Branched and cross-linked

When -xylene is used as the monomer feed in a plasma polymer process, PX may play an important role in the formation of the plasma polymer. The plasma polymer from -xylene closely resembles the Gorham process polymer in the infrared, although its spectmm contains evidence for minor amounts of nonlinear, branched, and cross-linked chains as well. Furthermore, its solubiUty and low softening temperature suggest a material of very low molecular weight (15). 

Other limitations of electrochemical fluorination ate that compounds such as ethers and esters ate decomposed by hydrogen fluoride and cannot be effectively processed. Branching and cross-linking often take place as a side reaction in the electrochemical fluorination process. The reaction is also somewhat slow because the organic reactant materials have to diffuse within 0.3 nm of the surface of the electrode and remain there long enough to have all hydrogen replaced with fluorine. The activated fluoride is only active within 0.3 nm of the surface of the electrode. 

Glass-Transition Temperature. The T of PVP is sensitive to residual moisture (75) and unreacted monomer. It is even sensitive to how the polymer was prepared, suggesting that MWD, branching, and cross-linking may play a part (76). Polymers presumably with the same molecular weight prepared by bulk polymerization exhibit lower T s compared to samples prepared by aqueous solution polymerization, lending credence to an example, in this case, of branching caused by chain-transfer to monomer. 

The presence of pendant reactive vinyl groups through 1,2 and 3,4 addition provides a site for branching and cross-linking since these may be involved in other chain reactions. Because of this a 1,4 polymer is generally to be desired. 

The basis of model calculations for copolymerization, branching and cross-linking processes is the stochastic theory of Flory and Stockmayer (1-3). This classical method was generalized by Gordon and coworkers with the more powerful method of probability generating functions with cascade substitution for describing branching processes (4-6). With this method it is possible to treat much more complicated reactions and systems (7-9). 

BRANCHING AND CROSS-LINKING IN VINYL ADDITION POLYMERS... 

In the absence of adsorption, inclusion, or exclusion, a polymer is fractionated on a GPC column according to the hydrodynamic volume.40138 The hydrodynamic volume is a function of monomer identity, as well as polymer molecular weight, branching, and cross-linking. The polymer chains in any given chromatographic fraction have roughly the same hydrodynamic volume. 

Branched and Cross-linked Silicones On hydrolysis, tnchlorosilance gives rise to branched as well as cross-linked silicones... 

Note Excess can lead to undesirable molecular branching and cross-linking. Chain branching can severely hamper the crystallization capability of PET and this may lead to a loss in performance properties. 

PET chain-extended with a diepoxide as chain extender can exhibit varying degrees of branching and cross-linking depending on the level of chain extender used [13, 14], The branched and cross-linked PETs exhibit significant improvement in tensile properties. 

The length, branching, and cross-linking of the polymers are.controlled by the timing of the three steps. A lot.of initiating catalyst will result in an abundance of free radicals. When that happens, the concentration of the monomer goes down rapidly as a relatively high number of polymers start... 

Effects of Branching and Cross-Linking on Poiymer Properties... 

Make sketches or diagrams showing (a) a linear polymer, (b) a polymer with pendant groups, (c) a polymer with short branches, (d) a polymer with long branches, and cross-linked polymers with (e) low and (f) high cross-linked density. 

Branching and cross-linking in fibers are undesirable since they disrupt crystal formation. However, a small amount of cross-linking may increase some physical properties such as tensile strength if incorporated in the polymer after the material is suitably drawn and processed. 

All the polyrotaxanes discussed thus far are based on linear backbones. Viewing new properties and applications of branched and cross-linked polymers, three-dimensional polyrotaxanes will surely be interesting in terms of both topology and potential applications. Gong and Gibson extended the hydrogen-bonding theo-... 

The same concept was used in polycondensation systems for the preparation of branched and cross-linked polymers [121]. Copolyurethanes 73 were prepared from tetra(ethylene glycol), bis(5-hydroxymethyl-l,3-phenylene)-32-crown-10 (74)... 

Solid-state NMR has done much to dispel the mysteries of humin compositions, and significant advances have recently been made using proton NMR in the liquid state (see Section 15.3.3 of Chapter 15). Based on solid-state 13C NMR spectra, Hatcher et al. (1980) concluded that a repeating aliphatic structural unit, possibly attributable to branched and cross-linked algal or microbial lipids, is common to both soil and sediment humin samples. Hatcher et al. (1983) viewed the increase in humin relative to the other humic fractions as a selective preservation of the aliphatic compounds of the sediments and did not support condensation theories. 

Polymers are more fundamentally categorized as linear, branched, and cross-linked structures. Linear polymers (e.g., polyesters) are constructed from strictly... 

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