Oxazolidone resins

Numata and Kinjo (52) have shown rubber-modified isocyanurate-oxazolidone resins may be effectively modified with carboxyl-reactive nitrile liquids. The viscoelastic behavior of models using a polyglycidyl ether of phenol-formaldehyde novolac resin and di-phenylmethane-4,4 -diisocyanate is discussed. Such resins have suggested utility in thin films as electrical varnishes. 

Casting Oxazolidone Resin Films. To explore further the structural property relationships in epoxy resins cured with isocyanate, a series of films were cast, and then IR absorption spectra and softening behaviour examined. 

By using isocyanates as hardeners, more complicated cured resins are obtained. It is well known that poly-2-oxazolidone is obtained by the reaction of a diepoxide and a diisocyanate compound 49 50). 

By changing the ratio epoxy/isocyanate, the cured resins are composed of oxazolidone and isocyanurate rings in a varying ratio. 

Ho et al (1996) examined polyol or polysiloxane thermoplastic polyurethanes (TPUs) as modifiers in cresol-formaldehye novolac epoxy resins cured with phenolic novolac resin for computer-chip encapsulation. A stable sea-island dispersion of TPU particles was achieved by the epoxy ring-opening with isocyanate groups of the urethane prepolymer to form an oxazolidone. The flexural modulus was reduced by addition of TPU and also the Tg was increased due to the rigid oxazolidone structure. Mayadunne et al (1999) extended this work to a series of phenol- and naphthol-based aralkyl epoxy resins. 

Oxazolidone-isocyanurate polymers were prepared by reacting five glycidyl ethers with 4, 4 -diisocyanato-diphenylmethane in the presence of 2-ethyl-4-methylimidazole. The degree of cure of the resins was followed by IR spectroscopy by measuring the fraction of the isocyanurate to oxazolidone linkages (377). 

In the conventional curing processes of epoxy resins, the crosslinks developed are of a single strand structure involving ether or amine extension points. The object of this study is the formation of the oxazolidone ring which by reaction of epoxy and isocyanate groups, affords an alternative type of crosslink, which it was anticipated will have a significant influence on the T of the cured epoxy resin. 

As indicated above, the objective of this study was to explore oxazolidone formation expecially as a means of crosslinking epoxy resins. This... 

Epoxy Resin Isocyanate Q Catalyst Solvent Reaction Reaction Oxazolidone Spt., C Yield Characteristic IR... 

Kinjo coined the term ISOX to identify resins combining isocyanurate and oxazolidone structures, in which the isocyanurate structure preponderates through using a threefold excess of isocyanate over that required for oxazolidone formation. In consequence of their high degree of isocyanurate cross-linking, such resins may have high T s (ca. 300 C). Pyridines and ter-... 

DSC Study of Oxazolidone Containing Resins. The DSC results of the PGE/ MDI model reaction, using R NBr or EMI as catalyst, showed that both promoted the trimerisation and the oxazolidone formation, with the latter catalyst being more powerful in respect of each reaction. The gained information suggested that by a careful choice of catalyst, catalyst concentration, and... 

Table 11 compares the peak heights for oxazolidone and isocyanurate absorptions, with these frequencies normalised to the absorption at 1510 cm From these results, we concluded hat HEXA had the greatest efficiency as an oxazolidone forming catalyst under the conditions of the film casting procedure. In contrast, the DABCO catalysed resin had the strongest isocyanurate... 

The calculated isocyanurate/oxazolidone ratio, as described above, is not enough to evaluate the properties of the resin, and so, their softening points and glass transition temperatures were determined and related to the reaction conditions used to prepare the films. The reaction parameters were studied systematically to establish the influence of the following variables on the relaxation temperatures of the resultant resins ... 

From Table 13 it is apparent that the HEXA catalysed oxazolidone containing resin had the highest softening point and glass transition temperature, superior not only to the other oxazolidone containing resins cured with EMI or with DABCO, by 40°C, but also to a conventionally cured epoxy resin. 

First, the optimum condition for curing BADGE epoxy resins with a diisocyanate, MDI, to produce castings of high softening point and glass transition temperature and high oxazolidone content, are ... 

Second, for the preparation of ISOX resins, the preliminary finding is that EMI, being an effective catalyst for the formation of both oxazolidone and isocyanurate, is the preferred catalyst. This conclusion is based on finding that DABCO is a strong catalyst for isocyanurate formation and HEXA a good catalyst for oxazolidone formation. This latter conclusion is to be regarded as preliminary. 

The use of substituted ureas as curing agents for epoxy resins has been the subject of few studies. Ywakura and Izawa [70] analyzed the reactions between phenylglycidyl ether and substituted ureas. In every case, the reaction, carried out under mild conditions (T = 90°C, t = 1 h, mol ratio of epoxy/urea = 1-3, with or without the use of NfCiHs), as catalyst), led to the formation of a 2-oxazolidone and a secondary amine ... 

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