Polar molecular groups

Dipole forces are effective when polarity is present and can be generated from permanent or induced dipoles. Polar molecular groups of adhesives must contact the substrate surface in the distance of 10 cm or less. An example for adhesion between polar binder and polar substrate is pictured in Fig. 43. 

The 4-Hydroxy-thiazoles are characterized by infrared absorption near 1610 cm (KBr) (3) or 1620 to 16.S0cm (CCI4) (8), indicating a strongly polarized carbonyl group. H-5 resonates near 5.6 ppm in the NMR spectrum like similar protons in other mesoionic compounds (3). Two fragmentations of the molecular ion are observed in the mass spectra. The first involves rupture of the 1,2 and 3,4 bonds with loss of C2R 0S . In the second, the 1,5 and 3,4 bonds are cleaved with elimination of C2R 0. ... 

Polyurethane adhesives are formed by the reaction of various types of isoeyanates with polyols. The polar urethane group enables adhesion to various surfaees. Depending on the raw materials, glue lines with rubber-like elastic to brittle-hard behavior ean be aehieved. The presence of reactive terminal groups provides a ehemieally hardened adhesive. When polymerized to a high enough molecular weight, the adhesive ean be physically rather than chemically hardened, i.e. a hot melt. 

The molecular structure of nylon 6 is shown in Fig. 23.2 a). Its repeat unit consists of an amide group and a pentamethylene sequence, i.e., -(CH2)5CONH- The polar amide groups from adjacent chains interact with each other to form hydrogen bonds, which link the chains. 

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