Porous biodegradable polyesters. I. Preparation of porous poly(L‐lactide) films by extraction of poly(ethylene oxide) from their blends

Porous poly(L ‐lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution‐cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film porosity and extracted weight ratio were in good agreement with the expected for porous films prepared using PEO of low molecular weight (M_w = 1 × 10³), but shifted to lower values than expected when high molecular weight PEO (M_w = 1 × 10⁵) was utilized. The maximum pore size was larger for porous films prepared from PEO having higher molecular weight, when compared at the same blending ratio of PLLA and PEO before water extraction. Differential scanning calorimetry of as‐cast PLLA and PEO blend films revealed that PLLA and PEO were phase‐separated at least after solvent evaporation. On the other hand, comparison of blend films before and after extraction suggested that a small amount of PEO was trapped in the amorphous region between PLLA crystallites even after water extraction and hindered PLLA crystallization during solvent evaporation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 629–637, 2000     

Blends of aliphatic polyesters. III. Biodegradation of solution-cast blends from poly(L-lactide) and poly(ε-caprolactone)

Phase-separated blend films were prepared with the solution casting method from poly(L -lactide) (PLLA) and poly(ε-caprolactone) (PCL) with different PLLA contents [X_PLLA (w/w) = PLLA/(PCL + PLLA)] and their biodegradation was investigated in soil up to 20 months by gravimetry, gel permeation chromatography, tensile testing, differential scanning calorimetry, and scanning electron microscopy. The nonblended PCL film and the blend film with X_PLLA = 0.25 disappeared in 4 and 12 months, respectively, while most of the initial mass remained for the blend film of X_PLLA = 0.75 and the nonblended PLLA film. The decrease in weight remaining, molecular weight, tensile strength, and elongation-at-break was higher for blend films of low X_PLLA. The melting temperature of PLLA in blend films of X_PLLA = 0.5 and 0.75, and of nonblended film, remained around 179°C upon biodegradation in soil for 20 months. The preferred biodegradation of PCL in blend films resulted in formation of microspheres of a PLLA-rich phase at the surface for the blend film of X_PLLA = 0.25 and the porous structure for blend films of X_PLLA = 0.5 and 0.75. Comparison of the weight loss of blend films in biodegradation in soil with that of the nonenzymatic hydrolysis in phosphate-buffered solution revealed preferred enzymatic degradation of PCL and insignificant attack to PLLA in the blends. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2259–2268, 1998     

Blends of aliphatic polyesters. II. Hydrolysis of solution-cast blends from poly(L-lactide) and poly(E-caprolactone) in phosphate-buffered solution

Blend films were prepared from poly(L -lactide) (PLLA) and poly(E-caprolactone) (PCL) with different PLLA contents [X_PLLA (w/w) = PLLA/(PCL + PLLA)] by the solution-casting method and their hydrolysis behaviors were investigated up to 20 months in a phosphate-buffered solution of pH 7.4 at 37°C by gel permeation chromatography, tensile testing, differential scanning calorimetry, and gravimetry. Polarizing microscopic observation and dynamic mechanical analysis revealed that PCL and PLLA were phase-separated in blend films before hydrolysis. The mass remaining, molecular weight, and tensile strength of the blend films with X_PLLA of 0.5 and 0.75 decreased more rapidly by hydrolysis than those of the nonblended PLLA, while the elongation at break of the blend film of X_PLLA = 0.25 decreased the slowest. The rate constant for hydrolysis (k) calculated from the M_n change during hydrolysis was higher for blend films of X_PLLA = 0.5 and 0.75 than those expected from k of nonblended PLLA and PCL. The melting temperature (T_m) of PLLA in the blend and nonblended films of X_PLLA = 0.5, 0.75, and 1 decreased from 179 to 161, 160, and 175°C upon hydrolysis for 20 months, respectively, while that for X_PLLA = 0.25 slightly increased from 176 to 177°C. On the other hand, T_m and the crystallinity of PCL was significantly increased by hydrolysis for 20 months, irrespective of X_PLLA. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 405–415, 1998     

