Pore structure and glass transition temperature of nanoporous poly(ether imide)

The effect of nanopores on the glass transition temperature (T_g) of poly(ether imide) was studied with differential scanning calorimetry. Nanoporous poly(ether imide) samples were obtained through the phase separation of immiscible blends of poly(ether imide) and polycaprolactone diol and by the removal of the dispersed minor phase domains with a selective solvent. Microscopy and statistical methods were used to characterize the pore structure and obtain the pore structure parameters. The pore size was found to depend on the processing time and the initial blend composition, mainly because of phase-coarsening kinetics. A decrease in T_g was observed in the nanoporous poly(ether imide) in comparison with the bulk samples. The change in T_g was strongly influenced by the pore structure and was explained by the percolation theory. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3546–3552, 2006     

Study of poly(lactic-co-glycolic acid) interactions with collagen

Poly(lactic-co-glycolic acid) (PLGA) is excellent to fabricate drug delivery systems that prolong the release of recombinant human growth hormone (rhGH), with current research focusing on their possible use for bone regeneration in odontological practice.Herein, we evaluate PLGA interactions with a component of the buccal cavity, as collagen, using monolayers and differential scanning calorimetry (DSC) techniques.Our results indicate that interactions in the PLGA-collagen mixtures showed no phase separation and attraction forces were detected irrespective of the concentration ratio.     

CURING KINETICS AND PROPERTIES OF ACRYLIC RESIN CURED WITH AZIRIDINE CROSSLINKER

A kind of aziridine crosslinkers was synthesized and used to crosslink acrylate copolymers. The crosslinkingproperties and curing kinetics of the resin were studied. It was found that with the increase of the content of crosslinker in theemulsion, the mechanical properties and solvent resistance of the resin will be apparently improved, but its glass transitiontemperature (T_g) is very low. The lowest amount of crosslinker used in the acrylic resin emulsion is 0.25%. Curing kineticsstudied by DSC show that this curing reaction occurs readily because the apparent activation energy of the reaction is low(65.1 kJ/mol). These results demonstrate that the aziridine crosslinker is indeed a low temperature crosslinking agent and canbe used at room temperature.     

Thermal analysis of the double-melting behavior of poly(L-lactic acid)

The melting and crystallization behavior of poly(L -lactic acid) (PLLA; weight-average molecular weight = 3 × 10⁵) was studied with differential scanning calorimetry (DSC). DSC curves for PLLA samples were obtained at various cooling rates (CRs) from the melt (210 °C). The peak crystallization temperature and the exothermic heat of crystallization determined from the DSC curve decreased almost linearly with increasing log(CR). DSC melting curves for the melt-crystallized samples were obtained at various heating rates (HRs). The double-melting behavior was confirmed by the double endothermic peaks, a high-temperature peak (H) and a low-temperature peak (L), that appeared in the DSC curves at slow HRs for the samples prepared with a slow CR. Peak L increased with increasing HR, whereas peak H decreased. The peak melting temperatures of L and H [T_m(L) and T_m(H)] decreased linearly with log(HR). The appearance region of the double-melting peaks (L and H) was illustrated in a CR–HR map. Peak L decreased with increasing CR, whereas peak H increased. T_m(L) and T_m(H) decreased almost linearly with log(CR). The characteristics of the crystallization and double-melting behavior were explained by the slow rates of crystallization and recrystallization, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 25–32, 2004     

Linear versus nonlinear determinations of equilibrium melting temperatures of poly(trimethylene terephthalate) and miscible blend with poly(ether imide) exhibiting multiple melting peaks

Multiple melting peaks in some semicrystalline polymers such as poly(trimethylene terephthalate) (PTT) have caused some difficulty in estimating accurately the equilibrium melting points. PTT forms a miscible blend with amorphous poly(ether imide) (PEI); for comparison purposes, a miscible system of a fixed composition (PTT/PEI of weight ratio = 9/1) was determined. PTT and its miscible blend both exhibited dual melting peaks (labeled as low and high peaks: T_m,L, T_m,H), and the first peaks (T_m,L), not the second peak (T_m,H), should be used for extrapolation. The equilibrium melting temperatures (T) of neat PTT and its blend PTT/PEI (9/1) were 245.2 and 242.4 °C, respectively, by the linear Hoffman–Weeks treatment using the corrected values of T_m,L (i.e., values obtained using a heating rate close to zero). Linear and nonlinear treatments led to a significant difference in estimated T, and the relative validity of these two methods is discussed. The nonlinear estimate yielded a higher value by about 27.3 °C for neat PTT and 23.1 °C for the PTT/PEI (9/1) blend, respectively (also the correction in T_m,L at the same condition mentioned previously). Results showed melting depression in miscible PTT/PEI (9/1). In addition, the T value of neat PTT was higher than that of PTT/PEI (9/1) owing to much thicker and more‐perfect crystals in neat PTT. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1571–1581, 2002     

