Epoxies cycloaliphatic type

The present study, by contrast, deals with toughening of cycloaliphatic type epoxies with anhydride curing agents normally used in industrial applications. In addition to developing mechanical property data, the morphological characteristics were also studied. 

The DIBF OPPI combination has been shown to efficiently cure a wide variety of epoxies including cycloaliphatics. With this photoinitiator it is possible to cure bisphenol A epoxies such as Epon 828 quickly without the need for acrylation of the epoxy. Cycloaliphatic epoxies were of special interest because they were expected to react much faster than bisphenol A type epoxies. Those tested include 3,4-epoxycyclohexylmethyl-3 ,4 -epoxycyclohexyl-carboxylate (UVR 6110), bis(3,4 epoxy-cyclohexylmethyl) adipate (UVR 6128), and 1,2-epoxy-4-vinylcyclohexane (vinyl cyclohexene oxide). It was found that the vinyl cyclohexene oxide reacted rapidly, but work with it was discontinued because it has a fairly high vapor pressure (2 torr at 20 °C), an intense odor, and the photoinitiator does not dissolve in this resin. 

Bisphenol A type epoxies such as Epon 828, were also cured with the DIBF OPPI combination. When a modifier, Heloxy 505 (a low viscosity polyepoxide modifier) was added, viscosity was reduced and adhesion to the metal surface and impact resistance were improved as compared with the bisphenol A only. Surprisingly cure was faster than with the Union Carbide cycloaliphatic resins, but charring of the resin during cure was a problem. 

Thus it was decided to examine the viscoelastic response and ultimate mechanical behavior of several systems based on a typical cycloaliphatic and a blsphenol-A-type epoxy prepolymer, using a variety of epoxldlzed botanical oils as reactive diluents. This paper describes the first results of this Investigation, In which epoxldlzed linseed, lunarla, and crambe oils were selected as diluents. 

As far as the addition of aniline to the ACECs is concerned, the principal conclusions in [50] were confirmed glycidyl type epoxy groups are more reactive than those attached to the cyclohexane ring. Moreover, there is a very distinct induction period in the case of glycidyl groups. The appearance of the induction period is connected with the accumulation of hydroxyl groups which serve as an accelerator of the epoxy-amine addition. This acceleration effect is little noticeable as far as cycloaliphatic epoxy groups are concerned. 

However, boron trifluoride amine complexes are used to polymerize epoxies, especially the cycloaliphatic type. The cured product has very good electrical properties but relatively poor adhesive properties as indicated above. 

Two types of epoxy resins were used in this study. They were bisphenol A type epoxy resins (EPON 828 fiom Shell Chemicals), and cycloaliphatic qwxy resins (ERL 4221 from Union Carbide). The epoxy equivalent weight (EEl of ERL 4221 was 134 g/mol, and the EEW of EPON 828 was 188 g/mol. The curing agent used in this study was hexahydro-4-meth)dphthalic anhydride (HMPA), purchased from Lindau Chonicals. The molecular weight of HMPA was 168.2 g/mol. The chemical structures of the epoxy resins and HMPA are shown in Figure 1. 

The best performing coatings studied were a vinyl ester, a bisphe-nol A epoxy cured with an aliphatic amine, and a novolac epoxy cured with a mixed aromatic/cycloaliphatic amine. A saturated polyester, and a bisphenol A epoxy cured with a polyamide amine showed significant deterioration in the acid and corrosion of the underlying steel. Two types of novolac epoxies cured with aromatic amines showed intermediate performance. 

Curing agents account for much of the potential hazard associated with use of epoxy resins. There are several major types of curing agents aliphatic amines, aromatic amines, cycloaliphatic amines, acid anhydrides, polyamides, and catalytic curing agents. The latter two types are true catalysts, in that they do not participate in the curing process. 

