Search

Copolyesters containing rigid aromatic units based on 4,4'-sulfonylbisphenol (bisphenol S) have been prepared by melt mixing poly(propylene terephthalate) (PPT) with an ethoxylated bisphenol S (sulfonyldiphenol). The insertion of the bisphenol units inside the polymer chain occurred quantitatively and no side reaction has been observed. The copolymers displayed good thermal stability. The main effect of copolymerization was a lowering in the degree of crystallinity and a decrease of the melting temperature with respect to PPT. On the contrary, an increment of T-g as the content of bisphenol S units increased due to the stiffening effect of the moieties deriving from bisphenol S. The Wood equation described well the correlation between T-g and composition.

Poly(butylene succinate/diglycolate) copolymers by reactive blending were subjected to molecular and solid-state characterization to study the effects of transesterification reactions. 13C-nuclear magnetic resonance analysis evidenced the formation of block copolymers. Thermal measurements showed that all the samples were semicrystalline, with a soft amorphous phase and a rigid crystal phase. Wide-angle x-ray diffraction measurements indicated that the copolymers are characterized by cocrystallization. The mechanical properties were found related to crystallinity degree. The random copolymer, characterized by the lowest crystallinity degree, exhibits the lowest elastic modulus and the highest deformation at break. Therefore, solid-state properties of poly(butylene succinate/diglycolate) copolymers can be tailored by acting on the molecular architecture. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers

Poly(butylene succinate/diglycolate) random copolymers (P(BSxBDGy)) of various compositions were synthesized and characterized from the molecular, thermal, structural and mechanical point of view. All the polymers showed a good thermal stability and at room temperature they appeared as semicrystalline materials. The main effect of copolymerization was a lowering in the crystallinity and a decrease of T-m respect to homopolymers. The dependence of T-m on composition for copolymers with high butylene succinate unit content was well described by Baur's equation. WAXD measurements indicated that two different crystalline phases are present, depending on composition: copolymers with high BS unit content are characterized by PBS crystal phase, whereas those rich in BDG co-units crystallized in PBDG lattice. Amorphous samples showed a monotonic increment of; as the content of BDG units is increased and this can be explained on the basis of interchain interactions, due to the high electronegativity of ether-oxygen atoms. A Fox-type equation was found to fit the T-g data of completely amorphous samples, permitting the extrapolation of pure PBS T-g value for the completely amorphous polymer. (C) 2012 Elsevier Ltd. All rights reserved.

Poly[butylene-co-(triethylene succinate)] block copolymers (PBSPTES), prepared by reactive blending of the parent homopolymers (PBS and PTES) in the presence of Ti(OBu)4, were analysed by nuclear magnetic resonance (NMR), wide angle X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry techniques, in order to investigate the effects of the transesterification reactions on the molecular structure and thermal properties. 1H-NMR analysis evidenced the formation of copolymers whose degree of randomness increased with mixing time. After melt quenching, all the copolymers were found to be semicrystalline with the exception of a random copolymer. The results obtained indicated that the block size has a fundamental role in determining the rate of crystallization and therefore the phase behavior of the block copolymers. Copyright (c) 2012 Society of Chemical Industry

The melting behavior and crystallization kinetics of PBN–PDEN and PBN–PTDEN copolymers were investigated using differential scanning calorimetry. Multiple endotherms were observed in all of the copolymers under investigation, originating from melting and recrystallization processes. By applying the Hoffman–Weeks method, the Tm1 of the a and b¢-PBN phases were derived. The Tm1 value of the b¢-form, which has not been determined before, is significantly higher, as expected, because the b¢-phase is thermodynamically favored and more tightly packed. The isothermal crystallization kinetics were analyzed according to the Avrami treatment. The presence of either oxygen or sulfur atoms in the PBN polymeric chain was found to reduce its crystallizability. In particular, the crystallization rate regularly decreased as the co-unit content was increased. Lastly, the a-PBN phase was found to crystallize faster than b¢-one, which is expected, as it the more kinetically favored phase.

