Characteristics of the surface modification of montmorillonite with a bifunctional block copolymer

Abstract

A bifunctional polystyrenic block copolymer with 4-vinyl pyridine (4VP) units in one block and pendant methacrylate units in the other block (MMSP) was prepared and employed as a surface modifier for montmorillonite (MMT). The interaction of the 4VP units with the surface of MMT layers was examined by using spectroscopic methods. X-ray diffraction spectroscopy data exhibited an increase in the interlayer spacing (D value) of MMSP-MMT with an increased amount of MMSP, confirming the high reactivity of 4VP units and the effective intercalation of MMSP to MMT (MMSP-MMT). In a Fourier transform infrared spectroscopy study, linear shifting and a narrower band width of the SiAOASi stretching vibration with increased MMSP content indicated effective intercalation and surface modification processes. With an increased amount of MMSP, the relative amount of free pyridyl units to pyridinium units increased, indicating plausible saturation of the MMT surface at high MMSP content. POLYM. COMPOS., 34:1640COMPOS., 34: -1647COMPOS., 34: , 2013. V C 2013 Society of Plastics Engineers INTRODUCTIONSurface modification, which is one of the most effective methods for designing and tuning the properties of materials, has been successfully applied to change the hydrophilic properties of the layer surfaces of montmorillonite (MMT). The resulting hydrophobic nature of MMT leads to enhanced miscibility with polymer matrices, affording successful polymer-clay nanocomposites [1]. The favorable interaction between the MMT layers and polymer hosts plays an important role in delaminating ordered layers of the clay galleries into individual disordered nanometer scale layers, which homogenously disperse in polymer matrices [2,3].However, the choice of a suitable surface modifier among the various commercially available products is often limited because there are few variations in their structural and compositional characteristics. Polymeric surface modifiers are often the best choices for broadening the spectrum of the surface modifier, especially to afford sufficient steric repulsion between the closely stacked layers [3][4][5][6][7]. Among the polymeric modifiers, a copolymer of styrene (St) with cationic comonomers such as chloromethylstyrene and maleic anhydride (MA) has been widely employed to facilitate the penetration of the copolymers into MMT layers [8][9][10][11][12].Although block copolymers (BCP) provide additional options in terms of molecular structure and functionality, relatively little attention has been given to the application and characteristics of BCPs [13][14][15][16][17]. For example, one block of the BCP can be designed to have specific interactions with the MMT surface, while the other block acts as a spacer to increase the interlayer distance, allowing efficient and tailored surface modification behavior of MMT [18]. Selected functionality can also be introduced to the BCP to cause a specific interaction or reaction with the polymer host. A representative example is a BCP composed of poly(4-vinyl pyridine) (P4VP) and po...