Enthalpy Of Polymerization Research Articles

Aliphatic Polyester Block Polymer Design

Aliphatic polyester block polymers constitute a highly useful and amazingly versatile class of self-assembled materials. Analogous to styrenic block polymers in both design and function, the property profiles of these degradable materials can be precisely tailored by altering the chemical structure of the components. Driven by this ideal, we have examined the impact of n-alkyl substituents on the polymerization thermodynamics and kinetics of substituted δ-valerolactone monomers and developed guiding design principles based on critical structure–property relationships in the resulting aliphatic polyesters. Under bulk room temperature conditions the polymerization rate depends strongly on substituent position and exhibits a more modest dependence on alkyl length (from −CH3 to −(CH2)8CH3). The enthalpy and entropy of polymerization are significantly influenced by substituent position, but both are largely insensitive to n-alkyl length. However, the physical properties of the resulting aliphatic polyesters de...

Kinetics and thermodynamics of l-lactide polymerization studied by differential scanning calorimetry

Kinetics of l-lactide polymerization was studied by differential scanning calorimetry in isothermal mode at various temperatures and catalyst concentrations. The enthalpy of l-lactide polymerization measured directly in DSC cell was found to be ΔH=−19±0.5kJmol−1. Kinetic curves of l-lactide polymerization and propagation rate constants were determined for polymerization with stannous octoate at concentrations 200–1100ppm at temperatures 180, 190, 200 and 220°C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy Ea=50±5kJmol−1, preexponential constant lnA=18±1, entropy of polymerization ΔS=−12±1Jmol−1K−1.

ATRP of POSS Monomers Revisited: Toward High-Molecular Weight Methacrylate–POSS (Co)Polymers

For the first time, ATRP was successfully employed for homopolymerization of a commercial methacrylate-functionalized polyhedral oligomeric silsesquioxane (POSS) monomer, iBuPOSSMA, to high molecular weights. It was found that iBuPOSSMA has a low ceiling temperature (Tc); therefore, low temperatures and/or high initial monomer concentrations need to be used in order to avoid low degrees of polymerization that had been observed previously. The values of Tc, as well as of the polymerization enthalpy ΔHp and entropy ΔSp were determined to be 130 °C (at [M]0 = 1 M), −41 kJ mol–1, and −101 J mol–1 K–1, respectively. Under optimized conditions, poly(iBuPOSSMA) homopolymers having low dispersity and high Mn, ranging from 23 000 to 460 000, were obtained in a well-controlled ATRP process. Moreover, various block copolymers having high-Mn poly(iBuPOSSMA) blocks were prepared by copolymerization of iBuPOSSMA with methyl methacrylate and styrene.

Ionic liquid-initiated polymerization of epoxides: A useful strategy for the preparation of Pd-doped polyether catalysts

Palladium compounds (Pd(OAc)2 and Pd(acac)2) were dissolved in commercially available epoxy resins (glycidyl derivatives of bisphenol A and p-aminophenol) and the formulations were polymerized employing the ionic liquid 1-ethyl-2-methylimidazolium acetate (EMIM acetate) as polymerization initiator. Thus, palladium species could be incorporated in the network of the resulting polyether materials. Polymerization reactions were investigated by DSC and the curing behavior of different formulations was compared. High polymerization enthalpies were observed indicating high crosslinking in the materials. Accordingly, the materials exhibited high glass transition temperatures and thermogravimetric data revealed high thermal stability. Due to the good solubility of the palladium compounds in the epoxy resins, a widely homogeneous dispersion of palladium species in the polyether matrix could be realized. This was confirmed by SEM-EDX and TEM measurements. XPS measurements revealed that reduction of Pd(II) to Pd(0) species occurred during catalyst preparation and this was also proven by XRD. The materials were ground and successfully employed as catalysts for the hydrogenation of several alkenes under mild reaction conditions. High conversions and selectivities could be reached within a few hours at room temperature and moderate hydrogen pressure of 2.5bar. Palladium leaching from the catalysts to reaction solutions was investigated. To determine very low quantities, metal concentrations were enriched by removal of volatile components. Subsequent ICP-AES measurements revealed low palladium contents in the range of a few μg. These amounts correspond to values around 0.007% with respect to palladium originally loaded on the polymer. Catalyst recycling experiments were also carried out and it was shown that the catalysts can be employed in numerous consecutive reactions without any catalyst treatment and without loss of activity. Within a series of reactions, palladium leaching decreased while catalytic activity was not affected.

