SYNOPSISIn general, segmented polyurethane elastomers are prepared by reacting an isocyanatecapped polyol prepolymer with a short-chain diol chain extender, yielding an elastomer with hard segments of uniform size. However, the hard segment size will not be uniform if the polyurethane polymer is prepared by forming the hard segment first, followed by soft segment formation. Because the mechanical properties of polyurethane elastomers depend on the relative ratio of the hard to soft segments as well as the effectiveness of the hard segment as a physical crosslinker, the control of the size distribution of the hard segment is a key factor in designing polyurethane elastomers. It was found that reaction conditions can affect the size distribution of hard segments derived from an aliphatic diisocyanate with differential reactivity between the two isocyanate groups. Lower reaction temperatures and simultaneous mixing of all reactants gave the preferred size distribution of hard segments. 0 1995 John Wiley & Sons, Inc.

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α,ω‐Bis(4‐hydroxybutyl) polydimethylsiloxane (molecular weight 1500 to 4500) can be pre‐pared with well‐controlled molecular weight through the reaction of 1,3‐bis(4‐hydroxybu‐tyl)tetramethyl disiloxane and dimethoxydimethyl silane or diethoxydimethyl silane in the presence of a stoichiometric amount of water and hydrochloric acid. The molecular weight of these hydroxybutyl‐terminated polysiloxanes can be determined fairly consistently by a titration method. These polysiloxanes are stable toward cyclization. © 1995 John Wiley & Sons, Inc.

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SYNOPSISUV-curable polyurethane prepolymers were prepared from the following components: isophorone diisocyanate, hydroxybutyl-terminated polysiloxane, and 2-hydroxyethyl methacrylate with diethylene glycol or neopentyl glycol added as an optional chain extender. These prepolymers, with hard segments of different structures, were characterized by high resolution NMR, FTIR, and gel permeation chromatography. Model oligomers were prepared to confirm the structures of the prepolymers. The structure-property relationship of cured prepolymers were determined. 0 1995 John Wiley & Sons, Inc.