Neil T. McManus

A detailed study of the hydrogenation of nitrile-butadiene rubber and other substrates catalyzed by Ru(II) complexes

Abstract Development of a computer controlled apparatus for measurement of gas uptake at elevated temperatures and pressures has made possible a study of the kinetics of NBR hydrogenation at conditions approaching those that are used in commercial operations. Complexes of the form Ru(X)Cl(CO)L 2 where X = H or β-styryl (CH  CH(Ph)) and L is a bulky phosphine such as tricyclohexyl- or triisopropyl-phosphine are excellent catalysts for the hydrogenation of CC in a variety of polymers and are superior to other Ru complexes for the hydrogenation of CC in nitrile-butadiene rubber. This report describes comparative studies using these complexes for the hydrogenation of CC in various polymer and small molecule substrates. Also presented are complete details of an in depth mechanistic study into the hydrogenation of NBR catalyzed by the complex Ru(CHCH(Ph))Cl(CO)(PCy 3 ) 2 .

A kinetic investigation of styrene/ethyl acrylate copolymerization

An experimental study of the bulk-free radical copolymerization of styrene (STY)/ethyl acrylate (EA) initiated by 2,2′-azobisisobutyronitrile was conducted. Reactivity ratios were evaluated using both nonlinear least-squares (NLLS) and error-in-variables model (EVM) techniques. A thorough study of the kinetics over the full conversion range was subsequently carried out at a variety of feed compositions, initiator concentrations, and temperatures, with and without added chain transfer agent (CTA).

Controlled Free‐Radical Copolymerization Kinetics of Styrene and Divinylbenzene by Bimolecular NMRP using TEMPO and Dibenzoyl Peroxide

An experimental study on the kinetics of nitroxide‐mediated free radical copolymerization (NMRP) of styrene (STY) and divinylbenzene (DVB) is presented. The experiments were carried out in bulk from a mixture of monomers, stable free radical controller (2,2,6,6‐Tetramethyl‐1‐piperidinyloxy, TEMPO), and initiator (dibenzoyl peroxide, BPO), at 120°C, without using a TEMPO‐capped prepolymer in the initial mixture. The system studied is a case of bimolecular NMRP, as opposed to the monomolecular NMRP of styrene and other crosslinker previously addressed in the literature by others. The results on total monomer conversion (polymerization rate), molecular weight development, gel fraction, and swelling index are compared against a conventional reference system (a STY/DVB copolymer, also synthesized for this study). No significant auto‐acceleration effect was observed in the early and intermediate conversion ranges of the TEMPO‐controlled copolymerization of STY/DVB, and the gelation point was significantly delayed. †On research leave from UNAM.

High‐temperature solution polymerization of butyl acrylate/methyl methacrylate: Reactivity ratio estimation

Solution copolymerizations of butyl acrylate/methyl methacrylate in toluene were performed over an expanded temperature range (60–140°C) compared to more typical ranges that do not exceed 80°C. From a large amount of data collected independently at two laboratories, reactivity ratios were estimated at five different temperatures. The reactivity ratios were estimated from low conversion copolymer composition data using both the error-in-variables model method and a nonlinear parameter estimation based on the integrated copolymer composition equation. Using all of the available data, temperature-dependent expressions were developed for the reactivity ratios and compared to previously published bulk copolymerization values. No significant differences appeared to exist between the bulk and solution polymerization reactivity ratios. Furthermore, the copolymer composition data conformed to the Mayo-Lewis kinetic model over the entire temperature range.

Another Perspective on the Nitroxide Mediated Radical Polymerization (NMRP) of Styrene Using 2,2,6,6‐Tetramethyl‐1‐piperidinyloxy (TEMPO) and Dibenzoyl Peroxide (BPO)

Polymerization conditions for the bimolecular NMRP of styrene using TEMPO and BPO were revisited and expanded with the objective of creating a more complete and reliable source of experimental data for parameter estimation and model validation purposes. Three different experimental techniques were assessed for the NMRP of styrene. The reliability of results produced in vials with inert nitrogen atmosphere was evaluated, taking as reference the more reliable technique using sealed ampoules with inert atmosphere. Polymerization rate data obtained in vials could be considered reliable if monomer loss was taken into account, but the reliability of molecular weight data at high conversions may be questionable. Polymerizations at 120 and 130°C and with TEMPO to BPO, molar ratios of 0.9 to 1.5 were carried out. Comparison of the experimental data collected against predictions obtained with a detailed kinetic model previously reported in the literature suggest that either the present understanding of the reaction system is incomplete, or some of the kinetic rate constants reported in the literature are not accurate, or both. Guidelines on how to address and design future experimental and modeling studies are offered.

