Melting behavior and crystallization kinetics of poly(butylene terephthalate‐co‐diethylene terephthalate) and poly(butylene terephthalate‐co‐triethylene terephthalate) copolyesters

The melting behavior of poly(butylene terephthalate‐co‐diethylene terephthalate) and poly(butylene terephthalate‐co‐triethylene terephthalate) copolymers was investigated by differential scanning calorimetry after isothermal crystallization from the melt. Multiple endotherms were found for all the samples, and attributed to the melting and recrystallization processes. By applying the Hoffman‐Weeks' method, the equilibrium melting temperatures of the copolymers under investigation were obtained. Two distinct peaks in the crystallization exothermic curve were observed for all the samples. Both of them appeared at higher times than that of PBT, indicating that the introduction of a comonomer decreased the crystallization rate. The observed dependence of this latter on composition was explained on the basis of the content of ether–oxygen atoms in diethylene and triethylene terephthalate units, and of the different sizes of these units. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3545–3551, 2001     

Aliphatic–aromatic poly(butylene carbonate‐co‐terephthalate) random copolymers: Synthesis,cocrystallization, and composition‐dependent properties

A series of aliphatic–aromatic poly(carbonate‐co‐ester)s poly(butylene carbonate‐co‐terephthalate)s (PBCTs), with weight‐average molecular weight of 113,000 to 146,000 g/mol, were synthesized from dimethyl carbonate, dimethyl terephthalate, and 1,4‐butanediol via a two‐step polycondensation process using tetrabutyl titanate as the catalyst. The PBCTs, being statistically random copolymers, show a single T_g over the entire composition range. The thermal stability of PBCTs strongly depends on the molar composition. Melting temperatures vary from 113 to 213°C for copolymers with butylene terephthalate (BT) unit content higher than 40 mol %. The copolymers have a eutectic melting point when about 10 mol % BT units are included. Crystal lattice structure shifts from the poly(butylene carbonate) to the poly(butylene terephthalate) type crystal phase with increasing BT unit content. DSC and WAXD results indicate that the PBCT copolymers show isodimorphic cocrystallization. The tensile modulus and strength decrease first and then increase according to copolymer composition. The enzymatic degradation of the PBCT copolymers was also studied. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41952.     

Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

Synthesis and characterization of poly[(butylene succinate)‐co‐(butylene terephthalate)]‐b‐poly(tetramethylene glycol) segmented block copolymer

Polyester‐polyether segmented block copolymers of poly[(butylene succinate)‐co‐poly(butylene terephthalate)] (PBS–PBT) and poly(tetramethylene glycol) (PTMG) (M_n = 2000) with various compositions were synthesized. PBT content in the PBS was adjusted to ca. 5 mol %. Their thermal and mechanical properties were investigated. In the case of copolymer, the melting point of the PBS–PBT control was 107.8°C, and the melting point of the copolymer containing 70 wt % of PTMG was 70.1°C. Crystallinity of soft segment was 5 ∼ 17%, and that of hard segment was 42 ∼ 59%. The breaking stress of the PBS–PTMG control was 47 MPa but it decreased with increasing PTMG content. In the case of copolymer containing 70 wt % of PTMG, breaking stress was 36 MPa. Contrary to the decreasing breaking stress, breaking strain increased from 300% for PBS–PBT control to 900% for a copolymer containing 70 wt % of PTMG. The shape recovery ratios of the copolymer containing 70 wt % PTMG were almost twice of those of copolymers containing 40 wt % PTMG. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2067–2075, 2001     

Effects of shearing and comonomer content on the crystallization behavior of poly(butylene succinate‐co‐butylene 2‐ethyl‐2‐methyl succinate)

Poly(butylene succinate‐co‐butylene 2‐ethyl‐2‐methyl succinate) (PBSEMS) random copolymers were prepared with different comonomer compositions. The effects of shearing and comonomer content on the crystallization behavior of these copolymers were investigated at 80 °C. The thermal and morphological properties of the resulting samples were also discussed. The copolymers showed a longer induction time and a slower crystallization rate with increasing comonomer content. The promoting effect of shear on the overall crystallization behavior was more notable for those copolymers containing more 2‐ethyl‐2‐methyl succinic acid (EMSA) units. The melting temperature of ‘as‐prepared’ poly(butylene succinate) (PBS) was ca. 115 °C, while that of the copolymers varied from 112 to 102 °C. Higher comonomer contents in the copolymers gave rise to lower melting temperatures and broader melting peaks. In addition, the isothermally crystallized samples showed multiple melting endothermic behavior, the extent of which depended on the comonomer content. The copolymers showed different wide‐angle X‐ray diffraction (WAXD) patterns from that of neat PBS, depending on the comonomer content and shear applied during crystallization. With increasing comonomer content, the copolymers crystallized without shearing, showing the shifting of a diffraction peak to a higher angle, while those crystallized under shear did not show any peak shift. Copyright © 2004 Society of Chemical Industry     

