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1987
Naoum, M. M., G. R. Saad, M. M. Abdel-Moteleb, H. G. Shinouda, and H. A. Rizk, "Dielectric polarization and molecular interaction. Part I. Acetoacetanilide and benzoylacetanilide-triethylamine-benzene systems", Canadian Journal of Chemistry, vol. 65, issue 12, pp. 2760 - 2763, 1987. AbstractWebsite

The apparent molecular polarization at infinite dilution of acetoacetanilide, and benzoylacetanilide in five constant-ratio mixtures of triethylamine in benzene leads to the inference that the equilibrium constants of the association process between the anilide and the amine in benzene are 357 and 600, and that the dipole moments of the complexes formed are 4.43 and 5.25 D, respectively.

1988
Naoum, M. M., and G. R. Saad, "Solvent effect on tautomeric equilibria and dipole moments of some alpha substituted benzoylacetanilides", Journal of Solution Chemistry, vol. 17, issue 1, pp. 67 - 76, 1988. AbstractWebsite

Based on dipole moment measurements, a study was made of the keto-enol equilibria of five alpha substituted benzoylacetanilide derivatives in two non-polar and one polar solvents at 30°C. The enol mole fractions of the compounds investigated were determined by analysis of their ultraviolet spectra. The same type of study was extended to salicylanilide for its resemblance to the enol tautomer of these compounds. A deduction of the most probable configurations of the keto and enol forms was tentatively made through a comparison between the dipole moments of some suggested configurations for these forms of benzoylacetanilide and those measured in benzene for the alpha methyl benzoylacetanilide and salicylanilide, respectively. These inferred configurations were used to calculate the dipole moments of both tautomers of the other compounds, and consequently, the dipole moment values of their tautomeric mixtures in dioxane and chloroform. A comparison between the dipole moment values of their tautomeric mixtures in dioxane and chloroform. A comparison between the dipole moment values calculated in this way and those measured indicated a solute-solvent interaction with dioxane, which chloroform behaved as a non-interacting solvent. © 1987 Plenum Publishing Corporation.

1989
Mikhael, M. G., S. M. Mokhtar, G. R. Saad, M. M. Naoum, and M. Z. Elsabee, "Copolymerization and interaction of acrylonitrile and indene", Journal of Polymer Science Part A: Polymer Chemistry, vol. 27, issue 1, pp. 185 - 191, 1989. AbstractWebsite

The donor–acceptor interaction of acrylonitrile (AN) with indene (In) has been investigated by means of ultraviolet spectroscopy and dielectric polarization measurements. The latter method yielded a value of 0.5 for the association constant of the charge‐transfer‐complex (CTC) and a 4.02 D for its dipole moment. The copolymerization of the two monomers was characterized by a tendency towards alternation when conducted in the bulk. This might be due to the participation of a weak CTC in the process of copolymerization. However, this tendency disappeared in polar solvents such as DMF. Copyright © 1989 John Wiley & Sons, Inc.

1992
Saad, G. R., M. G. Botros, and R. I. Nessim, "Dielectric study of acetylated cotton cellulose and saponified cellulose acetate", Die Angewandte Makromolekulare Chemie, vol. 197, issue 1, pp. 23 - 39, 1992. AbstractWebsite

Dielectric relaxation data are reported at frequencies of 0.1 – 10000 kHz over a temperature range of 10–80°C on cellulose acetates of different degrees of substitution, and on saponified cellulose acetate. The acetyl substitution is found to remove the low‐frequency relaxation process, γ, previously observed in medicated cotton cellulose, and to affect the other higher‐frequency process, β, in different ways, depending on the acetyl content. Conversely, saponification of cellulose acetate leads to the reversion of these two processes but with different features. Analysis of the absorption bands is made, and an assessment of the results obtained is given. © 1992 Hüthig & Wepf Verlag, Basel

