Experimental partPoly(dipropylsiloxane)a) (PDPS) was obtained by anionic polymerization of hexapropylcyclotrisiloxane in the presence of KOH under an argon flux at 115°C. The polymer obtained was fractionated from a toluene/methanol (1 : 99 by vol.) solution at 25 "C. Fractions were taken 24 h after reaching equilibrium conditions. The molecular weights were determined by light scattering in toluene at 25 "C. In our study the fraction with an intrinsic viscosity [q] = 0,26 dl/g in toluene at 25 "C and a weight-average molecular weight M, = 82000 was used. Calorimetric and X-ray studies were carried out on the sample which after fractionation was heated to 500 K and cooled slowly to room temperature.Systematic name: poly(oxydipropylsily1ene).

We report studies of the collapse of monolayers of cyclolinear poly(organosiloxane)s that consist of six-membered rings joined by oxygen bridges and that contain two phenyl groups per monomer unit. Surface pressure−area isotherms show that these films undergo a stepwise collapse. The organization within the films has been examined at different stages of the collapse process by Brewster-angle microscopy. Films transferred to mica by the Langmuir−Blodgett technique have been imaged by scanning force microscopy. Five fractions of an atactic polymer with molecular weights (M W) ranging from 8900 to 85 000 and one trans-tactic polymer (M W = 8100) have been investigated. Bilayers of the fractions with the highest M W's appear in the form of islands but the bilayers in the other samples have the form of ribbons 50−250 nm wide.

The crystalline structure and semicrystalline morphology of poly(di-n-propyl siloxane), PDPS, were studied with powder and fiber X-ray diffraction, differential scanning calorimetry, solid-state nuclear magnetic resonance and atomic force microscopy (AFM). PDPS exhibits two crystalline phases, α (−45.5 °C < T < 62 °C) and β (T < −45.5 °C), and a hexagonal columnar mesophase which is stable in a broad temperature range between 62 and 197 °C. The low-temperature crystalline phase β is found to be monoclinic with lattice parameters a = 20.60 Å, b = 19.22 Å, c = 4.95 Å, γ = 93.1°. The α crystalline phase has a pseudo-tetragonal unit cell with a = b = 19.15 Å and c = 5.00 Å and is characterized by monoclinic C2/c (No. 15) group symmetry. In the refined unit cell (R wp = 0.127) the PDPS chains adopt a planar cis−trans conformation with the plane of the chain parallel to the b axis. The semicrystalline morphology of the α crystal was studied with AFM. The crystallization of PDPS from the hexagonal mesophase results in very thick (100−150 nm thick) crystalline lamellae, which implies that the chains are fully extended in the crystal. This feature, which is found in few polymers, makes PDPS similar to such systems as HDPE at high pressure or 1,4-trans-poly(butadiene).