Precision Synthesis of ω‑Branch, End-Functionalized Comb Polystyrenes Using Living Anionic Polymerization and Thiol–Ene “Click” Chemistry

A combination of living anionic polymerization and thiol–ene “click” chemistry provides an efficient and convenient method for synthesis of well-defined comb polystyrenes with precisely controlled architecture details and a wide selection of functionalities. ω-(p-Vinylbenzyl)­polystyrene macromonomer was synthesized by sec-butyllithium-initiated polymerization of styrene followed by termination with 4-vinylbenzyl chloride (VBC). For the synthesis of α-4-pentenyl-ω-(p-vinylbenzyl)­polystyrene macromonomer, an unsaturated initiator, 4-pentenyllithium, was used followed by termination with VBC. To ensure successful living anionic polymerization of macromonomers, impurities present in the macromonomers and glass reactors were readily removed by titration with excess sec-butyllithium initiator right before initiation, resulting in polymacromonomers with controlled Mn (74 000, 130 000 g/mol) and narrow Mw/Mn. Living anionic copolymerization of mixtures of both types of macromonomers yielded a well-defined comb-shape precursor with controlled fractions of ω-vinyl branch end groups, which were subsequently subjected to facile and efficient functionalization by photoinitiated thiol–ene “click” reactions with diverse functional groups (−OH, −CO2H, and −C8F17). Characterization by NMR, SEC, and MALDI-TOF mass spectrometry established their chemical structures and chain-end functionalities, which indicates precisely defined comb polystyrenes with controlled degrees of functionalization

Synthesis of Cyclic Polystyrenes Using Living Anionic Polymerization and Metathesis Ring-Closure

A combination of living anionic polymerization and metathesis ring-closure provides an efficient method for synthesis of well-defined, macrocyclic polymers over a broad molecular weight range. A series of well-defined, α,ω-divinylpolystyrene precursors (Mn = 2800, 8600, 17000, and 38000 g/mol) were synthesized by 4-pentenyllithium-initiated polymerization of styrene followed by termination with 4-chloromethylstyrene. Efficient cyclization of these α,ω-divinylpolystyrene precursors was effected in CH2Cl2 and CH2Cl2/cyclohexane mixtures using a Grubb’s catalyst, bis(tricyclohexylphosphine)benzylidine ruthenium(IV) chloride. As the precursor Mn increased, more cyclohexane was added and the concentration of the precursor was decreased from 1.41 × 10–4 to 2.15 × 10–6 M. The macrocyclic polymers were uniquely characterized by MALDI–TOF mass spectrometry in terms of peaks that appeared characteristically 28 m/z units lower than those of the corresponding open-chain precursor peaks, corresponding to the loss of an ethylene unit. Relative to linear analogues, the macrocycles exhibited longer SEC retention volumes, lower intrinsic viscosities, and higher Tgs at the lower Mn values