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Bio-degradable/bio-compatible poly(lactide-co-glycidyl methacrylate), P(LA-co-GMA), a copolymer has been synthesized. The material contains curable C C groups, which enable its self-curing and grafting reactions with other vinyl monomers. The copolymer was grafted with a pH-responsive polyacrylamide (PAAm), by UV-assisted reactions using acrylamide (AAm) and N,N′-methylene bisacrylamide monomers, and various photoinitiator systems. The original copolymer and its partially-cured counterpart were employed in the grafting reaction. Chemical structures and properties of the resulting materials were characterized. Standard quantitative analysis techniques for measurement of the grafted AAm content and the degree of C C conversion have been developed by 1H NMR and FTIR spectroscopy. FTIR offers more advantages, in terms of non-destructive analysis, ease of operation, and lower cost of analysis. The results show that the grafted products from pre-cured P(LA-co-GMA) copolymers contain higher grafted AAm contents than their uncured counterparts. The highest grafted AAm content was obtained by using benzophenone (BP) as an initiator, while camphorquinone (CQ) led to the lowest content. In contrast, the degree of C C conversion of the copolymer from the two initiator systems shows a reverse trend. These amphiphilic and pH-responsive grafted copolymers with tunable AAm contents have a high potential for use in various applications, especially in biomedical and environmental fields.

Summary A method for preparation of silica particles from rice husk ash (RHA) is developed for use as fillers in an enhancement of gas permeability of polylactic acid (PLA) resin. Silica particles are produced in a one-step process by employing PLA-grafted-chitosan copolymer (PCT) as a polymeric surfactant. Particles with an average size of ca. 30 micron, which are smaller than those obtained from a conventional method, are obtained. The major advantage of this technique is its ease of operation, in which mechanical grinding is not required. The resulting particles are then used in preparation of PLA/silica composites by varying the silica contents from 0–2.0 wt %. The PCT copolymer is present as a coating layer on the particles surface, which promotes compatibility with the PLA matrix. Gas permeability (water vapor, carbon dioxide, and oxygen) and mechanical properties of the composite films are examined. Enhancements in gas permeability and selectivity are achieved, with slight drops in mechanical properties. The materials have high potential for use as degradable packaging films with tunable gas permeability.

Multi-branched poly(D-lactide)s (mbPDLAs) with various structures are synthesized via ring-opening polymer- ization by using polyglycidol (PG) macro-initiators. Their chemical structures and thermal properties are controlled by adjusting feed ratios of D-lactide (DLA) and PG. The materials are blended with commercial linear poly(L-lactide) (l-PLLA) to form a stereocomplex structure. Effects of mbPDLAs structures and l-PLLA/mbPDLA ratios on the blends' thermal, mechanical, and rheological properties are evaluated. Mechanical properties of the stereocomplex blends, espe- cially elongation at break and toughness, are dependent on the blend compositions, in which a 90:10 ratio exhibits the most desirable properties. The material also exhibits the lowest complex viscosity, which provides easy processing conditions. This is achieved by the incorporation of copolymers with multi-branched structures and an ability to form a much stronger stereocomplex structure.

Nanofibers of poly(L-lactide-co-DL-Lactide) (PDLLAx) copolymers with DL-lactate (DLLA) contents of 0, 2.5, 7.5, and 50%, which exhibit strong structure/properties correlation, were fabricated by electrospinning. Effect of the copolymer structure and electrospinning conditions on morphology and properties of the fibers were examined by SEM, DSC, XRD, and tensile measurements. Bead-free fibers of PDLLAx prepared from a DMF/CHCl3 mixed solvent are roughly 10-times smaller in size (600–800 nm), with lower degree of surface porosity, compared to those of CHCl3. When CHCl3 is employed, an increase in size (2.4–5.5 μm) and surface porosity (0–45%) with relative humidity value is observed in crystallizable copolymers, whereas an amorphous copolymer shows a reverse trend. Thermal properties and chain arrangements of the electrospun fibers are critically affected by DLLA content of the copolymers and electrospinning conditions, as a result from interplay between intermolecular and intramolecular hydrogen bonding. Contents of crystalline domains and “physical crosslinks” generated from DL lactate segments are proposed as the origin of this phenomenon. Fiber mats of PDLLA with 50% DLLA content show a large improvement in all aspects of mechanical properties, which are suitable for various biomedical applications. POLYM. ENG. SCI., 54:472–480, 2014. © 2013 Society of Plastics Engineers

