Synthesis and characterizations of branched poly(butylene succinate) copolymers with 1,2‐octanediol segments

Branched poly(butylene succinate) (PBS) copolymers were synthesized, from succinic acid (SA), 1,4‐butanediol (1,4‐BD), and 1,2‐octanediol (1,2‐OD) through a two‐step process containing esterification and polycondensation, with different mole fractions of 1,2‐OD segments. The branched PBS copolymers were characterized with ¹H‐NMR, differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD), thermogravimetric analysis (TGA), dynamic rheological testing, and tensile properties analysis. The results of DSC and WAXD show that, with the increasing of the 1,2‐OD segments content, the glass transition temperature (T_g), melting temperature (T_m), crystallization temperature (T_c), and the degree of crystallinity (X_c) decrease. While the crystal structure of PBS does not change by introducing 1,2‐OD segments. The results of TGA and dynamic rheological testing indicate that the thermal stability of neat PBS is improved with the addition of 1,2‐OD segments. The incorporation of 1,2‐OD segments has some effects on the rheological properties of PBS, such as complex viscosities (|η*|), storage modulus (G′), and loss modulus (G″). Tensile testing demonstrates that the elongation at break is improved significantly with increasing 1,2‐OD segments content, but without a notable decrease of tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of biodegradable poly(butylene succinate‐co‐propylene succinate)s

Biodegradable polyesters such as poly(butylene succinate) (PBS), poly(propylene succinate) (PPS), and poly(butylene succinate‐co‐propylene succinate)s (PBSPSs) were synthesized respectively, from 1,4‐succinic acid with 1,4‐butanediol and 1,3‐propanediol through a two‐step process of esterification and polycondensation in this article. The composition and physical properties of both homopolyesters and copolyesters were investigated via ¹H NMR, DSC, TGA, POM, AFM, and WAXD. The copolymer composition was in good agreement with that expected from the feed composition of the reactants. The melting temperature (T_m), crystallization temperature (T_c), crystallinity (X), and thermal decomposition temperature (T_d) of these polyesters decreased gradually as the content of propylene succinate unit increased. PBSPS copolyesters showed the same crystal structure as the PBS homopolyester. Besides the normal extinction crosses under the polarizing optical microscope, the double‐banded extinction patterns with periodic distance along the radial direction were also observed in the spherulites of PBS and PBSPS. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Biodegradable composites of poly(butylene succinate‐co‐butylene adipate) reinforced by poly(lactic acid) fibers

Biodegradable composites of poly(butylene succinate‐co‐butylene adipate) (PBSA) reinforced by poly(lactic acid) (PLA) fibers were developed by hot compression and characterized by Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analyzer, and tensile testing. The results show that PBSA and PLA are immiscible, but their interface can be improved by processing conditions. In particular, their interface and the resulting mechanical properties strongly depend on processing temperature. When the temperature is below 120 °C, the bound between PBSA and PLA fiber is weak, which results in lower tensile modulus and strength. When the processing temperature is higher (greater than 160 °C), the relaxation of polymer chain destroyed the molecular orientation microstructure of the PLA fiber, which results in weakening mechanical properties of the fiber then weakening reinforcement function. Both tensile modulus and strength of the composites increased significantly, in particular for the materials reinforced by long fiber. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43530.     

Thermal and mechanical properties of poly(butylene succinate) nanocomposites with various organo‐modified montmorillonites

Nanocomposites based on biodegradable poly(butylene succinate) (PBS) and layered silicates were prepared by melt intercalation. Nonmodified montmorillonite (MMT) and MMTs (DA‐M, ODA‐M, ALA‐M, LEA‐M, and HEA‐M) organo‐modified by protonated ammonium cations {i.e., those of dodecylamine, octadecylamine, 12‐aminolauric acid, N‐lauryldiethanolamine, and 1‐[N,N‐bis(2‐hydroxyethyl)amino]‐2‐propanol, respectively} were used as layered silicates. From morphological studies using transmission electron microscopy, DA‐M, ODA‐M, and LEA‐M were found to be dispersed homogeneously in the matrix polymer, whereas some clusters or agglomerated particles were observed for ALA‐M, HEA‐M, and MMT. The enlargement of the difference in the interlayer spacing between the clay and PBS/clay composite, as measured by X‐ray diffraction, had a good correlation with the improvement of the clay dispersion and with the increase in the tensile modulus and the decrease in the tensile strength of the PBS composites with an inorganic concentration of 3 wt %. Dynamic viscoelastic measurements of the PBS/LEA‐M nanocomposite revealed that the storage modulus and glass‐transition temperature increased with the inorganic concentration (3–10 wt %). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1463–1475, 2004     

