Synthesis and Properties in Solution of Gaussian Homo Asymmetric Polysiloxanes with a Bulky Side Group
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Synthesis and Properties in Solution of Gaussian Homo Asymmetric Polysiloxanes with a Bulky Side Group Javier Vallejo-Montesinos • Antonio Villegas • Araceli Jacobo-Azuara • J. Merced Martı´nez • Eulalia Ramı´rez • Jorge Cervantes
Received: 31 May 2012 / Accepted: 18 September 2012 Ó Springer Science+Business Media New York 2012
Abstract Ring opening polymerization (ROP) of 1,3,5-trin-hexyl,1,3,5-trimethylcyclotrisiloxane (DHexa ) and 1,3,53 tri-n-heptyl,1,3,5-trimethylcyclotrisiloxane (DHepta ) was 3 promoted by acid-treated synthetic silica–alumina to obtain Gaussian homo asymmetric polysiloxanes. Mw was above 70 kg/mol, meaning that homo asymmetric bulky side-group polysiloxane chains with high molecular weight were obtained. The material was treated in an acidic medium to improve the contents of acid sites and successfully tested as an inorganic acidic catalyst for ROP of DHexa and 3 DHepta cyclosiloxanes. The samples of poly(meth3 ylhexylsiloxane) (PMHS) and poly(methylheptylsiloxane) (PMHepS) obtained were structurally characterized mainly by 29Si NMR. All the experimental values including the refractive index increment (dn/dc), the second virial coefficient (A2), the square root of the mean square radius of gyration (hRMSradius 2 i1=2 ), the average molecular weight (Mw), the average molecular numeral (Mn), and the weight polydispersity (Mw/Mn) were obtained using a gel permeation chromatography/light scattering (GPC/LS) coupled system. The A2 experimental value for the two polymers (between 4 and 6.5 9 10-4 mol/mL g2) indicated that toluene was a good solvent. In addition, PMHS and PMHepS hRMSradius 2 i1=2 were greater than 30 nm, indicating that larger chains of high molecular weight were obtained.
J. Vallejo-Montesinos A. Villegas (&) A. Jacobo-Azuara J. M. Martı´nez E. Ramı´rez J. Cervantes Divisio´n de Ciencias Naturales y Exactas, Universidad de Guanajuato, Campus Guanajuato, Col. Noria Alta s/n, 36050 Guanajuato, GTO, Mexico e-mail: [email protected]
Keywords Gaussian homo asymmetric polysiloxanes Bulky side group Polysiloxane chains Ring opening polymerization Silica–alumina GPC/LS coupled system
1 Introduction Polysiloxanes are materials that generate great interest due to their unusual properties and potential applications. One of the most important characteristics of the polysiloxane chain is its high torsional flexibility due to the difference between the Si–O–Si (&145°) and O–Si–O (&110°) bond angles and low bond torsional barrier around the Si–O bond, which is practically 0.0 kcal/mol. As a consequence of the high flexibility, the glass transition temperature (Tg) is very low (&-120 °C); therefore, polysiloxanes are amorphous at room temperature [1, 2]. Homo asymmetrical polysiloxanes with bulky side groups (PBSG) form an interesting family of materials; however, little information about these polymers has been reported in the literature [3–5]. These materials exhibit properties that differ significantly from those of symmetrical alkyl polysiloxanes [3–6]. Homo asymmetrica
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