Synthesis and characterization of ladder-like copolymethyl-epoxysilsesquioxane

doi:10.1016/S1381-5148(00)00018-3

Reactive and Functional Polymers

Volume 45, Issue 2, September 2000, Pages 119-130

https://doi.org/10.1016/S1381-5148(00)00018-3 Get rights and content

Abstract

A new kind of copolymethyl-epoxysilsesquioxane (CPMES) was synthesized for the first time by hydrosilation reaction of allyl glycidyl ether (AGE) with the ladder-like polymethylhydrosilsesquioxane (Me-H-T) in the presence of dicyclopentadienylplatinum dichloride (Cp₂PtCl₂) as catalyst. The graft polymer was characterized by infrared spectroscopy (IR), ¹H-NMR, ²⁹Si-NMR, X-ray diffraction (XRD), gel-permeation chromatography (GPC), vapour pressure osmometry (VPO), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results indicate that CPMES possesses good solubility in organic solvents, and a greatly improved thermostability compared with polymethyl-epoxysiloxane with a single backbone.

Introduction

Epoxy resins are not only widely used as adhesives, coatings, etc., but are also commonly employed in the electrical and microelectronic field because they have superior adhesive, corrosion- and stress-resistant properties, and the high electrical insulation required between very closed-packed elements. Recently, many investigations have focused on improving properties such as thermostability by synthesizing new kinds of epoxy polymers or modifying commercial epoxy resins. For example, the solidified product of the bisphenol A type epoxy resin not only has high adhering and insulating ability, but also has improved thermostability, and that of the heterocyclic epoxy resin features superior thermostability and remarkable weather-proofing properties.

In 1994, Matisons et al. [1] synthesized three kinds of linear polymethylhydrosiloxane with a single main chain having the empirical formula Me₃SiO(SiMe₂O)_x(SiMeH)_ySiMe₃, which were then hydrosilated with allyl glycidyl ether (AGE) to form polymethylepoxysiloxanes in high yield, but the content of epoxy groups is so low (ca. 7%) that its application for thermo-resistant adhesives is greatly restricted. On the other hand, much interest in functional silsesquioxanes has been reported in the literature in recent years [2], [3]. For example, in 1997 Crivello [4] reported that the epoxy group was attached to the core of octahydrotetrasilsesquioxane (T₈^H) by the hydrosilation reaction with an appropriate epoxy precursor.

It is known that the ladder-like polysilsesquioxane (LPS) is more superior with respect to thermostability and film-forming properties than the usual single main chain polysiloxane. Brown et al. [5] first reported ladder-like polyphenylsilsesquioxane (Ph-T) in 1960, which was prepared by the so-called ‘thermal equilibration polymerization’ of hydrolates of PhSi(OEt)₃ or PhSiCl₃ using KOH as the catalyst at 250°C. Interestingly, the film cast from Ph-T can even withstand very high temperatures (400°C) in air and hence it is used as a thermo-resistant protective coating. It is hoped that grafting epoxy groups to the LPS backbone instead of a single main chain polysiloxane is an effective method for improving the thermostability of commercial epoxy resin. To carry out the hydrosilation-based graft reaction there must be a reactive ladder-like polyhydrosilsesquioxane (H-T) or copolymethyl-hydrosilsesquioxane (Me-H-T), which, however, cannot be prepared under the severe reaction conditions employed in the above-mentioned Brown’s method.

Since the early 1990s, a series of novel reactive LPSs and their copolymers [6], [7] (such as ladder-like polyhydrosilsesquioxane (H-T), ladder-like polyvinylsilsesquioxane (Vi-T) and ladder-like polyallylsilsesquioxane (Allyl-T)) have been synthesized by the so-called ‘stepwise coupling polymerization’ [8], [9] in our laboratory and many other different functional groups were selected to graft on the active LPS backbone. In particular, the successful functionalization of LPS has resulted in a new family of functional mesomorphic ladder-like polymers, including fishbone-like (end-on fixed type) [10], [11], [12], [13] and rowboat-like (side-on fixed type) [14] liquid crystalline polymers.

This paper describes the synthesis of copolymethyl-epoxysilsesquioxane (CPMES) by grafting the epoxy monomer AGE onto the backbone of LPS and the resultant great increase in thermostability.

Section snippets

Materials and techniques

Reagents AGE, trichlorosilane, trichloromethylsilane and 1,4-phenylendiamine (PDA) were commercially available and purified prior to use. All solvents were also dried in advanced according to standard procedures. Polymethyl-epoxysiloxane was purchased from Chenguang Research Institute of Chemical Industry, China.

IR measurements were carried out on a Perkin-Elmer 683 Infrared Spectrophotometer. ¹H-NMR and ²⁹Si-NMR studies were performed with a JNH-FX100 (JBOX), 200 MHz. GPC and VPO were measured

Synthesis reaction

Me-H-T is synthesized by a stepwise coupling polymerization, during which PDA is first coupled with two molecules of MeSiCl₃ and HSiCl₃. Because the rate of hydrolysis of the Si–Cl bond is much faster than that of the Si–N bond of the bridge Si–NH–C₆H₄–NH–Si in neutral solution, an Si–NH–C₆H₄–NH–Si bridged silanol oligomer is first generated and then the oligomer is hydrolyzed to remove the organic bridge and to form a silsesquioxane oligomer with four hydroxy groups. Finally, LPS is

Conclusion

Copolymethyl-epoxysilsesquioxane was successfully prepared by grafting allyl glycidyl ether to a ladder-like polysilsesquioxane backbone via the hydrosilation reaction. It was found that the hydrosilation reaction did not proceed to completion due to steric hindrance of allyl glycidyl ether. Characterization of the product by GPC, VPO, TGA, DSC, X-ray, ¹H- and ²⁹Si-NMR and IR demonstrated that CPMES was obtained and possessed greatly improved thermostability.

Acknowledgements

This project was financially supported by NSFC (No. 29874034).

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Synthesis and characterization of ladder-like copolymethyl-epoxysilsesquioxane

Abstract

Introduction

Section snippets

Materials and techniques

Synthesis reaction

Conclusion

Acknowledgements

Organomet. Chem.

J. Organomet. Chem.

Macromolecules

J. Polym. Sci., Part A: Polym. Chem.

J. Am. Chem. Soc.

Chin. J. Polym. Sci.

React. Polym.