An investigation of stress oscillation in poly(butylene succinate‐co‐cyclohexanedimethylene succinate)

Biodegradable poly(butylene succinate‐co‐cyclohexanedimethylene succinate) (PBCS) was synthesized via polycondensation. The composition of PBCS was characterized by ¹H‐nuclear magnetic resonance (¹H‐NMR). By incorporation of 20 wt% of cyclohexanedimethylene succinate, stress oscillation behavior in stress–strain curve was observed during cold drawing. The stress was no longer stable, but exhibited constantly periodic fluctuations. Morphology and crystalline structure of oscillatory portion were evaluated by scanning electron microscopy, and X‐ray diffraction (XRD), respectively. The melting behavior was studied using differential scanning calorimetry (DSC). The surface morphology of oscillatory portion presented alternating opaque and transparent bands, which were perpendicular to the cold‐drawing direction. By comprehensive analysis of stress–strain curve, surface morphology, XRD, and DSC, the formation of stress oscillation was discussed. To describe stress oscillation, a new mathematical model was proposed to simulate stress oscillation and its viscoelastic behaviors were well explained. The novelty of the mathematical model was that new oscillatory cells consisting of a dashpot with free inextensible strings were adopted to instead of fiber bundle cells. POLYM. ENG. SCI., 55:966–974, 2015. © 2014 Society of Plastics Engineers     

Dielectric spectroscopy of poly(butylene succinate‐co‐butylene adipate) films

The results of dielectric studies in semicrystalline poly (butylene succinate‐co‐butylene adipate) (PBSA) by means of dielectric relaxation spectroscopy from 163 to 353 K and in the frequency range of 0.056–17,800 Hz are reported. The subglass β process is found to follow an Arrhenius temperature dependence, whereas the segmental α process follows a Vogel–Fulcher–Tammann temperature dependence. The higher temperature Maxwell–Wagner–Sillars (MWS) process was studied by applying the Bruggeman‐Hanai equation, which helped to understand the underlying relaxation dynamics. The MWS process originates from the charge accumulation at the interface between the low‐conductivity continuous medium and the high‐conductivity dispersed particles. A three‐phase model in which the medium comprises the crystalline and rigid amorphous phases (RAPs) and the particle comprises solely the mobile amorphous phases (MAPs) is required to explain the particle fraction variation with temperature. With increasing temperature, the MAP fraction increases at the expense of the RAP fraction within the continuous medium. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Pressure‐volume‐temperature behavior of polylactide,poly(butylene succinate), and poly(butylene succinate‐co‐adipate)

Pressure‐Volume‐Temperature (PVT) behavior of three biodegradable polymers, Polylactide, poly(butylene succinate), and poly(butylene succinate‐co‐adipate), was measured at temperatures from 313 to 493 K and pressures up to 200 MPa. The PVF data in molten state were compared with predicted values of a group contribution modified cell model equation of state (GCMCM EOS). It was found that the GCMCM EOS coupled with one specific volume datum at atmospheric pressure could predict the PVT of the polymer melts to within 0.46% in an average relative deviation of specific volume.     

