A NEW GROUP CONTRIBUTION METHOD FOR ESTIMATING MELTING AND BOILING POINTS OF ORGANIC COMPOUNDS

A new division method of molecular structural units involving group-adjacent atom pairs has been developed. Expressions for estimating basic physical properties T_b and T_m have been proposed, with the numerical values of relative structural unit parameters presented. The average percent deviations of estimation of the above two physical properties are 1.20 and 7.75, respectively.     

Crystal structure and thermodynamic parameters of Nylon-1010

WAXD, SAXS, FTIR, DSC and density techniques have been used to investigate the crystal structure, crystal density ρ_c, amorphous density p_a equilibrium heat of fusion δH°_m and equilibrium melting temperature T°_m. By extrapolating the straight lines in the FTIR absorbance against density plot to zero intensity. ρ_c and ρ_a were estimated to be 1.098 and 1.003 g/cm³ respectively. The ρ_c obtained was too low in value. From X-ray diffraction patterns of uniaxially oriented fibres, the crystal structure of Nylon-1010 was determined. The Nylon-1010 crystallized in the triclinic system, with lattice dimensions: a = 4.9 Å, b = 5.4 Å, c = 27.8 Å, α = 49°, β = 77°, γ = 63.5°. The unit cell contained one monomeric unit, the space group was P1 , and the correct value of ρ_c was 1.135 g/cm³. The degree of crystallinity of the polymer was determined as about 60% (at RT) using Ruland's method. SAXS has been used to investigate the crystalline lamellar thickness, long period, transition zone, the specific inner surface and the electron density difference between the crystalline and amorphous regions for Nylon-1010. The analysis of data was based upon a one-dimensional electron-density correlation function. δ H°_m was estimated to be 244.0 J/g by extrapolation of δH°_m in the plot of heat of fusion against specific volume of semicrystalline specimens to the completely crystalline condition (V = 1/ρ_c). Owing to the ease of recrystallization of melt-crystallized Nylon-1010 specimens, the well-known Hoffman's T_m-T_c method failed in determining T°_m and a Kamide double extrapolation method was adopted. The T°_m value so obtained was 487 K.     

Reduced state correlations of the enskog modulus for gases and liquids

The Enskog modulus, bρ x, has been subjected to a generalized treatment to develop reduced state correlations for nonpolar and polar substances that exhibit hydrogen bonding. These correlations present relationships between 1 + bρx and ρ_R, the reduced density. For nonpolar substances, the PVT data of argon, nitrogen, methane, ethane, and carbon dioxide were used for the development of these relationships, which were found to depend on z_c, the critical compressibility factor. PVT data for ammonia, methyl alcohol, and water yielded a different correlation, which is applicable to polar substances which exhibit hydrogen bonding. These relationships were found to depend on the parameter, β = (T_b-T_m)/M, which quantitatively describes the extent of hydrogen bonding for polar compounds.     

Structure-property relationships in thermoplastic elastomers: I. Segmented polyether-polyurethanes

