Polymer Applications of CNSL, Cardanol and Cardol

The oligomerisation stage with an acidic catalyst is likely to involve the reactive terminal double bond of the side chain in cardanol and formation of an allylic carbocation (ref. 2). It has been studied by initiation with boron trifluoride etherate (ref. 243) and the effect of temperature, ratio of catalyst to cardanol and duration of reaction time on its dimerisation examined (ref.244). In the following scheme represents for example HOCeH4(CH2)7- 

The cardol present in CNSL, if in high proportion can lead to an exothermic reaction with formaldehyde and also It appears desirable for the phenolic components to have a high proportion of triene in order for the first acid-catalysed side chain oligomerisation stage to proceed. CNSL-formaldehyde polymers have greater flexibility than those from phenol-formaldehyde, due to internal plasticising, they are also more soluble in solvents, and due to their hydrophobicity they have resistance to water penetration, and hence acidic and alkaline media. For some applications highly methylolated cardanol is useful and this can be formed with formaldehyde, by the use of adipic or succinic acid as catalysts, and subsequently rapidly cured with hexamine (ref. 245). 

There has been great interest in thermally stable materials having ablative and fire-retardant applications. Phosphorylated CNSL has been prepared many years ago (ref.246) but phosphorylated cardanol prepolymers, containing the dihydrogenphosphate group, have been obtained from CNSL by phosphorylation with orthophosphoric acid and dimeric products by simultaneous phosphorylation and oligomerisation (ref. 247). 

By reaction of phosphorylated materials with aldehydes, amines or with isocyanates highly thermally stable products have been then produced. TGA studies have indicated their superior properties compared to conventional cardanol/formaldehyde resins of the novolac type. It was also found that a phosphorylated CNSL polymer had improved adhesive properties when compared with conventional CNSUformaldehyde resins (ref.248) and certain compounded products had wear, fade and frictional properties comparable to those of conventional PhOH/formaldehyde/copolymer brake Hnings (ref.249). The phosphorylated product from CNSL and its bromination derivative possessed good fire-retardant characteristics (ref. 250). Phosphorus derivatives of cardanol and of 3-pentadecylphenol have been studied by reaction with phosphorus oxychloride and its thio analogue (ref. 251). 

The resins in the friction dust area tend to be rigid and the flexibility and plasticity associated with the long alkyl chain of phenolic lipids have been used in natural rubber vulcanisation by for example incorporating crosslinking with phosphorylated cardanol (ref. 252). Unpolymerised CNSL phenols have been used in natural or diene rubber compositions for tyre treads to give an improved dynamic elastic modulus but with the same hardness as formulations without the phenolic addition (ref. 253). 

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