Cross-linking and branching

Monomers such as aUyl methacrylate and diaUyl maleate have appUcations as cross-linking and branching agents selected especiaUy for the different reactivities of their double bonds (90) some physical properties are given in Table 8. These esters are colorless Uquids soluble in most organic Uquids but htde soluble in water DAM and DAF have pungent odors and are skin irritants. 

DiaUyl fumarate polymerizes much more rapidly than diaUyl maleate. Because of its moderate reactivity, DAM is favored as a cross-linking and branching agent with some vinyl-type monomers (1). Cyclization from homopolymerizations in different concentrations in benzene has been investigated (91). DiaUyl itaconate and several other polyfunctional aUyl—vinyl monomers are available. 

Figure 17 Schematic representation of heterogeneous portions of curdlan hydrogel (left) (A) liquid-like portion, (B) portion of intermediate mobility, and (C) triple-helical cross-links in the solid-like portion and crystallites as additional cross-links, and branched glucans (triple helical chains) (right). From Ref. 117 with permission.

In general, three major macromolecular classes, namely linear, cross-linked, and branched architectures, are produced by statistical polymerization processes. Therefore their architectures are not structurally-controlled as in many biological systems [37]. However, the discovery of dendrimers has changed this paradigm. 

Lignin is a complex amorphous polymer composed of a cross-linked and branched network phenylpropane units. Thermal analyses such as TG, DTA, and DSC are useful for elucidating the physicochemical properties of lignin. 

It is useful to discuss these results within a model of the radiation-damaged polymer. Our original report (.10) on x-irradiation of PTFE concluded that the damaged material was a highly cross-linked and branched network. The new observations, reported here, permit further elaboration of the model. 

The functionalization of polymers is another useful feature of the hydrosilation reaction. The introduction of highly fluorinated alkyl chains by the hydrosilation of Si-H groups of the polymer with fluorinated aUcenes is a typical example. Poly(phenylsilanes) obtained by the dehydrocouphng polymerization of phenylsilane undergo AIBN initiated free radical hydrosilation with aUcenes, ketones and aldehydes. Cross-linking and branching of polymers can also be easily accomplished using hydrosilation. 

The investigation of cross-linked and branched polymers by the PL method permits to obtain information on the dynamic characteristics of both cross-linked junctions and linear fragments of the polymer system. Depending on the aims of the investigations, LM shoidd be located either in a cross-linked junction or in a linear fragment of the polymer. 

The physical reasons for the appearance of relaxation spectra in polymer chains can differ. They comprise 1) the cooperative character of the motion of a multiparticle polymer chain, 2) the anisotropy of the shape of a kinetic chain segment and consequently the appearance of several relaxation times, 3) the chemical and structural heterogeneity of the chain (copotymers, structurized macromolecules, polymers with ade chains, etc., and cross-linked and branched-chain systems). 

Cross-linking and branching.. 98 6.5 Metastable crystalline structure 115... 

Effect of Side Chain Substitution, Cross-Linking, and Branching... 

The Michael addition is a very efficient reaction that has been widely applied for dendrimer synthesis due to a small amount of side reactions and mild reaction conditions, poly (amido amine) (PAMAM) or poly(propylene imine) (PPI) dendrimers are two well-known examples that rely on the Michael addition. Long et al. reviewed the synthetic approaches to linear, cross-linked, and branched polymers via step-growth Michael polyaddition.Thermally stable, high-Tg poly... 

Crystal-phase I APP (APP I) is characterized by a variable linear chain length, showing a lower decomposition temperature (approximately 150 °C) and a higher water solubility than crystal phase II (APP II). APP II has a cross-linked and branched structure. The molecular weight is much higher than that of APP I with n > 1000. APP 11 has a higher thermal stability and lower water solubility than AP PI (see Tables 17.9 and 17.10). 

In contrast to the other possible monomer components, butadiene possesses two double bonds both of which can act as polymerization sites. Binders based on a styrene-butadiene combination therefore have a more cross-linked and branched polymer structure. The extent of cross-linking affects the dry and wet pick strength, the print gloss and the degree of blistering, which is a highly significant parameter in... 

This first systematic XPS analysis has shown that it is possible to sputter-deposit compounds whose surface properties (fluorine to carbon ratio, cross-linking and branching) can be varied over a large range of values, as it has already been observed for polymer films prepared by plasma polymerization. We note here that a film very similar to polytetrafluoroethylene... 

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