The results of studies of the physico-chemical changes of a polyester, poly(ethylene isophthalate), subjected to gamma irradiation up to 1 MGy, are reported. Viscometric measurements were carried out to monitor variations of the molecular weight. Changes in the amorphous fraction of the polymer were observed by means of differential scanning calorimetry. Positron annihilation lifetime spectroscopy was used to show possible modifications of the free volume as a consequence of irradiation. The results allow us to conclude that the polymer shows a good resistance to radiation damage.

The miscibility of poly(propylene succinate)/poly(propylene adipate) blends was investigated by means of DSC, WAXS and NMR techniques. Poly(propylene succinate) and poly(propylene adipate) were found to be completely immiscible in as blended-state. The miscibility changes upon extended mixing at elevated temperature: for enough long mixing time, the original two phases gradually merged into a single one because of transesterification reactions. The NMR analysis showed that the transesterifications led to block copolymers whose average sequence length decreased as the mixing time is increased at a fixed temperature. Upon very long mixing time (150 min), all PPS and PPA chains are fully transformed into a random copolymer characterized by a single amorphous phase.

Poly(butylene/diethylene naphthalate) copolymers (PBN-PDEN) were synthesized in bulk according to the polycondensation procedure and examined by NMR, GPC, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and XRD. At room temperature they appeared as semicrystalline materials; the copolymerization caused a lowering in the Tg value, a decrement of Tm and of the crystallization rate. Pure α or β′ form was obtained at low and high DEN unit content, respectively; crystalline form transition never occurred in the solid state, analogously to PBN. After cooling from the melt, the pure α form was always evidenced in PBN-PDEN10 and PBN-PDEN20, whereas the pure β′ crystal phase develops in the copolymer containing 40 mol % DEN units, independently on the cooling rate. In the case of PBN-PDEN30 a pure α or β′ form was obtained at low and high cooling rate, respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1356–1367, 2009

Poly(butylene/diethylene succinate) block copolymers (PBSPDGS), prepared by reactive blending of the parent homopolymers (PBS and PDGS) in the presence of Ti(OBu)(4), were analyzed by H-1-NMR, TGA and DSC, in order to investigate the effects of the transesterification reactions on the molecular structure and thermal properties. H-1-NMR analysis evidenced the formation of copolymers whose degree of randomness increases with the mixing time. The thermal analysis of the melt-quenched samples showed that the melting peak, due to the crystalline phase of PBS, tends to disappear with increasing mixing time and therefore with decreasing the block length in the copolymers. As concern miscibility, a single homogeneous amorphous phase always occurred, independently on block length. Nevertheless, a phase separation, due to the tendency of the PBS blocks to crystallize, was evidenced in the copolymers with long butylene succinate sequences. The results obtained indicated that the block size had a fundamental role in determining the crystallizability and, therefore, phase behavior of the block copolymers. (C) 2008 Elsevier Ltd. All rights reserved.

The crystal structure of poly(dithiotriethylene adipate) has been determined through the best fitting of calculated and experimental X-ray diffraction powder profiles. A triclinic cell was found with dimensions a = 4.942 (7) A, b = 4.702 (2) A, c = 20.56 (2) A, α = 88.9 (2)°, β = 61.0 (1)°, γ = 67.8 (1)°, P-1 space group, and one chain in the unit cell. A full extended trans conformation of the chain fitted satisfactory the experimental data, yielding to a discrepancy factor Rp = 0.073. A comparison between the crystal structures of poly(dithiotriethylene adipate) and poly (thiodiethylene adipate) is proposed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2677–2682, 2005

The full-profile refinement of X-ray diffraction patterns was used to investigate two poly(thiodiethylene terephthalate) (PSDET) samples with different thermal history in order to thoroughly analyze their polymorphic aspects. In each sample, a crystalline (a or b) and a microcrystalline (a0 or b0) phase were identified together with an amorphous component. The crystal structures of all the ordered phases were determined. The data indicated an appreciable difference between the two crystalline forms, while the microcrystalline were rather similar. The results reported in this paper agree with the hypothesis that the polymorphic and morphological aspects of PSDET have to be correlated with the order degree and reorganization of crystallites and microcrystallites.

