Morphology and barrier mechanism of biaxially oriented poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends

To improve the barrier properties of poly(ethylene terephthalate) (PET), PET/poly(ethylene 2,6‐naphthalate) (PEN) blends with different concentrations of PEN were prepared and were then processed into biaxially oriented PET/PEN films. The air permeability of bioriented films of pure PET, pure PEN, and PET/PEN blends were tested by the differential pressure method. The morphology of the blends was studied by scanning electron microscopy (SEM) observation of the impact fracture surfaces of extruded PET/PEN samples, and the morphology of the films was also investigated by SEM. The results of the study indicated that PEN could effectively improve the barrier properties of PET, and the barrier properties of the PET/PEN blends improved with increasing PEN concentration. When the PEN concentration was equal to or less than 30%, as in this study, the PET/PEN blends were phase‐separated; that is, PET formed the continuous phase, whereas PEN formed a dispersed phase of particles, and the interface was firmly integrated because of transesterification. After the PET/PEN blends were bioriented, the PET matrix contained a PEN microstructure consisting of parallel and extended, separate layers. This multilayer microstructure was characterized by microcontinuity, which resulted in improved barrier properties because air permeation was delayed as the air had to detour around the PEN layer structure. At a constant PEN concentration, the more extended the PEN layers were, the better the barrier properties were of the PET/PEN blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1309–1316, 2006     

Effects of electron beam irradiation on poly(ethylene 2,6‐naphthalate)/poly(ethylene terephthalate) blends

The effect of electron beam (EB) irradiation on the properties and compatibility of poly(ethylene 2,6‐naphthalate) (PEN)/poly(ethylene terephthalate) (PET) blends was investigated. Upon EB irradiation, PEN/PET blends underwent transesterification reactions, resulting in the formation of more random copolymers from the original binary pair. The degree of transesterification increased with dose rate, and all of the irradiated blends exhibited a single glass transition temperature. This indicated that transesterification reactions promoted by EB irradiation led to the formation of a single phase. Transesterification reactions promoted by EB irradiation led to more random copolymers, and the reduced regularity in the irradiated blends decreased the melting temperature. A higher degree of randomness and lower number‐average sequence lengths for the blend systems indicated that a more random chain structure was formed in the blends. The rheological measurements demonstrated that the irradiated PEN/PET blends were miscible. EB irradiation could promote transesterification reaction, thus enhancing the compatibility of PEN/PET blends.     

Role of 2‐hydroxyethyl end group on the thermal degradation of poly(ethylene terephthalate) and reactive melt mixing of poly(ethylene terephthalate)/poly(ethylene naphthalate) blends

In an attempt to minimize the acetaldehyde formation at the processing temperatures (280–300°C) and the outer–inner transesterification reactions in the poly (ethylene terephthalate) (PET)–poly(ethylene naphthalate) (PEN) melt‐mixed blends, the hydroxyl chain ends of PET were capped using benzoyl chloride. The thermal characterization of the melt‐mixed PET–PEN blends at 300°C, as well as that of the corresponding homopolymers, was performed. Degradations were carried out under dynamic heating and isothermal conditions in both flowing nitrogen and static air atmosphere. The initial decomposition temperatures (T_i) were determined to draw useful information about the overall thermal stability of the studied compounds. Also, the glass transition temperature (T_g) was determined by finding data, indicating that the end‐capped copolymers showed a higher degradation stability compared to the unmodified PET and, when blended with PEN, seemed to be efficient in slowing the kinetic of transesterification leading to, for a finite time, the formation of block copolymers, as determined by ¹H‐NMR analysis. This is strong and direct evidence that the end‐capping of the ? OH chain ends influences the mechanism and the kinetic of transesterification. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Effects of molecular weight on phase structure of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends

The phase structure of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) (PET/PEN) blends was studied in relation to the molecular weight. The samples were prepared by both solution blends, which showed two glass‐transition temperatures (T_g), and melt blends (MQ), which showed a single T_g, depending on the composition of the blends. The T_g of the MQ series was independent of the molecular weight of the homopolymer, although the degree of transesterification in the blends was affected by the molecular weight. The MQ series showed two exotherms during the heating process of a differential scanning calorimetry scan. The peak temperature and the heat flow of the exotherms were affected by the molecular weight of the homopolymers. The strain‐induced crystallization of the MQ series suggested the independent crystallization of PET and PEN. Based on the results, a microdomain structure of each homopolymer was suggested. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2428–2438, 2005     