Abdel Moteleb, M. M., G. R. Saad, and R. I. Nessim, "The effects of preheating on the dielectric relaxation, and of temperature on the 'static' dielectric constant, of cellulose acetate fibers", Polymer Degradation and Stability, vol. 36, issue 3, pp. 217 - 224, 1992. AbstractWebsite

The effect of preheating at 140°C and 180°C on the dielectric relaxation of cellulose acetate of degree of substitution 1·90 has been investigated, together with the dependence on temperature over the range 80-200°C of the 'static' dielectric constant of variously acetylated cellulose samples. The results obtained are discussed in terms of progressive gain of compact structure, together with the initiation of crystallization at a temperature governed by the acetyl content in the fiber. Phase changes involving discontinuity in the first variation of the 'static' dielectric constant on heating, and irreversibility of the temperature dependence path on cooling are thus observed. © 1992.

1993
El-Shafee, E., and G. R. Saad, "Dielectric analysis of poly(vinyl chloride) films doped with cobalt(II) chloride", Polymer Degradation and Stability, vol. 41, issue 1, pp. 25 - 29, 1993. AbstractWebsite

The dielectric behaviour of solution-grown thin films of poly(vinyl chloride) containing cobalt(II) chloride as dopant was investigated within the temperature range 20-120°C and a 1-100 kHz frequency band. When correction was made for a conduction effect at low frequency, a high-temperature glass-transition relaxation process was observed in addition to the ordinary glass-transition process of pure PVC. The former was thus considered to be a cluster-ionic transition process which might be due to a phase-separation behaviour. The effect of moisture uptake by the doped films on the electrical properties is discussed. © 1993.

Nessim, R. I., M. G. Botros, G. R. Saad, and M. M. Shalaby, "Frequency dependence of the complex dielectric constant of sodium carboxymethyl cellulose", Die Angewandte Makromolekulare Chemie, vol. 204, issue 1, pp. 51 - 61, 1993. AbstractWebsite

The dielectric constant, ε′, and dielectric loss, ε″, were determined for three solid carboxymethyl cellulose samples having different levels of substitution and different degrees of polymerization over a frequency range of 0.1 – 10 000 kHz at temperatures from 10–60°C. In contrast to the two relaxation processes, γ and β, previously observed in native cotton cellulose, only one relaxation process within a frequency range of 0.1 – 1 kHz was identified. It was found that the dielectric properties do not only depend on the degree of substitution, but also on the weight‐average degree of polymerization and uniformity of distribution. © 1993 Hüthig & Wepf Verlag, Basel

1994
Saad, G. R., "Dielectric behaviour of cyanoethylated cellulose", Polymer International, vol. 34, issue 4, pp. 411 - 415, 1994. AbstractWebsite

The dielectric characteristics of cyanoethylated cellulose samples having different degrees of substitution have been investigated at different frequencies from 0.1 to 10 KHz and at temperatures from −40°C to 180°C. Two relaxation processes, designated as α and β in order of decreasing temperature, were recognised. The low temperature β‐relaxation is expected to be due to local motion of anhydroglucose rings, while the α‐relaxation is related to the side group motion. The data obtained are discussed in terms of the progressive destruction of the fibre structure, together with the increase of side group polarity due to cyanoethylation. © 1994 Society of Chemical Industry

Moteleb, M. M. A., M. M. Naoum, M. M. Shalaby, and G. R. Saad, "Dielectric investigation of isotropic and anisotropic solutions of hydroxypropyl cellulose in dioxan", Polymer International, vol. 34, issue 4, pp. 363 - 367, 1994. AbstractWebsite

The dielectric behaviour of hydroxypropyl cellulose in dioxan has been studied at 10–50°C over a range of concentration of 10–55 wt% to include the isotropic and anisotropic phases. The study showed that the loss maximum ε″ max magnitude of polarization ε 0 − ε ∞ relaxation time 1/2πf m degree of broadening of the absorption curves 1–h or α, and the mean‐square dipole moment 〈gμ 2 〉, steadily increase with concentration up to 42 wt%, above which a rapid decrease takes place. This indicates that the isotropic solution transforms to an anisotropic solution with a smaller mean dipole moment. The critical concentration is realized to be temperature invariant. This was evidenced by measuring the refractive index of solutions covering the same concentration and temperature ranges. © 1994 Society of Chemical Industry