Poly(propylene terephthalate) (PPT) was subjected to aging at high temperatures (150–190°C) in air and some mechanical (impact strength), physical (weight loss), and electrical (dc conductivity and ac electrical strength) properties were determined as a function of aging time and temperature. Some chemical–physical characteristics (such as the average molecular weight, the carboxyl end-group content, and crystallinity degree) were investigated during the degradation process, as well. From the collected data, the thermal endurance parameters (i.e., the temperature index and the halving interval), which are key parameters in the determination of materials reliability and design of electrical insulating system, were derived according to IEC 216 Standard, and compared with those relevant to other thermoplastic polyesters. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2848–2854, 2004

The melting behavior and crystallization kinetics of poly(thiodiethylene adipate) (PSDEA) were investigated with differential scanning calorimetry and hot-stage optical microscopy. The observed multiple endotherms, commonly displayed by polyesters, were influenced by the crystallization temperature (Tc) and ascribed to melting and recrystallization processes. Linear and nonlinear treatments were applied to estimate the equilibrium melting temperature for PSDEA with the corrected values of the melting temperature. The nonlinear estimation yielded a higher value by about 9 °C. Isothermal crystallization kinetics were analyzed according to Avrami's treatment. Values of Avrami's exponent close to 3 were obtained, independently of Tc, in agreement with a crystallization process originating from predetermined nuclei and characterized by three-dimensional spherulitic growth. As a matter of fact, space-filling spherulites were observed by optical microscopy at all Tc's. The rate of crystallization became lower as Tc increased, as usual at a low undercooling, the crystallization process being controlled by nucleation. Moreover, the crystal structure of PSDEA was determined from powder X-ray diffraction data by full profile fitting. A triclinic unit cell containing two polymer chains arranged parallel to the c axis was found. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 553–566, 2004

The complex multiple melting behavior of poly(thiodiethylene terephthalate) (PSDET) was investigated by means of differential scanning calorimetry, X-ray diffraction and hot-stage optical microscopy. The phenomenon was ascribed to the existence of two different crystal structures (a and b), each of them being able to melt and recrystallize under the experimental conditions adopted. Linear and nonlinear treatments were applied in order to estimate the equilibrium melting temperature for a PSDET, by using the corrected values of Tm. The nonlinear estimation led to a higher value by about 25 8C. Isothermal crystallization kinetics of each crystalline form were analyzed according to Avrami’s treatment. In both cases, values of Avrami’s exponent, n, close to 3 were obtained, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three dimensional spherulitic growth. The rate of crystallization of each crystalline structure was found to become lower as the crystallization temperature is increased, as usual at low undercooling, where the crystallization process is controlled by nucleation.

In this contribution a new class of aliphatic poly(butylene succinate) (PBS)-based poly(ester urethane)s has been synthesized and characterized from the molecular, thermal and mechanical point of view. Hydrolytic degradation studies under physiological conditions have been conducted to assess their biodegradation rate. To obtain copolymers showing both thermoplastic and elastomeric properties, the chain-linking strategy has been considered. In particular, two hydroxyl-terminated oligomers have been synthesized by melt polycondensation: poly(butylene succinate) (PBS), as a “hard segment”, and two poly(butylene adipate/diglycolate) P(BAmBDGn) random copolymers as a “soft segment”. The introduction of ether-linkages along the PBA chain permitted to depress its crystallinity degree and to enhance the wettability. Multiblock copolymers were finally obtained by chain extending with hexamethylene diisocyanate each P(BAmBDGn) copolymer with two different mass percentages of PBS: 30% and 50%. All copolymers maintained good thermal stability and were characterized by melting temperatures above 100 °C. Elastic modulus (E) and stress at break (σb) varied with the chemical composition: the higher the PBS amount, the higher E and σb. No yield and very high elongations at break were observed. Hydrolytic degradation studies highlighted an increase of the degradation rate with the increase of the BDG content.