Transesterification reactions in triphenyl phosphite additivated‐poly(ethylene terephthalate)/poly(ethylene naphthalate) blends

The occurrence of transesterification reactions in poly(ethylene terephthalate) (PET)/poly(ethylene naphthalate) (PEN) blends prepared in presence of triphenyl phosphite (TPP) was investigated. When PEN was processed with TPP, which is a known chain extender for PET, chain extension reactions also took place. Torqueprocessing time curves obtained during preparation of 75/25 PET/PEN blends containing TPP, showed a build‐up profile followed by a fast decrease that was interpreted as chain extension between blend components and degradation due to phosphite residues formation, respectively. Although transesterification inhibition was expected, this type of reaction was not suppressed by TPP.     

Crystallization kinetics of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends

The crystallization kinetics of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) (PET/PEN) blends were investigated by DSC as functions of crystallization temperature, blend composition, and PET and PEN source. Isothermal crystallization kinetics were evaluated in terms of the Avrami equation. The Avrami exponent (n) is different for PET, PEN, and the blends, indicating different crystallization mechanisms occurring in blends than those in pure PET and PEN. Activation energies of crystallization were calculated from the rate constants, using an Arrhenius‐type expression. Regime theory was used to elucidate the crystallization course of PET/PEN blends as well as that of unblended PET and PEN. The transition from regime II to regime III was clearly observed for each blend sample as the crystallization temperature was decreased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 23–37, 2001     

Primary structure and physical properties of poly(ethylene terephthalate)/poly(ethylene naphthalate) resin blends

The morphology and properties of blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) that were injection molded under various conditions were studied. Under injection molding conditions that make it possible to secure transparency, blends did not show clear crystallinity at blending ratios of more than 20 mol% in spite of the fact that crystallinity can be observed in the range of PEN content up to 30 mol%. Because both transparency and crystallinity could be secured with a PEN 12 mol% blend, this material was used in injection molding experiments with various injection molding cycles. Whitening occurred with a cycle of 20 sec, and transparency was obtained at 30 sec or more. This was attributed to the fact that transesterification between PET and PEN exceeded 5 mol% and phase solubility (compatibility) between the PET and PEN increased when the injection molding time was 30 sec or longer. However, when the transesterification content exceeded 8 mol%, molecularly oriented crystallization did not occur, even under stretching, and consequently, it was not possible to increase the strength of the material by stretching. PET/PEN blend resins are more easily crystallized by stretch heat‐setting than are PET/PEN copolymer resins. It was understood that this is because residual PET, which has not undergone transesterification, contributes to crystallization. However, because transesterification reduces crystallinity, the heat‐set density of blends did not increase as significantly as that of pure PET, even in high temperature heat‐setting. Gas permeability showed the same tendency as density. Namely, pure PET showed a substantial decrease in oxygen transmission after high temperature heat‐setting, but the decrease in gas permeability in the blend material was small at heat‐set temperatures of 140°C and higher.     

Reactive blending of poly(ethylene terephthalate)(pet)/ poly(ethylene 2,6‐naphthalate)(pen). I: Effect of mixing conditions on chain structure

Reactive blending of poly(ethylene terephthalate)/poly(ethylene naphthalene 2,6dicarboxylate) with addition of 2,2'‐bis(1,3‐oxazoline) (BOZ) has been studied under various mixing conditions for the different compositions. The transesterification level, the sequence length of both PET and PEN short blocks, and the degree of randomness were estimated using¹H NMR. The results indicate that both mixing time and temperature are the primary factors controlling the transesterification, while the chain extender BOZ can significantly accelerate the transesterification between PET and PEN at 275°C. The composition also, to some extent, influences the transerification level as the mixing time is increased. As a consequence of transesterification proceeding, the sequence structures of the reactive blends are also markedly changed, which corresponds to a transfer from an initial block structure to a multiblock structure with higher randomness. The change in the microstructure of the reactive blends has also been analyzed by a Bernoullian statistics model. The effect of the BOZ on the intrinsic viscosity of the reactive blends is discussed.     

