Les polymères semi-cristallins à chaînes semi-rigides, bien qu’abondamment utilisés dans la vie quotidienne, représentent des systèmes complexes qui ne sont pas encore parfaitement compris. Parmi les nombreux domaines de recherche sur cette famille de polymères, l’étude de la morphologie semi-cristalline et des processus de cristallisation et de fusion de ceux-ci restent des sujets très importants. L’investigation de la morphologie semi-cristalline est rendue difficile car elle présente une structure hiérarchique composée de plusieurs niveaux d’organisation, dont le plus petit est observable à une échelle très réduite de quelques nanomètres. De plus, les aspects liés à la cinétique des processus de cristallisation et de fusion n’ont pas toujours permis de bien les mettre en évidences, les rendant ainsi par très bien compris. Cependant, les nouvelles avancées technologiques dans le domaine de la physique expérimentales ont beaucoup profité à la science des polymères. Dans ce travail, une contribution originale est apportée à cette étude, et cela en combinant diverses techniques expérimentales permettant des mesures calorifiques et structurales en températures et temps réels. L’intérêt c’est porté sur les polymères linéaires aromatiques tels que le polyéthylènes teréphthalate, PET, et le polytriméthylène téréphthalate, PTT, caractérisés par une température de transition vitreuse supérieure à l’ambiante ( Tg > 50°) et une température de fusion élevée (Tm>220°C), offrant ainsi une assez large gamme de température de cristallisation (Tm-Tg). L’étude de la structure semi-cristalline du PET à l’échelle du nanomètre et de la relaxation des phases amorphes présentes dans sa structure est facilitée par l’utilisation d’un diluant amorphe tel que le polyétherimide (PEI), qui forme un mélange miscible avec le PET. L’utilisation de microscopie de force atomique AFM à haute température a permis d’observer la cristallisation isotherme de PET en temps réel et de décrire ainsi la cristallisation secondaire comme un processus d'épaississement des piles lamellaires. De plus, l’analyse de la structure semi-cristalline du PET et du PTT, dans l’espace direct, sont en faveur d’un modèle structural homogène, où l’épaisseur lamellaire moyenne est légèrement inférieure à l’épaisseur moyenne des régions amorphes interlamellaires. Ces résultats ont permis, d’une part, d’apporter une meilleure interprétation aux données obtenues par diffusion des rayons X aux petits angles (SAXS), et d’autre part, d’ interpréter le comportement de fusion multiple caractéristique des polymères semi-cristallin à chaînes semi-rigides par le seul processus de fusion-recristallisation. Dans l’étude investiguée sur les mélanges PET/PEI et sur le PTT pur, on montre que la cinétique d’un tel processus est particulièrement rapide comparée à la cristallisation. De plus, les observations par AFM et par microscopie optique de même que les mesures SAXS en temps réel ont montré la simultanéité et la compétition existant entre la fusion des cristaux et leur réorganisation durant la chauffe. Par ailleurs, la relaxation des régions amorphes interlamellaires, souvent considérées comme rigides, a pu être mise en évidence par les mesures AFM et SAXS réalisées à haute température sur des échantillons de PET/PEI semi-cristallins.

Oral drug administration remains the most popular route of drug delivery. Absorption of the dissolved drug through the intestinal epithelial membrane is a prerequisite to systemic bioavailability and drug efficacy. In efforts to reduce the long lead times, attrition rates, and costs of drug discovery and development, computational models have been developed to predict the membrane permeability and absorption efficiency of a dosed drug. Many models utilize various molecular descriptors to correlate with in vitro permeability or human intestinal absorption data. It is widely accepted that the two most significant physicochemical properties that control a compound's passive transport process are its aqueous solubility and lipophilicity characteristics.This work will discuss the theoretical background of passive transport, a number of computational models developed to predict in vitro permeability, other models that predict human fraction of dose absorbed, and predicting absorption efficiency relative to a maximum dose. A newly developed prediction method is also presented, that reveals an interesting relationship between fraction absorbed and the melting point of the drug.

No description available.

