Quantification of surface-anchored RAFT chain transfer agent on silica particles

Abstract

Surface-initiated RAFT polymerization has received much attention in the fabrication of spherical brushes. The grafting density of surface-anchored RAFT chain transfer agents (SA-RAFT CTA) exerts great influence on the properties of the resulting spherical brushes. In this paper, we proposed a modified measurement approach named fitting method to determine the grafting density of SA-RAFT CTA by means of UV–vis spectrometry using about 100-nm silica particles (SiPs) as model materials. On the basis of an in-depth investigation on the UV absorption and scattering characteristics of SiPs, the background absorption of SiPs in RAFT CTA modified SiPs (SiP@RAFT) was accurately identified by fitting method and the error introduced by the scattering interference of SiPs was greatly suppressed. With such improvement, the present method exhibits a much higher accuracy and sensitivity (the detection limit is 2.6μmol/g), which makes it an ideal method for SA-RAFT CTA quantification, especially for particles with a relatively large size. The present method was successfully applied in the study of RAFT CTA immobilization kinetics and the synthesis of spherical poly(tert-butyl ester) brushes (SiP@P(t-BA)) with tunable brush thickness.