El-Shafee, E., and G. R. Saad, "A dielectric study of the photodegradation of poly(vinyl chloride) in air", Polymer Degradation and Stability, vol. 43, issue 3, pp. 315 - 318, 1994. AbstractWebsite

The dielectric absorption caused by dipolar relaxation of poly(vinyl chloride) photolytically degraded in air, using ultraviolet radiation, was studied on samples in the form of cast thin films. It was found that with the progress of photodegradation over a period of 10 h at 35 ± 2°C, the change in the magnitude of the dielectric parameters ε{lunate}m′', ε{lunate}0-ε{lunate}∞, ΔHε{lunate}0 and α can be practically represented as a three-staged process. © 1994.

1995
Saad, G. R., E. El-Shafee, and M. W. Sabaa, "Dielectric and mechanical properties in the photodegradation of poly(vinyl butyral) films", Polymer Degradation and Stability, vol. 47, issue 2, pp. 209 - 215, 1995. AbstractWebsite

The dielectric behaviour of unirradiated and irradiated PVB films, using UV radiation, was investigated as a function of temperature and frequency. The results obtained are discussed in terms of the dielectric parameters εmaxH, Δε, β and ΔE. These experimental results, in combination with the temperature dependence of dynamic mechanical measurements in the tensile mode and with d.s.c measurements, show that during UV irradiation of PVB, besides other changes, cross-linking predominates. A mechanism of photodegradation has been proposed and is supported by gel content determination and IR spectra. © 1995.

Naoum, M. M., M. M. A. Moteleb, M. M. Shalaby, and G. R. Saad, "Dielectric investigation of isotropic and anisotropic solutions of cellulose acetate in dioxane", Polymer International, vol. 37, issue 1, pp. 27 - 32, 1995. AbstractWebsite

The dielectric and optical characteristics of a sample of cellulose acetate (DS = 2.45) in dioxane solutions were studied at 10–50°C of concentration 10–50 wt% to include both isotropic and anisotropic phases. The study showed that the loss maximum, εmax″, magnitude of polarization, (ε0 − ε∞), static dielectric constant, ε0, time of relation, (2πfm)−1, and refractive index, nD, steadily increase with concentration up to the critical concentration (41 wt%) and then decrease. The mean‐square dipole moment, 〈gμ2〉, decreases steadily up to the critical concentration then remains nearly constant, indicating that the isotropic solution changes to anisotropic, with smaller mean‐square dipole moment. Comparison between the results of cellulose acetate (CA) and those of hydroxypropyl cellulose (HPC) reveals that, at the critical concentration in dioxane, the cholesteric structure of HPC possesses a greater mean‐square dipole moment with higher temperature coefficient than does CA. The activation energy of the relaxation process for hydroxypropyl cellulose is higher, indicating a greater intrachain interaction compared with cellulose acetate. © 1995 Society of Chemical Industry

Moteleb, M. M. A., and G. R. Saad, "Effect of high temperatures on the dielectric behaviour of viscose fibres at low frequency", Polymer International, vol. 37, issue 4, pp. 261 - 265, 1995. AbstractWebsite

Commercial and purified viscose fibres exhibit dielectric dispersion and a loss peak within the frequency range 0.05–1 k c/s and at temperatures of 80–140°C. Such high temperature relaxation is local in nature and is attributed to side group motion. The characteristics of the absorption bands of these samples are compared and the results obtained are interpreted. The variation of the dielectric constant with temperature showed a second order transition at about 110°C with these samples, which disappears on hydrolysis. © 1995 Society of Chemical Industry

1996
Saad, G. R., "Dielectric study of β-relaxation in some cellulosic substances", Polymer International, vol. 41, issue 3, pp. 293 - 299, 1996. AbstractWebsite