Segmented poly(ether-b-urethanes) have been synthesized with 2000 MW polypropylene oxide coupled with diisocyanates and diol type chain extenders. The diisocyanates used were symmetric rigid 4, 4′-diphenylmethane diisocyanate (MDI), linear aliphatic hexamethylene diisocyanate (HDI), and unsymmetric rigid toluene-2, 4-diisocyanate (TDI). The chain extenders were symmetric N, N′-bis(2-hydroxyethyl) terephthalamide (BT) and N, N′-bis(2-hydroxyethyl)-hydroquinone (BH) unsymmetric N, N′-bis(2-hydroxyethyl)isophthalamide, and linear aliphatic 1, 4-butanediol (B). Hard segment contents ranged from 20 to 40 wt percent. The thermal behavior of these materials is consistent with phase separation into separate hard and soft domains, In order of increasing temperature above the soft segment T_g, there are transitions which occur in the regions ?56 to ?36°C (T_a), 70 to 90°C (T_b), and 138 to 168°C (T_m). The former is probably associated with soft segment change from a viscoelastic to an elastomeric state. Values of T_a are ～ ?51 C and ?56°C for the MDI-BT and HDI-BT polymers, respectively, and are independent of hard segment content. Microscopy showed that the former polymers have spherulitic morphology, so these materials have good microphase separation and exhibit crosslinked elastomeric properties. The TDI-BT or BI and MDI-B polyurethane have composition-independent T_a values of ?41 and ?36°C, respectively. These materials probably have considerable “domain-bound-ary-mixing”. At low hard segment content the MDI-B polymers behave as non-crosslinked elastomers. Only the MDI-BI polymers have _Ta values, which are strongly affected by composition, increasing in magnitude with increasing of hard segment content. This is interpreted as significant “mixing-in-domains” and is supported by morphology observed by microscopy. The next higher transition, T_b, probably involves dissociation of interdomain hydrogen bonding. In the case of the MDI-BT polyurethanes, the spherulites associated with the hard domains had disappeared at 141°C and the few small spherulites in the MDI-BI polymers disappeared at 130°C. The T_b values are 70, 83 to 90, and 100°C for the MDI-B, HDI-BT, and HDI-BI polymers, respectively. The melting transitions occurred between 138 to 168°C for the various polyurethanes except for the MDI-BT systems which decompose before melting. Thermal decomposition is a two-stage process. Hard segments decompose between 200 and 300°C. The initial decomposition temperatures are lowered in the presence of strong acid. Soft segments decompose at higher temperatures. The mechanical properties of the MDI-BI polyurethanes are charateristic of crosslinked elastomer, the results of which will be presented in a subsequent paper.     

Synthesis and characterization of poly(L‐lactide‐co‐ϵ‐caprolactone)‐b‐poly(L‐lactide) biodegradable diblock copolyesters: Effect of the block lengths on their thermal properties

Poly(L ‐lactide‐co‐ε‐caprolactone)‐b‐poly(L ‐lactide) [P(LL‐co‐CL)‐b‐PLL] diblock copolyesters were synthesized in a two‐step process with 1‐dodecanol (DDC) and stannous octoate as the initiating system. In the first‐step reaction, a 50:50 mol % amorphous poly(L ‐lactide‐co‐ε‐caprolactone) [P(LL‐co‐CL)] copolyester was synthesized via the bulk copolymerization of L ‐lactide and ε‐caprolactone, which was followed by the polymerization of the PLL crystalline block at the end chain in the second‐step reaction. The yielded copolyesters were characterized with dilute‐solution viscometry, gel permeation chromatography, ¹H‐ and ¹³C‐NMR, and differential scanning calorimetry methods. The molecular weights of the P(LL‐co‐CL) copolyesters from the first‐step reaction were controlled by the DDC concentrations, whereas in the second‐step reaction, the molecular weights of the P(LL‐co‐CL)‐b‐PLL diblock copolyesters depended on the starting P(LL‐co‐CL) copolyester molecular weights and L ‐lactide/prepolymer molar ratios. The starting P(LL‐co‐CL) copolyester molecular weights and PLL block lengths seemed to be the main factors affecting specific thermal properties, including the melting temperature (T_m), heat of melting (ΔH_m), crystallizing temperature (T_c), and heat of crystallizing (ΔH_c), of the final P(LL‐co‐CL)‐b‐PLL diblock copolyester products. T_m, ΔH_m, T_c, and ΔH_c increased when the PLL block lengths increased. However, these thermal properties of the diblock copolyesters also decreased when the P(LL‐co‐CL) block lengths increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

An improved method for determining polymer melting temperatures

A method for determining polymer melting temperatures, T_m, based on a simple modification of thermo-optical analysis is described. The method makes use of a small, highly conducting substrate and a preselected T_m, procedure which results in rapid heating rates (～1500°C/min) without temperature overshoot or superheating. Accuracies to within ±0.15°C are readily obtained. Application of the method to isothermally crystallized polyoxymethylene (Delrin 100 and 500) shows that T_m, increases with both time and temperature of crystallization as well as with increasing molecular weight. The potential of the method for characterizing polymer thermal history and molecular weight is discussed.     