Mechanisms and kinetics of thermal degradation of poly(butylene succinate‐co‐propylene succinate)s

Poly(butylene succinate) (PBSu) and two PBSu‐rich poly(butylene succinate‐co‐propylene succinate)s were studied. Copolyesters were characterized as random copolymers, based on ¹³C‐NMR spectra. TGA‐FTIR was used to monitor the degradation products at a heating rate of 5°C/min under N₂. FTIR spectra revealed that the major products were anhydrides, which were formed following two cyclic intramolecular degradation mechanisms by the breaking of the weak O‐CH₂ bonds around succinate groups. Thermal stability at heating rates of 1, 3, 5, and 10°C/min under N₂ was investigated using TGA. The model‐free methods of the Friedman and Ozawa equations are useful for studying the activation energy of degradation in each period of mass loss. The results reveal that the random incorporation of minor propylene succinate units into PBSu did not markedly affect their thermal resistance. Two model‐fitting mechanisms were used to determine the mass loss function f(α), the activation energy and the associated mechanism. The mechanism of autocatalysis nth‐order, with f(α) = α^m(1 ? α)ⁿ, fitted the experimental data much more closely than did the nth‐order mechanism given by f(α) = (1 ? α)ⁿ. The obtained activation energy was used to estimate the failure temperature (T_f). The values of T_f for a mass loss of 5% and an endurance time of 60,000 h are 160.7, 155.5, and 159.3°C for PBSu and two the copolyesters, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Crystallization behavior and mechanical strength of poly(butylene succinate‐co‐ethylene glycol)‐based nanocomposites using functionalized multiwalled carbon nanotubes

Biodegradable poly(butylene succinate‐co‐ethylene glycol) (PBSG)/multiwalled carbon nanotube (MWCNT) nanocomposites were successfully prepared through physical blending and silication between PBSG and acyl aminopropyltriethoxysilane functionalized multiwalled carbon nanotube (MWCNT‐APTES). Nuclear magnetic resonance (NMR) spectra observations revealed that the PBSG chains were covalently attached to the MWCNT‐APTES by hydrolysis. PBSG/MWCNT‐APTES nanocomposites after hydrolysis showed excellent interfacial compatibility between PBSG and MWCNT‐APTES, which was helpful for the dispersion of MWCNT in the PBSG matrix. The incorporation of MWCNT‐APTES accelerated the crystallization of PBSG in the nanocomposites for both approaches of physical blending and hydrolysis due to the heterogeneous nucleation effect of MWCNT while the crystal structure of PBSG was remained. Furthermore, the crystallization rate of PBSG in PBSG/MWCNT‐APTES nanocomposites after hydrolysis was slower than that in the nanocomposite by physical blend. The tensile strength and modulus of the nanocomposites increased about 6% and 11% with the addition of only 1 wt% MWCNT‐APTES compared with that of neat PBSG, and was larger for the PBSG/MWCNT‐APTES nanocomposites after hydrolysis. POLYM. ENG. SCI., 2012. © 2012 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     

Enhanced mechanical and thermal properties of biodegradable poly(butylene succinate‐co‐adipate)/graphene oxide nanocomposites via in situ polymerization

Poly(butylene succinate‐co‐butylene adipate) (PBSA)/graphene oxide (GO) nanocomposites were synthesized via in situ polymerization for the first time. Atomic force microscopy demonstrated the achievement of a single layer of GO, and transmission electron microscopy proved the homogeneous distribution of GO in the PBSA matrix. Fourier transform infrared spectroscopy results showed the successful grafting of PBSA chains onto GO. With the incorporation of 1 wt % GO, the tensile strength and flexural modulus of the PBSA were enhanced by 50 and 27%, respectively. The thermal properties characterized by differential scanning calorimetry and thermogravimetric analysis showed increases in the melting temperatures, crystallization temperatures, and thermal stability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4075–4080, 2013     

Elongational rheology of biodegradable poly(lactic acid)/poly[(butylene succinate)‐co‐adipate] binary blends and poly(lactic acid)/poly[(butylene succinate)‐co‐adipate]/clay ternary nanocomposites

