Propylene Adipate Research Articles

Exploring the effect of hemp fibers’ addition on the properties of PLA/PPAd biodegradable blends

Poly(lactic acid) (PLA) is a compostable aliphatic polymer with enhanced strength and toughness, and it is a promising material for packaging products. Polymer blending is a financially feasible and easy way to upgrade its properties, such as its slow degradation and crystallization rates and its modest elongation, and thus, make it more adaptable. Furthermore, the use of natural fibers as fillers can reinforce the biobased character of the final composite materials and enhance their antioxidant activity values, a crucial property of polymers that are addressed for active packaging. Herein, the influence of the addition of hemp fibers (HF) on the features of poly(lactic acid)/poly(propylene adipate) blends containing 85/15 w/w PLA/PPAd, was investigated. The utilization of a poly(lactic acid)-co-poly(propylene adipate) block copolymer (cop) as a compatibilizer was also examined. The thermal, morphological and mechanical assets of the composite materials were evaluated with the implementation of multiple techniques. The addition of HF enhanced the hydrophobicity and biodegradation of the composites, render them as candidates for several applications. Furthermore, the introduction of the compatibilizer successfully increases the adhesion between the polymeric matrices and the HF, resulting in enhanced properties.

Doxorubicin-loaded mPEG-pPAd-mPEG triblock polymeric nanoparticles for drug delivery systems: Preparation and in vitro evaluation

Conventional methods in chemotherapy and radiotherapy do not target tumor sites treating breast cancer. Therefore, they cause some extra adverse effects on healthy tissues and cells, which bring fatal results. In recent applications, drug delivery systems have been used to target tumors directly or their environment indirectly. The new approach has attracted considerable interest due to its promise to overcome breast cancer with little adverse effect. Synthetic or natural polymer shell capsules are generally used to deliver therapeutic agents due to their biocompatibility and biodegradability. Doxorubicin (DOX), a convenient chemotherapeutic agent, was encapsulated using produced monomethyl ether ended poly(ethylene glycol)-poly(propylene adipate)- monomethyl ether ended poly(ethylene glycol) (mPEG-pPAd-mPEG) triblock copolymers in this study. The nanoparticle form of the prepared mPEG-pPAd-mPEG tri-block copolymer system was produced by a double emulsion-solvent evaporation method. To prepare triblock copolymer, firstly, poly (propylene adipate) (pPAd) was synthesized and characterized by using Fourier Transform Infrared (FT-IR) spectroscopy structurally and end-group analysis method to determine the number average molecular weight. The nanoparticle's size characteristics were measured by the Dynamic Light Scattering (DLS) method, while encapsulation efficacy and DOX-release profile were determined by spectrofluorometer instrument. Following the production of the nanoparticles, the antiproliferative effect and cellular uptake efficiency of the mPEG-pPAd-mPEG nanoparticles (PANPs), the doxorubicin-loaded mPEG-pPAd-mPEG nanoparticles (DPANPs), ICG-loaded mPEG-pPAd-mPEG nanoparticles (IPANPs), free-DOX, and free-ICG were tested on MCF-7 and MDA-MB-231 breast cancer cell line. The cytotoxicity analysis revealed that the DPANPs exhibited low toxicity compared to free-DOX. The physical and chemical analysis showed that the nanoparticles produced within this study's scope could be used as new drug delivery systems for breast cancer treatment.

Revisiting Non-Conventional Crystallinity-Induced Effects on Molecular Mobility in Sustainable Diblock Copolymers of Poly(propylene adipate) and Polylactide

