Synthesis of organic–inorganic hybrid microspheres and the corresponding mesoporous silica nanoparticles

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Highlights

Abstract

Poly(methacrylic acid-co-3-(methacryloxy)propyltrimethoxysilane) (P(MAA-co-MPS)) organic–inorganic hybrid microspheres were prepared by distillation–precipitation copolymerization of MAA and MPS in acetonitrile in absence of any surfactant and additive. The resultant hybrids had a spherical shape when the MPS inorganic precursor was varied from 0% to 60% in the comonomers during the polymerization. The hybrid microspheres can be facilely cross-linked via the hydrolysis of methoxy groups of polyMPS network and further self-condensation of the hydroxyl groups of silanols. As a result, the hybrid microspheres were facilely converted to mesoporous silica particles via the removal of the organic component through calcination. The narrow dispersed mesoporous silica had a high surface area of 554.2 m2/g as well as the average pore size of 8 nm and pore volume of 0.24 cm3/g. The corresponding microspheres were characterized by TEM, FT-IR, TGA, and nitrogen sorption–desorption.

Introduction

The development of materials with novel structure and component has been a fundamental concern of chemical research, which promotes the advancement in both academic and industrial fields. In recent years, organic–inorganic hybrid materials, which combine the properties of inorganic and organic components within a single material, have attracted expanding interest of material scientists due to their advantages of the organic polymer matrix having facile process-ability, flexibility, and various functional groups, together with characteristics of the inorganic particles in terms of mechanical strength, modulus, and thermal stability [1], [2], [3]. The organic–inorganic hybrid materials can exhibit novel and excellent properties, such as mechanical, chemical, electrical, rheological, magnetic, optical, and catalytic, by varying the composition, dimensions, and structures, which have proven the diverse applications as drug-delivery system, diagnostic, coating, and catalyst.

In the past few years, many approaches have been developed for preparation of hybrid microspheres, such as core–shell microspheres with an inorganic core coated by a polymer shell or inverse [4], [5], [6], multilayer hollow hybrid microspheres containing the polymer electrolytes and inorganic colloidal particles [7], [8], polymer microspheres dotted with inorganic nanoparticles on the surface or in the polymer matrix [9], [10], hollow polymer hybrid microspheres with inorganic nanoparticles located on the shell layer [11], raspberry-like hybrid microspheres with different components between the core and the corona [12], and block polymer containing organic block chain with an inorganic block chain [13], [14]. However, the homogeneous hybrid materials contain inorganic and organic components have been seldom reported because of the distinct difference between the inorganic component and the organic component. Recently, Bourgeat-Lami et al. [15], [16] prepared poly(styrene-co-MPS) hybrid microspheres through emulsion polymerization using water as solvent. The control of the hydrolysis process was difficult because the MPS molecule was hydrolyzed quickly during the polymerization process with water as the solvent. As a result, the P(St-co-MPS) microspheres with uniform shape can be only obtained in the case of MPS component less than 50% in the comonomers. Therefore, it is still necessary to develop a facile way for the preparation of hybrid microsphere with a uniform shape and homogeneous structure.

Porous material has been found applications in a wide range of fields, such as gas storage [17], [18], [19], drug delivery [20], [21], and separation [22], [23]. Mesoporous silica has been considered as a promising porous material due to its large specific surface area, good biocompatibility, and easy functionalization with the presence of many Si–OH groups on the surface [24], [25]. Many efforts have been devoted to prepare mesoporous silica microspheres [26], [27], [28]. Among these methods, surfactant assisted template method is one of the most popular ways for synthesis of mesoporous silica microspheres. However, the surfactants were toxic and noxious to the environment and difficult to be removed from the microspheres. Thus, it is still a challenge to prepare mesoporous silica through a facile method in absence of surfactants or additives.

In this paper, poly(methacrylic acid-co-3-(methacryloxy)propyltrimethoxysilane) (P(MAA-co-MPS)) organic–inorganic hybrid microspheres were facilely prepared by distillation–precipitation polymerization. The organic component and inorganic components were homogenously copolymerized as a microspherical matrix. The ratio between the organic and the inorganic component can be tuned by varying the comonomer feed during the polymerization process. The resultant P(MAA-co-MPS) hybrid microspheres can be facilely cross-linked through the hydrolysis of the Si–OMe groups with the further condensation between the reactive silanols. The mesoporous silica nanoparticles can be afforded by the calcination of the organic–inorganic P(MAA-co-MPS) hybrid microspheres to remove the organic component, during which the pores were left in the matrix for the formation of meosoporous silica nanoparticles.

Section snippets

Chemicals

3-(Methacryloxy)propyltrimethoxysilane (MPS) was purchased from Aldrich and purified by distillation under vacuum. Methacrylic acid (MAA, Tianjin Reagent Factory I, China) was purified by vacuum distillation before use. 2,2′-Azobisisobutyronitrile (AIBN) was provided by Chemical Factory of Nankai University and recrystallized in methanol. Acetonitrile (analytical grade, Tianjin Chemical Reagents II Co.) was dried over calcium hydride and purified by distillation before use. All the other

Results and discussion

In our previous works, distillation–precipitation polymerization has been proved to be a powerful method for preparation of monodisperse polymer microspheres with various functional groups, core–shell polymer microspheres by two stage polymerization, and the corresponding hollow microspheres, core–shell inorganic–organic hybrid microspheres performed on inorganic templates then for hollow microspheres [6], [29], [30], [31], [32], [33]. In this paper, hybrid P(MAA-co-MPS) microspheres with

Conclusion

Organic–inorganic P(MAA-co-MPS) hybrid microspheres with tunable components were synthesized by a distillation–precipitation polymerization method in acetonitrile in absence of any surfactants or additives. These P(MAA-co-MPS) microspheres were facilely crosslinked through the hydrolysis of the methoxy groups and further self-condensation of the silanols in acetonitrile with aqueous ammonium hydroxide as a catalyst. The mesoporous silica microspheres with pore size of 8 nm and high surface area

Acknowledgments

This work has been supported by the NSFC (21174065), Tianjin Science Technology Research Funds of China (11JCYBJC02100) and PCSIRT (IRT1257).

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