A series of blends based on poly(lactic acid) (PLA) and poly[(butylene succinate)‐co‐adipate] (PBSA) as well as their nanocomposites with nanoclay (PLA/PBSA/Clay ternary nanocomposites) were prepared using the twin‐screw extruder. The blends were prepared for PBSA contents ranging from 25 to 75 wt % and their corresponding nanocomposites were prepared at a single‐clay concentration. The morphology and structure of the blends and the nanocomposites were examined using field emission scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. Rheological properties (dynamic oscillatory shear measurements and elongational viscosities) of the blends, nanocomposites, and pure components were studied in detail. The strain hardening intensity of different blends and nanocomposites was compared with the behavior of the pure components. Strong strain hardening behavior was observed for blends composed of 50 wt % and higher PBSA content. However, the effect of PBSA content on the elongational viscosity was less pronounced in PLA/PBSA/Clay ternary nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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     

Miscibility,crystallization, and mechanical properties of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)/ poly(butylene succinate) blends

Naturally amorphous biopolyester poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) containing 21 mol % of 4HB was blended with semi‐crystal poly(butylene succinate) (PBS) with an aim to improve the properties of aliphatic polyesters. The effect of PBS contents on miscibility, thermal properties, crystallization kinetics, and mechanical property of the blends was evaluated by DSC, TGA, FTIR, wide‐angle X‐ray diffractometer (WAXD), Scanning Electron Microscope (SEM), and universal material testing machine. The thermal stability of P3/4HB was enhanced by blending with PBS. When PBS content is less than 30 wt %, the two polymers show better miscibility and their crystallization trend was enhanced by each other. The optimum mechanical properties were observed at the 5–10 wt % PBS blends. However, when the PBS content is more than 30 wt %, phase inversion happened. And the two polymers give lower miscibility and poor mechanical properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Biodegradable poly (butylene succinate‐co‐cyclohexanedimethylene succinate): Synthesis,crystallization, morphology,and rheology

Poly (butylene succinate‐co‐cyclohexanedimethylene succinate) (PBCSs), which are composed of various amounts of cyclohexanedimethylene succinate (CS) with butylene succinate (BS) were synthesized via polycondensation. The composition of PBCSs was analyzed by a ¹H‐nuclear magnetic resonance (¹H‐NMR). Crystallization, morphology, and rheological properties of PBCSs were investigated by a polarized optical microscopy (POM), a differential scanning calorimetry (DSC), a X‐ray diffraction (XRD), and a parallel‐plate rheometer (PPR). The studies revealed that the composition of PBCSs played an important role in controlling their properties. Only one T_g can be seen for PBCSs by DSC, which demonstrate they are miscible copolymers. PBCSs exhibited lower crystallization capacity than its homopolyesters either Poly (butylene succinate) (PBS) or poly (cyclohexanedimethylene succinate) (PCS). It also proved that the cyclohexyl group of CHDM not only affected the crystalline formation, but also changed spherulitic morphology during crystallization. The spherulitic size gradually decreased with an increase of CS content. When CS content approached 50 wt %, the crystallization ability reached minimum. By comparing the effect of temperature with shear rate, it concluded that the viscosities of PBCSs were more sensitive to temperature rather than shear rate, and flow activation energies of PBCSs linearly increased with an increase of CS content. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40103.     

Hydrolytic degradation of biobased poly(butylene succinate‐co‐furandicarboxylate) and poly(butylene adipate‐co‐furandicarboxylate) copolyesters under mild conditions

It is indispensable to investigate hydrolytic degradation behavior to develop novel (bio)degradable polyesters. Biobased and biodegradable copolyesters poly(butylene adipate‐co ‐butylene furandicarboxylate) (PBAF) and poly(butylene succinate‐co ‐butylene furandicarboxylate) (PBSF) with BF molar fraction (?_BF) between 40 and 60% were synthesized in this study. The hydrolytic degradation of film samples was conducted in a pH 7.0 PBS buffer solution at 25 °C. Slight mass loss (1–2%) but significant decrease in intrinsic viscosity (35–44%) was observed after 22 weeks. The apparent hydrolytic degradation rate decreased with increasing ?_BF and initial crystallinity. Meanwhile, PBAFs degraded slightly faster than PBSFs with the same composition. The ?_BF and crystallinity increased slowly with degradation time, suggesting the aliphatic moiety and the amorphous region are more susceptible to hydrolysis. And high enough tensile properties were retained after hydrolysis degradation, indicating PBAF and PBSF copolyesters are hydrolytically degradable, with tunable hydrolytic degradation rate and good balance between hydrolytic degradability and durability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44674.     

