Highly cross-linked network

Bismaleimides are best defined as low molecular weight, at least diftinctional monomers or prepolymers, or mixtures thereof, that carry maleimide terminations (Eig. 3). Such maleimide end groups can undergo homopolymerization and a wide range of copolymerizations to form a highly cross-linked network. These cure reactions can be effected by the appHcation of heat and, if required, ia the presence of a suitable catalyst. The first patent for cross-linked resias obtained through the homopolymerization or copolymerization of BMI was granted to Rhc ne Poulenc, Erance, ia 1968 (13). Shordy after, a series of patents was issued on poly(amino bismaleimides) (14), which are synthesized from bismaleimide and aromatic diamines. 

Figure 2. The elastic (G7) and viscous modulus (G") as a function of the frequency of oscillation at three different UV exposure times. At t = 1660 s, G7 and G" are parallel, indicating the sample has reached its gel point. Note that G is initially smaller than G" throughout the frequency range (t = 1280 s), but becomes larger than G" and independent of frequency towards the end of the reaction (t = 2780 s), indicating that the sample has been transformed from a liquid to a highly cross-linked network.

To date there have been few reliable measurements of Hittorf transference numbers in solid polymer electrolytes because of experimental difficulties in applying the technique. Leveque, Le Nest, Gandini and Cheradame (1983) have, however, applied it to highly cross-linked networks where cells could be formed using a series of non-adherent thin... 

Phenol-formaldehyde adhesives are produced by a condensation polymerization reaction between phenol and formaldehyde. The phenolics used for exterior particleboard are made at a formalde-hyde/phenol ratio greater than 1.0 i.e., they are classified as resoles and additional formaldehyde is not required to complete the curing reaction to a highly cross-linked network structure. Many characteristics can be incorporated into the adhesives by changes in the F/P ratio, condensation pH, and condensation time. The reactive solids content is normally between kO and 50 percent since the stability and viscosity are adversely affected at higher solids. 

Ala. The action of lysyl oxidase to produce allysine allows three of these modified residues to condense with one lysine residue to form the heterocyclic complex amino acid desmosine. which cross-links two or even three chains. A highly cross-linked network results. 

Summary Systematic investigations enabled a broad synthetic access to the nitridosilicate class of compounds. Typical building blocks in these compounds are SiN4 tetrahedra, which may be linked via common vertices forming complex network structures. The first results suggest that the structural variabilities of nitridosilicates are more versatile as compared to the oxosilicates. Highly cross-linked network structures are accessible, which cause the remarkable stability of nitridosilicates. 

POLYESTER RESINS FORM HIGHLY CROSS-LINKED NETWORKS, which result in brittle composites prone to microcracking and damage under impact. A better system is one that retains the desirable properties of polyester—stiffness and chemical resistance—and at the same time has higher impact resistance and increased strain to failure. Synthesis of a simultaneous interpene-... 

Thiol-Ene Photopolymerization The thiol-ene polymerization of suitable systems (10.84) in film is insensitive to oxygen. The reaction refers to the addition of a thiol to a double bond (e.g., vinyl, allyl, acrylate, and methacrylate) [310] and has led in these past years to a new revival of interest [311,312]. Thiol-vinyl ether or -allyl ether polymerization shows some following interesting features very fast process, low or even no oxygen inhibition effect and formation of highly cross-linked networks with good adhesion, and physical and mechanical properties. 

Structure and Fracture of Highly Cross-linked Networks... 

This correction formula may not be used for very highly cross-linked networks, since additional free ends occur. 

Rolla et ah, used microwave dielectric measurements to monitor the polymerization process of mono functional n-butyl acrylate as well as 50/50 w/w blends with a difunctional hexane-diol diacrylate that gave highly cross-linked networks. In these real time cure experiments the decreasing acrylate monomer concentration was studied via a linear correlation with the dielectric loss index at microwave frequencies. This correlation is a result of the largely different time scales for dipolar polarization in the monomer on one hand and in the polymerized reaction product on the other hand. 

For a loosely cross-linked network, polymerized above the glass transition temperature, R should approach the flexible limit, i.e., R, because the distance from the last attachment to the network is significantly larger and the overall mobility of the system is increased by polymerization above the Tg, As the polymerization temperature is lowered below Tg, the distance back to the last network attachment point (or entanglement) becomes less important, and the mobility of the radical chain end is reduced to the point where it is virtually immobile on the time scale of propagation. In this case, the rigid limit should be applicable, and R should approach R m, just as it would for a highly cross-linked network. 

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