Phenolic resins addition cure polymers

HDPE -1- butadiene/acrylonitrile rubber was compatibilized by addition of dimethylol phenolic resin, which cured and compatibilized the blend [61, 62]. Cure reactions of diene rubbers with phenolic resins have been observed before [159], and probably formed an interpenetrating polymer network in this study. 

The cross-linked polymers obtained from the addition-cure approach are often a complex arrangement of atoms bonded in heterocyclic and carbocyclic rings. However, the objective in the preparation of these systems is not simplicity. It is to obtain systems with the desirable properties of phenolic resins retained and the undesirable properties improved or removed. Voids are an undesirable result in the synthesis of both resols and novolacs. Hence, addition-cure phenolic resins are designed to avoid this result. Ease and flexibility of processing are also sought in the addition-cure systems. 

A well-studied addition-cure phenolic resin utilizes the Diels-Alder reaction for its preparation. The result is a complex polymer that originates from a diallyl phenol and a diimide (for example, see structures 2 and 3, respectively). Initially, compounds 2 and 3 react across the double bond of the imide ring and the allylic group to generate a diene [see Eq. (6)]. Compound 2 then serves as the dienophile. The polymer forms from the reaction of the diene with 2. The amount of 2 relative to the diene affects the properties of the resulting polymer, as does the cure temperature. Some of these properties will be summarized... 

The modified-classical phenolic resins are particularly noteworthy for their effect on the mechanical and thermal properties of the cured resin. The processing of these systems is very similar to the classical systems. The nonclassical phenolic resins utilize phenol, but in many cases give a cured product with a chemical structure having little resemblance to the classical system. In future articles, it would be best to develop independent grouping for addition-cure phenolics resins. This redefinition of polymer types is not within the scope of this entry and instead, this interesting class of polymers has been viewed based on current designations. 

Nair, C.P.R. Advances in addition-cure phenolic resins. Prog. Polym. Sci. 2004, 29, 401 98. 

Addition of 2 to 5 phr of alkyl-phenol resins improve tackiness of EPDM stocks. In blends with other synthetic rubbers such as SBR, the co-curability is an important factor while designing the overall curing system while compounding. The important factors to be considered here is to synchronise the curing speed between two polymers, using studies in oscillating disk rheometer charts. However, blends with styrene-butadiene rubber do not have as much acid resistance as 100% EPDM. 

Cellobond phenolic resins are available from Borden Chemicals in the UK. These resole resins are made with an excess of formaldehyde to produce a water-based polymer capable of crosslinking or curing purely by the application of heat. A range of grades is available for processing via the full range of composite techniques into inherently fire resistant products without the addition of flame retardants or fillers. 

In addition to these reactions, the liquid polymers may be cured by other systems including epoxide resins, phenolic resins and diisocyanates. 

A variety of polymers, both thermosets as well as thermoplastics, can be blended and coreacted with epoxy resins to provide for a specific set of desired properties. The most common of these are nitrile, phenolic, nylon, poly sulfide, and polyurethane resins. At high levels of additions these additives result in hybrid or alloyed systems with epoxy resins rather than just modifiers. They differ from reactive diluents in that they are higher-molecular weight-materials, are used at higher concentrations, and generally have less deleterious effect on the cured properties of the epoxy resin. 

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