Enthalpy Of Polymerization Research Articles

Equilibrium polymerization in the Stockmayer fluid as a model of supermolecular self-organization

A diverse range of molecular self-organization processes arises from a competition between directional and isotropic van der Waals intermolecular interactions. We conduct Monte Carlo simulations of the Stockmayer fluid (SF) with a large dipolar interaction as a minimal self-organization model and focus on basic thermodynamic properties that are needed to characterize the polymerization transition that occurs in this fluid. In particular, we determine the polymerization transition lines from the maximum in the specific heat, C(v), and the inflection point in the extent of polymerization, Phi. We also characterize the geometry (radius of gyration R(g), chain length L, chain topology) of the clusters that form in this associating fluid as a function of temperature, T, and concentration, rho . The pressure, P, and the second virial coefficient, B2, were determined, since these properties contain essential information about the strength of the isotropic (van der Waals) interactions. Our simulations indicate that the locations of the polymerization lines are quantitatively consistent with a model of equilibrium polymerization with the enthalpy of polymerization ("sticking energy") fixed by the minimum in the intermolecular potential. The polymerization transition in the SF is accompanied by a topological transition from predominantly linear to ring polymers upon cooling that is driven by the minimization of the dipolar energy of the clusters. We also find that the basic interaction parameters describing polymerization and phase separation in the SF can be estimated based on the existing theory of equilibrium polymerization, but the theory must be refined to account for ring formation in order to accurately describe the configurational properties of this model self-organizing fluid.

Thermal stability and bond dissociation energy of fluorinated polymers: A critical evaluation

Intrinsic bond dissociation energies (BDEs) of selected fluorinated polymers are critically evaluated. Two distinctive approaches were followed. In the first one, according to Wu and Rodgers [E.-C. Wu, A.S. Rodgers, J. Am. Chem. Soc. 98 (1976) 6112–6115], starting from the gas-phase enthalpy of polymerization we obtained the polymer backbone BDE through appropriate thermodynamic cycles. Revised experimental results indicate that the C C BDEs of all the polymers taken into account fall within a limited energy interval, comparable to the average experimental uncertainty. Central to the second methodology adopted, is a model compound approach. Thanks to the large number of reliable thermodynamic data available in the scientific literature and to simple end-capping rules, C 2 molecules were chosen as suitable models for infinite linear polymers and alternating copolymers between ethylene and fluorinated olefins. For partially fluorinated polymers, like polyvinylidene fluoride (PVDF), alternating ethylene–tertrafluoroethylene (ETFE) and alternating ethylene–chlorotrifluoroethylene (ECTFE), the weight loss due to HF and HCl evolution during heating experiments was successfully related to the threshold energy E o(HX) for 1,2-elimination from chemically activated hydrofluoro and hydrofluorochlorocarbons according to the modified Rice–Rampsberger–Kassel (RRKM) unimolecular theory.

A critical evaluation of reaction calorimetry for the study of emulsion polymerization systems: thermodynamic and kinetic aspects

Protocols were examined for the measurement of rates and enthalpies of polymerization (Δ H p) using reaction calorimetry. Δ H p was determined to be 70.2 kJ mol −1 for a series of seeded styrene emulsion polymerizations under typical emulsion conditions, in good agreement with literature values. However, there was a significant deviation from this value for small-particle systems, which is ascribed to surface effects, i.e. environmental effects on Δ H p. Careful comparison between rate data obtained by calorimetry and by dilatometry leads to recommended procedures for obtaining reliable and accurate rate data using the former technique.

A new tool for the study of polymerization under supercritical conditions – preliminary results

AbstractEfficient stirring is needed to realize heat flow analysis with a thermally homogeneous medium. Because dispersion polymerization with supercritical fluids can be destabilized under stirring, a preliminary target has been to find a compromise between synthesis and basic reaction calorimetry requirements. This paper describes the use of poly (dimethylsiloxane) macromonomer with a molecular weight 5000 g/mol as stabilizer for the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide. The effect of stirring speed and stabilizer concentration has been examined. This study has shown that poly (methyl methacrylate) can be produced at high yield and molecular weight using 10 wt% (respect to monomer) poly (dimethylsiloxane) macromonomer at stirring speeds up to 600 rpm. A polymerization enthalpy of −57.6±2 kJ/mol has been calculated being in good agreement with previously reported data. Thus, preliminary results for the heat balance using the newly developed high pressure reaction calorimeter for supercritical fluid applications have shown the important potential of reaction calorimetry to promote supercritical fluid technologies at industrial scale allowing for the determination of kinetics and thermodynamic and safety data, respectively.

