Preparation and characterization of aliphatic/aromatic copolyesters based on 1,4-cyclohexanedicarboxylic acid

A series of biodegradable aliphatic/aromatic copolyesters, poly(butylene terephthalate)-co-poly(butylene cyclohexanedicarboxylate)-b-poly(ethylene glycol) (PTCG), were prepared by a two-step melt polycondensation method and characterized by means of GPC, FTIR, NMR, DSC, TGA, etc. The effects of aliphatic ester content on the physical, mechanical and thermal properties, as well as in vitro and in vivo degradation behaviors were investigated. The decrease in mechanical strength was observed with an increase in poly(butylene cyclohexanedicarboxylate) (PBC) molar fraction. DSC results showed one melting point and two glass transition temperatures in all samples, and the melting temperature was found to go down gradually as more cyclohexanedicarboxylic acid (CHDA) was added. During the in vitro and in vivo degradation processes, erosion of the surface was dominant as evidenced by scanning electron microscopic observations. The copolyesters containing many CHDA units were featured by the higher water uptake and faster degradation due to much richer amorphous phase within them.     

Degradation of cross-linked aliphatic polyester composed of poly(?-caprolactone-co-d,l-lactide) depending on the thermal properties

In this study, we prepared cross-linked aliphatic polyester derived from branched poly(?-caprolactone (abbreviated as CL)-co-d,l-lactide (abbreviated as LA)) macromonomers with different CL and LA compositions and investigated the effect of thermal properties on their degradation. According to the degradation study, the weight loss became larger with increasing LA composition in poly(CL-co-LA). The introduction of LA units that can degrade easily disturbed the crystallinity of the PCL segments; as result, the hydrolysis became accelerated. Also, we studied the temperature dependency of degradation of a series of cross-linked poly(CL-co-LA) materials with different melting points. We found that the degradation of these materials related closely to the crystallinity, which could be controlled by the composition of CL and LA.     

Synthesis and hydrolytic degradation of poly(ethylene succinate) and poly(ethylene terephthalate) copolymers

The conditions of synthesis of statistical poly(ethylene succinate-co-terephthalate) copolymers (2GTS) and high molecular weight poly(ethylene succinate) (PES) with good hydrolytic and optical parameters, designed for the production of biodegradable products and resins, are presented in this article. Copolymers were prepared by melt polycondensation of bis-(β-hydroxyethylene terephthalate) (BHET) and succinic acid (SA) with excess of ethylene glycol (2G) in the presence of a novel titanium/silicate catalyst (C-94) and catalytic grade of germanium dioxide (GeO₂) as cocatalyst. The chemical structure and physical properties of those materials were characterized by ¹H NMR, FT-IR, dynamical-mechanical thermal analyses (DMTA), differential scanning calorimetry (DSC), solution viscosity and spectroscopic methods. The hydrolytic degradation was performed in a water solution with variable pH, also in garden soil and in compost. The highest hydrolytic degradation rate was observed for pH 4 and for compost. Better hydrolytic degradation values in compost medium were observed for copolyester prepared in the presence of GeO₂ as polycondensation cocatalyst. The copolyester with 40 mol% of aliphatic units was chosen for industrial syntheses which were performed in ELANA and subsequently the processing parameters and compatibility with potato starch of this polyester were checked by BIOP Biopolymer Technologies AG.     

Effect of copolymerized butylene terephthalate chains on polymorphism and enzymatic degradation of poly(butylene adipate)

