Preparation of Styrene Block Copolymers Using Nitroxide Mediated Polymerization

Preparation of Styrene Block Copolymers Using Nitroxide Mediated Polymerization 

Styrene-containing block copolymers are commercially very important materials. Over a billion pounds of these resins are produced annually. They have found many uses, including reinforcement of plastics and asphalt, adhesives, and compatibilizers for polymer blends, and they are directly fabricated into articles. Most styrene-containing block copolymers are manufactured using anionic polymerization chemistry. However, anionic polymerization is one of the more costly polymerization chemistries because of the stringent requirements for monomer and solvent purity. It would be preferred, from an economic cost perspective, to have the capability to utilize free radical chemistry to make block polymers because it is the lowest cost mode of polymerization. The main reasons for the low cost of FR chemistry are that minimal monomer purification is required and it can be carried out in continuous bulk polymerization processes. 

Modern Styrenic Polymers Polystyrene and Styrenic Copolymers. Edited by J. Scheirs and D. B. Priddy c 2003 John Wiley Sons Ltd 

Nitroxide mediated radical polymerization (NMRP) was pioneered by Riz-zardo and Solomon in the mid-1980s [1]. Their work went unnoticed for almost a decade until Georges et al. reported the preparation of narrow polydispersity (PD) ( 1.2) polystyrene using NMRP [2]. This report initiated an explosion of research aimed at both understanding the mechanism of NMRP and also utilizing it to prepare block copolymers. This chapter describes the application and limitations of NMRP for making styrene-containing block copolymers. 

NMRP is not a true living polymerization but it has some attributes of a living polymerization, e.g. rather narrow polydispersity polymers can be produced, polymer molecular weight increases linearly with monomer conversion, and sequential addition of monomers leads to block copolymers. However, no one has yet produced truly monodisperse polymer using NMRP. Therefore, there are likely side reactions going on during chain growth that lead to adventitious termination. 

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