Properties of the Cured Resins

The resins are cross-linked and the molecular segments between the cross-links are rigid and inflexible. As a consequence the resins have an excellent heat resistance, as measured in terms of maintenance of rigidity on heating, but are rather brittle. 

Cured resins have excellent chemical resistance. This is probably because, although the resins have some reactive groupings, most of the reactions occurring do not result in the disintegration of the polymer molecules. Therefore, whilst surface layers of molecules may have undergone modification they effectively shield the molecules forming the mass of the resin. The resins have very good resistance to water penetration. 

Compared with the phenolics and polyesters the resins have better heat resistance, better chemical resistance, particularly to alkalis, greater hardness and better water resistance. In these respects they are similar to, and often slightly superior to, the epoxide resins. Unlike the epoxides they have a poor adhesion to wood and metal, this being somewhat improved by incorporating plasticisers such as poly(vinyl acetate) and poly(vinyl formd) but with a consequent reduction in chemical resistance. The cured resins are black in colour. 

The principal applications for furan resins are in chemical plant. Specific uses include the lining of tanks and vats and piping and for alkali-resistant tile cements. The property of moisture resistance is used when paper honeycomb structures are treated with furan resins and subsequently retain a good compression strength even after exposure to damp conditions. 

Laminates have been prepared for the manufacture of chemical plant. They have better heat and chemical resistance than the polyester- epoxide- phenolic- or aminoplastic-based laminates but because of the low viscosity of the resins were not easy to handle. Because they were also somewhat brittle, furan-based laminates have been limited in their applications. 

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The polymers of the 2-cyanoacryhc esters, more commonly known as the alkyl 2-cyaiioacrylates, are hard glassy resins that exhibit excellent adhesion to a wide variety of materials. The polymers are spontaneously formed when their Hquid precursors or monomers are placed between two closely fitting surfaces. The spontaneous polymerisation of these very reactive Hquids and the excellent adhesion properties of the cured resins combine to make these compounds a unique class of single-component, ambient-temperature-curing adhesives of great versatiUty. The materials that can be bonded mn the gamut from metals, plastics, most elastomers, fabrics, and woods to many ceramics. 

In addition to the considerable difference of the properties of the cured resins with different hardeners it must also be stressed that the time and temperatures of cure will also have an important effect on properties. As a very general rule, with increasing aliphatic amines and their adducts the time of cure and temperature of cure (up to 120°C at least) will improve most properties . ... 

Amines were one of the first hardeners of epoxy resins 1 12), and at present they retain their leading position among all known hardeners of this type. The amine hardeners will most likely also be used in the future because they are fairly accessible, highly reactive, and their properties can be readily modified. The mechanical properties of the cured resins obtained are far better than those of the known polymer binders 2 -4), they have high dielectric characteristics, chemical resistance, etc. 

The catalyst does not make up part of the final epoxy network structure or have a significant effect on the final properties of the cured resin. Thus, the final cured properties of the epoxy system are primarily due to the nature of the epoxy resin alone. Homopolymerization normally provides better heat and environmental resistance than polyaddition reactions. However, it also provides a more rigidly cured system, so that toughening agents or flexibilizers must often be used. In adhesive systems, homopolymerization reactions are generally utilized for heat cured, one-component formulations. 

The aromatic amine eutectics may crystallize on storage. They can be reliquefied by heating to 40°C with stirring. This liquefaction can be accomplished without sacrificing either the curing properties or the final physical and chemical properties of the cured resins. 

Difunctional epoxy diluents are low-viscosity, low-MW epoxy resins. These diluents may be used at very high concentrations, and they do not greatly affect the properties of the cured resin. In some instances the difunctional epoxy diluents will actually improve properties. These materials include butadiene dioxide, vinyl cyclohexane dioxide, and diglycidyl ether of resorcinol. 