The introduction of aromatic butylene terephthalate (BT) units into the backbone chains of aliphatic poly(butylene adipate) (PBA) not only changes the mechanical performance of the resultant P(BA-co-BT) copolymers but also affects their biodegradability. Because of the polymorphism of PBA homopolymer, the copolymerized BT units may also influence the polymorphic crystal structure as well as the biodegradation behavior. In this work, three P(BA-co-BT) copolymers with BT contents as 10, 20, and 25 mol% were chosen to study their polymorphic crystal structure, thermal properties and enzymatic degradation by means of wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and gravimetric methods. The results reveal that the P(BA-co-BT) copolymers with BT contents below 25 mol% can form polymorphic crystal structures after melt-crystallization at different temperatures. However, the recrystallization and transformation of polymorphic crystals are strongly affected by the rigid BT units. The enzymatic degradation rates of P(BA-co-BT) copolymers decrease with increasing the BT contents. The influences of the BT units on the polymorphism and enzymatic degradation are discussed in terms of the motion of PBA chains that copolymerized with BT units. It has been concluded from the examination of solid-state microstructure that the influence of the aromatic BT units on the motion of biodegradable PBA chains heavily influences the biodegradability.     

Synthesis, crystallization and hydrolysis of aromatic-aliphatic copolyester: Poly(trimethylene terephthalate)-co-poly(l-lactic acid)

In this study, poly(trimethylene terephthalate)-co-poly(l-lactic acid) (PTT-co-PLLA) copolyesters with different compositions were synthesized by melt polycondensation. The crystal morphologies of PTT-co-PLLA copolyesters were investigated with polarized light microscope (PLM). It was found that PTT-co-PLLA copolyesters exhibited banded spherulites with smaller band spacing at the same degree of super-cooling compared with PTT homopolymer. The PLLA segments in those copolyesters ranged from 0 to 28.4 mol% and did not form crystals during crystallization. Hydrolysis study on PTT homopolymer and PTT-co-PLLA copolyesters was carried out in buffer solutions. PTT-co-PLLA copolyesters represented pronounced hydrolytic degradation, which increased with the content of lactyl units. And it was concluded that degradation of PTT-co-PLLA was mainly attributed to the scission of PLLA segments.     

Characterization and enzymatic degradation of microbial copolyester P(3HB-co-3HV)s produced by metabolic reaction model-based system

The two types of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s [P(3HB-co-3HV)s] were produced by Paracoccus denitrificans ATCC 17741 using two different feeding methods. The produced P(3HB-co-3HV)s were fractionated and the copolymer sequence distributions were analyzed by ¹H and ¹³C NMR spectroscopy. It was found that the P(3HB-co-3HV) samples produced by conventional feeding method were statistically random copolymers. The sequence distributions of P(3HB-co-3HV) samples produced by optimization method were different from random P(3HB-co-3HV)s. The thermal properties and melting behaviors were analyzed by differential scanning calorimetry (DSC). These results demonstrated that P(3HB-co-3HV) samples produced by optimization method are close in nature to P(3HB-co-3HV)s rich in long-sequence of block 3HB units, but less in 3HV random regions. The enzymatic degradation profile of P(3HB-co-3HV) films was investigated in the presence of 3-hydroxybutyrate depolymerase from Pseudomonase lemoignei. The degradation process was observed by monitoring the time-dependent change in the weight loss of copolymer films. The surface erosion of copolymer films was qualitatively monitored by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The highest degradation rate of 2.6% per day was observed for random P(3HB-co-38%3HV) produced by conventional method. In comparison, the hydrolysis degradation rates of random P(3HB-co-3HV)s were about one time faster than those of P(3HB-co-3HV)s produced by optimization method.     

Photocatalytic degradation of methyl methacrylate copolymers

The photolytic and photocatalytic degradation of the copolymers poly(methyl methacrylate-co-butyl methacrylate) (MMA-BMA), poly(methyl methacrylate-co-ethyl acrylate) (MMA-EA) and poly(methyl methacrylate-co-methacrylic acid) (MMA-MAA) have been carried out in solution in the presence of solution combustion synthesized TiO₂ (CS TiO₂) and commercial Degussa P-25 TiO₂ (DP 25). The degradation rates of the copolymers were compared with the respective homopolymers. The copolymers and the homopolymers degraded randomly along the chain. The degradation rate was determined using continuous distribution kinetics. For all the polymers, CS TiO₂ exhibited superior photo-activity compared to the uncatalysed and DP 25 systems, owing to its high surface hydroxyl content and high specific surface area. The time evolution of the hydroxyl and hydroperoxide stretching vibration in the Fourier transform-infrared (FT-IR) spectra of the copolymers indicated that the degradation rate follows the order MMA-MAA > MMA-EA > MMA-BMA. The same order is observed for the rate coefficients of photocatalytic degradation. The photodegradation rate coefficients were compared with the activation energy of pyrolytic degradation. In degradation by pyrolysis, it was observed that MMA-BMA was the least stable followed by MMA-EA and MMA-MAA. The observed contrast in the order of thermal stability compared to the photo-stability of these copolymers was attributed to the two different mechanisms governing the scission of the polymer and the evolution of the products.     