6-(2-Cyanoethylamino)-6-deoxycellulose (Cell-CEA) as a novel cellulose derivative was prepared from 6-bromo-6-deoxycellulose. The influence of the reaction conditions on the degree of substitution was studied in detail. The dielectric characteristics of a Cell-CEA sample having degree of substitution of 0-86, together with those of microcrystalline and regenerated celluloses, have been investigated in the temperature range from -60 to 120°C, and frequency range 30 Hz to 100 kHz. One relaxation process, designated as β, was recognised, which was attributed to side-group motions, probably -CH2X (X = OH or NHCH2CH2CN). The higher activation energy of this process and the shift to higher temperature in Cell-CEA, compared with microcrystalline and regenerated celluloses, reflects the enhanced steric constraints involved in the motion of the bulkier, -CH2NHCH2CH2CN, side groups. The results obtained are discussed in terms of the dielectric parameters ε″max β̄ and Δε. © 1996 SCI.

1997
Saad, G. R., A. A. Mansour, and A. H. Hamed, "Dielectric investigation of cold crystallization of poly(3-hydroxybutyrate)", Polymer, vol. 38, issue 16, pp. 4091 - 4096, 1997. AbstractWebsite

The dielectric behaviour of poly(3-hydroxybutyrate) (PHB) has been investigated for the glass (α) relaxation in the temperature and frequency ranges of -60 to 100deg;C and 103-105Hz, respectively. Also, the crystallization kinetics of PHB has been studied dielectrically as a function of heating rate, time and temperature. Crystallinity has a marked influence on the glass relaxation characteristics owing to the relative constraint imposed on the amorphous phase by the crystallites. Furthermore, the results obtained showed that: (1) the optimum crystallization temperature is about 25°C; (2) the time at which crystallization starts is a function of the working temperatures and apparently is reduced to just a few minutes at 40°C; and (3) the crystallization process is completed within a period of less than 1 h in the temperature range 20-40°C. The bulk crystallization phenomena could be also described by the Avrami equation with an exponent ∼ 3.8. © 1997 Elsevier Science Ltd.

Naoum, M. M., G. R. Saad, R. I. Nessim, T. A. Abdel-Aziz, and H. Seliger, "Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures. II. 4-Hexadecyloxyphenyl arylates and aryl 4-hexadecyloxy benzoates", Liquid Crystals, vol. 23, issue 6, pp. 789 - 795, 1997. AbstractWebsite

4-Hexadecyloxyphenyl-4′-substituted benzoates, Ia-d, and 4-substituted phenyl-4′-hexadecyloxy benzoates, IIa-d, with the substituents CH3O, Cl, CN, and NO2, respectively, were prepared and characterized by infrared spectroscopy and the apparent solution dipole moment measured using cyclohexane as a solvent. Smectic A mesophase stability was investigated by differential scanning calorimetry and polarized light microscopy. The effects of structural changes on phase transitions in these two series of compounds are discussed in terms of dipole and mesomeric effects.

Saad, G. R., and K. - I. Furuhata, "Effect of substituents on dielectric β-relaxation in cellulose", Polymer International, vol. 42, issue 4, pp. 356 - 362, 1997. AbstractWebsite

The dielectric characteristics for some cellulose derivatives, namely chlorodeoxycellulose (Cell-Cl; degree of substitution of chlorine, DSCl = 0·87), bromodeoxycellulose (Cell-Br; DSBr = 0·92)and thiocyanatodeoxycellulose (Cell-SCN; DSSCN = 0·88), all substituted only at C-6, together with those of regenerated cellulose, have been investigated in the temperature range -60 to 120°C, and in the frequency range 0·2-100 kHz. Only one relaxation process, designated as β, was identified within the frequency and temperature ranges studied. The activation energy of this relaxation increases in the order Cell-Cl < Cell-Br < Cell-SCN, suggesting that the bulkiness of the substituent was the determining factor of the activation energy. The characteristic dielectric parameters, namely polarization magnitude (Δε) and shape parameter (α or β̄), were obtained by the analysis of absorption bands and are discussed in relation to the substituent effect.

