No abstract

The effects of the addition of sodium hyaluronate segments (sHA) with different chain lengths on the viscoelasticity of high molecular weight sodium hyaluronate (HA) aqueous solutions were studied. The additive effects of sHA depended on the chain length of sHA. Shorter sHA decreased storage (G') and loss (G") moduli, whereas longer sHA increased both moduli. In physiological saline, the effects of the addition of sHA depended on the chain length of sHA, as in aqueous solutions, except that shorter segments did not decrease both moduli. The effects of the addition of monosaccharides, i.e., N-acetyl glucosamine (GlcNAc) and sodium glucuronate (GlcANa), were also studied. Although GlcNAc increased G' and G", GlcANa decreased both moduli. A shift factor "A," which depended on chain-length effects, a sugar effect, and a salt effect, was developed to explain these additive effects quantitatively.

New polydimethylsiloxane (PDMS)‐polyimide block copolymers were synthesized by the solution polycondensation of aminopropyl‐terminated polydimethylsiloxane, 1,1‐bis(4‐aminophenyl)‐2,2‐diphenylethylene, and 3,3′,4,4′‐benzophenonetetracarboxylic dithioanhydride in pyridine. New 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane (BADS)‐based random copolyimides were also prepared. The inherent viscosities of all the random and block copolyimides were in the range of 0.13–0.90 dL/g in N‐methyl‐2‐pyrrolidone. These copolymers were soluble in N,N‐dimethylacetamide, N‐methyl‐2‐pyrrolidone, and m‐cresol. All the BADS‐based random copolymers and PDMS‐containing copolymers with PDMS content above 42 wt % were soluble in tetrahydrofuran and chloroform. Transparent or somewhat cpaque films were prepared by casting from the reaction solutions. The BADS‐based random copolyimides had one glass transition temperature (Tg) in the whole composition ranges, which showed single phase nature of the copolymers. On the other hand, the PDMS‐polyimide block copolymers had double TgS, indicating phase‐separated morphology. The block copolymers containing PDMS content above 73 wt % behaved like a high temperature elastomer. © 1993 John Wiley & Sons, Inc.

No abstract

No abstract