Experimental study of the spontaneous thermal homopolymerization of methyl andn‐butyl acrylate

Abstract

This article presents an experimental study of the spontaneous thermal homopolymerization of methyl acrylate (MA) and n-butyl acrylate (nBA) in the absence of any known added initiators at 120 and 140 C in a batch reactor. The effects of the solvent type, oxygen level, and reaction temperature on the monomer conversion and polymer average molecular weights were investigated. Three solvents, dimethyl sulfoxide (DMSO; polar, aprotic), cyclohexanone (polar, aprotic), and xylene (nonpolar) were used. The spontaneous thermal polymerization of MA and nBA in DMSO resulted in a lower conversion and higher average molecular weights in comparison to polymerization in cyclohexanone and xylene under the same conditions. The highest final conversion of both monomers was obtained in cyclohexanone. The high polymerization rate in cyclohexanone was most likely due to an additional initiation mechanism where cyclohexanone complexed with the monomer to generate free radicals. Bubbling air through the mixture led to a higher monomer conversion during the early stage of the polymerization and a lower polymer average molecular weight in xylene and cyclohexanone; this indicated the existence of a distinct behavior between the air-and nitrogen-purged systems. Matrixassisted laser desorption/ionization time-of-flight analysis of the polymer samples taken from nitrogen-bubbled batches did not reveal fragments from initiating impurities. On the basis of the identified families of peaks, monomer self-initiation is suggested as the principal mode of initiation in the spontaneous thermal polymerization of MA and nBA at temperatures above 100 C.

Backbiting and β-scission reactions in free-radical polymerization of methyl acrylate

“…Grady et al and Quan et al reported reproducible monomer conversions of 70–90% in homopolymerization and copolymerization of a class of alkyl acrylates and methacrylates at 120–200°C in the absence of any conventional thermal initiators. Density functional theory (DFT) studies combined with experimental mass spectrometric analysis revealed that the Flory mechanism is responsible for the monomer self‐initiation at high temperatures. It was shown that two types of monoradicals (shown in Chart ), monomeric monoradical (MMR), and dimeric monoradical (DMR), are the initiating species in the self‐initiated homopolymerization of alkyl acrylates and methacrylates …”

Stimuli-responsive 4-acryloylmorpholine/4-acryloylpiperidine copolymers via nitroxide mediated polymerization

“…All of this suggests a dead macroinitiator. The reasons for this are not entirely clear at this point but it is possible that the second batch was polymerized strictly thermally at high temperatures, which has been observed in acrylate polymerizations …”

Study of n-Butyl Acrylate Self-Initiation Reaction Experimentally and via Macroscopic Mechanistic Modeling

“…Studies using electron spray ionization-Fourier transform mass spectrometry (ESI-FTMS), nuclear magnetic resonance (NMR) spectroscopy, and macroscopic mechanistic modeling did not identify the initiating species or the mechanism of initiation in the spontaneous thermal polymerization [7,9]. However, quantum chemical calculations [10][11][12][13] together with matrix-assisted laser desorption ionization (MALDI) [14] showed that monomer self-initiation is one of the likely mechanisms of initiation in spontaneous thermal polymerization of alkyl acrylates.…”