Synthesis and characterization of novel poly(ester‐carbonate)s by copolymerization of trans‐4‐hydroxy‐L‐proline with cyclic carbonate

The melt ring‐opening/condensation reaction of trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L‐proline (N‐CBz‐Hpr) with cyclic carbonate [trimethylene carbonate (tri‐MC) or tetramethylene carbonate (tetra‐MC)] at a wide range of molar fractions in the feed produced new degradable poly(ester‐carbonate)s. The influence of reaction conditions such as polymerization time and temperature on the yield and inherent viscosity of the copolymers was investigated. The polymerizations were carried out in bulk at 140 °C with 1.5 wt % stannous octoate as a catalyst for 30 h. The poly(ester‐carbonate)s obtained were characterized by Fourier transform infrared spectroscopy, ¹H NMR, differential scanning calorimetry, gel permeation chromatography, and Ubbelohde viscometry. The copolymers synthesized exhibited moderate molecular weights with rather narrow molecular weight distributions. The values of the glass‐transition temperature (T_g) of the copolymers depend on the molar fractions of cyclic carbonate. For the poly(N‐CBz‐Hpr‐co‐tri‐MC) system, with a decreased tri‐MC content from 93 to 16 mol %, the T_g increased from ?10 to 60 °C. Similarly, for the poly(N‐CBz‐Hpr‐co‐tetra‐MC) system, when the tetra‐MC content decreased from 80 to 8 mol %, the T_g increased from ?18 to 52 °C. The relationship between the poly(N‐CBz‐Hpr‐co‐tri‐MC) T_g and the compositions was in approximation with the Fox equation. In vitro degradation of these poly(N‐CBz‐Hpr‐co‐tri‐MC)s was evaluated from weight‐loss measurements. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1435–1443, 2003     

Synthesis and characterization of block poly(ester‐ether‐urethane)s from bacterial poly(3‐hydroxybutyrate) oligomers

Telechelic hydroxylated poly(3‐hydroxybutyrate) (PHB‐diol) oligomers have been successfully synthesized in 90–95% yield from high molar mass PHB by tin‐catalyzed alcoholysis with different diols (mainly 1,4‐butanediol) in diglyme. The PHB‐diol oligomers structure was studied by nuclear magnetic resonance, Fourier transformed infrared spectroscopy MALDI‐ToF MS, and size exclusion chromatography, whereas their crystalline structures, thermal properties and thermal stability were analyzed by wide angle X‐ray scattering, DSC, and thermogravimetric analyses. The kinetic of the alcoholysis was studied and the influence of (i) the catalyst amount, (ii) the diol amount, (iii) the reaction temperature, and (iv) the diol chain length on the molar mass was discussed. The influence of the PHB‐diol molar mass on the thermal stability, the thermal properties and optical properties was investigated. Then, tin‐catalyzed poly(ester‐ether‐urethane)s (PEEU) of M_n = 15,000–20,000 g/mol were synthesized in 1,2‐dichloroethane from PHB‐diol oligomers (P_ester) with modified 4,4'‐MDI and different polyether‐diols (P_ether) (PEG‐2000, PEG‐4000, and PPG‐PEG‐PPG). The influence of the PHB‐diol chain length, the P_ether/P_ester ratio, the polyether segment nature and the PEG chain length on the thermal properties and crystalline structures of PEEUs was particularly discussed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1949–1961     

Catalysts and temperature driven melt polycondensation reaction for helical poly(ester‐urethane)s based on natural L‐amino acids

