Block Copolyesters Research Articles

Water-Stable All-Biodegradable Microparticles in Nanofibers by Electrospinning of Aqueous Dispersions for Biotechnical Plant Protection

Pheromone eluting oligolactide (OLA) microcapsules immobilized in electrospun biodegradable polyester nanofibers were obtained by electrospinning of aqueous dispersions of the microcapsules. OLA was prepared by conventional melt polycondensation of lactic acid. Following the protocol of the solvent displacement method, OLA was dissolved in acetone and mixed with Brij S20 and the pheromone of the European grape vine moth, Lobesia Botrana, (E,Z)-7,9-dodecadien-l-yl acetate (DA). Up to 32 wt % of this mixture could be dispersed in water with colloidal stability of several weeks without any sedimentation. Without DA as well as OLA, no stable dispersions of OLA in water were obtained. Replacement of DA by classical hydrophobes typically used for miniemulsions did not yield stable dispersions, but the addition of octyl acetate, which shows structural similarity to DA, yielded stable dispersions in water up to 10 wt %. Dispersions of OLA/DA were successfully electrospun in combination with an aqueous dispersion of a biodegradable block copolyester resulting in water-stable nanofibers containing OLA/DA microcapsules. Release of DA from microcapsules and fibers was retarded in comparison with non-encapsulated DA, as shown by model studies.

Aromatic-aliphatic random and block copolyesters: synthesis, sequence distribution and thermal properties

A series of poly(butylene terephthalate)-poly(butylene succinate) (PBT-PBS) copolyesters were synthesized by the melt chain-extension reaction of dihydroxyl terminated PBT (HO-PBT-OH) and PBS (HO-PBS-OH) prepolymers using toluene-2,4-diisoyanate (TDI) as a chain extender. Transesterification between PBT and PBS during the chain-extension reaction has been investigated in detail. Both random and block PBT-PBS copolymers can be synthesized by changing the prepolymers' molecular weights at a given reaction time and temperature. The chemical structures and sequence distributions of the copolyesters were analyzed by proton nuclear magnetic resonance (1H-NMR) spectroscopy. The thermal transition behaviours of copolyesters with different sequence distribution were characterized by differential scanning calorimeter (DSC). The number-average molecular weight (Mn) of HO-PBT-OH played a dominant role in the sequence distribution of the resulting copolyesters. The degree of randomness of the copolymer was around 1 when Mn of HO-PBT-OH was 5000 g mol−1 regardless of that of HO-PBS-OH, it decreased to less than 1 when Mn of HO-PBT-OH was more than 10 000 g mol−1, and it gradually decreased with the increase in Mn of HO-PBS-OH. The copolyesters with different degrees of randomness showed different thermal transition and crystallization behaviours.

Ring-opening polymerization of lactones using supramolecular organocatalysts under simple conditions

Ring-opening polymerizations of δ-valerolactone (δ-VL) and e-caprolactone (e-CL) were catalyzed by a metal-free system composed of two H-bonding components, a phenol derivative to activate the monomer, and DBU, which enhanced the nucleophilicity of the initiator and the propagating chain. Compared to other H-bonding systems for the ROP of lactones, phenol + DBU catalysts had the practical advantages of being commercially available and inexpensive, efficient at room temperature and under simple experimental conditions that avoid drying of reactants and the use of a glove-box. In addition, the obtained polyesters had a narrow dispersion of molar masses which were controlled by the concentration ratio of monomer versus initiator. Moreover, the initiation of the polymerization by DBU and residual water molecules (despite no specific drying of reagents) was shown to be very minor under the experimental conditions. No initiation by the phenol catalysts was observed. Block copolyesters PVL-PLA and PCL-PLA were also prepared using these conditions.