Reaction Calorimetry as a New Tool for Supercritical Fluids

Reaction calorimetry is an efficient tool used to obtain kinetic, thermodynamic, and safety data. A new tool, composed of a high-pressure reactor (HP350) coupled with a Mettler-Toledo RC1e reaction calorimeter, is developed for the investigation of chemical reactions, under supercritical conditions. The reactor (V = 1.2 L) can be pressurized up to 350 bar and heated to 300 °C. Results presented in this contribution are divided into three sections. The first part concerns some highlights of the technical challenge related to supercritical reaction calorimetry in comparison with the classical liquid calorimetry. The second part presents a Wilson plot analysis with pure supercritical CO2 and shows that, in contrast to classical liquids, the lower the temperature (above the critical point) the better the heat transfer coefficient. This tendency can be explained by the evolution of scCO2 thermodynamical and transport properties around the critical point. The third part contains preliminary results from the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide using poly(dimethylsiloxane) macromonomer as stabilizer. Poly (methyl methacrylate) can be produced with high yield, high molecular weight, and nar-row particle size distribution, using 10 wt % (with respect to monomer) stabilizer under efficient stirring. A polymerization enthalpy of −58.8 ± 3 kJ/mol has been calculated with high reproducibility, being in good agreement with previously reported data. This confirms that the employed heat balance model is correct and shows the important potential of reaction calorimetry for the promotion of supercritical fluid technologies at industrial scale, since it allows the determination of kinetics, thermodynamic, and safety data.

Equilibrium and non-equilibrium polycondensation process of segmented poly-perfluoro(oxymethylene- ran-oxyethylene)-carbonates

The melt transesterification polyreaction between diphenyl carbonate and poly-perfluoro(oxymethylene- ran-oxyethylene)dimethylol terminated oligomers (briefly perfluoropolyethers or PFPE diols) to give linear, highly fluorinated polycarbonates was investigated. The PFPE-polycarbonates were characterised by GPC and 19 F NMR spectroscopy. The polycondensation was catalysed by Zn(Ac) 2 at temperatures comprised between +120 and +200 °C. The polymerisations carried out in closed systems (no by-product distillation) gave information on some aspects of the equilibrium thermodynamics of the process. The effects of temperature and stoichiometric ratio were particularly studied. It resulted that the equilibrium degree of polymerisation ( X n) eq is inversely proportional on a semi-log scale to the temperature of polymerisation as typical of exothermal processes. The standard enthalpy of polymerisation was calculated (Δ H 0=−31±3 kJ/mol). It was found, in apparent disagreement with theory, that maximum molecular weights were achieved when an excess of diphenyl carbonate monomer is used. In equilibrium conditions low molecular weights ( M n≤10 4) were generally obtained. The non-equilibrium conditions focused to the obtainment of high molecular weight polycarbonates were also investigated, using temperature ramps and pressure steps to get the phenol off the reaction medium. A comparison between two different functionality PFPE oligomers was finally done in non-equilibrium conditions, showing that M n as high as 10 5 can be obtained starting from a PFPE macromonomer with a OH functionality as high as 2.

Kinetic and Thermodynamic Studies of Emulsion Polymerization of a Sugar Monomer by Calorimetry with Compensation Heating and Differential Cooling

AbstractThe kinetic and thermodynamic features of free‐radical batch emulsion polymerization of a sugar monomer (3‐MDG) and butyl acrylate (BA) were investigated in a power compensation calorimeter. The homopolymerizations as well as the copolymerization have been studied. The overall activation energy of 3‐MDG homopolymerization was 140 ± 3.8 kJ · mol−1, the polymerization enthalpy was ΔHMDG = −51.6 ± 1.9 kJ · mol−1 and the calculated adiabatic temperature rise was ΔTad = 78.5 K. The effects of the initiator and the emulsifier concentrations on the 3‐MDG/BA batch copolymerization kinetics and on the colloidal properties of the final sugar latexes were studied at 60 °C. At higher emulsifier and initiator concentration, respectively, the polymerization rate increases and the particle size decreases, but the trends do not conform to the Smith‐Ewart theory. Polydisperse sugar latex particles with a mean diameter in the range of 50–67 nm were obtained.Relationship between the activation energy and the conversion for BA (open symbols) and 3‐MDG (solid symbols).magnified imageRelationship between the activation energy and the conversion for BA (open symbols) and 3‐MDG (solid symbols).

