Pulsed-laser and quantum mechanics study of n-butyl cyanoacrylate and methyl methacrylate free-radical copolymerization†
The free-radical polymerization (FRP) kinetics for n-butyl cyanoacrylate (BCA) and methyl methacrylate (MMA) copolymerization are studied in bulk at 30–70 °C using both a pulsed-laser polymerization technique and Quantum Mechanics (QM). Through the addition of 1 v% dichloroacetic acid, the notoriously rapid anionic polymerization of alkyl-cyanoacrylates (ACA) is successfully suppressed without affecting the FRP process. A strongly alternating copolymer sequence distribution is confirmed by reactivity ratio estimates determined using 1H-NMR composition analysis (rBCA = 0.236 ± 0.042 and rMMA = 0.057 ± 0.008), in excellent agreement with QM predictions (rBCA = 0.272 and rMMA = 0.057) made at 50 °C. For MMA-rich monomer mixtures (0.50 ≤ fMMA ≤ 0.97), overall propagation rate coefficients (kp,cop) greater than twice the value for MMA homopolymerization (kp,MMA) are facilitated by the strongly alternating copolymerization kinetics, whereas the BCA propagation rate coefficient (kp,BCA) is estimated to be only 336 ± 20 L mol−1 s−1 at 50 °C, approximately half the value of kp,MMA. These detailed results renew our understanding of the FRP kinetics for this class of monomer, important to adhesive and biomedical applications, and illustrate that an extensive and otherwise inaccessible (via anionic polymerization) level of control can be achieved over poly(ACA) final properties.