Porous biodegradable polyester blends of poly(L‐lactic acid) and poly(ε‐caprolactone): physical properties,morphology, and biodegradation

Poly(L ‐lactic acid) (PLLA), poly(ε‐caprolactone) (PCL), and their films without or blended with 50 wt% poly(ethylene glycol) (PEG) were prepared by solution casting. Porous films were obtained by water‐extraction of PEG from solution‐cast phase‐separated PLLA‐blend‐PCL‐blend‐PEG films. The effects of PLLA/PCL ratio on the morphology of the porous films and the effects of PLLA/PCL ratio and pores on the physical properties and biodegradability of the films were investigated. The pore size of the blend films decreased with increasing PLLA/PCL ratio. Polymer blending and pore formation gave biodegradable PLLA‐blend‐PCL materials with a wide variety of tensile properties with Young's modulus in the range of 0.07–1.4 GPa and elongation at break in the range 3–380%. Pore formation markedly increased the PLLA crystallinity of porous films, except for low PLLA/PCL ratio. Polymer blending as well as pore formation enhanced the enzymatic degradation of biodegradable polyester blends. Copyright © 2006 Society of Chemical Industry     

Blends of aliphatic polyesters. IV. Morphology,swelling behavior,and surface and bulk properties of blends from hydrophobic poly(L-lactide) and hydrophilic poly(vinyl alcohol)

Blend films were prepared from hydrophobic poly(L -lactide) (PLLA) and hydrophilic poly(vinyl alcohol) (PVA) with different PLLA contents [X_PLLA (w/w) = PLLA/(PVA + PLLA)] by solution casting and melt quenching. Their morphology, swelling behavior, and surface and bulk properties were investigated. Polarizing optical microscopy, scanning electron microscopy, differential scanning calorimetry, X-ray diffractometry, and tensile testing revealed that PLLA and PVA were phase separated in these blend films and the PLLA-rich and PVA-rich phases both formed a continuous domain in the blend film of X_PLLA = 0.5. The water absorption of the blend films was higher for the blend films of low X_PLLA values when compared at the same immersion time, and it was larger than expected from those of nonblended PLLA and PVA films. The dynamic contact angles of the blend films were linearly increased with an increase in X_PLLA. The tensile strength and Young's modulus of the dry blend films decreased with a rise in X_PLLA, but this dependence was reversed because of the large decreases in tensile strength and Young's modulus for the blend films having high X_PLLA values after immersion in water. The elongation at break was higher for the wet blend film than for the dry blend film when compared at the same X_PLLA and that of the dry and wet blend films decreased with an increase in X_PLLA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2151–2160, 2001     

Stereocomplex formation between poly(L‐lactic acid) and poly(D‐lactic acid) with disproportionately low and high molecular weights from the melt

Poly(L ‐lactic acid) (PLLA) and poly(D ‐lactic acid) (PDLA) with very different weight‐average molecular weights (M_w) of 4.0 × 10³ and 7.0 × 10⁵ g mol^?1 (M_w(PDLA)/M_w(PLLA) = 175) were blended at different PDLA weight ratios (X_D = PDLA weight/blend weight) and their crystallization from the melt was investigated. The presence of low molecular weight PLLA facilitated the stereocomplexation and thereby lowered the cold crystallization temperature (T_cc) for non‐isothermal crystallization during heating and elevated the radial growth rate of spherulites (G) for isothermal crystallization, irrespective of X_D. The orientation of lamellae in the spherulites was higher for the neat PLLA, PDLA and an equimolar blend than for the non‐equimolar blends. It was found that the orientation of lamellae in the blends was maintained by the stereocomplex (SC) crystallites. Although the G values are expected to decrease with an increase in X_D or the content of high‐molecular‐weight PDLA with lower chain mobility compared with that of low‐molecular‐weight PLLA, G was highest at X_D = 0.5 where the maximum amount of SC crystallites was formed and the G values were very similar for X_D = 0.4 and X_D = 0.6 with the same enantiomeric excess. This means that the effect of SC crystallites overwhelmed that of chain mobility. The nucleating mechanisms of SC crystallites were identical for X_D = 0.1–0.5 in the T_c range 130–180 °C. Copyright © 2011 Society of Chemical Industry     