Synthesis and characterization of new type soluble poly(amide–imide)s based on 6FDA imide modified polyterephthalamides

A series of new poly(amide–imide)s (PAIs, series III ) with good processability and characteristics was synthesized by utilizing organosoluble polyimide (PI, 6FDA–PI series) to improve poor‐solubility polyamide (PA, PTPA series), which used terephthalic acid (TPA) as a monomer. The III series PAIs were synthesized starting from the 2 : 1 molar ratio of aromatic diamines ( I ) and 6FDA to prepare imide ring‐preformed diamines ( II ) and then reacted with equimolar amount of TPA by direct polycondensation. Furthermore, by adjustment of the stoichiometry of the I , II, and TPA monomers, PAIs IV having various components were prepared. Most of the resulting PAIs having inherent viscosities between 0.70 and 1.74 dL/g were obtained in quantitative yields, and they were readily soluble in polar solvents such as N,N‐dimethylacetamide, N‐methyl‐2‐pyrrolidone, dimethylformamide, and dimethyl sulfoxide. All of the soluble PAIs afforded transparent, flexible, and tough films. The glass‐transition temperatures of PAIs III were in the range of 236–256 °C, and the 10% weight loss temperatures were recorded at 522–553 °C in nitrogen. The char yields of the III series polymers in nitrogen atmosphere were all higher than 56% even at 800 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 93–104, 2001     

Crystallization measurements via ultrasonic velocity: Study of poly(lactic acid) parts

Crystallization has significant effects on the physical and mechanical properties of polymer products; therefore, crystallization measurements are important for understanding and predicting polymer products' properties. However, traditional crystallization measurement methods have disadvantages in practical applications because they can be destructive, offline, unsafe, and expensive. Recently, ultrasonic technology has shown great potential as a nondestructive, online, real‐time, and environmentally friendly measurement method for polymer characterization. In this study, a novel measurement method based on ultrasonic technology was proposed to study the crystallization characteristics of poly(lactic acid) (PLA) parts. An annealing process was employed to produce PLA parts with different degrees of crystallinity. A new ultrasonic water immersion method was used to measure the ultrasonic velocities of these annealed PLA parts. It has been found that the plot of the inverse ultrasonic velocity versus the degree of crystallinity shows good linearity over the whole crystallinity range for all three annealing temperatures. The linear relationship between the inverse of the ultrasonic velocity and the crystallinity observed in this study could provide a nondestructive method for investigating the degree of crystallinity of polymers, which can be implemented both offline and online. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 700–708     

Isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone)

The isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone) are investigated by differential scanning calorimetry over two temperature regions. The Avrami equation describes the primary stage of isothermal crystallization kinetics with the exponent n ≈ 2 for both melt and cold crystallization. With the Hoffman–Weeks method, the equilibrium melting point is estimated to be 406 °C. From the spherulitic growth equation proposed by Hoffman and Lauritzen, the nucleation parameter (K_g) of the isothermal melt and cold crystallization is estimated. In addition, the K_g value of the isothermal melt crystallization is compared to those of the other poly(aryl ether ketone)s. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1992–1997, 2000     

Synthesis and characterization of poly(aryl amide imide)s derived from diphenyltrimellitic anhydride

The synthesis and characterization of a series of novel poly(aryl amide imide)s based on diphenyltrimellitic anhydride are described. The poly(aryl amide imide)s, having inherent viscosities of 0.39–1.43 dL/g in N-methyl-2-pyrrolidinone at 30°C, were prepared by polymerization with aromatic diamines in N,N-dimethylacetamide and subsequent chemical imidization. All the polymers were amorphous, readily soluble in aprotic polar solvents such as DMAC, NMP, dimethylsulfoxide, N,N-dimethylformamide, and m-cresol, and could be cast to form flexible and tough films. The glass transition temperatures were in the range of 284–366°C, and the temperatures for 5% weight loss in nitrogen were above 468°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4541–4545, 1999     

Synthesis and characterization of poly(ethylene glycol) polymers functionalized by terminal tributyltin carboxylate moieties

