Polymerization branched

Whea there are reactants with three or more functionahties participating ia the polymerization, branching and the formation of iatermolecular linkages, ie, cross-linking of the polymer chains, become definite possibiUties. If extensive cross-linking occurs in a polymer system to form network stmctures, the mobiUty of the polymer chains is greatiy restricted. Then the system loses its fluidity and transforms from a moderately viscous Hquid to a gelled material with infinite viscosity. The experimental results of several such reaction systems are collected in Table 6. 

Puskas, J.E., Antony, P., Paulo, C., Kwon, J., Kovar, M., Norton, P., and Altstadt, V. Macromolecular engineering via carbocationic polymerization Branched and hyperbranched stmctures, block copolymers and nanostructures, Macromol. Mater. Eng., 286, 565-582, 2001. 

Matsuzaki et al. (129) prepared grafted Nylon with branches of methyl methacrylate and methacrylic acid units by exposure of the trunk polymer to gamma-rays from a cobalt-60 source. They studied the tacticity of the polymeric branches which were separated from the skeleton chain by mild hydrolysis in 6N hydrochloric acid for several hours and determined the stereoregularity in a 100 MHz NMR spectrometer. 

Hay also found that the oxidative polymerization of 2-chloro-6-methylphenol gave high molecular weight polymers with lower than expected intrinsic viscosities (35). Analysis of the polymers also showed loss of chlorine (10—15%) during the polymerization. Branch points such as (XIII) were assumed in this instance. In the case of the polyhalophenol... 

Polymacromonomers with polymeric branches on every second carbon atom of the backbone have an extremely high branched chain density. In other words, one polymacromonomer chain of degree of polymerization, DP has DP+2 ends. 

Thermoplastics, i. e. polymers with linear chains, are mainly prepared by polymerization. Branched or cross-linked macromolecules are only needed in special cases. When a polymer is produced for further processing, a cross-... 

Figure 24.6 General approach to post-polymerizer branching...

Figure 24.7 An example of the post-polymerizer branching approach to branch polystyrene using a BCB-functional initiator...

Unlike radical polymerization, branched polystyrenes having a variety of controlled structures have been synthesized (Figure 24.10). This is because termination can be precisely controlled. The branched polystyrenes synthesized using anionic chemistry have been used to study the effect of branch structure on rheology [15]. As will be discussed in the next section, branch architecture (like those presented in Figure 24.10) can influence the rheological properties of polystyrene resins. 

In the course of polymerization, branching grows with increasing conversion. The rubber s properties are strongly influenced by the final monomer conversion [95]. 

Another example of ionic graft copolymerization is a reaction carried out on pendant olefinic groups using Ziegler-Natta catalysts in a coordinated anionic-type polymerization. The procedure consists of two steps. In the first, diethylaluminum hydride is added across the double bonds. In the second the product is treated with a transition metal halide. This yields an active catalyst for polymerizations of a-olefms. By this method polyethylene and polypropylene can be grafted to butadiene styrene copolymers. Propylene monomer polymerization results in formations of isotactic polymeric branches ... 

Bottlebmsh copolymers are a class of shape-persistent macromolecules that possess a highly branched comblike architecture. Steric repulsion between densely grafted polymeric branches causes the backbone to adopt an extended conformation. By combining this feature with grafts that are... 

Polymers can be effective stabilisers of NPs through electronic and steric effects. Dendrimers are highly branched polymers only a few nanometers in diameter. Dendrimers are defined by a central core, interior polymeric branches and an exterior functionalized surface. Their uniform size, dispersity and water solubility (due to outer hydrophilic and metal encapsulating functional groups) make them ideal candidates as polymeric stabilizers for NP catalysed cross-coupling reactions. The encapsulated NPs are primarily eonfined sterically... 

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