Preparation of exfoliated graphite/polystyrene composite by polymerization-filling technique

doi:10.1016/S0032-3861(00)00819-3

Polymer

Volume 42, Issue 11, May 2001, Pages 4813-4816

https://doi.org/10.1016/S0032-3861(00)00819-3 Get rights and content

Abstract

A composite based on exfoliated graphite (EG) and polystyrene was prepared by a polymerization-filling technique. With augmentation of filled EG, the molecular weight of polystyrene in the resulting composite increased and the molecular weight distribution decreased. The glass transition temperature of the polystyrene was determined by dynamic mechanical analysis (DMA) and showed that it increases to 123.74°C. The thermal degradation behavior of the composite was studied using thermogravimetry (TG) and showed a higher thermal stability than that of pure polystyrene and polystyrene/EG composite prepared by melt-blending. The DC conductivity of the composites prepared by the polymerzation-filling technique and melt-blending, respectively, were measured.

Introduction

Conducting polymer composites are of great interest from a practical point of view, because their electrical properties can be tailored by properly choosing the components and their relative concentration. Of the various methods, the formation of conducting polymer composites by melt-blending is the most straightforward. But due to the absence of specific interfacial interaction, the mechnical properties are often drastically reduced. Polymerization-filling technique is a new way to produce polyolefin-based composites with remarkbly improved perfomances [1]. By this method, composites are produced in a single step as the olefin is polymerized by a coordination catalyst anchored on the surface of filler. One of the main targets of the polymerization-filling method is homogeneity of the final composites and the combination of high impact strength, ductile fracture, and high modulus that can be achieved by this method. The mentioned properties have been sought in composites for a long time.

Exfoliated graphite (EG) has excellent conductivity which can be obtained by exfoliation of graphite intercalate [2]. EG flakes have an accordion-shaped appearance and the expansion along the c-direction can be as much as two orders of magnitude when the intercalate is heated over a critical temperature. As a conductive filler, EG has been incorporated successfully into polymer matrix by mechanically mixing [3], static melt dispersion mixing [4] or in situ exfoliation [5]. These composites have many important uses, such as electrode material [6], electrical and thermal conductors [7], [8], sealing material [9]. More recently, Shiratori and his coworkers [10] prepared a poly(methyl methacrylate) (PMMA) encapsulated EG composite by polymerization of methyl methylacrylate in the presence of EG. The composite could be directly molded by hot press and the electrical conductivity and the shielding effect for electromagnitic interference of the molded product were superior to those of the EG–PMMA composite made by mechanical mixing. This paper is concerned with the preparation of EG/polystyrene composite by the polymerization-filling technique and the melt-blending method. The thermal and electrical properties of the composite were studied in detail.

Section snippets

Experimental

The expandable graphite (supplied by Bao Ding Lianxin Carbide Ltd.), which was prepared with H₂SO₄ as an intercalant and HNO₃ as an oxidant, with average particles 300 μm in size were dried at 60°C for 12 h to remove any moisture before heat treatment. Heat treatment was performed by inserting a steel crucible containing ca. 2 g of expandable graphite powders into the furnace held at a constant temperature of 800°C and being kept for 30 s in an air atmosphere. Expansion and exfoliation occurred

Results and discussion

For the radical polymerization of styrene, the molecular weight and molecular weight distribution of polystyrene synthesized in the presence of 2.78, 5.56 and 11.11% EG are shown in Table 1. It is clear that with increment of the amount of filled EG the M_w of polystyrene increases and the distribution of molecular weight widens. Similar results were also reported by Ignatov et al. [11].

The effect observed is caused by reduced contributions of the side process, which resulted in the termination

Conclusions

EG/polystyrene composite has been prepared by the polymerization-filling technique. With increase in the amount of EG, the molecular weight of polystyrene increases and the molecular weight distribution widens. DMA demonstrates that two glass transition temperatures of polystyrene chain block appear at 91.04 and 123.74°C, respectively. The decomposition temperature of the polymerization-filled composite is 28.66°C higher than that of polystyrene, but the thermal stability of the melt-blended

Acknowledgements

Financial Support from Key Project of the National Science Foundation of China (No. 59836232) is gratefully acknowledged.

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Preparation of exfoliated graphite/polystyrene composite by polymerization-filling technique

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgements

J Phys Chem Solids

J Macromol Sci — Rev Macromol Chem Phys

J Mater Res

Polym Compos