Interrelationship of thermal and mechanical properties of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate)/graphene nanocomposites

In the present work, attempts were made to investigate the thermal and mechanical properties of melt‐processed poly(ethylene terephthalate) (PET)/poly(ethylene 2,6‐naphthalate) (PEN) blends and its nanocomposites containing graphene by using differential scanning calorimetry and tensile test experimenting. The results showed that crystallinity, which depends on a blend ratio, completely disappeared in a composition of 50/50. By introducing graphene to PET, even in low concentrations, the crystallinity of samples increased, while the nanocomposite of PEN indicated reverse behavior, and the crystallinity was reduced by adding graphene. In the case of PET‐rich (75/25) nanocomposite blends, by increasing the nano content in the blend, the crystallinity of the samples was enhanced. This behavior was attributed to the nucleating effect of graphene particles in the samples. From the results of mechanical experiments, it was found in PET‐rich blends that by increasing the PEN/PET ratio, the modulus of samples decreased, whereas in the case of PEN‐rich blends, a slight increment of modulus is seen as a result of the increment of the PEN/PET ratio. The two contradicting behaviors were attributed to the reduction of crystallinity of PET‐rich blends by enhancement of PEN/PET ratio and the rigid structure of PEN chains in PEN‐rich blends. Unlike the different modulus change of PET‐rich and PEN‐rich blends, the nanocomposites of these blends similarly indicated an increment of modulus and characteristics of rigid materials by increasing the nano content. Furthermore, the same behavior was detected in nanocomposites of each polymer (PET and PEN nanocomposites). The alteration from ductile to rigid conduction was related to the impedance in the role of graphene plates against the flexibility of polymer chains and high values of graphene modulus. J. VINYL ADDIT. TECHNOL., 23:210–218, 2017. © 2015 Society of Plastics Engineers     

Transesterification reaction kinetics of poly(ethylene terephthalate/poly(ethylene 2,6‐naphthalate) blends

The transesterification reaction of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends during melt‐mixing was studied as a function of blending temperature, blending time, blend composition, processing equipment, and different grades of poly(ethylene terephthalate) and poly(ethylene 2,6‐naphthalate). Results show that the major factors controlling the reaction are the temperature and time of blending. Efficiency of mixing also plays an important role in transesterification. The reaction kinetics can be modeled using a second‐order direct ester–ester interchange reaction. The rate constant (k) was found to have a minimum value at an intermediate PEN content and the activation energy of the rate constant was calculated to be 140 kJ/mol. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2422–2436, 2001     

Melt rheology and properties of compatibilized recycled poly(ethylene terephthalate)/(styrene‐ethylene‐ethylene‐propylene‐styrene) block copolymer blends

Blends of recycled poly(ethylene terephthalate) (R‐PET) and (styrene‐ethylene‐ethylene‐propylene‐styrene) block copolymer (SEEPS) compatibilized with (maleic anhydride)‐grafted‐styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MAH) were prepared by melt blending. The compatibilizing effects of SEBS‐g‐MAH were investigated systematically by study of the morphology, linear viscoelastic behavior, and thermal and mechanical properties of the blends. The results show that there is good agreement between the results obtained by rheological measurement and morphological analysis. The rheological test shows that the melt elasticity and melt strength of the blends increase with the addition of SEBS‐g‐MAH. The Cole‐Cole plots and van Gurp‐Palmen plots confirm the compatibilizing effect of SEBS‐g‐MAH. However, the Palierne model fails to predict the linear viscoelastic properties of the blends. The morphology observation shows that all blends exhibit a droplet‐matrix morphology. In addition, the SEEPS particle size in the (R‐PET)/SEEPS blends is significantly decreased and dispersed uniformly by the addition of SEBS‐g‐MAH. Differential scanning calorimeter analysis shows that the crystallization behavior of R‐PET is restricted by the incorporation of SEEPS, whereas the addition of SEBS‐g‐MAH improves the crystallization behavior of R‐PET compared with that of uncompatibilized (R‐PET)/SEEPS blends. The Charpy impact strength of the blends shows the highest value at SEBS‐g‐MAH content of 10%, which is about 210% higher than that of pure R‐PET. J. VINYL ADDIT. TECHNOL., 22:342–349, 2016. © 2014 Society of Plastics Engineers     