Solvent-free copolymerization of rigid and flexible bis-1,3-benzoxazines: Facile tunability of polybenzoxazine network properties

We report the copolymerization of a flexible aliphatic-bridged bisphenol-based benzoxazine monomer comprising ten methylene units (BZ(10)BA) with two rigid benzoxazine monomers (commercially available Araldite 35600 and 35900) via a solvent-free cationic ring-opening polymerization process. The effects of monomer feed composition on polymerization behavior, thermomechanical transitions, and thermal degradation properties are reported. DSC of the ring-opening copolymerizations showed that the copolymerization behavior – in terms of polymerization onset temperature and total exothermic transition – depend greatly on the composition of the monomer feed. Samples containing larger concentrations of BZ(10)BA exhibited higher onset temperatures with lower polymerization enthalpies. The thermomechanical properties of the copolybenzoxazine networks, as evaluated by DMA, show a strong dependence on the monomer feed ratio, where higher Araldite content resulted in a higher Tg of the network. The most salient feature of benzoxazine copolymerization was revealed in the tailorability in thermomechanical properties, which were varied by 149 °C simply by changing the monomer feed ratio and the Tg was observed to be accurately predicted using the Fox equation.

Thermodynamics of the Carbon Dioxide–Epoxide Copolymerization and Kinetics of the Metal-Free Degradation: A Computational Study

The copolymerization reactions of carbon dioxide and epoxides to give polycarbonates were examined by density functional theory (DFT), and chemically accurate thermochemical data (benchmarked to experimental values) were obtained via composite ab initio methods. All of the examples studied, i.e., formation of poly(ethylene carbonate), poly(propylene carbonate), poly(chloropropylene carbonate), poly(styrene carbonate), poly(cyclohexene carbonate), and poly(indene carbonate), exhibited enthalpies of polymerization of 21–23 kcal/mol, with the exception of poly(cyclopentene carbonate) (15.8 kcal/mol) which suffers both ring strain and intramolecular steric repulsion caused by the cyclopentane ring fused to the polymer chain. The metal-free carbonate backbiting reaction by a free anionic polycarbonate strand is inhibited by bulky groups at the methine carbon but is accelerated by resonance stabilization of the pentavalent transition state in the case involving poly(styrene carbonate). Nucleophilic attack at the methylene carbon of a substituted epoxide has a lower barrier than for the corresponding reaction involving ethylene oxide due to charges being distributed onto the pendant groups. The undesired backbiting reaction to afford cyclic organic carbonates observed under polymerization conditions for many systems due to the low activation barrier (ΔG‡ = 18–25 kcal/mol) was negligible for poly(cyclohexene carbonate) because, in this instance, it must overcome an additional endergonic conformational change (ΔG = 4.7 kcal/mol) before traversing the activation barrier (ΔG‡ = 21.1 kcal/mol) to cyclization. Backbiting from an alkoxide chain end is proposed to proceed via a tetrahedral alkoxide intermediate, where formation of this intermediate is barrierless. Further reaction of this intermediate to the cyclic carbonate has a free energy barrier 10 kcal/mol less than the carbonate chain end backbiting reaction.

