Isothermal Melt Crystallization Kinetics for Poly(Trimethylene Terephthalate)/Poly(Butylene Terephthalate) Blends

The kinetics of isothermal melt crystallization of poly(trimethylene terephthalate) (PTT)/poly(butylene terephthalate) (PBT) blends were investigated using differential scanning calorimetry (DSC) over the crystallization temperature range of 184–192°C. Analysis of the data was carried out based on the Avrami equation. The values of the exponent found for all samples were between 2.0 and 3.0. The results indicated that the crystallization process tends to be two‐dimensional growth, which was consistent with the result of polarizing light microscopy (PLM). The activation energies were also determined by the Arrhenius equation for isothermal crystallization. The values of ΔE of PTT/PBT blends were greater than those for PTT and PBT. Lastly, using values of transport parameters common to many polymers (U*=6280 J/mol, T _∞=T _g – 30), together with experimentally determined values of T _m ⁰ and T _g, the nucleation parameter, K _g, for PTT, PBT, and PTT/PBT blends was estimated based on the Lauritzen–Hoffman theory.     

Enthalpy Relaxation Study of Poly(Vinyl Chloride) Films Based on the Time-Temperature Superposition Principle

Abstract

In the enthalpy relaxation of poly(vinyl chloride), a decrease in enthalpy upon the isothermal ageing was measured using the differential scanning calorimetry method as a function of ageing time (t_A) and ageing temperature. The range of the ageing temperature was from 56?°C (T_g ? 25?°C) to 72?°C (T_g ? 9?°C) where T_g denotes the glass transition temperature. The limiting value of the decrease in enthalpy was determined by applying a stretched exponential function to the measured enthalpy data. The relaxation function (?) was derived from the measured enthalpy and the construction of a master curve was tried by shifting the ? ? t_A curves of the respective ageing temperatures horizontally. Although there was no agreement between the shift factors (a_T) and the relaxation times of the ? ? t_A curves, the superposition was successfully constructed and the a_T values obtained for the poly(vinyl chloride) sample were found to be comparable to those reported for viscoelastic experiments over a broad temperature range above and below T_g carried out for different polymers. The origin of the decrease in enthalpy was briefly discussed in terms of the chain dynamics in the isothermal condition.     

Concerning free volume quantities and the glass temperature

Free volume quantities proposed earlier by Boyer and Simha in connection with the glass transition are reformulated by taking into account the temperature dependence of the thermal expansivities α _l and α_g for the liquid and the glass, respectively. This necessitates an extrapolation of the liquid to temperatures below Tg which is performed by means of the reduced volume-temperature function established and given a theoretical foundation previously. For the glass, low temperature experimental data, encompassing all relaxations occuring below T_g, are required.

Two polymer series are examined in detail, namely, poly(methacrylates) and poly(vinyl) alkyl ethers, where α_g has been measured between at least 30°K and T_g. Results for poly(methylacrylate) and poly(styrene) are also given. The systematic decrease in the product (αl - αg) · T|_T=Tg with increasing length of the side chain noted previously is considerably reduced but not eliminated when the appropriately corrected expression is substituted instead. However, the free volume fraction related to the quantity αlT|_T=Tg remains more nearly invariant in the polymers analyzed.

An alternative treatment is discussed which considers an occupied volume expanding below T_g by a mechanism of thermal vibrations solely. Experimental and theoretical means of obtaining this quantity arc suggested.     

Segmental Dynamics in net -poly(methyl methacrylate)- co -poly(n-butyl acrylate) Copolymer Networks

Dynamic mechanical spectroscopy and differential scanning calorimetry investigations of segmental dynamics are reported for net-poly(methyl methacrylate)-co-poly(n-butyl acrylate) copolymer networks. Three characteristic temperatures, namely, Vogel (T_∞), glass transition (T _g ), and crossover (T _c ), were used to define cooperativity range and a new reduced temperature parameter (Solidness, S). The results showed that broadness of the α -dispersion (glass transition) and cooperativity length scale at the glass transition temperature decreased with increasing butyl acrylate content and T _g -scaled temperature dependence of the relaxation time (fragility). However, the cooperativity range (T _c –T_∞), decreased with increasing fragility index. Furthermore, the solidness at T _g (S(T _g )) was nearly independent of chemical structure of the samples. Finally, a correlation was found between two measures of cooperativity length scale in the glass transition region, namely, average volume of cooperatively rearranging regions, V _CRR , and the number of basic units in an act of rearrangement in the glass transition region, Z(T _g ), determined from two completely independent experimental techniques.     

