2,5-Di-(2-ethylhexanoylperoxy)-2,5-dimethylhexane as difunctional radical initiator in reverse iodine transfer polymerization (RITP) of styrene, methyl methacrylate and butyl acrylate

The use of 2,5-di-(2-ethylhexanoylperoxy)-2,5-dimethylhexane (T141) as difunctional radical initiator in Reverse Iodine Transfer Polymerization (RITP) was studied at 80 °C (k _d,T141 = 9.6 × 10⁻⁵ s⁻¹) for styrene (St), methyl methacrylate (MMA) and butyl acrylate (BuA). Firstly, the apparent efficiency coefficients α and β were determined by RITP of St, MMA and BuA using monofunctional initiators such as dilaurylperoxide (LYP) at 73 °C (k _d,LYP = 9.6 × 10⁻⁵ s⁻¹) and bis(4-tert-butylcyclohexyl)peroxydicarbonate (P16S) at 59 °C (k _d,P16S = 9.6 × 10⁻⁵ s⁻¹). The decomposition of the monofunctional initiators LYP and P16S generates free radicals with similar structures as those produced during the homolysis of T141. Once the polymerization reactions were performed, monomer conversions were determined by proton nuclear magnetic resonance and the molecular weights M_n,exp were obtained by size exclusion chromatography. Thus, the following apparent efficiency coefficients were calculated: α = 0.41 and β = 1.00 for St, α = 0.14 and β = 0.75 for MMA and α = 0.07 and β = 0.14 for BuA. Afterwards, these values were successfully tested in RITP using an asymmetric initiator such as tert-amyl peroxy-2-ethylhexanoate (T121). In addition, the RITPs were performed for all three monomers using T141 as difunctional initiator. The results prove that the calculated values for α and β were consistent, since the theoretical molecular weights in all polymeric samples match well with the M_n,exp.