The relaxation dynamics of poly(pentamethylene terephthalate) has been investigated by means of dielectric spectroscopy. The sub-glass dynamics is characterized by the existence of a bimodal β process whose faster and slower components have been assigned to the relaxation of the bond between the ester oxygen and the aliphatic carbon and to the link between the aromatic ring carbon and the ester carbon, respectively. By comparison with other closely related aromatic polyesters it is shown that the faster component strongly depends on the amount of methylene groups while the slower one is not considerably affected by the nature of the glycol subunit. The changes in the α process associated to the segmental relaxation during cold crystallization reveal the formation of a rigid amorphous phase fraction. Combination of dielectric experiments with X-ray scattering ones suggests that during cold crystallization PPT crystal lamellae tend to fill the space homogeneously. © 2014 Elsevier Ltd. All rights reserved., Financial support by MAT2008-03232, MAT2011-23455, and MAT2012-33517 from MINECO is gratefully acknowledged. M.S. thanks CSIC and the Fondo Social Europeo (FSE) for cofinancing the JAE-Doc contract.

Radial symmetry is essential for the conventional view of the polymer spherulite microstructure. Typically it is assumed that, in the course of the spherulite morphogenesis, the lamellar crystals grow radially. Using submicron X-ray diffraction, it is shown that in banded spherulites of poly(propylene adipate) the crystals have the shape of a helix with fl at-on crystals winding around a virtual cylinder of about 6 ¿m in diameter. The helix angle of 30 °?implies that the crystal growth direction is tilted away from the spherulite radius by this angle. The implications of the helical crystal shape contradict the paradigm of the spherulitic microstructure. The radial growth rate of such spherulites does not correspond to the crystal growth rate, but to the propagation rate of the virtual cylinder the ribbons wind around. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., IUPAC Project PAC-PAL-10–02–26; Grant Number: 11.G34.31.0055; MINECO. Grant Number: MAT2011–23455 CSIC; Fondo Social Europeo (FSE)

The structure-dynamics relationships in random copolymers of poly(trimethylene terephthalate) and poly(neopenthyl terephthalate) (PTT-PNT) have been investigated by means of X-ray scattering and dielectric loss spectroscopy experiments. The results show that the incorporation of neopenthyl terephthalate units into PTT chain decreases the ability to crystallize of the resulting copolymers as compared to that of PTT. The subglass dynamics of the copolymers is characterized by the existence of two processes, β 1 and β 2. We propose that the high frequency secondary relaxation β 1 is associated with the most flexible part of the repeat unit, whereas the low frequency mode β 2 has been assigned to the carbon of the ester groups linked to the aromatic ring. On the contrary the poly(neopenthyl terephthalate) (PNT), presents only one subglass process, that we hypothesize to have the same origin of the relaxation of β 2 relaxation in PTT. The segmental dynamics for the amorphous specimens, characterized by the α-process, follows an expected molar ratio behavior. A particular effect characterized by a reduction of the segmental mobility induced by the presence of the counits is observed in the copolymers. © 2011 American Chemical Society., Financial support from Grants MAT2008-03232 and MAT2009-07789 from MICINN, Spain.

A multiblock bioresorbable copolyester, poly(butylene/diethylene glycol succinate), was synthesized by reactive blending, and it was used, together with the corresponding poly(butylene succinate) homopolymer, to form films and to fabricate biomimetic electrospun scaffolds. The poly(butylene/diethylene glycol succinate) scaffold had a more pronounced elastomeric behavior than poly(butylene succinate). It also underwent hydrolytic degradation faster than poly(butylene succinate) since the incorporated diethylene glycol succinate units rendered the copolymer more hydrophilic than poly(butylene succinate). The films degraded faster than electrospun samples due to the autocatalytic effect of carboxylic end-groups. The biodegradable poly(butylene/diethylene glycol succinate) scaffold supported the growth and preserved the cardiac phenotype markers of H9c2 cells, demonstrating its potential utility in soft tissue engineering applications.