Amphiphilic Block Co-polyesters Bearing Pendant Cyclic Ketal Groups as Nanocarriers for Controlled Release of Camptothecin

Amphiphilic block co-polymers consisting of hydrophilic poly(ethylene glycol) and hydrophobic polyester bearing pendent cyclic ketals were synthesized by ring-opening co-polymerization of ε-caprolactone (CL) and 1,4,8-trioxaspiro-[4,6]-9-undecanone (TSU) using α-hydroxyl, ω-methoxy, poly(ethylene glycol) as the initiator and stannous octoate as the catalyst. Compositional analyses indicate that TSU was randomly distributed in the hydrophobic blocks. When the TSU content in the co-polymers increased, the polymer crystallinity decreased progressively and the glass transition temperature increased accordingly. The hydrophobic, anticancer drug, camptothecin (CPT), was successfully encapsulated in the block copolymer nanoparticles. The CPT encapsulation efficiency and release kinetics were strongly dependent on the co-polymer composition and crystallinity. CPT release from nanoparticles constructed from co-polymers containing 0, 39 and 100 mol% TSU in the hydrophobic block followed the same trend, with an initial burst of approx. 40% within one day followed by a moderate and slow release lasting up to 7 days. At a TSU content of 14 mol%, CPT was released in a continuous and controlled fashion with a reduced initial burst and a 73% cumulative release by day 7. The in vitro cytoxicity assay showed that the blank nanoparticles were not toxic to the cultured bone metastatic prostate cancer cells (C4-2B). Compared to the free drug, the encapsulated CPT was more effective in inducing apoptotic responses in C4-2B cells. Modulating the physical characteristics of the amphiphilic co-polymers via co-polymerization offers a facile method for controlling the bioavailability of anticancer drugs, ultimately increasing effectiveness and minimizing toxicity.

Study on micro-phase separation structure of poly(ethylene terephthalate)-poly(hexylene terephthalate) (PET-PCT) copolymer

AbstractPET-PCT copolyesters were prepared from terephthalic acid (PTA), ethylene glycol (EG) and 1,4-cyclohexane dimethanol (CHDM) through direct esterification and the subsequent polycondensation. The chemical composition and sequence length distribution of the copolyesters were investigated by 1H-NMR and 13C-NMR. The dynamic rheological behavior and dynamic mechanical property were studied by means of ARES-RFS and DMA. The results demonstrated that the obtained PET-PCT copolyesters were random block copolyesters and the content of PCT units incorporated was always greater than the feed and the numberaverage sequence length of each block in the copolyesters was in proportion to its content. The relation between storage modulus (G’) and frequency (freq) deviated from linearity as the frequency (freq) tend to zero (the terminal region effect), and the frequency band where the terminal region effect appeared would shift to higher value with the increasing content of PCT, suggesting the presence of phase separations. Moreover, two glass transition temperatures were observed from DMA curves, which revealed the incompatibility of PET segments and PCT segments, i.e. the micro-phase separation took place in PET-PCT copolyesters.

Nanofibers by Green Electrospinning of Aqueous Suspensions of Biodegradable Block Copolyesters for Applications in Medicine, Pharmacy and Agriculture

Poly(hexamethylene adipate)-PEO block copolymers (PHA-b-PEO) with different PEO contents were synthesized and processed to aqueous suspensions with high solid contents by a solvent displacement method followed by dialysis. The best suspension displayed a solid content of 16 wt.-% and an average particle size of 108 nm. This suspension was mixed with a small amount of high molecular weight PEO and Brij78 and electrospun into corresponding nanofibers. After extraction with water, nanofibers of PHA-b-PEO were obtained. Electrospinning of aqueous suspensions of biodegradable polyesters alleviates concerns regarding safety, toxicology and environmental problems, which are associated with spinning of such polyesters from harmful organic solvents and thereby offers novel perspectives for applications in medicine, pharmacy and agriculture. Electrospinning of polymers from aqueous suspensions avoiding harmful organic solvents is suggested to be "green electrospinning".

Block Copolymers Containing (R)-3-Hydroxybutyrate and Isosorbide Succinate or (S)-Lactic Acid Mers

