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 methacryloyl isocyanate (MAI). Immobilization of methacrylate functions was carried out at 40°C with or without dibutyl tin dilaurate (DBTL) as a catalyst. The reaction was fast and nearly instantaneous with DBTL. Methacrylate moieties were introduced quantitatively at the rate of 1.2, 2 and 2.4 per polymer chain. The photoinitiated radical kinetic of crosslinking shows that conversion increases with temperature and light intensity. A preliminary thermal polymerization alters the experimental results at temperatures above 80°C. 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 temperature, of the concentration of initiator and of the number of methacrylate moieties per polymer chain were investigated by measuring swelling and mechanical properties (storage modulus E′ and maximum of tan δ). The participation of polybutadiene double bonds to the crosslinking is clearly shown. Depending on the experimental conditions, ranging from a few minutes to a few hours, various crosslinked materials can be obtained with controlled mechanical properties.