Novel polymeric derivatives of various average molecular weights bearing tributyltin carboxylate moieties as terminal groups have been prepared by esterification with bis(tributyltin) oxide of the corresponding poly(ethylene glycol)s functionalized with dimethylenecarboxylic end groups. Low‐molecular‐weight compounds have also been synthesized, with the aim of investigating the influence of the polymeric chain on tin properties. As investigated by Sn NMR and Fourier transform infrared, the metal center appears to be completely tetracoordinated in chloroform solution at room temperature, whereas at low temperature, the tin atom undergoes a fast exchange between intramolecular pentacoordination with the ethereal oxygen atoms and the unassociated form. In the solid state, even at room temperature, all the polymeric products exhibit both tetracoordination and pentacoordination at tin, the latter achieved by interaction with both ethereal and carbonyl oxygens. The thermal behavior of the series of compounds indicates the presence of crystalline domains in the material, which can be ascribed either to intermolecular interactions at tin, giving rise to organometal aggregates, or to the formation of an ordered phase induced by the presence of the macromolecular chain, depending on the more or less elevated relative concentration of the organotin moieties in the sample. These findings are also confirmed by the X‐ray diffractions patterns of the investigated products. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3091–3104, 2005     

Synthesis and characterization of polyamides and poly(amide-imide)s derived from 2,2-bis(4-aminophenoxy) benzonitrile

A series of polyamides and poly(amide-imide)s were prepared by the direct poly-condensation of 2,2-bis(4-aminophenoxy) benzonitrile [4-APBN] with aromatic dicarboxylic acids and bis(carboxyphthalimide)s in N-methyl-2-pyrrolidone [NMP] with triphenyl phosphite and pyridine as condensing agents. The synthesis of 4-APBN involves a nucleophilic displacement reaction in dipolar aprotic solvent with the alkali metal salt of p-aminophenol and an activated aromatic dichloro compound. Bis(carboxyphthalimide)s were prepared by condensation of 4,4^′-diaminodiphenylsulfone, 3,3^′-diaminodiphenylsulfone, 4,4^′-diaminodiphenylether, 4,4^′-diaminodiphenylmethane, 3,3^′-diaminobenzophenone, and trimellitic anhydride at a 1:2 molar ratio. The inherent viscosities of the resulting polymers were found to be in the range of 0.31-0.93 dl/g and glass transition temperatures between 235 and 298 °C. All polymers were soluble in aprotic polar solvents such as dimethylsulfoxide and NMP. The results of thermogravimetry revealed that all the polymers showed no significant weight loss before 400 °C. Wide-angle X-ray diffractograms revealed that all polymers were found to be amorphous except for the polyamide derived from isophthalic acid and polyamide-imides derived from diaminodiphenylether and diaminobenzophenone based bis(carboxyphthalimide)s.     

Step-scan TMDSC and high rate DSC study of the multiple melting behavior of poly(1,3-propylene terephthalate)

The multiple melting behavior of poly(1,3-propylene terephthalate) (PPT) samples after isothermal crystallization from the melt was studied. The step-scan temperature-modulated differential scanning calorimetry (TMDSC) and high rate DSC were used to investigate this behavior in conjunction with standard DSC, wide-angle X-ray diffraction (WAXD) and polarizing light microscopy (PLM). The effect of PPT average molecular weight on the melting was also examined. In general multiple endotherms after isothermal crystallization of PPT were attributed to a continuous crystal perfection process during the subsequent heating scan via melting-recrystallization-remelting. Multiple melting behavior was more pronounced for the low molecular weight PPT. Step-scan TMDSC showed that extensive recrystallization occurs in PPT samples, especially after rapid isothermal crystallization. In fact two recrystallization exothermic peaks were observed. High rate DSC revealed the initial morphology generated during the isothermal step and showed that the low and middle peaks are associated with melting of primary crystals while the high temperature peak should be attributed to melting of recrystallized material.     

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

A new chiral half‐titanocene complex, [CpTiCl₂(O‐(S)?2‐Bu)], is synthesized and characterized by ¹H and ¹³C NMR spectroscopy. This complex is employed for the coordination polymerization of n‐butyl and n‐hexyl‐ isocyanate leading to chiral polymers, as revealed by their CD spectra. Only the left‐handed helix is produced, due to the chiral (S)?2‐butoxy group, which is bound to the polymer chain end. The polymerization of 3‐(triethoxysilyl)propyl isocyanate produces less soluble polymers. On the other hand, phenyl isocyanate reacts slowly with the complex leading quantitatively and selectively to triphenyl isocyanurate. 2‐Ethylhexyl isocyanate is slowly and selectively cyclotrimerized in the presence of the half‐titanocene complex. However, a statistical copolymer of 2‐ethylhexyl isocyanate and hexyl isocyanate is produced. The reaction of benzyl isocyanate with the complex leads to a mixture of low molecular weight polymer and cyclotrimer. The polymers are characterized using SEC, NMR, and CD spectroscopy and their thermal properties are investigated by TGA/DSC analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2141–2151     