Aliphatic/aromatic copolyesters, which possess good mechanical property and degradability, are of immense interest. Standard characterization techniques for the copolymer structure and degradation behaviors have been developed. The techniques are applied to examine hydrolytic degradation of poly(ethylene terephthalate- co -lactic acid) in a phosphate buffer solution (pH 7.2) at 60 °C. The weight loss of the copolymer and pH of the medium as a function of time are examined. 1 H NMR spectra provide information on microstructure and molecular weight of the samples, where deviations of the results from the actual values are observed, due to low solubility of the copolymer. More accurate results are obtained from TGA and FTIR experiments, as the samples are characterized in bulk. Insight into degradation mechanisms of the copolymer is derived from FTIR spectra. The content of aromatic esters in the soluble degraded species is determined from UV–Vis spectroscopy. These standard methods can be applied to various types of degradable aliphatic/aromatic copolyesters, which are essential in property assessment and determination of their potential applications.

Crosslinkable poly(lactic acid-co-glycidyl methacrylate), P(LLA-co-GMA), copolymer was systematically synthesized by ring-opening polymerization. Synthesis parameters, i.e., catalyst type, comonomer ratio and polymerization time and temperature were studied. The incorporated GMA content strongly affected the physical and thermal properties of the obtained copolymers, which varied from semi-crystalline to completely amorphous polymers. Melting and glass transition temperatures, and molecular weights of the copolymers decreased as the GMA content in the copolymer increased. Curing behavior of the copolymers was assessed by employing thermo- and photo-crosslinking processes, and the crosslink density was evaluated via their gel content and solvent swelling ratio. A photo-crosslinking process was proven as a practical method in the curing of the copolymers, as the reaction was almost complete within 2 min, as indicated by a gel content of 96%. In the thermo-crosslinking process, at least a 15-min curing time was required at 120 °C. The cured products of copolymers with 19.2 mol% GMA showed the highest compressive stress at 25.5 MPa. Random copolymer of poly(lactic acid-co-glycidyl methacrylate), P(LLA-co-GMA) was systematically synthesized by ring-opening polymerization. Synthesis parameters, that is, catalyst type, comonomer ratio and polymerization time and temperature were studied. The incorporated GMA content strongly affected physical and thermal properties of the obtained copolymers, which varied from semi-crystalline to completely amorphous polymer. Curing behaviors of the copolymers were assessed by employing thermo- and photo-crosslinking processes, where the crosslink density was evaluated via their gel content and solvent swelling ratio.

Poly(L)lactide (PLLA), aliphatic polyester, and poly(LLA-co-DLLA) copolymers consisting of 2.5, 7.5, 50% of DLLA content were also synthesized. PLLA was successfully electrospun by using 15wt% solution in (1DMF:3CHCl3) mixed solvent. 2.5, 7.5, 50% P(LLA-co-DLLA) copolymers were then spun at 8, 10, and 15wt% concentration in a single chloroform solvent, respective. The lactide-based polymeric nanofibers were characterized by Scanning Electron Microscope (SEM). Smooth surface morphology was observed in nanofibers produced from PLLA and 50% P(LLA-co-DLLA) copolymer. However, surface porosity was observed in the corresponding fibers from 2.5 and 7.5% P(LLA-co-DLLA) copolymers. These nanofibers have high potential for wide range of applications such as filter media, nano-sensor, drug delivery and tissue scaffold, especially, those derived from 2.5 and 7.5% P(LLA-co-DLLA) copolymers which contain high degree of porosity.

Poly(lactic acid-co-ethylene glycol) (PLLA/PEG) copolymers were synthesized and their properties were characterized. The PLLA/PEG/PLLA triblock copolymers were synthesized by ring-opening polymerization from l-lactide (LLA) and PEG macroinitiator. Stannous octoate, Sn(Oct)2 was used as a catalyst. Effects of molecular weight of PEG (600, 2000 and 4000), LLA/OH molar ratios (95:5, 98:2) and a sequence of addition of the reactants on properties of the copolymers were investigated. The triblock copolymers were subsequently used in a production of multiblock copolymers by reacting with a chain-extending agent, hexamethylene diisocyanate (HMDI). Chemical structure and molecular weight of the copolymers were characterized by 1H-NMR, FTIR and GPC. The results showed that molecular weight of triblock copolymers varied from 4,500 to 10,200. After chain extension, multiblock copolymer with molecular weight of 16,490 was produced. Thermal properties of the copolymers were also examined by DSC.