Catalyst and temperature driven melt polycondensation reaction was developed for natural L‐amino acid monomers to produce new classes of poly(ester‐urethane)s. Wide ranges of catalysts from alkali, alkali earth metal, transition metal and lanthanides were developed for the condensation of amino acid monomers with diols to yield poly(ester‐urethane)s. A‐B Diblock and A‐B‐A triblock species were obtained by carefully choosing mono‐ or diols in model reactions. More than two dozens of transition metal and lanthanide catalysts were identified for the polycondensation to yield high molecular weight poly(ester‐urethane)s. Theoretical studies revealed that the carbonyl carbon in ester possessed low electron density compared to the carbonyl carbon in urethane which driven the thermo‐selective polymerization process. Optical purity of the L‐amino acid residues in the melt polycondensation process was investigated using D‐ and L‐isomers and the resultant products were analyzed by chiral‐HPLC and CD spectroscopy. CD analysis revealed that the amino acid based polymers were self‐assembled as β‐sheet and polyproline type II secondary structures. Electron and atomic force microscopic analysis confirmed the formation of helical nano‐fibrous morphology in poly(ester‐urethane)s. The newly developed melt polycondensation process is very efficient and optimized for wide range of catalysts to produce diverse polymer structures from natural L‐amino acids. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1065–1077     

New segmented poly(ester‐urethane)s from renewable resources

The physical and mechanical properties of aliphatic homopolyesters from monomers obtainable from renewable resources, namely, 1,3‐propanediol and succinic acid, were improved by their combination with aromatic urethane segments capable of establishing strong intermolecular hydrogen bonds. Segmented poly(ester‐urethane)s were synthesized from dihydroxy‐terminated oligo(propylene succinate)s chain‐extended with 4,4′‐diisophenylmethane diisocyanate. The newly synthesized materials were exhaustively characterized by ¹H NMR spectroscopy, size exclusion chromatography, differential scanning calorimetry, dynamic mechanical analysis, and with respect to their main static mechanical properties, an Instron apparatus was used. The average repeat number of the hard segments, evaluated by NMR, ranged from 4 to 9, whereas that of the flexible segments was about 14. The degree of crystallinity, glass‐transition temperature, melting point, tensile strength, elongation, and Young's modulus were influenced by the ratio between hard and soft segments of the segmented copolymer in a predictable way. The results demonstrated that poly(ester‐urethane)s from 1,3‐propanediol and succinic acid are promising thermoplastics. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 630–639, 2001     

Novel,biodegradable, functional poly(ester‐carbonate)s by copolymerization of trans‐4‐hydroxy‐L‐proline with cyclic carbonate bearing a pendent carboxylic group

Water‐soluble poly(ester‐carbonate) having pendent amino and carboxylic groups on the main‐chain carbon is reported for the first time. This article describes the melt ring‐opening/condensation reaction of trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline (N‐CBz‐Hpr) with 5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one (MBC) at a wide range of molar fractions. The influence of reaction conditions such as catalyst concentration, polymerization time, and temperature on the number average molecular weight (M_n) and molecular weight distribution (M_w/M_n) of the copolymers was investigated. The polymerizations were carried out in bulk at 110 °C with 3 wt % stannous octoate as a catalyst for 16 h. The poly(ester‐carbonate)s obtained were characterized by Fourier transform infrared spectroscopy, ¹H NMR, differential scanning calorimetry, and gel permeation chromatography. The copolymers synthesized exhibited moderate molecular weights (M_n = 6000–14,700 g mol^?1) with reasonable molecular weight distributions (M_w/M_n = 1.11–2.23). The values of the glass‐transition temperature (T_g) of the copolymers depended on the molar fractions of cyclic carbonate. When the MBC content decreased from 76 to 12 mol %, the T_g increased from 16 to 48 °C. The relationship between the poly(N‐CBz‐Hpr‐co‐MBC) T_g and the compositions was in approximation with the Fox equation. In vitro degradation of these poly(N‐CBz‐Hpr‐co‐MBC)s was evaluated from weight‐loss measurements and the change of M_n and M_w/M_n. Debenzylation of 3 by catalytic hydrogenation led to the corresponding linear poly(ester‐carbonate), 4 , with pendent amino and carboxylic groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2303–2312, 2004     

Calorimetric and Dielectric Study of the Segmented Biodegradable Poly(ester‐urethane)s Based on Bacterial Poly[(R)‐3‐hydroxybutyrate]

