Physicochemical characterization of poly(tert-butyl acrylate-b-methyl methacrylate) prepared with atom transfer radical polymerization by inverse gas chromatography

Poly(tert-butyl acrylate) (PtBuA) was synthesized by atom transfer radical polymerization (ATRP) using methyl-2-bromo propionate (MBP) as an initiator in bulk at 80 °C. The successive ATRP of methyl methacrylate in diphenyl ether at 80 °C using previously obtained PtBuA as a macroinitiator led to formation of poly(tert-butyl acrylate-b-methyl methacrylate) (poly(tBuA-b-MMA)). The synthesized macroinitiator and block copolymer have controlled molecular weight and low polydispersity (M_w/M_n<1.2). The block copolymer was characterized by gel permeation chromatography (GPC) and ¹H NMR. The retention diagrams of poly(tBuA-b-MMA) for some aliphatic esters and aromatic hydrocarbons were obtained using inverse gas chromatography (IGC) technique. The glass transition temperatures, T_gs of poly(tBuA-b-MMA) were determined by both differential scanning calorimeter (DSC) and IGC. It was observed that the block copolymer represents three T_gs at 50, 75 and 100 °C by IGC although it represents only one T_g at 71 °C by DSC. After the column was quenched from 180 to 0 °C, the T_g at 100 °C shifted to 105 °C however others did not change. Specific retention volumes, and the thermodynamical polymer-solvent interaction parameters such as Flory-Huggins, , equation-of-state, and effective exchange energy, X_eff were found for all studied solvents. Partial molar heat of sorption, , partial molar heat of mixing, and molar heat of vaporization, ΔH_v, were determined. In addition, the solubility parameter of the corresponding block copolymer, δ₂ was determined as 11.0 (cal/cm³)^1/2 at 25 °C.     

Chemical and phase equilibria calculation of α-pinene hydration in CO2-expanded liquid

Modeling of chemical and phase equilibria of α-pinene hydration in subcritical CO₂ was carried out by calculation. A simplified scheme of the conversion includes 6 reaction routes. Thermochemical and physicochemical parameters of individual compounds (T_cr, P_cr, T_b, (298.15 K), (298.15 K), C_p (T), ω) were preliminary estimated. Phase diagrams of the model reaction mixtures were calculated, coordinates of the critical point were found, and the region of subcritical parameters T and P, where the initial mixture divides into the gas phase and CO₂-expanded liquid, was located. Dependence of the products distribution and yield of CO₂-expanded liquid on the reaction temperature and pressure was studied. The reaction equilibrium as a function of temperature and pressure was determined, and heat effects of all reactions under consideration were calculated. The drift of critical parameters versus reaction mixture composition was examined. It was shown that during the hydration and alcohols accumulation the critical pressure of reaction mixture increases continuously, the critical temperature at first elevates and then begins to decrease, and the phase diagrams starts to degenerate. If amount of alcohols becomes more than 80 mol%, the mixture has no critical point and cannot pass to a supercritical state.     

Carbodiimide-mediated synthesis of poly(l-lactide)-based networks

Poly(l-lactide-co-succinic anhydride) networks were synthesised via the carbodiimide-mediated coupling of poly(l-lactide) (PLLA) star polymers. When 4-(dimethylamino)pyridine (DMAP) alone was used as the catalyst, gelation did not occur. However, when 4-(dimethylamino)pyridinium p-toluenesulfonate (DPTS), the salt of DMAP and p-toluenesulfonic acid (PTSA), was the catalyst, the networks obtained had gel fractions comparable to those which were reported for networks synthesised by conventional methods. Greater gel fractions and conversion of the prepolymer terminal hydroxyl groups were observed when the hydroxyl-terminated star prepolymers reacted with succinic anhydride in a one-pot procedure than when the hydroxyl-terminated star prepolymers reacted with presynthesised succinic-terminated star prepolymers. The thermal properties of the networks, glass transition temperature (T_g), melting temperature (T_m) and crystallinity (X_c) were all strongly influenced by the average molecular weights between the crosslinks (). The network with the smallest (1400 g/mol) was amorphous and had a T_g of 59 °C while the network with the largest (7800 g/mol) was 15% crystalline and had a T_g of 56 °C.     

Dynamic Monte Carlo study on the polymer chain in random media filled with nanoparticles

The effect of nanoparticles on the dynamic and configurational properties of a single polymer chain has been studied by using dynamic Monte Carlo simulation. An attractive potential, ε, is considered between fixed nanoparticles and polymer beads. The diffusion coefficient of the polymer D remains constant for weak interactions, i.e. small β=−ε/k_BT, and then gradually drops to zero at a critical value . However, the mean square end-to-end distance 〈R²〉 shows a different behavior with an increase in the attractive interaction. 〈R²〉 decreases at small β and reaches a minimum at , then goes up slowly and at last saturates at strong interaction. The values and scale with the concentration of nanoparticles. Interesting findings are: (1) a chain has its minimum size before the chain stops its diffusion, and (2) a chain continues its configuration adjustment even for .     