This work deals with molecular mobility in renewable block copolymers based on polylactide (PLA) and poly(propylene adipate) (PPAd). In particular, we assess non-trivial effects on the mobility arising from the implementation of crystallization. Differential scanning calorimetry, polarized light microscopy and broadband dielectric spectroscopy were employed in combination for this study. The materials were subjected to various thermal treatments aiming at the manipulation of crystallization, namely, fast and slow cooling, isothermal melt- and cold-crystallization. Subsequently, we evaluated the changes recorded in the overall thermal behavior, semicrystalline morphology and molecular mobility (segmental and local). The molecular dynamics map for neat PPAd is presented here for the first time. Unexpectedly, the glass transition temperature, Tg, in the amorphous state drops upon crystallization by 8-50 K. The drop becomes stronger with the increase in the PPAd fraction. Compared to the amorphous state, crystallization leads to significantly faster segmental dynamics with severely suppressed cooperativity. For the PLA/PPAd copolymers, the effects are systematically stronger in the cold- as compared to the melt-crystallization, whereas the opposite happens for neat PLA. The local βPLA relaxation of PLA was, interestingly, recorded to almost vanish upon crystallization. This suggests that the corresponding molecular groups (carbonyl) are strongly involved and immobilized within the semicrystalline regions. The overall results suggest the involvement of either spatial nanoconfinement imposed on the mobile chains within the inter-crystal amorphous areas and/or a crystallization-driven effect of nanophase separation. The latter phase separation seems to be at the origins of the significant discrepancy recorded between the calorimetric and dielectric recordings on Tg in the copolymers. Once again, compared to more conventional techniques such as calorimetry, dielectric spectroscopy was proved a powerful and quite sensitive tool in recording such effects as well as in providing indirect indications for the polymer chains' topology.

Direct and indirect effects on molecular mobility in renewable polylactide-poly(propylene adipate) block copolymers as studied via dielectric spectroscopy and calorimetry.

In this work, we study a series of sustainable block copolymers based on polylactide, PLA, and poly(propylene adipate), PPAd, both polymers being prepared from renewable resources. Envisaging a wide range of future applications in the frame of a green and circular economy, e.g., packaging materials replacing conventional petrochemicals, the employment of PPAd aims at lowering the glass transition and melting temperatures of PLA and, finally, facilitation of the enzymatic degradation and compostability. The copolymers have been synthesized via ring opening polymerization of lactides in the presence of propylene adipate oligomers (5, 15 and 25%). The direct effects on the molecular mobility by the structure/composition are assessed in the amorphous state employing broadband dielectric spectroscopy (BDS) and calorimetry. BDS allowed the recording of local PLA and PPAd dynamics in all cases. The effects on local relaxations suggest favoring of interchain interactions, both PLA-PPAd and PPAd-PPAd. Regarding the more important segmental dynamics, the presence of PPAd leads to faster polymer chain diffusion, as monitored by the significant lowering of the dielectric and calorimetric glass transition temperature, Tg. This suggests the plasticizing role of PPAd on PLA (majority) in combination with the lowering of the average molar mass, Mn, in the copolymers from ∼75 to ∼30 kg mol-1, which is the actual scope for the synthesis of these materials. Interestingly, a strong suppression in fragility (chain cooperativity) is additionally recorded. In contrast to calorimetry and due to the high resolving power of BDS, for the higher PPAd fraction, the weak segmental relaxation of PPAd was additionally recorded. Overall, the recordings suggest a strong increase in free volume and two individual dynamic states, one for 0 and 5% PPAd and another for 15 and 25% PPAd. Within the latter, we gained indications for partial phase nano-separation of PPAd. Regarding indirect effects, these were followed via crystallization. Independent of the method of crystallization, namely, melt or cold, the presence of PPAd led to the systematic lowering of crystallization and melting temperatures and enthalpies. The effects reflect the decrease of crystalline nuclei, which is confirmed by optical microscopy as in the copolymers fewer although larger crystals are formed.

Synthesis, Properties, and Enzymatic Hydrolysis of Poly(lactic acid)-co-Poly(propylene adipate) Block Copolymers Prepared by Reactive Extrusion.

Poly(lactic acid) (PLA) is a biobased polyester with ever-growing applications in the fields of packaging and medicine. Despite its popularity, it suffers from inherent brittleness, a very slow degradation rate and a high production cost. To tune the properties of PLA, block copolymers with poly(propylene adipate) (PPAd) prepolymer were prepared by polymerizing L-lactide and PPAd oligomers via reactive extrusion (REX) in a torque rheometer. The effect of reaction temperature and composition on the molecular weight, chemical structure, and physicochemical properties of the copolymers was studied. The introduction of PPAd successfully increased the elongation and the biodegradation rate of PLA. REX is an efficient and economical alternative method for the fast and continuous synthesis of PLA-based copolymers with tunable properties.

New Biodegradable Poly(l-lactide)-Block-Poly(propylene adipate) Copolymer Microparticles for Long-Acting Injectables of Naltrexone Drug.