A new aliphatic block copolyester was synthesized in bulk from transesterification techniques between poly((R)-3-hydroxybutyrate) (PHB) and poly(isosorbide succinate) (PIS). Additionally, other two block copolyesters were synthesized in bulk either from transesterification reactions involving PHB and poly(l-lactide) (PLLA) or from ring-opening copolymerization of l-lactide and hydroxyl-terminated PHB, as result of a previous transesterification reactions with isosorbide. Two-component blends of PHB and PIS or PLLA were also prepared as comparative systems. SEC, MALDI-TOF mass spectrometry (MALDI-TOFMS), 1H and 13C NMR spectroscopy, WAXD, solubility tests, and TG thermal analysis were used for characterization. The block copolymer structures of the products were evidenced by MALDI-TOFMS, 13C NMR, and WAXD data. The block copolymers and the corresponding binary blends presented different solubility properties, as revealed by solubility tests. Although the incorporation of PIS sequences into PHB main backbone did not enhance the thermal stability of the product, it reduced its crystallinity, which could be advantageous for faster biodegradation rate. These products, composed of PHB and PIS or PLLA sequences, are an interesting alternative in biomedical applications.

Enzyme-Catalyzed Polycondensation of Polyester Macrodiols with Divinyl Adipate: A Green Method for the Preparation of Thermoplastic Block Copolyesters

Enzyme-catalyzed polycondensation for the synthesis of block copolymers was reported for the first time. Thermoplastic block copolyesters containing poly[(R)-3-hydroxybutyrate] (PHB) and poly[(R)-3-hydroxyoctanoate] (PHO) blocks were enzymatically prepared by one- or two-step lipase-catalyzed polycondensation. Novozym 435-catalyzed reaction of PHB-diol (M(n) of 3100 g/mol, GPC), PHO-diol (M(n) of 3200 g/mol, GPC), and divinyl adipate gave block poly(HB-co-HO) (M(n) of 9800 g/mol, GPC) with randomly arranged blocks in 55% yield. In two-step polycondensations, Novozym 435-catalyzed reaction of PHB-diol and divinyl adipate afforded 73% of PHB containing two vinyl ester end groups (M(n) of 2700 g/mol, GPC), which was further reacted with PHO-diol in the presence of Novozym 435 to give block poly(HB-co-HO)s (M(n) of 8800-14 200 g/mol, GPC) with A-B-type arranged blocks in 55-62% yield. The enzymatically prepared block copolyesters demonstrated T(m) of 136-142 degrees C and 142-153 degrees C and T(g) of -37 to -39 degrees C and were potentially useful thermoplastic biodegradable and biocompatible materials.

Effect of di-n-dodecyl phosphate on the transesterification reaction in a poly(butylene terephthalate)/polycarbonate blend

The transesterification behavior of a poly(butylene terephthalate) (PBT)/polycarbonate (PC) blend with the addition of di-n-dodecyl phosphate was studied with differential scanning calorimetry (DSC) and infrared spectroscopy. The effects of triphenyl phosphate (TPP) and di-n-dodecyl phosphate on the suppression of transesterification were compared. The differences in the crystallization and melting temperatures during the two heating and cooling cycles in the DSC measurements were lower than those of the virgin PBT/PC blend, and di-n-dodecyl phosphate inhibited the formation of a random copolyester but did not suppress the formation of a block copolyester. The crystallization temperature of the PBT/PC blend in the presence of di-n-dodecyl phosphate was higher than that of the blend in the presence of TPP. Di-n-dodecyl phosphate was thus more effective than TPP in the inhibition of transesterification between PBT and PC. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.

Synthesis of Poly[(ethylene terephthalate)‐co‐(ε‐caprolactone)]‐Poly(propylene oxide) Block Copolyester by Direct Polyesterification of Reactive Oligomers

AbstractSummary: The objective of this study was to synthesize thermoplastic elastomers by the direct copolyesterification of reactive oligomers of poly[(ethylene terephthalate)‐co‐(ε‐caprolactone)] (PET) and poly(propylene oxide) (PPO). The synthesis of hard segment oligomers was achieved in two steps. The first step consisted of the glycolysis of PET leading to α,ω‐hydroxyl functionalized oligomers. The second step corresponded to the ring opening polymerization of ε‐caprolactone onto the hydroxyl end groups of the PET oligomers. Commercially available hydroxytelechelic poly(propylene oxide) was modified to obtain carboxytelechelic poly(propylene oxide). The chemical structure of the product was investigated by 1H NMR and size exclusion chromatography (SEC). Multiblock poly(ester‐ether) was then synthesized by polyesterification of hydroxytelechelic poly[(ethylene terephthalate)‐co‐(ε‐caprolactone)] with carboxytelechelic poly(propylene oxide) oligomers, using different catalysts and reaction conditions. The best stoichiometric ratio for the reaction was determined in order to obtain the highest possible $\overline M _{\rm n}$. The chemical structure of the synthesized poly(ester‐ether) was investigated by size exclusion chromatography and 1H NMR. The thermal and thermomechanical behavior of the synthesized poly(ester‐ether) was investigated by differential scanning calorimetry and dynamic mechanical analysis, which showed that the poly(ester‐ether) behaved as a thermoplastic elastomer. This product could also be an interesting way for chemical recycling of PET waste.Synthesis of multiblock co‐poly(ester‐ether).magnified imageSynthesis of multiblock co‐poly(ester‐ether).

