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.     

Surface structure of thin asymmetric PS-b-PMMA diblock copolymers investigated by atomic force microscopy

Asymmetric poly(styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymers of molecular weight M_n = 29,700 g mol⁻¹ (M_PS = 9300 g mol⁻¹M_PMMA = 20,100 g mol⁻¹, PD = 1.15, χ_PS = 0.323, χ_PMMA = 0.677) and M_n = 63,900 g mol⁻¹ (M_PS = 50,500 g mol⁻¹, M_PMMA = 13,400 g mol⁻¹, PD = 1.18, χ_PS = 0.790, χ_PMMA = 0.210) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Atomic force microscopy (AFM) was used to investigate the surface structure of thin films, prepared by spin-coating the diblock copolymers on a silicon substrate. We show that the nanostructure of the diblock copolymer depends on the molecular weight and volume fraction of the diblock copolymers. We observed a perpendicular lamellar structure for the high molar mass sample and a hexagonal-packed cylindrical patterning for the lower molar mass one. Small-angle X-ray scattering investigation of these samples without annealing did not reveal any ordered structure. Annealing of PS-b-PMMA samples at 160 °C for 24 h led to a change in surface structure.     

Kinetics of copolymerization and degradation of poly[acrylonitrile-co-(amino ethyl-2-methyl propenoate)]

Amino ethyl-2-methyl propenoate was firstly used to successfully copolymerize with acrylonitrile in a H₂O/dimethylsulfoxide (DMSO) mixture between 50 °C and 70 °C under N₂ atmosphere. This was achieved by using azobisisobutyronitrile as the initiator. Kinetics of copolymerization of acrylonitrile with amino ethyl-2-methyl propenoate was investigated. The kinetic equation of copolymerization was obtained and the apparent activation energy of degradation of poly[acrylonitrile-co-(amino ethyl-2-methyl propenoate)] was determined. Increasing DMSO concentration in the solvent mixture leads to a rapid increase in the degradation apparent activation energy. The apparent activation energy decreases quickly with an increase in the comononer amino ethyl-2-methyl propenoate concentration, and such a change becomes less prominent as the molar ratio of amino ethyl-2-methyl propenoate/acrylonitrile goes beyond 2/100. The apparent activation energy also increases along with the copolymerization temperature. The resultant fibers prepared from poly[acrylonitrile-co-(amino ethyl-2-methyl propenoate)] were obtained with the fineness at 1.03 dtex and the tenacity at 6.18cN dtex⁻¹.     

Degradation of commercially important polyhydroxyalkanoates in tropical mangrove ecosystem

This paper presents the degradation trends of selected polyhydroxyalkanoate (PHA) films in a tropical mangrove environment. The biodegradability of homopolymer poly(3-hydroxybutyrate) [P(3HB)] and its co-polymers, poly(3-hydroxybutyrate-co-5 mol% 3-hydroxyvalerate) [P(3HB-co-5 mol% 3HV)] and poly(3-hydroxybutyrate-co-5 mol% 3-hydroxyhexanoate) [P(3HB-co-5 mol% 3HHx)], was investigated along with P(3HB) films containing 38 wt% titanium dioxide (TiO₂) [P(3HB)-38 wt% TiO₂]. The degradation of these formulations was monitored for 8 weeks at three different zones in an intermediate mangrove compartment along Sungai Pinang, adjacent to a famous fishing village on south of Penang Island. The degradation rate was observed both on the surface and in the sediment and was expressed in percentage of weight loss. The microbial enumeration done using sediment from the different zones indicated similar colony-forming unit (CFU) counts even though differences were noticed in the degradation profile of the various films in the respective zones. The results obtained revealed that co-polymers disintegrated at similar or higher rate than the homopolymer, P(3HB). However, the incorporation of TiO₂ into PHB films caused the degradation rate of P(3HB)-38 wt% TiO₂ composite film to be far slower than all the other PHA films. The overall rate of degradation of all PHA films placed on the sediment surface was slower than those buried in the sediment. Microscopic analyses showed that the surface morphology of P(3HB-co-5 mol% 3HHx) was more porous compared to P(3HB) and P(3HB-co-5 mol% 3HV) films, which may be an important factor for its rapid degradation.     