Synthesis and Characterization of Biodegradable Poly(lactic-co-glycolic acid)

A series of poly(lactic-co-glycolic acid) (PLGA) was synthesized by bulk ring-opening copolymerization with different ratios of L-lactic acid (L-LA) to glycolic acid (GA); stannous octoate [Sn(Oct)2] was used as catalyst. The structures were characterized by FT-IR. The crystallinity and the glass-transition temperature (T_g) were studied by differential scanning calorimeter (DSC). T_g decreased with the increase of GA and the rate of degradation and degree of hydrophilicity increased with the increased content of GA.     

Viscoelastic Behavior of Poly(Methyl Methacrylate-Co-Methyl Acrylate) Random Copolymer Studied by Dynamic Mechanical Analysis and Nanoindentation

The viscoelastic behavior of poly(methyl methacrylate) (PMMA) homopolymer and poly(methyl methacrylate-co-methyl acrylate) random copolymers was characterized by dynamic mechanical analysis and nanoindentation. Differential scanning calorimetric results showed only one glass transition, indicating the random distribution of comonomers in the copolymers. The α relaxation temperature (T_α) and activation energy (H_α) decreased with increasing content of methyl acrylate monomers (C_MA%). The β relaxation temperature (T_β) also decreased whereas the activation energy (H_β) showed only small variations compared with H_α. Moreover, the indention displacement and creep compliance strongly depended on C_MA%. Two creep stages were found in the creep compliance curves.     

Nonisothermal Crystallization of Recycled Poly(Ethylene Terephthalate)/Poly(Ethylene Octene) Blends

Recycled poly(ethylene terephthalate) (r-PET) was blended with poly(ethylene octene) (POE) and glycidyl methacrylate grafted poly(ethylene octene) (mPOE). The nonisothermal crystallization behavior of r-PET, r-PET/POE, and r-PET/mPOE blends was investigated using differential scanning calorimetry (DSC). The crystallization peak temperatures (T _p ) of the r-PET/POE and r-PET/mPOE blends were higher than that of r-PET at various cooling rates. Furthermore, the half-time for crystallization (t _1/2 ) decreased in the r-PET/POE and r-PET/mPOE blends, implying the nucleating role of POE and mPOE. The mPOE had lower nucleation activity than POE because the in situ formed copolymer PET-g-POE in the PET/mPOE blend restricted the movement of PET chains. Non-isothermal crystallization kinetics analysis was carried out based on the modified Avrami equation, the Ozawa equation, and the Mo method. It was found that the Mo method provided a better fit for the experimental data for all samples. The effective energy barriers for nonisothermal crystallization of r-PET and its blends were determined by the Kissinger method.     

Fluorene-Based Poly(imino ketone) with Fluorine Atoms on the Side Chains as an Intelligent High-Performance Polymer

Abstract

Fluorene-based poly(imino ketone) with fluorine atoms in the side chains (PIKF-F), as an intelligent, high-performance polymer, was synthesized by the reaction of 4,4′-dibromobenzophenone and 9,9-bis(3-F-4-aminophenyl) fluorene via a palladium catalyzed C-N cross-coupling reaction. Its structure was characterized by means of FT-IR and ¹H NMR spectroscopy. The results showed a good agreement with the proposed structure. The molecular weights of the PIKF-F were measured by GPC (calibrated by polystyrene standards). The M_n and M_w values were 64,800 and 153,300, respectively. Thermogravimetric analysis and differential scanning calorimetry measurements showed that the polymer possessed good thermal stability with a high 10% decomposition temperature (450?°C) and a high glass transition temperature (T_g = 250?°C). The PIKF-F exhibited UV (ultra violet) absorption bands at 340–370?nm in NMP solution, while the fluorescence spectra showed maximum emission of PIKF-F at 498?nm in NMP solution. Both optical properties indicate the PIKF-F is of potential use as an organic photoelectric material. Additionally, due to its special conjugated system and the intramolecular hydrogen bonding (N–H···F), it was endowed with significantly strong photonic luminescence and the change of fluorescent intensity was reversible as the temperature was changed.     

Crystallization Behavior of Poly(Trimethylene Terephthalate)/Polycarbonate Blends

