Atom Transfer Radical Polymerization in the Solid-State.

Hong Y Cho,Christopher W Bielawski

doi:10.1002/anie.202005021

Abstract

Poly(2‐vinylnaphthalene) was synthesized in the solid‐state by ball milling a mixture of the corresponding monomer, a Cu‐based catalyst, and an activated haloalkane as the polymerization initiator. Various reaction conditions, including milling time, milling frequency and added reductant to accelerate the polymerization were optimized. Monomer conversion and the evolution of polymer molecular weight were monitored over time using 1H NMR spectroscopy and size exclusion chromatography, respectively, and linear correlations were observed. While the polymer molecular weight was effectively tuned by changing the initial monomer‐to‐initiator ratio, the experimentally measured values were found to be lower than their theoretical values. The difference was attributed to premature mechanical decomposition and modeled to accurately account for the decrement. Random copolymers of two monomers with orthogonal solubilities, sodium styrene sulfonate and 2‐vinylnaphthalene, were also synthesized in the solid‐state. Inspection of the data revealed that the solid‐state polymerization reaction was controlled, followed a mechanism similar to that described for solution‐state atom transfer radical polymerizations, and may be used to prepare polymers that are inaccessible via solution‐state methods.

Highlights

Ball milling (BM) processes have garnered attention because they can provide efficient and environmentallyfriendly alternatives to solution-based reactions.[1]
A zirconium dioxide milling jar was charged with a 50:1:1 molar ratio of 2-VN, phenylethyl bromide (PE-Br), and CuIBr/tris(2-pyridylmethyl)amine (TPMA) under nitrogen (N2)
A linear correlation between the polymer molecular weight (MW) and monomer conversion was observed (Figure 1 C), the experimentally determined number average MW (Mn,size exclusion chromatography (SEC)) was lower than its theoretical value (Mn,Theory),[16] and attributed to premature mechanical degradation. These and other results indicated that the solid-state polymerization reaction was proceeding in a manner consistent with those described for the solution-state atom transfer radical polymerization (ATRP) and other controlled radical polymerization reactions.[12b]

Summary

Introduction

Ball milling (BM) processes have garnered attention because they can provide efficient and environmentallyfriendly alternatives to solution-based reactions.[1]. Kim reported a BM method for facilitating the ring-opening polymerization of d-lactide in the presence of catalytic amount of an organic base (Scheme 1 C).[7d] After 2 h of milling, 81 % of the monomer was converted to high MW poly(lactic acid) (PLA). To quantify the decomposition processes, models were created to accurately predict polymer MW as a function of milling time It will be shown how the technique may be used to prepare copolymers comprised of monomers that exhibit different solubilities and be used to circumvent fundamental challenges commonly encountered with the synthesis of such types of materials

Results and Discussion

Conclusion

Conflict of interest