Bond cycles

Fig. 4. Diagrammatic representation of layered crystal structures of rigid diols, with closed hydrogen bonding cycles. Open circles are oxygen atoms, filled circles hydrogen atoms, and the solid lines represent the connecting diol. Hydrogen bonds are shown as broken lines, (a) The structure of 2,6-dihydroxy-2,6-dimethyltricyclo[3.3.1.13,7]decane (4). (b) The structure of erafo-2,e do-6-dihydroxy-2,6-dimethylbicyclo[3.3.1]nonane, (7)...

When one monomer has two or more reactive sites (double bonds, cycles, etc.), thermosetting polymers may be obtained. 

Figure 7.10 Crystal structures of (a) D-tartaric acids, with no hydrogen bond between hydroxyl groups. Only hydroxyl-carboxyl hydrogen bonds are formed, (b) D,L-tartaric acid (= racemic acid) crystals contain strong hydrogen bond cycles between the hydroxyl groups of opposite enantiomers. The racemate is therefore much less soluble in water than the pure enantiomef. ...

Figure 7.12 Crystal structures of (a) J -octyl-D-gluconamide (head-to-tail homodromic intralayer hydrogen bond cycle) and (b) bi-octyl-i>gulonamide (tail-to-tail interlayer hydrogen bonds)P...

Fig. 4.2.7a). d- and L-Tartaric acids are both easily soluble in water (133 g/L), because there is no special stabilization of the crystals, d,L-Tartaric acid (racemic acid), on the other hand, contains a strong hydrogen bond cycle between the hydroxyl groups of opposite enantiomers (Fig. 4.2.7b). As a result, the racemate is less soluble than the enantiomers by a factor of 12 (10.6 g/100 mL) This phenomenon is quite common mirror-image molecules often tend to stick together... 

Figure 4.2.7 Crystal structures of (a) D-tartaric acid with hydrogen bonds including COOH groups and (b) racemic acid showing OH-OH hydrogen bond cycles.

H-bond acceptor with respect to the water molecule, while the two benzenes build a polar H-tt bond with each other. As a result, a H-bonding cycle exists also in this trimer. On the other hand, in the second one-water-two-benzene complex WlB2b, the water donates H-bonds to both benzenes and the many-body polarization becomes destructive. 

Quality control systems and procedures are a requirement in almost every bonding application. Quality control should cover all phases of the bonding cycle from inspection of incoming material to the inspection of the completed assembly. In fact, good quality control will start even before receipt of materials. Quality control will encompass, at a minimum ... 

Heated platen presses are good for bonding flat or moderately contoured panels when faster cure cycles are desired. Platens are heated with steam, hot oil, or electricity and are easily adapted with cooling water connections to further speed the bonding cycle. 

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