1998
Naoum, M. M., G. R. Saad, R. I. Nessim, and T. A. A. Aziz, "Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures III. Binary mixtures of alkoxyphenyl arylates and arylalkoxybenzoates", Liquid Crystals, vol. 25, issue 2, pp. 165 - 173, 1998. AbstractWebsite

4-Substituted phenyl-4-hexadecyloxybenzoates and 4-hexadecyloxyphenyl-4-substituted benzoates were prepared and thermally characterized by differential scanning calorimetry. Transition temperatures were identified by polarized-light microscopy. Substituents were chosen to cover a wide range of electronic and dipolar characteristics. Binary mixtures of different components were prepared and similarly characterized to construct their phase diagrams. In mixtures of the 4-CN and 4-NO2 analogues, enhanced SmA mesophases were found when either of these esters was mixed with one of the methoxy analogues. A weak molecular complex is proposed to account for this non-ideal solution behaviour. Linear or slightly enhanced mixture behaviours were found for the nitro or cyano derivatives when mixed with each other. The results are interpreted in terms of electronic, dipolar, and molecular interactions. © 1998 Taylor & Francis Group, LLC.

Naoum, M. M., R. I. Nessim, G. R. Saad, and T. A. A. Aziz, "Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures IV. Dependence of Tc on the anisotropy of the aryl-X of polarizability bond", Liquid Crystals, vol. 25, issue 1, pp. 73 - 83, 1998. AbstractWebsite

Transition temperatures of binary mixtures of the two series, 4-hexadecyloxyphenyl-4- substituted benzoates (Ia-d) and 4-substituted phenyl-4-hexadecyloxybenzoates (IIa-d), have been determined on cooling and the phase diagrams compared with those previously obtained on heating. Tc values for the monotropes and the non-LC analogues have been evaluated by extrapolation. Examination of both series revealed that the square root of Tc is related to the polarizability anisotropy, Delta alphaX, of the CAr-X bond, except for the methoxy derivatives. © 1998 Taylor & Francis Group, LLC.

Saad, G. R., R. I. Nessim, and M. M. Naoum, "Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures V. Mixtures of bimolecular smectics and linear mesogens", Liquid Crystals, vol. 25, issue 6, pp. 655 - 660, 1998. AbstractWebsite

Two binary mixtures, prepared from either 4-cyanophenyl 4-hexadecyloxybenzoate (Ib) or 4-nitrophenyl 4-hexadecyloxybenzoate (Ic), with 4-carboxyphenyl 4-hexadecyloxybenzoate (Ia), were thermally characterized to construct the phase diagrams for the two systems Ia/Ib and Ia/Ic. Due to differences in the smectic layering between the individual components of each system, phase separation took place either in the solid or in the mesophase. A mathematical relation was derived to calculate the composition of each phase in the solid state. Another two phase diagrams were constructed for binary mixtures of the linear dimer molecule, 4-hexadecyloxybenzoic acid (III) with either the acid Ia or its isomeric derivative, 4-hexadecyloxyphenyl 4-carboxybenzoate (II).

1999
Saad, G. R., and R. I. Nessim, "Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures VI[1]. The effect of molecular length", Liquid Crystals, vol. 26, issue 5, pp. 629 - 636, 1999. AbstractWebsite

The apparent solution dipole moments of compounds based on 4,4-di-substituted phenyl benzoate (ROC6H4COOC6H4X), I, where X is a cyano group and R a terminal linear alkyl chain ranging from C12 to C20, were determined in cyclohexane at 30 C. The compounds were also thermally characterized by polarized light microscopy and differential scanning calorimetry. Phase diagrams were constructed for various binary mixtures prepared from any two homologues of series I as well as for every one of them with the nitro analogue II, where X is a nitro group and R C16H33. The study was undertaken in order to investigate the effect of the alkyl chain length on the mesophase behaviour. In order to assess the influence of structural variation in the central mesogenic group on the mesophase stability of pure and mixed compounds, the investigation was extended to cover binary mixtures of any two of the three compounds: analogue II (X=OC16H33), and the symmetric dialkoxy substituted phenyl esters (C16H33OC6H4COO)2 A, where A is the 1,4-phenylene group (IV) or 4,4-biphenylene (V). © 1999 Taylor & Francis Group, LLC.

