Elsevier

Polymer

Volume 54, Issue 9, 19 April 2013, Pages 2315-2323
Polymer

Effect of substituted groups on characterization and water vapor sorption property of polyhedral oligomeric silsesquioxane (POSS)-containing methacryl polymer membranes

https://doi.org/10.1016/j.polymer.2013.03.002Get rights and content

Abstract

The effects of substituted groups on the characteristics and water vapor sorption property of polyhedral oligomeric silsesquioxane (POSS)-containing methacryl polymers were investigated. A broad halo was observed in the X-ray diffraction profile, which suggests that all membranes were amorphous structure. Interestingly, the smaller volume of substituted groups tended to induce the larger deformation of POSS structure resulting from the packing of polymer segments. The introduction of ring-substituted POSS unit improved their thermal stability due to the increase in the rigidity. The sorption behavior for all POSS-containing polymer membranes obeyed the dual-mode model at lower relative pressure and then upturns at higher pressure. The phenyl-POSS shows the high solubility due to the large excess free volume and suppression of hydrophobic POSS unit covered by the stacking effect. Based on these results, the introduction of POSS unit enhances the hydrophobic property, while the polarity of substituted groups strongly affects the water vapor clustering.

Introduction

T8-Polyhedral oligomeric silsesquioxane (POSS) cages have recently gained increasing attention. POSS is a hybrid inorganic/organic structure that possesses an inner inorganic silicon, oxygen, and external organic substituent. Furthermore, this organic substituent can be specifically designed either as reactive or non-reactive for polymerization and compatibility, respectively. POSS ranges from 1 nm to 3 nm in size and is considered as the smallest nano-sized and inorganic particle of silica [1], [2]. POSS components have improved thermal stability, mechanical strength, and optical and dielectric properties. Recent investigations for related POSS are nanocomposite materials, including polymer composites [3], [4], [5], [6], [7], [8], [9], [10] and copolymers [3], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]. Thus, their use in several industrial applications, such as electrical [15] and optical devices [7], gas separation membrane [8], [9], [10], [16], fuel cells [21], [22], [23], and water treatment [24] has been investigated. Although POSS-containing homo-polymers investigation is important to discuss its nanocomposite materials, systematic research for homo-polymers has not been conducted. The difficulty in membrane fabrication is one of the reasons for the lack in polymer chains entanglements [2], [18], [25], [26], [27].

Siloxane linkage shows a general hydrophobic property (low sorption property of water molecules) as demonstrated by siloxane polymer, such as polydimethylsiloxane [28]. Therefore, POSS-containing polymer materials are expected to show hydrophobic property and applied in semiconductor, printed-circuit board, and liquid-crystal display applications in electrical devices and as barrier membrane materials in solar batteries. These materials are exposure under atmospheric conditions, including the presence of moisture and oxygen. These conditions cause performance degradation due to the aging.

A water molecule can strongly interact with itself and with the polymer by hydrogen bonding. Thus, the polymer membranes are swollen and plasticized [29]. For example, water molecules are known to decrease the polymer membranes separation performance in CO2 separation applications, including CO2 capture and natural gas purification, which involves water as the minor greenhouse gas component [30], [31]. This phenomenon is closely related to the sorption property of polymer materials. Therefore, determining the water vapor sorption property of POSS-containing polymer membranes is important in developing novel functional materials for industrial applications.

In the current study, a series of POSS-containing methacryl polymers was synthesized through free radical polymerization. The physical, thermal, and water vapor sorption properties of these polymers were investigated in terms of the effects on the substituted groups in the POSS unit.

Section snippets

Chemicals

The polymers were synthesized through free radical polymerization using substituted POSS-containing methacryl monomers, ethyl-POSS (MEPOSS), isobutyl-POSS (MIPOSS), phenyl-POSS (MPPOSS), and cyclopentyl-POSS (MAPOSS). All POSS-containing monomers were purchased from Hybrid Plastic, Inc. without further purification. The initiator, a,a′-azobis (isobutyronitrile) (AIBN, Junsei Chemical Co. Ltd., Tokyo, Japan), was purified by recrystallization using a methanol solution. The polymerization

Structure analysis and characterization

The chemical structures of the synthesized polymers, which are confirmed by 1H NMR, and FT-IR analyses of the polymer. Details of polymer spectroscopic data for NMR and FT-IR are given in Supplementary information.

The solvent solubility of POSS-containing polymers series is summarized in Table 1. All polymers were dissolved into the THF and chloroform. The polymers were insoluble in aprotic polar solvents for DMAc and DMF, proticpolar solvents for methanol, and water, and organic solvent for

Conclusion

The physical and thermal water vapor sorption properties of polyhedral oligomeric silsesquioxane (POSS)-containing methacryl polymers were investigated with focusing on the effects of the substituted groups. The polymers were synthesized through free radical polymerization. The WAXD result showed that the all membranes are amorphous structure based on the broad halo, suggesting that the POSS unit could be deformed affected by the polymer chain packing. The glass transition temperature increased

Acknowledgment

This research was partially supported by a Grant-in-aid for Scientific Research C (24560862) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, the Japanese Society of the Promotion of Science, Research Project Grant B (3) from the Institute of Science and Technology, Meiji University, Japan, and Grant-in-Aid for the Japan Society for the Promotion of Science (JSPS) Fellows (2410856).

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