Oxirane group

Specialty Epoxy Resins. In addition to bisphenol, other polyols such as aUphatic glycols and novolaks are used to produce specialty resins. Epoxy resins may also include compounds based on aUphatic, cycloaUphatic, aromatic, and heterocycHc backbones. Glycidylation of active hydrogen-containing stmctures with epichlorohydrin and epoxidation of olefins with peracetic acid remain the important commercial procedures for introducing the oxirane group into various precursors of epoxy resins. 

The cycloahphatic products are generally Hquids of lower viscosity than the standard glycidyl ether resins. The peroxidized resins contain no chlorine and low ash content and their ring-contained oxirane group (cyclohexene oxide type) reacts more readily with acidic curing agents than the bisphenol A-derived epoxy resins. 

Absorptions in the UV spectra of thiiranes are observed around 260 nm ( - other transitions are reported in the vacuum UV spectrum, and the calculated lowest singlet transition energies correspond to n - electron withdrawing substituents when attached to aromatic rings as indicated by the UV spectra of 2-arylthiiranes. 

In nuclear magnetic resonance (NMR) spectra the protons of the oxirane ring are usually shifted out of the steroid methylene envelope. Tori et al have tabulated the relationships of the angular methyl proton resonances and the oxirane proton signals with respect to location and configuration of the oxirane group. 

The effect of an a-substituted oxirane group on the optical rotatory dispersion of steroidal ketones should be interpreted with caution an inverted octant rule for a-epoxy ketones has been proposed/although recent data indicate that the normal octant rule may still be valid. 

An epoxide or oxirane group can react with nucleophiles in a ring-opening process. The reaction can take place with primary amines, sulfhydryls, or hydroxyl groups to create secondary... 

Beginning in 1978, the program was broadened to include polymers containing oxirane groups. Two types of materials were examined ... 

Cafionic photoinitiation is based on the ring opening of the oxirane group. The photoinitiators of practical importance belong to three main classes of compounds diazonium salts, onium (e.g., iodonium and sulfonium) salts, and organometallic complexes, which upon irradiation by UV light decompose and yield an acid catalyst. 

The epoxy or oxirane group is characterized by its reactivity toward both nucleophilic and electrophilic species and it is thus receptive to a wide range of reagents. Epoxy monomers polymerize through step-growth and chain-growth processes. The ionic polymerization initiated by both Lewis bases or acids will be discussed later (Sec. 2.3.4). The case of polyaddition polymerizations is mainly represented by epoxy-amine reactions. 

Another approach to the formation of the oxirane groups is the peroxidation of a carbon-carbon double bond. Various types of oligomers fall into this category epoxidized oils, epoxidized rubbers, and cycloaliphatic... 

The simultaneous formation of the polyimide and the three dimensional epoxy network occurs because of the polyamic acid containing reactive groups that can initially open the oxirane groups of the DGEBA and then subsequently intramolecularly cyclize to become polyimide as the epoxy network extends. These reactions are summarized in Fig. 4. 

Epoxide adhesives are based on precursors containing the three-membered, oxygen-containing oxirane group ... 

The higher-molecular-weight epoxy resins can be produced commercially either through the direct reaction of bisphenol A, NaOH, and epichlorohydrin or by chain extension of the DGEBA with bisphenol A. For resins with n > 2, the number of secondary hydroxyls exceeds the number of oxirane groups. They are often used as the reactive site for coatings. 

The same TBD 2 was also grafted to silica but by means of a different electrophilic linker [3-(glycidyloxy)propyl]trimethoxysilane was first grafted and then TBD reacted with the oxirane group to give the hydroxy guanidine (Figure 9). 

Photoinitiated epoxy crosslinking is generally based (with one exception on cationic ring-opening polymerization of the oxirane group, yielding polyether structures. 

The resulting stable prepolymers or adducts are end-capped with oxirane groups, which can be cured with any of the following hardeners (Rees... 

The reactivity of epoxy groups towards nucleophilic and electrophilic species can be explained through the release of ring strain in the three member oxirane group. Nucleophilic curatives such as amines or mercaptans attack the secondary ring carbon while electrophilic curatives behave as Lewis or Bronsted acids. The epoxy ring can be opened by hydroxyl or other epoxy group aided by tertiary amines, Lewis acids or coreactants such as primary amines, mercaptans and dicarboxylic acids ... 

CAS 75-21-8. HjCOC,. A synonym for ethylene oxide. An oxirane group is one having the structure... 

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