Controlled synthesis of amphiphilic biodegradable polylactide‐grafted dextran copolymers

The whole controlled synthesis of novel amphiphilic polylactide (PLA)‐grafted dextran copolymers was achieved. The control of the architecture of such biodegradable and potentially biocompatible copolymers has required a three‐step synthesis based on the “grafting from” concept. The first step consisted of the partial silylation of the dextran hydroxyl groups. This protection step was followed by the ring‐opening polymerization of D ,L ‐lactide initiated from the remaining OH functions of the partially silylated polysaccharide. The third step involved the silylether group deprotection under very mild conditions. Based on previous studies, in which the control of the first step was achieved, this study is focused on the last two steps. Experimental conditions were investigated to ensure a controlled polymerization of D ,L ‐lactide, in terms of grafting efficiency, graft length, and transesterification limitation. After polymerization, the final step was studied in order to avoid degradation of both polysaccharide backbone and polyester grafts. The chemical stability of dextran backbone was checked throughout each step of the synthesis. PLA‐grafted dextrans and PLA‐grafted (silylated dextrans) were proved to adopt a core‐shell conformation in various solvents. Furthermore, preliminary experiments on the potential use of these amphiphilic grafted copolymers as liquid/liquid interface stabilizers were performed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2577–2588, 2004     

Biodegradable stereocomplex materials of polylactide‐grafted dextran exhibiting soft and tough properties in dry and wet states

Water‐swellable biodegradable materials exhibiting mechanically tenacious and tough characters in the wet state were prepared by a simple blend of two enantiomeric polylactide‐grafted dextran copolymers (Dex‐g‐PLLA and Dex‐g‐PDLA). DSC and WAXD analyses demonstrated the formation of SC crystals in the copolymer blend films. SC blend films showed lamellar‐type microphase‐separated structures. When swollen with water, these blend films showed the same level of tensile strengths and Young's modulus as the films in the dry state. SC blend films degraded gradually over a month under physiological conditions with a degradation rate faster than the corresponding Dex‐g‐PLLA films. The SC‐forming enantiomeric mixture of polylactide‐grafted polysaccharides should be a good candidate for an implantable biocompatible material exhibiting favorable mechanical properties and degradation behavior. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Characteristics of the biodegradability and physical properties of stereocomplexes between poly(L‐lactide) and poly(D‐lactide) copolymers

Random and block copolymerizations of L ‐ or D ‐lactide with ε‐caprolactone (CL) were performed with a novel anionic initiator, (C₅Me₅)₂SmMe(THF), and they resulted in partial epimerization, generating D ,L ‐ or meso‐lactide polymers with enhanced biodegradability. A blend of PLLA‐r‐PCL [82/18; PLLA = poly(L ‐LA) and PCL = poly(ε‐caprolactone)] and PDLA‐r‐PCL [79/21; PDLA = poly(D ‐LA)] prepared by the solution‐casting method generated a stereocomplex, the melting temperature of which was about 40 °C higher than that of the nonblended copolymers. A blend of PLLA‐b‐PCL (85/15) and PDLA‐b‐PCL (82/18) showed a lower elongation at break and a remarkably higher tensile modulus than stereocomplexes of PLLA‐r‐PCL/PDLA‐r‐PCL and PLLA/PDLA. The biodegradability of a blend of PLLA‐r‐PCL (65/35) and PDLA‐r‐PCL (66/34) with proteinase K was higher than that of PLLA‐b‐PCL (47/53) and PDLA‐b‐PCL (45/55), the degradability of which was higher than that of a PLLA/PDLA blend. A blend film of PLLA‐r‐PDLLA (69/31)/PDLA‐r‐PDLLA (68/32) exhibited higher degradability than a film of PLLA/PDLLA [PDLLA = poly(D ,L ‐LA)]. A stereocomplex of PLLA‐r‐PCL‐r‐PDMO [80/18/2; PDMO = poly(L ‐3,D ,L ‐6‐dimethyl‐2,5‐morpholinedion)] with PDLA‐r‐PCL‐r‐PDMO (81/17/2) showed higher degradability than PLLA‐r‐PDMO (98/2)/PDLA‐r‐PDMO (98/2) and PLLA‐r‐PCL (82/18)/PDLA‐r‐PCL (79/21) blends. The tensile modulus of a blend of PLLA‐r‐PCL‐r‐PDMO and PDLA‐r‐PCL‐r‐PDMO was much higher than that of a blend of PLLA‐r‐PDMO and PDLA‐r‐PDMO. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 438–454, 2005     