Poly(butylene/thiodiethylene succinate) block copolymers (PBSPTDGS), prepared by reactive blending of the parent homopolymers (PBS and PTDGS) in the presence of Ti(OBu)(4), underwent molecular and solid-state characterization, in order to investigate the effects of the transesterification reactions. C-13 NMR analysis demonstrated the formation of copolymers whose degree of randomness increased with the mixing time. Thermal measurements showed that all the samples were semicrystalline, with a soft amorphous phase and a rigid crystal phase. WAXD measurements indicated that the copolymers are characterized by the presence of a pure PBS crystal phase, with the exception of physical mixture. The mechanical properties were related to degree of crystallinity. The random copolymer, characterized by the lowest crystallinity degree, exhibits the lowest elastic modulus and the highest deformation at break. When evaluated for indirect cytotoxicity, all the polymers under investigation appeared entirely biocompatible. In addition, positive results from cellular adhesion and proliferation assays carried out with H9c2 cells seeded and grown up to 14 days in culture over films of PBSPTDGS30 and PBSPTDGS240 demonstrated that these new materials might be of interest for tissue engineering applications. (C) 2012 Elsevier Ltd. All rights reserved.

We show that the combination of dielectric with neutron spin echo measurements performed in a model deuterated polymer as poly(ethylene terephthalate) suggests that the dynamics of semicrystalline polymers occurs in an homogeneous scenario similar to that valid to describe the dynamics of amorphous polymers. Accordingly, the intermolecular cooperativity is expected to be rather similar in both amorphous and semicrystalline polymers. The reduced segmental mobility of the semicrystalline polymer is restricted to well differentiate regions, probably in the crystal-amorphous interface. The significant broadening of the dielectric segmental relaxation in semicrystalline polymers can be attributed to the averaging effect of measuring a homogeneous relaxation with similar stretching exponents over an inhomogeneous environment. © 2011 American Chemical Society., We are indebted to MICINN (Spain) for financial support through Grants MAT2009-07789 and MAT2008-03232. A.S. thanks the Spanish Research Council (CSIC) for a JAE-doc tenure.

Novel copolyesters have been prepared by polycondensation and by melt mixing of poly(butylene terephthalate) with an ethoxylated bisphenol S. No side reactions occur during the synthesis of the samples, as proved by NMR analysis. The polyesters were examined by TGA and DSC. The insertion of the bisphenol S (sulfonyldiphenol) group significantly improved the thermal stability of the polymer. The thermal analysis carried out using DSC technique showed that the T m of the copolymers decreased with increasing co-unit content, differently from T g , which on the contrary increased, exceeding in some cases 100 °C, and crystallization rate decreased. A polymer containing only terephthalate moieties and ethoxylated bisphenol S has been prepared for the first time.

This work presents an experimental study on the interplay between structure and dynamics during isothermal and nonisothermal cold crystallization of poly(trimethylene terephthalate). Simultaneous X-ray scattering and dielectric spectroscopy measurements revealed that, during cold crystallization, crystalline lamellae tend to be homogeneously distributed along the sample. A significant amount of rigid amorphous phase is formed during cold crystallization, and its location is assigned to the crystal-amorphous interface. The formation of the rigid amorphous phase during cold crystallization is less effective for poly(trimethylene terephthalate) than for other similar aromatic polyesters like poly(ethylene terephthalate). The mobile amorphous phase, giving rise to the dielectric a relaxation, is mainly located between consecutive crystalline lamellae. The segmental dynamics of the amorphous phase is restricted by the growing crystals during both primary and secondary crystallization. © 2009 American Chemical Society., Funded by the Spanish CICYT (MAT2008-03232). Higher Council for Scientific Research (CSIC), JAE-doc .

