Formation of a glyptal resin

In a 250 ml. beaker place 15 g. of powdered phthahc anhydride and 10 g. of glycerol mix thoroughly with a thermometer. Heat the mix-tme gently to 150-180° on a wire gauze water vapour is evolved. 

Raise the temperature gradually to 200-250° until the mass finally forms large bubbles and puffs up into a voluminous mass. At this point allow the beaker to cool. Remove the brittle mass from the beaker as completely as possible and powder it in a mortar. 

The solid polymer tends to stick to glass for this reason, it is preferable to employ a metal beaker for the erperiment. 

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Thermosetting space-network polymers can be prepared through the reaction of polybasic acid anhydrides with polyhydric alcohols. A linear polymer is obtained with a bifunctional anhydride and a bifunctional alcohol, but if either reactant has three or more reactive sites, then formation of a three-dimensional polymer is possible. For example, 2 moles of 1,2,3-propane-triol (glycerol) can react with 3 moles of 1,2-benzenedicarboxylic anhydride (phthalic anhydride) to give a highly cross-linked resin, which usually is called a glyptal ... 

More usually, phthalic anhydride is reacted with a polyfunctional material such as glycerol to form a network polyester (a glyptal). This class of polymer, modified with monofunctional additives and known as alkyd resins, is very important in the paint and plastics industry. Consequently most of the theoretical studies have been concerned with the formation of infinite networks ( microgel ) and the distinction between this and the so-called gel-point [75]. 

A new wooden fume cupboard was varnished with glyptal (glyceryl phthalate) resin. After a few weeks use with nitrous fumes , the resin spontaneously and violently ignited. This was attributed to formation and decomposition of glyceryl trinitrate or similar compounds. 

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