Characteristic properties of film prepared from poly(L‐lactide)‐grafted dextran of a relatively high sugar unit content as a degradable biomaterial

To develop novel biomedical soft materials with degradability, amphiphilic poly(L ‐lactide)‐grafted dextrans (Dex‐g‐PLLAs) of relatively high sugar unit contents were synthesized with the trimethylsilyl protection method. The characteristic properties of solution‐cast films prepared from the obtained Dex‐g‐PLLAs were investigated. The water absorption and degradation rate of the Dex‐g‐PLLA films increased with increasing sugar unit content. The morphology of the bulk phase and top surface of the Dex‐g‐PLLA films was evaluated with transmission electron microscopy and atomic force microscopy, respectively. The bulk phase of the Dex‐g‐PLLA films with a sugar unit content of 16–25 wt % was found by transmission electron microscopy to form a lamellar type of phase‐separated structure composed of approximately 80–100‐nm‐wide nanodomains because of their amphiphilic and branched structures. The hydrophobic top surface for a Dex‐g‐PLLA film with a sugar unit content of 25 wt % covered with PLLA segments was confirmed by atomic force microscopy phase images to be easily converted to a wettable top surface covered with hydrophilic dextran aggregates showing an 8–10‐nm‐wide honeycomb pattern by means of annealing in water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6402–6409, 2006     

Microcellular antibacterial polylactide‐based systems prepared by additive extrusion with ALUM

This work investigates preparation by extrusion of microcellular antimicrobial polylactide (PLA) with an additive, the latter comprising 1% potassium aluminum sulfate dodecahydrate (ALUM), and 3% or 5% of a mixture of sodium hydrogen carbonate and sodium dihydrogen phosphate (1:1). Study was made as to the properties of the materials, their hydrolysis, release profiles, and antimicrobial properties in comparison with the pure polymer. Measuring the molecular weight of samples by gel permeation chromatography revealed that, during thermal processing, the molecular weight of the PLA prepared with additives mentiond above had reduced by approximately 43%. A mechanical test confirmed a decline in mechanical properties after processing as compared with the pure PLA. Release of the antimicrobial compound and the subsequent antimicrobial activity against Staphylococcus aureus and Escherichia coli was evaluated according to ISO 22196:2007. The release of ALUM from the microcellular specimens took place in two steps. During the first 10 days, the rate of release was extremely high in contrast with the remaining period. However, the release rate of the nonporous sample was seen to equal less than 1% in the first 10 days, a phenomenon probably arising through its less active surface.     

Third‐generation amphiphilic conetworks. III. Permeabilities and mechanical properties

While two of our earlier papers on poly(dimethyl acryl amide)/polymethylhydrosiloxane/polydimethylsiloxane (PDMAAm/PMHS/PDMS) amphiphilic conetworks concerned synthesis and biological properties, respectively, the present contribution focuses on oxygen and insulin permeabilities, and select mechanical properties. We show that by increasing the PDMAAm content from 20 to 60% (i.e., by decreasing the hydrophobic content from 80 to 40%), oxygen permeabilities decrease from ～240 to ～130 barrers. Evidently, oxygen permeability is a function of the sum of the oxyphilic components, PDMS + PMHS, in the conetworks. In contrast, insulin permeability is a function of the hydrophilic component, and reaches a desirable 1.5 × 10^?7 cm²/s at 61% PDMAAm. We also studied the permeabilities of glucose, dextran, and albumin through a PDMAAm₆₁/PMHS₆/PDMS₃₃ membrane and found, unsurprisingly, that the permeability of these molecules follows their hydrodynamic radii, and we project that the permeability of IgG is infinitesimally low. Tensile strengths and ultimate elongations of water‐swollen membranes are also a function of conetwork composition: by increasing the PDMAAm content from 30 to 60%, strengths decrease from 1.6 to 1.2 MPa, and elongations from ～60 to ～40%. Overall, the permeabilities and the mechanical properties of these membranes are appropriate for implantation and, specifically, for immunoisolation of living tissue. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4276–4283, 2007     

Solid‐supported amphiphilic triblock copolymer membranes grafted from gold surface

