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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

To develop new types of biodegradable polymers possessing predictable responses to changes in temperature, ABA-type and BAB-type triblock copolymers composed of various polydepsipeptides (PDP) and poly(ethylene glycol) (PEG) (PDP-PEG-PDP and PEG-PDP-PEG) were synthesized. The specific focus of this study was on the effect of the different side-chain groups of various amino acids on the temperature-responsive behavior of the triblock copolymers. An ABA-type triblock copolymer containing the less hydrophobic glycine (PGG-PEG-PGG) did not exhibit any temperature-responsive behavior; however, ABA-type triblock copolymers containing the hydrophobic α-amino acids, L-leucine and L-phenylalanine (PGL-PEG-PGL or PGF-PEG-PGF), did exhibit temperature-responsive behavior. The cloud point of PGF-PEG-PGF was 10 °C lower than that of PGL-PEG-PGL. It can be possible to control temperature-sensitivity by changing not only PDP segment length but also kind of α-amino acid in PDP segment. Moreover, BAB-type triblock copolymer containing L-leucine (PEG-PGL-PEG) showed temperature-responsive sol-gel transition. Because polydepsipeptides are biodegradable polymers, the information obtained in this study is useful to design biodegradable injectable polymers having controllable temperature-sensitivity for biomedical use.© 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3892–3903, 2009

Starburst triblock copolymers consisting of 8-arm poly(ethylene glycol) (8-arm PEG) and biodegradable poly(L-lactide) (PLLA) or its enantiomer poly(D-lactide) (PDLA), 8-arm PEG-b-PLLA-b-PEG (Stri-L), and 8-arm PEG-b-PDLA-b-PEG (Stri-D) were synthesized. An aqueous solution of a 1:1 mixture (Stri-Mix) of Stri-L and Stri-D assumed a sol state at room temperature, but instantaneously formed a physically crosslinked hydrogel in response to increasing temperature. The resulting hydrogel exhibited a high-storage modulus (9.8 kPa) at 37 °C. Interestingly, once formed at the transition temperature, the hydrogel was stable even after cooling below the transition temperature. The hydrogel formation process was irreversible because of the formation of stable stereocomplexes. In aqueous solution, gradual hydrolytic erosion was observed because of degradation of the hydrogel. The combination of rapid temperature-triggered irreversible hydrogel formation, high-mechanical strength, and degradation behavior render this polymer mixture system suitable for use in injectable biomedical materials, for example, as a drug delivery system for bioactive reagents or a biodegradable scaffold for tissue engineering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6317–6332, 2008

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

Poly(L-lactide) (PLLA) with terminal primary amino groups (ALLA-NH 2 ) was synthesized and used to construct PLLA-grafted pullulan (Pul-g-PLLA). It consisted of a hydrophilic carboxymethyl Pul (CM-Pul) main chain and hydrophobic PLLA graft chains that were created through a direct coupling reaction between PLLA-NH 2 and CM-Pul using 2-ethoxy-1-(ethoxycarbonyl)-1,2-dihydroquinoline as a condensation reagent. Pul-g-PLLAs with over 78 wt % sugar unit content were found to form nanometer-sized aggregates in water.

Polylactide (PLA)-grafted dextran was synthesized with a trimethylsilyl protection method to produce novel biodegradable, biomedical materials. PLA-grafted dextrans with various lengths and numbers of graft chains were synthesized. The properties of solution-cast films prepared from PLA-grafted dextrans were investigated with thermal and dynamic mechanical analyses. The graft-copolymer films exhibited lower glass-transition temperatures, melting temperatures (Tm's), and crystallinities as well as higher viscosity properties as compared with poly-L-lactide film. The Tm and crystallinity and mechanical properties at 37 °C could be adjusted by controlling the molecular structure such as the lengths and numbers of graft chains. Furthermore, the biodegradability of PLA-grafted dextran films was investigated through the weight change of film and the molecular weight change of polymer during the in vitro degradation test. PLA-grafted dextrans exhibited different degradation behavior from poly-L-lactide with the introduction of a polysaccharide segment and branched structure as well as the change of end-functional group. The degradation rate of PLA-grafted dextran and the cast film prepared from PLA-grafted dextran could be adjusted by controlling the sugar content or the length of graft chains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2462–2468, 2003