The effect of poly(ethylene glycol) mixed with poly(l‐lactic acid) on the crystallization characteristics and properties of their blends

The non‐isothermal and isothermal crystallizations of extruded poly(l ‐lactic acid) (PLLA) blends with 10, 20 and 30 wt% poly(ethylene glycol) (PEG) were investigated with differential scanning calorimetry. The formation of α‐form crystals in the blend films was verified using X‐ray diffraction and an increase in crystallinity indexes using Fourier transformation infrared spectroscopy. Crystallization and melting temperatures and crystallinity of PLLA increased with decreasing cooling rate (CR) and showed higher values for the blends. Although PLLA crystallized during both cooling and heating, after incorporation of PEG and with CR = 2 °C min^?1 its crystallization was completed during cooling. Increasingly distinct with CR, a small peak appeared on the lower temperature flank of the PLLA melting curve in the blends. A three‐dimensional nucleation process with increasing contribution from nuclei growth at higher CR was verified from Avrami analysis, whereas Kissinger's method showed that the diluent effect of 10 and 20 wt% PEG in PLLA decreased the effective energy barrier. During isothermal crystallization, crystallization half‐time increased with temperature (T_ic) for the blends, decreased with PEG content and was lower than that of pure PLLA. In addition, the Avrami rate constants were significantly higher than those of pure PLLA, at the lower T_ic. Different crystal morphologies in the PLLA phase were formed, melting in a broader and slightly higher T_m range than pure PLLA. The crystallization activation energy of PLLA decreased by 56% after the addition of 10 wt% PEG, increasing though with PEG content. Finally, PEG/PLLA blends presented improved flexibility and hydrophilicity. © 2019 Society of Chemical Industry     

Syntheses of poly(lactic acid)‐poly(ethylene glycol) serial biodegradable polymer materials via direct melt polycondensation and their characterization

Directly starting from lactic acid (LA) and poly(ethylene glycol) (PEG), biodegradable material polylactic acid‐polyethylene glycol (PLEG) was synthesized via melt copolycondensation. The optimal synthetic conditions, including prepolymerization method, catalyst kinds and quantity, copolymerization temperature and time, LA stereochemical configuration, feed weight ratio m_LA/m_PEG and M_n of PEG, were all discussed in detail. When D ,L ‐LA and PEG (M_n = 1000 Da) prepolymerized together as feed weight ratio m_{D ,l‐LA}/m_PEG = 90/10, 15 h copolycondensation under 165°C and 70 Pa, and 0.5 wt % SnO as catalyst, gave D ,L ‐PLEG1000 with the highest [η] of 0.40 dL/g, and the corresponding MW was 41,700 Da. Using L ‐LA instead of D ,L ‐LA, 10 h polymerization under 165°C and 70 Pa, and 0.5 wt % SnO as catalyst, gave L ‐PLEG1000 with the highest [η] of 0.21 dL/g and MW of 15,600 Da. Serial D ,L ‐PLEG with different feed weight ratio and M_n of PEG were synthesized via the simple and practical direct melt copolycondensation, and characterized with FTIR, ¹H NMR, GPC, DSC, XRD, and contact angle testing. D ,L ‐PELG not only had higher MW than PDLLA, PLLA and L ‐PELG, but also better hydrophilicity than PDLLA. The novel one‐step method could be an alternative route to the synthesis of hydrophilic drug delivery carrier PLEG instead of the traditional two‐step method using lactide as intermediate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 577–587, 2006     

Cold‐crystallization behavior of poly(L‐lactide)/ACR blend films investigated by in situ FTIR spectroscopy

The cold crystallization behavior of poly (L ‐lactide) (PLLA) blend films modified by small amount of acrylic rubber particles (ACR) have been investigated by in situ Fourier‐transform infrared (FTIR) spectroscopy. During the isothermal cold crystallization, the crystallization rate of PLLA is greatly improved with addition of only 1 wt % ACR. However, for PLLA with 8 wt % ACR, the crystallization rate is slower than that of neat PLLA. The relative crystallinity of PLLA with the addition of 1–5 wt % ACR is obviously higher than that of the neat PLLA. For the PLLA blend film with 3 % ACR, the relative crystallinity reaches a maximum. It was found that the addition of ACR particles below 5% accelerated the cold crystallization nucleation process and made the cold‐crystallization rate of PLLA/ACR be quicker than that of neat PLLA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Decomposition of poly(ethylene glycol) in nanocomposites

