Carbon nanotubes bearing imide groups for anionic polymerization of ε-caprolactam

Abstract

Acyllactam groups and aromatic polyimides were grafted to the surface of single walled carbon nanotubes. The modified nanotubes were characterized by X ray photoelectron spectro scopy, scanning electron microscopy, thermogravimetric analysis, and elemental analysis. It was shown that the nanotubes with grafted acyllactam groups or polyimide macromolecules form homogeneous stable in time dispersions in a melt of  caprolactam.Efficience of using carbon nanotubes (CNTs) for the design of polyfunctional polymer materials mainly depends on the uniformity of the filler distribution in the polymer bulk and on the adhesion interaction of the CNT surface with the polymer matrix. 1-3 Functional groups grafted to CNTs provide a uniform dispersion of the latter in the solvent 4-6 or polymer 5,7 and also can favor the forma tion of a covalent bond with the polymer matrix, 8,9 which substantially affects the properties of the final nanocom posites. 10-14Polycaproamide (PCA) is a commercial polymer with high strength, tribological, and other performance char acteristics. Therefore, it is of considerable interest as an engineering plastic. The synthesis of PCA filled with CNTs was considered in a set of publications, 15-19 but only some of them report  caprolactam (CL) polymerization via the anionic mechanism using low molecular weight activa tors. 20,21 Meanwhile, the activated anionic polymeriza tion of  caprolactam (AAPCL) characterized by relative ly mild temperature conditions provides the high quality product by the method of reaction molding, which is most preferential for manufacturing engineering materials. 22 Recently, we have shown 23,24 that the introduction of 0.1-5 wt.% multiwalled CNTs into PCA at the stage of its synthesis substantially improves its thermal, strength, and tribological characteristics. It can be assumed that a more significant effect will be achieved by covalent bonding of the nanotube surface with the polymer ma trix. Nevertheless, the most methods for the preparation of PCA nanocomposites imply the improvement of the dispersability of CNTs in CL and PCA rather than the enhancement of the interaction between the matrix and filler. 25- 27 We discovered the activating effect on AAPCL of poly imides (PI) soluble in a CL melt that require no special functionalization. 28-30 This discovery stimulated us to de velop methods for synthesis of three component compos ites based on PCA and CNTs with grafted PI macromole cules. This approach will facilitate the covalent bonding of the PCA matrix with the filler. It should be noted that aromatic PI used by us are characterized by good solubili ty in a wide range of available organic solvents and in a series of monomers and high thermal and mechani cal characteristics 31 and thus favor the preparation of PCA co PI that significantly exceed homo PCA in ther mal and water resistance, impact strength, and other per formance parameters. 32, 33 To improve uniformity of the CNT distribution in the CL bulk and the subsequent covalent bonding with PCA, we functiona...

Effect of single-walled carbon nanotubes with imide cycles on the synthesis and properties of polycaproamide

“…It was shown in [39] that the dispersions of 0.001-0.1 wt % nanotubes with grafted acyllactam groups or PI macromolecules treated with ultrasound for 1 h in a CL melt are stable for 20 h, as opposed to systems with intact single-walled CNTs, which are stable against aggregation for 30 min at most. However, the addition of a polymerization catalyst, MgBrCL, to CNT dispersions substantially decreases the stability of systems containing functionalized single-walled CNTs.…”