Resole polyesterimide blends,

The solubility parameter values of the polyesterimide (10.76 [182]), the novolae (10.7), and the resole (11.1), imply that these polymers should be thermodynamieally miseible beeause the differenee of these parameters between the polyesterimide and a phenolie resin is a small number. The theoretieally predieted miseibility of polyesterimide with novolae or resole appears to be bom out experimentally sinee differential thermal analysis shows a single glass transition temperature for all the blends, and seanning eleetron... 

When the blend of polyesterimide and phenol-formaldetyde resin is heated in air, it forms a crosslinked product. Cross-linking reaction is facilitated at about 300 C and 150 C for no-volac and resole, respectively. The onset of crosslinking reaction by heating the polyblend has been suggested on the baisis of solvibility, thermal and dielectric behavior of the heated blend. 

Resole on the other hand, does not require hexamethylenetetramine, for crosslinking because resole type resin contains relatively large amounts of ether-linkages in its structure. It is, therefore, expected that a blend of polyesterimide and resole will result in a crosslinked product on heating at lower teannpera-ture than novolac. 

When the blends of polyesterimide-novolac and polyesterimide-resole are heated separately to 300 C or above and 200 C or above, respectively, it is found that the heated products are insoluble in solvents like N,N-dimethyl foimiamide (DMF), l methyl-pyrroli-done (NMP), 1,4-dioxane, m-cresol, etc. The insolubilil of the blends after heating is believed to be due to crosslinking. It is very likely that the phenolformaldehyde resin component of the polyblend provides the crosslinks. It has been observed that the blend containing as low as 10% P-F resin is capable of cross-linking. 

Fig. 8 TGA thermograms for polyesterimide, resole and their blend in air at the heating rate of 5 C/min.

But contrary to the findings of PEI-novolac blend we have noticed that the TG profile of resole is not significantly altered in case of PEI-resole blend (Fig. 8). The TG profile of the blend containing resole is not altered because above 150 C resole also behaves as a thentostable resin. The thenrostability of resole is greater than that of polyesterimide due to its enhanced crosslinking tendency. The thermostability of the PEI-resole blend depends on the amount of resole present in the blend. 

Thus from Table 7 it is apparent that incorporation of novo-lac or resole in polyesterimide increases the activation energy for degradation indicating theretf that the blend is more stable than pure polyesterimide, particularly in the temperatixre zone 300-600 C. 

Fig. 12 Softening (Un) teirperature of polyesterimide-resole blend vs. resole content of the blend.

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