Ring-opening polymerization epoxy resins

Curing of epoxy resins can also be achieved by ring-opening polymerization of epoxide groups using either Lewis acids (including those generated photochemically) or Lewis bases (Sec. 7-2). 

Fig. 136 Epoxy resins for cross-linking by cationic ring-opening polymerization...

Polyethers are obtained from three different classes of monomers, namely, carbonyl compounds, cyclic ethers, and phenols. They are manufactured by a variety of polymerization processes, such as polymerization (polyacetal), ring-opening polymerization (polyethylene oxide, polyprophylene oxide, and epoxy resins), oxidative coupling (Polyphenylene oxide), and polycondensation (polysulfone). 

Scheme 3A Ring-opening polymerization of epoxy resins.

Epoxy resin-based materials are available for use as endodontic sealers [64], They set by a ring-opening polymerization reaction between hexamethylene tetratramine (Fig. 10.5), which is part of the powder component, and iiw-phenol resin monomer, which comprises the liquid component [13]. In addition to the reactive molecule, the powder contains bismuth oxide (50%) to impart radiopacity and titanium dioxide (5%) as a pigment. The powder also contains silver particles (10%) to make the set material anti-bacterial. 

The first step reaction example involves the preparation of water-based epoxy resins via ring-opening polymerizations of different epoxides with various diamines, dithiols or diols residing in the miniemulsion droplets at 60°C [75]. The basic requirement for successful miniemulsion polymerization is that both reactive components exhibit relatively low solubility in the continuous aqueous phase. The diepoxide Epikote E828, triepoxide Decanol EX-314, and tetraepoxide EX-411 are potential candidates for this purpose. Furthermore, incorporation of conventional costabilizers such as hexadecane into the... 

Imidazole is a well-known initiator for the anionic ring-opening polymerization of epoxides. The photogeneration of imidazole and its subsequent use as an initiator for the polymerization of multifunctional epoxy-novolak resins have been reported by Nishikubo et Photolysis of the nitro-benzyl derivative 119 as shown in Scheme 36 generates imidazole, 120, which forms zwitterionic intermediate, 121, by reaction with the epoxide. The latter species is a rather weak nucleophile and the application of heat (120 °C) was required to drive the polymerization to completion. 

In the spectrum of the polymerized epoxy resin, the opening of the epoxide ring results in the shift of the two epoxide resonances downfield. The aromatic peaks in the spectra of all phases are identical. Because the crystalline environment has high regularity, the resonance lines are narrow. The amorphous phase has a distribution of local environments and exhibits broad lines these factors limit the detection of structural detail. The polymerized epoxy freezes in the random distribution of orientations, an effect that further decreases the resolution. 

---