Polymers crosslinks

The presence of the unsaturated substituent along this polyester backbone gives this polymer crosslinking possibilities through a secondary reaction of the double bond. These polymers are used in paints, varnishes, and lacquers, where the ultimate cross-linked product results from the oxidation of the double bond as the coating cures. A cross-linked polyester could also result from reaction (5.J) without the unsaturated carboxylic acid, but the latter would produce a gel in which the entire reaction mass solidified and is not as well suited to coatings applications as the polymer that crosslinks upon drying. ... 

A significant step towards commercial success came with a discovery in the late 1950s by E. Ulrich at 3M when he found that copolymerization of hydrogen bonding monomers, like acrylic acid with alkyl acrylates resulted in cohesively strong, yet tacky materials [63]. Since then, newer developments in such areas as polymer crosslinking, and the synthesis and copolymerization of new monomers, have led to a rapid penetration of acrylics throughout the PSA industry. 

Crosslinker Si-H funetionalized polymer Crosslink alkenyl PDMS... 

Fig. 1. Solvent swelling experiments with ECA polymers crosslinked with 7.

Solvent swelling experiments, with CH2CI2 and ECA polymer crosslinked with 7, demonstrate that the addition of a difunctional cyanoacrylate monomer does improve solvent resistance [6], shown in Fig. 1. 

Homopolymerization of macroazoinimers and co-polymerization of macroinimers with a vinyl monomer yield crosslinked polyethyleneglycol or polyethyleneglycol-vinyl polymer-crosslinked block copolymer, respectively. The homopolymers and block copolymers having PEG units with molecular weights of 1000 and 1500 still showed crystallinity of the PEG units in the network structure [48] and the second heating thermograms of polymers having PEG-1000 and PEG-1500 units showed that the recrystallization rates were very fast (Fig. 3). 

The second step is the condensation reaction between the methylolphe-nols with the elimination of water and the formation of the polymer. Crosslinking occurs hy a reaction between the methylol groups and results in the formation of ether bridges. It occurs also by the reaction of the methylol groups and the aromatic ring, which forms methylene bridges. The formed polymer is a three-dimensional network thermoset ... 

This is one of the most universal techniques for obtaining hydrogels from water-soluble polymers. Crosslinked PEO, PVA, PAAm, PAAc and its salts, as well as some polymer blends were obtained by this method. Although all polymers mentioned above have their own specific features, in most cases the gelation doses do not exceed 1-2 Mrad, i.e. they are substantially lower than for the same polymer in bulk. This is due to the fact that in aqueous media crosslinking occurs indirectly, namely because of the OH radical formation and their attack on the macromolecules. There exists a developed theory of these processes [73],... 

Aryloxyphosphazene copolymers can also confer fireproof properties to flammable materials when blended. Dieck [591] have used the copolymers III, and IV containing small amounts of reactive unsaturated groups to prepare blends with compatible organic polymers crosslinkable by the same mechanism which crosslinks the polyphosphazene, e.g. ethylene-propylene and butadiene-acrylonitrile copolymers, poly(vinyl chloride), unsaturated urethane rubber. These blends were used to prepare foams exhibiting excellent fire retardance and producing low smoke levels or no smoke when heated in an open flame. Oxygen index values of 27-56 were obtained. 

Small-particle-size cement has found a number of uses in production and injection well casing repair jobs [440]. Oil-based cement is particularly useful for water shutoff jobs, because the hydrocarbon slurry sets only in the presence of water, so the oil-producing sections of a reservoir remain relatively damage free after water shutoff. The selective water shutoff with oil-based cement also has been used with polymers crosslinked by metal crosslinkers [442,1178]. 

Metallophosphazenes are a new type of macromolecule designed to bridge the gap between polymers and metals. Although still at an exploratory stage of laboratory development, they may provide access to electronically-conducting polymers, magnetically-active polymers, macromolecular catalysts, electrode mediator systems, or polymers crosslinked by metal atoms. 

The reactive Cr(III) species in polymer crosslinking are the dates derived from the hydrolysis of hydrated Cr(III) cations. 

Huffman BS, Schultz RA, Schlom PJ, Nowicki JW, Hung JW. Nitrile oxide reagents for heat activaled polymer crosslinking, PCT Int Appl. WO 2002006391 [Chem. Abstr. 2002 136 135592],... 

The polymer used in this study was a m,p-cresol novolak ( 1 =14000, Mn =1300). Melamine resins were obtained from American Cyanamid Co. Polymer/crosslinker formulations were prepared using 23 wt % novolak in cellosolve acetate and 15 parts per hundred crosslinker based on novolak solids. p-Toluenesulfonic acid was... 

The presence of these ionic materials at the interface, as well as the corresponding reduction of polymer crosslink density associated with this degradative process, likely contribute to the observed reduction in bond durability. 

Despite the fact that a full assignment of all the observed absorptions to the respective macromolecule s natural frequencies is not possible in all cases - in particular for complex co- and terpolymers, stereoregular polymers, crosslinked systems, composites, compounds or blends this is very difficult - there are many bands caused by local group vibrations of a few atoms which can be interpreted very nicely. As an example, the C=0 band (stretching vibration) is usually observed as an intense absorption between v = 1850-1650 cm. Because of the coupling with other vibrations of the molecule its frequency is characteristic for the constitution and the neighborhood of the observed atom group. 

This contribution will provide a review of polylectrolytes as biomaterials, with emphasis on recent developments. The first section will provide an overview of methods of synthesizing polyelectrolytes in the structures that are most commonly employed for biomedical applications linear polymers, crosslinked networks, and polymer grafts. In the remaining sections, the salient features of polyelectrolyte thermodynamics and the applications of polyelectrolytes for dental adhesives and restoratives, controlled release devices, polymeric drugs, prodrugs, or adjuvants, and biocompatibilizers will be discussed. These topics have been reviewed in the past, therefore previous reviews are cited and only the recent developments are considered here. 

Figure 5.71 Dependence of shear modulus on temperature for three common engineering polymers crosslinked natural rubber, amorphous polyvinyl chloride (PVC), and crystalline Nylon 6. The typical use temperatures are indicated by dotted lines. Reprinted, by permission, from N. G. McCrum, C. P. Buckley, and C. B. Bucknall, Principles of Polymer Engineering, 2nd ed., p. 154. Copyright 1997 by Oxford University Press.

The maleimide functionality has also been utilized as a modifying group to obtain polymers crosslinkable by free radical chemistry. Thus, hydroxy-terminated poly(oxy-2,6-dimethyl-1,4-phenylene) (164) was treated with p-maleimidobenzoyl chloride (165) to obtain resin (166 Scheme 81) (72FRP2122181). Resin (166) melted at 155 °C and could be coated on to... 

Table VI. Properties of SIS Polymers Crosslinked by Dicumyl Peroxide...

For many years, several authors have tried to explain and predict the yield stress of polymers (crosslinked or not), as a function of the experimental test parameters (T, e) and/or structural parameters (chain stiffness, crosslinking density). These models would be very useful to extrapolate yield stress values in different test conditions and to determine the ductile-brittle transition. 

The alternate sequence is undegraded polymer crosslinked and insoluble polymer —> dehydrochlorinated insoluble polymer. Here a small hydrogen chloride loss would be expected to occur during cross-linking. Most of the hydrogen chloride loss would however be attributable to the subsequent reactions of the crosslinked polymer. Such a sequence can be rationalized. 

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