Monitoring dispersion polymerisations of methyl methacrylate in supercritical carbon dioxide

This paper describes the development and application of power compensation calorimetry equipment to monitor the dispersion polymerisation of methyl methacrylate in supercritical carbon dioxide. We have studied the polymerisation of methyl methacrylate using a macromonomer (poly(dimethylsiloxane) monomethacrylate) as stabiliser and initiator azoisobutylnitrile. The calorimetric data allow monitoring of the polymerisation process. Through monitoring the changes in reaction exotherm and system pressure during the polymerisation one can clearly observe the point at which the polymerisation starts and effectively ceases. The effect of initiator concentration and stabiliser on the reaction was studied and the enthalpy of polymerisation obtained from the apparatus was found to correlate with previously reported data.

Bulk free‐radical photopolymerizations of 1‐vinyl‐2‐pyrrolidinone and its derivatives

AbstractAn investigation of the free‐radical bulk photopolymerization of 1‐vinyl‐2‐pyrrolidinone (NVP) with an NVP‐based crosslinker, 1,6‐(bis‐3‐vinyl‐2‐pyrrolidinonyl)hexane (BNVP), and an NVP‐based comonomer, 3‐hexyl‐1‐vinyl‐2‐pyrrolidinone (VHP), was carried out. The enthalpies of polymerization were determined for NVP and VHP to be 30.8 and 35.7 kJ/mol, respectively. The rates of polymerization were determined for NVP/VHP and NVP/BNVP systems at various temperatures. These photopolymerization studies revealed that the overall rates of polymerization of these 3‐alkylated‐2‐pyrrolidinone derivatives increased with substitution onto the pyrrolidinone ring. A series of pyrrolidinone‐based additives in bulk NVP were used in model photopolymerizations of NVP for the evaluation of plasticizer effects. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 694–706, 2002; DOI 10.1002/pola.10142

Epoxy + montmorillonite nanocomposite: Effect of composition on reaction kinetics

AbstractThe objective of this investigation is to determine the effects of montmorillonite layered silicates on the curing kinetics of an epoxy resin. Differential scanning calorimetry was used to probe the changes in reactivity due to the presence of montmorillonite and due to the diamine hardener. The enthalpy of polymerization was strongly affected at compositions greater than 5% (wt) montmorillonite for epoxy + montmorillonite reactions. On introduction of the hardener, epoxy + amine kinetics dominate the reaction for all compositions except for a montmorillonite concentration of 2.5 wt%. X‐ray diffraction was used to determine if the reacted system was exfoliated. The results show a strong montmorillonite composition dependence on the exfoliated state. Transmission electron microscopy of the cured epoxies confirmed a mixed intercalated and exfoliated dispersion at compositions having montmorillonite greater than 2.5 wt%.

METHACRYLOYL DERIVITIZED HYPERBRANCHED POLYESTER. 1. SYNTHESIS, CHARACTERIZATION, AND COPOLYMERIZATION

Three hyperbranched multi-methacrylates (H20-MMA, H30-MMA and H40-MMA) have been synthesized by reacting Boltorn dendritic polyols with methacrylic anhydride and methacryloyl chloride. Their structures were characterized by FT-IR and NMR (1H and 13C) and molecular weights were measured by GPC. These multi-methacrylates (H-MMAs) mixed well with a variety of monomers such as acrylic acid (AA), methacrylic acid (MA), methyl methacrylate (MMA), 2-hydroxy-ethyl methacrylate (HEMA), tri(ethylene glycol) dimethdimethacrylate (TEGDMA), and bisphenol A glycidyl dimethacrylate (BisGMA). The initial studies on thermal polymerization activities of 10% of H-MMAs with AA, MA, and MMA showed that they gave higher polymerization enthalpy than the corresponding homopolymerization. The resulting materials showed one glass transition temperature, indicating a typical single-phase resin. The H-MMAs can effectively copolymerize with AA, MA, and MMA, with essentially no homopolymers produced, as indicated by acetone extraction studies. This indicated that the hyperbranched multi-methacrylates have the potential to be used as crosslinking agents or modifiers with a number of monomers to produce new thermosets.

