Low molar mass polybutadiene made crosslinkable by the introduction of methacrylate moieties via urethane linkage. 5. Synthesis and crosslinking study

Hydroxy telechelic low molar mass polybutadiene was modified by using metha cryloyl isocyanate (MAI). Immobilization of methacrylate functions was carr ied out at 40 degreesC with or without dibutyl tin dilaurate (DBTL) as a ca talyst. The reaction was fast and nearly instantaneous with DBTL. Methacryl ate moieties were introduced quantitatively at the rate of 1.2, 2 and 2.4 p er polymer chain. The photoinitiated radical kinetic of crosslinking shows that conversion increases with temperature and Light intensity. A prelimina ry thermal polymerization alters the experimental results at temperatures a bove 80 degreesC. Catalyzed thermal crosslinking was carried out with three initiators: dibenzoyl peroxide (POB), dicumyl peroxide (DCUP) and t-butyl perbenzoate (TBPB). The effects of the nature of the initiator, of the temp erature, of the concentration of initiator and of the number of methacrylat e moieties per polymer chain were investigated by measuring swelling and me chanical properties (storage modulus E ' and maximum of tan delta). The par ticipation of polybutadiene double bonds to the crosslinking is clearly sho wn. Depending on the experimental conditions, ranging from a few minutes to a few hours, various crosslinked materials can be obtained with controlled mechanical properties. (C) 2001 Elsevier Science Ltd. All rights reserved.