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

• Published in: Macromolecules Vol. 44; no. 19; pp. 7538 - 7545
• Main Authors: Quirk, Roderic P, Wang, Shih-Fan, Foster, Mark D, Wesdemiotis, Chrys, Yol, Aleer M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11-10-2011
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymerization; Preparation, kinetics, thermodynamics, mechanism and catalysts; Intramolecular reaction; End group; Metathesis; Experimental study; Monodispersed polymer; Chemical modification; Cyclization; Cyclic polymer; Styrene derivatives; Chlorocarbon; Preparation; Anionic polymerization; Styrene polymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma200931n

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 (M n = 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 M n 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 T gs at the lower M n values.