Fractal Dimensions of Simulated and Real Fat Crystal Networks in 3D Space

The microstructure of fat crystal networks is closely related to rheological properties of fat products, and thus is of particular interest to food scientists. The fractal dimensions of fat crystal networks calculated by microscopy methods such as box-counting, D _b, particle-counting, D _f, and mass fractal dimension, D _m, have been extensively employed to quantify the microstructure of fats. This work revealed the microstructural basis of D _b, D _f, and D _m in 3D space through both computer simulation and experiments on the high melting fraction of milk fat crystal networks. Similar to our previous simulation study on the fractal dimensions of fat crystal networks in 2D space, D _b is sensitive to crystal size, area fraction, and not sensitive to distribution orderliness of crystals, which is the percentage of evenly distributed fat crystals within the simulated fat crystal networks. D _f and D _m were not affected by any of the microstructural factors studied in the simulation.     

Diffusion and permeation of gases in undrawn and radially drawn films of native and commercial gutta-percha (trans-Polyisoprene)

The permeability of native and commercial grades of gutta-percha (trans-polyisoprene), was determined and related to diffusion rate both below and above the glass transition temperature (T_g) and the melting point (T_m). Both radially drawn and undrawn membranes were evaluated. Five gases (O₂, N₂, CO₂, H₂ and He) were used as permeants and the measurements were taken both above and below the polymers' crystalline T_m. The diffusivity of the gases was found to have an increased rate above the T_m. The reduction of solubility, diffusivity and permeability with increasing draw ratio was attributed to an increase in crystallinity.     

Nonisothermal crystallization of s‐PP fractions

Syndiotactic polypropylene (s‐PP) was prepared by metallocene catalyst and was fractionated with the temperature rising elution fractionation (TREF) technique. The nonisothermal behavior of the obtained fractions was investigated. Fractions was first cooled at different rates and then heated at a constant rate. The parameters such as the peak crystallization temperature (T_c), the onset crystallization temperature (T_on), the difference between T_on and T_c (ΔT₁ = T_on − T_c), the crystallization enthalpy (ΔH), the peak melting temperatures (T_m1, T_m2), and the difference between the T_m1 and T_m2 (ΔT₂ = T_m2 − T_m1) were obtained. The dependence of these parameters on cooling rate, syndiotacticity, and molecular weight was discussed. It is found that T_c, T_on, ΔH, T_m1, and T_m2 systematically increase with increasing syndiotacticity and are depressed on increasing the cooling rate. Cooling rate, syndiotacticity, and molecular weight show different influences on ΔT₁. In the melting process of s‐PP, double peaks were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 897–901, 1999     

Structures and properties of blown moulding LLDPE films

Abstract

The crystalline structures, mechanical properties, transparence and fracture behaviours of linear low density polyethylene blown moulding films with nucleating agents incorporated in were investigated. The results indicated that with the nucleating agents used, the melting temperature T _m, crystalline structures, general profile of the stress–strain curves, tensile yield strength σ _y and essential work of fracture parameters before yield of the films, were almost unchanged, while the strain hardening phenomenon, tensile fracture strength σ _b, elongation at break &epsi _b, transparence and fracture parameters w _e and βw _p were enhanced greatly. As the loading content of nucleating agent increasing, the crystallinity first decreased and then increased rapidly; the strain hardening phenomenon ? _b and σ _b increased to a maximum and then decrease to a stable value, while the T _m and σ _y were also unchanged; the haze decreased first and then reached a stable value; the w _e and w _e,y decreased remarkably first and then rapidly increased, even enormously exceeding the w _e of pure linear low density polyethylene, while βw _p and β _y w _p,y increased to a quite high value first and then dropped to a lower level.     