Thermal and dynamic mechanical characterization of acrylic bone cements modified with biodegradable polymers

AbstractIn this work, a thermal and a dynamic mechanical study of new formulations self‐curing acrylic bone cements is reported. The basic formulation of poly(methylmethacrylate) (PMMA)‐based acrylic bone cements has been modified with biodegradable polyesters such as poly(l‐lactic acid), poly(β‐hydroxybutyrate), and different kinds of thermoplastic starches. Differential scanning calorimetry (DSC) (dynamic and isothermal conditions), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy (SEM) were used to determine the influence of the biodegradable polymer in the behavior of the biomedical formulations. DSC assay revealed a strong dependence of the polymerization enthalpy (ΔHcur) with increasing solid : liquid ratio and a low influence of the nature of the added biodegradable polymer on glass transition. TGA analysis showed the different mechanism of PMMA‐biodegradable polymer interaction depending on the solubilization of the added polymer in methylmethacrylate monomer during curing. DMTA showed the reinforcing capacity of segregated phases of the polymer included in the cement. The solubilization of aliphatic polyesters in the resulting PMMA polymerized phase led to a drop in mechanical stiffness observed from storage modulus (E′) profiles. Moreover, tan δ shifts to higher temperatures (4–7°C) during a second scan, confirming the presence of residual monomer content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Thermodynamic and kinetic evaluation of the polymerization process of epoxidized biodiesel with dicarboxylic anhydride

This paper reports on a polymerization study of the epoxidized methyl esters (EME) obtained from soybean oil, with phthalic anhydride (PA) and 2‐methyl‐imidazole in the presence of soybean oil biodiesel (BD) as solvent. The gelation region for the system EME/PA/2MI without BD was determined using the Flory's theory occurring between X EME = 0.33 to 0.54. The evaluation of the polymerization enthalpy (ΔH) indicates that the experimental stoichiometric composition of the system EME/PA/2MI without solvent is near to X EME = X PA = 0.5. ΔH values higher than 76 J/g were observed for samples located in the theoretical gelation region. Different polymers were produced using the stoichiometric composition and varying only the amount of BD. Kinetics and thermodynamics of the polymerization reaction, using solvent, were evaluated by DSC technique. The results show that BD acts as solvent in the polymerization reaction and a compensation effect between activation energy and logarithm of pre‐exponential factor was observed. Thermogravimetric analysis indicated that the degradations of the products include two well‐defined processes. The compensation effect was observed in the thermal degradation kinetics too.

Thermal processes in methacrylamide after high-pressure plastic deformation

The effect of high pressure (0.5–2.0 GPa) on the methacrylamide polymerization under the conditions of plastic deformation performed on high-pressure anvil-type devices was studied. Thermal processes in samples subjected to deformation at different pressures and the effect of UV irradiation on the enthalpies of the monomer polymerization in a melt and of the high-temperature endothermic process in deformed samples were examined.

Thermodynamic and stereochemical aspects of the polymerizability of glycolide and lactide

The ring-opening polymerizations of the dilactones glycolide and the S,S- and S,R-stereoisomers of lactide were studied using quantum mechanical methods. The ring strain and the conformational distribution of these cyclic monomers and of the polymers were calculated, and the effect of the medium on the polymerization was predicted, for both bulk and solution. The polymerizability of the three monomers in the gas phase, that is, nonpolar medium, is much greater than that of δ-valerolactone or 1,4-dioxan-2-one. This difference vanishes in the polar medium chloroform, which is attributed to the fact that, while all of these monomers possess polar cis-lactone bonds, the three dilactones possess small dipole moments. The data are combined to give polymerization enthalpy and free energy values. The four stereoregular lactide polymers did not differ significantly in energy. Accordingly, the ability to synthesize any one of these rests on catalyst specificity (“polymer chain-end control”). Although introduction of sterically demanding methyl groups into glycolide is expected to favor coiled conformations and decrease polymerizability, this was not found to be the case. Good agreement of calculated values with experimental data from the literature was achieved.

