Polymers properties in solution

The conformation of polymers governs their various physicochemical properties. When the conformation is reversibly controlled by external stimulation, such as photons, or chemicals, the conformation change should produce a concomitant change in polymer properties in solution as well as in the gel. Polymers which change their properties reversibly by such external stimulation may be referred to as stimuli-responsive polymers. 

Polymers with which we will deal throughout this chapter are water soluble. They can be either ionic or nonionic. Some of them are synthetic, others are of biological origin (proteins, for instance). Both homopolymers and heteropolymers exist. Some polymers own amphiphilic monomers that induce surface-active properties to the whole polymeric structure. Water plays a very important role in determining the polymer properties in solution. The properties are also greatly modified by the addition of salts or by a pH modification. Frequently encountered nonionic polymers in polymer-surfactant interactions and their subsequent adsorption behavior at solid surfaces are poly(ethylene oxide) (PEO), poly(vinyl pyrrolidone) (PVP), polyacrylamide, and poly(vinyl alcohol). 

Polymer Properties in Solutions 1 Y Nakamura, Kyoto University, Kyoto, Japan 1 T Norisuye, Osaka University, Osaka, Japan J 2012 Eisevier B.V. Aii rights reserved. ... 

There have been some attempts to compute nonlinear optical properties in solution. These studies have shown that very small variations in the solvent cavity can give very large deviations in the computed hyperpolarizability. The valence bond charge transfer (VB-CT) method created by Goddard and coworkers has had some success in reproducing solvent effect trends and polymer results (the VB-CT-S and VB-CTE forms, respectively). 

Solution Polymerization These processes may retain the polymer in solution or precipitate it. Polyethylene is made in a tubular flow reactor at supercritical conditions so the polymer stays in solution. In the Phillips process, however, after about 22 percent conversion when the desirable properties have been attained, the polymer is recovered and the monomer is flashed off and recyled (Fig. 23-23 ). In another process, a solution of ethylene in a saturated hydrocarbon is passed over a chromia-alumina catalyst, then the solvent is separated and recyled. Another example of precipitation polymerization is the copolymerization of styrene and acrylonitrile in methanol. Also, an aqueous solution of acrylonitrile makes a precipitate of polyacrylonitrile on heating to 80°C (176°F). 

SBR latices are high-solids dispersions of rubber particles in water, the viscosity and rheology of which are, in general, independent of the polymer properties, unlike solutions. They offer a wide range of molecular weight and glass transition temperature. Three classes of SBR latices are available in the market. 

The dynamical properties of polymer molecules in solution have been investigated using MPC dynamics [75-77]. Polymer transport properties are strongly influenced by hydrodynamic interactions. These effects manifest themselves in both the center-of-mass diffusion coefficients and the dynamic structure factors of polymer molecules in solution. For example, if hydrodynamic interactions are neglected, the diffusion coefficient scales with the number of monomers as D Dq /Nb, where Do is the diffusion coefficient of a polymer bead and N), is the number of beads in the polymer. If hydrodynamic interactions are included, the diffusion coefficient adopts a Stokes-Einstein formD kltT/cnr NlJ2, where c is a factor that depends on the polymer chain model. This scaling has been confirmed in MPC simulations of the polymer dynamics [75]. 

It has been shown, by theories of the frictional properties of polymer molecules in solution, that the intrinsic viscosity is proportional to the effective hydrodynamic volume of the molecule in solution divided by its Molecular weight. The effective volume is proportional to the cube of a linear dimension... 

Polymers having ionisable groups along the chain are known as polyelectrolytes. They generally exhibit properties in solution which are quite different from those with non-ionisable structures. Examples of polyelectrolytes include polyacids like poly (acrylic acid) and hydrolysed copolymers of maleic anhydride, polybases like poly (vinyl amine) and poly (4-vinyl pyridine), polyphosphates, nucleic acids, and proteins. 

To make further use of the azo-initiator, tethered diblock copolymers were prepared using reversible addition fragmentation transfer (RAFT) polymerization. Baum and co-workers [51] were able to make PS diblock copolymer brushes with either PMMA or poly(dimethylacrylamide) (PDMA) from a surface immobihzed azo-initiator in the presence of 2-phenylprop-2-yl dithiobenzoate as a chain transfer agent (Scheme 3). The properties of the diblock copolymer brushes produced can be seen in Table 1. The addition of a free initiator, 2,2 -azobisisobutyronitrile (AIBN), was required in order to obtain a controlled polymerization and resulted in the formation of free polymer chains in solution. 

As already shown, conventional macromolecules (or polymers) consist of a minimum of a several hundred covalently linked atoms and have molar masses clearly above 10 g/mol. The degree of polymerization, P, and the molecular weight, M, are the most important characteristics of macromolecular substances because nearly all properties in solution and in bulk depend on them. The degree of polymerization indicates how many monomer units are linked to form the polymer chain. The molecular weight of a homopolymer is given by Eq. 1.1. 

Hydrogen bonding interactions are important for the development of selfassembling supramolecular materials, which are defined as materials in which monomeric units are reversibly bound via secondary interactions to form polymer-like stmctures that exhibit polymeric properties in solution as well as in bulk (Bmnsveld et al. 2001). Rotello used hydrogen bond functional polymers to direct the formation of large vesicles (lUian et al. 2000), reversibly attach polymers on... 

Use of the optically resolved complex leads to the optically active polymer, but this property, which arises from the helical chain structure, is found only in the swollen polymer and is easily lost in toluene or dichloroacetic acid solution 144). The polymerization occurs with a high degree of enantioface selection, and the model for the product backbone is indeed chiral. However, because of the presence of a mirror, plane in the polymer chain (effects of chain termini neglected), the product does not have chiral properties in solution. 

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