Resorcinol Based Diols

Resorcinol diols represent a new class of aromatic dihydroxylic compounds with the general formula (15.33)  

Resorcinol diols are obtained by the reaction of resorcinol with ethylene carbonate or propylene carbonate (reaction 15.34), in the presence of basic catalysts (K2COs, KOH, NaOH, tertiary amines), or even in the absence of catalysts, at higher temperatures (150-170 °C)  

A resorcinol diol based on 1 mol of resorcinol and 2 EO units is a solid with a melting point of 87-89 °C and an hydroxyl number of 555 mg KOH/g [34]. All the resorcinol diols having PO units or PO and EO units are liquids at room temperature, with a viscosity of between 3,900 -20,000 mPa-s at 25 °C and hydroxyl numbers between 345-485 mg KOEl/g [34]. The resorcinol diols based on resorcinol and more than 2 EO units are liquid at room temperature, with a viscosity of around 2000 mPa-s at 25 °C and 375-385 mg KOH/g [34]. 

It is very interesting that a resorcinol diol based on propylene carbonate has 85% secondary hydroxyl groups and 15% primary hydroxyl groups. In the resorcinol diols based on propylene carbonate and ethylene carbonate (terminal units), the terminal primary hydroxyl is around 50% [33, 34]. 

Resorcinol diols are superior to the well known hydroquinone di(beta-hydroxyethyl) ether (HQEE), which is a solid with a melting point of 100 °C  

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The variation in the initial Tg s show the effect on processability of the structures of the diol and the dibromobenzene. Two of the systems, those based on thiodiphenol and dihydroxybiphenyl, gave crystalline products which could not be made amorphous upon heat treatment. The effect on chain flexibility of dibromobenzene structure could be seen with the two hydroquinone systems. In this case, the meta isomer gave an initial Tg of 12°C while the more rigid para system had a Tg of 59°C. Variation of diol structure shows a parallel effect as shown with the resorcinol/j>-dibromobenzene system. This material has a softening temperature of 20°C. 

The nucleophilic route seems to be favored by industrial processes. Polymers are prepared from dichlorobenzonitrile, aromatic diols such as resorcinol, HQ, and biphenol. The reaction proceeds in polar solvents using a base as a catalyst. ... 

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