The crystallization behavior of poly(trimethylene terephthalate (PTT) in compatibilized and uncompatibilized PTT/polycarbonate (PC) blends are investigated in the research reported in this paper. The differential scanning calorimetry (DSC) results showed that the crystallization behaviors of PTT/PC blends were very sensitive to PC content. The onset (T_ci) and the peak (T_c) crystallization temperatures shifted to lower temperatures whereas the area of the exotherm decreased quickly as the PC content was increased. The Avrami exponent, n, decreased from 4.32 to 3.61 as the PC content was increased from 0 to 20 wt %, and the growth rate constant, Z _c , decreased gradually as well. This suggests that the nucleation mechanism exhibits the tendency of changing gradually from a thermal nucleation to an athermal mode although the growth mechanism still remains three‐dimensional. When epoxy (2.7 phr) was added as a compatibilizer during melt blending, the T_ci and T_c shifted slightly to higher temperature (≤2°C), and the crystallization enthalpy, however, exhibited an increased crystallinity with the exception of the 90/10/2.7 phr PTT/PC/Epoxy. This suggests that the epoxy make a positive contribution to the PTT crystallization. Moreover, the influences of epoxy on the crystallization behaviors of PTT/PC blends are related to the epoxy content. By contrast, the compatibilizer of ethylene‐propylene‐diene copolymer graft glycidyl methacrylate (EPDM‐g‐GMA, ≤6.3 phr) had little effect on the crystallization behavior of PTT/PC blends. For PTT/PC/Epoxy (2.7 phr) blends, the Avrami exponent, n, decreased to near 3, while the growth rate constant, Z _c , increased slightly as PC content was increased from 0 to 20 wt %. It is suggested that epoxy accelerated the process of the nucleation mechanism changing from thermal nucleation to an athermal mode. The EPDM‐g‐GMA had little effect on the nucleation mode and spherical growth mechanism. The PTT spherulite morphologies in PTT/PC blends were very sensitive to blend composition. Completely different morphologies were observed in pure PTT, PTT/PC, PTT/PC/Epoxy, and PTT/PC/EPDM‐g‐GMA blends.     

Monte Carlo Simulations of Chain Dimensions and Conformational Properties of Various Poly(n-alkyl methacrylates) in Solution

Rotational Isomeric State (RIS) Metropolis Monte Carlo (RMMC) simulations of the conformational properties and chain dimensions of a series of chemically different poly(n-alkyl methacrylates) including poly(methyl methacrylate), poly(n-butyl methacrylate), poly(n-hexyl methacrylate), and poly(phenyl methacrylate), in the θ state were investigated, and (〈r²〉/M)^1/2, (〈s²〉/M)^1/2 and C _n were calculated and compared in order to obtain fundamental understanding of the influence of the chemical structure. Simulations were conducted for different molecular weights. Results obtained from the simulations are compared with experimentally obtained dimensions in the literature using the Mark-Houwink relationship as well as, in some cases, data available from direct determinations in θ solvents. Good agreement between simulation and experimental data was obtained. The backbone conformation is predominantly trans in these polymers. Increase in bulkiness and rigidity of the substituting acrylate side group results in an increase in trans and a decrease in gauche backbone conformer population. In the case of rotatable bonds in the side-group structure, increase in rigidity of the side group leads to a decrease in the trans population, although this effect is not uniformly observed.     

Miscibility and Isothermal Crystallization Behavior of Poly (Butylene Succinate-co-Adipate) (PBSA)/Poly (Trimethylene Carbonate) (PTMC) Blends

Poly(butylene succinate-co-adipate) (PBSA)/poly (trimethylene carbonate) (PTMC) blend samples with different weight ratios were prepared by solution blending. The morphologies after isothermal crystallization and in the melt were observed by optical microscopy (OM). Differential scanning calorimetry (DSC) was used to characterize the isothermal crystallization kinetics and melting behaviors. According to the OM image before and after melting, it was found that the blends formed heterogenous morphologies. When the PTMC content was low (20%), PBSA formed the continuous phase, while when the PTMC contents was high (40%), PBSA formed the dispersed phase. The glass transition temperatures (T_g) of the blends were determined by DSC and the differences of the T_g values were smaller than the difference between those of pure PBSA and PTMC. In addition, the equilibrium melting points were depressed in the blends. According to these results, the PBSA/PTMC blends were determined as being partially miscible blends. The crystallization kinetics was investigated according to the Avrami equation. It was found that the incorporation of PTMC did not change the crystallization mechanism of PBSA. However, the crystallization rate decreased with the increase of PTMC contents. The change of crystallization kinetics is related with the existences of amorphous PTMC, the partial miscibility between PLLA and PTMC, and the changes of phase structures.     

Hansen Solubility Parameters for the Solid Surface of Cellulose Acetate Propionate by Inverse Gas Chromatography

The specific retention volumes, V ⁰ _g , for adsorption of 21 solute probes on the solid surface of cellulose acetate propionate (CAP) were determined in the temperature range 343.15–403.15 K by inverse gas chromatography. In the temperature range studied the retention diagrams drawn between vs. 1/T were found to be linear for all the solutes. Hansen solubility parameters (HSPs) were calculated by relating with the cohesive energy of adsorption of the solutes on the surface of CAP following the Snyder and Karger adsorption model. The three components of HSP decreased linearly with increase of temperature. The HSP of CAP were compared with the corresponding values determined on cellulose acetate butyrate (CAB) and discussed in the light of the chemical nature of the two solid surfaces. Enthalpies of adsorption were found to be more negative for CAP than for CAB.     