Doped Polyaniline for the Detection of Formaldehyde

Polyaniline (PANI) and PANI doped with NiO and/or Al2O3 were tested for their sensing properties towards formaldehyde. It was found that at concentrations above 1 ppm, PANI doped with 5% NiO and 15% Al2O3 had both the sensitivity and selectivity needed, whereas, below 1 ppm, PANI doped with 15% NiO had the sensitivity, but not the selectivity required. By combining both sensing materials into one sensor, a highly sensitive and selective sensor could be made for the detection of formaldehyde at very low concentrations at the toxicity limit of 0.08 ppm.

Assessing the importance of diffusion-controlled effects on polymerization rate and molecular weight development in nitroxide-mediated radical polymerization of styrene

A previously derived kinetic model for the nitroxide‐mediated radical polymerization (NMRP) of styrene has been modified by considering diffusion‐controlled (DC) effects on the bimolecular radical termination, monomer propagation, dormant polymer activation, and polymer radical deactivation reactions. Free‐volume theory was used to incorporate the DC‐effects into the model. It was found that DC‐termination enhances the living behavior of the system, whereas DC‐propagation, DC‐activation and DC‐deactivation worsen it. Although the inclusion of overall DC‐effects into the kinetic model improved the performance of the model by slightly reducing the deviations obtained from experimental data of polymerization rate and molecular weight in the bimolecular NMRP of styrene with 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) and dibenzoyl peroxide (BPO), it does not seem to justify adding the extra four free‐volume parameters. In the case of the semi‐batch addition of azo‐bis‐iso‐butyronitrile (AIBN) (several single shots at definite time intervals) in the NMRP of styrene, recently reported in the literature, it was found that DC effects are more significant, but it was observed that there was a strong dependence of polymerization rate on the frequency of addition of the shots of initiator (a maximum on polymerization rate being observed at a given frequency of addition of the shots), which could not be adequately explained in terms of DC‐effects.

High Temperature Bulk Copolymerization of Butyl Acrylate/Methyl Methacrylate: Reactivity Ratio Estimation

ABSTRACTIn order to extend the validity of existing mechanistic polymerization models, it is necessary to conduct experiments beyond typical temperature ranges. Bulk copolymerizations of butyl acrylate/methyl methacrylate were performed over an expanded temperature range (60 to 140°C) compared to most studies published to date which have focused on a more limited temperature range (60 to 80°C). From the large amount of collected data, reactivity ratios were estimated at five different temperatures. The reactivity ratios were estimated from low conversion copolymer composition data using the error-in-variables model method (EVM). The low conversion data were subsequently coupled with high conversion data and the reactivity ratios were re-estimated using non-linear parameter estimation based on the integrated copolymer composition equation. Using all of the available data, temperature-dependent expressions were developed for the reactivity ratios. The copolymer composition data conformed to the Mayo-Lewis k...

Ligand exchange processes of OsHCl(CO)(L)(PR3)2 (L=vacant, H2, R′CN, O2; R=Cy, i-Pr)

Abstract The reactivity of complexes formed by the addition of O2, H2 and R′CN to OsHCl(CO)(PR3)2 (1a:R=Cy; 1b:R=i-Pr) has been examined. Under 24 bar H2 and 65°C, the dioxygen ligand of OsHCl(CO)(O2)(PR3)2 (2a,b) is displaced to yield the trans-hydridodihydrogen complexes OsHCl(η2-H2)(CO)(PR3)2 (3a,b). Measurements of the equilibrium constant, KH2=[3a]/[1a][H2], for the direct addition of H2 to 1a yield ΔH°=−49.1±2.4 kJ/mol and ΔS°=−95.7±7.9 J/mol K. 1a,b react reversibly with aryl and alkyl nitriles to produce the isolable complexes, OsHCl(CO)(R′CN)(PR3)2 (4a,b). The phosphine ligands of 1a,b and 3a,b exchange with unbound, bulky alkyl phosphines at a rate that is slow relative to the NMR timescale. In the presence of excess PCy3, complex 3b yields the exchange products OsHCl(η2-H2)(CO)(Pi-Pr3)(PCy3) and 3a. While a tris-phosphine complex cannot be detected, limited kinetic data characterize the exchange as associative process.

Copolymerization of Alpha‐Methyl Styrene with Butyl Acrylate: Parameter Estimation Considerations

Abstract The kinetics of the copolymerization of alpha‐methyl styrene (AMS) and butyl acrylate (BA) have been revised to include both the bulk and solution systems. Reactivity ratios and other kinetic parameter estimates based upon a copolymerization model developed by Kruger have been ascertained for a range of temperatures (60–140°C) and at a single solvent level (23 wt%). Full conversion range studies have been completed at two different solvent levels to determine the effects of feed composition, solvent, and chain transfer agent (CTA) on the rate of polymerization, copolymer composition, and the resulting molecular weight.