Synthesis, Characterization and Microstructure of New Liquid Poly(methylhydrosiloxanes) Containing Branching Units SiO4/2

Jerzy Chruściel,Witold Fortuniak,Marzena Fejdyś

doi:10.3390/polym10050484

Abstract

Six liquid branched poly(methylhydrosiloxanes) of new random structures (PMHS-Q), containing quadruple branching units SiO4/2 (Q), both MeHSiO (DH) and Me2SiO (D) chain building units (or only mers MeHSiO), and terminal groups Me3SiO0.5 (M) were prepared by a hydrolytic polycondensation method of appropriate organic chlorosilanes and tetraethyl ortosilicate (TEOS), in diethyl ether medium at temperature below 0 °C. Volatile low molecular weight siloxanes were removed by a vacuum distillation at 150–155 °C. Yields of PMHS-Q reached from 55–69 wt%. Their dynamic viscosities were measured in the Brookfield HBDV+IIcP cone-plate viscometer and ranged from 10.7–13.1 cP. Molecular weights (MW) of PMHS-Q (Mn = 2440–6310 g/mol, Mw = 5750–10,350 g/mol) and polydispersities of MW (Mw/Mn = 2.0–2.8) were determined by a size exclusion chromatography (SEC). All polymers were characterized by FTIR, 1H- and 29Si-NMR, and an elemental analysis. A microstructure of siloxane chains was proposed on a basis of 29Si-NMR results and compared with literature data.

Highlights

Poly(methylhydrosiloxanes) (PMHS) are inorganic–organic hybrid polymers with inorganic backbone, composed of alternatively bound silicon and oxygen atoms
We describe the hydrolytic polycondensation synthetic route to new liquid branched poly(methylhydrosiloxanes) of random structures (PMHS-Q), containing both MeHSiO (DH )
All products were analyzed by a nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR)

Summary

Introduction

Poly(methylhydrosiloxanes) (PMHS) are inorganic–organic hybrid polymers with inorganic backbone, composed of alternatively bound silicon and oxygen atoms. MeHSiO units in macromolecules [9,24] This synthetic method is based on a non-stoichiometric polycondensation of appropriate dimethylsiloxane-α,ω-diols HO(Me2 SiO)m H with siloxane oligomers of a general formula Cl(MeHSiO)k-1 SiHMeCl, having chloro(hydro)silyl functionalities, followed by termination reactions with chlorotrimethylsilane Me3 SiCl, when PDMS-b-PMHS chains were blocked with (CH3 ) SiO0.5 (M) groups. Methyl-substituted silica gels with Si-H functionalities were prepared by hydrolysis and condensation reactions of triethoxysilane and methyldiethoxysilane, used in various molar ratios [62] They gave higher ceramic residue after pyrolysis than gels based only on MeSiO1.5 branching units [63]. We describe the hydrolytic polycondensation synthetic route to new liquid branched poly(methylhydrosiloxanes) of random structures (PMHS-Q), containing both MeHSiO (DH ). Me2 SiO (D) chain building units (or only mers MeHSiO), quadruple branching units SiO4/2 (Q), and terminal groups Me3 SiO0.5 , from appropriate organic chlorosilanes and tetraethoxysilane

Materials and Methods

Results and Discussion

H–NMR spectra

50 M8 were

H H to resonances atomsofofend endgroups groups M

H H HH the following: following:DD