Effect of heat treatment on the optical and electrical transport properties of Ge15Sb10Se75 and Ge25Sb10Se65 thin films

The effect of heat treatment on the optical and electrical properties of Ge₁₅Sb₁₀Se₇₅ and Ge₂₅Sb₁₀Se₆₅ thin films in the range of annealing temperature 373-723 K has been investigated. Analysis of the optical absorption data indicates that Tauc's relation for the allowed non-direct transition successfully describes the optical processes in these films. The optical band gap (E_g^opt.) as well as the activation energy for the electrical conduction (ΔE) increase with the increase of annealing temperature (T_a) up to the glass transition temperature (T_g). Then a remarkable decrease in both the E_g^opt. and ΔE values occurred with a further increase of the annealing temperature (T_a>T_g). The obtained results were explained in terms of the Mott and Davis model for amorphous materials and amorphous to crystalline structure transformations. Furthermore, the deduced value of E_g^opt. for the Ge₂₅Sb₁₀Se₆₅ thin film is higher than that observed for the Ge₁₅Sb₁₀Se₇₅ thin film. This behavior was discussed on the basis of the chemical ordered network model (CONM) and the average value for the overall mean bond energy 〈E〉 of the amorphous system Ge_xSb₁₀Se_90−x with x=15 and 25 at%. The annealing process at T_a>T_g results in the formation of some crystalline phases GeSe, GeSe₂ and Sb₂Se₃ as revealed in XRD patterns, which confirms our discussion of the obtained results.     

Sorption of Organic Solvents in Poly(Dimethyl Siloxane) Membrane. II. Effect of Sorption on the Polymer Crystals upon Cooling

Polymer crystalline properties in poly(dimethyl siloxane) (PDMS) film after solvation by various solvents was determined using low temperature differential scanning calorimetry (DSC). At various solvent uptake levels, the crystalline thermal properties of the solvated polymer were modified to different extents as revealed by the shifts in crystalline melting point (T_m) and its enthalpy (ΔH_m). Water uptake in PDMS was very limited (<0.01 g/g) and T_m did not significantly change during the sorption process. For toluene and cyclohexane penetrants, T_m moved toward a much lower temperature depending on the sorption levels. At low solvent uptakes, the T_m values decreased linearly with solvent uptakes due to formation of a miscible phase. Beyond a threshold, the T_m remained stable and an additional penetrant fusion peak appeared, implying the onset of a microphase separation phenomenon. The ΔH_m values for the swollen membranes were decreased, with the exception of the water penetrant. This indicates that a lower percentage of polymer chains were involved in the crystalline domain for swollen PDMS.     

Study on Phase Formation and Evolution of High Impact Polystyrene with Poly(Cis‐Butadiene) Rubber Blends

Phase formation and evolution of high‐impact polystyrene with poly(cis‐butadiene) rubber blends was studied. The characteristic length, L, was defined to describe the size of particles, and the graph‐estimation method was introduced to determine the width of the distribution of L. Based on the method, the distribution of L proved to be a log‐normal distribution and the distribution width of L was calculated. The phase structure was also discussed in the wave‐number space. The correlation distance, a _c , was defined and computed, applying light‐scattering theory to power spectrum images obtained by 2‐dimensional Fourier transformation (2DFT). The change of a _c was in accord with that of L, which meant 2DFT was valid to study the phase structure. A fractal dimension, D _c , was introduced to describe the uniformity of the spatial distribution. The result showed that D _c was an effective parameter to study the distribution of particles of the dispersed phase.     

On the Electrical and Optical Properties of Some Poly(Azomethine Sulfone)s in Thin Films

Poly(azomethine sulfone)s were synthesized by reacting 4,4′-sulfonyl bis(4-chlorophenyl) with 2,2-bis(4-hydroxyphenyl)propane and azomethine bisphenol in different molar ratios. Thin films were deposited from solution onto glass substrates. Study of the temperature dependences of the electrical conductivity, σ, and Seebeck coefficient, S, were performed in the temperature range 300 K–500 K. Thermal activation energies of electrical conduction, E_a , calculated from these dependences, ranged between 1.50 eV and 1.85 eV. The values of E_a were smaller for polymers with extended conjugation systems. The possibility to use the polymers in thermistor technology is discussed. The aspect of the temperature dependences of σ and S shows that a model based on the energy band-gap representation can be successfully used for explaining the electronic transport mechanism in the higher temperature range. In the lower temperature range, the mechanism of the electrical conduction is discussed in terms of the Mott variable range hopping conduction. The values of some optical parameters (absorption coefficient, optical band gap, etc.) were determined from transmission spectra.