Determination of the Propagation Rate Constant in the Carbocationic Polymerization of 2,4,6-Trimethylstyrene

Abstract

The living carbocationic polymerization of 2,4,6-trimethylstyrene (TMeSt) was studied using the 1-chloro-1-(2,4,6-trimethylphenyl)ethane/BCl3 initiating system in CH2Cl2 from −70 to −20 °C. The equilibrium constant of ionization (K i) was calculated from the cation concentration determined by UV−visible spectroscopy. From the apparent rate constant of propagation (k p app) and K i, the absolute rate constant of propagation for ion pairs k p ± = 1.4 × 104 L mol-1 s-1 was calculated at −70 °C. The rate constant of ion collapse, k - i was determined from the polydispersity vs conversion plots. From K i and k - i, the rate constant of ionization, k i were also calculated. From the temperature dependence of K i, and k - i the enthalpy and entropy of the ionization and deactivation were obtained, respectively. Competition experiments i.e., polymerization carried out in the presence of 2-chloropropene as a π-nucleophile, were also carried out at −70 °C to determine k p ± separately. NMR spectroscopy, gel permeation chromatography, and elemental analysis suggested complete capping of the polymeric cation and the absence of side reactions. From the limiting number-average degree of polymerization and the known rate constant of capping k c = 62.0 L mol-1 s-1, k p ± = 8.3 × 104 L mol-1 s-1 was determined. This value is similar to that determined from k p app and K i; thus, the utility of competition experiments is corroborated.

Organometallic‐Mediated Alternating Radical Copolymerization of tert‐Butyl‐2‐Trifluoromethacrylate with Vinyl Acetate and Synthesis of Block Copolymers Thereof

“…When there is no more VAc in the comonomer feed, the polymerization stops. The apparent propagation rate constant of the copolymerization ( k p(app) ) was determined from the slope of the first‐order kinetic plots (ln([M] 0 /[M]) vs t , Figure S17a, Supporting Information) . The k p(app) versus f MAF‐TBE plot (Figure S17b, Supporting Information) reveals a bell‐shaped curve with a maximum at f MAF‐TBE = 0.5 ( k p(app) = 3.9 × 10 −4 s −1 ) that is in further agreement with an alternating copolymerization.…”

Cationic polymerization in rotating packed bed reactor: Experimental and modeling

“…Two general methods, diffusion clock (DC) and ionic species concentration methods, are typically used to determine the propagation rate constants in cationic polymerization of vinyl monomers. Both of the methods give similar values of k p ( k p = 10 4 –10 5 L mol −1 s −1 ) for the polymerization of some substituted styrenes, while considerable higher values of k p ( k p = 10 9 L mol −1 s −1 ) are obtained by DC method in the case of styrene and isobutylene 16–18. Despite large variation with some monomers, it is generally accepted that the rate constants of propagation in the cationic polymerization of alkenes are similar for most systems with k p = 10 5 ± 1 L mol −1 s −1 16, 19.…”

High‐Molecular‐Weight Polynucleotides by Transferase‐Catalyzed Living Chain‐Growth Polycondensation

“…which is awell-known equation in polymer science to describe the kinetics of living polymerization reactions. [16] To experimentally study TcEP kinetics,w ec hose Cy5-(dT) 10 and deoxythymidine triphosphate (dTTP) as the initiator and monomer,r espectively,f or the following reasons:1)the Cy5 labeling allows us to measure the progress of the TcEP reaction quantitatively by fluorescence gel electrophoresis;2 )during the polymerization reaction the homopoly(dT) does not form secondary structures that could impede the polymerization;a nd 3) ar ange of unnatural nucleotides (i.e., dTTP analogs) are available for further studies.W ef ocus our experiments here on dTTP,b ut our kinetics model is applicable,w ithout loss of generality,a lso for other nucleotides (see Figures S2 and S3 in the Supporting Information). [9a, 17] To verify our hypothesis that TcEP follows al iving polymerization mechanism, we first studied the effect of varying the initial monomer concentrations on the DP of our synthesized polynucleotides.W eused three different starting molar ratios of monomer to initiator (200, 500, and 1000), and determined the DPs of the reaction products at different reaction times by fluorescence gel electrophoresis.T oo btain more accurate estimates of the DP from fluorescence gel electrophoresis,w ed eveloped aC y5 labeled poly(dT) x standard (see the Supporting Information) that retains the same chemical identity as TcEP synthesized polynucleotides, and these standards are shown in the lane labeled as "L"i n When fitting the experimental data to living polymerization kinetics [Eq.…”