Toughening agents butadiene copolymers

The homopolymers, which are formed from alkyl cyanoacrylate monomers, are inherently brittle. For applications which require a toughened adhesive, rubbers or elastomers can be added to improve toughness, without a substantial loss of adhesion. The rubbers and elastomers which have been used for toughening, include ethylene/acrylate copolymers, acrylonitrile/butadiene/styrene (ABS) copolymers, and methacrylate/butadiene/styrene (MBS) copolymers. In general, the toughening agents are incorporated into the adhesive at 5-20 wt.% of the monomer. 

The term acrylonitrile-butadiene-styrene copolymer (ABS) is used very broadly to define an important class of thermoplastic materials of which there are many different grades. These materials are used extensively in electrical a pliances, in the building and construction industries and in automotive componoits. Certain grades of ABS also find use as toughening agents in blends with other polymers, for example polycarbonates and polyamides (see Sections 19.8 and 19.9.3). 

With very densely crosslinked polymers, rubbers are ineffective as toughening agents. Thermoplastic additives are used instead, such as polyethersulphones, polyamides and polyetherimides. Like the butadiene-acrylonitrile copolymers mentioned above, the sulphone additives can be fimctionalised with hydroxyl or amine end-groups. 

Treverton, J.A., Paul, A.J. (1995) A TOF-SIMS study of an acid-terminated butadiene-acrylonitrile copolymer used as a toughening agent in modem adhesive formulations. Int. J. Adhes. Adhes., 15,237-248. 

Low molecular weight polybutadiene and butadiene-acrylonitrile copolymers terminated with carboxyl, vinyl, amine, epoxy, phenol, and hydroxyl groups have been widely used as toughening agents both for epoxy and polyester resins. Thermally reactive isoprene-acrylonitrile and ethylacrylate-butylacrylate copolymers have also been used [82,83]. 

Effect of Molecular Configuration of Elastomer. The extent of the impact and strength improvements of ERL-4221 depends on the chemical structure and composition of the elastomer modifier. The data shown in Table I indicate that the carboxyl terminated 80-20 butadiene-acrylonitrile copolymer (CTBN) is the most effective toughening and reinforcing agent. The mercaptan terminated copolymer (MTBN) is considerably less effective as far as tensile strength and heat distortion temperature are concerned. The mercaptan groups are considerably less reactive with epoxides than carboxyls (4), and this difference in the rate of reaction may influence the extent of the epoxy-elastomer copolymerization and therefore the precipitation of the rubber as distinct particles. 

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