Tethered polymer chains

A study by Shah et on die moisture diffusion of a (non-epoxy) vinyl ester resin-based layered silicate nanocomposite also reported a deereased moisture diffiisivity of the nanocomposite, ascribed to the restricted mobility of the polymer chains tethered to the clay particles. A reverse effect, however, could be observed for the equilibrium water uptake of one of the two fillers investigated. The equilibrium water uptake of a vinyl-monomer containing clay nanocomposites increased from 0.012% (neat resin) to 0.021 (5% clay). The water uptake of the other, an alkyl ammonium-treated montmorillonite clay, Cloisite lOA, remained relatively unaffected by the filler addition. The increase of the first nanocomposites system was related to the strong, hydrophilic behaviour of the clay, which remains to some degree in the surface treated state. 

Highly branched polymers, polymer adsorption and the mesophases of block copolymers may seem weakly connected subjects. However, in this review we bring out some important common features related to the tethering experienced by the polymer chains in all of these structures. Tethered polymer chains, in our parlance, are chains attached to a point, a line, a surface or an interface by their ends. In this view, one may think of the arms of a star polymer as chains tethered to a point [1], or of polymerized macromonomers as chains tethered to a line [2-4]. Adsorption or grafting of end-functionalized polymers to a surface exemplifies a tethered surface layer [5] (a polymer brush ), whereas block copolymers straddling phase boundaries give rise to chains tethered to an interface [6],... 

REMP, the acronym for ring expansion metathesis polymerisation is a special case of ROMP, where the growing polymer chain stays attached to the catalyst at both ends nntil a macrocycle is released. This requires that the active carbene be tethered... 

The rheological properties of insitu polymerized nanocomposites with end-tethered polymer chains were first described by Krisnamoorti and Giannelis [33]. The flow behavior of PCL- and Nylon 6-based nanocomposites differed extremely from that of the corresponding neat matrices, whereas the thermorheological properties of the nanocomposites were entirely determined by the behavior of the matrices [33]. The slope of G (co) and G"(co) versus flxco is much smaller than 2 and 1, respectively. Values of 2 and 1 are expected for linear mono-dispersed polymer melts, and the large deviation, especially in the presence of a very small amount of layered silicate loading, may be due to the formation of a network structure in the molten... 

Currie EPK, Norde W, Cohen Stuart MA (2003) Tethered polymer chains surface chemistry and their impact on colloidal and surface properties. Adv Colloid Interf Sci 100-102, 205-265... 

In the case of PEMs, the situation is more complicated because the sulfonate counter-ions (in the case of a PEM such as Nafion ) are bound to the polymer chain and are thus relatively immobile, in contrast to the free counter-ion in a small molecule acid such as sulfuric or acetic acid. Tethering of the sulfonate group can be considered to be an impediment to the mobility of the proton as it traverses the membrane. Proton mobility is also affected by the effective mean-free path of connectivity of the conduction pathway as shown in Figure 3.2. In situation (a), the increased number of dead ends and tortuosity of the aqueous domains through which proton transport occurs over the situation in (b) leads to lower overall mobility. This has been demonstrated by Kreuer and will be discussed later in this section. 

The non-aqueous system of spherical micelles of poly(styrene)(PS)-poly-(isoprene)(PI) in decane has been investigated by Farago et al. and Kanaya et al. [298,299]. The data were interpreted in terms of corona brush fluctuations that are described by a differential equation formulated by de Gennes for the breathing mode of tethered polymer chains on a surface [300]. A fair description of S(Q,t) with a minimum number of parameters could be achieved. Kanaya et al. [299] extended the investigation to a concentrated (30%, PI volume fraction) PS-PI micelle system and found a significant slowing down of the relaxation. The latter is explained by a reduction of osmotic compressibihty in the corona due to chain overlap. 

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. 

SIP involves the growth of a polymer chain from an initiator moiety that has been covalently tethered to a surface. The advent of this reaction approach, along... 

By definition, polymer brushes are made up of polymer chains grafted (tethered) by one end to a surface or an interface (Fig. 1) [ 1 - 3]. The density can be small or high in the latter case, the polymer chains are crowded and forced to stretch in order to avoid other chains. This results eventually in an equilibrium condition where no external field is necessary to force the chains into this geometry. 

Fig. 3.16 Star polymer model for chains tethered to a curved surface. Chains are represented as a string of blobs extending radially from the core of the star.

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