CTBN, carboxy-terminated

Figure 13.8 Fracture energy of epoxy networks cured with DDS (diamino dipheny sulfone) versus the initial DGEBA (diglycidyl ether of bisphenol A) ( ) neat systems ( ) with 10% CTBN (27% AN). Rubber = CTBN carboxy-terminated butadiene acrylonitrile random copolymer. (Pearson and Yee, 1989 with kind permission from Kluwer Academic Publisher.)... 

CTBN carboxy-terminated butadiene-acrylonitrile copolymer... 

CTBN carboxy-terminated butadiene nitrile rubbers... 

CTBN Carboxy terminated butadiene-acrylonitrile random copolymer... 

Abbreviations-. EPDM, ethylene-propylene-diene monomer (a copolymer elastomer) CTBN, carboxy-terminated butadiene nitrile (an elastomer prepolymer) ABS, acrylonitrile-butadiene-styrene (a complex latex structure used both independently and to toughen other polymers) SBR, styrene-butadiene rubber (an elastomer). 

Carboxy-terminated curative, such as CTBN, provides excellent toughening in part due to its miscibility in many epoxy resins. Phase separation during cure is required to obtain toughening, and generally the phase separation requires an elevated-temperature cure. However, by prereacting the CTBN with a portion of the epoxy to obtain an adduct, a room temperature curing toughened epoxy is possible. Adduction reduces the likelihood of early phase separation and maintains the solubility of the elastomer in the uncured resin system. 

The separate phases will be rich in one component but may have the other present as a minor component. In order to control compatibility the elastomer may have reactive end groups to enhance interfacial adhesion. A common example in epoxy-resin technology is the carboxy-terminated butadiene-acrylonitrile copolymer (CTBN). The structure is shown in Scheme 1.47. In this resin the solubility in the epoxy resin is conferred by the acrylonitrile group, and an increase in the fraction present decreases the upper critical solution temperature, with 26% acrylonitrile conferring total miscibility of CTBN with a DGEBA-based epoxy resin (Pascault et al, 2002). 

The incorporation of elastomers into epoxy resins has been an active area of research over the past decade (1-11). The primary reason for this interest has been the improved toughness of the modified materials. We have limited our work to the carboxy-terminated butadiene-acrylonitrile copolymers (CTBN) produced by... 

Thus, with two equations and two unknowns, a unique solution to X and Y can be calculated. Carboxy-terminated copolymers of butadiene and acrylonitrile (CTBN) can be incorporated into the epoxy resin through a simple esterification reaction. One equivalent of carboxylic acid is esterified by one equivalent of epoxide. This reaction is again catalyzed by triphenylphosphine. Since, for our reactions, the limiting reagent in the esterification is the CTBN elastomer, the product is an elastomer capped with an epoxy resin. The epoxy terminated rubber is then capable of reacting in the usual manner with curing agents or in the previously discussed advancement reaction (Reaction Scheme 2). 

Thermoplastic rubber block copolymers, with completely new adhesive performance, were developed in 1965 [21]. The first commercial product was Shell Chemical s Kraton 101, of styrene polybutadiene-styrene composition. This development led to the carboxy-terminated nitrile (CTBN) rubber modifiers used to flexibilize epoxy and other brittle resin adhesives in the late 1960s. Today, the thermoplastic rubber block copolymer adhesives are used in hot melt-, solvent- and water-based adhesives, and as hot melt- and solvent-based sealants. Major applications are as pressure-sensitive adhesives, construction adhesives and sealants, and general assembly adhesives. 

The B. F. Goodrich Chemical Company produces monopolymers and copolymers with acrylonitrile. These are known as the Hylar series. Acrylonitrile increases the viscosity and imparts oil resistance, adhesion, and compatibility with epoxy resins. Carboxy-terminated butadiene-acrylonitrile copol)uner (CTBN) improves impact strength, low-temperature shear strength, and crack resistance in epoxy formulations. 

Amine-cured epoxy resins are extensively used as structural matrices in composite manufacture and as such the improvement of their mechanical properties is very desirable. As in the case of polystyrene the addition of a rubber phase provides an energy dissipation mechanism below and this increases the toughness of the overall material. Carboxy-terminated butadiene acrylonitrile (CTBN) is initially soluble in the reaction mixture of digylcidyl ether of bisphenol A (DGEBA) and the low-temperature cure system triethylenetetra-amine (TFTA) ... 

Thermoset epoxy resins were toughened by small elastomeric inclusions of a carboxy terminated butadiene-acrylonitrile (CTBN) random copolymer by Visconti and Marchessault [198], who showed the variation in size as a function of CTBN content by TEM and light scattering. A major study of rubber modified epoxy resins has been reported by Manzione et al. [202,203], who showed a range of morphologies which result in a range of mechanical properties, even for a single polymer. An amine cured rubber modified epoxy... 

Block copol3nners form a new class of molecular composite materials by the phase separation of incompatible hard and soft segments which form their macro-molecular structure. Thermoplastic elastomers where the soft segments form the continuous phase have been extensively investigated by means of an adsorption-interdiffusion (A-I) model for the interfacial phase which bonds the hard and soft phases. The molecular structure and rheological activity of the interfacial phase in thermoplastic elastomer block copolymers is shown to play a dominant role in nonlinear viscoelastic response, mechanical hysteresis and energy absorption. Creation of elastomeric microphases in epoxy structural adhesives has been recently identified with in situ block copol3nnerization between carboxy terminated nitrile (CTBN) rubber and the diepoxide. 

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