Methylol-terminated phenol-formaldehyde resin

With EPDM/PP, the rubber is EPDM and the thermoplastic resin is polypropylene. Even though early patents show the vulcanizing agent to be sulfur with an accelerator such as 2-bis(benzothiazolyl)disulfide (MBTS) or tetramethyl thiuram disulfide (TMTD), these sulfur-based curatives are not used today for TPVs. Likely a methylol-terminated phenol-formaldehyde resin curative with a tin chloride activator is used. For a lighter color, sometimes a peroxide crosslinker is used instead. Also, paraffinic... 

Certain difunctional compoimds are used to crosslink elastomers by reaeting to bridge polymer chains. For example, diamines (e.g., hexamethylenedia-mine carbamate) are used as crosslinks for fluoroelastomers p-quinone dioxime is oxidized to p-dinitrosobenzene as the active crosslink for bridging at the polymer double bonds of butyl rubber and methylol terminated phenol-formaldehyde resins will likewise bridge butyl rubber chains (with SnCl2 activation) as well as other unsaturated elastomers. 

A very small amount of the total formaldehyde is used to make methylol-terminated phenol formaldehyde curing resins, usually used in rubber bladders for tire curing. 

The phenol/formaldehyde molar ratio, coupled with the type of catalyst used, determines whether the polymer is phenol terminated or methylol terminated phenol-terminated resins are referred to as novolacs, or two-step resins. Because phenol is nominally trifunctional and formaldehyde is difunctional, novolacs are produced from a reaction mixture having a formaldehyde/phenol molar ratio between 0.5 and 0.8 in the presence of an acid catalyst. Such resins are not heat reactive until a second ingredient is added that supplies additional formaldehyde needed for a cure. Novolacs are employed as solid products. 

Figure 6.15 The phenolic curative (methylol terminated, para-alkyl substituted, phenol-formaldehyde resin) synthesis...

Methylol-terminated para-alkyl-substituted phenol formaldehyde resin is used as the vulcanizing agent for compounds based on butyl and EPDM rubber. The alkyl group is usually octyl. It is commonly used to cure butyl rubber where superior heat resistance is needed. Therefore, this vulcanizing agent is commonly used as the curative to make butyl bladders for repetitive curing of tires. It is also sometimes used in dynamic vulcanization with a tin chloride activator to make thermoplastic vulcanizates (TPVs). 

Phenolic adhesives are structural adhesives with specific applications, e.g. where wide gap bonding is required and where large structures need to be bonded. Phenolic resins are the product of a special reaction ratio of a phenol and formaldehyde in the presence of an organic catalyst. There are two main types of phenolic resins phenol or methylol terminated. The phenol terminated are called novalacs, while the methylol terminated are called resoles (one step resins). Modem phenolic resins are prepared in the presence of metal carboxylates and these resins contain a large number of benzylic ether linkages and have open para positions which have good temperature stability and are usually of low viscosity. 

Methylol-terminated resins are referred to as resoles, or one-step resins. Formaldehyde/phenol molar ratios between 1.0 and 3.0 and a basic catalyst are used to produce resoles, which will cure to a thermoset structure upon the application of heat. These resins, therefore, have to be stored under refrigerated conditions. The largest volume usage for resoles is in liquid form. 

Methylol Terminated, p-Alkyl Substituted, Phenol-Formaldehyde Curing Resin... 

Methylol-terminated para-alkyl-substituted phenol formaldehyde curing resin is a condensation product from a reaction of the proper proportions of para-alkyl phenol with formaldehyde under controlled conditions see Figure 10.67. 

Figure 10.67 Reaction of para-octyl phenol with formaldehyde to produce methylol-terminated para-octyl-substituted phenol formaldehyde curing resin...

Methylol-terminated p-alkyl-substituted phenol formaldehyde curing resin... 

Phenolics which are formed when the molar ratio of formaldehyde to phenol is greater than one are called resoles. The phenol moieties are terminated with reactive hydroxymethyl groups (—CH2OH), known as methylol groups. If the mole ratio of formaldehyde to phenol is less than one, the polymer becomes phenol terminated and is called a novolak. All phenolic chemistry today revolves about these two basic chemistry strategies. Although phenol is most commonly involved in phenolics, resins containing p-r-butylphenol, p-r-amylphenol, p-nonylphenol, mixed cresols, and substituted... 

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