Gold‐supported amphiphilic triblock copolymer brushes composed of two hydrophilic poly(2‐hydroxyethyl methacrylate) (PHEMA) blocks and a hydrophobic poly(n‐butyl methacrylate) (PBMA) middle part were synthesized using a surface‐initiated ATRP. Attenuated total reflectance Fourier transform infrared spectroscopy, polarization modulation infrared reflection absorption spectroscopy (PM‐IRRAS), ellipsometry, contact angle measurements, and atomic force microscopy were used for the characterization of PHEMA‐co‐PBMA‐co‐PHEMA brushes. The PM‐IRRAS analysis revealed an increase of the chain tilt toward the gold surface during growth of the individual blocks. We suggest that the orientation of the amphiphilic polymer brushes is influenced by both the chain length and the interchain interactions. Additionally, a detachment of the polymer membranes from the solid support and subsequent gel permeation chromatography analyses allowed us to establish their compositions. We applied block‐selective solvents (water and hexane) as well as a good solvent for the whole polymer chain (ethanol) to study the morphology and solvent responsive behavior of the amphiphilic brushes. The presented results could serve as a good starting point for the fabrication of functional solid‐supported membranes for biosensing applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1–13, 2009     

Conformational changes and phase transformation mechanisms in PVDF solution‐cast films

The supramolecular crystal structure in poly(vinylidene fluoride) (PVDF) solution‐cast films is studied through changing crystallization conditions in two solvents of different structures and polarities. The crystalline‐state chain conformations of isothermally solution‐crystallized PVDF in N, N‐dimethylacetamide (DMAc), and cyclohexanone are studied through the specific FTIR absorption bands of α, β, and γ phase crystals. There are no changes in the FTIR spectra of cyclohexanone solution‐crystallized films in the temperature range of 50–120 °C. In the case of DMAc solution‐crystallized films, low temperature crystallization mainly results in formation of trans states (β and γ phases), whereas at higher temperatures gauche states become more populated (α phase). This is due to the variations in solvent polarity and ability to induce a specific conformation in PVDF chains, through the changes in chain coil dimensions. This indicates that in spite of cyclohexanone solutions, the intermolecular interactions between PVDF and DMAc are temperature‐sensitive and more important in stabilizing conformations of PVDF in crystalline phase than temperature dependence of PVDF chain end‐to‐end distance <r²>. The high‐resolution ¹⁹F NMR spectroscopy also showed little displacement in PVDF characteristic chemical shifts probably due to changes in PVDF chain conformation resulting from temperature variations. Upon uniaxial stretching of the prepared films under certain conditions, contribution of trans state becomes more prominent, especially for the originally higher α phase‐containing films. Due to formation of some kink bands during film stretching and phase transformation, α phase absorption bands are still present in infrared spectra. Besides, uniaxial stretching greatly enhances piezoelectric properties of the films, maybe due to formation of oriented β phase crystals, which are of more uniform distribution of dipole moments. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3487–3495, 2004     

Novel antibacterial fibers of amphiphilic N‐halamine polymer prepared by electrospinning

As a significant role in subcategory of halogen antibacterial field, amphiphilic N‐halamine polymers show a promise as potential antimicrobials having a broad spectrum of microorganisms, long‐term stability, and renewal of their antibacterial properties. By controlling the process parameters, electrospinning has been well recognized as a versatile and effective method being capable of making fibers and could be easily engineered with desired pore size and porosity to enhance the antimicrobial properties. The amphiphilic N‐halamine P (ADMH‐MMA‐HEMA) terpolymer fibers showed efficient antimicrobial properties against both Gram‐positive and Gram‐negative bacteria within brief contact time. The result meant that the polymer fibers of macromolecular architecture with control of structural parameters such as hydrophobicity/hydrophilicity balance achievement improved antimicrobial activities via electrospinning technique. In vitro cytotoxicity study demonstrated that the polymer was biocompatible. As a result, the integration of amphiphilic antibacterial materials and the electrospinning technique provided us a feasible method to fabricate biocompatible antimicrobial products easily with low manufacturing cost and would be applied in many promising application areas.     