A small amount of poly(trimethylene succinate) (PTSu) were copolymerized or blended with poly(butylenes succinate) (PBSu) in this study. The range of intrinsic viscosity for PBSu and PBSu-enriched copolymers are between 1.62 and 0.97 dL/g; number-average molecular weights are in the range of 2.5x104 and 11.9x104 g/mol with polydispersity indices ranging from 1.52 to 3.94. Copolymer composition is calculated from 1H and 13C NMR spectra, and the distribution of BS and TS units in these copolymers are supported to be random from the evidence of a single glass transition temperature (Tg) and a randomness value close to 1.0. Tg of PBSu is -40.8 ¢XC. The Tg values of copolymers and blends increased with TS contents. The melting temperature (Tm) and the exothermic heat of crystallization of blends were not strongly affected by blending with PTSu. The values of Avrami exponent (n) for PBSu, copolymers and blends ranging from 2.3 to 3.1 indicate that heterogeneous nucleation with three-dimensional growth and homogeneous nucleation with two-dimensional growth might happen during the crystallization process. Multiple melting behavior was observed for PBSu, PBSu- enriched copolyesters and blends. Their peak temperatures are denoted as Tm1, Tm2 and Tm3 in order of increasing temperature. Tm1 corresponds to the melting temperature of the so-called annealing peak which might be resulted from the competition between continuous melting and re-crystallization. In contrast the peak at Tm2 is attributed to the melting of the primary crystals formed during isothermal crystallization. The peak at Tm3 may arise from the melting of re-crystallized primary crystals. Equilibrium melting temperatures were determined by the Hoffman-Weeks linear extrapolations which yield of 127.4 ¢XC for PBS, 125.7 ¢XC for PBTSA95/05, 120.6 ¢XC for PBTSu90/10, 128.6 ¢XC for PBSu/PTSu 98/02, 127.0 ¢XC for PBSu/PTSu 95/05 and 125.5 ¢XC for PBSu/PTSu 90/10. The thickness coefficient ( ) is located between 0.77 and 0.80. Three characteristics temperatures of thermal degradation, defined as temperature of thermal degradation at begining (Tstart), weight losses of 2% (Tloss2%) and maximum degradation rate (Tmax), were employed to characterize the thermal stability of polyesters and blends. The Tloss2% and Tstart values of PBTSu90/10 are higher than the values of the others because of its unusually high molecular weight. Wide-angle x-ray diffraction patterns were obtained after complete isothermal crystallization. Diffraction peaks are in the same positions, and these peaks become sharper and increase in intensity as the crystallization temperature increases. This indicates that during the heating process, only one crystal form appears and both of the crystallite size and perfect degree increase. The isothermal growth rate of PBSu spherulite increases from 0.01 £gm/sec at 103 ¢XC to 3.33 £gm/sec at 75 ¢XC. When the TS units increase, the spherulitic growth rates of PBTSu95/05 and PBTSu90/10 copolyesters decline dramatically. One of the reasons is that the incorporation of TS units into PBSu significantly inhibits the crystallization behavior of PBSu. Growth rates data were treated with Lauritzen-Hoffman secondary nucleation theory to find the regime transition. Using the Williams-Landel-Ferry (WLF) values, regime II to III transition is found at 95.1 ¢XC for PBSu, 84.4 ¢XC PBTSu95/05, and 77.1 ¢XC for PBTSu 90/10. All melt-crystallized specimens formed two dimensional axial-like spherulites with negative birefringence. Extinction bands were observed when PBSu, PBSu- enriched copolymers and blends specimens were crystallized at large undercooling.