Study of amphiphilic poly(1-dodecene-co-para-methylstyrene)-graft-poly(ethylene glycol). Part II: Preparation and micellization behavior of the amphiphilic copolymers

Poly(1-dodecene-co-pMS) copolymers were brominated by HBr/H₂O₂ system with high selectivity at the methyl groups of pMS units. It was found that longer reaction time, higher pMS content, and lower molecular weight of the copolymers were helpful for higher degree of bromination. Through a modified Williamson ether synthesis, poly(ethylene glycol) monomethyl ethers (PEG) were grafted onto the brominated copolymers, and the amphiphilic poly(1-dodecene-co-pMS)-graft-PEG copolymers which can be readily dissolved in n-octane were successfully synthesized. Due to their amphiphilic characteristics, they can self-assemble spontaneously into reverse micelles in n-octane. Their micellization behaviors were investigated by fluorescence probe technique, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The critical micelle concentrations of the three copolymers in n-octane were determined at about 1.26 × 10⁻⁴, 1.58 × 10⁻⁴, and 1.95 × 10⁻⁴ g ml⁻¹ by fluorescence measurements. The morphologies of micelles were preliminarily explored by TEM and were found to be spheres.     

Investigation of swelling and network parameters of poly(ethylene glycol)-crosslinked poly(methyl vinyl ether-co-maleic acid) hydrogels

The influence of poly(ethylene glycol) (PEG) plasticiser content and molecular weight on the physicochemical properties of films cast from aqueous blends of poly(methyl vinyl ether-co-maleic acid) was investigated using thermal analysis, swelling studies, scanning electron microscopy (SEM) and attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy revealed a shift of the CO peak from 1708 to 1731 cm⁻¹, indicating that an esterification reaction had occurred upon heating, thus producing crosslinked films. Higher molecular weight PEGs (10,000 and 1000 Da, respectively), having greater chain length, producing hydrogel networks with lower crosslink densities and higher average molecular weight between two consecutive crosslinks. Accordingly, such materials exhibited higher swelling rates. Hydrogels crosslinked with a low molecular weight PEG (PEG 200) showed rigid networks with high crosslink densities and, therefore, lower swelling rates. Polymer:plasticizer ratio alteration did not yield any discernable patterns, regardless of the method of analysis. The polymer-water interaction parameter (χ) increased with increases in the crosslink density. SEM studies showed that porosity of the crosslinked films increased with increasing PEG MW, confirming what had been observed with swelling studies and thermal analysis, that the crosslink density must be decreased as the M_w of the crosslinker is increased. Hydrogels containing PMVE/MA/PEG 10,000 could be used for rapid delivery of drug, due to their low crosslink density. Moderately crosslinked PMVE/MA/PEG 1000 hydrogels or highly crosslinked PMVE/MA/PEG 200 systems could then be used in controlling the drug delivery rates. We are currently evaluating these systems, both alone and in combination, for use in sustained release drug delivery devices.     

Highly phosphonated polypentafluorostyrene: Characterization and blends with polybenzimidazole

In this study we present results of the conductivity and resistance to thermooxidative and condensation reactions of a highly phosphonated poly(pentafluorostyrene) (PWN2010) and of its blends with poly(benzimidazole)s (PBI). This polymer, which combines both: (i) a high degree of phosphonation (above 90%) and (ii) a relatively high acidity (pK_a (–PO₃H₂ ↔ –PO₃H⁻) ∼ 0.5) due to the fluorine neighbors, is designed for low humidity operating fuel cell. This was confirmed by the conductivity measurements for PWN2010 reaching σ = 5 × 10⁻⁴ S cm⁻¹ at 150 °C in dry N₂ and σ = 1 × 10⁻³ S cm⁻¹ at 150 °C (λ = 0.75). Furthermore, this polymer showed only 48% of anhydride formation when annealing it at T = 250 °C for 5 h and only 2% weight loss during a 96 h Fenton test. These properties combined with the ability of the PWN2010 to form homogeneous blends with polybenzimidazoles resulting in stable and flexible polymer films, makes PWN2010 a very promising candidate as a polymer electrolyte for intermediate- and high-temperature fuel cell applications.     

