Elsevier

European Polymer Journal

Volume 43, Issue 2, February 2007, Pages 644-651
European Polymer Journal

Organosilicon hydrides in macromolecular design: Reactions of chain-transfer and hydrosilylation

https://doi.org/10.1016/j.eurpolymj.2006.10.026Get rights and content

Abstract

The chain-transfer constants through silicon hydrides in bulk polymerization of styrene and methyl methacrylate (MMA) were measured with using 15 organosilicon compounds belonging to four classes: oligoorganohydrosilanes, oligoorganohydrosiloxanes, disilalkanes and alkylhydrosilanes. The linear dependences of the logarithm of chain-transfer constant on the sum of the Taft inductive constants of substituents at silicon atoms of a Si–H group were found. The negative values of reaction constants ρ indicate that an electrophilic attack of macroradical onto a hydrogen atom occurs at the limiting stage of the process. Oligoorganohydrosilanes proved to be the most effective chain-transfer agents that can be explained by high electron-donating properties of R3Si substituents. The increase of the chain-transfer constant values takes place on the accumulation of both trimethylsilyl and silicon hydride groups in a molecule of hydrosilane. The high electrophilicity of PMMA macroradical as compared with a macroradical of polystyrene (PS) is responsible for a greater sensitivity of the polymerization reaction of MMA to the change of the electron density on a hydrogen atom of the organosilicon chain-transfer agent. In the radical polymerization of MMA and styrene in the presence of the chain-transfer agents till high conversion the polymers with a narrower molecular weight distribution (MWD) in comparison with those synthesized by usual polymerization in bulk are formed. The polymers prepared in the presence of multifunctional silanes can be functionalized by the reaction of hydrosilylation and further used in the synthesis of block copolymers.

Introduction

Earlier [1] on an example of polymerization MMA it has been shown that organohydrodisilanes are effective chain-transfer agents comparable to the strongest ones of the known molecular-weight regulators of polymers, e.g. mercaptans [2]. A special feature of these chain-transfer agents proved to be a strong influence of silicon atom sequences on their reactivity.

The goal of the present paper was the comparison of the reactivity of silicon hydrides as chain-transfer agents in the polymerization of monomers of a different polarity such as styrene and methyl methacrylate and the study of molecular weight characteristics of the polymers prepared in the presence of these compounds.

Section snippets

Materials

Fifteen organosilicon hydrides (OSH) containing of 98–99 % the basic substance were investigated in this work (Table 1). Pentamethyldisilane (1), 1,1,2,2-tetramethyldisilane (4), 1,2-dimethyldisilane (7), bis(trimethylsilyl)methylsilane (8), tris(trimethylsilyl)silane (9) were synthesized by the known methods described in Refs. [3], [4], while bis(trimethylsiloxy)methylsilane (13) and 1,2-bis(silyl)ethane (14) were prepared as demonstrated elsewhere [5], [6], respectively. The syntheses of

Reactivity of organosilicon hydrides as chain-transfer agents in radical polymerization of styrene and methyl methacrylate

The experimental values of the relative constants of the chain-transfer onto OSH in the polymerization of styrene and MMA up to 10 wt.% of conversion are given in Table 2. As the data in Table 2 show, the activity of OSH in the chain-transfer reaction in the radical polymerization depends on their chemical structure and the monomer nature. The influence of the chemical structure of OSH on their reactivity is mainly explained by the availability in their molecules of a sequence from two and more

Conclusions

Organosilicon hydrides as a new class of chain-transfer-agents in radical polymerization are investigated. We found that the reactivity of organosilicon hydrides depends on its chemical structure and activity of monomer. It is shown that the organosilicon hydrides may be used in macromolecular design. Block copolymer PMMA-polystyrene was prepared by means of combination of the chain-transfer reaction and the reaction of hydrosilylation.

Acknowledgements

The IR-spectra of the polymers were measured at the Analytical center of the Institute of Organometallic Chemistry of Russian Academy of Science with financial support of RFBR (Project 96-03-40-042). The authors express their sincere appreciation to S.Ya. Khorshev and T.G. Mushtina for the measurement of IR-spectra and M.A. Lopatin for the help rendered in the construction of correlation dependences.

References (17)

  • M. Kumada et al.

    Aliphatic organopolysilanes

    Adv Organomet Chem

    (1968)
  • S.A. Bulgakova et al.

    Organodisilane hydrides: a promising new class of chain-transfer agents in free-radical polymerization

    Polym Sci B

    (1998)
  • Ch. Walling

    Free radicals in a solution

    (1960)
  • E. Hengge

    Properties and preparation of Si–Si linkages in inorganic and organic silicon compounds

    Top Curr Chem

    (1974)
  • M.C. Musolf et al.

    The addition of silicon hydrides to olefinic double bonds. X. Addition to phenylalkenes. The nuclear magnetic resonance proton spectra of (phenylalkyl)silanes

    J Org Chem

    (1964)
  • A.D. Petrov et al.

    Synthesis and properties of disilylmethane, 1,3-disilylpropane and 1,3,5-trisilen-2,4,6-trimethylencycloalkane

    Dokl AN SSSR

    (1953)
  • V.V. Semenov et al.

    Reactions of methylchlorodisilanes with Grignard reagents

    Izv Acad Nauk Ser Chem

    (1995)
  • V.V. Semenov et al.

    The methylsubstituted disilanylsesquioxanes and disilanylsiloxanes

    J Obshch Khim

    (1990)
There are more references available in the full text version of this article.

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