Glass‐transition and melting behavior of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends

The glass‐transition temperatures and melting behaviors of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) (PET/PEN) blends were studied. Two blend systems were used for this work, with PET and PEN of different grades. It was found that T_g increases almost linearly with blend composition. Both the Gibbs–DiMarzio equation and the Fox equation fit experimental data very well, indicating copolymer‐like behavior of the blend systems. Multiple melting peaks were observed for all blend samples as well as for PET and PEN. The equilibrium melting point was obtained using the Hoffman–Weeks method. The melting points of PET and PEN were depressed as a result of the formation of miscible blends and copolymers. The Flory–Huggins theory was used to study the melting‐point depression for the blend system, and the Nishi–Wang equation was used to calculate the interaction parameter (χ₁₂). The calculated χ₁₂ is a small negative number, indicating the formation of thermodynamically stable, miscible blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 11–22, 2001     

Phase separation,physical properties and melt rheology of a range of variously transesterified amorphous poly(ethylene terephthalate)–poly(ethylene naphthalate) blends

Amorphous, partially transesterified poly(ethylene terephthalate)/poly(ethylene naphthalate) (PET/PEN) blends of different levels of transesterification and blend composition were investigated in terms of resultant phase behavior, thermal transitions, and melt rheological properties. Intrinsic viscosities of the lowest transesterified material were found to be significantly below those of a physical blend of an identical composition, but at higher levels of transesterification, there was little difference. This was similarly found in melt rheometry measurements, where the zero‐shear rate viscosity of the low and highly transesterified mixtures were similar. Both solution and melt rheometry indicated that the molecular weight decreased by thermal degradation from processing. This is believed to play an important role in determining the final molecular architecture and properties. For similar levels of ester interchange, there was a minimum observed in zero shear melt viscosity at around 40 wt % PEN. This is likely due to competition between the slightly transesterified copolymer chains having poorer packing in the melt and reduced entanglement. Differential scanning calorimetry and dynamic mechanical thermal analysis were used to investigate the phase behavior of partially and fully transesterified blends. Results for the glass transition of the highly transesterified blends were compared with the theoretical values calculated from the Fox equation and were found to be close, although slightly lower. A correlation between the melting temperature of the blend and the degree of transesterification was shown to exist. This correlation can be used to estimate the degree of ester exchange reaction from these melting transitions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1556–1567, 2002     

Isothermal‐crystallization kinetics and melting behavior of crystalline/crystalline blends of poly(trimethylene terephthalate) and poly(ethylene 2,6‐naphthalate)

The isothermal crystallization and crystal morphology of poly(trimethylene terephthalate) (PTT)/poly (ethylene 2,6‐naphthalate) (PEN) blends were investigated with differential scanning calorimetry and polarized optical microscopy. The commonly used Avrami equation was used to fit the primary stage of isothermal crystallization. The Avrami exponents were evaluated to be in the range of 3.0–3.3 for isothermal crystallization. The subsequent melting endotherms of the blends after isothermal crystallization showed multiple melting peaks. The crystallization activation energies of the blends with 20 or 40% PTT was ?48.3 and ?60.9 kJ/mol, respectively, as calculated by the Arrhenius formula for the isothermal‐crystallization processes. The Hoffman–Lauritzen theory was also employed to fit the process of isothermal crystallization, and the kinetic parameters of the blends with 20 or 40% PTT were determined to be 1.5 × 10⁵ and 1.8 × 10⁵ K², respectively. The spherulite morphology of the six binary blends formed at 190°C showed different sizes and perfect Maltese crosses when the PTT or PEN component was varied, suggesting that the greater the PTT content was, the larger or more perfect the crystallites were that formed in the binary blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3316–3325, 2007     