Fabrication of 3D electrospun structures from poly(lactide‐co‐glycolide acid)–nano‐hydroxyapatite composites

The fabrication of three‐dimensional (3D) electrospun composite scaffolds was presented in this study. Layers of electrospun meshes made from composites of poly(lactide‐co‐glycolide acid) (PLGA) and hydroxyapatite (HA) were stacked and sintered using pressurized gas. Three HA concentrations of 5, 10, and 20 wt % were tested, and the addition of the HA nanoparticles decreased the tensile mechanical properties of the meshes with 20 wt % HA. However, after the gas absorption process, the fibers within the mesh sintered, which improved the mechanical properties more than twofold. The fabrication of 3D, porous, electrospun scaffolds was also demonstrated. The resulting 3D scaffolds had open porosity of up to 70% and modulus of ～20 MPa. This technique improves on the current electrospinning technology by overcoming the challenges of depositing a thick, 3D structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Amphiphilic PEG/alkyl‐grafted comb polylactides

Amphiphilic polylactides (PLAs) with well‐defined architectures were synthesized by ring‐opening polymerization of AB monomers (glycolides) substituted with both a long chain alkyl group and a triethylene glycol segment terminated in either a methyl or benzyl group. The resulting amphiphilic PLAs had number average molecular weights >100,000 g/mol. DSC analysis revealed a first‐order phase transition at ～ 20 °C, reflecting the crystalline nature of the linear alkyl side chains. Polymeric micelles were prepared by the solvent displacement method in water. Dynamic light scattering measurements support formation of a mixture of 20‐nm‐diameter unimolecular micelles and 60‐nm particles comprised of an estimated 25 polymer molecules. UV–vis characterization of micelles formed from acetone–water solutions containing azobenzene confirmed encapsulation of the hydrophobic dye, suggesting their potential as new amphiphilic PLAs as drug delivery vehicles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5227–5236, 2007     

Mechanical and thermal properties of green polylactide composites with natural fillers

Green composites of PLA with micropowders derived from agricultural by-products such as oat husks, cocoa shells, and apple solids that remain after pressing have been prepared by melt mixing. The thermal and mechanical properties of the composites, including the effect of matrix crystallization and plasticization with poly(propylene glycol), have been studied. All fillers nucleated PLA crystallization and decreased the cold-crystallization temperature. They also affected the mechanical properties of the compositions, increasing the modulus of elasticity but decreasing the elongation at break and tensile impact strength although with few exceptions. Plasticization of the PLA matrix improved the ductility of the composites.     

Synthesis and characterization of hyperbranched amphiphilic block copolymers prepared via self‐condensing RAFT polymerization

Four families of hyperbranched amphiphilic block copolymers of styrene (Sty, less polar monomer) and 2‐vinylpyridine (2VPy, one of the two more polar monomers) or 4‐vinylpyridine (4VPy, the other polar monomer) were prepared via self‐condensing vinyl reversible addition‐fragmentation chain transfer polymerization (SCVP‐RAFT). Two families contained 4VPy as the more polar monomer, one of which possessing a Sty‐b‐4VPy architecture, and the other possessing the reverse block architecture. The other two families bore 2VPy as the more polar monomer and had either a 2VPy‐b‐Sty or a Sty‐b‐2VPy architecture. Characterization of the hyperbranched block copolymers in terms of their molecular weights and compositions indicated better control when the VPy monomers were polymerized first. Control over the molecular weights of the hyperbranched copolymers was also confirmed with the aminolysis of the dithioester moiety at the branching points to produce linear polymers with number‐average molecular weights slightly greater than the theoretically expected ones, due to recombination of the resulting thiol‐terminated linear polymers. The amphiphilicity of the hyperbranched copolymers led to their self‐assembly in selective solvents, which was probed using atomic force microscopy and dynamic light scattering, which indicated the formation of large spherical micelles of uniform diameter. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1310–1319     

Synthesis and characterization of poly(vinyl amine)‐based amphiphilic comb‐like dextran glycopolymers by a two‐step method