Investigation of crystallization of PVCH‐PE‐PVCH triblock copolymer in supercritical carbon dioxide

Crystallization of glassy‐crystalline‐glassy poly(vinylcyclohexane)‐b‐polyethylene‐b‐poly(vinylcyclo hexane) (PVCH‐PE‐PVCH) triblock copolymer treated in supercritical Carbon Dioxide (scCO₂) was investigated by using differential scanning calorimetry (DSC) and atomic force microscope (AFM). It was found that the melting temperatures (T_m) and the crystallinity (X_c) of the PVCH‐PE‐PVCH samples treated in scCO₂ at different annealing temperatures (T) were all much higher than those of the untreated PVCH‐PE‐PVCH, indicating that the scCO₂ could effectively induce the samples to further crystallize. With increasing the T, the T_m of the samples linearly increased, even up to 108°C, close to the T_m (～ 110°C) of the PE homopolymer hydrogenated from polybutadiene which is equal to the PE block in the triblock copolymer. The results could be ascribed to the released PE chain ends linked to the PVCH block due to the lowered T_g of the PVCH block swollen by scCO₂. It suggested that the origin of the confined crystallization in PVCH‐PE‐PVCH was the fixed PE chain ends by the glassy PVCH. AFM images of the samples treated in scCO₂ showed that the PVCH lamella phase tended to connect each other and led to the aggregated structures. The result indicated that the PVCH block could be availably swollen by scCO₂. It supported the DSC experiment results of the samples treated in scCO₂. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2584–2589, 2006     

Optical rotation of dilute aqueous xanthan solutions at elevated hydrostatic pressure

The optical rotation of dilute aqueous xanthan solutions of ultrasonically depolymerized xanthan have been measured in the pressure range from 0.1 to 50 MPa. This was achieved using a high-pressure cell in a spectropolarimeter of original design. The conformational melting temperature T_m of xanthan was found to decrease with increasing pressure. The pressure coefficients of the melting temperature at constant ionic strengths, I, was found to be (ΔT_m/Δp)_I = ?(9.5 ± 4.0) 10^?8 K Pa^?1 and (ΔT_m/Δp)_I = ?(20 ± 10) 10^?8 K Pa^?1 for solution ionic strengths of 10 mM NaCl and 25mM NaCl, respectively. The largest shift in T_m of xanthan for an increase in hydrostatic pressure from 0.1 to 50 MPa is less than ?10 K. The observed decrease in conformational transition temperature can have significant implications when xanthan is used in polymer or micellar flooding processes in high-salinity, high-temperature oil reservoirs where the reservoir temperature is close to the structural transition temperature at ambient pressure.     

Mechanical and nuclear shielding properties of sodium cadmium borate glasses: Impact of cadmium oxide additive

In this study, highly effective radiation shielding glass materials with different amount of CdO additive were investigated in terms of nuclear shielding performance. Moreover, mechanical properties have been determined. The μ_m values were computed using XCOM and XMuDat program. The gamma and neutron shielding parameters such as μ_m, HVL, Z_eff, EBF, EABF, SAFE, b_co, b_ico, σ_co and σ_abs are calculated to understand the radiation shielding performances of investigated glasses. The results show that μ_m, Z_eff and σ_abs values increase as the CdO content increases. The S7 sample has the lowest HVL, MFP, EBF, EABF, SAFE, b_co, b_ico and σ_co values. Therefore, S7 glass sample (70 mol% of CdO) which has also the highest number of bonds per unit volume can be considered as a superior material for radiation shielding applications. The outcomes of this study can be very useful for future applications of investigated glass materials in medical and industrial radiation fields.     