Minor amounts of monomers or homopolymer of poly(butylene succinate) (PBS) were copolymerized or blended with monomers or homopolymer of poly(ethylene succinate) (PES). PEBSA 95/05 represents a copolymer synthesized from a feed ratio of 95 mol% ethylene glycol and 5 mol% 1,4-butanediol with 100 mol% succinic acid. Copolymers PEBSA 90/10 and 50/50 were also synthesized. Blends of PES and PBS were prepared in solution with ratios of PES/PBS: 98/02, 95/05 and 90/10. Molecular weights of homopolymers and copolymers were measured using capillary viscometer and gel permeation chromatography. The results indicate that polyesters used in this study have high molecular weights. The chemical composition and the sequence distribution of co-monomers in copolyesters were determined using 1H NMR and 13C NMR. The distribution of ES and BS units in these copolyesters was found to be random from the evidence of a single Tg and a randomness value close to 1.0 for a random copolymer. Thermal properties of polyesters and blends were characterized using differential scanning calorimeter (DSC), temperature-modulated DSC (TMDSC) and thermogravimeter. For copolymers, melting point of PES significantly decreases from 100.9 to 94.5 to 89.8 oC with an increasing in BS units from 0 to 5 to 10 mol%. Blends keep the intrinsic melting points of PES and PBS homopolymers. There is no significant difference or no trend about the thermal stability of these polyesters and blends. Wide-angle X-ray diffractograms (WAXD) were obtained for specimens after complete isothermal crystallization. Diffraction peaks indicate that the crystal structure of PES is dominated in PES-enriched copolymers. However, PEBSA 50/50 displays weak diffraction peaks of the characteristic peaks of PBS homopolymer. Isothermal crystallization of copolyesters and blends were performed using DSC. Their crystallization kinetics and melting behavior after complete crystallization were analyzed. The n1 values of the Avrami exponent for copolyesters increased from 2.54 to 2.84 as the isothermal temperature (Tc) increased. The Hoffman-Weeks linear plots yielded an equilibrium melting temperature of 111.1 and 107.0 oC, respectively, for PEBSA 95/05 and 90/10. Homopolymer PES has an equilibrium melting temperature of 112.7 oC. For blends, the n1 value has a minimum at Tc of 40 oC then it increases with an increase in Tc or in PBS. At the same Tc, n1 increases slightly and the rate constant (k1) decreases when the ratio of PBS in blends increases. All of these blends gave an equilibrium melting temperature of 113.1 oC. Multiple melting behavior involves melting-recrystallization-remelting and various lamellar crystals. As Tc or BS unit in copolymer increases, the contribution of recrystallization slowly declines. Acetophenone was used a diluent for PES homopolymer. Five concentrations were used to estimate the melting point depression, and the heat of fusion of PES was obtained to have a value of 163.3 J/g according to Flory equation. Spherulitic growth rates of copolymers were measured at Tc between 30 and 80 oC using polarized light microscope (PLM). Maximum growth rates occurred at Tc around 50 oC. It is found that the growth rate of copolymer decreases significantly after randomly incorporating BS units into PES. Non-isothermal method at a cooling rate of 2, 4 or 6 oC/min was used to calculate the isothermal growth rates of copolymers. These continuous data fit very well with the data points measured isothermally. Growth rates data are separately analyzed using the Hoffman-Lauritzen equation. A regime II-III transition is found at 59.4 and 52.4 oC, respectively, for copolyesters PEBSA 95/05 and PEBSA 90/10. The results of DSC and PLM indicate that blend PES/PBS 98/02 not only retains the melting point and the crystallinity of PES homopolymer, but also increases the nucleation rate of this blend. The effect of blending 2 mol% PBS with PES on the biodegradability of PES is deserved to be investigated furthermore.