Synthesis and characterization of poly(butylene terephthalate)‐co‐poly(butylene succinate)‐block‐poly(ethylene glycol) segmented block copolymers

Poly(butylene terephthalate)‐co‐poly(butylene succinate)‐block‐poly(ethylene glycol) segmented random copolymers, with poly(butylene succinate) (PBS) molar fraction (M_PBS) varying from 10 to 60 %, were synthesized through a melt polycondensation process and characterized by means of GPC, NMR, DSC and mechanical testing. The number‐average relative molecular mass of the copolymers was higher than 4 × 10⁴ g mol^?1 with polydispersity below 1.9. Sequence distribution analysis on the two types of hard segments by means of ¹H NMR revealed that the number‐average sequence length of PBT decreased from 2.80 to 1.23, while that of PBS increased from 1.27 to 4.76 with increasing M_PBS. The random distribution of hard segments was also justified because of the degree of randomness around 1.0. Micro‐phase separation structure was verified for the appearance of two glass transition temperatures and two melting points, respectively, in DSC thermograms of most samples. The crystallinity of hard segments changed with the crystallizability controlled by the average sequence length and reached the minimum value at an M_PBS of about 50–60 mol%. The results can also be ascribed to the co‐crystallization between two structurally analogous hard segments. Mechanical testing results demonstrated that incorporating a certain amount of PBS moieties (less than 30 mol%), at the expense of a minute depression of the elastic modulus, that higher relative elongation and more flexibility of polymer chain could be expected. Maximum equilibrium water absorption and faster degradation rates were observed on samples with higher M_PBS values and lower crystallinity of hard segments were better hydrophilicity of the polymer chain, through in vitro degradation experiments. Copyright © 2003 Society of Chemical Industry     

Peroxide modification of poly(butylene adipate‐co‐succinate)

We attempted to introduce crosslinking into poly(butylene adipate‐co‐succinate) (PBAS) to improve the properties, such as the mechanical strength and elasticity, by a simple addition of dicumyl peroxide (DCP). Prior to curing, the thermal stability of PBAS was investigated. Above 170°C PBAS was severely degraded, and the degradation could not be successfully stabilized by an antioxidant. The PBAS was effectively crosslinked by DCP, and the gel fraction increased as the DCP content increased. A major structure of the crosslinked PBAS was an ester and aliphatic group. The tensile strength and elongation of PBAS were improved with an increasing content of DCP, but there was little affect on the tear strength. The biodegradability of crosslinked PBAS was not seriously deteriorated. A higher degree of crosslinking gave a lower heat of crystallization and heat of fusion. However, the melt crystallization temperatures of the crosslinked PBAS were higher than that of PBAS. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 637–645, 2001     

Crystallization,morphology, and mechanical properties of poly(butylene succinate)/poly(ethylene oxide)‐polyhedral oligomeric silsesquioxane nanocomposites

The biodegradable poly(butylene succinate) (PBS)/poly(ethylene oxide)‐polyhedral oligomeric silsesquioxane (PEO‐POSS) nanocomposites were prepared by the solution blending and melt‐injection methods. The effect of PEO‐POSS on the non‐isothermal and isothermal crystallization, morphology, as well as mechanical properties of PBS was carefully investigated. The PEO‐POSS nanoparticles dispersed well in the PBS matrix, with the diameters around 30 nm. From isothermal crystallization analysis, the incorporation of PEO‐POSS enhanced the crystallization of PBS due to the heterogeneous nucleation effect while the crystal structure of PBS remained. PBS/PEO‐POSS nanocomposites showed of higher glass transition temperatures than that of neat PBS, attributing to the existence of PEO‐POSS decreasing the flexibility of PBS chains. The elongation at break of the PBS/PEO‐POSS nanocomposites reached the maximum value with PEO‐POSS content of 5 wt%. However, the elastic modulus of PBS decreased after the incorporation of PEO‐POSS. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

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