Physicochemical characterization of poly(tert-butyl acrylate-b-methyl methacrylate) prepared with atom transfer radical polymerization by inverse gas chromatography

Poly(tert-butyl acrylate) (PtBuA) was synthesized by atom transfer radical polymerization (ATRP) using methyl-2-bromo propionate (MBP) as an initiator in bulk at 80 °C. The successive ATRP of methyl methacrylate in diphenyl ether at 80 °C using previously obtained PtBuA as a macroinitiator led to formation of poly(tert-butyl acrylate-b-methyl methacrylate) (poly(tBuA-b-MMA)). The synthesized macroinitiator and block copolymer have controlled molecular weight and low polydispersity (M_w/M_n<1.2). The block copolymer was characterized by gel permeation chromatography (GPC) and ¹H NMR. The retention diagrams of poly(tBuA-b-MMA) for some aliphatic esters and aromatic hydrocarbons were obtained using inverse gas chromatography (IGC) technique. The glass transition temperatures, T_gs of poly(tBuA-b-MMA) were determined by both differential scanning calorimeter (DSC) and IGC. It was observed that the block copolymer represents three T _gs at 50, 75 and 100 °C by IGC although it represents only one T_g at 71 °C by DSC. After the column was quenched from 180 to 0 °C, the T_g at 100 °C shifted to 105 °C however others did not change. Specific retention volumes, Vg0 and the thermodynamical polymer-solvent interaction parameters such as Flory-Huggins, χ12∞, equation-of-state, χ12* and effective exchange energy, X_eff were found for all studied solvents. Partial molar heat of sorption, ΔH̄1,sorp, partial molar heat of mixing, ΔH̄1∞ and molar heat of vaporization, ΔH_v, were determined. In addition, the solubility parameter of the corresponding block copolymer, δ₂ was determined as 11.0 (cal/cm³)^1/2 at 25 °C.