The compositions of a series of poly (ethylene/trimethylene terephthalate) copolyesters were identified by 1H-NMR and 13C-NMR. The ethylene terephthalate (ET) units are 8.9, 33.7, 37.9, 50.1, 72.5, 77.8, and 90.8% in the copolyesters with sample codes of C2, C3, C4, C5, C6, C7, and C8, respectively. The triad sequence probabilities were determined from the normalized areas of aromatic quaternary carbons. The calculated average-number sequence lengths of ethylene- and trimethylene- terephthalate units range from 1.0 to 10.2 that depends on the relative ratio of both units in the copolymer. The values of randomness parameter for all of these copolyesters are between 0.96 and 1.1. Both values of sequence length and randomness parameter indicate that these copolyesters are random copolymers. Differential scanning calorimeter (DSC) was used to study the isothermal crystallization kinetics and the melting behaviors at heating rates of 10 and 50¢XC/min. The average enthalpy of isothermal crystallization (DH) decreased from 47 to 28 J/g when the ET units in the copolymer increased from 8.9% (C2) to 72.5% (C6), and then the enthalpy increased up to 42 J/g for the C8 copolymer with 90.8% of ET units. The results of Avrami analysis yielded one (n1) or two exponents. The n1 values of all of these copolymers were between 2.03 and 2.98. It suggests that the primary crystallization followed a heterogeneous nucleation with two-three dimensional form of growth. While investigating the isothermal crystallization, DSC specimens were crystallized for 9-14 times of the peak time to ensure the completion of crystallization. Both heating curves at 10 and 50¢XC/min showed multiple endothermic peaks. Triple-melting peaks were detected at lower crystallization temperature (Tc), then the medium and the highest temperature peaks merged gradually to form double-melting peaks with increase in Tc, finally, all three peaks merged together to become a single peak at higher Tc. The low temperature melting peak was associated with the last step of secondary crystallization. The middle temperature melting peak was considered to be characteristic of the melting of the crystals formed in the primary crystallization. The highest temperature melting peak may be due to the melting of crystallite formed by melting and recrystallization during the DSC heating scans. From the results of multiple melting behaviors at a heating rate of 50¢XC/min, the melting peak temperatures of primary crystals were plotted versus the crystallization temperature, Tc. The Hoffman-Weeks plot gave an equilibrium melting temperature, . Using the half-time of crystallization (t1/2) for analysis, regime II¡÷III transition was found for each copolyester. The pairs of ( , ) in unit of ¢XC are (237.1, 193.6), (198.9, 147.3), (187.9, 140.4), (226.6, 164.8), (230.1, 172.0), and (261.1, 208.4) for C2, C3, C4, C6, C7, and C8, respectively. Finally, the overall crystallization rates (1/ t1/2) were compared at equivalent supercooling, DT ( - Tc). The C2 copolyester crystallized the fastest and at lower supercooling. C3 and C4 copolyesters had very similar rates. The C6 copolyester crystallized the slowest and at higher supercooling. At DT = 50~60¢XC, the rates of C7 were close to those of C3 and C4 copolyesters, then the C7 copolyester crystallized faster at higher supercooling. The average value of DH or crystallinity decreased from ¡V47 to ¡V32 J/g when the minor component, ET unit, increasesd from 8.9% (C2) to 37.9% (C4), and then the crystallinity increased from ¡V28 to ¡V42 J/g as the ET unit increases from 72.5% (C6) to 90.8% (C8). It indicated that the number and the distribution of minor component in the main chain should affect the nucleation rate, the growth rate and the final crystallinity of the copolyesters.

Differential scanning calorimeter (DSC) and temperature modulated differential scanning calorimeter (TMDSC) were used to study the isothermal crystallization kinetics and the melting behaviors at heating rates of 2, 10, 50, and 80