Poly(ethylene glycol) (PEG) has been widely used in studies of polymer–clay nanocomposites because it readily intercalates in smectite clays. Nanocomposites were formed from PEG with molecular weights (M_w) ranging from 300 to 20,000, as evidenced by expansion of the basal planar spacing of the clay (d₀₀₁) in X‐ray diffraction. However PEG with high molecular weight (≥ 10,000) readily underwent degradation during preparation of composites when heated at low temperature (60°C) due to oxidative attack. Molecular weight distribution determined by gel permeation chromatography showed that this degradation always happened with or without the presence of clay and it became more serious when the molecular weight was higher. The reduction in pH of aqueous PEG solutions after degradation increased with molecular weight. Since d₀₀₁ was independent of molecular weight over a wide range, such degradation cannot be detected by this method. Precautions against oxidative attack are therefore recommended to avoid decomposition when preparing PEG–clay nanocomposites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 548–552, 2004     

Fabrication of honeycomb‐structured porous films from poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) via the breath figures method

Formation of porous films from poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) using the breath figures (BF) method was investigated by evaporating solutions in chloroform in humid air and examining film structure using optical and scanning electron microscopy (SEM). BF films were successfully fabricated from PHB (M_w = 486,000 g/mol) and displayed hexagonal arrays of pores, which varied in diameter (D = 7–2 μm) with solution concentrations (0.5–2.00%). SEM of fractured films also showed subsurface closed nano‐pores (D = 500–700 nm). BF films cast from PHBV (5% HV) formed arrays with smaller pores and apparent surface defects. Differential scanning calorimetry showed that porous PHB and PHBV films produced using the BF method were more crystalline than nonporous solvent cast films of PHB and PHBV. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Characterization of films from chitosan and quaternized poly(4‐vinyl‐N‐butyl) pyridine solutions

All Blend films were prepared from a mixture of 2 wt % chitosan in acetate solution and 4 wt % quaternized poly(4‐vinyl‐N‐butyl) pyridine (QPVP) in aqueous solution and dried at room temperature for 72 h to obtain the films. Their structure and properties were studied by infrared (IR), wide‐angle X‐ray diffraction (WXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), and differential scanning calorimetry (DSC). Crystallinities of the blend films decreased with the increase of QPVP when weight of QPVP content was less than 15.0 wt %. The thermostability, tensile strength, and breaking elongation of the films in dry state were better than those of chitosan film. Tensile strength of the blend film dried at 40°C under vacuum for 24 h achieved 56.38 MPa when the weight ratio of chitosan to QPVP was 9 : 1. The structural analysis indicated that there was a strong interaction between chitosan and QPVP resulting from strong adhesion between both polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 559–566, 2004     

Thermally induced crystallization and enzymatic degradation studies of poly (L‐lactic acid) films

Poly(L ‐lactic acid) (PLLA) films with different crystallinities were prepared by solvent casting and subsequently annealed at various temperatures (T_a) (80–110°C). The effects of crystallinity on enzymatic degradation of PLLA films were examined in the presence of proteinase K at 37°C by means of weight loss, DSC, FTIR spectroscopy, and optical microscopy. DSC and the absorbance ratio of 921 and 956 cm^?1 (A₉₂₁/A₉₅₆) were used to evaluate crystallinity changes during thermally induced crystallization and enzymatic hydrolysis. The highest percentage of weight loss was observed for the film with the lowest initial crystallinity and the lowest percentage of weight loss was observed for the film with highest crystallinity. FTIR investigation of degraded films showed a band at 922 cm^?1 and no band at 908 cm^?1 suggested that all degraded samples form α crystals. The rate of degradation was found to depend on the initial crystallinity of PLLA film and shown that enzymatic degradation kinetics followed first‐order kinetics for a given enzyme concentration. DSC crystallinity and IR absorbance ratio, A₉₂₁/A₉₅₆ ratio, showed no significant changes with degradation time for annealed PLLA films whereas as‐cast PLLA film showed an increase in crystallinity with degradation; this revealed that degradation takes place predominantly in the free amorphous region of annealed PLLA films without changing long range and short range order © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Poly(L‐lactide). X. Enhanced surface hydrophilicity and chain‐scission mechanisms of poly(L‐lactide) film in enzymatic,alkaline, and phosphate‐buffered solutions

