Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1987-10-05
1990-08-07
Carrillo, Ana L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525181, 525184, 525426, 526262, C08L 7908, C08F 2240
Patent
active
049469070
DESCRIPTION:
BRIEF SUMMARY
This invention relates to thermosetting imide resin compositions containing elastomers, to methods of preparing these compositions, and to elastomer-toughened polyimides cured from these compositions. In particular but not exclusively, this invention is concerned with the elastomer-toughening of addition-type polyimides which are produced from the polymerisation and crosslinking of bismaleimide prepolymers.
Thermoset polyimides are organic polymers which in general have very high thermal and oxidative stabilities. They are used in a number of industrial applications, especially as adhesives and structural composites. Most polyimides fall within the category of addition-type or condensation-type polymides according to the type of polymerization reaction which produces them from their prepolymer constituent or constituents. Condensation-type polyimides are generally produced from dianhydrides and diamines via the formation of a soluble polyamic acid precursor. The formation of the polyimide from the polyamic acid is known as cyclodehydration and entails the liberation of water which, under the reaction conditions, is liberated as a vapour which can create voids in the polymer. Addition-type polyimide prepolymers are cured by an addition reaction which overcomes the problem caused by volatile evolution of water, and thus addition-type polyimides possess a significant advantage over condensation type polyimides.
One disadvantage of addition-type polyimides however is that they depend to a large degree on a highly crosslinked structure for high temperature capabilities, which structure can result in brittle behaviour. Some of the more brittle addition-type polyimides have been toughened by the chain extension of the imide prepolymer molecules, which has resulted in the polyimides cured therefrom having more open flexible molecular structures than their unmodified, brittle counterparts. However, this increase in toughness has usually been found to be offset by a major reduction in other desirable properties of the polyimides, such as glass transition temperature, thermal stability and mechanical strength, because chain extension of the prepolymer reduces the density of inter-molecular cross-links in the polyimide structure.
Attempts have been made to improve the toughness of addition-type polyimides by the addition of elastomers. St Clair et al (Int J Adhesion, Jul. 1981 page 249) reported an up to 5 fold increase in the toughness (in terms of increased fracture energy) of an addition-type polyimide prepared from a bisimide prepolymer having nadic end groups, by the addition of either aromatic amine-terminated butadiene/acrylonitrile (AATBN) or aromatic amine-terminated silicone (AATS) to the prepolymer. However, one disadvantage of using either of these two elastomers is that they do not appear suitable for toughening some other types of addition-type polyimides. Gollob et al (Massachusetts Institute of Technology School of Engineering Research Report R79-1, August 1979) reported that the toughness of a bismaleimide-type polyimide was little changed by the addition of either of these two elastomers to the bismaleimide prepolymer prior to curing.
It is one object of the present invention to provide a novel method for preparing an elastomer-toughened polyimide whereby the above disadvantage is overcome or at least mitigated in part.
According to the present invention there is provided a method for preparing a curable thermosetting prepolymerised imide resin composition which comprises chemically reacting, at a temperature below 150.degree. C., a liquid mixture of a carboxy-terminated polybutadiene-acrylonitrile (CTBN) and a co-reactant comprising formula I ##STR2## wherein B represents a divalent radical containing a carbon-carbon double bond and A represents a divalent radical having at least two carbon atoms, or general fromula I and at least one primary organic diamine or organic hydrazide, or formula I, at least one monoimide, and at least one organic hydrazide, containing copolymerised CTBN and co-reactant,
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Kinloch Anthony J.
Shaw Stephen J.
Carrillo Ana L.
The Secretary of State for Defense in Her Britannic Majesty's Go
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