The melting behaviour, the crystallization kinetics and the morphology of block poly(butylene/diethylene succinate) copolymers (PBSPDGS) were investigated by means of differential scanning calorimetry and hot stage optical microscopy. Multiple endotherms were evidenced in the PBSPDGS samples, due to melting and recrystallization processes, similarly to PBS. By applying the Hoffman–Weeks’ method, the T m 0 of both the homopolymer and the copolymers was derived. The isothermal crystallization kinetics was analyzed according to the Avrami’s treatment. The copolymers with long PBS blocks are characterized by a very similar behaviour with respect to pure poly(butilene succinate), indicating that PBS macromolecular folding is not affected by the presence of non-crystallizable diethylene succinate blocks. On the contrary, the copolymers characterized by very short PBS block length were found to crystallize at a slower rate than the homopolymer. As a matter of fact, a higher value of the work of chain folding was also derived on the basis of Hoffman–Lauritzen nucleation theory. Anyway, in all cases the crystallization mechanism (heterogeneous nucleation and three-dimensional growth) was found to be the same.

The dynamic behavior of a series of polymers based on 2,6- naphthalenedicarboxylic acid where the chemical structure of the monomer has been systematically modified was studied. The effect of the different chemical structure of the monomelic unit on the subglass dynamics has been evaluated. The β relaxation has a complex character. The slowest subglass relaxation, labeled as β* relaxation, is directly related to motions of the naphthyl moiety. However, the observed variations of the position of this relaxation, compared with analogues' more rigid polymers, indicate a certain degree of cooperativity of the subglass dynamics. © 2008 American Chemical Society., financial support from the MEC (MAT2005-01768), Spain

The dielectric spectra of two aliphatic polyesters, poly(propylene succinate) and poly(propylene adipate), are reported. For these two model aliphatic polyesters the α and β relaxations appear simultaneously and well resolved in the experimental frequency window. During isothermal crystallization, this fact allows one to use the β relaxation to characterize the crystalline structural development while the α relaxation provides information about the evolution of the amorphous phase dynamics. In this way structural development and dynamics evolution can be characterized by a single experiment during the crystallization process. Additionally, the unambiguous determination, in the amorphous polymers, of the relaxation times for the α and β relaxations further support a close relationship between local and segmental dynamics in polyesters as proposed by the coupling model. © 2007 Elsevier Ltd. All rights reserved.

Poly(propylene isophthalate) (PPI), poly(propylene succinate) (PPS), and poly(propylene isophthalate/succinate) (PPI-PPS) random copolymers were synthesized and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by TGA and DSC. All the polymers showed a good thermal stability. At room temperature, they appeared as semicrystalline materials, except 20PPI-PPS and 30PPI-PPS: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of T-m with respect to homopolymers. A crystalline phase of PPI and PPS was evidenced at high content of PI or PS units, respectively. Amorphous samples were obtained after melt quenching and an increment of T-g, with the increment of PI units, was observed. This behavior was explained as due to the presence of stiff phenylene groups. The Wood equation described well T-g-composition data. Lastly, the presence of a rigid-amorphous phase was evidenced in copolymers, differently from the two homopolymers. (c) 2006 Wiley Periodicals, Inc.

Polyesters based on 1,3-propanediol glycol and aliphatic dicarboxylic acids with different chain length were synthesized by melt polycondensation, obtaining samples characterized by high and comparable Mn. The polymers were subjected to molecular and thermal characterization. All polymers showed a good thermal stability, even though depending on the chain length. At room temperature all the polymers appeared as semicrystalline materials; the effect of the chain length was a lowering in the Tg value, an odd–even fluctuation for Tm and an increase of the crystallization rate. A comparison of the X-ray data revealed that the polymers with odd carbon number per repeat unit, show similar patterns, different from those of samples with even carbon atoms number. Multiple endotherms were evidenced in melt isothermally crystallized samples, due to melting and recrystallization processes. By applying the Hoffman–Weeks' method, the T m 0 of the samples was derived. Lastly, the presence of an interphase was not evidenced.