Two series of segmented poly(ester‐urethane)s were synthesized from bacterial poly[(R)‐3‐hydroxybutyrate]‐diol (PHB‐diol), as hard segments, and either poly(ε‐caprolactone)‐diol (PCL‐diol) or poly(butylene adipate)‐diol (PBA‐diol), as soft segments, using 1,6‐hexamethylene diisocyanate as a chain extender. The hard‐segment content varied from 0 to 50 wt.‐%. These materials were characterized using ¹H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the T_g of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard‐segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results also showed that the crystallization of soft or hard segments was physically constrained by the microstructure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester‐urethane)s, based on PCL and PHB, showed two primary relaxation processes, designated as α_S and α_H, which correspond to glass–rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester‐urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard‐segment content. It was concluded from these results that our investigated materials exhibit micro‐phase separation of the hard and soft segments in the amorphous domains.     

Synthesis and thermal behavior of poly(ethylene oxide) poly(N‐substituted urethane)

Poly(N‐substituted urethane)s with an alkyl or ligo(ethylene oxide) monomethyl ether side chain were synthesized by the reaction operating in the following two‐step process: first, by metalation of the starting polymer with potassium tertiary butoxide (t‐BuOK) and then by treatment of the obtained urethane polyanion with tosylate in dimethyl sulfoxide. The thermal properties of poly(ethylene oxide) poly(N‐substituted urethane) (N‐sub PEOPU) were investigated in view of the N‐substitution degree and properties of the substituent. The chemical structures were characterized by Fourier transform infrared, ¹H NMR, and ¹³C NMR spectroscopies. DSC and thermogravimetric analysis (TGA) were used to investigate the thermal properties of N‐sub PEOPUs. As the degree of N‐methylation increased, the glass‐transition temperature (T_g) of the N‐sub PEOPUs linearly decreased from 6 to ?29 °C, and the weight‐loss temperature of 5% (T) from TGA in air increased from 278 to 360 °C. In the fully N‐substituted PEOPUs, the behavior of the thermal decomposition of the PEOPU that was processed in two stages was changed to one‐step decomposition in the temperature range of 360–440 °C. The T_g was shifted to a lower temperature with an increasing length of the substituent in N‐sub PEOPU. Improvement of the thermal stability by N‐substitution was more significant in N‐alkyl PEOPU than in N‐ethoxylate PEOPU. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4129–4138, 2001     

Synthesis and properties of cationic ionomers from poly(ester‐urethane)s based on polylactide

l ‐Lactide (l ‐LA) was polymerized in the presence of N‐methyldiethanolamine as an initiator and Sn(Oct)₂ as a catalyst to give hydroxy‐telechelic poly(l ‐lactide) (PLLA‐diol) bearing a tertiary amine group at the center of the polymer chain. Successive chain extension of the PLLA‐diol with hexamethylene diisocyanate afforded PLLA‐based poly(ester‐urethane)s (PEU) with equally spaced tertiary amine groups. Treatment of the PEU with iodomethane converted tertiary amine groups to quaternary ammonium groups to give cationic ionomers (PEU‐MeI). The thermal, mechanical, hydrophilic, and biodegradation properties of the obtained polymers were investigated. The thermal properties of the PEUs and the PEU‐MeIs were similar each other. The PEU‐MeIs exhibited higher tensile modulus than those of the starting PEUs. The contact angles of water on the PEU‐MeIs were lower than those of the PEUs with similar NMDA content indicating their higher hydrophilicity. In compost degradation tests, the PEU‐MeIs showed slower degradation than those of the PEUs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4423–4428     

Pseudopoly(amino acid)s: Copolymerization of trans‐4‐hydroxy‐L‐proline and α‐hydroxy acids

