Low molar mass polybutadiene made crosslinkable by silane moities introduced via addition of thiol to double bond: 4. Crosslinking study

The effect of the number of triethoxy silane functions introduced onto low molar mass hydroxy telechelic polybutadiene was investigated by using swell ing measurements and mechanical properties (storage modulus E' at the rubbe ry plateau and maximum of tan delta). These triethoxy silane functions were distributed all along the polymer chain by the addition of mercapto propyl triethoxy silanes to vinyl double bonds. Influence of catalyst, temperatur e, moisture and time were studied. The best experimental conditions corresp ond to 80 degrees C under moisture with dibutyl tin dilaurate as catalyst. A large increase in T-g (from -70 to -20 degrees C) and E' (6.5-130 MPa) wa s observed from 1.05 to 7.9 triethoxy silane groups per chain. These result s are due to a decrease of the average molar mass per crosslinked unit ((M) over bar(c)) which was not observed when the modification was performed es sentially at chain extremities (hydroxy functions) via urethane Linkage. (C ) 1999 Elsevier Science Ltd. All rights reserved.