Blends as a strategy towards tailored hydrolytic degradation of poly(?-caprolactone-co-d,l-lactide)-poly(ethylene glycol)-poly(?-caprolactone-co-d,l-lactide) co-polymers

Binary blends were prepared from poly(?-caprolactone) (PCL), and P(CL-co-d,l-lactic acid)-P(ethylene glycol)-P(CL-co-d,l-lactic acid) co-polymers, where the d,l-LA content in the side chains varied from 0 to 70 mol%. Blend discs were fabricated by melt-molding, and the effect of blend composition on hydrolytic degradation was studied. Variations in medium pH were monitored, and morphological changes were observed using scanning electron microscopy. Blending of these co-polymers was found to constitute a simple means by which intermediate rates of water absorption and mass loss were obtained, compared to those observed in pure co-polymer preparations. In one of the blends, prepared from the two components containing 70 or 0 mol% d,l-LA in the side chains and thereby exhibiting large differences in degradation rate, hydrolysis resulted in the formation of a porous material over time. Furthermore, all blend samples maintained their initial shape throughout the study. Such materials may be interesting for further investigations for applications in cellular therapy and controlled release.     

Environmental Degradation of Microbial Polyhydroxyalkanoates and Oil Palm-Based Composites

This paper investigates the degradation of polyhydroxyalkanoates and its biofiber composites in both soil and lake environment. Time-dependent changes in the weight loss of films were monitored. The rate of degradation of poly(3-hydroxybutyrate) [P(3HB)], poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-23?mol% 4HB)] and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate) [P(3HB-co-9?mol% 3HV-co-19?mol% 4HB)] were investigated. The rate of degradation in the lake is higher compared to that in the soil. The highest rate of degradation in lake environment (15.6?% w/w week^?1) was observed with P(3HB-co-3HV-co-4HB) terpolymer. Additionally, the rate of degradation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-38?mol% 3HV)] was compared to PHBV biofiber composites containing compatibilizers and empty fruit bunch (EFB). Here, composites with 30?% EFB displayed the highest rate of degradation both in the lake (25.6?% w/w week^?1) and soil (15.6?% w/w week^?1) environment.     

Copolymerization of ethylene with a vinyl ether bearing a fluorinated group

The copolymerization of ethylene (E) with 1H,1H,2H,2H-perfluorodecyl vinyl ether (FAVE8) by oxidative addition of salicylaldimine ligand to bis(1,5-cyclooctadiene)nickel(0)/methylaluminoxane (MAO) at room temperature and at different ethylene pressures is reported. The homopolymerization of ethylene is known to be highly active with this catalyst in contrast to the fluorinated vinyl ether which does not homopolymerize. The copolymerization of E with FAVE8 led to linear poly(E-co-FAVE8) statistic copolymers that were characterized by means of various techniques. The obtained copolymers, analyzed by FT-IR and solid state NMR spectroscopy, showed a small incorporation of the fluorinated vinyl ether. Three copolymerization reactions were investigated with different ethylene pressures (5, 10 and 50 bar) and the copolymer compositions indicated that the content of FAVE8 units depends on the ethylene pressure. The lower this pressure, the higher the content of such a fluorinated comonomer and for a 50 bar-pressure, no FAVE8 was incorporated. Thermogravimetric and differential scanning calorimetry analyses of these resulting copolymers exhibited high thermal stability, the thermal degradation starting from ca. 300 °C whereas high melting point (T_m = 129 °C) were achieved with these copolymers. Original films processed from these poly(E-co-FAVE8) copolymers illustrated hydrophobic and oleophilic characters as evidenced by water and diiodomethane contact angles of 104° and 49°, respectively.     