A series of novel copolymers of trans‐4‐hydroxy‐L ‐proline (Hpr) and α‐ hydroxy acids [D,L ‐mandelic acid (DLMA) and D,L ‐lactic acid (DLLA)] were synthesized via direct melt copolymerization with stannous octoate as a catalyst. These new copolymers had pendant amine functional groups along the polymer backbone chain. The optimal reaction conditions for the synthesis of the copolymers were obtained with 4 wt % stannous octoate at 140 °C under vacuum for 16 h. The synthesized copolymers were characterized by IR spectrophotometry, proton nuclear magnetic resonance, differential scanning calorimetry, and Ubbelohde viscometry. The effects of the kinds of comonomers and the comonomer molar ratio on the polycondensation and glass‐transition temperature (T_g) were investigated. The T_g's of the copolymers shifted to lower temperatures with an increasing comonomer molar ratio. As expected, the T_g's of the N‐Z‐Hpr/DLMA copolymers were higher than the N‐Z‐Hpr/DLLA copolymers, the pendant groups on the monomers (N‐Z‐Hpr) became larger and more flexible, and the T_g's of the resulting polymers declined. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 724–731, 2001     

Silicone‐urethane membranes for lithium batteries. Part 1. Moisture‐cured poly(siloxane‐urethane‐urea) elastomers containing polyethylene oxide (PEO) segments – synthesis and characterization as potential membrane materials

Poly(siloxane‐urethane‐urea) elastomers containing both polysiloxane and polyethylene oxide (PEO) segments in the polymer chain were obtained by moisture‐curing of NCO‐terminated poly(siloxane‐urethane) prepolymers synthesized from isophorone diisocyanate and mixtures of polyoxyethylene diols and polysiloxane diols with various molecular weights. Mechanical properties of the moisture‐cured films and their swelling ability in solvent mixtures commonly used in lithium batteries were investigated, and it was found that they were greatly influenced by PEO content in the polymer. PEO content in the polymer was also found to affect very much the electric conductivity of the films after immersion in lithium salt solution in ethylene carbonate–dimethyl carbonate solvent mixture. At high contents of PEO in the polymer chain specific conductivities of the films in a range of 10^?3, Scm^?1 could be achieved at room temperature. Based on the results of Scanning Electron Microscopy with X‐ray Analysis (SEM/EDS) investigations and wide‐angle X‐ray scattering and small‐angle X‐ray scattering studies, it could be anticipated that the reason for good conductivity of the films might be their specific supramolecular structure that potentially facilitated lithium ion mobility. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization of polysuccinate and hydroxyapatite‐based nanocomposites containing poly(ester‐anhydride) microspheres

Repair and regeneration of bone defects with particular shape may be enhanced by in situ forming biomaterials which can be used in minimal invasive surgery. This study is aimed to prepare novel in situ forming biodegradable nanocomposites based on poly(3‐allyloxy‐1,2‐propylene) succinate (PSAGE) and nanosized hydroxyapatite (HA). These nanocomposite materials contain poly(ester‐anhydride) (PEA) microspheres embedded in a polyester matrix prepared by crosslinking PSAGE with oligo(1,2‐propylene maleate) and methacrylic monomers. Methyl methacrylate and one of hydrophilic oligo(ethylene glycol) methacrylates with different functionality and various length of oligooxyethylene chains were used as polymerizable diluents. Incorporation of microspheres which degrade faster than crosslinked polyester matrices enables formation of porous structure in situ. The obtained materials are liquid before curing and harden in several minutes with moderate exothermic effect. The effect of the composition of nanocomposite materials on selected properties, such as water sorption, mechanical strength, porosity and hydrolytic degradation process, was investigated. Rheological behavior and injectability of liquid formulations were studied. Analysis by energy dispersive spectroscopy confirmed the presence of characteristic features of HA in the nanocomposite materials. The morphology of the cured nanocomposites subjected to hydrolytic degradation was evaluated by scanning electron microscopy. The MTS cytotoxicity assay was carried out for extracts from crosslinked materials using hFOB1.19 cells. It was found that the extracts exhibit a dose‐dependent cytotoxic response. Copyright © 2014 John Wiley & Sons, Ltd.     