Kinetics of Polymerization of a Liquid with Nanosize Structural Heterogeneities

We report the effects of chemically reacting, nanometer-size structural heterogeneity on a polymerization process. Heterogeneity is introduced by adding 2 nm size molecules of polyhedral oligomeric silsesquioxane with multiepoxide groups (POSS) while maintaining stoichiometry of a polymerizing triamine-diepoxide mixture. Calorimetric studies show that POSS addition first increases the polymerization rate and then decreases it progressively more. In the presence of nanometer-scale structural heterogeneity, diffusion-controlled kinetics begins sooner in time. The enthalpy of polymerization decreases with the amount of POSS heterogeneity according to the mixture rule; the glass-liquid transition endotherm of the partially polymerized state becomes broader, and the enthalpy of post polymerization decreases. The POSS-alone mixture polymerizes relatively slower, and the glass-liquid transition exotherm of the polymerized state is indistinguishably broad. Both are attributed to the distribution of diffusion rates or dispersive kinetics, and the development of dynamic heterogeneity more rapidly for the POSS-only mixture than for others. Increase in the polymerization rate on initial addition of nanometer-size POSS and then decrease on further addition is explained in terms of decoupling of diffusion from viscous flow, that is, when the diffusion rate decreases less rapidly with the polymerization time than the viscosity increases.

Novel 2-(ω-phosphonooxy-2-oxaalkyl)acrylate monomers for self-etching self-priming one part adhesive

Novel hydrolysis stable 2-(ω-phosphonooxy-2-oxaalkyl)acrylate monomers 3 with phosphoric acid moieties were synthesized by a three step synthesis via Baylis–Hillman reaction of ethyl acrylate and formaldehyde, and subsequent etherification of the obtained product with diols and phosphorylation using POCl3. The polymerization enthalpy of 2-(ω-phosphonooxy-2-oxaalkyl)acrylates 3 as measured by DSC ranges from −29 to −53 kJ·mol−1. The shear bond strength of adhesive compositions 4, comprising of polymerizable acids 3, ranges from 5.8 to 19.3 MPa on enamel and from 8.7 to 16.9 MPa on dentin.

N-alkyl-N-(phosphonoethyl) substituted (meth)acrylamides – new adhesive monomers for self-etching self-priming one part dental adhesive

Novel N-alkyl-N-(phosphonoethyl) substituted mono-, bis- and tris(meth)acrylamides 3 were synthesized by two different three-step reactions and characterized by IR, 1H NMR and 13C NMR spectroscopy as well as refractive index and viscosity. The phosphonoethyl substituted (meth)acrylamide monomers show improved hydrolytic stability compared to carboxylic esters. The highest stability was found for the phosphonoethyl substituted acrylamide monomers. Acrylamides have a larger polymerization enthalpy ranging from −50 to −70 kJ·mol−1 per double bond compared to methacrylamides which show −8.57 to −25.1 kJ·mol−1 per double bond. Depending on their structure (meth)acrylamides 3 exhibit an adhesion to enamel and dentin up to 19.5 MPa. The monomer 3c shows the highest adhesion values to both substrates, namely 15.3 ± 3.4 MPa to enamel and 18.5 ± 2.3 MPa to dentin.

Examination of the Thermal and Thermomechanical Behavior of Novel Cyanate Ester Homopolymers and Blends with Low Coefficients of Thermal Expansion

A new four-step synthetic method is presented and applied to the preparation in high purity of three novel dicyanate monomers that comprise aryl/alkylene ether backbones with high molecular flexibility. The multistep route involves four individually high-yielding steps (each ≥70%), thus giving overall reaction yields for total synthesis of 42−50% depending on the length of the backbone. All products are characterized using FT-IR and 1H NMR spectroscopy, elemental analysis, and melting point determination. DSC analysis of “uncatalyzed” samples displays relatively sharp melting endotherms ranging from 66 to 125 °C depending on the length (i.e., flexibility) of the backbone. All monomers display broad polymerization exotherms (87 ± 2 kJ/mol cyanate), although the polymerizations occur in different temperature regimes. When catalyzed (aluminum(III) acetylacetonate/dodecylphenol), the exothermic polymerization peaks occur at significantly lower temperatures than the uncatalyzed analogues and have much narrower profiles but tend to occur in a similar temperature regime (i.e., peak maxima 205−216 °C). The polymerization enthalpies for the catalyzed monomers are ca. 93 ± 9.9 kJ/mol cyanate. TGA shows that the polymers typically lose 5% of their masses by ca. 346−366 °C, which is comparable to AroCy B10. DMTA analysis of cured AroCy B10 yields results that are consistent with published data, and Tg values (tan δmax) of the homopolymers are 221 (4a), 139 (4b), and 121 °C (4c) and fall with increasing backbone length/flexibility. The storage moduli at 25 °C for the binary blends are significantly lower than the respective homopolymers, but the reduction in E′ (25−200 °C) is significantly improved compared with AroCy B10. When combined with AroCy B10 in binary blends, the new monomers showed a reduction in CTE of up to 12 ppm/°C while maintaining the same value of Tg.

