Molecular weight epoxide resins

Epoxynovolak resin and BPA/DC-BMI prepolymer, tert.butyl peroxide and Zn acetate [106, 107] or 2-phenylimidazole and other catalysts [108] were filled with wollastonite. Carbon-fiber reinforced composites were obtained using a binder, which consisted of BPA/DC, BMI, an epoxynovolak, 2-ethyl-4-methylimidazole and an organic solvent [109]. A BPA/DC-BMI prepolymer in methylethylketone was mixed with middle-molecular-weight epoxide resin (Epikote 1001), 2-ethyl-4-methyl-imidazole, Zn acetate and triethylenediamine thermal shock resistant GRP was thus obtained [110]. 

Figures 14 and 15 show the relations between the amount of iron arene initiator, the reaction enthalpy (AHj and the glass transition temperature Tg of the polymerized Bisphenol-A diglycidylether (cf. Table 2, structure I, x = 0.15) and the oligomer product based on the former compound (cf. Table 2, structure I, x = 11.8). The maximum polymerization heat per mole of epoxide is observed ivith an initiator concentration of 1.5-2.5% (w/w). At this concentration, Tg of the crosslinked resin is about 115 °C for the polymerized low-molecular-weight expoxide and about 80 "C for the polymerized high-molecular-weight epoxide resin.

As with polybasic carboxylic acids, phenols have not achieved significant importance as curing agents however, the reaction of phenols with epoxides is technologically important. For example, the reaction of blsphenols with the diglycidyl ethers of the bisphenol is used conimercially to prepare higher molecular weight epoxy resins (12). 

All of the above solid rubber-modified epoxy resins visually displayed clearly biphasic morphological properties (i.e., discreet rubber domains in a continuous epoxy matrix). If there is a reaction between a rubber moiety and an epoxide, it would best be studied in a homogeneous reaction mixture. Lower molecular weight epoxy resins are more compatible with CTBN elastomers and will form homogeneous solutions at elevated temperatures. Reaction of an epoxide with a reactive moiety contained in the elastomer, R, will most likely obey the following rate law ... 

Resin Average Molecular Weight Epoxide Equivalent Melting Point (°C)... 

Dow Plastics manufactures a range of Derakane epoxy vinyl ester resins and the simplest is made by reacting low molecular weight epoxides with either AA or MAA to produce a chain structure ... 

The viscosity of a resin system can be reduced by the addition of a diluent, which can be non-reactive (e.g. dibutyl phthalate, benzyl alcohol and furfuryl alcohol) or reactive (a low molecular weight epoxide, triphenyl phosphite or x-butyrolactone). The x-butyrolactone can, for example, act as a solvent for a catalyst system used in a solventless system and take part in the reaction. Diluents tend to be rather volatile and could be partially lost in cure systems operating under a vacuum. Flexibilizers can impart toughness but at the expense of mechanical properties, chemical resistance and heat resistance. 

Another type of soHd supetacid is based on perfluorinated resin sulfonic acid such as the acid form of Du Font s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid or soHd, high molecular weight petfluotoalkanesulfonic acids such as petfluotodecanesulfonic acid, CF2(CF2)qS02H. Such sohd catalysts have been found efficient in many alkylations of aromatic hydrocarbons (225) and other Friedel-Crafts reactions (226). 

Low molecular weight liquid nitrile rubbers with vinyl, carboxyl or mercaptan reactive end groups have been used with acrylic adhesives, epoxide resins and polyesters. Japanese workers have produced interesting butadiene-acrylonitrile alternating copolymers using Ziegler-Natta-type catalysts that are capable of some degree of ciystallisation. 

They have found use as hardeners-eum-flexibilisers for epoxide resins (see Chapter 26) and are of interest in the production of thixotropic paints and adhesives. Related higher molecular weight materials are tough and flexible and find use as hot melt adhesives (Versalons). 

Their main point of difference is that the phenoxies are of much higher molecular weight ( 25 000). The phenoxies are also said to be slightly branched. Like the epoxide resins they are capable of cross-linking via the pendant hydroxyl groups, in this instance by di-isocyanates and other agents. 

Since both phenol and acetone are available and the bis-phenol A is easy to manufacture, this intermediate is comparatively inexpensive. This is one of the reasons why it has been the preferred dihydric phenol employed in epoxide resins manufacture. Since most epoxide resins are of low molecular weight and because... 

Table 26.1 shows the effect of varying the reactant ratios on the molecular weight of the epoxide resins. ... 

Epoxy resins have a wide range of molecular weights (=1,000-10,000). Those with higher molecular weights, termed phenoxy, are hydrolyzed to transparent resins that do not have the epoxide groups. These could he used in molding purposes, or crosslinked hy diisocyanates or hy cyclic anhydrides. 

Polyamides (nylons) The main types of nylon are oil and petrol resistant, but on the other hand susceptible to high water absorption and to hydrolysis. There are a few solvents such as phenol, cresol and formic acid. Special grades include a water-soluble nylon, amorphous copolymers and low molecular weight grades used in conjunction with epoxide resins. Transparent amorphous polyamides are also now available. 

An homologous series of epoxy resins with constant epoxide equivalent weight and increasing branch concentration displayed increased melt viscosity and weight average molecular weight. 

Epoxy resins are made with a reaction producing a resin with a molecular weight between 350 and 6000. These resins are terminated with an epoxide group. Figure 5.4 illustrates a basic unhardened epoxy resin. 

A composition consisting of low-molecular-weight BPA/ECH epoxide resin, tetraethylenepentaamine as a curing agent and 25 % BPA/DC was suggested [73], A similar composition contains tetraethylammonium bromide and l-(2-cyanoethyl)-2-... 

If the resin chains are assumed to be linear with no side branching, and it is further assumed that an epoxy group terminates each end of the molecule, then the epoxide equivalent weight is one-half the average molecular weight of the epoxy resin. 

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