Cancer‐associated pH‐responsive tetracopolymeric micelles composed of poly(ethylene glycol)‐b‐poly(L‐histidine)‐b‐poly(L‐lactic acid)‐b‐poly(ethylene glycol)

To create a novel vector for specifically delivering anticancer therapy to solid tumors, we used diafiltration to synthesize pH‐sensitive polymeric micelles. The micelles, formed from a tetrablock copolymer [poly(ethylene glycol)‐b‐poly(L ‐histidine)‐b‐poly(L ‐lactic acid)‐b‐poly(ethylene glycol)] consisted of a hydrophobic poly(L ‐histidine) (polyHis) and poly(L ‐lactic acid) (PLA) core and a hydrophilic poly(ethylene glycol) (PEG) shell, in which we encapsulated the model anticancer drug doxorubicin (DOX). The robust micelles exhibited a critical micellar concentration (CMC) of 2.1–3.5 µg/ml and an average size of 65–80 nm pH 7.4. Importantly, they showed a pH‐dependent micellar destabilization, due to the concurrent ionization of the polyHis and the rigidity of the PLA in the micellar core. In particular, the molecular weight of PLA block affected the ionization of the micellar core. Depending on the molecular weight of the PLA block, the micelles triggering released DOX at pH 6.8 (i.e. cancer acidic pH) or pH 6.4 (i.e. endosomal pH), making this system a useful tool for specifically treating solid cancers or delivering cytoplasmic cargo in vivo. Copyright © 2008 John Wiley & Sons, Ltd.     

Isothermal crystallization behavior of poly(L‐lactide) in poly(L‐lactide)‐block‐poly(ethylene glycol) diblock copolymers

The crystal unit‐cell structures and the isothermal crystallization kinetics of poly(L ‐lactide) in biodegradable poly(L ‐lactide)‐block‐methoxy poly(ethylene glycol) (PLLA‐b‐MePEG) diblock copolymers have been analyzed by wide‐angle X‐ray diffraction and differential scanning calorimetry. In particular, the effects due to the presence of MePEG that is chemically connected to PLLA as well as the PLLA crystallization temperature T_C are examined. Though we observe no variation of both the PLLA and MePEG crystal unit‐cell structures with the block ratio between PLLA and MePEG and T_C, the isothermal crystallization kinetics of PLLA is greatly influenced by the presence of MePEG that is connected to it. In particular, the equilibrium melting temperature of PLLA, T, significantly decreases in the diblock copolymers. When the T_C is high so that the crystallization is controlled by nucleation, because of the decreasing T and thereafter the nucleation density with decreasing PLLA molecular weight, the crystallinity of PLLA also decreases with a decrease in the PLLA molecular weight. While, for the lower crystallization temperature regime controlled by the growth mechanism, the crystallizability of PLLA in copolymers is greater than that of pure PLLA. This suggests that the activation energy for the PLLA segment diffusing to the crystallization site decreases in the diblocks. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2438–2448, 2006     

Tunable poly(hydroxyl urethane) from CO2‐Based intermediates using thiol‐ene chemistry

CO₂‐based, crosslinked poly(hydroxyl urethane)s (PHUs) are accessed via a set of efficient reactions based on the addition chemistry of thiol‐ene and amines‐cyclic carbonates. This strategy to utilize 5‐membered cyclic carbonates produced from CO₂ is robust, facile, modular, and atomically efficient in nature. The thiol‐ene reaction was utilized to access bis(cyclic carbonate), tris(cyclic carbonate), and tetrakis(cyclic carbonate) in quantitative yield from 4‐vinyl‐1,3‐dioxolan‐2‐one and thiols. Multi‐functional cyclic carbonates were simply mixed with diethylenetriamine and/or 1,6‐diaminohexane to generate crosslinked PHUs from 25 to 80 °C. These materials are easy to scale‐up and are potential candidates in many applications such as coatings, binders, and resins. The resulting polymers have glass transition temperatures between ?1 and 16 °C and thermal decomposition temperatures from 190 to 230 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and properties of new organo‐soluble and strictly alternating aromatic poly(ester‐imide)s from 3,3‐bis[4‐(trimellitimidophenoxy)phenyl]phthalide and bisphenols

