Zwitterionic polymerization of butyl cyanoacrylate by triphenylphosphine and pyridine

Abstract

This paper describes a re-examination of the kinetics and molecular weights formed in the zwitterionic polymerization of butyl cyanoacrylate by triphenylphosphine ( P h P) and pyridine (Py) in THF, and an extension to include the solvents, diethyl ether (EGO), dimethoxyethane (DME) and hexane. In THF, the previously observed kinetics were confirmed, yielding evidence for absence of termination, and values for rate constants for initiation (4 ) and propagation (la) with substantial agreement between the values for /$, obtained from both systems. At 20"C, the mean value found for kp in THF was 3 . lo5 1 . mol-' . s -' ; in EGO, some 10 times lower, and in hexane, 10 times lower again. The temperature dependence of /$ in THF was confirmed to be extremely low and anomalous; in EbO rather greater and near-normal, corresponding to an energy of activation of ca. 5 kcal. mol-' . A correction procedure enabled the large experimental scatter in the kp values to be reduced sufficiently to reveal trends downwards at higher concentrations of propagating species, i. e. evidence for their dissociation on dilution.In Py-initiated polymerizations, excess of pyridinium salts did not depress kp ; evidence that the propagating species are preponderately paired ions, not free. It is concluded that at 20°C these species are mainly 'tight' ion-pairs in all solvents, and remain so in EGO at all temperatures down to -80 "C. In THF, over this temperature range, there is increasing solvation producing an increasing proportion of more reactiveLsolvent-separated' ion-pairs. The molecular weights produced under all conditions were high ( M , usually 1 to 3 . lo6). Those produced by high concentration of Ph,P did not conform to theory; others followed the 'no-termination' theory as modified to allow for a small effect of transfer. I COOBu which propagate anionically without termination, provided acidic contaminants or additives are excluded;2) that in THF, triethyl and triphenyl phosphines initiate sufficiently fast as to be effectively completely converted to propagating species, so that the overall kinetics 9 In what follows, th charge signs w i l l be omitted, and the concentration of zwitterions of all chain lengths be represented simply by [Z].

Stationary‐state kinetics in the polymerization of ethyl α‐cyanoacrylate by phenazines

“…The kinetics were concluded to follow the SINT pattern found with other tertiary amines 2 , 3 ) (an equation of the same form as found for this monomer and its butyl homologue initiated by several different tertiary amines).…”

Rubbery wound closure adhesives. II. initiators for and initiation of 2-octyl cyanoacrylate polymerization

“…These CAs, due to the strongly electron‐withdrawing 2‐cyanide and ‐ester substituents at the vinyl function, are extremely reactive monomers that rapidly polymerize anionically upon contact with a variety of initiators, including even the weakest nucleophiles …”

Radical Polymerization of Alkyl 2-Cyanoacrylates

“…Initiation can rapidly occur upon contact with anions, as well as with non-dissociated base species, such as tertiary amines and tertiary phosphines, leading to zwitterionic polymerization [23,24,25,26,27,28]. Regardless of whether polymerization is initiated by an anionic or non-dissociated nucleophilic base, a propagating carbanion is formed on the α-carbon, which is resonance stabilized through the CN and CO 2 R groups (Scheme 2).…”

“…The investigations carried out by Pepper et al demonstrated that in the absence of strong acid, the polymerization has no intrinsic termination reactions, and the poly(CA) carbanions are stable enough to remain active, even after addition of small amounts of common terminating agents, such as water, oxygen or CO 2 [23,24,25,26,27,28,32]. The stability of the propagating species is in stark contrast to other common monomers like styrenics or (meth)acrylates, for example, where, in the case of organolithium-initiated anionic polymerizations, the introduction of trace amounts of air or moisture terminates polymer growth by reacting with the active chain-end anions or the (often organometallic) initiator.…”