Enhanced dynamic mechanical and shape‐memory properties of a poly(ethylene terephthalate)–poly(ethylene glycol) copolymer crosslinked by maleic anhydride

Dimethyl terephthalate (DMT) and ethylene glycol (EG) were used for the preparation of poly(ethylene terephthalate) (PET), and poly(ethylene glycol) (PEG) was added as a soft segment to prepare a PET–PEG copolymer with a shape‐memory function. MWs of the PEG used were 200, 400, 600, and 1000 g/mol, and various molar ratios of EG and PEG were tried. Their tensile and shape‐memory properties were compared at various points. The glass‐transition and melting temperatures of PET–PEG copolymers decreased with increasing PEG molecular weight and content. A tensile test showed that the most ideal mechanical properties were obtained when the molar ratio of EG and PEG was set to 80:20 with 200 g/mol of PEG. The shape memory of the copolymer with maleic anhydride (MAH) as a crosslinking agent was also tested in terms of shape retention and shape recovery rate. The amount of MAH added was between 0.5 and 2.5 mol % with respect to DMT, and tensile properties and shape retention and recovery rate generally improved with increasing MAH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 27–37, 2002     

Improvement of compatibility of poly(ethylene terephthalate) and poly(ethylene octene) blends by γ‐irradiation

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene octene) (POE) were prepared by melt blending with various amounts of trimethylolpropane triacylate (TMPTA). The mechanical properties, phase morphologies, and gel fractions at various absorbed doses of γ‐irradiation have been investigated. It was found that the toughness of blends was enhanced effectively after irradiation as well as the tensile properties. The elongation at break for all studied PET/POE blends (POE being up to 15 wt %) with 2 wt % TMPTA reached 250–400% at most absorbed doses of γ‐irradiation, approximately 50–80 times of those of untreated PET/POE blends. The impact strength of PET/POE (85/15 wt/wt) blends with 2 wt % TMPTA irradiated with as little as 30 kGy absorbed dose exceeded 17 kJ/m², being approximately 3.4 times of those of untreated blends. The improvement of the mechanical properties was supported by the morphology changes. Scanning electron microscope images of fracture surfaces showed a smaller dispersed phase and more indistinct inter‐phase boundaries in the irradiated blends. This indicates increased compatibility of PET and POE in the PET/POE blends. The changes of the morphologies and the enhancement of the mechanical properties were ascribed to the enhanced inter‐phase boundaries by the formation of complex graft structures confirmed by the results of the gelation extraction and Fourier Transform Infrared analyses. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Reactive extrusion of poly(ethylene terephthalate)–(ethylene/methyl acrylate/glycidyl methacrylate)–organoclay nanocomposites

This study was conducted to investigate the effects of component concentrations and addition order of the components on the final properties of ternary nanocomposites composed of poly(ethylene terephthalate), organoclay, and an ethylene–methyl acrylate–glycidyl methacrylate (E‐MA‐GMA) terpolymer acting as an impact modifier for PET. In this context, first, the optimum amount of the impact modifier was determined by melt compounding binary PET‐terpolymer blends in a corotating twin‐screw extruder. The amount of the impact modifier (5 wt%) resulting in the highest Young's modulus and moderate elongation at break was selected owing to its balanced mechanical properties. Thereafter, by using 5 wt% terpolymer content, the effects of organically modified clay concentration and addition order of the components on the properties of ternary nanocomposites were systematically investigated. Mechanical testing revealed that different addition orders of the materials significantly affected the mechanical properties. Among the investigated addition orders, the best sequence of component addition (PI‐C) was the one in which poly(ethylene terephthalate) was first compounded with E‐MA‐GMA. Later, this mixture was compounded with the organoclay in the subsequent run. In X‐ray diffraction analysis, extensive layer separation associated with delamination of the original clay structure occurred in PI‐C and CI‐P (Clay + Impact Modifier followed by PET) sequences with both 1 and 3 wt% clay contents. X‐ray diffraction patterns showed that at these conditions exfoliated structures resulted as indicated by the disappearance of any peaks due to the diffraction within the consecutive clay layers. POLYM. COMPOS., 28:251–258, 2007. © Society of Plastic Engineers     

