Synthesis of Poly(n-butyl acrylate)-b-poly(ε-caprolactone) through Combination of SG1 Nitroxide-Mediated Polymerization and Sn(Oct)₂-Catalyzed Ring-Opening Polymerization: Study of Sequential and One-Step Approaches from a Dual Initiator

Abstract

A hydroxyl-functionalized alkoxyamine derived from the SG1 nitroxide was used as a dual initiator for ring-opening polymerization (ROP) of ε-caprolactone (CL) and nitroxide-mediated polymerization (NMP) of n-butyl acrylate (BA) to obtain the corresponding block copolymer. Both sequential and one-step strategies were investigated, using the tin(II) 2-ethylhexanoate (Sn(Oct)2) ROP catalyst. The NMP first sequential approach (consisting of performing the NMP before the ROP) successfully provided the diblock copolymer through well-controlled NMP and ROP processes. This copolymer was fully characterized by size exclusion chromatography (SEC), liquid chromatography at the critical conditions (LC-CC) of PBA and PCL, and gradient polymer elution chromatography (GPEC). Conversely, the ROP first strategy led to badly defined PCL (bimodal distribution) in the first ROP step. This was attributed to a side reaction of Sn(Oct)2 with the SG1 nitroxide arising from the alkoxyamine dissociation at the ROP temperature. This strategy was consequently not suitable for obtaining the diblock copolymers. Finally, PBA-b-PCL copolymers were successfully prepared from the dual initiator through a NMP/ROP one-step process in toluene, as shown by 1H NMR spectroscopy, SEC, and GPEC. The success of this one-step approach was explained by a much faster consumption of the BA by NMP than that of the CL by ROP, making the process looking like a NMP first in a one pot experiment.

Transformation of macromonomers into ring‐opening polymerization macroinitiators: A detailed initiation efficiency study

“…Previously, Chagneux et al described the characterization of pBA‐ b ‐pCL block copolymers via LCCC at the critical conditions of pBA and pCL, respectively 32. The block copolymers have been synthesized by the combination of NMP and Sn(Oct) 2 catalyzed ROP.…”

“…Recently, Schmid et al used this chromatography technique for the characterization of block copolymers synthesized by combining RAFT polymerization with ROP 22, 24. Earlier, the characterization of a block copolymer based on pBA and poly(ε‐caprolactone) (pCL), which were synthesized by a combination of nitroxide‐mediated polymerization (NMP) and ROP, was reported by Chagneux et al32…”

Nitroxides: Applications in Synthesis and in Polymer Chemistry

“…The thus obtained poly(e-caprolactone) containing an alkoxyamine was subjected to controlled living radical polymerization of n-butyl acrylate to eventually give poly(nbutyl acrylate)-b-poly(e-caprolactone). [271] The same concept for the synthesis of the block copolymer was applied by using an ATRP initiator which also carries an alkoxyamine. Under ATRP conditions, the alkoxyamine stays dormant and subsequent NMP allows the synthesis of diblock copolymers.…”

Nitroxide: Anwendungen in der Synthese und in der Polymerchemie

“…Das erhaltene Alkoxyamino(ecaprolactam)-Polyamid wurde dann einer kontrollierten radikalischen Polymerisation von n-Butylacrylat unterzogen; das resultierende Copolymer ist Poly(n-butylacrylat)-bpoly(e-caprolactam). [271] Das gleiche Konzept verfolgt ein ATRP-Initiator mit Alkoxyamineinheit: Während der ATRPolymerisation "ruht" das Alkoxyamin, die anschließende NMP führt zur Bildung eines Diblockcopolymers. [272] Schema 51 zeigt, wie der ATRP-NMP-Initiator 140 sozusagen bidirektional agiert und zunächst MMA über ATRP zu einem Makroalkoxyamin umsetzt, das wiederum in der anschließenden NMP von Styrol das Diblockcopolymer 141 liefert.…”