A series of new strictly alternating aromatic poly(ester‐imide)s having inherent viscosities of 0.20–0.98 dL/g was synthesized by the diphenylchlorophosphate (DPCP) activated direct polycondensation of the preformed imide ring‐containing diacid, 3,3‐bis[4‐(trimellitimidophenoxy)phenyl]phthalide (I), with various bisphenols in a medium consisting of pyridine and lithium chloride. The diimide–diacid I was prepared from the condensation of 3,3‐bis[4‐(4‐aminophenoxy)phenyl]phthalide and trimellitic anhydride. Most of the resulting polymers showed an amorphous nature and were readily soluble in a variety of organic solvents such as N‐methyl‐2‐pyrrolidone (NMP) and N,N‐dimethylacetamide (DMAc). Transparent and flexible films of these polymers could be cast from their DMAc solutions. The cast films had tensile strengths ranging 66–105 MPa, elongations at break from 7–10%, and initial moduli from 1.9–2.4 GPa. The glass‐transition temperatures of these polymers were recorded between 208–275 °C. All polymers showed no significant weight loss below 400 °C in the air or in nitrogen, and the decomposition temperatures at 10% weight loss all occurred above 460 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1090–1099, 2000     

Novel biomimetic composite based on collagen and poly(γ‐benzyl L‐glutamate)‐co‐poly(glutamic acid)

Novel biomimetic composite was prepared by the reaction of collagen and poly(γ‐benzyl L ‐glutamate)‐co‐poly(glutamic acid) (PBLG‐co‐PGA), which were crosslinked by non‐toxic crosslinking reagents 1‐ethyl‐(dimethylaminopropyl) carbodiimide (EDC) and N‐hydroxysuccinimide (NHS). The composite was characterized by FTIR and DSC. FTIR results confirmed that the collagen in the composite was successfully crosslinked with PBLG‐co‐PGA. DSC results showed that the composites possessed higher shrinkage temperature and higher thermal stability than the collagen. The water absorption test showed that the water absorbency of the composites increased with the increase in PBLG‐co‐PGA content in the composite. The studies of collagenase degradation and the tensile strength showed that the biostability and the tensile strength of the composites were significantly improved in comparison with that of the collagen. According to the investigations of cell adherent ratio and cell proliferation in vitro, the composite possessed good biocompatibility. Copyright © 2007 John Wiley & Sons, Ltd.     

Preparation and characterization of poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D,L‐lactide) polymer nanoparticles

A poly(D,L ‐lactide)–bromine macroinitiator was synthesized for use in the preparation of a novel biocompatible polymer. This amphiphilic diblock copolymer consisted of biodegradable poly(D,L ‐lactide) and 2‐methacryloyloxyethyl phosphorylcholine and was formed by atom transfer radical polymerization. Polymeric nanoparticles were prepared by a dialysis process in a select solvent. The shape and structure of the polymeric nanoparticles were determined by ¹H NMR, atomic force microscopy, and ζ‐potential measurements. The results of cytotoxicity tests showed the good cytocompatibility of the lipid‐like diblock copolymer poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D,L ‐lactide). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 688–698, 2007     

Melt‐processable poly(oxyphenylalkanoate): Synthesis,properties, and in vitro degradation of poly(4‐oxyphenylacetate)

