Carboxyl-terminated copolymer

Carboxyl-terminated copolymer of butadiene and acrylonitrile CTBN, Goodrich company... 

To the vinylester resins, thixotropic agents are added, for example silica fume (silicon dioxide in microspheres, which is a by-product of the glass industry), to obtain a behaviour adequate to their use also in open moulds. In addition, to improve their toughness, CTBN polymers (carboxyl-terminated copolymers of butadiene and acrylonitrile) are widely employed as reactive modifiers. This occurs since the CTBN-modified vinylester oligomers act as compatibilizers for blending additional butadiene copolymer (Burchill and Pearce, 1996). 

Figure 2 The chemical structure of a carboxyl-terminated copolymer of butadiene-acrylonitrile (CTBN).

To illustrate the specific operations involved, the scheme below shows the first steps and the final detachment reaction of a peptide synthesis starting from the carboxyl terminal. N-Boc-glycine is attached to chloromethylated styrene-divinylbenzene copolymer resin. This polymer swells in organic solvents but is completely insoluble. ) Treatment with HCl in acetic acid removes the fert-butoxycarbonyl (Boc) group as isobutene and carbon dioxide. The resulting amine hydrochloride is neutralized with triethylamine in DMF. 

This paper discusses the three butadiene prepolymers which have been used most extensively in solid rocket propellants—i.e., the copolymer of butadiene and acrylic acid (PBAA), the terpolymer of butadiene, acrylic acid, and acrylonitrile (PBAN), and the carboxyl-terminated polybutadiene (CTPB). Since the chemistry of all of these carboxyl-containing prepolymers is essentially the same, the discussion of butadiene propellants in this paper is concerned mainly with those based on CTPB. 

Piperidine and carboxyl terminated butadiene acrylonitrile copolymer (CTBN) at 75 °C. 

Rubber was a carboxyl-terminated butadiene-acrylonitrile copolymer. Mean diameter of rubber particles =1.6 pm. Rubber concentration was 15 phr, giving volume fraction of 0.18 4 Containing vf (glass) = 0.1 rubber = 15 phr... 

A 3300 molecular weight carboxyl terminated 80-20 butadiene-acrylonitrile random copolymer designated CTBN (I) (Figure 3). 

It is obvious from these data that CTBN (the carboxyl terminated butadiene-acrylonitrile copolymer) is the most effective modifier, and therefore it was selected for further study. As the concentration of the elastomer was increased to levels up to 100 parts, the impact also increased. The data in Table II show that the room temperature impact of ERL-4221 increased from 40 inch-lbs to greater than 320 inch-lbs by adding 100 phr or 33 wt % of CTBN. At very low temperatures ( —160°F) the impact of the system modified with 60 parts, or 23 wt %, of CTBN was 120 inch-lbs. These impact improvements appear to be directly proportional to the concentration of the elastomer modifier. 

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. 

Carboxyl-terminated butadiene-acrylonitrile copolymer, mentioned above, was found to have 4-cyanopentanoic acid end-group originating from 4,4,7-azobis(4-cyanopentanoic acid) initiator [32],... 

Epoxy-nitrile Nitrile-epoxy adhesives are composed of solid epoxy resin modified with carboxyl-terminated butadiene nitrile (CTBN) copolymer. The CBTN is introduced into die epoxy resin at elevated temperatures. The modification provides toughness and high peel strength without sacrificing heat and chemical resistance. The film adhesives are widely used in the aerospace industry in the construction of jetliners. 

The epoxy-nitrile adhesives were introduced commercially in the late 1960s. They consisted primarily of DGEBA epoxy resin modified with carboxyl-terminated butadiene nitrile (CTBN) rubber. These first nitrile copolymers were available from B.F. Goodrich under the trade name of Hycar. The most convenient form of epoxy nitrile adhesive, especially when one is bonding large parts (aircraft structures), is a supported film. However, solvent solutions of epoxy-nitrile adhesives have also been commercially available. 

However, newer adhesives systems having moderate temperature resistance have been developed with improved toughness but without sacrificing other properties. When cured, these structural adhesives have discrete elastomeric particles embedded in the matrix. The most common toughened hybrids using this concept are acrylic and epoxy systems. The elastomer is generally a amine- or carboxyl-terminated acrylonitrile butadiene copolymer (ATBN and CTBN). 

Materials. Hycar CTBN is a registered trade name of a carboxyl-terminated, liquid copolymer of butadiene and acrylonitrile (B. F. Goodrich Chemical Co.). For most purposes it can be represented structurally as ... 

Effect of Molecular Structure. Table III shows the effects of the molecular structure of the liquid polymer on the fracture energy of toughened systems. The CTIN is a carboxyl terminated isoprene-acrylonitrile copolymer CTBS is a carboxyl terminated butadiene and styrene copolymer, and CTA is a copolymer of ethyl acrylate-butyl acrylate. 

Fig. 13. TXT cure diagram temperature of cure vs. the times to phase separation (doud point), gelation and vitrification for a neat and two rubber-modified systems. of the neat system is also included. The systems studied were DER331/TMAB O, gelation , vitrificaticm modified with IS parts rubber per hundred parts epoxy 1) pr eacted carboxyl-terminated butadiene-acrylonitrile (CTBN) copolymer containing 17% acrylonitrile (K-293, Spencer Kellog Co.) A, phase separation , gelation , vitrification, and 2) polytetramethylene oxide terminated with anmiatic amine (ODA2000, Polaroid Corp.) A. phase separation O, gelation O, vitrification. (DER331/TMAB/ K-293 data from Ref. )...

The hydroxytelechelic polybutadienes also can be reacted with epoxides and maleic anhydride 236,258) with carboxyl-terminated polystyrenes194 , or with a,[Pg.218]

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