Molecularly defined (L)‐lactic acid oligomers and polymers: Synthesis and characterization

The synthesis of (L )‐lactide oligomers from dimer to 64mer via an exponential growth strategy is described. By careful selection of orthogonal protective groups, the synthesis were conducted using a t‐butyldimethylsilyl (TBDMS) ether as the protective group of the hydroxyl group and benzyl (Bn) ester as the protective group of the carboxylic acid group. The yields of both the deprotection steps and coupling reactions using 1,3‐dicyclohexylcarbodiimide or 1‐[3‐(dimethylamino)propyl]‐3‐ethylcarbodiimide hydrochloride were high (70–100%) and the absence of a requirement for conducting the majority of reactions under an inert atmosphere permitted a robust and efficient synthetic strategy to be developed. This allowed monodisperse dimer, tetramer, octamer, 16mer, 32mer, and 64mer materials to be prepared in gram quantities and fully characterized using mass spectrometry and size exclusion chromatography. Evaluation of the thermal and physical properties using thermogravimetric analysis, differential scanning calorimetry, and small angle X‐ray scattering demonstrated a close correlation between the molecular structure of the well‐defined Poly(lactide) oligomers and their physical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5977–5990, 2008     

Isothermal crystallization of layered silicate/starch-polycaprolactone blend nanocomposites

The isothermal crystallization behavior of layered silicate/starch-polycaprolactone blend nanocomposites was studied by means of differential scanning calorimetry (DSC) measurements. The theoretical melting point was higher for the matrix than for nanocomposites. At low clay concentration, the induction time decreased and the overall crystallization rate increased acting as nucleating agent whereas at higher concentrations became retardants. Classical Avrami equation was used to analyze the crystallization kinetic of these materials. n values suggested that clay not only affected the crystallization rate but also influenced the mechanism of crystals growth. An Arrhenius type equation was used for the rate constant (k). Models correctly reproduced the experimental data.     

Polyiodized‐PCL as multisite transfer agent: Towards an enlarged library of degradable graft copolymers

Poly(ε‐caprolactone)‐based graft copolymers were prepared via a “grafting from” technique derived from iodine transfer polymerization. This copolymerization was done thanks to a poly(ε‐caprolactone‐co‐α‐iodo‐ε‐caprolactone) (PCL‐I), which was used as a multisite transfer agent. Styrene (Sty) and n‐butyl acrylate (n‐BuA) were firstly used as model monomers to establish the feasibility of using PCL‐I as multisite transfer agent, and investigate some general properties of the polymerization. The formation of PCL‐g‐PSty and PCL‐g‐P(n‐BuA) copolymers was confirmed by SEC and NMR analyzes of the copolymers before and after degradation of the PCL backbone. This method was extended to an acrylamide monomer, namely (N,N‐dimethyl) acrylamide (DMA), to prepare original amphiphilic copolymers with PCL as hydrophobic backbone and amido‐functionalized hydrophilic grafted chains. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5006–5016, 2009     

Ecotoxicity of the Adipate Plasticizers: Influence of the Structure of the Alcohol Substituent

A significant increase in the production of plastic materials and the expansion of their areas of application contributed to the accumulation of a large amount of waste of polymeric materials. Most of the polymer composition is made up of plasticizers. Phthalate plasticizers have been recognized as potentially hazardous to humans and the environment due to the long period of their biodegradation and the formation of persistent toxic metabolites. It is known that the industrial plasticizer dioctyl adipate is characterized by reduced toxicity and a short biodegradation period. The paper describes the synthesis of a number of new asymmetric esters based on adipic acid and ethoxylated butanol by azeotropic esterification. The receipt of the products was confirmed by IR spectra. The physicochemical properties of the synthesized compounds were investigated. The glass transition temperatures of PVC composites plasticized with alkyl butoxyethyl adipates were determined using DSC analysis. The ecological safety of esters was assessed by the phytotesting method. Samples of adipates were tested for fungal resistance, and the process of their biodegradation in soil was also studied. It is shown that the synthesized esters have good plasticizing properties and are environmentally safe. When utilized under natural conditions, they can serve as a potential source of carbon for soil microorganisms and do not form stable toxic metabolites; therefore, they are not able to accumulate in nature; when the plasticizers under study are disposed of in the soil, toxic substances do not enter.     

Synthesis and chemical structural analysis of nitroxyl‐radical‐incorporated poly(acrylic acid/lactide/ϵ‐caprolactone) copolymers

The goal of this research is to synthesize biodegradable polymers that would have nitroxyl radical biological functions. Linear aliphatic polyesters were chosen as the starting materials. The hydroxyl‐terminated polylactide/?‐caprolactones (PBLC‐OHs) were first synthesized by melt ring‐opening copolymerization in the presence of benzyl alcohol and stannous octoate. PBLC‐OHs were used as the precursor for the synthesis of double bond‐functionalized polylactide/?‐caprolactones (PBLC‐Mas) by reacting the hydroxyl end groups of PBLC‐OH with maleic anhydride in melt at 130 °C. Acrylic acid/lactide/?‐caprolactone graft copolymers (PBLCAs) were then successfully carried out by the radical copolymerization of acrylic acid and PBLC‐Ma initiated by azobisisobutyronitrile. Finally, nitroxyl radicals [4‐amino‐2,2,6,6‐tetramethylpiperidine‐1‐oxy (TAM)] were incorporated into the carboxylic acid sites of the acrylic acid/lactide/?‐caprolactone copolymer (TAM‐PBLCA) by reacting TAM with PBLCA in the presence of N,N′‐carbonyl diimidazole. A high content of TAM was incorporated into the PBLCA copolymer. The polymers synthesized were characterized by ¹H and ¹³C NMR, Fourier transform infrared spectroscopy, and electron paramagnetic resonance spectra. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4214–4226, 2001     

