Changes in properties of silane-water crosslinked metallocene ethylene-octene copolymer after prolonged crosslinking time

The silane-water crosslinking of metallocene ethylene-octene copolymer is described. Particular consideration is made on the changes in mechanical, thermal, and rheological properties of crosslinked polymers after prolonged crosslinking time. The silane grafting is carried out in a twin-screw extruder, using a free-radical reaction of vinyl trimethoxysilane and dicumyl peroxide. The crosslinking reaction is conducted at 70degreesC in the presence of water. The results show that the rate of gel formation is very high in the early stage of crosslinking process and decreases thereafter. The maximum gel content of 77% is obtained after 60 h of immersing time. Increasing the immersing time beyond 60 h, the gel content does not increase further. However, the FTIR results reveal an increase in siloxane linkages in those samples, indicating an increase in crosslink density without a simultaneous increase in gel content. This finding is supported by a rheological study where a significant increase in storage modulus is clearly observed. As a result of denser network, movement and flexibility of polymer chains are more restricted, leading to some changes in tensile properties. (C) 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 901-906, 2004.