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This application claims the benefit of U.S. Provisional Application No. 60/255,649, filed Dec. 14, 2000. 

This invention relates to controlled conversion epoxy resins, hereinafter referred to as CCR resins, to a process for preparing said resins and to compositions containing these resms. 

High molecular weight epoxy resins are generally pre› pared by a two-step process wherein a lower molecular weight epoxy resin is prepared initially by reacting a poly› hydric phenol with epichlorohydrin and alkali metal hydrox- ide in the presence of a catalyst. Thereafter, the initial polyepoxide reaction product is advanced by its reaction with additional amounts of polyhydric phenol to form the higher molecular weight material. In conventional tech› niques for preparing the epoxy resins, the reaction of the polyepoxide and polyhydric phenol is typically carried out to complete conversion such that the final, advanced epoxy resin, also known as fully advanced resin, contains relatively low amounts of residual phenolic hydroxyl groups. For example, epoxy resins having an EEW ( epoxy equivalent weight) between about 500 and about 700 prepared from bisphenol A and the diglycidyl ether of bisphenolA typically contain less than about 800 parts per million of phenolic hydroxyl groups which represents more than about 98 percent conversion of the phenolic hydroxyl groups employed in preparing the epoxy resin. A higher molecular weight epoxy resin having an EEW from greater than about 2000 to about 4000 typically contains less than about 2500 ppm of phenolic OH groups which represents more than about 95 percent conversion of the phenolic hydroxyl groups. Any residual hydroxyl groups in the advanced resin have been stated to cause viscosity instability of the result› ing resin mixture, particularly at elevated temperatures. 

Controlled conversion epoxy resins (CCR resins) are known and are described, for example, in U.S. Pat. No. 4,722,981, incorporated herein by reference. As described in this patent, CCR resins have improved cure rate over stan› dard fully advanced resins. The cure rate of CCR resins has been further improved by increasing its functionality through the addition of a multi-functional phenol epoxy novolac to the CCR resins as described in copending U.S. patent application Ser. No. 08/875,969, filed Feb. 10, 1995. Since multi-functional phenol epoxy novolac resins usually have a lower softening point than the CCR resins, addition of novolac resins to CCR resins tend to decrease the soft- ening point of the CCR resins. 

Copending U.S. patent application Ser. No. 60/213,965, filed Jun. 23, 2000, describes increasing the functionality of fully advanced resins by using acid anhydride as a branching agent. The resulting product has increased viscosity com- pared to the standard fully advanced resin and standard CCR resm. 

It would be desirable to provide a process for preparing CCR resins with increased functionality, and thus, cure rate, without lowering its softening point or increasing its vis- cosity. 

As used herein, the term "functionality" refers to the average number of epoxy groups per resin molecule. 

In one aspect, the present invention is a controlled con› version epoxy resin (CCR resin) containing both epoxy and 

# EPOXY RESINS AND PROCESS FOR MAKING THE SAME 

## BACKGROUND OF THE INVENTION 

## SUMMARY OF THE INVENTION 

terminal hydroxyl groups and having an epoxy functionality of greater than 2 and comprising moieties derived from an epoxy resin and a dihydric phenolan acid anhydride, or an amine. 

By the term "epoxy group" it is meant a radical of the following structural formula: 

having an equivalent weight of 43 and by the term "terminal hydroxyl group" it is meant a terminal hydroxyl group having an equivalent weight of 17. For the purposes of this invention, the percent epoxy groups and the terminal phe› nolic hydroxyl groups in the CCR resin reaction product are determined by the methods described in U.S. Pat. No. 4,722,981, Footnotes 1 and 2, respectively, the descriptions incorporated herein by reference. 

In a second aspect, the present invention is a process for preparing the CCR resin of the first aspect which comprises branching an epoxy resin by reacting a liquid epoxy resin and a dihydric phenol with an acid anhydride or an amine in the presence of a catalyst and terminating the reaction at a point such that the reaction product contains both epoxy and terminal hydroxyl groups, the acid anhydride being employed in an amount sufficient to achieve the desired epoxy functionality but insufficient to form gels in the anhydride-modified epoxy resin. 

The present reaction can be done in one step wherein a liquid epoxy resin (LER), anhydride, dihydric phenol and catalyst are reacted and the reaction terminated at a point such that the reaction product contains both epoxy and terminal hydroxyl groups. 

Alternatively, the liquid epoxy resin and the dihydric phenol are reacted first and then the anhydride is added or, the LER and anhydride are reacted first, and then the dihydric phenol is added to the reaction and the reaction terminated at a point when the reaction product contains both epoxy and terminal hydroxyl groups. 

The reaction can be done using a batch process or a continuous process conducted in a reactive extruder, such as that described in European Patent No. EP 0193809. 

In preparing the CCR resins, the dihydric phenol, the acid anhydride and the epoxy resin components are contacted in the presence of a catalyst for the reaction between the hydroxyl groups of the dihydric phenol or the acid anhydride groups and the epoxy groups of the epoxy resin and at conditions sufficient to form the desired CCR resin. Preferably, this reaction is conducted neat, i.e., in the absence of any reaction diluent. 

Although not preferred, the reaction of the dihydric phenol, acid anhydride and epoxy resin components can be conducted in the presence of a reaction diluent. If employed, the reaction diluent is preferably a solvent for or miscible with both the dihydric phenol, acid anhydride groups and the epoxy resin. Representative solvents which can be employed include various glycol ethers such as ethylene or propylene glycol monomethylether and esters thereof such as ethylene glycol monoethylether acetate; ketones such as methylisobutylketone, methylethylketone and acetone; and aromatic hydrocarbons such as toluene, xylene or mixtures 

## DETAILED DESCRIPTION OF THE INVENTION 

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