Poly(lactic acid)/coplasticized thermoplastic starch blend: Effect of plasticizer migration on rheological and mechanical properties

Polylactic acid (PLA) and thermoplastic starch (TPS) are known as bio‐based and biodegradable thermoplastic polymers that can be used in different applications owing to their inherent physical and mechanical properties. In order to reduce the higher costs of PLA and tuning its physical and mechanical properties suitable for short life packaging applications, blending of PLA with the TPS, more economical biodegradable polymer, has been considered in academic and industrial researches. However, melt blending of PLA with TPS without compatibilization process caused some drawbacks such as coarsening morphology and declining mechanical properties and ductility because of thermodynamic immiscibility, which may restrict its usage in packaging applications. Subsequently, our approach in this research is compatibilization of PLA/TPS blends by utilization of primary well tuning of TPS formulation with a combination of sorbitol and glycerol plasticizers. In this work, the wide composition range of melt mixed PLA/TPS blends was prepared using a laboratory twin screw extruder. The effects of microstructure on the rheological and mechanical properties of PLA/TPS blends were studied using different methods such as scanning electron microscopy (SEM) images, contact angle, oscillatory shear rheological measurements, and tensile and impact strength mechanical tests. The rheological and mechanical properties were interpreted according to the morphological features and considering the possibility of plasticizer migration from TPS to PLA phase during melt blending. Reduction in complex viscosity and storage modulus of PLA matrix samples indicates the improved melt processability of blends. Finally, in comparison with mechanical results reported in literature, our simple approach yielded the blends with elastic modulus and ductility comparable with those of chemically compatibilized PLA/TPS blends.     

Syntheses of biodegradable polymer networks based on polycaprolactone and glutamic acid

Biodegradable trifunctional oligomer was synthesized from polycaprolactone and glutamic acid and characterized by Fourier‐transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectroscopies. Injectable and in situ crosslinkable polymer networks were fabricated by the copolymerization of oligomer with triethylene glycol dimethacrylate (TEGDMA) and used to evaluate the initial compressive strengths, viscosities, shrinkages, thermal stabilities, and biodegradabilities in the forms of polymer network neat resin and their composites with β‐tricalcium phosphate. The initial compressive strengths (CS) values of neat resins ranged from 9.54 to 187.6 MPa. Both neat resins and composites had polymerization shrinkage ranging from 0% to 11.7%, which increased with increasing of TEGDMA contents in resin. Moreover, in polymer composite resins, shrinkage values decreased with increasing filler level from 0% to 4.6%, and exothermic evolution values decreased from 33.5°C to 29.7°C as increasing filler level. The composite with the formulation of (polycaprolactone)‐glutamate triacrylate (PCLGTA)/TEGDMA (25/75) and powder/liquid (P/L) ratio of 1.0 exhibited the highest exothermal and lowest shrinkage values. The increase of oligomer in the formulation led to an increase in viscosity.     

Biadhesive Peptides for Assembling Stainless Steel and Compound Loaded Micro‐Containers

Biadhesive peptides (peptesives) are an attractive tool for assembling two chemically different materials—for example, stainless steel and polycaprolactone (PCL). Stainless steel is used in medical stents and PCL is used as a biodegradable polymer for fabrication of tissue growth scaffolds and drug delivering micro‐containers. Biadhesive peptides are composed of two domains (e.g., dermaseptin S1 and LCI) with different material‐binding properties that are separated through a stiff peptide‐spacer. The peptesive dermaseptin S1‐domain Z‐LCI immobilizes antibiotic‐loaded PCL micro‐containers on stainless steel surfaces. Immobilization is visualized by microscopy and field emission scanning electron microscopy analysis and released antibiotic from the micro‐containers is confirmed through growth inhibition of Escherichia coli cells.     

Comparative Study of PHA Degradation in Natural Reservoirs Having Various Types of Ecosystems

The kinetics of polyhydroxyalkanoate (PHA) degradation in natural environment in two water reservoirs having various ecological characteristics was studied. It was shown that biodegradation of polymer essentially depends on the environment temperature and inorganic composition of water. The processes of polymer degradation under aerobic and anaerobic conditions were compared. The polymer degradation was slower under anaerobic conditions.     

Nonwoven Releasing Propolis as a Potential New Wound Healing Method—A Review

Wound healing poses a serious therapeutic problem. Methods which accelerate tissue regeneration and minimize or eliminate complications are constantly being sought. This paper is aimed at evaluation of the potential use of biodegradable polymer nonwovens releasing propolis as wound healing dressings, based on the literature data. Propolis is honeybee product with antioxidant, antibacterial, antifungal, anticancer, anti-inflammatory, analgesic, and regenerative properties. Controlled release of this substance throughout the healing should promote healing process, reduce the risk of wound infection, and improve aesthetic effect. The use of biodegradable aliphatic polyesters and polyester carbonates as a propolis carrier eliminates the problem of local drug administration and dressing changes. Well-known degradation processes and kinetics of the active substance release allows the selection of the material composition appropriate to the therapy. The electrospinning method allows the production of nonwovens that protect the wound against mechanical damage. Moreover, this processing technique enables adjusting product properties by modifying the production parameters. It can be concluded that biodegradable polymer dressings, releasing a propolis, may find potential application in the treatment of complicated wounds, as they may increase the effectiveness of treatment, as well as improve the patient’s life quality.