Novolac cure

The number of remaining ortho reactive sites versus the number of para reactive sites can also be calculated using 13C NMR (Table 7.4). Since the rates of novolac cure reactions differ with the amount of ortho versus para reactive sites available, it is of great interest to calculate these parameters. 

Biernath et al. concluded that phenolic novolac and epoxidized cresol novolac cure reactions using triphenylphosphine as the catalyst had a short initiation period wherein the concentration of phenolate ion increased, followed by a (steady-state) propagation regime where the number of reactive phenolate species was constant.85 The epoxy ring opening was reportedly first order in the steady-state regime. 

Benzoxazines are heterocyclic compounds obtained from reaction of phenols, primary amines, and formaldehyde.98,99 As described previously, they are key reaction intermediates in the HMTA-novolac cure reaction.40,43 Crosslinking benzoxazine monomers at high temperatures gives rise to void-free networks with high Tgs, excellent heat resistance, good flame retardance, and low smoke toxicity.100 As in HMTA-cured novolac networks, further structural rearrangement may occur at higher temperatures. 

Phenolic networks, 411 Phenolic-novolac-cured systems, 415 Phenolic novolac-epoxy networks, flame retardance of, 415 Phenolic oligomers, 375... 

Novocamid, molecular formula and structure, 5 90t Novolac cure, 18 771-772... 

Ea, above and below Tg. Three case studies illustrate the range of applicability of the bending beam setup and factors contributing to the stress state. The first is a comparison of two polymers for interlayer dielectrics PMDA-ODA (pyromellitic acid dianhydride - oxydiamine) and a bis-benzocyclobutene. The second is of a neat epoxy resin commonly used for microelectronics encapsulation (epoxidized ortho-cresol novolac cured with a phenolic novolac). The third is a screen-printable polyimide coating used for protection of the integrated-circuit chip. An outline of our stress model is sketched, and example results are presented. 

In many adhesives formulations, the resin portion is the same or similar and what determines its properties is the hardener or catalyst that is used to cure the resin. Thus, depending on the hardener, epoxy adhesives may be referred to as amine-cured, anhydride-cured, polyamide-cured, or novolac-cured. Polyurethanes may be polyol-cured or hydroxypolyester-cured. 

Uses Chemical intermediate accelerator for phenolic novolac curing agent for epoxies catalyst for PU elastomers, shoe soles, coatings pharmaceuticals... 

Novolac formation occurs under acidic conditions at 100°C with the excess of phenol (about one mole phenol to 0.7 to 0.85 mole formaldehyde is reacted). Novolac curing is accomplished by addition of crosslinking agents, usually HEXA (hexamethylenetramine) or HMTA whose reaction products form urea and formaldehyde when heated (110°C). 

The novolacs cure more rapidly than DGEBA resins and have higher exotherms. The cured novolacs have higher heat deflection temperatures than DGEBA resins. They have excellent resistance to solvents and chemicals. Novolacs also have excellent electrical properties, which are retained at high service temperatures. 

Pure resorcinol novolacs cured with paraformaldehyde. 

Novolacs with some branched molecules [61] are produced by the reaction of 1.0 mole of phenol and 3.0 moles of formaldehyde (37% aqueous solution) using 0.06 mole of calcium hydroxide and heating at SO C until 2.4 moles of formaldehyde have reacted. Then 2.6 moles of phenol are added and the mixture is neutralized with dilute sulfuric acid. Then more acid is added and a novolac is prepared in the usual manner, as described above. This novolac cures faster with hexamethylenetetramine (Hexa) and does not produce a foamy mass [61]. 

Fig. 2 Rigidity(G) and logarithmic decrement(A) vs. temperature relation of films by torsional pendum method made from --- phenol novolac cured with 5% hexa ...

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