Structure of the lowest triplet states of poly-α-methylstyryl sodium.Ab initio calculations

Ab initio optimization of a poly-α-methylstyryl sodium (PMSNa) fragment consisting of two eis units yields a triplet state energy which is close to the ground state energy. A new mechanism is proposed for depolymerization of “living” polymers, which implies that an elementary step involves excitation to the low-lying triplet state with a charge transfer and with further bond cleavage. In the reaction structure, electronic excitation occurs with a minor (≈0.5 A) displacement of the Na+ cation between the last and the last but one monomer units. The reversible polymerization/depolymerization reaction of PMSNa in THF was studied experimentally. The experimental (5.6 kcal/mole) and calculated (7.3 kcal/mole) polymerization enthalpies are in reasonable agreement.

Photoinitiated cationic polymerization of 1,3-dioxepane

Homopolymerization of 1,3-dioxepane was photoinitiated by a mixture of triarylsulphonium salts in the temperature range of 30–60°C. Kinetics was followed both by gas chromatography and by differential photocalorimetry with power compensation. An enthalpy of polymerization of −10.5 kJ/mol was found and final monomer concentrations of 0.2–0.6 mol/l, depending on temperature, were determined. Polymerizations yielded a homopolymer having ηred up to 0.35 dl/g.

The polymerization of actin: Study by small angle neutron scattering

We report measurements of small angle neutron scattering from solutions of rabbit muscle G-actin at 3.00 mg/mL in D2O buffer solution, with [Ca2+]=0.52 mM and with [KCl]=15, 8.9, and 5.4 mM. We observe the onset of the polymerization of G-actin to F-actin as the temperature is increased. The polymerization takes place on a time scale of 30–45 min for each temperature jump of 2 °C–3 °C. As the temperature is increased further, the average size of the polymers increases, and the characteristic length scale (or correlation length), ξ, of the F-actin in the dilute solution grows: ξ is about 10 Å below Tp, and about 70 Å a few degrees above Tp. The transition is sharper for lower concentrations of KCl. For the sample with [KCl]=8.9 mM, we observe a peak in ξ at about 2 °C above Tp, which indicates a crossover into the semidilute regime. The transition is essentially reversible, but shows evidence of incomplete depolymerization on cycling. We are unable to apply the available theoretical model for reversible polymerization to rabbit muscle actin because of a lack of information on the enthalpy and entropy of polymerization. However, our observations for rabbit muscle actin are quite analogous to observations on the equilibrium polymerization of α-methylstyrene [A. P. Andrews, K. P. Andrews, S. C. Greer, F. Boué, and P. Pfeuty, Macromolecules 27, 3902 (1994)].

Simulation of Temperature Distributions Within Monomer Film During Photopolymerization

Photoinitiated polymerizations are very fast reactions, and consequently significant thermal effects are observed during the reactions. Nevertheless, isothermal conditions are necessary to measure the kinetic constants of polymerization. In the simulation of heat transfer reported in this paper, it is shown that the use of a thin film of monomer at the bottom of a DSC pan, even in the presence of an intermediate polyethylene film, is convenient if the reaction rate is not too high. For example, the temperature increase of the film does not exceed 1°C for a reaction half-time (time to reach 50% conversion) higher than 10 s when the enthalpy of polymerization is chosen as ΔHR=115 J g−1.

Equilibrium Polymerization of 7-(Alkoxycarbonyl)-7-cyano-1,4-benzoquinone Methides, Substituent Effect on Polymerizability, and Copolymerization with Styrene

