Graft copolymerization of acrylic acid on to styrene butadiene rubber (SBR) to improve morphology and mechanical properties of SBR/polyurethane blend

Graft copolymerization of acrylic acid (AA) on to styrene butadiene rubber (SBR) is carried out via free radical polymerization using benzoyl peroxide (BPO) as initiator. Graft yield (GY) and graft efficiency (GE) measurements reveal that the optimum grafting is achieved when 100 wt % of AA and 3 wt % of BPO are used for a reaction time of 6 h at 60 °C. The execution of the grafting process is confirmed through ATR‐IR spectroscopy and DMTA analysis. Tan δ thermograms indicate that the graft copolymerization occurs in the styrene segments of the SBR backbone. An in situ polymerized, semicrystalline polyurethane (PU) is then used to prepare a series of SBR‐g‐PAA/PU blends. It is found that the SBR‐g‐PAA with the highest GY exhibits the best compatibility with PU matrix. One‐phase morphology (SEM), as well as the appearance of only one glass transition (DMTA) verify the homogeneous miscibility of the modified blend compositions. Moreover, the integration of PUs crystalline structure into blends gives rise to elongation‐induced crystallinity as the prominent phenomenon in tensile testing, which proves to synchronously enhance tensile strength, modulus, elongation at break, and toughness.