Degradation of aliphatic and aliphatic–aromatic co-polyesters by depolymerases from Roseateles depolymerans strain TB-87 and analysis of degradation products by LC-MS

The degradation activities of bacterium, Roseateles depolymerans TB-87 and its depolymerases Est-H and Est-L against aliphatic as well as aliphatic–aromatic co-polyesters, were investigated. Strain TB-87 and its enzymes exhibited an ability to degrade aliphatic and aliphatic–aromatic co-polyesters. Monomers produced as a result of degradation of aliphatic polyesters [poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA)] as well as aliphatic–aromatic co-polyester [poly(butylene succinate/terephthalate/isophthalate)-co-(lactate) (PBSTIL) by depolymerases Est-H and Est-L were investigated by liquid chromatography mass-spectrometry (LC-MS). Some common monomers like succinic acid and 1,4-butanediol were detected besides adipic acid and terephthalic/isophthalic acids as degradation products from PBSA and PBSTIL, respectively, whereas lactic acid was not detected. The succinic acid monomer was detected prior to adipic acid as a result of degradation of PBSA. The enzymes depolymerized PBS also into respective monomers. The analysis of PBSTIL degradation products revealed that enzymes easily degraded aliphatic segments as compared to aromatic segments and resulted in production of succinic acid prior to terephthalic and isophthalic acid. On the basis of these results, we speculate that both the enzymes Est-H and Est-L, attacked succinic acid segments (BS) first instead of adipic acid (BA) and terephthalic/isophthalic acid (BT or BI) segments of PBSA and PBSTIL, respectively. It is concluded from the results that R. depolymerans strain TB-87 can depolymerize aliphatic as well as aliphatic–aromatic co-polyesters; therefore, its enzymes can be applied in the process of biochemical monomer recycling.     

Anthranilamide-protected vinylboronic acid: rational monomer design for improved polymerization/transformation ability providing access to conventionally inaccessible copolymers

We have studied several protecting groups for vinylboronic-acid derivatives as monomers in radical polymerizations with the objective to improve the polymerization ability and C–B bond-cleaving post-transformation performance. Anthranilamide (aam)-protected vinylboronic acid (VBaam) exhibited experimentally a relatively high polymerization activity, which was theoretically corroborated by density functional theory (DFT) calculations that revealed a peculiar effect of the interaction between the aam groups on the polymerization behavior. The VBaam units in the copolymers can subsequently be transformed into vinyl alcohols or into ethylene units through C–B-bond-cleaving side-chain replacement, which affords valuable copolymers such as poly(vinyl alcohol-co-styrene), poly(ethylene-co-styrene), and poly(ethylene-co-acrylate).

We designed a vinyl-boronic-acid protected by anthranilamide as a “transformable” monomer in radical polymerization to synthesize conventionally inaccessible copolymers, such as poly(vinyl alcohol-co-styrene) and poly(ethylene-co-acrylate).     

Thermal properties of poly(butylene oxalate) copolymerized with azelaic acid

Poly(butylene oxalate) (PBO) and poly(butylene oxalate/butylene azelate) random copolymers (PBOBAz) of various compositions were synthesized in bulk and characterized in terms of chemical structure and thermal properties. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. All copolymers were found to be partially crystalline and thermally stable up to about 290 °C. The main effect of copolymerization was a decrease in melting and glass transition temperatures with respect to PBO homopolymer. The pure crystalline phase characteristic of PBO was evidenced by means of X-ray measurements in all the copolymers under investigation. The fusion temperatures appeared to be well correlated to composition by Baur's equation.Amorphous samples were obtained after melt quenching and showed a monotonic decrease of glass transition temperatures as the content of the flexible butylene azelate units is increased. Fox equation described well the T_g-composition data. Lastly, the overall crystallization rate of PBO was found to decrease regularly with increasing butylene azelate unit content.     