The temperature dependence of the dynamic mechanical properties of the cured resins is similar as in Fig. 5 33). This shows that the physical properties of cured resins are mostly characterized by the differences of Tg. 

TMAH is a diamine having a primary amine group in the center of the molecule, and the dynamic mechanical properties of the cured resin are interesting (cf. Table 3). Both Tg and q(E. are almost the same as for TETA, which suggests that such a slight... 

The mercaptan hardener is one of a very few hardeners which can cure the resin at low temperature even below the freezing point in a few minutes using basic catalysts such as amines. There are only very few studies of the curing reaction mechanism and the physical properties of the cured resin available 42 45). 

Accordingly, the structure of the cured resin with polymercaptans having more than three functional groups would be close to that shown in Fig. 1 a. Thioglycolate of pentaerythritol (PnEThGE) (structure [I] below) is a hardener with four functional groups, and the physical properties of the cured resin can be compared with those cured with diamine or dihydrazide. 

The dynamic mechanical properties of the cured resin are very similar to those of resins cured with amines or acid anhydrides (Fig. II)44. ... 

In the preceding sections, Tg and the structures which determine the properties of the cured resins were discussed. These cured resins can be exploited as structural materials at temperatures below Tg. 

Although the processing and final physical properties of epoxy-curing agent systems depend primarily on their chemical composition and degree of cure, the corresponding relations are often empirical or semiempirical and are not well understood. The tie between the cure chemistry and structure and properties of the cured resins consists in the theoretical and experimental study of network formation as a function of the depth of cure. 

Control over the properties of the cured resin vehicle may be exercized In a number of ways ... 

PET is useful polymer used for fiber, film, and plastic containers such as carbonated beverage bottles. Recently, the recycling of polymers such as PET after use is attracting the attention of many researchers aware of environmental problems and wishing to find ways to save earth resources. Previous studies showed that unsaturated polyester resins can be economically prepared from recycled PET and the resins may be useful for resin concretes (1 4). However, there is little information on the molecular features of the UPE resins. Thus, we synthesized various UPE resins from PET. Especially, the PET content, chain flexibility and degree of unsaturation of the resins were systematically varied and the effects of those variables on the mechanical properties of the cured resins and polymer mortars made therefrom were studied. 

Various UPE resins based on recycled poly ethylene terephthalate(PET) were prepared and the properties of the polymer mortar made with the UPE as well as those of the cured resin itself were investigated. It was found that degree of unsaturation of the resins was the most important property affecting thermal and mechanical properties of the cured resin and PM. The cured unsaturated polyester resin or polymer mortar made from resins of higher unsaturation, i.e., less PET content or adipic acid content in the resin, showed higher glass transition temperatures,... 

Research has been aimed at understanding the mechanism of these linking reactions. This includes the reactivity of the ortho and para sites, possible intermediates involved in these linking reactions and behaviour of these higher units to further crosslinking. Attempts have been made to link the properties of the cured resin or carbon derived from these resins to the initial resin formulation and structure. As the crosslinking in a resole is very complicated, various model compounds have been used to investigate the chemistry. 

The modified-classical phenolic resins are particularly noteworthy for their effect on the mechanical and thermal properties of the cured resin. The processing of these systems is very similar to the classical systems. The nonclassical phenolic resins utilize phenol, but in many cases give a cured product with a chemical structure having little resemblance to the classical system. In future articles, it would be best to develop independent grouping for addition-cure phenolics resins. This redefinition of polymer types is not within the scope of this entry and instead, this interesting class of polymers has been viewed based on current designations. 

The electrical properties of the cured resins, containing various quaternary phosphonixim additives are shown in Table IV. 

T. Mika Cll) has reviewed the chemistry of curing agents and how these influence the properties of the cured resins. Compounds such as phenol and boron trifluoride are effective accelerators for epoxide-amine reactions, while solvents usually slow down this same reaction due the lower concentration of reactants and/or to specific hydrogen bond interactions. 

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