Poly(vinyl amine) (PVAm)‐based amphiphilic glycopolymers were synthesized by a two‐step method, that is dextran molecules (Dex, M_w = 1500) were attached to the PVAm backbone by reacting amine groups with dextran lactone, and then, hexanoyl groups (Hex) were attached by reacting the PVAm free amine groups with N‐(hexanoyloxy)succinimide. By adjustment of the feed ratios of Dex/Hex, amphiphilic comb‐like glycopolymers with various hydrophilic and hydrophobic balances were prepared, and their structures were characterized by ¹H NMR. Surface activity of the amphiphilic glycopolymers at the air/water interface was demonstrated by reduction in water surface tension. Adsorption of the amphiphilic glycopolymers at the solid/water interface was examined on octadecyltrichlorosilane (OTS)‐coated coverslips by water contact angle measurements. The results show that the amphiphilic glycopolymers need about 20 mol % of dextran attachment to make an effective hydrophilic coating. In comparison with the one‐step reaction by addition of dextran lactone and alkyl succinimide simultaneously, the two‐step approach can attach Dex on PVAm as high as possible in the first step, and offers quantitative advantages in controlling the ratio of hydrophilic and hydrophobic chains along the PVAm backbone, resulting in increased water solubility for the final amphiphilic glycopolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 192–199, 2006     

Synthesis of biodegradable amphiphilic AB‐type diblock copolymers of lactide and depsipeptide with pendant reactive groups

The syntheses of amphiphilic AB‐type diblock copolymers composed of hydrophobic polylactide segment and hydrophilic polydepsipeptide segment with amino or carboxyl groups were performed. The protected cyclodepsipeptides cyclo[Glc‐Lys(Z)] and cyclo[Glc‐Asp(OBzl)] (where Glc is glycolic acid, Lys is lysine, Asp is aspartic acid, Z is benzyloxycarbonyl, and OBzl is benzyl) were first polymerized in tetrahydrofuran (THF) with potassium ethoxide as an initiator to obtain the corresponding protected polydepsipeptides. After the terminal hydroxyl groups of the protected polydepsipeptides were converted into the potassium alcoholates with K/naphthalene, L ‐lactide was polymerized in the presence of the corresponding polymeric alcoholates as macroinitiators in THF to obtain poly[Glc‐Lys(Z)]‐block‐poly(L ‐lactide) and poly[Glc‐Asp(OBzl)]‐block‐poly(L ‐lactide). Subsequent deprotection of Z and OBzl groups gave the objective amphiphiles poly(Glc‐Lys)‐block‐poly(L ‐lactide) and poly(Glc‐Asp)‐block‐poly(L ‐lactide), respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1218–1225, 2002     

Chromatographic characterization of amphiphilic di‐ and tri‐block copolymers of poly(ethylene oxide) and poly(ε‐caprolactone)

Amphiphilic di‐ and tri‐block copolymers based on poly(ethylene oxide) as a hydrophilic segment and poly(ε‐caprolactone) as a hydrophobic part are synthesized by the ring‐opening polymerization of ε‐caprolactone while using poly(ethylene glycol)s and methoxy poly(ethylene glycol)s of varying molar masses as macro‐initiators. The synthesized block copolymers are characterized with respect to their total relative molar mass and its distribution by size exclusion chromatography. Liquid chromatography at critical conditions of both blocks is established for the analysis of individual block lengths and tracking presence of unwanted homopolymers of both types in the block copolymer samples. New critical conditions of polycaprolactone on reversed phase column are reported using organic mobile phase. The established critical conditions of polycaprolactone extended the applicable molar mass range significantly compared to already reported critical conditions of polycaprolactone in aqueous mobile phase. Block copolymers are also analyzed at critical conditions of poly(ethylene glycol). Complete analysis of the di‐ and tri‐block copolymers at corresponding critical conditions provided a fair estimate of molar mass of non‐critical block besides information regarding presence of homopolymers of both types in the samples.     

Synthesis,crystalline morphologies,self‐assembly,and properties of H‐shaped amphiphilic dually responsive terpolymers

