Modified phenol resins
Modified phenolic resins and processes for producing these are described, as also are phenolic-resin formulations which comprise the modified phenolic resins, and processes for producing these. Specific uses of appropriate phenolic resins and, respectively, phenolic-resin formulations, and the use of block copolymers for producing phenolic resins, are also described.
1. A phenolic resin with increased crosslinked density, comprising: a block copolymer, said block copolymer being a reaction product of a soft segment which is a liquid rubber with a hard segment which comprises aromatic units, wherein the phenolic resin is characterized by stable methylene bridges joined to said aromatic unit residue and formed by a chemical reaction of a phenolic compound with an aldehyde compound, such that the block copolymer is incorporated into the phenolic resin by way of increased crosslinking, wherein the proportion of block copolymer in the phenolic resin is from 0.5 to 15% by weight, based on the phenolic component wherein the phenolic resin is transparent and homogenous and exhibits no phase separation within 2 months at 8° C.
2. The stabilized phenolic resin of claim 1 , wherein the proportion of block polymer is from 4 to 6% by weight based on the phenolic component.
3. The phenolic resin as claimed in claim 1 , wherein the rubber has been selected from the group consisting of homopolymers of butadiene, copolymers of butadiene with acrylonitrile, carboxy-functional, amine-functional, or methacrylate-functional homopolymers of butadiene, carboxy-functional, amine-functional, or methacrylate-functional copolymers of butadiene with acrylonitrile, carboxy-functional or methacrylate-functional terpolymers of butadiene, acrylonitrile, and acrylic acid, carboxy-functional, epoxy-functional, hydroxy-functional, and acrylate-functional polybutadienes, isocyanate-functional liquid rubbers, and maleic-acid-grafted polybutadienes.
4. The phenolic resin as claimed in claim 1 , wherein the aromatic system has been selected from the group consisting of the condensates of epichlorohydrin and bisphenol, epoxidized novolaks, solid DGEBA resins, cresol-novolak epoxy resins, epoxidized cashew nut shell oils, tolyloxymethyloxirane, phenalkamines, and aromatic anhydrides.
5. The phenolic resin as claimed in claim 4 , wherein an epoxy equivalent of the block copolymer is more than 1000.
6. The phenolic resin as claimed in claim 4 , wherein an acid number of the block copolymer is less than 5.
7. The phenolic resin as claimed in claim 1 , wherein the phenolic component is selected from the group consisting of phenol; alkyl-substituted derivatives of phenol, halogen-substituted phenols, polyhydric phenols, phenolic melamine and polynuclear phenols.
8. The phenolic resin as claimed in claim 1 , wherein the aldehyde component is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, glyoxal, and furfural.
9. A stabilized phenolic resin obtained from liquid rubber, an aldehyde compound and a phenolic compound via a process which comprises the following steps:
reacting the liquid rubber, as a soft segment with a hard segment having reactive aromatic units to form a block copolymer with aromatic units;
reacting the phenolic component with the aldehyde component in a condensation reaction to form a phenol-aldehyde condensate, wherein said aromatic units when reacting with the aldehyde component are forming methylol groups that participate in the condensation reaction with the phenolic component and reaction of all phenol and aldehyde used to produce the phenolic resin takes place in the presence of the block copolymer;
incorporating the block copolymer into the phenolic resin by way of the methylol groups that are forming stable crosslinks through methylene bridges between the phenolic compound and the block polymer resulting in a stabilized phenolic resin, wherein the proportion of block copolymer in the phenolic resin is from 0.5 to 15% by weight, based on the phenolic component, wherein the phenolic resin is transparent and homogenous and exhibits no phase separation within 2 months at 8° C.
10. The phenolic resin as claimed in claim 9 , wherein the block copolymer is reacted without work-up, isolation, or purification wherein the two reaction steps proceed in a single reaction vessel.