In the present study, novel block copolymers of poly(l-lactide)-block-poly(propylene adipate) (PLLA-b-PPAd) were synthesized in two ratios, 90/10 and 75/25 w/w and were further investigated as long-acting injectable (LAI) polymeric matrices in naltrexone base microparticle formulations. The synthesized polymers were characterized by 1H-NMR, 13C-NMR, FTIR, XRD, TGA and DSC. NMR and FTIR spectroscopies confirmed the successful synthesis of copolymers while DSC showed that these are block copolymers with well-defined and separated blocks. Microparticles were prepared by single emulsification method and were further characterized. Nanoparticles in the range of 0.4–4.5 μm were prepared as indicated by SEM, with copolymers giving the lowest particle size. By XRD and DSC it was found that naltrexone was present in the amorphous state in its microparticles. Dissolution study showed a drug release extending over seven days, indicating that these novel PLLA-b-PPAd copolymers could be promising matrices for naltrexone’s LAI formulations. It was evidenced that drug release depended on the copolymer composition. Model release studies showed that drug release is controlled by diffusion.

Risperidone Controlled Release Microspheres Based on Poly(Lactic Acid)-Poly(Propylene Adipate) Novel Polymer Blends Appropriate for Long Acting Injectable Formulations.

The present study evaluates the preparation of risperidone controlled release microspheres as appropriate long-acting injectable formulations based on a series of novel biodegradable and biocompatible poly(lactic acid)–poly(propylene adipate) (PLA/PPAd) polymer blends. Initially, PPAd was synthesized using a two-stage melt polycondensation method (esterification and polycondensation) and characterized by 1H-NMR, differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD) analyses. DSC and XRD results for PLA/PPAd blends (prepared by the solvent evaporation method) showed that these are immiscible, while enzymatic hydrolysis studies performed at 37 °C showed increased mass loss for PPAd compared to PLA. Risperidone-polyester microparticles prepared by the oil–water emulsification/solvent evaporation method showed smooth spherical surface with particle sizes from 1 to 15 μm. DSC, XRD, and Fourier-transformed infrared (FTIR) analyses showed that the active pharmaceutical ingredient (API) was dispersed in the amorphous phase within the polymer matrices, whereas in vitro drug release studies showed risperidone controlled release rates in all PLA/PPAd blend formulations. Finally, statistical moment analysis showed that polyester hydrolysis had a major impact on API release kinetics, while in PLA/PPAd blends with high PLA content, drug release was mainly controlled by diffusion.

Preparation of New Risperidone Depot Microspheres Based on Novel Biocompatible Poly(Alkylene Adipate) Polyesters as Long-Acting Injectable Formulations

Risperidone (RIS)-loaded microspheres based on poly(alkylene adipate)s derived from dicarboxylic acids and different aliphatic diols were prepared by the oil in water emulsion and solvent evaporation method. Specifically, 3 polyesters, namely poly(ethylene adipate), poly(propylene adipate), and poly(butylene adipate), were prepared with the aid of a 2-stage melt-polycondensation method and characterized by gel permeation chromatography, proton nuclear magnetic resonance (1H NMR), differential scanning calorimetry, and X-ray diffraction analysis. Results showed that the molecular weight of the polyesters increased as the diol molecular weight increased, while all polymers were of semi-crystalline nature and the melting temperature was varying from 49.1°C to 51.8°C and 65.9°C for poly(propylene adipate), poly(ethylene adipate), and poly(butylene adipate), respectively. The particle size of the RIS-loaded microspheres varied from 10 to 100 μm depending on the polyester type and the drug loading, while X-ray diffraction analysis revealed amorphous active pharmaceutical ingredient in the cases of high drug-loaded microspheres. In vitro drug release studies along with scanning electron microscopy images of microspheres after the completion of dissolution process showed that in all cases RIS release was controlled by the glass transition temperature of polyesters and physical state of active pharmaceutical ingredients via diffusion.