Crystalline transitions and the solid-state extrusion of polymers

Extrusion experiments on eight polymers in our laboratory and eight additional polymers in other laboratories reveal that solid-state extrusion and malleability occur in semicrystalline polymers that have a reversible crystalline transition, T_c, and do not occur in crystalline polymers devoid of T_c, The solid-state extrusion takes place only in the temperature range of T_c ? T < T_m. The transparency of the solid-state extrudates was shown to be largely due to void disappearance and may be due in part to the diminution in size of the scattering species. Increases in T_m were shown not to be correlatable with lamellar thickening or chain extension.     

Effect of Pre-Melting Time on Crystallization of Poly(ethylene terephthalate)

In this study poly(ethylene terephthalate) (PET) was melted at 300°C, approximately 46°C above the crystalline melting point, T _m, for different times, i.e., Δt _m,=5, 8, and 10 min, and then quenched to different isothermal crystallization temperatures, T _c, ranging from 190°C to 230°C. The effect of pre-melting time, Δt _m, at 300°C on the degree of crystallinity and on crystalline morphology were investigated by differential scanning calorimetry (DSC) and polarized-light microscopy (PLM). After crystallization at low T _c, PLM data revealed the PET contained usual, positive, and unringed spherulites. After crystallization at high T _c PET contained unusual, ringed, and double-extinction spherulites. The experimental results reveal that increasing the pre-melting time Δt _m at 300°C causes an increment in T _c for usual–unusual, unringed–ringed, and positive–double-extinction transitions of the PET spherulites. The experimental results also show that PET with a pre-melting time Δt _m=8 min had higher crystallinity than those with pre-melting times Δt _m=5 and 10 min. These crystallization phenomena were attributed to the different numbers of residual unmelted PET crystallites as a result of the variation in pre-melting time, Δt _m, at 300°C.     

Generalized warpage parameter

A warpage index (Δψ_m) was introduced for studying warpage characteristics of a plastic part injection molded from PA66 compounded with 30 wt% glass fiber. Δψ_m is defined as Δψ_m = (Δψ_m)_max – (Δψ_m)_min, where ψ_m = ψ(θ)_max, where ψ(θ) = (ε(θ) – α(θ)ΔT)/| α(θ)ΔT|, where ε is the total strain, α is the linear thermal expansion coefficient, ΔT is temperature difference, and θ is the angle along which ε and α are calculated. Finite element analysis was used for calculating flow field in injection, fiber orientation, material anisotropy and warpage. ψ_m is calculated in each finite element, and Δψ_m is calculated in a whole finite element model. Δψ_m is a measure of the ratio of actual shrinkage to the amount of shrinkage that would occur if an element freely shrank. The characteristics of Δψ_m were studied. It has been found that warpage is null if Δψ_m = 0, but that null warpage generally does not indicate Δψ_m = 0. It is shown that Δψ_m quantitatively represents the warped and unwarped state. Δψ_m distinguishes the null warpage state with possible buckling from the null warpage state without possible buckling. It has been shown that material anisotropy is possibly described with Δψ_m, and that the cause of warpage is self-restrictive deformation in an injection molded part. It has been deduced that it is generally not possible to eliminate warpage only by controlling material properties. Δψ_m is obtainable for a plastic part with complex geometry and complex fiber orientation state, and for arbitrary materials. Applications of Δψ_m are left for future study.     

Compressibility and other thermodynamic properties of polymers

Experimental methods for estimating the thermodynamic derivative, (?T/?P)s, of both liquids and solids are described and discussed. The adiabatic heating parameter is shown to be useful, in conjunction with other more commonly measured properties, for estimating the heat capacity, C_p = T(?S/?T)_p, and the internal pressure, P_i = (?U/?V)_T. The principles for applying adiabatic heating measurements to the characterization of polymers are given with data for several common liquids and for filled and unfilled polyurethane rubbers.     