Lactic acid/ethylene terephthalate copolyesters were synthesized by the standard melt polycondensation of lactic acid (L), ethylene glycol (EG) and dimethyl-terephthalate (DMT). Effects of reaction temperatures and types of catalysts on the structures and properties of the copolymers were examined. In addition, feasibility of promoting the copolymerization process by a novel synthesis step of using thermo-stabilizers was investigated. The results show that a reaction temperature of higher than 180°C is necessary to produce copolymers with appreciable molecular weight. However, degradation was observed when the reaction temperature is higher than 220°C. Triphenyl phosphate (TPP) shows promising results as a potential thermo-stabilizer to minimize this problem. It was found that Sb2O3 and Tin(II) octoate are most effective among 4 types of catalysts employed in this study. 1H-NMR results indicate that copolymers have a random microstructure com- posed mainly of single L units alternately linked with ET blocks at various sequential lengths. The longer ET sequence in the chain structure leads to the increase in melting temperature of the copolymer. TGA results show that the resulting copolymers possessed greater thermal stability than commercially-available aliphatic PLA, as a result of the inclusion of T (terephthalate) units in the chain structure.

PLA-based aliphatic aromatic copolyesters have been synthesized and characterized in order to incorporate the degradability of PLA and good mechanical properties of aromatic species. Synthesis of the copolymers was conducted by polycondensation of lactic acid with dimethyl terephthalate (DMT) and various diols using stannous(II) octoate as a catalyst. Three types of diols with different methylene lengths were employed, i.e., ethylene glycol (EG), propylene glycol (PG) and 1, 4-butanediol (BD). Effects of diols and comonomer molar ratio on the extent of polycondensation reaction and molecular weight of the resulting copolymers were investigated. Diacids and diol ratios of L-lactic acid (LLA), dimethyl terephthalate (DMT) and diol of 1/1/2, 1/2/4 and 2/1/2 were employed. Characterization of chemical structure, molecular weight and thermal and physical properties of the resulting copolymers were conducted by FTIR, NMR, and DSC.

Because of their respective advantages, the combination of good material properties of poly(ethylene terephthalate) (PET) and degradability of polylactic acid (PLA) is researched as degradable copolymer for packaging and agricultural applications. Poly(ethylene terephthalate-co-lactic acid) (PET-co-PLA) has been synthesized by employing polycondensation of mixtures of dimethyl terephthalate (DMT), lactic acid (LA) and ethylene glycol (EG), using tin(II) octoate as a catalyst. A chain-extending reagent, hexamethylene diisocyanate (HMDI), was then used in the subsequent step to increase the chain length of the copolymer and improve its mechanical properties for suitable applications. The chemical structure and molecular weight of the copolymers were investigated by FTIR, NMR, and DSC. NMR results indicated the incorporation of lactic acid and PET units in the copolymer chain. Additionally, blends of the resulting copolymer with commercially-available PLA were studied. The blend miscibility was examined by DSC and FTIR spectroscopy.

Naproxen (NPX) drug-loaded magnetic nanoparticles (MNPs) have been prepared in a one-step process utilizing a biocompatible polylactide-grafted-chitosan copolymer. The copolymer serves both as a NPX drug carrier as well as a polymeric surfactant for the synthesis of MNPs without the use of any additional surfactant. Highly stable MNPs with high magnetization in the form of maghemite (γ-Fe2O3) are prepared in aqueous media. Effects of preparation conditions on structures and properties of the copolymer-coated and drug-loaded MNPs are investigated by employing particle size and zeta potential measurements, transmission electron microscopy, vibrating sample magnetometer, X-ray diffraction, Fourier-transform infrared, nuclear magnetic resonance, and confocal Raman spectroscopy. The results show that average particle size (150–300 nm), coating efficiency, and coating structures of the resulting MNPs materials are strongly dependent on MNP/copolymer and MNP/NPX ratios in feed. It is also observed that NPX acts as co-surfactant in the drug-loading process, resulting in different encapsulating structures with the variation in the MNP/copolymer and MNP/NPX ratios. Properties of the MNPs materials can be further optimized for use in specific biomedical applications.