Mansour, A. A., G. R. Saad, and A. H. Hamed, "II. Dielectric investigation of cold crystallization of poly(3- hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)", Polymer, vol. 40, issue 19, pp. 5377 - 5391, 1999. AbstractWebsite

The dielectric relaxation behavior of a series of amorphous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3-HB-co-3-HV) having the hydroxyvalerate content: 0, 7, 14, 20 and 24 mol%, was investigated at the temperature and frequency ranges of 0°-100 °C and 103-105 Hz, respectively. The dielectric spectra showed that the crystallization process starts during the temperature scan measurements at approximately 30 °C regardless of the 3-HV-content. All samples of P(3-HB-co-3-HV) exhibited very similar relaxation spectra indicating the preservation of the main features of P(3-HB). However, some differences were observed in the relaxation spectra including the peak height, the onset crystallization temperature and the activation behavior. It is suggested that these differences observed in the various samples of the copolyester containing different 3-HV content are mainly controlled by: (1) the rate of crystallization, (2) the ultimate percentage of crystallinity, and; (3) the heating rate of measurements. Comparison of the onset crystallization temperature, Tonset, of different samples showed that the higher the 3-HV contents, the higher is onset temperature. However, measurements of Tonest, at different heating rates showed the lower the rate, the weaker is the composition dependence of the onset temperature, so that the zero-rate onset temperature could be considered to be independent of the 3-HV content and equals that of pure P(3-HB). In addition, the study of the kinetics of cold crystallization showed that while the onset crystallization time is shortened from 14 to 4 min. by increasing the 3-HV-content from 0 to 24% HV, the offset crystallization time is extended from 65 to 150 min. Moreover, by fitting the experimental results using Avrami equation to calculate the mechanistic exponent `n' the results showed surprisingly that `n' changes from 3.8 to approximately 2, approximately 2 and approximately 1 for samples containing 0, 7, 14, 20 and 24% HV, respectively. This change indicated the existence of mechanistic changes in the cold crystallization process. The results obtained are discussed and correlated to the literature data.The dielectric relaxation behavior of a series of amorphous poly(3- hydroxybutyrate-co-3-hydroxyvalerate) P(3-HB-co-3-HV) having the hydroxyvalerate content: 0, 7, 14, 20 and 24 mol%, was investigated at the temperature and frequency ranges of 0°- 100°C and 103-105 Hz, respectively. The dielectric spectra showed that the crystallization process starts during the temperature scan measurements at ~ 30°C regardless of the 3-HV-content. All samples of P(3-HB-co-3-HV) exhibited very similar relaxation spectra indicating the preservation of the main features of P(3- HB). However, some differences were observed in the relaxation spectra including the peak height, the onset crystallization temperature and the activation behavior. It is suggested that these differences observed in the various samples of the copolyester containing different 3-HV content are mainly controlled by: (1) the rate of crystallization, (2) the ultimate percentage of crystallinity, and; (3) the heating rate of measurements. Comparison of the onset crystallization temperature, T(onset), of different samples showed that the higher the 3-HV contents, the higher is onset temperature. However, measurements of T(onest), at different heating rates showed the lower the rate, the weaker is the composition dependence of the onset temperature, so that the zero-rate onset temperature could be considered to be independent of the 3-HV content and equals that of pure P(3- HB). In addition, the study of the kinetics of cold crystallization showed that while the onset crystallization time is shortened from 14 to 4 min. by increasing the 3-HV-content from 0 to 24% HV, the offset crystallisation time is extended from 65 to 150 min. Moreover, by fitting the experimental results using Avrami equation to calculate the mechanistic exponent 'n' the results showed surprisingly that 'n' changes from 3.8 to ~2, ~2 and ~1 for samples containing 0, 7, 14, 20 and 24% HV, respectively. This change indicated the existence of mechanistic changes in the cold crystallization process. The results obtained are discussed and correlated to the literature data.

