Effects of Chain Transfer Agent and Temperature on Branching and β‐Scission in Radical Polymerization of 2‐Ethylhexyl Acrylate

Abstract

Poly(2‐ethylhexyl acrylate) is synthesized by conventional radical bulk polymerization both with and without 1‐dodecane thiol as chain transfer agent (CTA) at temperatures from 4 to 140 °C. Electrospray‐ionization mass spectrometry is used to analyze the polymer. This reveals the occurrence of significant β‐scission at high temperature and confirms the presence of CTA‐capped polymers at all temperatures, as well as combination products from 4 to 65 °C. Subsequent 13C melt‐state NMR analysis allows quantification of branching and β‐scission. Both are reduced when CTA is present, consistent with a “patching” effect. As expected, the amounts of β‐scission and branching increase with synthesis temperature, although β‐scission dominates at the highest temperature. The backbiting rate coefficient of 2‐ethylhexyl acrylate is determined from NMR results, taking β‐scission into account for the first time. Remarkable agreement with literature kbb values is obtained, especially for activation energy. This strongly suggests family‐type behavior for acrylate kbb.

Modeling of the Free Radical Copolymerization Kinetics of n-Butyl Acrylate, Methyl Methacrylate and 2-Ethylhexyl Acrylate Using PREDICI®

“…Termination by combination and disproportionation kinetic rate coefficients for BA and MMA copolymerizations were also taken from WATPOLY, as shown in Equations (22) and (23) [6,31].…”

“…Although MMA is a widely studied monomer, there are no reports that we are aware of where backbiting is important for this monomer. In the case of EHA, there is evidence that backbiting may become important at temperatures in the range of 100 to 140 • C [23]. Since the experiments used in our study were conducted at 60 • C, it is well justified to neglect backbiting for EHA.…”

“…Backbiting and the formation of tertiary radicals have been reported and measured in the polymerization of several acrylates [22,23], mainly BA, methyl acrylate (MA), EHA and dodecyl acrylate (DA). Backbiting for BA was included in our modeling approach because it has been reported to be important [24,25].…”

Influence of Acrylic Acid and Tert-Dodecyl Mercaptan in the Adhesive Performance of Water-Based Acrylic Pressure-Sensitive Adhesives

“…These promote polymer chain terminations and formation of new chains, thus resulting in low molecular weights. According the bibliography, this effect is called the "patching effect" [17,18]. Plessis and Arzamendi [19] showed that by increasing the concentration of the chain transfer agent from 0.00 to 0.15% the gel content decreased from 55 to 0%, as did the average molecular weight.…”

Identification of β scission products from free radical polymerizations of butyl acrylate at high temperature

“…39 Mass spectrometry analyses and in particular ESI-MS proved to be important for getting more insight into the β scission and subsequent migration mechanism. 28,33,34,[39][40][41] The goal of this work was to carefully analyze the products obtained from free radical acrylate polymerizations at temperatures of at least 120°C and to identify the low molar mass scission products. Studying free radical polymerizations appeared particularly important due to its high technical relevance.…”