Multiblock copolymers of polyamide 6 and diepoxy propylene adipate obtained by solid state polymerization

Polyesteramide multiblock copolymers based on polyamide 6 and diepoxy propylene adipate blocks were synthesized. For this purpose a carboxyl-terminated polyamide 6 (Mn=2400g/mol, Tm=205.5°C) and diepoxy propylene adipate (Mn=450g/mol) were separately synthesized and characterized. The incorporation of the oligoester into the polyamide 6 backbone was performed by solid state polymerization (SSP) well below the melting temperature of the polyamide (80–140°C) so that the physical and thermal properties of the original polyamide 6 block were retained. Formation of the multiblock structure was confirmed by following the increase in molecular weight by SEC, reaction of the end groups by 1H NMR and by following the maintained melting temperature after the copolymerization. These segmented copolymers have molecular weights up to 10kg/mol, thermal stability of 325°C at 5% weight loss and a melting temperature of 205°C.

New thermosensitive nanoparticles prepared by biocompatible pegylated aliphatic polyester block copolymers for local cancer treatment.

New pegylated thermosensitive polymers were developed to study them as drug vehicles in targeting release nanoparticulate systems of anticancer drugs. The drug vehicles were prepared in the form of core-shell nanoparticles using novel polymeric materials synthesized by copolymerization of poly(propylene adipate) (PPAd) and methoxy-polyethylene glycol (mPEG) with different molecular weights. The physical and chemical properties of the synthesized mPEG-PPAd copolymers were studied using several techniques, and their cytocompatibility was evaluated. For drug nanoencapsulation, a water in oil (W/O) emulsification and solvent evaporation technique was used and the prepared nanoparticles were studied for their physical properties, morphology, drug release and anticancer efficacy against cancer cell lines. The size of the nanoparticles lied in a range suitable for tumour targeting. Drug release was affected by the composition of polymer, the temperature and pH of the release medium. The release results obtained indicate that judicious selection of nanoparticles composition may allow for enhanced drug delivery to the tumours following application of local hyperthermia. The paclitaxel-loaded mPEG-PPAd nanoparticles were found to be cytotoxic against to the human hepatoma HepG2) and the human epithelial (HeLa) cancer cell lines. Enhanced cytotoxicity against the HeLa cells was observed at elevated temperature (42°C compared with 37°C), providing support for the potential usefulness of the mPEG-PPAd nanoparticles for the development of thermo-sensitive anticancer drug delivery systems.

Biodeterioration of plasticized PVC/montmorillonite nanocomposites in aerobic soil environment

The aim of this study was to assess the effect of montmorillonite nanofillers, Cloisite Na+ and Cloisite 30B, on the biodeterioration of PVC-based nanocomposites plasticized by means of dioctyl adipate (DOA), dioctyl phthalate (DOP) and modified poly(propylene adipate) (PPA), in the aerobic environment of soil (soil burial test, time of exposure: 198 days). Tests were carried out at 25 ± 1 °C, under moisture-controlled (55 %) and aerobic conditions. The extent of the biodeterioration process was evaluated on the basis of changes in weight, tensile strength and elongation-at-break values. Finally, analysing chemical structures using FTIR and visual observation, both macroscopic and microscopic via scanning electron microscopy assisted in the evaluation process. The results of this study suggested that plasticized PVC/montmorillonite nanocomposites have an increased susceptibility for undergoing biological deterioration in comparison with plasticized PVC. In each instance, adding Cloisite 30B resulted in reducing the resistance of PVC/montmorillonite nanocomposites to the actions of microorganisms. In the case of Cloisite Na+ as the filler, results cannot be clearly quantified, although a negative influence prevailed, particularly a change in colour, whose change intensity was also dependent on the type of plasticizer, increasing in the following sequence: PVC/DOA/Cloisite Na+ > PVC/DOP/Cloisite Na+ > PVC/PPA/Cloisite Na+. However, each sample containing Cloisite Na+ achieved a lower rate of degradation (by normalised weight loss and FTIR) compared with nanocomposites containing Cloisite 30B. This can be attributed to the migration and accumulation of Cloisite Na+ on the surface of the nanocomposites particles where the former phenomenon producing a surface barrier which caused a reduction in the permeability of the material toward water and microorganisms, during the test.

Non‐Radial Growth of Helical Homopolymer Crystals: Breaking the Paradigm of the Polymer Spherulite Microstructure

Radial symmetry is essential for the conventional view of the polymer spherulite microstructure. Typically it is assumed that, in the course of the spherulite morphogenesis, the lamellar crystals grow radially. Using submicron X-ray diffraction, it is shown that in banded spherulites of poly(propylene adipate) the crystals have the shape of a helix with flat-on crystals winding around a virtual cylinder of about 6 µm in diameter. The helix angle of 30° implies that the crystal growth direction is tilted away from the spherulite radius by this angle. The implications of the helical crystal shape contradict the paradigm of the spherulitic microstructure. The radial growth rate of such spherulites does not correspond to the crystal growth rate, but to the propagation rate of the virtual cylinder the ribbons wind around.

