000052150 001__ 52150
000052150 005__ 20190702135936.0
000052150 0247_ $$2doi$$a10.1002/(SICI)1099-0488(19990315)37:6<485::AID-POLB1>3.0.CO;2-T
000052150 037__ $$aARTICLE
000052150 245__ $$aReversible Gelation of Poly(dimethylsiloxane) with Ionic and Hydrogen-Bonding Substituents
000052150 269__ $$a1999
000052150 260__ $$c1999
000052150 336__ $$aJournal Articles
000052150 520__ $$aPoly(dimethylsiloxane) copolymers containing a small fraction of carboxylic acid or Zn-carboxylate groups were prepared and compared regarding reversible gelation by hydrogen-bonding and ion-pair interaction. The polymers were synthesized by condensation of a t-butylcarboxylate functionalized dichlorosilane with an α,ω-dihydroxy-poly(dimethylsiloxane), followed by thermal cleavage of the ester bond. Neutralization of the resulting carboxylic acid substituents was achieved by addition of Zn (acac)2. Reversible crosslinking was investigated by step stress and oscillating shear experiments. The carboxylic acid containing poly(dimethylsiloxane) became rubberlike upon increasing the temperature and liquified again when it was brought back to room temperature. This observation has been explained tentatively by segregation of the carboxylic acid groups into polar domains at high temperatures [i.e., a behavior like it is observed for systems with a lower critical solution temperature (LCST)]. At ambient temperature, the carboxylic acid groups undergo hydrogen bonding to the Si-O-Si backbone. Clustering of the carboxylic acid groups occurs only as these hydrogen bonds break upon raising temperature. Moisture was found to have a strong influence on the reversal of the crosslinking. Addition of zinc acetylacetonate resulted in the formation of an elastic network already at ambient conditions consistent with the concept of ionomers which undergo reversible gelation by formation of ion-pair multiplets and clusters in the hydrophobic polymer matrix in particularly at low temperatures. At high temperature, both the carboxylic acid and the carboxylate sample exhibited a rather similar viscoelastic behavior consistent with a common structure where transient crosslinks are formed by clusters of the carboxylic acid and the carboxylate groups. © 1999 John Wiley & Sons, Inc.
000052150 700__ $$0240029$$g156848$$aKlok, H.-A.
000052150 700__ $$aMichelberger, W.
000052150 700__ $$aMöller, M.
000052150 700__ $$aRebrov, E.A.
000052150 700__ $$aMuzafarov, A.M.
000052150 773__ $$q485-495$$k6$$j37$$tJournal of Polymer Science, Part B: Polymer Physics
000052150 8560_ $$fbeatrice.marselli@epfl.ch
000052150 909CO $$particle$$pSTI$$ooai:infoscience.tind.io:52150
000052150 909C0 $$xU10342$$0252017$$pLP
000052150 937__ $$aLP-ARTICLE-1999-001
000052150 970__ $$a39/LP
000052150 973__ $$sPUBLISHED$$aEPFL$$rREVIEWED
000052150 980__ $$aARTICLE