New telechelic polymers and sequential copolymers by polyfunctional initiator–transfer agents (inifers). XLI. Kinetic and reactivity studies on sterically hindered inifers

Abstract

SynopsisThe kinetics of chain transfer to the bifunctional initiating and transfer agents (binifem) 1,4di(2chloro-2-propyl)benzene (p-DCC), 1,3di(2chloro-2-propyl)-5-tert-butylbenzene (rn-tBuDCC), and 1,3di(2chloro-2-propyl)-4,6-dimethylbenzene (rn-DMeDCC) in the polymerization of isobutylene has been investigated. Chain transfer to monomer was shown to be absent up to -20°C in CH,Cl/n-hexane and CH,Cl,/n-hexane mixtures using the rn-tBuDCC/BCl, binifer system. Chain transfer constants (C,) to rn-tBuDCC and k J k , ratios determined in the range from -30°C to -80°C in CH,Cl/n-hexane mixtures and pure CH,Cl solvent are reported, and the activation energy differences E l , , -E , and E, -E , were calculated. Chain transfer constants to p-DCC and rn-DMeDCC were determined by the use of pure CH3C1 diluent at -50°C. The chain transfer reactivity of five different inifers is discussed and compared based on C, values obtained under identical conditions, with special regard to the new, sterically hindered binifer m-DMeDCC of extraordinary reactivity.Polymerizations were carried out in the range from -80°C to -20°C under a dry nitrogen atmosphere in a dry box using a three-necked flask (250 mL) equipped with a stirrer. Details of the procedures have been de~cribed.3*~,~ 'H-NMR spectra were taken by a Varian T-60 NMR spectrometer using carbon tetrachloride solutions (-20% by weight) and TMS standard. RESULTS AND DISCUSSIONChain transfer studies, where applicable, are based on m, equations derived earlier.'S2 Thus

Living carbocationic polymerization. 31. A comprehensive view of the inifer and living mechanisms in isobutylene polymerization

“…In CH3CI solvent (Figure 6), Ci = 0.96 is virtually identical with a value (0.95) obtained earlier with a similar system. 4 The fact that kt/kp ~0 indicates the absence of permanent termination, i.e., the living nature of this system. A similar inifer plot obtained with CH2CI2 (Figure 7) gave Ci = 0.49 and kt/kp ~0, indicating the absence of permanent termination in that system.…”

“…The answer comes from several sources: from an insufficient analysis of the effect of temperature on kt/kp, from not investigating the effect of polymerization time on inifer consumption, and from not appreciating the extraordinary sensitivity of inifer systems to medium polarity. In regard to the effect of temperature on the relative rate of termination, an analysis of pertinent inifer data published by Santos et al 4 and Fehervari et al 19 holds important clues: according to these sources, kt/kp obtained for similar binifer systems decreases as the polarity of the medium increases and the temperature decreases. Thus, it is not too surprising that at -75 °C (used in the present study) kt/kp ~0, in other words, irreversible termination was "frozen out".…”