Nonisothermal crystallization behavior of the poly(ethylene glycol) block in poly(L‐lactide)–poly(ethylene glycol) diblock copolymers: Effect of the poly(L‐lactide) block length

The confined crystallization behavior, melting behavior, and nonisothermal crystallization kinetics of the poly(ethylene glycol) block (PEG) in poly(L ‐lactide)–poly(ethylene glycol) (PLLA–PEG) diblock copolymers were investigated with wide‐angle X‐ray diffraction and differential scanning calorimetry. The analysis showed that the nonisothermal crystallization behavior changed from fitting the Ozawa equation and the Avrami equation modified by Jeziorny to deviating from them with the molecular weight of the poly(L ‐lactide) (PLLA) block increasing. This resulted from the gradual strengthening of the confined effect, which was imposed by the crystallization of the PLLA block. The nucleation mechanism of the PEG block of PLLA15000–PEG5000 at a larger degree of supercooling was different from that of PLLA2500–PEG5000, PLLA5000–PEG5000, and PEG5000 (the numbers after PEG and PLLA denote the molecular weights of the PEG and PLLA blocks, respectively). They were homogeneous nucleation and heterogeneous nucleation, respectively. The PLLA block bonded chemically with the PEG block and increased the crystallization activation energy, but it provided nucleating sites for the crystallization of the PEG block, and the crystallization rate rose when it was heterogeneous nucleation. The number of melting peaks was three and one for the PEG homopolymer and the PEG block of the diblock copolymers, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3215–3226, 2006     

Isothermal and nonisothermal crystallization kinetics of poly(propylene terephthalate)

The kinetics of crystallization of poly(propylene terephthalate) (PPT) samples of different molecular weights were studied under both isothermal and nonisothermal conditions. The Avrami and Lauritzen–Hoffmann treatments were applied to evaluate kinetic parameters of PPT isothermal crystallization. It was found that crystallization is faster for low‐molecular‐weight samples. The modified Avrami equation, and the combined Avrami–Ozawa method were found to successfully describe the nonisothermal crystallization process. Also, the analysis of Lauritzen–Hoffmmann was tested and it resulted in values close to those obtained with isothermal crystallization data. The nonisothermal kinetic data were corrected for the effect of the temperature lag and shifted alone with the isothermal kinetic data to obtain a single master curve, according to the method of Chan and Isayev, testifying to the consistency between the isothermal and corrected nonisothermal data. A new method for ranking of polymers, referring to the crystallization rates, was also introduced. This involved a new index that combines the maximum crystallization rate observed during cooling with the average crystallization rates over the temperature range of the crystallization peak. Furthermore, the effective energy barrier of the dynamic process was evaluated with the isoconversional methods of Flynn and Friedmann. It was found that the energy barrier is lower for the low‐molecular‐weight PPT. The effect of the catalyst remnants on the crystallization kinetics was also investigated and it was found that this is significant only for low‐molecular‐weight samples. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3775–3796, 2004     

KINETICS OF NON-ISOTHERMAL CRYSTALLIZATION OF POLY (ETHYLENE TEREPHTHALATE) MODIFIED BY POLY (ETHYLENE GLYCOL)

The non-isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) modified by poly (ethlene glycol) (PEG) were determined by DSC. The dual linear regression method was used to evaluate the relationship between the reciprocal of t 1/2 ( the half life of crystallization) and the appropriate temperature variable. The parameters such as the activation energy (Ed) for transport, the equilibrium melting temperature (T_m~0),the nucleation parameter (ψ),themaximum crystallization temperature (T_(e, max)), and the kinetic crystallizability (G) for the copolyesters were obtained. The influence of the PEG content in PET chains on the parameters characterizing crystallization kinetics and crystallization thermodynamics was discussed.     