Cover Picture: Macromol. Biosci. 4/2005

Cover: The Figure shows the structure of novel biodegradable block and statistical copolyesters composed of hydrophilic ((R,S)‐3,3‐dimethylmalic acid) and hydrophobic (hexyl (R,S)‐3,3‐dimethylmalate) repetitive units. These novel materials display amphiphilic properties and form micelles and nanoparticles usable as potential drug delivery system. Transmission electron microphotography shows regular spherical nanoparticles with mean size suitable for target molecules encapsulation. Micelles are characterized by the critical aggregation concentration determined by the plot of the ratio of two vibrational bands of pyrene (used as fluorescence probe) versus the concentration of the block copolyester. Further details can be found in the Full Paper by F. Ouhib, S. Randriamahefa, V. Wintgens, P. Guérin, and C. Barbaud on Page 299.

Polymeric Micelles and Nanoparticles from Block and Statistical Poly((RS)‐3,3‐dimethylmalic acid) Derivatives: Preparation and Characterization

Amphiphilic and biodegradable micelles and nanoparticles designed as potential drug carriers were prepared from biodegradable statistical and block copolyesters obtained by a living anionic ring-opening process. These novel materials display amphiphilic properties arising from the joint presence of hydrophilic poly((RS)-3,3-dimethylmalic acid) and hydrophobic poly(hexyl (RS)-3,3-dimethylmalate) segments. Micelles obtained from a well-defined block copolymer have been characterized by their critical aggregation concentration, and nanoparticles derived from statistical copolymer have been analyzed by transmission electron microscopy (TEM).

Studies on the enzymatic hydrolysis of polyesters. II. Aliphatic–aromatic copolyesters

The dependence of the enzymatic degradation of aliphatic–aromatic copolyesters on the polymer structure has been investigated. A number of defined model copolyesters containing terephthalate units as aromatic component were synthesized. The model polymers included random copolyesters, block copolyesters and also strictly alternating copolyesters, which were made from especially synthesized and purified pre-building blocks. The biodegradability was evaluated applying a laboratory degradation test under well-defined conditions with a lipase from Pseudomonas sp. It could clearly be proven that the selectivity of the lipase concerning the aliphatic or aromatic environment near the ester bonds is not the predominant factor controlling the biodegradability of the copolyesters. As already described for aliphatic homo polyesters the biodegradation rate of the copolyesters is mainly controlled by the chain mobility of the polymers, being correlated with the difference between the melting point of the polyester and the degradation temperature. The presence of longer aliphatic domains, e.g., in block copolyesters does not facilitate the hydrolytic attack by the lipase, but longer aromatic sequences, which control the melting point of the crystalline regions, reduce the biodegradation rate. The concept of chain mobility seems to be a quite universal way to describe and predict the biodegradation rate of synthetic polyesters, independent on their composition or micro-structure.

Synthesis of new statistical and block co-polyesters by ROP of α,α,β-trisubstituted β-lactones and their characterizations

The preparation of α,α,β-trisubstituted β-lactones has opened the route to living anionic ring-opening polymerization of these monomers. Therefore, transfer reactions due to hydrogen abstraction were limited and it is now possible to strickly control sample molecular weight. Moreover, living end-groups lead to the preparation of block co-polymers with block controlled lenghts. In the same way, high-molecular-weight statistical co-polymers have been synthesized. Hydrolyzable micelles and nanoparticles will be prepared from these co-polymers after chemical modifications to adjust the hydrophilic/hydrophobic balance.