Mixed-chain phospholipids: Structures and chain-melting behavior

It has long been established that diacyl phospholipids isolated from animal cell membranes are predominantly of a mixed-chain variety, meaning that the sn-1 and sn-2 acyl chains are saturated and unsaturated acyl chains, respectively. In general, monoenoic and dienoic acids are found in the sn-2 acyl chain of phosphatidylcholine (PtdCho), whereas polyenoic acids are in phosphatidylethanolamine (PtdEth). These unsaturated chains contain only cis-double bonds, which are always methylene-interrupted. In recent years, the structures and the chain-melting behavior of mixed-chain PtdCho and PtdEth have been systematically studied in this laboratory. Specifically, we have examined the effects of chain unsaturation of the sn-2 acyl chain on the phase transition temperature (T_m) of many PtdCho and PtdEth by high-resolution differential scanning calorimetry (DSC). The T_m values, for instance, obtained from all-unsaturated mixed-chain PtdEth derived from a common precursor can be grouped together according to their chemical formula to form a T_m-diagram. Hence, all the T_m values can be compared simply, systematically, and simultaneously using the T_m-diagram. In addition, the energy-minimized structures of mixed-chain phospholipids containing different numbers/positions of methylene-interruped cis-double bonds have been simulated by molecular mechanics calculations (MM). In this review, the results of our MM and DSC studies carried out with various mixed-chain phospholipids are summarized. In addition, we emphasize that the combined approach of MM and DSC yields unique uniformation that can correlate the various T_m-profiles seen in the T_m-diagram with the structural variation of mixed-chain lipids as caused by the introduction of different numbers/positions of methylene-interrupted cis-double bonds.     

High-concentration polyaluminum chloride: Preparation and effects of the Al concentration on the distribution and transformation of Al species

Using an instantaneous base-feeding method and a batch-feeding method, high-concentration polyaluminum chloride (PACl) products were prepared employing CaO as the basification reagent. The distribution and transformation of the Al species of PACl was explored for the first time over a broad total Al concentration (Al_T) range. There is always an optimal basicity (B value) at which the product has the highest Al_b content, whether Al_T is high or low. The optimal B value and the highest Al_b content obtained both decrease with increasing Al_T. When the B value is lower than optimal, the overall reaction mainly leads to the production of Al_b; when the B value is higher, the reaction leads to the production of Al_c. During the dilution process, high B value PACl has a tendency towards Al_b formation, while low B value PACl favors Al_c formation. The transformation behaviors of Al species are influenced by Al_T in the preparation or dilution process.     

The thermal transition behavior of polyorganophosphazenes

The thermal transition behavior of poly[bis(trifluoroethoxyphosphazene)] (I) and two samples of poly[bis(p-chlorophenoxyphosphazene)] (II) have been studied as representative alkoxy- and aryloxy-substituted polyorganophosphazenes. Several of the polymers of this class are reported to exhibit two first-order transitions, denoted herein as T (1) for the transition from a crystalline to mesomorphic state and T_m for the true melt. Studies of these two polymers were undertaken to gain a further understanding of this behavior. Optical microscopy on a solution-cast film of I showed that the details of spherulitic morphology persist through T(1) = 90°C and remain undisturbed through the temperature interval up to T_m = 240°C. The study of II by x-ray diffraction reveals that two sharp lines are observed above T(1) = 165°C and that orientation is not randomized upon heating to temperatures as high as 238°C. Considerable improvement in the crystalline diffraction pattern results from the thermal treatment. A detailed examination was also made by differential scanning calorimetry (DSC) of the effects of cycling through T(1), annealing in the temperature interval between T(1) and T_m and for I, the influence of controlled crystallization from the melt. The results indicate that the organization in the mesomorphic state, as influenced by thermal history, has a profound affect on the peak position, area, and sharpness of the endotherm at T(1). For I, the apparent heat of fusion at T(1) is about ten times greater than at T_m, whereas for II, no DSC peak is observed at T_m = 365°C, suggesting that the ratio of the heats of fusion at T(1) and T_m is greater than 50. However, estimated volume changes at the two transitions are nearly equal. These results are compared with those of other polymers which exhibit an intermediate state of order and with molecular liquid crystals.