Study on the synthesis, characterization, and kinetic of bulk polymerization of disproportionated rosin (β‐acryloxyl ethyl) ester

AbstractDisproportionated rosin ((β‐acryloxyl ethyl) ester (DR‐2‐HEA) was synthesized by esterification of dispoportionated rosin (DR) with 2‐hydroxyethyl acrylate (2‐HEA) and evaluated by FTIR spectroscopy, GC/MS, 13C‐NMR spectroscopy. Kinetics parameters of bulk polymerization of DR‐2‐HEA in the presence of initiator AIBN was studied by using DSC. It has been assumed that the process of polymerization obey nth order empirical kinetic model to evaluate the kinetic parameters. The relative molecular weight and glass transition temperature of polymer of DR‐2‐HEA at different temperature was measured by GPC and DSC, respectively. The results showed that the temperature had no significant effect on the enthalpy of polymerization and the velocity of polymerization increased by the increase of temperature. DSC experimental data fit the simulation well while the reacted fraction (α) in the interval of 0.4<α<1. The polymer of DR‐2‐HEA is oligomer. The molecular weight and Tg did not affect by polymerization temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Temperature excursions at the pulp–dentin junction during the curing of light-activated dental restorations

Objectives Excessive heat produced during the curing of light-activated dental restorations may injure the dental pulp. The maximum temperature excursion at the pulp–dentin junction provides a means to assess the risk of thermal injury. In this investigation we develop and evaluate a model to simulate temperature increases during light-curing of dental restorations and use it to investigate the influence of several factors on the maximum temperature excursion along the pulp–dentin junction. Methods Finite element method modeling, using COMSOL 3.3a, was employed to simulate temperature distributions in a 2D, axisymmetric model tooth. The necessary parameters were determined from a combination of literature reports and our measurements of enthalpy of polymerization, heat capacity, density, thermal conductivity and reflectance for several dental composites. Results of the model were validated using in vitro experiments. Results Comparisons with in vitro experiments indicate that the model provides a good approximation of the actual temperature increases. The intensity of the curing light, the curing time and the enthalpy of polymerization of the resin composite were the most important factors. The composite is a good insulator and the greatest risk occurs when using the light to cure the thin layer of bonding resin or in deep restorations that do not have a liner to act as a thermal barrier. Significance The results show the importance of considering temperature increases when developing curing protocols. Furthermore, we suggest methods to minimize the temperature increase and hence the risk of thermal injury. The physical properties measured for several commercial composites may be useful in other studies.

Structural characterization of pulsed laser deposited poly(methylmethacrylate) thin films

AbstractCross‐linking content and polymerization degree of poly(methylmethacrylate) PMMA thin films have been investigated by means of Fourier transform infrared and micro‐Raman spectroscopic techniques. The samples were deposited by means of pulsed laser ablation of a PMMA target at room temperature. The laser fluence was varied from 0.5 J/cm2 up to 4 J/cm2. Experimental results show that it is possible to deposit PMMA thin films with a very low monomer content (smaller than 3%) and to modulate the cross‐linking occurrence upon tuning the laser fluence. Moreover, the effect of the post‐deposition thermal treatment on the polymerization degree has been exploited. Then, we estimated the value of the polymerization enthalpy, which is comparable to the value at which the complete conversion of monomers in polymer is reached. Copyright © 2007 John Wiley & Sons, Ltd.

