Novel synthesis of a block copolymer consisting of styrene and ethylene by means of active site modification

Abstract

A block copolymer consisting of styrene and ethylene with a narrow molecular weight distribution has been synthesized by means of active site modification performed by the addition of tertiary diamines to living poly( styrene).It is well known that alkyl-lithium catalysts can cause anionic polymerizations of many unsaturated monomers including isoprene (IP) and styrene (St) to give living polymers bearing terminal carbon-lithium bonds.1.2 When effective modifiers such as N, N, N',N'-tetramethylethylenediamine (TMEDA) are added to the living polymers, the nature of the active site changes markedly, and then polymerization of ethylene (E) is induced subsequently to give block copolymers. We propose to term this modification process 'active site modification,' and briefly reported that block copolymers consisting of IP and E could be synthesized with this approach.3 The corresponding block copolymer can be also prepared with the active site transformation being achieved by the addition of TiC14 to the living polymers.4.5However, this transformation is not an effective method for synthesizing block copolymers consisting of St and E segments owing to chain breaking by P-hydrogen abstraction from the styryl chain.5 We have been attempting to synthesize such a block copolymer by means of active site modification, and now report our preliminary results.A 300 ml glass reactor equipped with a magnetic stirrer and connected to a vacuum system was used for the polymerizations. The polymerization of St was carried out under high vacuum, whereas in the polymerization of E, the pressure was kept at 2 atm.The results of the polymerization of St and E with s-butyl-lithium as catalyst are summarized in Table 1. Although St gave a living polymer in the absence of TMEDA, the polymerization of E proceeded only in the presence of TMEDA.6 These results suggested that the required block copolymer could be synthesized Ly means of active site modification. We therefore carried out the block copolymerization with E by using the living polymer of St.When TMEDA was added to the living poly(St), the cherry red solution turned wine red, indicating that active site modification had been performed. The polymerization of E was then induced and a polymer insoluble in cyclohexane was produced as the polymerization of E proceeded. However, in the absence of TMEDA the copolymerization with E did not take place, and only a homopolymer of St was recovered. The effect of other amines as a modifier was examined. Sparteine

Ethylene Polymerization Initiated by Tertiary Diamine/n-Butyllithium Complexes: An Interpretation from Density Functional Theory Study

“…11 However, signals corresponding to the side reactions were not observed in the 13 C NMR spectrum of polyethylene, and the intensities of the signals from both the initiation and the termination chain ends are almost the same. 12 End functional polyethylene [13][14][15] and block copolymers of ethylene with styrene, isoprene, and methyl methacrylate [16][17][18] could be prepared using anionic polymerization of ethylene.…”