Novel and well‐defined amphiphilic H‐shaped terpolymers poly(L‐lactide)‐block‐(poly(2‐(N,N‐dimethylamino)ethyl methacrylate) ‐block‐)poly(ε‐caprolactone)(‐block‐poly(2‐(N,N‐dimethylamino)ethyl methacrylate)) ‐b‐poly(L‐lactide) (PLLA‐b‐(PDMAEMA‐b‐)PCL(‐b‐PDMAEMA)‐b‐PLLA) were synthesized by the combination of ring‐opening polymerization, atom transfer radical polymerization, and click chemistry. The H‐shaped amphiphilic terpolymers can self‐assemble into spherical nano‐micelles in water. Because of the dually responsive (temperature and pH) properties of PDMAEMA segments, the hydrodynamic radius of the micelles of the H‐shaped terpolymer solution can be adjusted by altering the environmental temperature or pH values. The thermal properties investigation and the crystalline morphology analysis indicate that the branched structure of the H‐shaped terpolymers and the presence of amorphous PDMAEMA segments together led to the obvious decrease of PCL segments and the complete destruction of crystallinity of the PLLA segments in the H‐shaped terpolymers. In addition, the H‐shaped terpolymer film has better hydrophilicity than linear PCL or triblock polymer of PLLA‐b‐(N₃? )PCL(? N₃)‐b‐PLLA, due to the decrease or destruction of the crystallizability of the PCL or PLLA in the H‐shaped terpolymer and the presence of hydrophilic PDMAEMA segments. These unique H‐shaped amphiphilic terpolymers composed of biodegradable and biocompatible PCL and PLLA components and intelligent and biocompatible PDMAEMA component will have the potential applications in biomedical fields. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and new application of green and recyclable cyclic poly(L‐lactide)‐clay hybrid

We report on the application of biodegradable cyclic poly(L ‐lactide) (PLLA) as new stabilizer; synthesis and application of a cyclic PLLA‐clay hybrid material as recyclable catalyst support. Cyclic PLLAs were used to stabilize palladium nanoparticles synthesized by a wet chemical method. It was found that the palladium particles were smaller with cyclic PLLA stabilizer (～5–10 nm) than the particles obtained from linear PLLA. The cyclic PLLA‐clay hybrid was prepared by a zwitterionic ring‐opening polymerization catalyzed by in situ‐generated N‐heterocyclic carbene catalyst. Palladium (0) nanoparticles were supported and well dispersed on the cyclic PLLA‐clay hybrid to form a new nanocomposite. The nanocomposite was found to be a highly efficient and recyclable catalyst for the aminocarbonylation reactions of aryl halides with various amines. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4167–4174     

Processing and properties of melt spun polylactide–multiwall carbon nanotube fiber composites

This article reports on the fabrication of oriented composite fibers between polylactide (PLA) and multiwall carbon nanotube (MWNT). The fibers were fabricated using a custom‐built melt fiber‐drawing setup. The influence of processing parameters on the final fiber diameter and on the orientation were characterized and optimized. Composite fibers were fabricated at various MWNT contents. Addition of low amounts of MWNT (0.25–1 wt %) to PLA did not have a significant effect on the diameters of the fibers. Observations of the composite morphology under STEM indicated preferential orientation of the MWNTs along the draw direction of the fibers. Increasing amounts of MWNTs was found to increase crystallization kinetics and content. The crystalline content had a direct and profound implication on the mechanical properties with 0.5‐wt % MWNT fibers having the highest crystalline content and also the highest Young's modulus. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 477–484     

Synthesis and characterization of novel biodegradable block copolymer poly(ethylene glycol)‐block‐poly(L‐lactide‐co‐2‐methyl‐2‐carboxyl‐propylene carbonate)

An amphiphilic block copolymer, poly(ethylene glycol)‐block‐poly(L ‐lactide‐co‐2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate) [PEG‐b‐P(LA‐co‐MBC)], was synthesized in bulk by the ring‐opening polymerization of L ‐lactide with 2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate (MBC) in the presence of poly(ethylene glycol) as a macroinitiator with diethyl zinc as a catalyst. The subsequent catalytic hydrogenation of PEG‐b‐P(LA‐co‐MBC) with palladium hydroxide on activated charcoal (20%) as a catalyst was carried out to obtain the corresponding linear copolymer poly(ethyleneglycol)‐block‐poly(L ‐lactide‐co‐2‐methyl‐2‐carboxyl‐propylenecarbonate) [PEG‐b‐P(LA‐co‐MCC)] with pendant carboxyl groups. DSC analysis indicated that the glass‐transition temperature (T_g) of PEG‐b‐P(LA‐co‐MBC) decreased with increasing MBC content in the copolymer, and T_g of PEG‐b‐P(LA‐co‐MCC) was higher than that of the corresponding PEG‐b‐P(LA‐co‐MBC). The in vitro degradation rate of PEG‐b‐P(LA‐co‐MCC) in the presence of proteinase K was faster than that of PEG‐b‐P(LA‐co‐MBC), and the cytotoxicity of PEG‐b‐P(LA‐co‐MCC) to chondrocytes from human fetal arthrosis was lower than that of poly(L ‐lactide). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4771–4780, 2005