2001
Saad, G. R., "Calorimetric and Dielectric Study of the Segmented Biodegradable Poly(ester-urethane)s Based on Bacterial Poly[(R)-3-hydroxybutyrate]", Macromolecular Bioscience, vol. 1, issue 9, pp. 387 - 396, 2001. AbstractWebsite

Two series of segmented poly(ester-urethane)s were synthesized from bacterial poly[(R)-3-hydroxybutyrate]-diol (PHB-diol), as hard segments, and either poly(ε-caprolactone)-diol (PCL-diol) or poly(butylene adipate)-diol (PBA-diol), as soft segments, using 1,6-hexamethylene diisocyanate as a chain extender. The hard-segment content varied from 0 to 50 wt.-%. These material were characterized using 1H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the Tg of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard-segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results also showed that the crystallization of soft or hard segments was physically constrained by the microstructure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester-urethane)s, based on PCL and PHB, showed two primary relaxation processes, designate as aS and aH, which correspond to glass-rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester-urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard-segment content. It was concluded from these results that our investigated materials exhibit micro-phase separation of the hard and soft segments in the amorphous domains.

Saad, G. R., "Calorimetric and dielectric study of the segmented biodegradable poly(ester-urethane)s based on bacterial poly[(R)-3-hydroxybutyrate]", Macromolecular Chemistry and Physics, vol. 202, issue 18, pp. 387 - 396, 2001. AbstractWebsite

Two series of segmented poly(ester-urethane)s were synthesized from bacterial poly[(R)-3-hydroxybutyrate]-diol (PHB-diol), as hard segments, and either poly(ε-caprolactone)-diol (PCL-diol) or poly(butylene adipate)-diol (PBA-diol), as soft segments, using 1,6-hexamethylene diisocyanate as a chain extender. The hard-segment content varied from 0 to 50 wt.-%. These materials were characterized using 1H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the Tg of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard-segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results showed that the crystallization of soft or hard segments was physically constrained by the micro-structure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester-urethane)s, based on PCL and PHB, showed two primary relaxation processes, designated as αs and αH, which correspond to glass-rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester-urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard-segment content. It was concluded from these results that our investigated materials exhibit micro-phase separation of the hard and soft segment in the amorphous domains.

El-Shafee, E., G. R. Saad, and S. M. Fahmy, "Miscibility, crystallization and phase structure of poly(3-hydroxybutyrate)/cellulose acetate butyrate blends", European Polymer Journal, vol. 37, issue 10, pp. 2091 - 2104, 2001. AbstractWebsite

Blends of poly(3-hydroxybutyrate) (PHB) with cellulose acetate butyrate (CAB) were prepared by solution casting from chloroform solutions at different compositions. The miscibility, crystallization behavior and phase structure were investigated using differential scanning calorimetry, optical microscopy and small-angle X-ray scattering (SAXS). CAB/PHB blends were found to be miscible in the melt state as evidenced by the deduction of a single glass transition (Tg) for each composition, a depression in the equilibrium melting point of PHB, and a marked reduction in the spherulites growth rate of PHB in the PHB/CAB blends. The Flory-Huggins interaction parameter (χ12), obtained from melting point depression data, is composition dependent, and its value is always negative. The nucleation factor, Kg, was determined using Lauritzen-Hoffman model. The Kg values for the PHB in the blends are considerably lower than the Kg value in the pure homopolymer. The phase structure of the blend in the solid state as revealed by SAXS is characterized by the presence of a homogeneous amorphous phase situated mainly in the interlamellar regions of crystalline PHB and consisting of CAB molecules and uncrystalline PHB chains. © 2001 Elsevier Science Ltd. All rights reserved.