Poly(ethylene terephthalate) copolymers containing nitroterephthalic units. III. Methanolytic degradation

The methanolytic degradation of poly(ethylene terephthalate) (PET) copolymers containing nitroterephthalic units was investigated. Random poly(ethylene terephthalate‐co‐nitroterephthalate) copolyesters (PETNT) containing 15 and 30 mol % nitrated units were prepared from ethylene glycol and a mixture of dimethyl terephthalate and dimethyl nitroterephthalate. A detailed study of the influence of the nitro group on the methanolytic degradation rate of the nitrated bis(2‐hydroxyethyl) nitroterephthalate (BHENT) model compound in comparison with the nonnitrated bis(2‐hydroxyethyl) terephthalate (BHET) model compound was carried out. The kinetics of the methanolysis of BHENT and BHET were evaluated with high‐performance liquid chromatography and ¹H NMR spectroscopy. BHENT appeared to be much more reactive than BHET. The methanolytic degradation of PET and PETNT copolyesters at 80 °C was followed by changes in the weight and viscosity, gel permeation chromatography, differential scanning calorimetry, scanning electron microscopy, and ¹H and ¹³C NMR spectroscopy. The copolyesters degraded faster than PET, and the degradation increased with the content of nitrated units and occurred preferentially by cleavage of the ester groups placed at the meta position of the nitro group in the nitrated units. For both PET and PETNT copolyesters, an increase in crystallinity accompanied methanolysis. A surface degradation mechanism entailing solubilization of the fragmented polymer and consequent loss of mass was found to operate in the methanolysis of the copolyesters. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2276–2285, 2002     

Synthesis and characterization of serial random and block-copolymers based on lactide and glycolide

The objective of this study is to investigate the properties of poly(lactide-co-glycolide) with different composition ratios and PLGA-PEG-PLGA copolymers synthesized by ring-opening polymerization method. Their compositions, crystallization properties, thermal and degradation behaviors, hydrophilicity and biocompatibility were studied. Our results demonstrate that poly(lactide-co-glycolide) with a 90% lactide and PLGA-PEG-PLGA show some crystallization properties. While as the decrease of lactide content in polymers, poly(lactide-co-glycolide) become amorphous, whereas, their hydrophilicity have been improved on the contrary. Compared to poly(lactide-co-glycolide), the PLGA-PEG-PLGA copolymer has a better hydrophilicity for the existence of polyethylene glycol block. Furthermore, both these polymers display easy controlled degradation properties and good cell compatibility.     

Using Triethylborane to Manipulate Reactivity Ratios in Epoxide-Anhydride Copolymerization: Application to the Synthesis of Polyethers with Degradable Ester Functions

The anionic ring-opening copolymerization (ROCOP) of epoxides, namely of ethylene oxide (EO), with anhydrides (AH) generally produces strictly alternating copolymers. With triethylborane (TEB)-assisted ROCOP of EO with AH, statistical copolymers of high molar mass including ether and ester units could be obtained. In the presence of TEB, the reactivity ratio of EO (r_EO), which is normally equal to 0 in its absence, could be progressively raised to values lower than 1 or higher than 1. Conditions were even found to obtain r_EO equal or close to 1. Samples of P(EO-co-ester) with minimal compositional drift could be synthesized; upon basic degradation of their ester linkages, these samples afforded poly(ethylene oxide) (PEO) diol samples of narrow molar mass distribution. In other cases where r_EO were lower or higher than 1, the PEO diol samples eventually isolated after degradation exhibited a broader distribution of molar masses because of the compositional drift of initial P(EO-co-ester) samples.     

Investigations on equilibrium of poly(ethylene oxalate) and 1,4-dioxane-2,3-dione

Behavior of poly(ethylene oxalate) in a temperature range of 148–240°C was studied, and a new method of isolating 1,4-dioxane-2,3-dione from the products of decomposition of poly(ethylene oxalate) was used. The process of decomposition was second order. Equilibrium of poly(ethylene oxalate) and 1,4-dioxane-2,3-dione was registered at 148–240°C. The influence on this process of certain inorganic compounds as catalysts was investigated.     