Attempts were carried out to enhance the surface hydrophilicity of poly(L ‐lactide), that is, poly(L ‐lactic acid) (PLLA) film, utilizing enzymatic, alkaline, and autocatalytic hydrolyses in a proteinase K/Tris–HCL buffered solution system (37°C), in a 0.01N NaOH solution (37°C), and in a phosphate‐buffered solution (100°C), respectively. Moreover, its chain‐scission mechanisms in these different media were studied. The advancing contact‐angle (θ_a) value of the amorphous‐made PLLA film decreased monotonically with the hydrolysis time from 100° to 75° and 80° without a significant molecular weight decrease, when enzymatic and alkaline hydrolyses were continued for 60 min and 8 h, respectively. In contrast, a negligible change in the θ_a value was observed for the PLLA films even after the autocatalytic hydrolysis was continured for 16 h, when their bulk M_n decreased from 1.2 × 10⁵ to 2.2 × 10⁴ g mol^?1 or the number of hydrophilic terminal groups per unit weight increased from 1.7 × 10^?5 to 9.1 × 10^?5 mol g^?1. These findings, together with the result of gravimetry, revealed that the enzymatic and alkaline hydrolyses are powerful enough to enhance the practical surface hydrophilicity of the PLLA films because of their surface‐erosion mechanisms and that its practical surface hydrophilicity is controllable by varying the hydrolysis time. Moreover, autocatalytic hydrolysis is inappropriate to enhance the surface hydrophilicity, because of its bulk‐erosion mechanism. Alkaline hydrolysis is the best to enhance the hydrophilicity of the PLLA films without hydrolysis of the film cores, while the enzymatic hydrolysis is appropriate and inappropriate to enhance the surface hydrophilicity of bulky and thin PLLA materials, respectively, because a significant weight loss occurs before saturation of θ_a value. The changes in the weight loss and θ_a values during hydrolysis showed that exo chain scission as well as endo chain scission occurs in the presence of proteinase K, while in the alkaline and phosphate‐buffered solutions, hydrolysis proceeds via endo chain scission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1628–1633, 2003     

Poly(L‐Lactide), 8. High‐Temperature Hydrolysis of Poly(L‐Lactide) Films with Different Crystallinities and Crystalline Thicknesses in Phosphate‐Buffered Solution

Poly(L ‐lactide) (PLLA) films having different crystallinities (X_c's) and crystalline thicknesses (L_c's) were prepared by annealing at different temperatures (T_a's) from the melt and their high‐temperature hydrolysis was investigated at 97°C in phosphate‐buffered solution. The changes in remaining weight, molecular weight distribution, and surface morphology of the PLLA films during hydrolysis revealed that their hydrolysis at the high temperature in phosphate‐buffered solution proceeds homogeneously along the film cross‐section mainly via the bulk erosion mechanism and that the hydrolysis takes place predominantly and randomly at the chains in the amorphous region. The remaining weight was higher for the PLLA films having high initial X_c when compared at the same hydrolysis time above 30 h. However, the difference in the hydrolysis rate between the initially amorphous and crystallized PLLA films at 97°C was smaller than that at 37°C, due to rapid crystallization of the initially amorphous PLLA film by exposure to crystallizable high temperature in phosphate‐buffered solution. The hydrolysis constant (k) values of the films at 97°C for the period of 0–8 h, 0.059–0.085 h^–1 (1.4–2.0 d^–1), were three orders of magnitude higher than those at 37°C for the period of 0–12 months, 2.2–3.4×10^–3 d^–1. The melting temperature (T_m) and X_c of the PLLA films decreased and increased, respectively, monotonously with hydrolysis time, excluding the initial increase in T_m for the PLLA films prepared at T_a = 100, 120, and 140°C in the first 8, 16, and 16 h, respectively. A specific peak that appeared at a low molecular weight around 1×10⁴ in the GPC spectra was ascribed to the component of one fold in the crystalline region. The relationship between T_m and L_c was found to be T_m (K) = 467·[1–1.61/L_c (nm)] for the PLLA films hydrolyzed at 97°C for 40 h.     

