). 

Block copolymers are widely used industrially. In the solid and rubbery states they are used as thermoplastic elastomers, with applications such as impact modification, compatibilization and pressure-sensitive adhesion. In solution, their surfactant properties are exploited in foams, oil additives, solubilizers, thickeners and dispersion agents to name a few. Particularly useful reviews of applications of block copolymers in the solid state are contained in the two books edited by Goodman (1982,1985) and the review article by Riess etal. (1985). The applications of block copolymers in solution have been summarized by Schmolka (1991) and Nace (1996). This book is concerned with the physics underlying the practical applications of block copolymers. Both structural and dynamical properties are considered for melts, solids, dilute solutions and concentrated solutions. The book is organized such that each of these states is considered in a separate chapter. 

There is a substantial body of work using dynamic light scattering to probe the hydrodynamic properties of poly(oxyethylene)-based block copolymers in aqueous solution. The work of Brown and co-workers has been reviewed by... 

Almgren, M., P. Bahadur, M. Jansson, P. Li, W. Brown, and A. Bahadur. 1992. Static and dynamic properties of a (PEO-PPO-PEO) block copolymer in aqueous solutlofEolloid. Interface Sci151 157-165. 

Let us compare the kinetics of the selective-solvent-induced collapse of protein-like copolymers with the collapse of random and random-block copolymers [18]. Several kinetic criteria were examined using Langevin molecular dynamics simulations. There are some general results, which seem to be independent of the nature of interactions or the kinetic criteria monitored during the collapse. Here, we restrict our analysis to the evolution of the characteristic ratio f = (Rgp/Rg ) that combines the partial mean-square radii of gyration calculated separately for hydrophobic and hydrophilic beads, k2n and Rg . This ratio takes into account both the properties of compactness and solubility for a heteropolymer globule [70] (compactness is directly related to the mean size of the hydrophobic core, whereas solubility should be dependent on the size of the hydrophilic shell). 

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