Synthesis of Syndiotactic Macrocyclic Poly(methyl methacrylate) via Transformation of the Growing Terminal in Stereospecific Anionic Polymerization

Abstract

In this study, the synthesis of well-defined cyclic syndiotactic poly(methyl methacrylate) (st-PMMA) is investigated by transformation of the growing terminal in stereospecific anionic polymerization. st-PMMA is first synthesized by living syndiospecific anionic polymerization in tetrahydrofuran at a low temperature, which is started with a protected-alkyne initiator prepared in situ by metal-halogen exchange reaction of an α-haloester bearing a pendent protected-alkyne with 1,1-diphenylhexyl lithium. The anionic polymerization is terminated with halogenation of the growing enolate terminal by CBrCl 3 . The terminal halogen of the obtained st-PMMA is further converted into azide group, which is subsequently employed in the intramolecular copper-catalyzed click reaction in high dilution with the alkyne-initiating terminal after deprotection. The macrocyclic st-PMMA is confirmed by 1 H NMR, size exclusion chromatography, and MALDI-TOF MS analyses.

Synthesis of Isotactic-block-Syndiotactic Poly(methyl Methacrylate) via Stereospecific Living Anionic Polymerizations in Combination with Metal-Halogen Exchange, Halogenation, and Click Reactions

“…Methyl methacrylate (MMA; TCI, Tokyo, Japan, >99.8%), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU; TCI, Tokyo, Japan, >98.0%), and CCl 4 (Kanto, Tokyo, Japan, >99.9%) were distilled from calcium hydride before use. t -BuMgBr, diphenylhexyllithium (DPHLi), and 3-(trimethylsilyl)propargyl α-bromoisobutyrate ( 1 ) were prepared according to the literature [36,50,51,52,53]. Toluene (Kanto, Tokyo, Japan, >99.5%; H 2 O <0.001%) and tetrahydrofuran (THF; Kanto, >99.5%; H 2 O <0.001%) were dried and deoxygenized by passage through columns of Glass Contour Solvent Systems (Glass Contour, Nashua, NH, USA) before use.…”

“…The unique structures and properties of synthetic polymers have attracted attention from both fundamental and application viewpoints [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. Furthermore, these stereoregular polymer chains have been incorporated into various well-defined polymers, such as block, star, graft, and end-functionalized polymers, to create novel properties and functions [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ].…”

“…We have recently determined that the halogenation of the growing enolate terminal in the isotactic and syndiotactic living anionic polymerization of MMA is efficient and feasible upon the addition of CCl 4 or CCl 3 Br in the presence of a strong Lewis base, such as 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) [ 50 ]. Furthermore, the halogen terminal of PMMA can be almost quantitatively transformed into an azide terminal via a reaction with sodium azide [ 33 , 36 ]. In addition, an alkyne-capped PMMA can be synthesized by a living anionic polymerization of MMA that is initiated via an in situ metal-halogen exchange reaction between 1,1-diphenylhexyl lithium, i.e., the sacrificial anion source, and an α-haloester bearing a pendent silyl-protected alkyne group, i.e., a precursor of the functionalized initiator [ 36 ].…”

“…Furthermore, the halogen terminal of PMMA can be almost quantitatively transformed into an azide terminal via a reaction with sodium azide [ 33 , 36 ]. In addition, an alkyne-capped PMMA can be synthesized by a living anionic polymerization of MMA that is initiated via an in situ metal-halogen exchange reaction between 1,1-diphenylhexyl lithium, i.e., the sacrificial anion source, and an α-haloester bearing a pendent silyl-protected alkyne group, i.e., a precursor of the functionalized initiator [ 36 ]. In our previous report, both α-alkyne and ω-azide chain-end functionalizations were used in a single polymer chain of st -PMMA to enable the synthesis of cyclic st -PMMA.…”

Synthesis and stereocomplexation of PMMA‐based star polymers prepared by a combination of stereospecific anionic polymerization and crosslinking radical polymerization

“…Thus, the mechanistic transformation of an active species can be easily achieved through the halogenation from a living anionic polymerization to a living radical polymerization to form block copolymers. Therefore, a polymer with a higher stereoregularity due to anionic polymerization instead of radical polymerization could be used as a macroinitiator for a radical polymerization, resulting in the synthesis of novel stereoregular macromolecular architectures . In this study, the synthesis of novel core‐crosslinked star polymers with various stereoregular arm polymers was examined by introducing a halogen atom into the end of syndiotactic and isotactic PMMAs via an anionic polymerization and adapting the linking reaction via a radical polymerization of a divinyl compound using a transition metal catalyst (Scheme ).…”