Reactive blending of poly(L‐lactic acid) with poly(ethylene‐co‐vinyl alcohol)

Poly(L ‐lactic acid) (PLLA) was blended with poly(ethylene‐co‐vinyl alcohol) (EVOH) in the presence of an esterification catalyst to induce reaction between the hydroxyl groups of EVOH and the terminal carboxylic group of PLLA. Nascent low‐molecular‐weight PLLA, obtained from a direct condensation polymerization of L ‐lactic acid in bulk state, was used for the blending. Domain size of the PLLA phase in the graft copolymer was much smaller than that corresponding to a PLLA/EVOH simple blend. The mechanical properties of the graft copolymer were far superior to those of the simple blend, and the graft copolymer exhibited excellent mechanical properties even though the biodegradable fraction substantially exceeded the percolation level. The grafted PLLA reduced the crystallization rate of the EVOH moiety. Melting peak temperature (T_m) of the PLLA phase was not observed until the content of PLLA in the graft reaction medium went over 60 wt %. The modified Sturm test results demonstrated that biodegradation of EVOH‐g‐PLLA took place more slowly than that of an EVOH/PLLA simple blend, indicating that the chemically bound PLLA moiety was less susceptible to microbial attack than PLLA in the simple blend. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 886–890, 2005     

Analysis of low‐density polyethylene‐g‐poly(vinyl chloride) copolymers formed in poly(vinyl chloride)/low‐density polyethylene melt blends with gel permeation chromatography and solid‐state 13C‐NMR

Gel permeation chromatography (GPC) and solid‐state ¹³C‐NMR techniques were used to analyze the structural changes of poly(vinyl chloride) (PVC) in blends of a low‐density polyethylene (LDPE) and PVC during melt blending. The GPC results showed that the weight‐average molecular weight (M_w) of PVC increased with LDPE content up to 13.0 wt % and then decreased at a LDPE content of 16.7 wt %, whereas the number‐average molecular weight remained unchanged for all of LDPE contents used. The ¹³C‐NMR results suggest that the increase in M_w was associated with the formation of a LDPE‐g‐PVC structure, resulting from a PVC and LDPE macroradical cross‐recombination reaction during melt blending. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3167–3172, 2004     

Part 7. Effects of poly(L‐lactide‐co‐ϵ‐caprolactone) on morphology,structure, crystallization,and physical properties of blends of poly(L‐lactide) and poly(ϵ‐caprolactone)

Blended films of poly(L ‐lactide) [ie poly(L ‐lactic acid)] (PLLA) and poly(?‐caprolactone) (PCL) without or mixed with 10 wt% poly(L ‐lactide‐co‐?‐caprolactone) (PLLA‐CL) were prepared by solution‐casting. The effects of PLLA‐CL on the morphology, phase structure, crystallization, and mechanical properties of films have been investigated using polarization optical microscopy, scanning electron microscopy, differential scanning calorimetry and tensile testing. Addition of PLLA‐CL decreased number densities of spherulites in PLLA and PCL films, and improved the observability of spherulites and the smoothness of cross‐section of the PLLA/PCL blend film. The melting temperatures (T_m) of PLLA and PCL in the films remained unchanged upon addition of PLLA‐CL, while the crystallinities of PLLA and PCL increased at PLLA contents [X_PLLA = weight of PLLA/(weight of PLLA and PCL)] of 0.4–0.7 and at most of the X_PLLA values, respectively. The addition of PLLA‐CL improved the tensile strength and the Young modulus of the films at X_PLLA of 0.5–0.8 and of 0–0.1 and 0.5–0.8, respectively, and the elongation at break of the films at all the X_PLLA values. These findings strongly suggest that PLLA‐CL was miscible with PLLA and PCL, and that the dissolved PLLA‐CL in PLLA‐rich and PCL‐rich phases increased the compatibility between these two phases. © 2003 Society of Chemical Industry     

