Furan resins resinification

Whereas 2,5-dihydroxymethylfuran (DHMF) has been proposed frequently as a diol component for polyester synthesis, the high reactivity of the hydroxymethyl groups under acidic conditions primarily leads to resin formation, which is commercially exploited for the production of thermoset furan resins [55]. Although HMFA is more chemically stable than DHMF, it is also prone to resinification at high temperatures. In contrast, FDCA and derivatives have proven to be chemically stable under conditions relevant to polyester synthesis, making them the most versatile and industrially viable furan monomers for step growth polymers. 

The gas-phase photolysis of 2-furaldehyde in the it -n and ir <-it transitions76 proceeds with fragmentation to CO, furan and C3-hydrocarbons, but a certain amount of resinification is also noted (about 5% quantum yield with excitation of the it - n transition). The latter observation prompted a study of the vacuum liquid-phase photolysis by sunlight or by light from a medium-pressure mercury arc at room temperature24 7S. The resin obtained was submitted to fractionation and structural analysis. On the basis of the results obtained and other mechanistic evidence, the following sequence of events was postulated for the photopolymerization ... 

Direct halogenation of furan and its derivatives offers more difficulties. It leads to a mixture of either mono- and polysubstituted compounds or polymeric materials and resins. The reaction is usually carried out at temperatures of the order of — 40°, thereby hindering resinification. 

Poly(hydroxymethyl furfurylidene-acetone) adhesive resins were synthesized and characterized [68-70] through the 5-formaldehyde adduct (19) and its acid-catalyzed polymerization. The catalysts used were sulfuric, phosphoric, or p-toluenesulfonic acid. The authors postulated that the first condensation products resulted from the condensation of two methylol groups of two 19 molecules (adduct 20). They also proposed a hypothetical structure of the network formed after curing (21). It seems, however, difficult to envisage the acid-catalyzed resinification of 19 without the participation of hydrogen atoms at the C5 position of the furanic ring [2]. 

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