Synthesis and characterization of copolymers based on poly(butylene terephthalate) and ethylene oxide‐poly(dimethylsiloxane)‐ethylene oxide

A series of thermoplastic elastomers based on ethylene oxide‐poly(dimethylsiloxane)‐ethylene oxide (EO‐PDMS‐EO), as the soft segment, and poly(butylene terephthalate) (PBT), as the hard segment, were synthesized by catalyzed two‐step, melt transesterification reaction of dimethyl terephthalate (DMT) with 1,4‐butanediol (BD) and α,ω‐dihydroxy‐(EO‐PDMS‐EO). Copolymers with a content of hard PBT segments between 40 and 90 mass % and a constant length of the soft EO‐PDMS‐EO segments were prepared. The siloxane prepolymer with hydrophilic terminal EO units was used to improve the miscibility between the polar comonomers, DMT and BD, and the nonpolar PDMS. The molecular structure and composition of the copolymers were determined by ¹H‐NMR spectroscopy, whereas the effectiveness of the incorporation of α,ω‐dihydroxy‐(EO‐PDMS‐EO) into the copolymer chains was verified by chloroform extraction. The effects of the structure and composition of the copolymers on the melting temperatures and the degree of crystallinity, as well as on the thermal degradation stability and some rheological properties, were studied. It was demonstrated that the degree of crystallinity, the melting and crystallization temperatures of the copolymers increased with increasing mass fraction of the PBT segments. The thermal stability of the copolymers was lower than that of PBT homopolymer, because of the presence of thermoliable ether bonds in the soft segments. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electrospun fiber membranes of novel thermoplastic polyester elastomers: Preparation and characterization

Electrospinning nanotechnology has recently attracted lots of attention in different kinds of applications. Poly(butylene terephthalate) random‐segment copolymers, named poly[(butylene terephthalate)‐co‐(1,4‐cyclohexanedimethanol terephthalate)]‐b‐poly(tetramethylene glycol) (P(BT‐co‐CT)‐b‐PTMG), were synthesized in this study. On the basis of the new thermoplastic polyester elastomers (TPEEs), the fiber membranes were subsequently electrospun. With the aid of a cosolvent of trifluoroacetic acid and dichloromethane, the resulting solutions with a concentration between 24 and 32% w/v were electrospun into fibers without beads. The results also show a good spinnability for the copolymer solution in a range of voltages from 16 to 24 kV. When the molar ratio of 1,4‐cyclohexanedimethanol to 1,4‐butanediol was 10 : 90, the electrospun membrane prepared by the corresponding copolymers had a higher elastic modulus than the commercial TPEE (Hytrel 4056, 4.51 ± 0.35 MPa). Differential scanning calorimetry and X‐ray diffraction showed that a crystalline phase existed in the electrospun poly[(butylene terephthalate)‐co‐(1,4‐cyclohexanedimethanol terephthalate)]‐b‐poly(tetramethylene glycol) (P(BT‐co‐CT)‐b‐PTMG) copolymer fiber membranes. The melting point of the electrospun fibers was approximately less than that of the corresponding copolymers © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Isothermal crystallization kinetics and melting behaviors of poly(butylene terephthalate) and poly(butylene terephthalate‐co‐fumarate) copolymer

The isothermal crystallization kinetics and melting behaviors after isothermal crystallization of poly(butylene terephthalate) (PBT) and poly(butylene terephthalate‐co‐fumarate) (PBTF) containing 95/5, 90/10, and 80/20 molar ratios of terephthalic acid/fumaric acid were investigated by differential scanning calorimetry. The equilibrium melting temperatures of these polymers were estimated by Hoffman–Weeks equation. So far as the crystallization kinetics was concerned, the Avrami equation was applied and the values of the exponent n for all these polymers are in the range of 2.50–2.96, indicating that the addition of fumarate does not affect the geometric dimension of PBT crystal growth. Crystallization activation energy (ΔE) and nucleation constant (K_g) of PBTF copolymers are higher than that of PBT homopolymer, suggesting that the introduction of fumarate hinders the crystallization of PBT in PBTF. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Synthesis and characterization of poly(ethylene isophthalate‐co‐ethylene terephthalate) copolyesters