Crystallization of novel poly(ε-caprolactone)-block-poly(propylene adipate) copolymers

Poly(e-caprolactone)-block-poly(propylene adipate) (PCL-block-PPAd) copolymers were prepared using a combination of polycondensation and ring opening polymerization of e-CL. 1H-NMR and 13C-NMR spectroscopy showed that the prepared copolymers were block. Also, the copolymer composition was calculated from NMR spectra and was found similar to the feeding ratio. The copolymers formed PCL crystals as was proved by WAXD. The crystallization rates and degree of crystallinity, measured from DSC crystallization experiments, decreased with PPAd content. The equilibrium melting points of PCL were estimated applying the Hoffmann–Weeks method and the observed melting point depression was analyzed using the Nishi–Wang equation which showed that there is some miscibility of the copolymer segments. Isothermal crystallization experiments after self-nucleation were performed to distinguish the nucleation and crystal growth stages during isothermal crystallization. The secondary nucleation theory was then used and the obtained data for crystallization rates, estimated from the inverse of the crystallization half-times, were analyzed. The resulting values for nucleation constant K g, and also for the surface free energies and work of chain folding, increased with PPAd content due to topological restrictions.

New Biocompatible Aliphatic Polyesters as Thermosensitive Drug Nanocarriers. Application in Targeting Release Pharmaceutical Systems for Local Cancer Treatment

In the present study a new drug delivery system for the treatment of local cancer was developed. Two aliphatic polyesters namely poly(propylene adipate) (PPAd) and poly(propylene pimelate) (PPPim), were used as carriers in order to prepare nanoparticles loaded with paclitaxel. The starting materials as well as the nanoparticles were characterized with DSC, SEM and WAXD techniques. The nanoparticles had a mean particle size of 160-190nm and characterized for drug loading content, efficiency and in vitro dissolution at 37oC and 42oC in two different pH buffer solutions (pH 7.4 and pH 6.0). Results showed enhanced release rate of paclitaxel at 42oC compared to 37oC in both pH conditions. The degree of crystallinity plays also an important role to paclitaxel release. The cytotoxicity of the prepared paclitaxel/ polyester nanoparticles was studied in comparison with control samples using two cancer cell lines like Human hepatoma (HepG2) cells and Human Cervical Adenocarcinoma Cells (HeLa). In both cases it was found that cells are in the phase of necrosis or apoptosis after 20h of incubation. Finally, the temperature is also an important factor since this behaviour is faster in 42oC than in 37oC, indicating that the studied polyesters could act as thermosensitive carriers.

Synthesis of biocompatible poly(ε-caprolactone)-block-poly(propylene adipate) copolymers appropriate for drug nanoencapsulation in the form of core-shell nanoparticles

Poly(propylene adipate)-block-poly(ɛ-caprolactone) copolymers were synthesized using a combination of polycondensation and ring-opening polymerization of ɛ-caprolactone in the presence of poly(propylene adipate). Gel permeation chromatography was used for molecular weight determination, whereas hydrogen-1 nuclear magnetic resonance and carbon-13 nuclear magnetic resonance spectroscopy were employed for copolymer characterization and composition evaluation. The copolymers were found to be block while their composition was similar to the feeding ratio. They formed semicrystalline structures, while only poly(ɛ-caprolactone) formed crystals, as shown by wide angle X-ray diffraction. Differential scanning calorimetry data suggest that the melting point and heat of fusion of copolymers decreased by increasing the poly(propylene adipate) amount. The synthesized polymers exhibited low cytotoxicity and were used to encapsulate desferrioxamine, an iron-chelating drug. The desferrioxamine nanoparticles were self-assembled into core shell structures, had mean particle size <250 nm, and the drug remained in crystalline form. Further studies revealed that the dissolution rate was mainly related to the melting temperature, as well as to the degree of crystallinity of copolymers.