Miscibility and transesterification in ternary blends of poly(ethylene naphthalate)/poly(pentamethylene terephthalate)/poly(ether imide)

Miscibility and morphology of poly(ethylene 2,6‐naphthalate)/poly(pentamethylene terephthalate)/poly(ether imide) (PEN/PPT/PEI) blends were studied by differential scanning calorimetry (DSC), optical microscopy (OM), proton nuclear magnetic resonance imaging (¹H‐NMR), and wide‐angle X‐ray diffraction (WAXD). OM and DSC results from ternary blends revealed the immiscibility of PEN/PPT/PEI blends, but ternary blends of all compositions were phase‐homogeneous following heat treatment at 300°C for over 60 min. Annealing samples at 300°C yielded an amorphous blend with a clear and single T_g at the final state. Experimental data from ¹H‐NMR revealed that PEN/PPT copolymers (ENPT) were formed by the so‐called transesterification. The effect of transesterification on glass transition and crystallization was discussed in detail. The sequence structures of the copolyester were identified by triad analysis, which showed that the mean sequence lengths became shorter and the randomness increased with heating time. The results reveal that a random copolymer improved the miscibility of the ternary blends, in which, the length of the homo segments in the polymer chain decreased and the crystal formation was disturbed because of the irregularity of the structure, as the exchange reaction proceeded. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3840–3849, 2006     

Microstructure and crystallization of melt‐mixed poly(ethylene terephthalate)/poly(ethylene isophthalate) blends

Physical blends of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI), abbreviated PET/PEI (80/20) blends, and of PET and a random poly(ethylene terephthalate‐co‐isophthalate) copolymer containing 40% ethylene isophthalate (PET₆₀I₄₀), abbreviated PET/PET₆₀I₄₀ (50/50) blends, were melt‐mixed at 270°C for different reactive blending times to give a series of copolymers containing 20 mol % of ethylene isophthalic units with different degrees of randomness. ¹³C‐NMR spectroscopy precisely determined the microstructure of the blends. The thermal and mechanical properties of the blends were evaluated by DSC and tensile assays, and the obtained results were compared with those obtained for PET and a statistically random PETI copolymer with the same composition. The microstructure of the blends gradually changed from a physical blend into a block copolymer, and finally into a random copolymer with the advance of transreaction time. The melting temperature and enthalpy of the blends decreased with the progress of melt‐mixing. Isothermal crystallization studies carried out on molten samples revealed the same trend for the crystallization rate. The effect of reaction time on crystallizability was more pronounced in the case of the PET/PET₆₀I₄₀ (50/50) blends. The Young's modulus of the melt‐mixed blends was comparable to that of PET, whereas the maximum tensile stress decreased with respect to that of PET. All blend samples showed a noticeable brittleness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3076–3086, 2003     

Solid‐state polymerization of poly(ethylene 2,6‐naphthalate)

The solid‐state polymerization (SSP) of poly (ethylene 2,6‐naphthalate) (PEN) was studied and compared with that of poly(ethylene terephthalate) (PET). The SSP of PEN, like that of PET, could be satisfactorily described with a modified second‐order kinetic model, which was based on the assumptions that part of the end groups were inactive during SSP and that the overall SSP followed second‐order kinetics with respect to the active end‐group concentration. The proposed rate equation fit the data of the SSP of PEN quite well under various conditions. PEN prepolymers in pellet and cube forms with intrinsic viscosities (IVs) ranging from 0.375 to 0.515 dL/g, various particle sizes, and various carboxyl concentrations were solid‐state polymerized at temperatures ranging from 240 to 260°C to study the effects of various factors. The SSP data obtained in this study could be readily applied to the design of commercial PEN SSP processes. Because PEN and PET share the same SSP mechanism, in general, the SSP behaviors of PEN are similar to those of PET. Thus, the SSP rate of PEN increased with increasing temperature, increasing prepolymer IV, and decreasing prepolymer particle size. However, because of the much higher barrier properties of PEN, the prepolymer particle size and carboxyl concentration had much greater effects on the SSP of PEN than on the SSP of PET. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1075–1084, 2007