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 (T_g) as the content of ethylene terephthalate units increased. The Fox equation accurately describes the T_g–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     

Preparation and thermal behavior of random poly(butylene terephthalate/azelate) copolyesters

Poly(butylene terephthalate), poly(butylene azelate), and poly(butylene terephthalate/butylene azelate) random copolymers of various compositions were synthesized in bulk using the well‐known two‐stage polycondensation procedure, and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. As far as the thermal stability is concerned, it was found to be rather similar for all copolymers and homopolymers investigated. All the copolymers were found to be partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to pure homopolymers. Flory's equation was found to describe the T_m–composition data and permitted to calculate the melting temperatures (T^°_m ) and the heats of fusion (ΔH_u) of both the completely crystalline homopolymers. Owing to the high crystallization rate, the glass transition was observable only for the copolymers containing from 30 to 70 mol % of the terephthalate units; even though the samples cannot be frozen in a completely amorphous state, the data obtained confirmed that the introduction of the aromatic units gave rise to an increase of T_g, due to a chain stiffening. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2694–2702, 1999     

Synthesis and non‐isothermal crystallization behavior of poly(ethylene phthalate‐co‐terephthalate)s

A series of poly(ethylene phthalate‐co‐terephthalate)s were synthesized by melt polycondensation of ethylene glycol (EG) with dimethyl phthalate (DMP) and dimethyl terephthalate (DMT) in various proportions. The DMT‐rich polymers were obtained with reasonably high molecular weights, whereas the DMP‐rich polymers were synthesized with relatively low molecular weights due to steric effects associated with the highly kinked DMP monomer. The compositions and thermal properties of the polymers were determined. The copolymers containing DMP in amounts of ≤ 21 mol% were crystallizable, whereas the other polymers were not. All the polymers exhibited a single glass transition temperature. Analysis of the measured glass transition temperatures and crystal melting temperatures confirmed that the DMT‐rich copolymers are random copolymers. The non‐isothermal crystallization behaviors of the DMT‐rich copolymers were investigated by calorimetry and modified Avrami analysis. The Avrami exponents n were found to range from 2.7 to 3.8, suggesting that the copolymers crystallize via a heterogeneous nucleation and spherulitic growth mechanism; that is, the incorporation of DMP units as the minor component does not change the growth mechanism of the copolymers. In addition, the activation energies of the crystallizations of the copolymers were determined; the copolymers were found to have higher activation energies than the PET homopolymer. Polym. Eng. Sci. 44:1682–1691, 2004. © 2004 Society of Plastics Engineers.     

Crystallization and melting behavior of biodegradable poly(ethylene succinate‐co‐6 mol % butylene succinate)

The crystallization, melting behavior, and spherulitic growth kinetics of biodegradable poly(ethylene succinate‐co‐6 mol % butylene succinate) [P(ES‐co‐6 mol % BS)] were investigated and compared with those of the homopolymer poly(ethylene succinate) (PES) in this work. The crystal structure of P(ES‐co‐6 mol % BS) was the same as that of neat PES, but the crystallinity decreased slightly because of the incorporation of the butylene succinate content. The glass‐transition temperature decreased slightly for P(ES‐co‐6 mol % BS) compared to that for neat PES. The melting point of P(ES‐co‐6 mol % BS) decreased apparently; moreover, the equilibrium melting point was also reduced. Two melting endotherms were found for P(ES‐co‐6 mol % BS) after isothermal crystallization; this was ascribed to the melting, recrystallization, and remelting mechanism. The spherulitic growth rate of P(ES‐co‐6 mol % BS) was slower than that of neat PES at a given crystallization temperature. Both neat PES and P(ES‐co‐6 mol % BS) exhibited a crystallization regime II to III transition; moreover, the crystallization regime transition temperature of P(ES‐co‐6 mol % BS) shifted to a low temperature compared with that of neat PES. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characterization and biodegradability of poly(butylene adipate‐co‐succinate)/poly(butylene terephthalate) copolyester