Excess molar enthalpies of binary mixtures containing poly(ethylene glycol) 200+four cyclic ethers at (288.15, 298.15 and 313.15) K and at atmospheric pressure

Excess molar enthalpies, H_m^E, of binary mixtures containing poly(ethylene glycol) (PEG) 200+1,3-dioxolane, PEG 200+1,4-dioxane, PEG 200+oxolane and PEG 200+oxane were determined using a flow microcalorimeter at (288.15, 298.15 and 313.15) K and at atmospheric pressure. The H_m^E curves are always positive, with maxima varying from 393 J mol⁻¹ (1,3-dioxolane) to 658 J mol⁻¹ (oxolane), showing asymmetrical trends. The effect of the temperature is well marked on the calorimetric data that increase as the temperature is increased. The Redlich-Kister polynomial was used to estimate the binary fitting parameters. Root-mean-square deviations from the regression lines are reported.     

Mechanism of degradation induced embrittlement in polyethylene

The thermal oxidation of polyethylene films in air at 80 °C and 90 °C has been studied by tensile testing, IR spectrophotometry and molar mass determination from rheometric measurements. In the conditions under study, the polymer predominantly undergoes chain scission and embrittles suddenly when the weight average molar mass reaches a critical value (90 kg mol⁻¹), far before significant damage of the entanglement network (M_e = 1.9 kg mol⁻¹) in the amorphous phase.The following embrittlement mechanism is proposed: chain scission in the amorphous phase induces chemicrystallization. The thickness of the interlamellar amorphous layer (l_a) decreases until a critical value of the order of 6-7 nm, below which plasticity cannot be activated and the polymer behaves in a brittle manner, as previously shown for virgin polyethylene. Using (l_a, M_W) maps, it is possible to explain the differences observed in the embrittlement behaviour of semi-crystalline polymers predominantly undergoing chain scission.     

Synthesis, characterization and in vitro degradation study of a novel and rapidly degradable elastomer

Biodegradable elastomers represent a useful class of biomaterials. In this paper, a novel biodegradable elastomer, poly(PEG-co-CA) (PEC), was synthesized by condensation of poly(ethylene glycol) (PEG) and citric acid (CA) under atmospheric pressure without any catalyst. We first synthesized a pre-polymer by carrying out a controlled condensation reaction between PEG and citric acid, and then post-polymerised and simultaneously cross-linked the pre-polymer in the mould at 120 °C. The pre-polymer was characterized by FT-IR, ¹H NMR, ¹³C NMR, GPC and DSC. A series of polymers were prepared at different post-polymerisation time and different monomer ratios. Measurements on the mechanical properties of PEC testified that the new polymers are elastomers with low hardness and big elongation, and hydrolytic degradation of the polymer films in a buffer of pH 7.4 at 37 °C showed that PEC had excellent degradability (all the films show the weight losses more than 60% after 96 h incubation). The different post-polymerisation time and monomer ratio had strong influence on the degradation rates and mechanical performances. The material is expected to be useful for controlled drug delivery and other biomedical applications.     

Preparation and performance analysis of PE-supported P(AN-co-MMA) gel polymer electrolyte for lithium ion battery application

Copolymer, poly(acrylonitrile-co-methyl methacrylate) (P(AN-co-MMA)), was synthesized by solution polymerization with different mole ratios of monomers, acrylonitrile (AN) and methyl methacrylate (MMA). Polyethylene (PE) supported copolymer and gel polymer electrolyte (GPE) were prepared with this copolymer and their performances were characterized with FTIR, TGA, SEM, and electrochemical methods. It is found that the GPE using the PE-supported copolymer with AN to MMA = 4:1 (mole) exhibits an ionic conductivity of 2.06 × 10⁻³ S cm⁻¹ at room temperature. The copolymer is stable up to 270 °C. The PE-supported copolymer shows a cross-linked porous structure and has 150 wt% of electrolyte uptake. The GPE is compatible with anode and cathode of lithium ion battery at high voltage and its electrochemical window is 5.5 V (vs. Li/Li⁺). With the application of the PE-supported GPE in lithium ion battery, the battery shows its good rate and initial discharge capacity and cyclic stability.     

