Bisphenol based epoxy prepolymers

In some epoxy systems ( 1, ), it has been shown that, as expected, creep and stress relaxation depend on the stoichiometry and degree of cure. The time-temperature superposition principle ( 3) has been applied successfully to creep and relaxation behavior in some epoxies (4-6)as well as to other mechanical properties (5-7). More recently, Kitoh and Suzuki ( ) showed that the Williams-Landel-Ferry (WLF) equation (3 ) was applicable to networks (with equivalence of functional groups) based on nineteen-carbon aliphatic segments between crosslinks but not to tighter networks such as those based on bisphenol-A-type prepolymers cured with m-phenylene diamine. Relaxation in the latter resin followed an Arrhenius-type equation. 

This full IPN combines the network of an NLO active epoxy-based polymer and the network of an NLO active phenoxy-silicon polymer. l The epoxy-based NLO network is prepared from the epoxy prepolymer (BPAZO) based on the diglycidyl ether of bisphenol A and 4-(4 -nitrophenylazo)aniline functionalized with crosslinkable acryloyl groups. The second NLO network of a phenoxy-silicon polymer is based on an alkoxysilane dye (ASD) of (3-glycidoxypropyl)trimethoxysilane and 4(4 -nitrophenylazo)aniline, and the multifunctional phenoxyl molecule 1,1,1- tris(4-hydroxyphenyl)ethane (THPE).22 Figure 4 shows the chemical structures of BPAZO, ASD, and THPE. Each network can be formed... 

High molar mass epoxy prepolymers containing rabber dispersions based on carboxyl-terminated butadiene-acrylonitrile copolymer were prepared from initially miscible solution of low molar mass epoxy prepolymers, bisphenol A and carboxyl-terminated NBR. During chain extension inside a twin screw extruder due to epoxy-phenoxy and epoxy-carboxy reactions, a phase separation process occurs. Epoxy-phenoxy and epoxy-carboxy reactions were catalysed by triphenylphosphine. The effect of reaction parameters (temperature, catalyst, reactant stoichiometry) on the reactive extrasion process were analysed. The structure of the prepolymers showed low branching reactions (2-5%). Low molar mass prepolymers had a Newtonian rheological behaviour. Cloud-point temperatures of different reactive liquid butadiene aciylonitrile random copolymer/epoxy resin blends were measured for different rubber concentrations. Rubber... 

The most widely used epoxy resins and adhesives are based on a prepolymer made from bisphenol A and epichlorohydrin. On treatment with base under carefully controlled conditions, bisphenol A is converted into its anion, which acts as a nucleophile in an S142 reaction with epichlorohydrin. Each epichlorohydrin molecule can react with two molecules of bisphenol A, once by S 2 displacement of chloride ion and once by opening of the epoxide ring. At the same time, each bisphenol A molecule can react with two epichlorohydrins, leading to a long polymer chain. Each end of a prepolymer chain has an unreacted epoxy group, and each chain has numerous secondary alcohol groups. 

Epoxy resins are complex network polyethers usually formed in a two-staged process. The first stage involves a base-catalyzed step-growth reaction of an excess epoxide, typically epichlorohydrin with a dihydroxy compound such as bisphenol A This results in the formation of a low-molecular-weight prepolymer terminated on either side by an epoxide group. 

More recent efforts have focused on developments that create true hybrids. For example, blocked isocyanate prepolymers have been mixed with epoxy resins and cured with amines [68-70]. These blocked prepolymers will react initially with the amines to form amine-terminated prepolymers that cross-link the epoxy resin. Several blocked isocyanates are commercially available. The DESMOCAP (Bayer) llA and 12A products are isocyanates (believed to be blocked with nonylphenol) used as flexibilizing agents for epoxy resins. ANCAREZ (trademark. Pacific Anchor, Inc.) 2150 is a blocked isocyanate epoxy blend used as an adhesion promoter for vinyl plastisols. A one-package, heat-cured hybrid adhesive was reported consisting of isophorone diisocyanate, epoxy resin, and a dispersed solid curative based on the salt of ethylenediamine and bisphenol A [71]. Urethane amines are offered commercially that can be used with epoxy resins to develop hybrid adhesive systems [72]. 

The addition-reaction product of bisphenol A and glycidyl methacrylate or an epoxy resin and methacrylic acid is bis-GMA 2,2- 7Z5 4-(2-hydroxy-3-methacryloxypropoxy)phenyl propane (Fig. 5). Bis-GMA can therefore be classified as a dimethacrylated epoxy, although it does not contain a reactive epoxy group. Bis-GMA is the most commonly used prepolymer in dental composite restorative materials. Several similar compounds have also appeared as substitutes for Bis-GMA or in addition to it in dental resins. Such dimethacrylates based on bisphenol A with various chain lengths are bis-MA 2,2- fs(4-(metha-cryloxy)phenyl)-propane, bis-EMA 2,2-i7is(4-(2-met-hacryloxyethoxy)phenyl)-propane and bis-PMA 2,2- s(4-(3-methacryloxypropoxy)phenyl)-propane. 

The prepolymer contains a 1,2 epoxy linkage which is made by a base-catalysed step-growth reaction between a diol, e.g. bisphenol A, and a 1,2 epoxide, e.g. epichlorhydrin. 

Epoxy resins are formed from low molar mass prepolymers containing epoxide end-groups. The most important are the diglycidyl ether prepolymers prepared by reaction of excess epichlorohydrin with bisphenol-A in the presence of a base... 

These vinyl esters are di(meth)acrylic prepolymers obtained by the reaction of (meth)acrylic acid with diglycidic ether of bisphenol A (DGEBA) (precursor of epoxy resins) (see Section 16.6). The reaction can be catalyzed by amino or phosphonated bases... 

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