Poly(butylene naphthalate) (PBN), poly(diethylene naphthalate) (PDEN), and poly(thiodiethylene naphthalate) (PTDEN) were synthesized and characterized in terms of chemical structure and molecular weight. The polyesters were examined by TGA, DSC, and DMTA. All the polymers showed a good thermal stability, even though depending on chemical structure. At room temperature they appeared as semicrystalline materials; the effect of the introduction along the PBN polymer chain of ether oxygen atoms or sulfur ones was a lowering in the T g value, a decrement of T m , and a decrease of the crystallization rate. Changing in chemical structure also affects the main α absorption associated with the glass transition which moves to lower temperature and whose energetic requirements decrease. The results were explained as due to the presence of highly flexible C-S-C or C-O-C bonds in the polymeric chain.

Poly(neopenthyl azelate) (PNAz) and poly(propylene/neopenthyl azelate) random copolymers (PPAz–PNAz) (NAz unit content from 5 to 20 mol%) were synthesized and characterized in terms of chemical structure and molecular weight. Afterwards, the polyesters were examined by TGA, DSC and X-ray diffractometry. Good thermal stability was found for each sample. The thermal analysis showed that the Tm of the copolymers decreased with the increment in NAz unit content, differently from Tg, which on the contrary increased. X-ray diffraction measurements allowed the identification of the PPAz crystalline structure in all the copolymers. Multiple endotherms were shown in the PPAz–PNAz samples, due to melting and recrystallization processes, similarly to PPAz. The T m ∘ of the copolymers was derived from the application of the Hoffman-Weeks’ method. Baur’s equation described well the Tm-composition data. The isothermal crystallization kinetics were analyzed according to Avrami’s treatment. The introduction of NAz units decreased the crystallization rate compared to pure PPAz. Values of the Avrami’s exponent n close to 3 were obtained in all cases, regardless of Tc, in agreement with a crystallization process originating from predeterminated nuclei and characterized by a three dimensional spherulitic growth.

The following experimental study shows the dielectric relaxation behavior of random copolyesters formed by butylene terephthalate and butylene isophthalate comonomeric units. The experimental data were analyzed using two relaxation modes describing the sub-glass relaxation, characterized by different activation energies. We propose that the high frequency secondary relaxation β1 is associated to the most flexible part of the repeat unit, whereas the low frequency mode β2 has been assigned to atoms of the ester groups linked to the aromatic rings. A strong correlation between the dynamic fragility of these polymers and the monomer architecture was also demonstrated. © 2007 Elsevier B.V. All rights reserved., Ministerio de Educación y Ciencia (Spanish Ministry of Science and Education), Spain (Grant MAT2005-01768). Ramón y Cajal Program from the Spanish Ministry of Science and Education

Poly(propylene terephthalate/2,6-naphthalate) random copolyesters (PPT-PPN) were synthesized and characterized from the molecular and thermal point of view. All the polymers showed a good thermal stability. The main effect of copolymerization was a lowering in the crystallinity and a decrease of Tm respect to homopolymers. WAXD measurements indicated that PPT-PPN copolymers are characterized by isodimorphic cocrystallization. The defect free energies, calculated on the basis of the inclusion model proposed by Wendling and Suter, indicated that the amount of PT units incorporated in the poly(propylene 2,6-naphthalate) (PPN) β crystals is higher than the amount of PN units which cocrystallizes in the poly(propylene terephthalate) (PPT) crystalline phase, probably due to the larger molar volume of PN units compared to PT ones. Amorphous samples showed a monotonic increment of Tg as the content of PN units is increased, due to the stiffening effect of naphthalene rings in the chain. Finally, the Fox equation described well the Tg-composition data.