Diblock Copolymers Based on 1,4‐Dioxan‐2‐one and ε‐Caprolactone: Characterization and Thermal Properties

AbstractSummary: Various poly(ε‐caprolactone‐block‐1,4‐dioxan‐2‐one) (P(CL‐block‐PDX)) block copolymers were prepared according to the living/controlled ring‐opening polymerization (ROP) of 1,4‐dioxan‐2‐one (PDX) as initiated by in situ generated ω‐aluminium alkoxides poly(ε‐caprolactone) (PCL) chains in toluene at 25 °C.1 1H NMR, PCS and TEM measurements have attested for the formation of colloids attributed to a growing PPDX core surrounded by a solvating PCL shell during the polymerization of PDX promoted by ω‐Al alkoxide PCL chains in toluene. The thermal behavior of the P(CL‐block‐PDX) copolymers was studied by DSC; showing two distinct melting temperatures (as well as two glass transition temperatures) similar to those of the respective homopolyesters. Finally, the thermal degradation of the P(CL‐block‐PDX) block copolymers was investigated by TGA simultaneously coupled to a FT‐IR spectrometer and a mass spectrometer for evolved gas analysis (EGA). The degradation occurred in two consecutive steps involving a first unzipping depolymerization of the PPDX blocks followed by the degradation of the PCL blocks via both ester pyrolysis and unzipping reactions.TEM observation of P(CL‐block‐PDX) block copolyesters ($\overline M _{{\rm nPCL}}$ = 11 600 and $\overline M _{{\rm nPPDX}}$ = 22 100) as formed by vaporization starting from a diluted suspension in toluene/TCE mixture solvent (50/50 v/v).magnified imageTEM observation of P(CL‐block‐PDX) block copolyesters ($\overline M _{{\rm nPCL}}$ = 11 600 and $\overline M _{{\rm nPPDX}}$ = 22 100) as formed by vaporization starting from a diluted suspension in toluene/TCE mixture solvent (50/50 v/v).

Relationship between Sequence Distribution and Thermal Properties of the Transesterification Product between Poly(ethylene terephthalate) and Poly(butylene terephthalate)

The relationship between the number-average sequence length and the melting temperature of the block copolyesters prepared by quench after the transesterification reaction between poly(ethylene terephthalate) and poly(butylene terephthalate) was reported. The number-average sequence length was determined by the triad sequence analysis in a solvent system of o-chlorophenol/deuterated chloroform mixture (75/25 v/v) at 80 °C using 600 MHz 1H NMR. The melting temperature was observed using a differential scanning calorimeter. The linear correlation between the melting temperature and the inverse of the number-average sequence length was observed for the transesterification products with composition of PET/PBT from 20/80 to 80/20 mol %. This correlation was confirmed by the measurement of the long period using small-angle X-ray scattering. For the transesterification products obtained under definite conditions such as the quench after the transesterification reaction, it was confirmed that the number-average s...

Synthesis and Characterization of Novel Thermoplastic Polyester Containing Blocks of Poly[(R)-3-hydroxyoctanoate] and Poly[(R)-3-hydroxybutyrate

Novel block copolyester containing biocompatible and biodegradable biopolyester blocks was prepared by polycondensation of telechelic hydroxylated poly[(R)-3-hydroxyoctanoate] (PHO-diol) and telechelic hydroxylated poly[(R)-3-hydroxybutyrate] (PHB-diol) with terephthaloyl chloride (TeCl). Reaction of PHO-diol (Mp of 2100), PHB-diol (Mp of 3200), and TeCl at a ratio of 1.3:1:2.1 gave the block co-polyester PHOHBTe in 86% yield with a molecular weight Mp of 7200 (GPC). The chemical structure of the copolyester was confirmed by 1H-, 13C-, and COSY-NMR and IR spectra. On average, 2 PHO-diol, 1 PHB-diol, and 2 TeCl were incorporated in each molecule of the block copolyester PHOHBTe. For comparison, polyester PHOTe with a Mp of 7100 (GPC) was prepared in 81% yield by reaction of PHO-diol and terephthaloyl chloride at a molar ratio of 1:1.2. NMR analysis suggested that PHOTe contains 3 PHO and 3 Te units on average. While PHOTe containing no PHB block is soft-sticky, PHOHBTe containing both soft PHO and hard PHB blocks showed good thermoplastic properties with Tm of 129 and 140 °C and a Tg of −41 °C. Thus, for the first time, block copolyester containing PHO and PHB blocks has been prepared and demonstrated to be thermoplastic.

