Sequential Bulk Anionic Polymerization of α‐Methylstyrene and Isoprene to Form Diblock and Triblock Copolymers

Abstract

to polymer. [17][18][19][20] However, this strategy usually results in a low level of control when diene monomer is copolymerized with AMS, since the polar solvents or additives result in a preference for 1,2-addition over 1,4-addition of diene, [18,19] and it is well known that only the 1,4-structured polydiene leads to an elastomeric property.Research has also been directed to synthesize triblocks through difunctional initiators (e.g., dilithio compounds) with comonomer block in the middle and PAMS blocks on both ends. [21][22][23][24][25] In this case, the PAMS block is polymerized right after the completion of comonomer. This method allows the polymerization of diene monomer in nonpolar solvent, but the crossover reaction from polydiene to AMS polymerization is usually quite slow in nonpolar solvents. It is found that the crossover reaction to AMS can be significantly enhanced through the introduction of a small amount of styrene monomers or polar additives (e.g., dimethyl ether, tetrahydrofuran (THF), and trimethylamine) before AMS addition. [21,22,26] Our objective in this research was to investigate the relative reactivity of AMS and isoprene in a bulk polymerization to develop a sequential synthetic pathway for block copolymer formation. Our approach was to develop a bulk anionic polymerization method that utilizes the AMS as solvent for isoprene polymerization in order to polymerize the isoprene in a predominately 1,4-fashion. While it is well-known that dienes are preferentially polymerized in a 1,4-fashion in nonpolar solvents, the investigation of AMS as nonpolar medium has not been widely studied as a solvent for diene polymerization. The investigation of AMS-diene triblock copolymer by sequential polymerization strategy in bulk is very rare. In the current study, we first investigated the anionic polymerization of AMS in bulk without added solvent and the relative reactivity of AMS and isoprene under the bulk AMS conditions. We have developed a simple method to use sec-butyllithium as an initiator for AMS, and block copolymers are synthesized sequentially with good control over molecular weight with relatively narrow molecular weight distributions. The synthesis of diblock copolymer (PAMS-b-PI) involves the formation of a PAMS block first followed by the introduction of isoprene in order to switch the polymerization from AMS to isoprene. N,N,N′,N′-tetramethylethylenediamine (TMEDA) was introduced as a polar additive to crossover to AMS polymerization and produce Anionic Polymerization α-Methylstyrene (AMS) is determined to polymerize anionically by initiation with sec-bultyllithium under bulk conditions with control of molecular weight depending on reaction time. Furthermore, the reactivity between AMS and isoprene in a mixture at a high AMS concentration (90% v/v) indicates a strong inclination for almost sole isoprene polymerization (>97%). The microstructure of the polyisoprene is determined to be predominately 1,4-polyisoprene in the bulk AMS polymerization. These results afford a sequential pr...

Characterization and kinetics study of poly(α-methyl styrene) synthesized by living anionic polymerization

“…Free-radical polymerization of α-methyl styrene, hindered by a low ceiling temperature (T c =61°C), tends to be slow and predominantly yields low molecular weight products due to steric repulsions between substituents in consecutive monomer units [6,7]. Anionic polymerization is an alternative method which results in well-de ned macromolecular structures, providing PAMS with tailor-made properties for speci c applications.…”