Characterization of poly(butylene adipate‐co‐succinate) (PBAS)/poly(butylene terephthalate) (PBT) copolyesters resulting from the intermolecular ester‐exchange reaction between molten PBAS and PBT have been analyzed using ¹H‐NMR spectroscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction, and total organic carbon lab analyzer. Using the assignment of proton resonance due to homogeneous and heterogeneous dyads, the average block lengths were investigated over the entire range of copolymer composition. A decrease in melting temperature was observed with the increase of a terephthalate unit in the composition. The result of X‐ray diffraction curve matches well with that of average block length and thermal property. When a rich component is crystallized, the poor component is excluded completely in a crystal formation. The biodegradability in copolyesters also depended on the terephthalate unit in the composition and average block length of the aromatic unit. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 593–608, 1999     

Synthesis and characterization of poly(ethylene terephthalate‐co‐isophthalate)s with low content of isophthalate units

The objective of this work was to study the effect of the introduction of low amounts of isophthalate units on the mechanical properties, crystallization rates, and thermal parameters of poly(ethylene terephthalate). For this reason a series of five random poly(ethylene terephthalate‐co‐isophthalate) copolymers, containing 0.5, 1, 1.5, 2, and 4 mol % isophthalic acid, were prepared by the melt polycondensation process. The intrinsic viscosity of copolymers ranged between 0.7 and 0.8 dL/g. The increase of isophthalate content resulted in a significant decrease of the crystallization rates, but in a small decline of tensile strength, Young's modulus, and elongation at break, whereas tensile strength at yield point remained almost unaffected. Also, a decrease in the melting point was recorded, whereas the glass‐transition temperature was only very slightly affected. The higher decrease for the aforementioned parameters was noted for the copolymer with 4 mol % isophthalate units content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1931–1941, 2002     

Thermal,rheological, mechanical,and dyeing property studies of poly(ethylene‐co‐trimethylene terephthalate) copolymer filaments

The thermal and rheological properties of poly(ethylene‐co‐trimethylene terephthalate) (PETT) copolymer are investigated. The thermal behavior of PETT copolymers is dependent on the composition. The PETT‐15 and PETT‐85 copolymers can crystallize, whereas the PETT‐30 copolymer cannot crystallize at 5°C/min cooling rate. The copolymers have a good thermal stability, even though the addition of poly(trimethylene terephthalate) (PTT) chain causes a disadvantage to the thermal stability of the copolymers. Moreover, the PETT copolymers are a typical pseudoplastic fluid exhibiting shear thinning. With increasing the shear rate or the content of PTT units, the flow activation energy decreases and the sensitivity of the shear viscosity to the melt temperature declines. The PETT copolymer filaments have intermediate elastic recovery and dyeability between poly(ethylene terephthalate) (PET) and PTT filaments. With increasing the PTT content, the elastic recovery and dyeability of PETT copolymer filaments increase. That is to say, introducing PTT units as a minor component into the macromolecular chains is an available means to improve the properties of PET filament. The obtained PETT copolymer filaments blend the advantage of the mechanical property of PET and the elastic and dyeability of PTT filament together into one polymer and possess a softer feeling and a higher extension. POLYM. ENG. SCI., 50:1689–1695, 2010. © 2010 Society of Plastics Engineers     

Preparation and biodegradation of copolyesters based on poly(ethylene terephthalate) and poly(ethylene glycol)/oligo(lactic acid) by transesterification

The poly(ethylene terephthalate‐co‐ethyleneoxide‐co‐DL ‐lactide) copolymers were successfully prepared by the melt reaction between poly(ethylene terephthalate), poly(ethylene glycol), and DL ‐oligo(lactic acid) without any catalysts. The transesterification between ethylene terephthalate, ethyleneoxide, and lactide segments during the reaction was confirmed by the ¹H NMR analysis. The effect of reaction temperatures and the starting feed ratios on the molecular microstructures, molecular weights, solubility, thermal properties, and degradability of the copolyesters was extensively studied. The values of crystallization temperature, melting temperature, crystallization, and melting enthalpy of the copolyesters were found to be influenced by the reaction temperatures, starting feed ratios, etc. The copolyesters showed good tensile properties and were found to degrade in the soil burial experiments during the period of 3 months. The morphology of the copolyester films were also investigated by scanning electron microscopy during soil burial degradation. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Synthesis and properties of random copolymers of 2,2‐dimethyltrimethylene carbonate and ethylene carbonate catalyzed by lanthanide tris(2,6‐di‐tert‐butyl‐4‐methylphenolate)

