1  US 6,555,628 B2  2  EPOXY RESINS AND PROCESS FOR  MAKING THE SAME  BACKGROUND OF THE INVENTION  DETAILED DESCRIPTION OF THE  INVENTION  SUMMARY OF THE INVENTION  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  In one aspect, the present invention is a controlled con› version epoxy resin  (CCR  resin) containing both epoxy and  As used herein, the term "functionality" refers to the  average number of epoxy groups per resin molecule.  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.  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.  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.  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.  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 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.  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.  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.  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.  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.  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.  This application claims the benefit of U.S. Provisional  Application No. 60/255,649, filed Dec. 14, 2000.  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:  H  H  I  I  -C-CH  \/  0 