Methyl α‐cyanoacrylate. I. Free‐radical homopolymerization

Abstract

Methyl α‐cyanoacrylate, when suitably inhibited by Lewis acids against anionic polymerization, can be polymerized readily with free‐radical initiators to form hard, clear, high molecular weight polymers. The ratio of kp2/kt is approximately 0.021 at 60°C. if 100% efficiency of initiation by azobisisobutyronitrile is assumed. Acceleration occurs at very low conversion to polymer during bulk polymerizations. The homopolymer is thermally unstable at temperatures only slightly above the glass temperature (estimated to be 165–170°C.). Degradation of the polymer under gamma irradiation is pronounced, only 18 e.v. being required per main‐chain scission.

Developments and applications of cyanoacrylate adhesives

“…Alkyl 2-cyanoacrylates have been polymerized by both anionic and free radical initiations [80]. The successful preparation of the polymer by free radical initiation necessitated the exclusion of moisture from the system to avoid anionic polymerization.…”

“…Solubility parameters of poly (cyanoacrylates) were determined in 28 solvents [84]. These polymers could only be molded with great difficulty as they decomposed at elevated temperatures [80]. The cast sheets have properties comparable to those of polymethylmethacrylate.…”

Radical Polymerization of Alkyl 2-Cyanoacrylates

“…Poly(CAs) have relatively poor thermal stability [39,40,41,42,43,44,45,46,47,48], and start to degrade slightly above their T g , which is significantly less than their ceiling temperature ( T c ) [42,45]. The latter is the temperature at which the rates of polymerization and depolymerization are equal [49].…”

“…These act by proton transfer to terminate anionic or zwitterionic species, before significant chain growth occurs. Anionic inhibitors have included Lewis acids, such as BF 3 complexes [48], as well as, acetic acid [50,51,52,53], dichloroacetic acid [54], trifluoroacetic acid [55], methanesulfonic acid [47], and 1,3-propanesultone [51,56,57,58]. Excessive acidity should, however, be avoided, due to the potential for the hydrolysis of the monomer/polymer ester functionality leading to interference with the polymerization (see above).…”

“…The earliest report on the kinetics for the radical polymerization of CAs was by Canale et al in 1960, who carried out polymerizations of methyl 2-cyanoacrylate using a boron trifluoride acetic acid complex as an anionic inhibitor and AIBN as the initiator [48]. The bulk parameter, k p / k t 0.5 , (where, k p and k t are the rate coefficients for propagation and termination, respectively) was determined to be 0.021 L·mol −1 ·s −1 at 60 °C.…”