In addition to the DGEB A resins, there are several other types of epoxy resins of commercial significance. The most common of these are epoxy novolacs, glycidyl ether of tetraphe-nolethane, bisphenol F-based resins, and aliphatic and cycloaliphatic resins. 

Two types of epoxy resins are formed by this process (1) cycloaliphatic resins and (2) aliphatic resins. Of the many structures that can be synthesized by this process, the cycloaliphatic diepoxies offer the most interesting combination of properties. However, the aliphatic epoxy resins have the greatest utilization in epoxy adhesive formulation. 

In 1987, UVEXS [145] claimed simultaneous cationic and free radical polymerization of a mixture of a cycloaliphatic epoxy resin, a hydroxy functional polyether terminated polysiloxane, an acrylate functional resin, a triarylsulfonium salt, and a free radical photoinitiator. A simultaneously cured cationically and free radically polymerized system consisting of an epoxy resin, a methacrylate monomer, an onium salt, a carbonyl type free radical photoinitiator, and tetrahydrofurfuryl alcohol accelerator was patented by Cook Paint and Varnish [146] in 1987. 

There are three major types of epoxy resins cycloaliphatic epoxy resins (R and R are part of a six-membered ring), epoxidized oils (R and R are fragments of an unsaturated fatty acid, such as oleic acid in soybean oil), and glycidated resins (R is hydrogen and R can be a polyhydroxyphenol or a polybasic acid). The first two types of epoxy resins are obtained by the direct oxidation of the corresponding olefin with a peracid as illustrated by the following ... 

The polyethylenes with higher functionality were soluble in epoxy resin and required lower temperamre and time for forming homogeneous blend systems. The miscibility of the polymers was dependent on the type of epoxy resin also. Cycloaliphatic epoxy resin showed more miscibility with the polymers compared to DGEBA resin and phase separation occurred in these blend systems as a result of crystallization of PE. Upper critical solution temperature (UCST) behavior was... 

Expoxies [unmodified types of bisphenol A, higher functionalized resins, novolac epoxies, cycloaliphatic resins, heterocyclic resins one- and two-component systems curing at room temperature, at elevated temperatures, or by ultraviolet (UV) irradiation], used as mounting adhesives, coverings, and binders for laminates [1,2]... 

These new types and forms of fiber provided the industry with more freedom to select the most appropriate type of fiber reinforcement for a given application. Newly developed, high modulus plastics, such as cycloaliphatic epoxies and new-generation high-temperature plastics, such as polybenzimidazole and nylon plastics, offer another degree of fi-eedom in terms of material matrix selection. 

The compositions of materials photocrosslinkable by cationic mechanism consist of mixtures of various vinyl ethers, or epoxides, or both. Difunctional cycloaliphatic epoxides have been used extensively in some UV curable systems, often as diluents for the various epoxy resins described in Chapter 6. Use of various divinyl ethers is also extensive. Because some cationic photoinitiators also generate free radicals, some compositions may contain mixtures of both types of materials, those that cure by cationic and those that cure by free-radical mechanisms. 

A third type of epoxy resin is cycloaliphatic (Fig. 3.23). These are harder to cure but offer better electrical resistance and resistance to sunlight. 

Curing agents are used with epoxy resins, the most commonly used ones are aromatic amines, and two of the most common are 4,4-methylene-dianiline (MDA) and 4,4-sulfonyl-dianiline (DDS). Like the epoxies, these compounds have very low vapour pressures and in principle they should not present any airborne hazard, unless a mixture is sprayed or cured at high temperatures and certainly potential for dermal exposure is high. Several other types of curing agents to consider are aliphatic and cycloaliphatic amines, polyaminoamides, amides, and anhydrides. 

This type of behavior provides a means of controlling the degree of cure. Dialkylphenacyl sulfonium salts are thermally stable in epoxy resins at room temperature and up to 150°C for 1-2 h. Significant interest in thermal cationic cure of epoxies, especially cycloaliphatic epoxies, has developed (130). 

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