Preparation of polymer brushes on palygorskite surfaces via RAFT polymerization

https://doi.org/10.1016/j.reactfunctpolym.2007.10.035Get rights and content

Abstract

Polymer brushes on palygorskite are successfully prepared by reversible addition fragmentation chain transfer polymerization (RAFT) technique using palygorskite as a RAFT chain transfer agent (CTA) support. The dithioester groups are introduced onto the palygorskite surface and methyl methacrylate (MMA) polymerization is performed in the presence of palygorskite supported benzyl dithiopropyltrimethoxysilane (P–Si-BDPM) which is used as chain transfer agent (CTA). The observed narrow molecular weight distributions (Mw/Mn), linear kinetic plots and linear plots of molecular weight (Mn) versus conversion for the free polymer formed in solution indicate that the chain growth from the palygorskite surface is a controlled process with a “living” characteristic. The microstructures are studied by FT-IR, Scanning probe microscope (SPM) and X-ray photoelectron spectroscopy (XPS).

Introduction

Recently, the polymer/inorganic nanocomposites [1], [2], [3], [4] has gained great attention as their excellent properties, such as mechanical properties, thermal stability and flame retardance, gas barrier properties, biodegradation and abrasion resistance [5], [6], [7], [8]. The inorganic particles’ surface modification is a kind of typical method to prepare polymer/inorganic hybrid materials. There are two ways to attach the polymers chains to surface of the inorganic particles [9], [10], [11]: “grafting to” and “grafting from” techniques. In the “grafting to” method, the end-functional polymer chains react with the surface groups on the substrate. The disadvantage of this method is the reactivity and surface graft densities of the polymer chains are lower. In the “grafting from” method, a variety of polymers can easily graft from the surfaces of the inorganic particles with a higher graft density.

In order to prepare well-defined polymer brushes on inorganic particles’ surface via “grafting from” technique, controlled “living” radical polymerization has been employed. Atom transfer radical polymerization (ATRP) [12], [13], [14], [15] and reversible addition-fragmentation chain transfer (RAFT) polymerization [16], [17], [18], [19] are typical methods of controlled/living free radical polymerization. Huck’ group prepared a series of the controlled growth of P (OEGMA) brushes on silicon wafer via ATRP [20]. While ATRP systems are currently limited to monomers that do not strongly coordinate to the catalyst, some specific conditions for the reaction are needed and still difficult to use as a common method of surface modification [21]. Recently, Perrier [22], Benicewicz [23] and Boys’ groups [24] applied RAFT techniques to synthesize block copolymers on silicon or silica substrate, which afforded well-controlled polymer brushes.

Palygorskite is a kind of natural nanoparticle with abundant in west of China. It is easily to be modified [25]. In this study, palygorskite was used as inorganic substrate to prepare well-controlled polymer brush from its surface by RAFT polymerization and provided evidence of the effectiveness of modified palygorskite as CTA in AIBN-initiated MMA RAFT polymerization.

Section snippets

Materials

Palygorskite was purchased from Gansu Lintao, China. The Si–OH on the palygorskite surface was activated before use. Methyl methacrylate (MMA) (AR, Shanghai Chemical Reagent Plant) was washed with 10% NaOH and ion-free water, stirred over CaH2 and distilled under reduced pressure prior to use. (3-Chloropropyl)trimethoxysilane (97%, from ABCR GmbH & Co. KG) and all the other solvents were used as received.

The activation of the Si–OH on the palygorskite surface

The activation process was as following: 2 g of palygorskite were added into 20 mL of HCl

Immobilization of the RAFT agent on the palygorskite surface

To prepare the polymer brushes from the palygorskite surface by a RAFT technique, the immobilization of the thiocarbonylthio compounds on its surface is indispensable. The reaction schemes are illustrated in the schematic diagrams of Fig. 1. The presence of RAFT agent attached to the palygorskite surface is detected by XPS measurements (Fig. 2). From Fig. 2, we can see there are five characteristic signals, which are assigned to O1s, C1s, S2p, Si2p and Al2p. In addition, the characteristic

Conclusion

This study reports a new method to prepare controlled molecular weight and low polydispity organic/“inorganic” hybrid. The composition of the RAFT agents is determined by the XPS. The FT-IR and SPM analysis of the P-g-PMMA indicates that the PMMA have been “grafted from” the modified palygorskite and the TGA assesses the organic content of the materials. The GPC results show the RAFT polymerization is a controlled/“living” polymerization. The new method can broaden the route to various surface

Acknowledgment

The project was supported by the Natural Science Foundation of China (No. M03325005) and Key Laboratory of Eco-Environment-Related Polymer Materials (Northwest Normal University).

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