Cycloaliphatic resins

Because of the compact structure of the cycloaliphatic resins the intensity of cross-linking occurring after cure is greater than with the standard diglycidyl ethers. The lack of flexibility of the molecules also leads to more rigid segments between the cross-links. 

The cycloaliphatic resins also are clearly superior in arc resistance and arc track resistance. This has led to applications in the tension insulators, rocket motor cases and transformer encapsulation. 

The thermal properties of the resin are dependent on the degree of cross-linking, the flexibility of the resin molecule and the flexibility of the hardener molecule. Consequently the rigid structures obtained by using cycloaliphatic resins or hardeners such as pyromellitic dianhydride will raise the heat distortion temperatures. 

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. 

Metal complexes have been used as spectroscopic probes in several thermosetting resins, including various epoxy/anhydride mixtures. The systems investigated (3) have consisted of the cycloaliphatic resin, (3,4-epoxycyclohexyl)methyl-3,4-... 

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. 

Aliphatic and Cycloaliphatic Resins. Aliphatic and cycloaliphatic epoxy resins have been produced from the epoxidation of olefinic compounds. The epoxidation process involves the use of an olefinic or polyolefinic compound and a peracid (e.g., peracetic acid) or other... 

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. 

Linear resins or curing agents of the same molecular weight often give higher viscosity than do branched or cycloaliphatic resins. 

Table 21.2 Solubilization Temperature on Heating (Tij) and Phase-Separation Temperature on Cooling (Tp) for 50/50 Mixtures of AC 6702, AC 540, Unmodified, and Modified AC 5120, AC 1450, and AC 80, with Unmodified and Modified DGEBA Resin (Epikote 828) or Cycloaliphatic Resin (Araldite CY 179).

Because of their more compact structure, cycloaliphatic resins produce greater density of cross-links in the cured products than bisphenol A-based glycidyl resins. This generally leads to higher heat-distortion temperatures and to increased brittleness. 

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]... 

There are mainly two families of epoxies the glycidyl epoxies and non-glycidyl epoxies (also called aliphatic or cycloaliphatic epoxy resins). The absence of aromatic rings in aliphatic epoxies makes them UV resistant and suitable for outdoor applications and also reduces viscosity. The most common epoxy monomers of each family are diglycidylether of bisphenol A (known as DGEBA) and 3,4-Epoxycyclohexyl-3 4 -epoxycyclohexane carboxylate (ECC) respectively and their structures are given in Figure 2 (a, b). Cycloaliphatic resins are usually found in the form of pure chemicals with a definite... 

High-r die- attach adhesive High-purity Bisphenol-A (Epiclon) and cycloaliphatic resins (Araldite, ERL) 15-24% Anhydride curing agents 12-24% Catalysts 1-2% Filler 50-70% Epi-bond 7002, Epi-bond 7200... 

Underfill adhesive (snap cure) Epoxy resins (high purity Bisphenol-A and cycloaliphatic resins) 45-60% Resin modifier 1—5% Curing agents (amine) 3-5% Filler (amorphous silica) 50-80% Loctite 3563, Ablebond 7811... 

Cycloaliphatic resins were prepared by complete hydrogenation of selected aromatic resins. Molecular weight data were obtained by size exclusion chromatography, using a Styragel column set with THF as the mobile phase. Calculations were based on a polystyrene calibration. Glass transition temperatures were obtained by differential scanning calorimetry from the first break on the second heat. 

After determining the compatibility of an aromatic and a cycloaliphatic resin, it is of interest to examine an alkyl aromatic resin. Poly (tert-butyl styrene) 850, 1.3) was found to be compatible with both natural rubber, as shown in Fig. 7, and with styrene-butadiene rubber as shown in Fig. 8. The tert-butyl group on the polystyrene resin altered the compatibility of the resin in natural rubber, but did not detract from compatibility with styrene-butadiene rubber. 

The structure of the low molecular weight resin is very important to its compatibility with elastomers and, consequently, to its effect on viscoelastic properties and performance as a pressure sensitive adhesive. A completely aromatic resin such as polystyrene has poor compatibility with natural rubber, but is compatible with styrene-butadiene rubber. A cycloaliphatic resin such as poly(vinyl cyclohexane) is compatible with natural rubber and is incompatible with styrene-butadiene rubber. An alkyl aromatic resin such as poly-(tert-butyl styrene) is compatible with both elastomers. 

The product, 3,4-cyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, marketed as Ciba CY179, has a very low viscosity and can be used as a diluent, since it is an excellent solvent for other resin families and also is a good solvent for the curing agent 4,4 -diaminodiphenyl-sulfone (DDS). The absence of an aromatic ring is noticeable. Unfortunately, the range of cycloaliphatic resins on the market has been almost terminated due to difficulties in their manufacture. 

Another group of epoxy resins, the cycloaliphatics, is particularly important when superior arc track and weathering resistance are necessary requirements. A distinguishing feature of cycloaliphatic resins is the location of the epoxy group(s) on a ring structure rather than on an aliphatic chain. Cycloaliphatics can be produced by the... 

The modification of epoxy structural adhesives by the addition of flexibilizing and/or toughening agents has greatly increased the utility of these products. Most structural adhesives based on DGEBA or cycloaliphatic resins cure to give products which are very strong but brittle. Such adhesives perform well when loaded in tensile and shear, but poorly when... 

The cycloaliphatic resins are a paler colour than the standard diglycidyl ether resins and also have much lower viscosities. Typical examples are dicyclopentadiene dioxide, which is a solid at room temperature, and vinyl cyclohexene dioxide, which is a liquid... 

A more scientific classification takes into account resin structure. One can thus distinguish between aliphatic, cycloaliphatic, aromatic, and mixed HRs. Cycloaliphatic HRs include terpenic resins and cyclopentadiene-based resins. A similarity can be noticed, likely to cause confusion, between aliphatic and cycloaliphatic resins. This is because aliphatic resins often contain cyclic structures, arising from the presence of cyclopentadiene and cycloolefins in monomer mixtures subjected to polymerization and from cyclization accompanying some of the polymerization processes. Aromatic HRs include the products produced by polymerization of Cs-Cio fractions and CIRs. Mixed resins are made up of complex structures. Their properties will be modulated in terms of component proportion. Thus, these resins can produce various materials that also prove valuable from the technical point of view [8]. 

The reaction with MA is characteristic for the unsaturated compounds. As a result it is applied to liquid polydienes, to cyclopentadiene and dicyclopentadiene oligomers, to copolymeric aliphatic resins, and to cycloaliphatic resins. 

---