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Secondary bonds are considerably weaker than the primary covalent bonds. When a linear or branched polymer is heated, the dissociation energies of the secondary bonds are exceeded long before the primary covalent bonds are broken, freeing up the individual chains to flow under stress. When the material is cooled, the secondary bonds reform. Thus, linear and branched polymers are generally thermoplastic. On the other hand, cross-links contain primary covalent bonds like those that bond the atoms in the main chains. When a cross-linked polymer is heated sufficiently, these primary covalent bonds fail randomly, and the material degrades. Therefore, cross-linked polymers are thermosets. There are a few exceptions such as cellulose and polyacrylonitrile. Though linear, these polymers are not thermoplastic because the extensive secondary bonds make up for in quantity what they lack in quahty. 

In the reaction with sapphyrin 25, adduct 26 was produced with high selectivity (MW, 1 h, 200 °C), showing once again that the beta-pyrrolic double bond close to the pyrrole-pyrrole link contains the most reactive position of this type of macrocycle <06TL3131>. 

Responses to Center Correspondence You should include the actual comments, questions, and requests for additional information communicated in our letter sent to you, as well as your response to these items. You should bookmark each item to facilitate information access and make additional supporting information accessible through a hypertext link contained within your response. 

Biochemists studying the structure of collagen (a fibrous protein in connective tissue) found cross-links containing... 

In the above node-link-blob picture, the percolation cluster is self-similar up to a length scale in the sense that starting from the length scale the links contain blobs (and the dangling ends) which, in turn, are composed of links and blobs (and the dangling ends) up to the lowest scale (of the lattice). This self-similarity extends up to infinite scale at the percolation threshold (where becomes infinitely large). 

Involvement of esters in the intermolecular cross-links accounts for the dissolution of mature collagen by hydroxylamine, hydrazine or alkali in the presence of hydrogen-bond breakers. Similarly, the participation of hexoses accounts for the dissolution of collagen by periodic acid and a hydrogen-bond breaker. Recently, it has been shown that collagen can be completely dissolved by some proteolytic enzymes (see Section II). These enzymes also cleave the intramolecular cross-links (Kiihn et al, 1963a Rubin et al., 1963). It appears therefore that either the crosslinks include a peptide chain or the chain close to the cross-links contains pepsin- and trypsin-sensitive bonds. 

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Problem 1.7 A rubber contains 60% butadiene, 30% isoprene, 5% sulfur, and 5% carbon black. If each sulfide cross-link contains an average of two sulfur atoms, what fraction of possible cross-links are joined by vulcanization (Assume that all the sulfur is present in cross-links.)... 

A priori, masses have nothing to do with the problem. However, to measure the number of links contained in a sample, the simplest way is to weigh the sample. So, one immediately obtains the mass concentration... 

Pyrazines (Figure 5.1) are heterocycles with six links containing two nitrogen atoms and four carbon atoms bearing radicals, which largely determine their olfactory impact. They contribute to the aroma in Cabernet Sauvignon wines (Section 7.4). 

This allows a reader to approach a topic in a nonsequential manner that is said to be similar to normal human thought patterns. Web documents may contain links to other documents, and by selecting these links a user can access (or browse) other related material. In this second type of access each link contains information about identifying a particular piece of information on a particular server. As with explicit requests, it is the task of the browser to contact the server (usually on port 80) and request the information that has been cited. 

Biochemists studying the structure of collagen (a fibrous protein in connective tissue) found cross-links containing a,jG-unsaturated aldehydes between protein chains. Show the structures of the side chains that react to form these crosslinks, and propose a mechanism for their formation in a weakly acidic solution. 

There exist several reports on s5mtheses of polyarylketones, containing bisphthalasinone and methylene [361, 362], naphthalene [363-367] links containing sulfonic groups [368], carboxyl group in side chain Ref [369], fluorine [370-372] and on the basis of carbon monoxide and sty-rol or -sthylstirol [373], It is shown that methylene and bisphthalasinone links in main chain of polyketones are responsible for its good solubility in m-cresol, chloroform. The links of bisphthalasinone improve thermal property of pol mier. 

For comparison with experimental fractionation results, we have to find the total number of monomeric molecules which are contained in chains of a definite length. This number, as a function of the chain length, would give us the distribution curve of the molecular weight fractions, as defined on page 323. As a chain of s links contains (s + 1) monomeric molecules, the total number of fundamental molecules embodied in chains with s links would be... 

Bridged cross-links containing type / polymers (double-strand polymers) occur extensively in inorganic polymer chemistry. In general, they are fibrous products such as vaicntinite (/I-SbjOj) or chrysotile asbestos,... 

Si-O-Si links, contained in silicones, are extremely flexible, followed by CH2-CH2 and CH2-CH=CH-CH2. The great flexibility of the latter, despite the rigidity of the double bond it contains, stems from the very weak resistance to rotation around the two CH2-CH bonds. Introducing a ring into the main chain considerably increases the value of Tg. 

For example, in a hollow tetrahedron, the abstract simplicial complex A consisting of all subsets of 1,2,3,4 except for the set 1,2,3,4 itself, a link of an edge consists of the two vertices that do not belong to that edge. Note also that the void simplex can never be the link of anything, since any link contains an empty set. 

Palladium bound to polymeric support has been employed for allylic substitution. Amphiphilic resins based on block PS-PEG-bearing phosphine residues (cf. Scheme 49) were used for allyhc substitution in aqueous media both in achiral and in enantios-elective reactions, hi the latter, MOP-type ligand has been tethered by a chiral link containing a residue of natural amino acid to the amphiphilic block-copolymer... 

There is no question whether or not cross-linking is a necessary part of a system with an ultraphosphate composition. It is a structural-composition requirement, but where does cross-linking reside in potassium Kurrol s salt crystallized in ultraphosphate melts Are cross-links contained in crystalline phases and cause the formation of crystalline potassium ultraphosphates, or does a salt obey its phase diagram for a two-component K2O-P2O5 system (See Figure 3.1.)... 

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