Synthesis and characterization of graft copolymers of syndiotactic polystyrene with polybutadiene and 4-methylstyrene

• Published in: Journal of applied polymer science 2009-04, Vol.112 (1), p.335-344
• Main Authors: Srinate, Nathinee, Thongyai, Supakanok, Praserthdam, Piyasan
• Format: Article
• Language: English
• Subjects: Applied sciences; Copolymerization; Exact sciences and technology; graft copolymers; metallocene catalysts; Organic polymers; Physicochemistry of polymers; polybutadiene; polystyrene; Preparation, kinetics, thermodynamics, mechanism and catalysts; synthesis
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.29387

The basic method for synthesizing syndiotactic polystyrene-g-polybutadiene graft copolymers was investigated. First, the syndiotactic polystyrene copolymer, poly(styrene-co-4-methylstyrene), was prepared by the copolymerization of styrene and 4-methylstyrene monomer with a trichloro(pentamethyl cyclopentadienyl) titanium(IV)/modified methylaluminoxane system as a metallocene catalyst at 50°C. Then, the polymerization proceeded in an argon atmosphere at the ambient pressure, and after purification by extraction, the copolymer structure was confirmed with ¹H-NMR. Lastly, the copolymer was grafted with polybutadiene (a ready-made commercialized unsaturated elastomer) by anionic grafting reactions with a metallation reagent. In this step, poly(styrene-co-4-methylstyrene) was deprotonated at the methyl group of 4-methylstyrene by butyl lithium and further reacted with polybutadiene to graft polybutadiene onto the deprotonated methyl of the poly(styrene-co-4-methylstyrene) backbone. After purification of the graft copolymer by Soxhlet extraction, the grafting reaction copolymer structure was confirmed with ¹H-NMR. These graft copolymers showed high melting temperatures (240-250°C) and were different from normal anionic styrene-butadiene copolymers because of the presence of crystalline syndiotactic polystyrene segments. Usually, highly syndiotactic polystyrene has a glass-transition temperature of 100°C and behaves like a glassy polymer (possessing brittle mechanical properties) at room temperature. Thus, the graft copolymer can be used as a compatibilizer in syndiotactic polystyrene blends to modify the mechanical properties to compensate for the glassy properties of pure syndiotactic polystyrene at room temperature.