Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-09-13
2004-04-06
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S064000, C525S065000, C525S066000, C525S068000, C525S069000, C525S070000
Reexamination Certificate
active
06716915
ABSTRACT:
The present invention relates to a method of toughening thermoset polymers through incorporation of comb copolymers.
It is well known in the art that articles formed by shaping and curing thermosetting polymers are often brittle. Cured thermoset polymers may, however, be toughened through incorporation of toughening agents commonly known in the art as impact modifiers. An impact modifier may, typically, be mixed with a thermosetting polymer to form a thermosetting blend. The thermosetting blend may then be caused (e.g., in a mold) to take the shape desired for the article, followed by curing to produce a thermoset article.
Typically, an impact modifier is a particulate polymer having one or more phases, wherein at least one of those polymeric phases is characterized by a glass transition temperature, Tg, below the envisioned use temperature of the article into which it is to be incorporated. Although not wishing to be bound by theory, it is thought that the dispersed low Tg impact modifier phase serves to distribute and dissipate the energy associated with a narrowly focused impact event.
Core-shell impact modifiers are used commercially to toughen thermoset polymers. These core-shell polymers exist as particles having a diameter (i.e., particle size) of characteristically from 0.1 to one micron. The core is made of a low Tg polymer (e.g., less than 0° C.) which is crosslinked. The core polymer is further not miscible with the thermoset polymer due to its composition and its state of crosslinking. As a result, it is necessary to provide the core with a shell made of a polymer that is miscible with the thermoset polymer. During processing, the miscible shell polymer, which may be grafted to the core polymer to some extent, interacts with the thermoset polymer to speed the break up of the larger powder particles (typically a few hundred microns in diameter) into much smaller core-shell particles (0.1-1 micron), and to enhance dispersion of the individual core-shell particles into the thermoset melt. In this way, thermoset articles are made that contain uniformly distributed core-shell particles, and hence rubbery core domains, throughout. While these core-shell polymers perform as impact modifiers for many thermosets, they are limited in that their crosslinked cores have only a single size and not all of the compatibilizing chains of shell polymer are attached to the core network. Thus, the shell polymer never fully realizes its potential to compatibilize the core polymer.
U.S. Pat. No. 5,506,320 discloses a reactive polymeric modifier for improving the toughness and/or flexibility of thermosetting resins where the polymeric modifier has a comb configuration including a saturated polymeric backbone having reactive groups at each end and at least one pendent chain which is miscible with the thermosetting resin prior to curing. It is a requirement of the disclosure the terminal groups be present, and that they be reactive with the thermosetting resin. The reactive terminal groups of the backbone are carboxy, hydroxy, amino, vinyl, or thio groups. For each thermosetting polymer, the terminal groups of the polymeric modifier are chosen to be reactive with functional groups of that particular thermosetting polymer. The disclosed comb copolymer has a number average molecular weight of 1,000 to 20,000, and its backbone is a polymeric chain of carbon-carbon linkages free of olefinic unsaturation, having a glass transition temperature in the range of −100° C. to 25° C. Unfortunately, the disclosure of U.S. Pat. No. 5,506,320 is limited in that any toughening of the thermoset article being produced is confined to that which may be produced by crosslinking of the very low molecular weight comb copolymer with the thermosetting polymer.
We have, surprisingly, found that thermosetting blends which include thermosetting polymers and comb copolymers can be shaped and cured to form thermoset articles that are toughened when compared with similar articles prepared from the corresponding thermosetting polymers absent comb copolymer. These comb copolymers have a number average molecular weight greater than 25,000 and a corresponding weight average molecular weight of greater than 75,000, and their ability to toughen thermoset polymers does not require that the comb copolymers bear reactive functionality. Furthermore, the backbone portions of the comb copolymers are immiscible in the thermosetting polymer, and hence form rubbery domains within the cured, thermoset article, providing enhanced toughening.
One aspect of the present invention relates to a method comprising the steps of:
(a) forming a thermosetting blend comprising a thermosetting polymer and a comb copolymer;
(b) shaping said thermosetting blend; and
(c) curing said thermosetting blend to form an article;
wherein said comb copolymer comprises a backbone and at least one graft segment;
wherein said forming comprises mixing and, optionally, heating; and
wherein said article has a fracture toughness at least 15 percent greater than that of a second article formed identically, absent the comb copolymer.
A second aspect of the present invention relates to an article comprising a thermoset polymer and a comb copolymer, wherein said article has a fracture toughness at least 15 percent greater than that of a second article formed identically, absent said comb copolymer.
A third aspect of the present invention relates to an article produced by the method of the first aspect of the present invention.
The thermosetting polymer of the present invention is a polymer selected from the group consisting of: acrylate polymer; polyester polymer; polyurethane polymer, epoxy polymer, vinyl ester polymer; unsaturated polyester; phenol-formaldehyde formaldehyde polymer, melamine-formaldehyde polymer, urea-formaldehyde polymer, and combinations thereof.
Used herein, the following terms have these definitions:
A “thermosetting polymer” is a resin that typically is of low enough molecular weight that it is a pourable liquid, yet has the capability of being transformed into a high molecular weight, often crosslinked, polymer that is no longer a liquid, nor even a melt processable thermoplastic polymer. The cured polymer is permanently set, and cannot be converted to a fluid melt by heating and mixing. The curing, or setting, of a thermosetting polymer may be accomplished by heating. This heating may serve to activate thermally labile functional groups attached to the thermosetting polymer, if such groups are present. Alternatively, heating may be done in the presence of catalysts, initiators, or combinations thereof. These initiators and catalysts may be thermally activated, photochemically activated, or both. When photochemical activation, e.g., exposure to ultra-violet light, is used, a photosensitizing material may be added. The curing process may further be accomplished through the reaction of functional groups on the polymeric chain of the thermosetting polymer with reactive functional groups on another polymer or other additive with which it may be combined. Further, multiple curing methods may be combined, and there may be a post-cure step as well, to assure that full curing has occurred. In some cases, heating may not be required to adequately cure the thermosetting polymer, or a portion of the curing may occur at room temperature, followed by a “post-cure” at an elevated temperature.
A “thermosetting composition” is a composition that includes a thermosetting polymer.
A “thermosetting blend” is a blend that includes a thermosetting polymer and at least one other component. A “thermosetting blend” is a type of a “thermosetting composition”. The “thermosetting blend” of the present invention is a blend including a thermosetting polymer and a “comb copolymer”. The thermosetting blend is, preferably a liquid at room temperature. However, heating may be required to make the thermosetting blend fluid enough so that it can be shaped into the shape of the desired article before or during curing, preferably before curing.
A “thermoset polymer” is a polyme
Lau Willie
Van Rheenen Paul Ralph
Clikeman Richard R.
Mullis Jeffrey
Rohm and Haas Company
LandOfFree
Method of forming toughened thermoset articles and toughened... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of forming toughened thermoset articles and toughened..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of forming toughened thermoset articles and toughened... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3235713