Films from crosslinked resins

There is not enough space here to give a detailed classification, but only to delineate the major families from which resins for industrial coatings may be selected. Resins may be divided into two groups according to their modes of film formation which may or may not involve a chemical reaction. In the first, the components must react together to form a crosslinked structure which may require heat, radiation or catalysis to effect the reaction. The bulk of resins used in industrial finishes are of this type. They are commonly referred to as chemically convertible or, simply, convertible. 

Immobilization of (3-D-glucosidase from almonds on photo-crosslinkable resin prepolymer (ENTP-4000) was carried out by the following procedure. One gram of ENTP-4000 was mixed with 10 mg of a photosensitizer, benzoin ethyl ether, and 110 mg of (3-D-glucosidase from almonds (3.4 units mg ). The mixture was layered on a sheet of transparent polyester film (thickness, ca. 0.5 mm). The layer was covered with transparent thin film and then illuminated with chemical lamps (wavelength range 300 00 nm) for 3 min. The gel film thus obtained was cut into small pieces (0.5 x 5 x 5 mm) and used for bioconversion reaction. 

The degree of unsaturation in these oil-modified alkyds was controlled by the amount and type of unsaturated acid used in the formation of the polyester. These unsaturated polymers cured or "dried" through auto-oxldatlon by oxygen from the air which reacted with the unsaturated carbon atoms on the surface of the freshly deposited film. This crosslinking reaction, like that of the "drying" of oil-based paints, was catalyzed by heavy metal salts, such as lead or cobalt salts of organic acids. Alkyds, which are some of the most Important paint resins, are produced at an annual rate in excess of 300 thousand tons. 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

The crosslinkers examined in this study were aminoplast resins 1-4 selected from melamine-formaldehyde, urea-formaldehyde, benzoguanamine-formaldehyde, and glycoluril-formaldehyde resins, all of which undergo the crosslinking sequence shown in Scheme 1. The response of these crosslinkers to acid catalysis in thin films is compared on a relative basis to the well studied methylated melamine, 1 19-11). 

Although the cross-linked pyrazoline polymer is insoluble in common organic solvents by virtue of the crosslinks present, it was discovered that films of this material could be cast onto a variety of substrates from a suspension in a swelling solvent such as benzene. The ability to cast films is presumably related to the substantial change in polymer resin morphology after the coupling reaction has proceeded. The initial resin is hard, spherical and white in color, while the reacted bead is powdery, irregular in appearance and yellow, the color of the pyrazoline monomer. 

Enamel Properties. Clear coatings were formed by crosslinking the PHBA-modified oligomers with a standard melamine resin. Baking at 175° was necessary to obtain optimal properties. The cured films were glossy and nearly transparent except for films made from 60/40 PHBA ratio polyol. Adhesion was excellent. 

Polyimides for microelectronics use are of two basic types. The most commonly used commercial materials (for example, from Dupont and Hitachi) are condensation polyimides, formed from imidization of a spin-cast film of soluble polyamic acid precursor to create an intractable solid film. Fully imidized thermoplastic polyimides are also available for use as adhesives (for example, the LARC-TPI material), and when thermally or photo-crosslink able, also as passivants and interlevel insulators, and as matrix resins for fiber-reinforced-composites, such as in circuit boards. Flexible circuits are made from Kapton polyimide film laminated with copper. The diversity of materials is very large readers seeking additional information are referred to the cited review articles [1-3,6] and to the proceedings of the two International Conferences on Polyimides [4,5]. 

Another interesting procedure for obtaining a two-layer system involves [97] the formation of a base layer of the polymeric photoinitiator, through a spin coated film onto different substrates, followed by their immersion, under UV irradiation, into multifunctional acrylic formulations dissolved in solvents unable to remove the base layer from the substrate. By this method, a top layer of crosslinked acrylic resin is obtained, having strong adhesion to the substrate. The replacement of the polymeric photoinitiator by a low-molecular-weight analogue... 

To form crosslinked coatings, the polymer must be free of unreacted functional monomer that would act as a chain terminator in the crosslinking reaction. The unreacted VEC could be easily removed from the acrylic copolymer by passing the resin solution through a wiped film still under vacuum, then redissolving the polymer in solvent. GC analysis indicated that the unreacted VEC had been totally removed. 

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