Synthesis of poly(glycolic acid) in ionic liquids

The synthesis of poly(glycolic acid) (PGA) by polyesterification of glycolic acid was studied using ionic liquids, mainly 1,3‐dialkylimidazolium salts, as reaction media. The ¹H NMR spectra of PGA oligomers were assigned and end‐group signals were used to follow the reaction. Low PGA yields were obtained by the direct polyesterification of glycolic acid at 200–240 °C, because of monomer evaporation during the reaction. On the other hand, PGAs of DP _n up to 45 were obtained by the postpolycondensation of a preformed oligomer in 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIm⁺Tf₂N^?). The precipitation of PGA in reaction medium at long reaction times limited the achievable molar mass. Rate constants were determined for catalyzed and noncatalyzed reactions, assuming a second‐order reaction mechanism. The efficiency of esterification catalysts such as Zn(OAc)₂ was low in these media, as only about twofold increases in reaction rate were observed. This was assigned to the preferential interaction of Zn²⁺ with ionic liquid anion instead of the polymer carboxylic acid end‐groups. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3025–3035, 2006     

Synthesis and characterization of novel hyperbranched poly(imide silsesquioxane) membranes

A new family of hyperbranched polymers with chemical bonds between the hyperbranched polyimide and polysilsesquioxane network was synthesized by the reaction of an amine‐terminated aromatic hyperbranched polyimide with 3‐glycidoxypropyl trimethoxysilane, followed by hydrolysis and polycondensation in the presence of an acid catalyst. The hyperbranched poly(imide silsesquioxane) membranes were fabricated by the casting the aforementioned polymer solution onto a NaCl optical flat, which was followed by heating at 80 °C for 24 h. The membranes were characterized by Fourier transform infrared, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, N₂ adsorption and desorption, and CO₂ adsorption and desorption. The presence of covalent bonds between the hyperbranched polyimide and polysilsesquioxane segments had a significant effect on the properties of the membranes. N₂ adsorption–desorption isotherms for these membranes showed surface areas of 6–16 m²/g, whereas CO₂ adsorption–desorption isotherms showed much higher surface areas in the range of 106–127 m²/g. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3736–3743, 2003     

Nonisothermal crystallization kinetics of poly (phenylene sulphide) in composites with a liquid crystalline polymer

The article deals with the melting and nonisothermal crystallization behavior of neat poly (phenylene sulphide) (PPS) and its composites with a thermotropic liquid crystalline polymer (TLCP)—Vectra A950, prepared by melt mixing and probed by differential scanning calorimetry. The various macrokinetic models namely, the Ozawa, the modified Avrami, the Tobin, and the Mo models were applied to describe the crystallization kinetics under nonisothermal conditions. The kinetic crystallizabilty of PPS/TLCP composites calculated using the approach of Ziabicki varies depending on these two composite composition‐induced effects. Similarly Mo model predicts that to obtain a higher degree of crystallizabilty for PPS/TLCP composites, a higher cooling rate should be used. The effective energy barrier based on the differential isoconversional method of Friedman is found to be an increasing function of relative degree of melt conversion. The effect is explained in terms of nucleation theory proposed by Wunderlich to crystallization of polymers. The Lauritzen–Hoffman parameters are estimated using G = 1/t_0.5 effective activation energy equation proposed by Vyazovkin and Sbirrazzuoli. The K_g values estimated from latter equations are more comparable with values obtained using isothermal crystallization data than 1/t_0.5 method. Furthermore, the kinetic analysis using this equation shows a regime transition from regime II to regime III for 100/00, 90/10, 80/20 PPS/TLCP composites, basically attributed to reduced mobility of PPS chains in composites. This regime II to III transition is accompanied by a morphological transition from defective spherulitic sheaf‐like structures to ordered sheaf‐like structures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1070–1100, 2010     

The role of crystalline, mobile amorphous and rigid amorphous fractions in the performance of recycled poly (ethylene terephthalate) (PET)

The action of thermo-mechanical degradation induced by mechanical recycling of poly(ethylene terephthalate) was simulated by successive injection moulding cycles. Degradation reactions provoked chain scissions and a reduction in molar mass mainly driven by the reduction of diethyleneglycol to ethylene glycol units in the flexible domain of the PET backbone, and the formation of -OH terminated species with shorter chain length. The consequent microstructural changes were quantified taking into account a three-fraction model involving crystalline, mobile amorphous (MAF) and rigid amorphous fractions (RAF). A remarkable increase of RAF, to a detriment of MAF was observed, while the percentage of crystalline fraction remained nearly constant. A deeper analysis of the melting behaviour, the segmental dynamics around the glass-rubber relaxation, and the macroscopic mechanical performance, showed the role of each fraction leading to a loss of thermal, viscoelastic and mechanical features, particularly remarkable after the first processing cycle.