Thermally cured resins

Single-Cure (Thermal) Resin. Typically, thermally cured resins exhibit good adhesion strength to copper. Unfortunately, the rate of heat dissipation throughout the filled core material is unstable, making it difficult to achieve a reliable semicured state prior to planarization. 

Scanning probe microscopy techniques have been used to characterize surfaces related to the processing of benzocyclobutene (BCB) dielectric thin films. Thermally cured resins and photodefinable resins are used... 

Therefore, in general, a thermal curing resin contains a radical curable function that is activated by light and a hardening agent Acrylic resins such as urethane acrylate and epoxy acrylate are mainly used for the radically curable resin, and an epoxy resin is mainly used for thermal curing. The reaction mechanism due to the heat and UV irradiatiOTi are shown in Fig. 7.16. 

Both urea— and melamine—formaldehyde resins are of low toxicity. In the uncured state, the amino resin contains some free formaldehyde that could be objectionable. However, uncured resins have a very unpleasant taste that would discourage ingestion of more than trace amounts. The molded plastic, or the cured resin on textiles or paper may be considered nontoxic. Combustion or thermal decomposition of the cured resins can evolve toxic gases, such as formaldehyde, hydrogen cyanide, and oxides of nitrogen. 

Resin Cure. Resin cure systems yield carbon—carbon cross-links and, consequendy, thermally stable materials. Butyl mbber vulcanised with resins are used as tire-curing bladders, and have a life of 300—700 curing cycles at steam temperature of 175°C at about 20 m/cycle. 

An epoxy resin made by thermal curing of an araldite prepolymer with the 3,5-diaminophenylester of a peripherically modified vitamin as hardener on carbon... 

Urea-formaldehyde resins are used as the main adhesive in the forest product industry because they have a number of advantages, including low cost, ease of use under a wide variety of curing conditions, low cure temperatures, water solubility, resistance to microorganisms and to abrasion, hardness, excellent thermal properties, and a lack of color, especially in the cured resin. 

The thermal polymerization of reactive polyimide oligomers is a critical part of a number of currently important polymers. Both the system in which we are interested, PMR-15, and others like it (LARC-13, HR-600), are useful high temperature resins. They also share the feature that, while the basic structure and chemistry of their imide portions is well defined, the mode of reaction and ultimately the structures that result from their thermally activated end-groups is not clear. Since an understanding of this thermal cure would be an important step towards the improvement of both the cure process and the properties of such systems, we have approached our study of PMR-15 with a focus only on this higher temperature thermal curing process. To this end, we have used small molecule model compounds with pre-formed imide moieties and have concentrated on the chemistry of the norbornenyl end-cap (1). 

Thermal analysis, moisture uptake and dynamic mechanical analysis was also accomplished on cured specimens. Thermal analysis parameters used to study cured specimens are the same as those described earlier to test resins. The moisture uptake in cured specimens was monitored by immersing dogbone shaped specimens in 71 C distilled water until no further weight gain is observed. A dynamic mechanical scan of a torsion bar of cured resin was obtained using the Rheometrics spectrometer with a temperature scan rate of 2°C/minute in nitrogen at a frequency of 1.6Hz. The following sections describe the results obtained from tests run on the two different BCB resin systems. Unless otherwise noted all tests have been run as specified above. 

With the diglycidyl derivative of bisphenol A, aromatic amines such as 4,4 -methylene dianiline or diaminodiphenyl sulfone provide good thermal stability for the final cured resin. Although aliphatic primary amines react more rapidly (triethylenetetramine cures the above epoxy resin based on bisphenol A in 30 min at room temperature and causes it to exotherm up to 200°C), they are more difficult to handle and offer poor thermal stability. 

All of the monomers in Fig.46 were polymerized into neat resin castings using a thermal cure cycle with a maximum temperature of 250 °C. The polymers were then subjected to preliminary thermal and mechanical property screening and a summary of their physical properties is shown in Table 21. All of the polymers had Tgs above 200 °C (DSC) and 5% weight losses (TGA) in the range between 430 and 470 °C (air and nitrogen). Room temperature flexural moduli and strengths were 3.10-3.52 GPa and 152-207 MPa respectively. 

A solventless PMR resin became known under the designation LARC 160 (15), which could be processed as a hot melt. An exchange of MDA in PMR-15 with a liquid isomeric mixture of di- and trifunctional amines (Jeffamine 22) provided a mixture of monomeric reactants which was tacky at room temperature. In the presence of 3% methanol the resin could be processed via a hot melt process. Unfortunately, the cured resin was inferior with respect to thermal oxidative stability in comparison to PMR-15. 

Tertiary amines are used to accelerate both amine and anhydride cures of epoxy resins (B-67MI11501). Certain heterocyclic amines have been used for this purpose, including pyridine and piperidine. In the case of anhydride cures, the use of an amine catalyst not only accelerates the cure, but also improves the thermal stability of the cured resin. 

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