Synthesis, characterization and thermodynamic properties of poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone)

Poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone) P(MHPMA-co-VP) was synthesized in 1, 4-dioxane solution using benzoyl peroxide (BPO) as initiator at 60 °C. The copolymer was characterized by ¹H ¹³C NMR, FT-IR, DSC, TGA, size exclusion chromatography analysis (SEC) and elemental analysis techniques. According to SEC, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of PMHPMA-co-VP were found to be 58,000, 481,000 g/mol and 8.26, respectively. According to TGA, carbonaceous residue value of PMHPMA-co-VP was found to be 6% at 500 °C. Also, some thermodynamic properties of PMHPMA-co-VP such as the adsorption enthalpy, ΔH_a, molar evaporation enthalpy, ΔH_v, the sorption enthalpy, , sorption free energy, , sorption entropy, , the partial molar free energy, , the partial molar heat of mixing, , at infinite dilution was determined for the interactions of PMHPMA-co-VP with selected alcohols and alkanes by inverse gas chromatography (IGC) method in the temperature range of 323-463 K. According to the specific retention volumes, , the weight fraction activity coefficients of solute probes at infinite dilution, , and Flory-Huggins interaction parameters, between PMHPMA-co-VP-solvents were determined in 413-453 K. According to and , selected alcohols and alkanes were found to be non-solvent for PMHPMA-co-VP at 413-453 K. The glass transition temperature, T_g, of the PMHPMA-co-VP found to be 370 and 363 K, respectively, by IGC and DSC techniques, respectively.     

Macro- and micromixing studies in an unbaffled vessel agitated by a Rushton turbine

Macromixing characteristics, power number and visual observation of the vortex behaviour and micromixing in an unbaffled tank agitated with a Rushton turbine are reported. The latter has also been compared in detail with earlier results from an identical tank containing baffles. The maximum mean specific energy dissipation rate, , in the unbaffled tank that can be utilised without severe air incorporation is compared to with baffles. However, at this lower , the micromixing efficiency is always significantly greater without baffles except when addition is made onto the top of the liquid or into the trailing vortex very close to the impeller. In these latter cases, they are approximately the same but even a small submergence of the feed tube below the liquid surface greatly enhances micromixing in the unbaffled case whilst it is still very poor with baffles. This good micromixing performance of the unbaffled vessel was very unexpected. Furthermore, an established method of estimating the local ε_T gave values of at every feed position where measurement was undertaken. Since the spatially averaged value of φ=1, this result suggests the possibility that the accepted concept of micromixing being totally controlled by the local ε_T at the feed point may not be valid for such swirling flows.     

Fracture energy-fracture stress relationship for weak polymer-polymer interfaces

The bulk thick films of high-molecular-weight atactic polystyrene (PS) were brought into contact at a small contact pressure ≤0.2 MPa at a constant healing temperature T_h below the calorimetric glass transition temperature of the bulk . Fracture energy G and fracture stress σ of the auto-adhesive joints PS-PS were measured at ambient temperature in the T-peel test and the lap-shear joint geometry, respectively. In the framework of the diffusion controlled mechanism of the development of these two mechanical properties suggesting their evolution as and (t_h is the healing time), and as G∝1/T_h and σ∝1/T_h, a linear relationship between G^1/2 and σ, valid over a temperature range of , has been found. The penetration depth of 0.5 nm corresponding to the value of G calculated using the measured value of σ developed at for 24 h was reasonably smaller than the thickness of the surface mobile layer of 1 nm predicted by Wool's rigidity percolation theory for thick bulk PS films. The feasibility of a full healing of polymer-polymer interfaces below has been discussed. The dependence of an apparent activation energy characterising the process of segmental motions at PS surfaces and interfaces on the approach and the physical property chosen for its calculation has been analysed.     

Anion exchanged polymerized ionic liquids: High free volume single ion conductors

In this study, we investigate the isolated effect of anion type on the chemical, thermal, and conductive properties of imidazolium-based polymerized ionic liquids (PILs). PILs with various anions at constant average chain length were prepared by ion exchange with a water-soluble PIL precursor, (poly(1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium bromide) (poly(MEBIm-Br)). NMR, IR, and elemental analysis confirm that anion exchange of ploy(MEBIm-Br) with bis(trifluoromethanesulfonyl) imide (TFSI), tetrafluoroborate (BF₄), trifluoromethanesulfonate (Tf), and hexafluorophosphate (PF₆) in water resulted in nearly fully exchanged PILs. As a function of anion type, the glass transition temperature plays a dominant role, but not the sole role in determining ion conductivity. Other factors affecting ionic conductivity include the size and symmetry of the anion and dissociation energy of the ion pair. Both the Vogel-Fulcher-Tammann (VFT) and Williams-Landel-Ferry (WLF) equations were employed to investigate the temperature dependent ionic conductivities. The (9.03) and (168 K) values obtained from the WLF regression of these PILs greatly deviate from the classical WLF values originally obtained from the mechanical relaxation of uncharged polymers ( = 17.44,  = 51.6 K) and the WLF values obtained from the conductive properties of other polymer electrolytes. This suggests that the fractional free volume (f (T_g) = B/(2.303)) and Vogel temperature (T₀ = T_g − ) are strong functions of ion concentration, where high free volume allows for ion mobility at temperatures farther below the glass transition temperature of the polymer.     

On the quantification of energy dissipation in the impeller stream of a stirred vessel from fluctuating velocity gradient measurements

The turbulence energy dissipation rate (ε) in the impeller stream of a vessel of diameter stirred by a Rushton turbine of diameter D=T/3 was directly measured with particle image velocimetry (PIV). Both 2-D and 3-D PIV techniques were employed to measure the mean velocities, Reynolds stresses and ε in the vessel for Reynolds numbers of 15 000-40 000. ε was determined directly from measurements of the fluctuating velocity gradients by analysing the PIV images with a resolution of . The values of the normalised ensemble-averaged dissipation rate (ε/N³D²) in the impeller stream were in the range 5-10. The measured fluctuating velocity gradients compared well with similar data obtained using a four-channel laser anemometer. The results are also compared with those of earlier works employing non-direct methods to estimate ε and show that some of these methods yield comparable values, although the spread of the some of the data previously reported is significant. The present results show the feasibility of direct measurement of the ε distribution with PIV and provide useful information for the design of mixing processes as well as for its more accurate estimation in future work.