Synthesis and characterization of novel poly(propylene terephthalate-co-adipate) biodegradable random copolyesters

Novel aromatic/aliphatic poly(propylene terephthalate-co-adipate) (PPTAd) random copolymers were synthesized. Copolymer composition varied over the whole range from that of neat poly(propylene terephthalate) (PPT) to that of neat poly(propylene adipate) (PPAd). Interestingly, the copolymers showed that they can degrade via hydrolysis, especially in presence of enzymes, even for a terephthalate content as high as 66 mol%. Thermal behaviour and solid state as well as mechanical properties were studied. In contrast to hydrolysis rates, mechanical properties increase with terephthalate content. WAXD patterns indicate some extent of co-crystallization of both comonomers, especially for intermediate compositions. The thermodynamic analysis of the melting point depression showed that some portion of the adipate comonomer units participate in the formation of crystals, although the major portion of them is rejected from crystals and remain in the amorphous phase. WAXD patterns showed that even for a 60 mol% or more adipate content, the copolymers form PPT like crystals. Thus, the amorphous phase is enriched in adipate units, as is also shown by a lowering of the glass transition temperature of the crystallized copolymer samples, compared to glassy ones. Finally, multiple melting behaviour of the melt crystallized copolymer samples, as well as, banded spherulitic morphology was observed.

Effectiveness of Various Drug Carriers in Controlled Release Formulations of Raloxifene HCl Prepared by Melt Mixing

In the present study solid dispersions of Raloxifene HCl were prepared by melt mixing. As drug carriers, biodegradable/biocompatible aliphatic polyesters were used. These formulations were compared to those based on extensively used drug carriers such as PEG and Gelucire 50/13. The used aliphatic polyesters namely poly(propylene succinate) (PPSu) and poly(propylene adipate) (PPAd) were prepared by melt polycondensation. The polyesters have melting points close to human body temperature and were used for first time as drug carries. Polymer cytocompatibility based on HUVEC cells viability in the presence of increasing concentrations of polymer was investigated and it was found that PPSu and PPAd exhibit comparable cytocompatibility with poly(dl-lactide). The physical state of solid dispersions was evaluated by FTIR, SEM and XRD techniques. In all cases the interactions between drug and carriers are limited and thus the dispersed drug was mainly in the crystalline state. SEM revealed that the particles size of the dispersed drug increases with increasing the drug amount. The release behavior of the drug is affected from both the drug amount and the kind of the used carrier. The drug is released almost immediately from PEG formulations while Gelucire results in sustained release. In formulations that polyesters were used as drug carriers the release is slower.

Miscibility of biodegradable poly(propylene succinate)/poly(propylene adipate) blends: Effect of the transesterification reactions

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

Novel Biodegradable Polyesters. Synthesis and Application as Drug Carriers for the Preparation of Raloxifene HCl Loaded Nanoparticles

Raloxifene HCl is a drug with poor bioavailability and poor water solubility. Furthermore nο pharmaceutically acceptable organic solvent has been reported before to dilute the drug. It was observed that Raloxifene HCl can be diluted in a solvent mixture of acetone/water or ethanol/water. The aim of this study was to use biodegradable polymers in order to prepare Raloxifene HCl nanoparticles. For this purpose a series of novel biodegradable poly(ethylene succinate-co-propylene adipate) P(ESu-co-PAd) polyesters were synthesized following the polycondensation method and further, poly(ethylene succinate) (PESu) and poly(propylene adipate) (PPAd) were used. The prepared polyesters were characterized by intrinsic viscosity measurements, end group analysis, enzymatic hydrolysis, Nuclear Magnetic Resonance Spectroscopy (1Η-NMR and 13C-NMR) and Wide-angle X-ray Diffractometry (WAXD). The drug nanoparticles have been prepared by a variation of the co-precipitation method and were studied by Wide-angle X-ray Diffractometry (WAXD), FTIR spectrometry, light scattering size distribution, Scanning Electron Microscopy (SEM) and release behavior measurements. The interactions between the polymers and the drug seem to be limited, so the drug occurs in crystalline form in all nanoparticles. The size of the nanoparticles seems to be in the range of 150-350 nm, depending on the polymer that was used. The drug release depends on the melting point and degree of crystallinity of the polyesters used. An initial high release rate was recorded followed by very slow rates of controlled release.

The β relaxation as a probe to follow real-time polymer crystallization in model aliphatic polyesters

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