Polymerization kinetics of 7-(alkoxycarbonyl)-7-cyano-1,4-benzoquinone methides with alkoxy groups such as methoxy (3a), butoxy (3b), isopropoxy (3c), and sec-butoxy (3d) was investigated in chloroform in the presence of 2,2‘-azobis(isobutyronitrile) (AIBN) as an initiator. Their polymerizations were found to be typical equilibrium polymerization reactions, and on the basis of this polymerization behavior, the thermodynamic parameters of polymerization such as the enthalpy (ΔH) and entropy (ΔS) of polymerization were determined. To get information about the substituent effect on the homopolymerizability of 7-(alkoxycarbonyl)-7-cyano-1,4-benzoquinone methides, the ΔH values were compared with the substituent parameters for the alkyl group of the alkoxy substituents by means of a linear free energy relationship and the homopolymerizability was found to be determined mainly by the steric hindrance of the alkoxy groups. The copolymerization of 3a with styrene in chloroform with AIBN as an initiator was carried out above and below the equilibrium monomer concentration of 3a. Above the equilibrium monomer concentration of 3a, 3a copolymerized with styrene in a random fashion to afford the monomer reactivity ratios, r1(3a) = 4.70 ± 0.85 and r2(styrene) = 0.01 ± 0.01 at 60 °C. Alfrey−Price's Q and e values of 3a were calculated to be Q = 32 and e = +1.05, respectively, indicating that 3a is a highly conjugative (reactive) and electron-accepting monomer. On the other hand, below the equilibrium monomer concentration of 3a, 3a copolymerized with styrene in a perfectly alternating fashion. The change from random fashion to alternating one for this copolymerization was explained well in connection with the equilibrium polymerization behavior of 3a.

New approach to filled polymers

Mechanopolymerization of pentabromobenzyl (mono)acrylate (PBB-MA) on the surface of inorganic fillers Mg(OH)2 and CaCO3 was studied. The role of activated surface of fillers was investigated using DSC and FTIR. The influence of milling time and of the filler chemical content on polymerization starting temperature and polymerization enthalpy was studied using DSC. It was shown that an increase of the filler concentration leads to a higher maximum conversion degree. The correlation between conversion kinetics and polymerization enthalpy of the material notpolymerized during milling was shown.

Thermodynamics of polyvinylacetate from 0 to 350 K

The temperature dependence of the heat capacity of vinyl acetate in the range 13 to 330 K and of polyvinylacetate between 4.9 and 330 K was determined by adiabatic vacuum calorimetry with an error of about 0.2%. Temperatures and enthalpies of physical transitions were measured. From the data obtained, the thermodynamic characteristics of melting of vinyl acetate and parameters of glass transition and glassy state of the monomer and polymer were calculated. The thermodynamic functions Ho(T)-Ho(0), So(T), Go(T)-Ho(0) were estimated for both materials from 0 to 350 K. The results of calculation and the literature value of enthalpy of bulk polymerization of vinyl acetate at T=350 K were used for the estimation of the thermodynamic parameters of its polymerization process ΔHpol o, ΔSpol o, ΔGpol oin the interval 0 to 350 K. A ceiling limiting temperature of polymerization Tceil owas evaluated.

Living poly(α-methylstyrene) near the polymerization line. V. Heat capacity as a function of temperature

We present here measurements of the heat capacity at constant pressure near the ceiling temperature for the anionic polymerization of an organic monomer. The measurements support the suggestion [S. J. Kennedy and J. C. Wheeler, J. Chem. Phys. 78, 953 (1983); J. C. Wheeler and P. M. Pfeuty, Phys. Rev. Lett. 71, 1653 (1993)] that the onset of equilibrium polymerization in initiated monomer solutions as the temperature is changed can be viewed as a second-order continuous phase transition. We compare our measurements on living poly(α-methylstyrene) initiated by sodium naphthalide in tetrahydrofuran to the theoretical predictions, and find qualitative agreement. We attribute quantitative differences to the dependence of the enthalpy of polymerization on the degree of polymerization and on the tacticity.

Investigation of isothermal bulk polymerization ofo-alkyaryl methacrylates by DSC

The kinetics of the AIBN-initiated free radical bulk polymerization of fiveo-alkylphenyl methacrylates was studied by means of DSC in the temperature range 353–373 K, and the enthalpy of polymerization, the overall reaction rate constant and the activation energy were determined. The results were compared with those published recently on correspondingp-alkylaryl methacrylates. All measured reaction rate constants were found to increase with increasing temperature and to decrease with increasingo-alkyl substituent mass and size. It was shown thato-substituents influence the rates of polymerization to a greater extent thanp-substituents. At about 373 K, all differences in rate, most probably resulting from steric hindrance caused by the alkyl groups, disappear in both series, a phenomenon earlier observed for dimethyl phenyl methacrylates.