High dielectric constant PrYxOy sensing films electrolyte-insulator-semiconductor pH-sensor for the detection of urea

In this paper, we describe the structural and sensing properties of high-k PrY_xO_y sensing films deposited on Si substrates through reactive co-sputtering. Secondary ion mass spectrometry and atomic force microscopy were employed to analyze the compositional and morphological features of these films after annealing at various temperatures. The electrolyte-insulator-semiconductor (EIS) device incorporating a PrY_xO_y sensing membrane that had been annealed at 800 °C exhibited good sensing characteristics, including a high sensitivity (59.07 mV pH⁻¹ in solutions from pH 2 to 12), a low hysteresis voltage (2.4 mV in the pH loop 7 → 4 → 7 → 10 → 7), and a small drift rate (0.62 mV h⁻¹ in the buffer solution at pH 7). The PrY_xO_y EIS device also showed a high selective response towards H⁺. This improvement can be attributed to the small number of crystal defects and the large surface roughness. In addition, the enzymatic EIS-based urea biosensor incorporating a high-k PrY_xO_y sensing film annealed at 800 °C allowed the potentiometric analysis of urea, at concentrations ranging from 1 to 16 mM, with a sensitivity of 9.59 mV mM⁻¹.     

X-ray diffraction study on the thermal expansion behavior of cellulose Iβ and its high-temperature phase

Oriented films of cellulose prepared from algal cellulose were hydrothermally treated to convert them into highly crystalline cellulose Iβ. The lateral thermal expansion behavior of the prepared cellulose Iβ films was investigated using X-ray diffraction at temperatures from 20 to 300 °C. Cellulose Iβ was transformed into the high-temperature phase when the temperature was above 230 °C, allowing the lateral thermal expansion coefficient of cellulose Iβ and its high-temperature phase to be measured. For cellulose Iβ, the thermal expansion coefficients (TECs) of the a- and b-axes were α_a = 9.8 × 10⁻⁵ °C⁻¹ and α_b = 1.2 × 10⁻⁵ °C⁻¹, respectively. This anisotropic thermal expansion behavior in the lateral direction is ascribed to the crystal structure and to the hydrogen-bonding system of cellulose Iβ. For the high-temperature phase, the anisotropy was more conspicuous, and the TECs of the a- and b-axes were α_a = 19.8 × 10⁻⁵ °C⁻¹ and α_b = −1.6 × 10⁻⁵ °C⁻¹, respectively. Synchrotron X-ray fiber diffraction diagrams of the high-temperature phase were also recorded at 250 °C. The cellulose high-temperature phase is composed of a two-chain monoclinic unit cell, a = 0.819 nm, b = 0.818 nm, c (fiber repeat) = 1.037 nm, and γ = 96.4°, with space group = P2₁. The volume of this cell is 4.6% larger than that of cellulose Iβ at 30 °C.     

Electrosyntheses of poly(2,3-benzofuran) films in boron trifluoride diethyl etherate containing poly(ethylene glycol) oligomers

Visible-light transparent high-quality substrate-supported poly(2,3-benzofuran) (PBF) film has been successfully electrosynthesized by direct anodic oxidation of 2,3-benzofuran on stainless steel sheet in boron trifluoride diethyl etherate (BFEE) containing 10% poly(ethylene glycol) (PEG) with molar mass of 400 (by volume). The oxidation potential of 2,3-benzofuran in this medium was measured to be only 1.0 V vs. SCE, which is lower than that determined in acetonitrile + 0.1 M Bu₄NBF₄ (1.2 V vs. SCE). The PBF films obtained in this media showed good electrochemical behaviors and good thermal stability with conductivity of 10⁻² S cm⁻¹, and the doping level of as-prepared PBF films was determined to be only 8.9%. The structure and morphology of the polymer were investigated by UV-vis, infrared spectroscopy and scanning electron microscopy (SEM), respectively. To the best of our knowledge, this is the first case for the syntheses of PBF films.     

