While incorporation of only a few mol % of diphenylsiloxy-, DiPhS, repeat units into polydimethylsiloxane, PDMS, chains is enough to completely suppress their crystallization, it also leads, in polymers obtained by silanolate-initiated ring-opening polymerization, to a puzzling and yet unexplained chain branching which significantly distorts polymer molecular weight distributions and affects their chain conformation. In contrast to this, we found that introduction of comparable amounts (ca. 5 mol %) of diethylsiloxy-, DiEtS, units into the same type of polymers also suppresses polymer crystallization but does not lead to any detectable branching, yielding polymers with the most probable molecular weight distribution and typical random coil conformation in a thermodynamically good solvent, such as toluene. On the basis of the results of a 29 Si NMR and SEC-MALS study, we propose that branching in DiPhS-containing polymers is caused by a nucleophilic attack of initiating silanolate anions on their Si−C Ar side bonds and a resulting formation of phenyltrisiloxysilane T-branches. We also propose that because branching may seriously disrupt mechanical properties of elastomers if such DiPhS-containing PDMSs are used for cross-linking, the DiEtS-modified derivatives represent polymers of choice if applications of such elastomers at extremely low temperatures are desired.

Novel high hydroxyl number and high functionality polyols were developed using thiol-ene reaction of castor oil with mercaptoethanol or mercaptanized castor oil with allyl alcohol (by photochemical reaction) and 2-hydroxyethyl acrylate (by Michael thiol-ene reaction). The polyols had OH numbers of 220-295 mg KOH/g and functionalities close to 6. Cast polyurethane resins were prepared with methylene diphenyl diisocyanate (MDI), dicyclohexylmethane-4,4'diisocyanate (HMDI) and m-xylylene diisocyanate (XDI). XDI gave rubbery to leathery polyurethanes with all three polyols, while MDI and HMDI gave amorphous glasses with good mechanical properties. Rigid polyurethane foams of good properties were made with MDI and three castor oil-based polyols.

New monomers were prepared by introducing the azide groups in castor, canola, corn, soybean, and linseed oils. Polymerization of the azidated oils with alkynated soybean oil under thermal "click" chemistry conditions (without using a solvent or a catalyst) yielded fully cross-linked elastomers (1-5) of almost the same density (1.05 × 10(-3) kg/m(3)). The degree of cross-linking gradually increased from the castor-derived polymer (220 mol/m(3)) to the linseed-derived polymer (683 mol/m(3)). A systematic correlation between the degree of cross-linking and the thermal and mechanical properties was observed in these biopolymers. Tensile strength (0.62-3.39 MPa) and glass transition temperature (-5 to 16 °C) increased and the linear thermal expansion coefficient decreased in the series from the canola-derived polymer (2) to the linseed-derived polymer (5). The castor-derived polymer (1) that possesses an additional hydroxyl group per fatty acid chain behaved differently.

Triols of molecular weights (MWs) 1000-4000, suitable for flexible foams, were prepared by transesterification of methyl esters of ricinoleic acid with trimethylol propane. These polyols were noncrystallizing, relatively low-viscosity liquids. They were reacted with diphenylmethane diisocyanate (MDI) to obtain elastomers having glass transition temperatures below 2608C. Polymer networks from high-MW polyols exhibited relatively high sol fractions suggesting that some cyclization occurred during polyol preparation. The low Shore hardness, relatively low strength and modest elongation of the elastomers were attributed to the specific structure of polyricinoleic chains and the presence of dangling chains, serving as plasticizers.

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