Anti-biofouling by degradation of polymers

Copolymers of methyl methacrylate(MMA) and acrylate terminated poly(ethylene oxide-co-ethylene carbonate) (PEOC) macromonomer(PEOCA) were synthesized,and the degradation of the polymers was investigated by use of quartz crystal microbalance with dissipation(QCM-D).It is shown that the polymeric surface exhibits degradation in seawater depending on the content of the side chains.Field tests in seawater show that the surface constructed by the copolymer can effectively inhibit marine biofouling because it can be self-renewed due to degradation of the copolymer.     

Synthesis and characterization of biodegradable aliphatic copolyesters with poly(ethylene oxide) soft segments

A series of multiblock poly(ether-ester)s based on poly(butylene succinate) (PBS) as the hard segments and hydrophilic poly(ethylene oxide) (PEO) as the soft segments was synthesized with the aim of developing degradable polymers which could combine the mechanical properties of high performance elastomers with those of flexible plastics. The aliphatic poly(ether-ester)s were synthesized by the catalyzed two-step transesterification reaction of dimethyl succinate, 1,4-butanediol and α,ω-hydroxyl terminated poly(ethylene oxide) (PEO, = 1000 g/mol) in bulk. The content of soft PEO segments in the polymer chains was varied from about 10 to 50 mass%. The effect of the introduction of the soft PEO segments on the structure, thermal and physical properties, as well as on the biodegradation properties was investigated. The composition and structure of these aliphatic segmented copolyesters were determined by ¹H NMR spectroscopy. The molecular weights of the polyesters were verified by gel permeation chromatography (GPC), as well as by viscometry of dilute solutions and polymer melts. The thermal properties were investigated using differential scanning calorimetry (DSC). The degree of crystallinity was determined by means of DSC and wide-angle X-ray scattering. A depression of melting temperature and a reduction of crystallinity of the hard segments with increasing content of PEO segments were observed. Biodegradation of the synthesized copolyesters, estimated in enzymatic degradation tests in phosphate buffer solution with Candida rugosa lipase at 37 °C was compared with hydrolytic degradation in the buffer solution. The weight losses of the samples were in the range from 2 to 10 mass%. GPC analysis confirmed that there were significant changes in molecular weight of copolyesters with higher content of PEO segments, up to 40% of initial values. This leads to conclusion that degradation mechanism of the poly(ether-ester)s based on PEO segments occurs through bulk degradation in addition to surface erosion.     

Synthesis, characterization and degradability of the novel aliphatic polyester bearing pendant N-isopropylamide functional groups

The synthesis, characterization, and degradability of the novel aliphatic polyester bearing pendant N-isopropylamide functional group are reported for the first time. 2-(N-Isopropyl-2-carbamoylethyl)cyclohexanone (CCH) was first synthesized by the Michael reaction of N-isopropylacrylamide with cyclohexanone and was subsequently converted into 6-(N-isopropyl-2-carbamoylethyl)-?-caprolactone (CCL) by the Baeyer-Villiger oxidation reaction using 3-chloroperoxybenzoic acid (mCPBA) as the oxidant. Finally, the novel functionalized poly(?-caprolactone) bearing the pendant N-isopropylamide functional groups, poly(6-(N-isopropyl-2-carbamoylethyl)-?-caprolactone-co-?-caprolactone)s (poly(CCL-co-CL)), were carried out successfully by bulk ring-opening polymerization of CCL and ?-CL initiated by Sn(Oct)₂. Poly(CCL-co-CL) were characterized by ¹H NMR, ¹³C NMR, SEC and DSC. The copolymer containing 9.1 mol% CCL formed flexible films and was used to study its degradability. A phosphate buffer (pH = 7.4) with temperature 37 °C was adopted to proceed the degrading study all through. Compared with poly(?-caprolactone), the hydrolytic degradation of poly(CCL-co-CL) was much faster, which is confirmed by the weight loss and change of intrinsic viscosity.