Synthesis and Properties in Solution of Gaussian Homo Asymmetric Polysiloxanes with a Bulky Side Group

Ring opening polymerization (ROP) of 1,3,5-tri-n-hexyl,1,3,5-trimethylcyclotrisiloxane (D (3) (Hexa) ) and 1,3,5-tri-n-heptyl,1,3,5-trimethylcyclotrisiloxane (D (3) (Hepta) ) was promoted by acid-treated synthetic silica-alumina to obtain Gaussian homo asymmetric polysiloxanes. M-w 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 D (3) (Hexa) and D (3) (Hepta) cyclosiloxanes. The samples of poly(methylhexylsiloxane) (PMHS) and poly(methylheptylsiloxane) (PMHepS) obtained were structurally characterized mainly by Si-29 NMR. All the experimental values including the refractive index increment (dn/dc), the second virial coefficient (A(2)), the square root of the mean square radius of gyration (), the average molecular weight (M-w), the average molecular numeral (M-n), and the weight polydispersity (M-w/M-n) were obtained using a gel permeation chromatography/light scattering (GPC/LS) coupled system. The A(2) experimental value for the two polymers (between 4 and 6.5 x 10(-4) mol/mL g(2)) indicated that toluene was a good solvent. In addition, PMHS and PMHepS were greater than 30 nm, indicating that larger chains of high molecular weight were obtained.