Preparation and photoelectrocatalytic activity of a nano-structured WO3 platelet film

A tungsten trioxide (WO₃) film was prepared by calcination from a precursor paste including suspended ammonium tungstate and polyethylene glycol (PEG). The ammonium tungstate suspension was yielded by an acid-base reaction of tungstic acid and an ammonium solution followed by deposition with ethanol addition. Thermogravimetric (TG) analysis showed that the TG profile of PEG is significantly influenced by deposited ammonium tungstate, suggesting that PEG is interacting strongly with deposited ammonium tungstate in the suspension paste. X-ray diffraction (XRD) data indicated that the WO₃ film is crystallized by sintering over 400 °C. The scanning electron microscopic (SEM) measurement showed that the film is composed of the nano-structured WO₃ platelets. The semiconductor properties of the film were examined by Mott-Schottky analysis to give flat band potential E_FB=0.30 V vs. saturated calomel reference electrode (SCE) and donor carrier density N_D=2.5×10²² cm⁻³, latter of which is higher than previous WO₃ films by two orders of magnitude. The higher N_D was explained by the large interfacial heterojunction area caused by the nano-platelet structure, which apparently increases capacitance per a unit electrode area. The WO₃ film sintered at 550 °C produced 3.7 mA cm⁻² of a photoanodic current at 1.2 V vs. SCE under illumination with a 500 W xenon lamp due to catalytic water oxidation. This photocurrent was 4.5-12.8 times higher than those for the other control WO₃ films prepared by similar but different procedures. The high catalytic activity could be explained by the nano-platelet structure. The photocurrent was generated on illumination of UV and visible light below 470 nm, and the maximum incident photon-to-current conversion efficiency (IPCE) was 47% at 320 nm at 1.2 V. Technically important procedures for preparation of nano-structured platelets were discussed.     

Thermal aggregation of bovine serum albumin studied by asymmetrical flow field-flow fractionation

The use of asymmetrical flow field-flow fractionation (AsFlFFF) in the study of heat-induced aggregation of proteins is demonstrated with bovine serum albumin (BSA) as a model analyte. The hydrodynamic diameter (d_h), the molar mass of heat-induced aggregates, and the radius of gyration (R_g) were calculated in order to get more detailed understanding of the conformational changes of BSA upon heating. The hydrodynamic diameter of native BSA at ambient temperature was ∼7 nm. The particle size was relatively stable up to 60 °C; above 63 °C, however, BSA underwent aggregation (growth of hydrodynamic diameter). The hydrodynamic diameters of the aggregated particles, heated to 80 °C, ranged from 15 to 149 nm depending on the BSA concentration, duration of incubation, and the ionic strength of the solvent. Heating of BSA in the presence of sodium dodecyl sulfate (1.7 or 17 mM) did not lead to aggregation. The heat-induced aggregates were characterized in terms of their molar mass and particle size together with their respective distributions with a hyphenated technique consisting of an asymmetrical field-flow fractionation device and a multi-angle light scattering detector and a UV-detector. The carrier solution comprised 8.5 mM phosphate and 150 mM sodium chloride at pH 7.4. The weight-average molar mass (M_w) of native BSA at ambient temperature is 6.6 × 10⁴ g mol⁻¹. Incubation of solutions with BSA concentrations of 1.0 and 2.5 mg mL⁻¹ at 80 °C for 1 h resulted in aggregates with M_w 1.2 × 10⁶ and 1.9 × 10⁶ g mol⁻¹, respectively. The average radius of gyration and the average hydrodynamic radius of the heat-induced aggregate samples were calculated and compared to the values obtained from the size distributions measured by AsFlFFF. For comparison static light scattering measurements were carried out and the corresponding average molar mass distributions of solutions with BSA concentrations of 1.0 and 2.5 mg mL⁻¹ at 80 °C for 1 h gave aggregates with M_w 1.7 × 10⁶ and 3.5 × 10⁶ g mol⁻¹, respectively.     