The homopolyester of 4‐hydroxyphenylacetic acid (HPAA) was synthesized by one‐pot, slurry‐melt, and acidolysis melt polymerization techniques and was characterized by its inherent viscosity and IR and NMR spectra. Differential scanning calorimetry (DSC), polarizing light microscopy (PLM), and wide‐angle X‐ray diffraction (WAXD) studies of the homopolymer were carried out for its thermal and phase behavior. The results indicated that the yield and molecular weight of the polymer depended on the method of preparation; moreover, the acidolysis melt polymerization of the pure acetoxy derivative of HPAA was the best method for the preparation of high molecular weight poly(4‐oxyphenylacetate) (polyHPAA) without side reactions. DSC and PLM studies also showed that the thermal and optical properties depended largely on the polymerization conditions and inherent viscosity values. PolyHPAA did not show a clear texture typical of liquid‐crystalline polymers, whereas after cooling from the melt, structures similar to spherulitic crystals were observed. WAXD patterns showed a crystalline nature. The in vitro degradability of the polymer was also studied via the water absorption in buffer solutions of pH 7 and 10 at 30 and 60 °C; this was followed by Fourier transform infrared, inherent viscosity, DSC, thermogravimetric analysis, WAXD, and scanning electron microscopy techniques. Unlike Vectra®, which showed no degradation, polyHPAA showed an increase in hydrolytic degradation from 5.0 and 6.0% at 30 °C to 12.5 and 15.0% at 60 °C after 350 h in buffer solutions of pH 7 and 10, respectively. The results indicated a possible biomedical prosthetic application of poly(oxyphenylalkanoate)s such as polyHPAA with better crystallinity coupled with degradability as a substitute for poly(hydroxyalkanoates). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2430–2443, 2001     

Gas‐forming poly(ethylene glycol)‐b‐poly(L‐lactic acid) micelles

In this study, a novel drug‐carrying micelle composed of methoxy poly(ethylene glycol) (mPEG)‐b‐poly(L‐lactic acid) (PLLA) with gas‐forming carbonate linkage was fabricated. Here, the gas‐forming carbonate linkage was formed by the chemical coupling of the terminal hydroxyl group of the PLLA block and benzyl chloroformate (BC). mPEG‐b‐PLLA‐BC was self‐organized in aqueous solution: the PEG block on the hydrophilic outer shell and the PLLA‐BC block in the hydrophoboic innor core. The cleavage of carbonate linkage by hydrolysis and formation of carbon dioxide nanobubbles in the micellar core enabled an accelerated release of the encapsulated anticancer drug (doxorubicin: DOX) from the mPEG‐b‐PLLA‐BC micelles. The amount of drug (DOX) released from the mPEG‐b‐PLLA‐BC micelle was higher than that from the conventional mPEG‐b‐PLLA micelle, which allowed for increased in vitro toxicity against KB tumor cells. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of star‐shaped poly(D,L‐lactic acid‐alt‐glycolic acid)‐b‐poly(L‐lactic acid) with the poly(D,L‐lactic acid‐alt‐glycolic acid) macroinitiator and stannous octoate catalyst

Two types of three‐arm and four‐arm, star‐shaped poly(D,L ‐lactic acid‐alt‐glycolic acid)‐b‐poly(L ‐lactic acid) (D,L ‐PLGA50‐b‐PLLA) were successfully synthesized via the sequential ring‐opening polymerization of D,L ‐3‐methylglycolide (MG) and L ‐lactide (L ‐LA) with a multifunctional initiator, such as trimethylolpropane and pentaerythritol, and stannous octoate (SnOct₂) as a catalyst. Star‐shaped, hydroxy‐terminated poly(D,L ‐lactic acid‐alt‐glycolic acid) (D,L ‐PLGA50) obtained from the polymerization of MG was used as a macroinitiator to initiate the block polymerization of L ‐LA with the SnOct₂ catalyst in bulk at 130 °C. For the polymerization of L ‐LA with the three‐arm, star‐shaped D,L ‐PLGA50 macroinitiator (number‐average molecular weight = 6800) and the SnOct₂ catalyst, the molecular weight of the resulting D,L ‐PLGA50‐b‐PLLA polymer linearly increased from 12,600 to 27,400 with the increasing molar ratio (1:1 to 3:1) of L ‐LA to MG, and the molecular weight distribution was rather narrow (weight‐average molecular weight/number‐average molecular weight = 1.09–1.15). The ¹H NMR spectrum of the D,L ‐PLGA50‐b‐PLLA block copolymer showed that the molecular weight and unit composition of the block copolymer were controlled by the molar ratio of L ‐LA to the macroinitiator. The ¹³C NMR spectrum of the block copolymer clearly showed its diblock structures, that is, D,L ‐PLGA50 as the first block and poly(L ‐lactic acid) as the second block. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 409–415, 2002