Controlled synthesis of block polyesters by reactive extrusion

AbstractThe synthesis of block copolyesters by combining transesterification resistant oligoesters with poly(ethylene terephthalate) is described. Critical factors in the synthesis include processing conditions (temperature), end groups and catalysts used in oligoester synthesis. It is necessary to achieve a balance between ease of incorporation/synthesis and transesterification resistance. The process is discussed with reference to poly(neopentyl isophthalate) as a representative transesterification resistant oligoester. The primary motivation for the work has been the development of higher barrier poly(ethylene terephthalate) useful for making monolayer beverage containers.

Synthesis of (polyethylene terephthalate/polyϵ-caprolactone) copolyesters

Polyethylene terephthalate (PET) was alcoholised with ethylene glycol to synthesize hydroxytelechelic oligomers of PET. On the other hand, commercial hydroxytelechelic polyϵ-caprolactone was modified in order to synthesize carboxytelechelic polyϵ-caprolactone. The chemical structure of the products was investigated by 1H NMR. Multiblock copolyesters were then synthesized by polyesterification of hydroxytelechelic PET and carboxytelechelic polyϵ-caprolactone oligomers, using several catalysts and different reaction conditions, which have been linked with the average molecular weight of the obtained block copolyesters. It appeared that residual distannoxane species coming from glycolysis step are best catalyst for polyesterification reaction. The chemical structure of the synthesized copolyesters was investigated by size exclusion chromatography and 1H NMR. The thermal and thermomechanical behavior of the synthesized copolyesters was investigated by differential scanning calorimetry and by dynamic mechanical analyses. The ester–ester interchange reaction between the two types of oligopolyesters has been enlightened and estimated taking in account the different reaction parameters. This side reaction led to the miscibility of the two phases of the oligomers, that can be explained by a random structure of the copolyester, and prevented to obtain multiblock copolymer.

Block copolyesters of poly(pentamethylene 2,6‐naphthalenedicarboxylate) and poly(tetramethylene adipate)

AbstractHydroxy‐terminated poly(pentamethylene 2,6‐naphthalenedicarboxylate) oligomers were prepared by melt polycondensation of dimethyl 2,6‐naphthalenedicarboxylate with excess 1,5‐pentanediol followed by evacuating out some 1,5‐pentanediol. The molecular weight of the poly(pentamethylene 2,6‐naphthalenedicarboxylate) oligomers was controlled by the charge molar ratio of 1,5‐pentanediol to dimethyl 2,6‐naphthalenedicarboxylate and the amount of 1,5‐pentanediol removed under vacuum. The 1H‐NMR spectra of the poly(pentamethylene 2,6‐naphthalenedicarboxylate) oligomers indicate that the transesterification between dimethyl 2,6‐naphthalenedicarboxylate and 1,5‐pentanediol was almost complete. Block copolyesters with hard segments of poly(pentamethylene 2,6‐naphthalenedicarboxylate) and soft segments of poly(tetramethylene adipate) were prepared by coupling the poly(pentamethylene 2,6‐naphthalenedicarboxylate) oligomer and a poly(tetramethylene adipate) glycol with methylene‐4,4′‐diphenylene diisocyanate in solution. The block copolyesters were characterized by IR, 1H‐NMR, DSC, and X‐ray diffraction. The hard segments in the block copolyesters display an amorphous state. However, the thermal transitions of soft segments in the block copolyesters are strongly dependent on the composition. When the content of the hard segments increases, the glass transition temperature of the soft segments increases. Thus, the amorphous parts of the soft segments would be partially miscible with the hard segments. When the content of the hard segments is very low, the soft segments of the block copolyesters exhibit high crystallinity. But, as the content of the hard segments is about 30 wt % or more, the soft segments of the block copolyesters become amorphous. This is described as the effect of the presence of the hard segments which are partially miscible with the soft segments. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3652–3659, 2002