Random copolymers of 2,2‐dimethyltrimethylene carbonate and ethylene carbonate (EC) were synthesized with lanthanide tris(2,6‐di‐tert‐butyl‐4‐methylphenolate)s [Ln(DBMP)₃; Ln = La, Nd, Sm, or Dy] as catalysts, among which La(DBMP)₃ showed the highest activity. Poly(2,2‐dimethyltrimethylene carbonate‐co‐ethylene carbonate)s [poly(DTC‐co‐EC)]s with high molecular weights were prepared at room temperature and characterized with ¹H‐NMR and size exclusion chromatography. The thermal behavior and crystalline properties of the poly(DTC‐co‐EC)s were analyzed with differential scanning calorimetry, thermogravimetric analysis, and X‐ray diffraction. The crystallinity and melting temperatures of the poly(DTC‐co‐EC)s both decreased with increasing EC content in the copolymers. The mechanical properties of these copolymers were also investigated with dynamic mechanical analysis and tensile strength measurements, which revealed that a reduction of the glass‐transition temperature and great enhancement of the tensile properties could be achieved with higher EC contents. These improvements in the thermal and mechanical properties indicate potential applications in biomedical research for novel polycarbonates. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Melt characteristics,mechanical, and thermal properties of blown film from modified blends of poly(butylene adipate‐co‐terephthalate) and poly(lactide)

Blown films from poly(butylene adipate‐co‐terephthalate) and poly(lactide) (PLA) blends were investigated. The blends were prepared in a twin‐screw extruder, in the presence of small amounts of dicumyl peroxide (DCP). The influence of DCP concentration on film blowing, rheological, mechanical, and thermal properties of the blends is reported in this article. Rheological results showed a marked increase in polymer melt strength and elasticity with the addition of DCP. As a consequence, the film homogeneity and the stability of the bubble were improved. The modified blend films, compared with the unmodified blend, showed an improvement in tensile strength and modulus with a slight loss in elongation. Fourier transform infrared and gel results revealed that chain scission and branching were more significant than crosslinking when the DCP loadings in the blends were not higher than 0.7%. A reduction in melt temperatures of PLA was observed due to difficulty in chain crystallization. The concentrations of DCP strongly affected the melting temperatures but had an insignificant effect on the decomposition behavior of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Reactive compatibilization of PP/PBT blends by a mixture of PP‐g‐MA and epoxy resin

In this study, dual compatibilizers composed of the commercially available maleic anhydride‐grafted polypropylene (PP–MA) and a multifunctional epoxy resin were demonstrated to effectively compatibilize the immiscible and incompatible blends of PP and poly(butylene terephthalate) (PBT). The PP–MA with a low MA content is totally miscible with PP to make the PP phase quasi‐functionalized, so that the multifunctional epoxy has the chance to react with PBT and PP–MA simultaneously to form PP–MA‐co‐epoxy‐co‐PBT copolymers at the interface. These desired copolymers are able to anchor along the interface and serve as efficient compatibilizers. The compatibilized blends, depending on the quantity of dual compatibilizers employed, exhibit higher viscosity, finer phase domain, and improved mechanical properties. Epoxy does not show compatibilization effects for the PP/PBT blends without the presence of PP–MA in the blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2272–2285, 2001     

Crystallization and photo‐curing kinetics of biodegradable poly(butylene succinate‐co‐butylene fumarate) short‐segmented block copolyester

Short‐segmented block copolymers of poly(butylene succinate‐co‐butylene fumarate) were synthesized and their crystallinity and crosslinking behavior were investigated. ¹H NMR was used to characterize the microstructure and composition of the copolyesters. Molecular weight determination was performed using gel permeation chromatography. Based on the DSC results all copolyesters were crystalline and the degree of crystallinity of the copolymers did not change with butylene fumarate mole fraction due to co‐crystallization of the butylene succinate and butylene fumarate groups. Crosslinked copolyesters showed a lower crystallization rate and degree of crystallinity while the crystallization temperature shifted to higher temperatures compared with uncrosslinked copolyesters due to the formation of nucleating agents by crosslinkages. Photo‐DSC was used to investigate the crosslinking kinetics for UV‐initiated photo‐curing. Three kinetics parameters including the rate constant (k) and the orders of the initiation and propagation reactions (m and n, respectively) were determined for the quenched and unquenched copolymers. © 2016 Society of Chemical Industry