Лако-красочные материалы — производство

A. Definition

Acid-base interactions including hydrogen bonds are specific and not ubiquitous like the London dispersive interactions. They occur when a base (electron donor or a proton acceptor) and an acid (electron acceptor or proton donor) are brought close together. This can be described by the general equation

A + : B! A: B (1)

acid base acid—base complex

Table 1 shows the three possible types of acids and bases and examples of corresponding molecules. These types of acids and bases lead to nine possible acid-base adducts. Five of these combinations, namely n-n, n-ст*, n-л*, л-ст*, and л-л*, yield the addition type complexes whereas the other four combinations lead to adducts with displacement [23]. For example, the interaction of PMMA in chloroform results in the formation of an n-ст* acid-base adduct. PMMA is a Lewis base due to the nonbonding electron doublets from the oxygen in the C = O group whereas the acceptor site in chloroform is its C-H anti­bonding ст* orbital.

Amphoters are those species which bear both acidic and basic sites and can thus interact specifically with either pure acids or bases. In the terminology of van Oss et al. [22] pure acids and bases are called ‘‘monopolar’’ whereas amphoters are called ‘‘bipolar.’’ This is a rather unfortunate terminology since acid-base interactions are distinguished from ‘‘polar’’ interactions. For this reason, Berg [16] preferred the terms ‘‘monofunc­tional’’ for pure acids and pure bases, and ‘‘bifunctional’’ for amphoters.