Thermal behavior of europium tris(hexafluoroacetylacetonate) Eu(hfa)3 and the mixed-ligand 4-cyanopyridine-N-oxide complex [Eu(hfa)3(cpo)

The thermal behavior and thermodynamic properties of europium tris(hexafluoroacetylacetonate) Eu(hfa)3 and the mixed-ligand 4-cyanopyridine-N-oxide complex [Eu(hfa)3(cpo)] were investigated by thermal analysis and Knudsen effusion mass spectrometry. The compounds sublime congruently. The composition of the gas phase over the compounds and the partial pressures of the components were determined. The enthalpies of sublimation, polymerization, and dissociation of these compounds were derived from experimental data.

Monomers for Adhesive Polymers, 7a

AbstractHomopolymerization and copolymerization of N‐(2‐hydroxyethylmethyl)acrylamide (1) with N,N′‐diethyl‐1,3‐bis(acrylamido)propane (2) have been studied in ethanol/water solvents or in bulk. The polymerization rate exponent depends on the polymerization temperature and increased from 0.99 at 50 °C to 1.21 at 75 °C. The initial polymerization rate dependence on temperature between 50 and 75 °C in Arrhenius coordinates was linear. However, the slope increased with an increase in monomer concentration. The overall activation energy Ea varied from 64 kJ · mol−1 at 0.5 mol · L−1 to 76 kJ · mol−1 at 2.0 mol · L−1 monomer concentration. In addition, the reaction order with respect to the initiator AIBN deviated from the standard free radical polymerization kinetics. The exponent 0.42 indicated a significant participation of primary radicals in termination reactions. The polymerization reaction order declined from ideality as well, and the Ea and polymerization enthalpy changed with the batch composition variation, which could be explained through monomer/monomer, monomer/solvent, or monomer/polymer complexation. The chain transfer to polymer was considered as an origin for the polymer network formation in monomer 1 homopolymerization if its concentration in the batch was 1 mol · L−1 or higher. The more intensive polymerization acceleration with the monomer dilution and the greater heat released reduction with decrease in the monomer 1 to 2 ratios were evidenced in copolymerization. Nevertheless, the deviations from conventional reaction kinetics were not as pronounced as with acrylic or methacrylic acid polymerizations.magnified image

The kinetic study of the curing reaction of mono- and di-epoxides obtained during the reaction of divinylbenzene and hydrogen peroxide with acid anhydrides

In this paper, the non-isothermal differential scanning calorimetry (DSC) was employed to investigate the cure process and to determine the kinetic parameters of the curing reactions of mono- and di-epoxides with maleic and glutaric anhydrides. The epoxides were obtained during the epoxidation process of commercially available divinylbenzene by using 60% hydrogen peroxide as the oxidant in the presence of organic solvents and magnesium oxide as the catalyst. It was found that the cure process of epoxides with maleic anhydride was described through higher values of enthalpy of polymerization (Δ H R) and lower temperatures of the cure initiation ( T onset), the peak maximum temperature ( T max) and the final cure temperature ( T end). It can be considered to accelerate the rate of reaction and lead to an excellent network structure when maleic anhydride was used as curing agent. The kinetic analysis was firstly computed using a model free-estimation of the activation energy (Friedman, Ozawa–Flynn–Wall methods) and then the multivariate non-linear regression with a 6th degree Runge–Kutta process in a modified Marquardt procedure was employed to calculate the corresponding kinetic parameters ( E i , n i , A i ) using the nth-order reaction f( α). The unbranched three-step process of the nth-order reaction f( α) for each step was the best to describe the cure process of mono- and di-epoxide with acid anhydrides. The determined values of the activation energies were in the range 64.7–105.2 kJ/mol for epoxides/glutaric anhydride system and 64.7–82.7 kJ/mol when maleic anhydride was used as hardening agent.