ABSTRACT
This study introduces bis(1-cyanocyclohex-1-yl)trithiocarbonate (TTC-bCCH) as a novel trithiocarbonate chain transfer agent and compares its reactivity with the previously described bis(2-cyanopropan-2-yl)trithiocarbonate (TTC-bCP) for the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St), n-butyl acrylate (nBA), and methyl methacrylate (MMA). Significant findings include the effective control of Mn and low dispersities from the onset of polymerization of St and nBA showing swift addition-fragmentation kinetics, leading to similar behaviors between the two RAFT agents. In contrast, a fourfold decrease of the chain transfer constant to MMA is established for TTC-bCCH over TTC-bCP. This trend is confirmed through density functional theory (DFT) calculations. Finally, the study compares thermoplastic elastomer properties of all-(meth)acrylic ABA block copolymers produced with both RAFT agents. The impact of dispersity of PMMA blocks on thermomechanical properties evaluated via rheological analysis reveals a more pronounced temperature dependence of the storage modulus (G') for the triblock copolymer synthesized with TTC-bCCH, indicating potential alteration of the phase separation.
ABSTRACT
HYPOTHESIS: Random insertion of vinylphosphonic acid (VPA) units into a of PEG-PAA block copolymer improves the chemical stability and properties of hybrid nanoobjects obtained from the complexation of the copolymer with metal ions. EXPERIMENTS: Block polymers based on poly(acrylic acid) (PAA) and poly(ethylene glycol) (PEG) are modified by random insertion of 0 to 100 % of phosphonic acid functions in PAA block by a RAFT polymerization process. These polymers are then used to form hybrid polyionic complexes (HPICs) by complexation with gadolinium or europium ions. The properties of the obtained assemblies are evaluated by magnetic relaxivity, fluorescence and light scattering measurements. FINDINGS: The insertion of VPA units within the PAA block increases the chemical stability of the hybrid micelles by maintaining their integrity even at low pH. This insertion also minimizes the exchange of ions between HPICs and the surrounding medium thanks to a strengthening of interactions toward lanthanide ions. When such systems are used as MRI contrast agents or luminescent probe, 50/50 AA/VPA composition appears to be a good compromise to achieve optimal relaxivity or luminescent properties while ensuring a good chemical stability.
ABSTRACT
Bis(2-cyanopropan-2-yl)trithiocarbonate (TTC-bCP) is a new symmetrical trithiocarbonate with the best leaving group ever reported for reversible addition-fragmentation chain transfer (RAFT) polymerization. We propose an elegant route to obtain TTC-bCP starting from 2,2'-azobis(2-methylpropionitrile) (AIBN) as a donor of the 2-cyanopropan-2-yl group. TTC-bCP allowed the preparation of a high-molar-mass (Mn ≈ 135 kg mol-1) methyl methacrylate-n-butyl acrylate-methyl methacrylate triblock copolymer with unprecedented control (D̵ = 1.04) in reversible-deactivation radical polymerization. Rheology measurements of this triblock copolymer showed a typical thermoplastic elastomer behavior with a steady rubbery plateau up to 120 °C.