The melting behavior and the crystallization kinetics of poly(dithiotriethylene adipate) (PSSTEA) were investigated by differential scanning calorimetry and hot-stage optical microscopy. The observed multiple endotherms, commonly displayed by polyesters, were influenced by the crystallization temperature ( T c ) and ascribed to melting and recrystallization processes. Linear and nonlinear theoretical treatments were applied to estimate the equilibrium melting temperature for PSSTEA, using the corrected values of the melting temperature; the nonlinear estimation yielded a higher value by about 15 °C. Isothermal crystallization kinetics were analyzed according to the Avrami’s theory. Values of the Avrami’s exponent n close to 3 were obtained, independently of T c , in agreement with a crystallization process originating from predeterminated nuclei and characterized by three-dimensional spherulitic growth. As a matter of fact, space-filling spherulites were observed by optical microscopy at all T c ’s. The rate of crystallization became lower as T c increased, as usual at low undercooling, the crystallization process being controlled by nucleation.

The thermal behavior of poly(ethylene-co-2,2-bis[4-(ethylenoxy)-1,4-phenylene]propane terephthalate) (PET/BHEEBT) copolymers was investigated by thermogravimetric analysis and differential scanning calorimetry. A good thermal stability was found for all the samples. The thermal analysis carried out using DSC technique showed that the Tm of the copolymers decreased with increasing BHEEBT unit content, differently from Tg, which on the contrary increased. Wide-angle X-ray diffraction measurements permitted identifying the kind of crystalline structure of PET in all the semicrystalline samples. The multiple endotherms similar to PET were also evidenced in the PET/BHEEBT samples, due to melting and recrystallization processes. By applying the Hoffman–Weeks' method, the Tm° of PET and its copolymers was derived. The isothermal crystallization kinetics was analyzed according to Avrami's treatment and values of the exponent n close to 3 were obtained, independently of Tc and composition. Moreover, the introduction of BHEEBT units was found to decrease PET crystallization rate. Lastly, the presence of a crystal-amorphous interphase was evidenced. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1441–1454, 2005

The thermal behaviour of poly(propylene terephthalate) modified with 2,2-bis[4-(ethylenoxy)-1,4-phenylene]propane terephthalate) units (PPT/BHEEBT copolymers) was investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and hot-stage optical microscopy (MO). Good thermal stability was found for each sample. The thermal analysis carried out using the DSC technique showed that the T m of the copolymers decreased with the increment in BHEEBT unit content. This was different from the T g which, on the contrary, increased. Wide-angle X-ray diffraction measurements allowed the identification of the PPT crystalline structure in each semicrystalline sample. Multiple endotherms were shown in the PPT/ BHEEBT samples, due to melting and recrystallisation processes, similarly to PPT. The T o m of the copolymers was derived from the application of the Hoffman-Weeks' method. The isothermal crystallisation kinetics were analysed according to Avrami's treatment. The introduction of BHEEBT units was found to decrease the crystallisation rate compared to pure PPT. Values of the Avrami's exponent n close to 3 were obtained for PPT/BHEEBT6 and PPT/BHEEBT12, regardless of T c , in agreement with a crystallisation process originating from pre-determined nuclei and characterised by three-dimensional spherulitic growth. As a matter of fact, for these two copolymers, space-filling spherulites were observed through optical microscopy at all T c s. The heat of fusion (ΔH m ) was correlated to the specific heat increment (Δc p ) for samples with different degrees of crystallinity, and the results were interpreted on the basis of the existence of an interphase, whose amount was found to depend mainly on composition, despite the thermal treatment applied to the polymer also playing an important role.

Poly(ethylene isophthalate-co-ethylene terephthalate) (PEIPET) copolymers of various compositions and molecular weights were synthesized by melt polycondensation and characterized in terms of chemical structure and thermal and rheological properties. At room temperature, all copolymers were amorphous and thermally stable up to about 400°C. The main effect of copolymerization was a monotonic increase of glass transition temperature (Tg) as the content of ethylene terephthalate units increased. The Fox equation accurately describes the Tg–composition data. The presence of ethylene terephthalate units was found to influence rheological behavior in the melt, with the Newtonian viscosity increasing as the content of ethylene terephthalate units increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 186–193, 2004