Structural effect of emulsifiers on the emulsion stability of a water/benzene mixture

Core–shell‐type microspheres with microphase‐separated shells of polystyrene (PS) and poly(ethylene glycol) (PEG) (microsphere_block: molar ratio: PS/PEG 49.1/45.9 mol %; M_w: PS chain: 1.07 × 10⁴, PEG chain 1.0 × 10⁴; the ratio of arm numbers of PEG to PS: 1.0; microsphere_graft: molar ratio: PS/PEG 33.8/55.9 mol %; M_w: PS chain: 1.54 × 10⁴, PEG chain 1.0 × 10⁴, the ratio of arm numbers of PEG to PS: 2.55) were synthesized by crosslinking of spherical domains of poly(2‐hydroxyethyl methacrylate) (PHEMA) and poly(4‐vinyl pyridine) (P4VP) of the microphase‐separated films of poly(ethylene glycol)‐block‐poly(2‐hydroxyethyl methacrylate)‐block‐polystyrene triblock terpolymer (M_n: 2.18 × 10⁴; molar ratio: PS 49.1 mol %, PHEMA 5.0 mol %, PEG 45.9 mol %) and polystyrene‐block‐[poly(4‐vinyl pyridine)‐graft‐poly(ethylene glycol)] block–graft copolymer (M_n: 4.56 × 10⁴; molar ratio: PS 33.8 mol %, P4VP 10.3 mol %, PEG 55.9 mol %; branch number of PEG: 2.55), respectively. The structures of microphase‐separated films were investigated by transmission electron microscopy and small‐angle X‐ray scattering. The effects of the arm number ratio of PS to PEG and the total arm number on the stability of the water/benzene emulsion were investigated. The emulsion stability of oil in water was improved by using the microsphere synthesized with the microsphere_graft. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 321–331, 2004     

Blends of aliphatic polyesters. VIII. Effects of poly(L‐lactide‐co‐ε‐caprolactone) on enzymatic hydrolysis of poly(L‐lactide), poly(ε‐caprolactone), and their blend films

Poly(L ‐lactide), that is, poly(L ‐lactic acid) (PLLA), poly(ε‐caprolactone) (PCL), and their blend (50/50) films containing different amounts of poly(L ‐lactide‐co‐ε‐caprolactone) (PLLA‐CL), were prepared by solution casting. The effects of added PLLA‐CL on the enzymatic hydrolysis of the films were investigated in the presence of proteinase K and Rhizopus arrhizus lipase by use of gravimetry. The addition of PLLA‐CL decreased the proteinase K–catalyzed hydrolyzabilities of the PLLA and PLLA/PCL (50/50) films as well as the Rhizopus arrhizus lipase‐catalyzed hydrolyzability of the PCL and PLLA/PCL (50/50) films. The decreased enzymatic hydrolyzabilities of the PLLA and PCL films upon addition of PLLA‐CL are attributable to the fact that the PLLA‐CL is miscible with PLLA and PCL and the dissolved PLLA‐CL must disturb the adsorption and/or scission processes of the enzymes. In addition to this effect, the decreased enzymatic hydrolyzabilities of the PLLA/PCL (50/50) films upon addition of PLLA‐CL can be explained by the enhanced compatibility between the PLLA‐rich and PCL‐rich phases arising from the dissolved PLLA‐CL. These effects result in decreased hydrolyzable interfacial area for PLLA/PCL films. The decrement in proteinase K–catalyzed hydrolyzability of the PLLA film upon addition of PLLA‐CL, which is miscible with PLLA, was in marked contrast with the enhanced proteinase K–catalyzed hydrolyzability of the PLLA film upon addition of PCL, which is immiscible with PLLA. This confirms that the miscibility of the second polymer is crucial to determine the proteinase K–catalyzed hydrolyzabilities of the PLLA‐based blend films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 412–419, 2003