Novel polymeric metal complexes as dye sensitizers for Dye-sensitized solar cells based on poly thiophene containing complexes of 8-hydroxyquinoline with Zn(II),Cu(II) and Eu(III) in the side chain

Novel polymeric metal complexes as dye sensitizer for dye-sensitized solar cells (DSSCs) based on poly thiophene containing complexes of 8-hydroxyquinoline with Zn(II),Cu(II), and Eu(III) in the side chain have been synthesized according to the Stille coupling method and characterized by FTIR, GPC, and Elemental analysis. The UV-vis absorption spectroscopy, photoluminescence spectroscopy, cyclic voltammetry, and the applications in dye-sensitized solar cells (DSSCs) are also determined and studied. The DSSCs fabricated by PZn(Q)₂-co-3MT, PCu(Q)₂-co-3MT, and PEu(Q)₃-co-3MT exhibit good device performance with a power conversion efficiency of up to 0.56%, 0.78%, and 1.16%, respectively, under simulated AM 1.5 G solar irradiation (100 mW/cm²). They possess excellent stabilities and their thermal decomposition temperatures are 340 °C, 400 °C, and 540 °C, respectively, indicating polymeric metal complexes are suitable for the fabrication processes of optoelectronic devices.     

Detecting solution pH changes using poly (N-isopropylacrylamide)-co-acrylic acid microgel-based etalon modified quartz crystal microbalances

Poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgel-based etalons have been shown to have visible color and unique spectral properties, which both depend on solution temperature and pH. In this investigation, pNIPAm-co-AAc microgel-based etalons were fabricated on the Au electrode of a quartz crystal microbalance (QCM), and the resonant frequency of the QCM monitored as a function of temperature, at pH 3.0. Furthermore, the resonant frequency at either pH 3.0 or 7.0 was monitored while keeping the solution temperature constant at various temperatures. In all cases, when the solution temperature was below the collapse transition for the microgels (∼32 °C), the resonant frequency at pH 3.0 was lower than at pH 7.0, which we attribute to the film transitioning from a deswollen to swollen state, respectively. It was observed that the magnitude of the resonant frequency change increased as the solution temperature approached the collapse temperature for the microgels. The overall sensitivity to pH was determined to be 1.3 × 10⁻⁸ M [H⁺] Hz⁻¹ and a theoretical detection limit of 390 nM was obtained. This sensitivity will be exploited further for future biosensing applications.     

Synthesis of isotactic star-shaped poly(vinyl alcohol)

Isotactic 6-armed star-shaped poly(vinyl alcohol) (PVA) with a narrow molecular weight distribution was successfully prepared by the living cationic polymerization of 6-armed star-shaped poly(tert-butyl vinyl ether) (PTBVE) and subsequent acidic ether cleavage. The PTBVE was synthesized using hexa(chloromethyl) melamine (HCMM) as a hexafunctional initiator and ZnI₂ or ZnCl₂ as an activator in toluene/MC (1/1 v/v) at −70 °C. A better living stability of PTBVE was obtained in the ZnCl₂ activator system. The number average molecular weight and the polydispersity index of the 6-armed star-shaped PTBVE polymerized with ZnCl₂ at −70 °C for 24 h were 156,000 g/mol and 1.47, respectively. The fraction of the mm sequence of the resulting PVA was 52%.     

Phase behavior of biodegradable amphiphilic poly(l,l-lactide)-b-poly(ethylene glycol)-b-poly(l,l-lactide)

This study describes the miscibility phase behavior in two series of biodegradable triblock copolymers, poly(l-lactide)-block-poly(ethylene glycol)-block-poly(l-lactide) (PLLA-PEG-PLLA), prepared from two di-hydroxy-terminated PEG prepolymers (M_n = 4000 or 600 g mol⁻¹) with different lengths of poly(l-lactide) segments (polymerization degree, DP = 1.2-145.6). The prepared block copolymers presented wide range of molecular weights (800-25,000 g mol⁻¹) and compositions (16-80 wt.% of PEG). The copolymer multiphases coexistance and interaction were evaluated by DSC and TGA. The copolymers presented a dual stage thermal degradation and decreased thermal stability compared to PEG homopolymers. In addition, DSC analyses allowed the observation of multiphase separation; the melting temperature, T_m, of PLLA and PEG phases depended on the relative segment lengths and the only observed glass transition temperature (T_g) in copolymers indicated miscibility in the amorphous phase.