to their linear precursors, cyclic PAzoMA exhibited a lower T g , different phase
transition temperatures, as well as smaller phase transition enthalpy and entropy.
Differences in the liquid crystalline properties were also studied in detail.
Zhu and coworkers [89] reported cyclic polymers with pendant carbazole units.
4-Vinylbenzyl-carbazole (VBCZ) was polymerized by ATRP with an alkyne functional initiator. After azidation, cyclic PVBCZ was efficiently synthesized by CuAAC
in DMF (Scheme 40). Cyclic PVBCZ exhibited unique properties in comparison with
its linear counterpart: a higher T g , enhanced fluorescence with a longer fluorescence
lifetime, and different redox behavior. These results suggested that the structure–property relationship was strongly affected by the polymer topology.
The Diels–Alder reaction is another heterodifunctional coupling reaction that
has been applied for the synthesis of cyclic polymers. The first example was
reported by Mizawa et al in 2000 [90]. Linear PMMA was first synthesized by
living anionic polymerization with a silane-protected anionic initiator followed by a
two-step post-functionalization. The linear α-maleimide-ω-dienyl heterodifunctional PMMA was then cyclized in THF by refluxing for 24 h (Scheme 41).
With the great progress in LRP in the past decade, Durmaz et al. [91] again used
the Diels–Alder reaction to synthesize cyclic PSTY and cyclic PSTY-b-PCL. They
synthesized 9-anthyryl methyl 2-bromo-2-methyl propanoate as an ATRP initiator
for the polymerization of styrene to afford linear PSTY with anthyryl chain end.
After conversion of the bromo to azido group, the linear PSTY was then “clicked”
with a furan-protected maleimide-ω-alkyne heterofunctional linker. Cyclization
was achieved by Diels–Alder reaction in toluene with reflux for 48 h. Although
their results suggested the successful synthesis of the target cyclic product, the
involvement of another step of CuAAC click reaction makes the synthesis procedure more tedious (Scheme 42).
Scheme 40 Synthesis of cyclic polymer containing pendant carbazole units through the combination of ATRP and CuAAC reaction
Synthesis of Cyclic Polymers via Ring Closure
323
transition temperatures, as well as smaller phase transition enthalpy and entropy.
Differences in the liquid crystalline properties were also studied in detail.
Zhu and coworkers [89] reported cyclic polymers with pendant carbazole units.
4-Vinylbenzyl-carbazole (VBCZ) was polymerized by ATRP with an alkyne functional initiator. After azidation, cyclic PVBCZ was efficiently synthesized by CuAAC
in DMF (Scheme 40). Cyclic PVBCZ exhibited unique properties in comparison with
its linear counterpart: a higher T g , enhanced fluorescence with a longer fluorescence
lifetime, and different redox behavior. These results suggested that the structure–property relationship was strongly affected by the polymer topology.
The Diels–Alder reaction is another heterodifunctional coupling reaction that
has been applied for the synthesis of cyclic polymers. The first example was
reported by Mizawa et al in 2000 [90]. Linear PMMA was first synthesized by
living anionic polymerization with a silane-protected anionic initiator followed by a
two-step post-functionalization. The linear α-maleimide-ω-dienyl heterodifunctional PMMA was then cyclized in THF by refluxing for 24 h (Scheme 41).
With the great progress in LRP in the past decade, Durmaz et al. [91] again used
the Diels–Alder reaction to synthesize cyclic PSTY and cyclic PSTY-b-PCL. They
synthesized 9-anthyryl methyl 2-bromo-2-methyl propanoate as an ATRP initiator
for the polymerization of styrene to afford linear PSTY with anthyryl chain end.
After conversion of the bromo to azido group, the linear PSTY was then “clicked”
with a furan-protected maleimide-ω-alkyne heterofunctional linker. Cyclization
was achieved by Diels–Alder reaction in toluene with reflux for 48 h. Although
their results suggested the successful synthesis of the target cyclic product, the
involvement of another step of CuAAC click reaction makes the synthesis procedure more tedious (Scheme 42).
Scheme 40 Synthesis of cyclic polymer containing pendant carbazole units through the combination of ATRP and CuAAC reaction
Synthesis of Cyclic Polymers via Ring Closure
323