End-tethered

The rheological properties of insitu polymerized nanocomposites with end-tethered polymer chains were first described by Krisnamoorti and Giannelis [33]. The flow behavior of PCL- and Nylon 6-based nanocomposites differed extremely from that of the corresponding neat matrices, whereas the thermorheological properties of the nanocomposites were entirely determined by the behavior of the matrices [33]. The slope of G (co) and G"(co) versus flxco is much smaller than 2 and 1, respectively. Values of 2 and 1 are expected for linear mono-dispersed polymer melts, and the large deviation, especially in the presence of a very small amount of layered silicate loading, may be due to the formation of a network structure in the molten... 

F. J. Medellin-Rodriguez, C. Burguer, B. S. Flsiao, B. Chu, R. Vaia, S. Phillips, Time-resolved shear behavior of end tethered nylon 6-clay nanocomposites followed by non-isothermal crystallization, Polymer, vol. 42, pp. 9015-2023, 2001. 

Investigation of the Behavior of End-Tethered Weak Polyelectrolytes in Ionic Solutions Using Grafting Density Gradients... 

Thus, fundamentally the interest is in testing the limits and theory of polymer behavior in end-tethered systems, e.g., viscoelastic behavior, wetting and surface energies, adhesion, shear forces relevant to tribology, etc. It should be noted that relevant surfaces and interfaces can also refer to polymers adsorbed in liquid-liquid, liquid-gas, solid-gas, and solid-liquid interfaces, which makes these polymer systems also of prime importance in interfacial science and colloidal phenomena (Fig. 2). Correspondingly, a wide number of potential applications can be enumerated ranging from lubrication and microelectronics to bioimplant surfaces. 

Krishnamoorti R, Giannelis EP (1997) Rheology of end-tethered polymer layered silicate nanocomposites. Macromolecules 30 4097-4102... 

Rheology of various polymer layered-silicate nanocomposites - intercalated, exfoliated and end-tethered exfoliated (prepared by in-situ polymerization from reactive groups tethered to the silicate surface), have been performed in a conventional melt-state rheometer in both oscillatory and steady shear modes. These experimental studies have provided insight into the relaxation of polymer chains when confined by the layers of inorganic silicates, as well as the role of shear in orienting the layered nanocomposites. 

In addition, two end-tethered delaminated hybrid systems prepared by in-situ polymerization - (a) Poly( -caprolactone)-montmorillonite (PCLC) and (b) nylon-6-montmorillonite (NCH) - wherein the polymer chains are end-tethered to the silicate surface via cationic surfactants [54] (Fig. 20), were also studied. 

Fig. 20. Schematic diagram describing the end-tethered nanocomposites. The layered silicates are highly anisotropic with a thickness of lnm and lateral dimensions (length and width) ranging from -100 nm to a few microns. The polymer chains are tethered to the surface via ionic interactions between the silicate layer and the polymer-end. Adapted from Ref. [54].

The linear viscoelastic measurements of the end-tethered nanocomposites reveal several features unique to these materials. Time-temperature superposi-... 

Recently we have conducted rheological experiments wherein the end-tethered PCL nanocomposites were blended with pure PCL homopolymer. Rheological behavior, particularly the terminal zone slopes, obtained for 5% and 10% (obtained by blending equal weight fractions of PCL homopolymer with a 10 weight % PCL and 20 weight % PCL respectively) were found to be similar to those obtained from the as-prepared nanocomposites. 

Jin, L., Horgan, A. and Levicky, R. Preparation of end-tethered DNA monolayers on siliceous surfaces using heterobifunctional cross-linkers. Langmuir, 2003, 19 (17), p. 6968-6975. 

The mechanical properties of the C3, C6, and Cl2 nanocomposites were all significantly better than those of the neat phenolic resin, even if a very small amount of the silicate was used. Among the nanocomposites prepared, the organically modified MMT-resol systems showed better mechanical properties than those of the unmodified MMT-resol system. This improvement was attributed to the formation of an end-tethered structure due to the reaction of the carboxylic acid of the organic modifier with the methylol group of the phenolic resin. Thermogravimetric analysis reported by Byun and coworkers showed that the nanocomposite systems had similar thermal stability to that of the neat polymer. 

Fig. 14 Plot of ln(D/Do) vs Amin/Ay, for n = 30, 50 in diffusion Region II. The dashed and solid lines represent the best linear fits for n = 30 and n = 50, respectively. The excellent agreement between data points and fits shows that D of end-tethered PMOx chains in diffusion region II is well described by the free area model [31] (reproduced with permission from the American Chemical Society)...

Krishnamoorti, R., and Giannelis, E. P., Rheology of end-tethered polymer-layered sihcate nanocomposites. Macromolecules, 30, 4097 102 (1997). 

Huang, C. R, Kuo, S. W., Lin, R J., Huang, W. Wang, C. R, Chen, W. Y., and Chang, R C. 2006. Influence of PMMA-chain-end tethered polyhedral oligomeric silsesquioxanes on the miscibility and specific interaction with phenolic blends. Macromolecules 39 300-308. 

The modified montmorillonite prepared by cation exchange reaction with 12-aminolauric acid can chemically react with caprolactum molecules and makes the caprolactum polymer chain ends tethered to the silicate layers through the 12-aminolauric acid [41-42]. A. similar method has been used to prepare polyamide-6 nanocomposites [8,43-46]. 

Baneijee et al. [107] prepared polyimide-POSS (PI-POSS) nanocomposite membranes applying thermal imidization. At first, poly(amic acid)s were generated by the reaction of several diamine monomers, namely 4,4-( w[3 -trifluoromethyl-4 (4 -aminobenzo xy)benzyl]biphenyl l,4- w[3 -trifluoromethyl-4 (4 -aminobenzoxy)benzyl]benzene 2,6-te[3 -trifluorom ethyl-4 (4 -aminobenzoxy)benzyl]pyridine and 2,5 - w[3 -trifluoromethyl-4 (4 -aminobenzoxy)benzyl] thiophene with 6FDA as the dianhydride and 2 wt% POSS-NH2 as the nanofiller. The structure of poly(amic acid) intermediate, which was thermally imidized to form polyimide chain end tethered POSS, is shown in Scheme 6.25. 

Scheme 6.25 Structure of poly(amic acid) intermediate, which was thermally imidized to form polyimide chain end tethered POSS. Reproduced with permission from Ref. [107],...

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