A very important goal of researchers today is providing poly(L-lactide) (PLA)-based polymers with controllable degradation profiles, various (soft or elastic) mechanical properties, reactivity for chemical modification, and other functionalities while keeping the favorable characteristics of PLA. This article concerns the synthetic methods and properties of the following novel lactide copolymers: (1) random and block copolymers of depsipeptide and L-lactide with reactive (ionic) side-chain groups, (2) comb-type PLA and branched PLA, and (3) PLA-grafted polysaccharide and PLA with terminal saccharide residues. Poly(depsipeptide-random-L-lactide)s and polydepsipeptide-block-poly(L-lactide)s with reactive (ionic) side-chain groups should be useful for the preparation of matrices and microspheres with reactive surfaces because of their amphiphilic structures. Comb-type PLA and branched PLA show lower crystallinities than linear PLA. PLA-grafted polysaccharide should be useful for the preparation of matrices with various microstructures and mechanical and degradation properties through the introduction of hydrophilic segments. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 453–462, 2004

Amphiphilic AB-type diblock copolymers composed of hydrophobic poly(L-lactide) (PLA) segments and hydrophilic poly(glycolic acid lysine) [poly(Glc-Lys)] segments with amino side-chain groups self-associated to form PLA-based polymeric micelles with amino surfaces in an aqueous solution. The average diameter of the loose core–shell polymeric micelles for poly(Glc-Lys) [number-average molecular weight (Mn) = 1240]-b-PLA (Mn = 7000) obtained by a dimethyl sulfoxide/water dialysis method was estimated to be about 50 nm in water by dynamic light scattering measurements. The size and shape of the obtained polymeric micelles were further observed with transmission electron microscopy and atomic force microscopy. To investigate the possibility of applying the obtained PLA-based polymeric micelles as bioabsorbable vehicles for hydrophobic drugs, we tested the entrapment of drugs in poly(Glc-Lys) (Mn = 1240)-b-PLA (Mn = 7000) micelles and their release with doxorubicin as a hydrophobic drug. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1426–1432, 2002

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

Since poly(lactic acid) is the biodegradable polyester having low immunogenicity and good biocompatibility, it is utilized as a medical material. However, poly(lactic acid) is a water-insoluble crystalline polymer having no reactive side-chain group. Thus, the use of poly(lactic acid) is limited. To modify the properties of poly(lactic acid) and to introduce the functionalized pendant groups to poly(lactic acid), we synthesized two kinds of lactic acid-depsipeptide copolymers with reactive pendant groups, namely poly[LA-(Glc-Lys)] and poly[LA-(Glc-Asp)]. This was done through ring-opening copolymerizations of L-lactide with the corresponding protected cyclodepsipeptides, cyclo[Glc-Lys(Z)] and cyclo[Glc-Asp(OBzl)], and subsequent deprotection of benzyloxycarbonyl and benzyl groups, respectively. By changing the mole fraction of the corresponding depsipeptide units, the solubility, thermal transition and degradation behavior of the modified poly(lactic acid) could be varied. © 1997 John Wiley & Sons, Inc.

The initiation mechanisms of the uncatalyzed polymerization of methyl acrylate and methyl methacrylate by the system of starch, α-amylase or water-soluble nylon 3/copper(II) ion/H2O were investigated by spin trapping techniques. Using 2,4-dimethyl-3-nitrosobenzene sulfonate d8 and 5,5-dimethyl-1-pyrroline-N-oxide as the water-soluble spin trapping agents, the simultaneous generation of both monomer and hydroxyl radicals has been observed, and the propriety of the initiation mechanism proposed previously was confirmed. Thus, the initiation of polymerization in the presence of copper(II) ion was concluded to take place through a hydrogen atom transfer from the complexed water to the β-carbon of the complexed monomer.

Acryloyl-type polymer fixing 1-β-carbonylethyl-5-fluorouracil residues through D-glucofuranoses via ester bonds was synthesized by means of polymerization of the corresponding monomer and polymer reaction. In order to provide the water-soluble objective polymer, the copolymerization of the acryloyl-type monomer with acrylamide was carried out. The extent of release of 5-FU residues from the copolymer was investigated in the enzyme or nonenzyme system in vitro. Furthermore, the antitumor activities of the water-insoluble homopolymer and water-soluble copolymer obtained were tested in vivo.