The topics of this study are as follows: (a) Poly(butylene succinate) (PBSu) rich random copolymers containing ~20% and ~50% trimethylene succinate (TS), PBTSu 80/20 and PBTSu 50/50 that were synthesized from 1,4-butanediol, 1,3-propanediol and succinic acid: The influence of minor TS units on the thermal properties and crystallization rate of PBSu was investigated. (b) Random copolymer of ~90% PBSu and ~10% poly(1,4-cyclohexanedimethylene succinate), PBCHDMSu 90/10, that was synthesized from 1,4-butanediol, 1,4-cyclohexanedimethanol and succinic acid: The influence of cyclohexene unit on the thermal properties and crystallization rate of PBSu was investigated. (c) Blends of PBSu and poly(trimethylene succinate) (PTSu) or poly(ethylene succinate) (PESu): The weight ratio PBSu and PTSu (or PESu ) were 1:1. The crystallization and morphology of blends (PBSu/PTSu 50/50 and PBSu/PESu 50/50) were investigated and compared with PBTSu 50 and PBESu 50/50. The chemical composition and the sequence distribution of co-monomers in copolyesters were determined using NMR. Thermal properties of polyesters and blends were characterized using differential scanning calorimeter (DSC) and temperature-modulated DSC (TMDSC). The crystallization kinetics and equilibrium melting temperature were analyzed with Avrami equation and Hoffman-Weeks linear extrapolation. The thermal stability of polyesters was analyzed by thermogravimeter (TGA) and polarized light microscope (PLM) under nitrogen. Wide-angle X-ray diffractograms (WAXD) were obtained for specimens after complete isothermal crystallization. The growth rates, regime transition temperature, morphology and phase separation were studied using polarized light microscope (PLM) with isothermal method or nonisothermal method. The morphology of specimens after chemical etching were investigated using atomic force microscope (AFM) and scanning electron microscope (SEM). The distribution of butylene succinate (BS) and TS units in PBTSu 80/20 was found to be random from the evidence of a single Tg and a randomness value close to 1.0 for a random copolymer. With the increasing of minor amounts of comonomers, the sequence length of butylene succinate decreases, and the crystallization rate and the degree of crystallinity drop. DSC heating curves of isothermal crystallized PBTSu 80/20 and PBCHDMSu 90/10 showed triple melting peaks. Multiple melting behaviors indicate that the upper melting peaks are associated with the primary and the recrystallized crystals, or the crystals with different lamellar thickness. As the Tc increases, the contribution of recrystallization slowly decreases and finally disappears. Hoffman-Weeks linear plots gave an equilibrium melting temperature of 113.5

This study contains four main parts. Part 1, poly(butylene succinate) (PBSu) rich random copolymers containing ~20% 2-methyl-1,3-propylene succinate (MPS), PBMPSu 80/20. The influence of minor MPS units on thermal properties and crystallization rate was investigated. Part 2, poly(butylene succinate) (PBSu) rich random copolymers containing ~5% 1,4-cyclohexanedimethylene succinate (CHDMS), PBCHDMSu 95/5. The influence of cyclohexane unit on thermal properties and crystallization rate was investigated. Part 3, Poly(butylene succinate) (PBSu) random copolymers containing ~50% 2-methyl-1,3-propylene succinate (MPS), PBMPSu 50/50. Blend of PBSu with poly(2-methyl-1,3-propylene succinate) (PMPSu). The weight ratio of PBSu and PMPSu were 1:1. The crystallization behavior and morphology was compared. Part 4, Poly(ethylene succinate) (PESu) random copolymers containing ~50¢H trimethylene succinate (TS), PETSu 50/50. Blend of PESu with poly(trimethylene succinate) (PTSu). The weight ratio of PESu and PTSu were 1:1. The crystallization behavior and morphology was compared. Molecular weights of copolymers were measured using capillary viscometer and gel permeation chromatography (GPC). The results indicate that polyesters used in this study have high molecular weights. The chemical composition and the sequence distribution of co-monomers in copolyesters were determined using 1H NMR and 13C NMR. The distribution in these copolyesters was found to be random from the evidence of a randomness value close to 1.0 for a random copolymer. Thermal properties of blends and copolyesters were characterized using differential scanning calorimeter (DSC) and thermogravimeter (TGA). The crystallization kinetics and mleting behaviors was analyzed after isothermal crystallization by DSC. Wide-angle X-ray diffractograms (WAXD) were obtained for specimens after complete isothermal crystallization. The growth rates, morphology were studied using polarized light microscope (PLM). The morphology of specimens after chemical etching was investigated using scanning electron microscope (SEM) and atomic force microscope (AFM). AS the ratio of MPS units increase, the degree of crystallinity and crystallization rate drop, it was due to decrease of butylene succinate sequence length. The spherulite growth rate of PBCHDMSu 95/5 is much slower compare with PBSu rich copolymers containing 5% TS or MPS. It was due to the steric effect of cyclohexane unit in the polymer chains. The crystalline morphology of PBMPSu 50/50 and PETSu 50/50 were quite different. It was due to the short sequence length of butylene succinate and ethylene succinate. From the analysis results by DSC and observation by PLM and SEM, it indicates that PBSu was miscible with PMPSu while PESu was partial miscible with PTSu.

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, 1999. / Word processed copy. Summary in English. Includes bibliographical references (leaves 66-68). Also available online.