A Tetrameric Titanium Alkoxide as a Lactide Polymerization Catalyst

The tetrameric titanium alkoxide (MeC(CH₂‐μ₃‐O)(CH₂‐μ‐O)₂)₂Ti₄(O‐i‐Pr)₁₀ ( 1 ) catalyzes the ring‐opening polymerization (ROP) of lactide (LA) in toluene solution at various polymerization temperatures, and its bulk ROP at 130°C. Compound 1 facilitated reasonably controlled polymerization characteristics via a coordination/insertion mechanism in solution, whereas the bulk polymerization products displayed broad molecular‐weight distributions. The stereochemical microstructure of PLA was determined from homonuclear decoupled ¹H NMR spectroscopic studies.     

Bio-based photo-curable polyurethane composites

Polyurethane (PU) covers a range of applications in wearable circuits, coating materials, foaming industries, surgical equipments, packing materials and replacement of plastic materials. As per broad applications spectrum, huge data on PU synthesis has been reported so far, with different types of polyols, isocyanates, organic acids, acrylates with different chain extenders, catalysts, emulsifiers and/or PI. In this review, for a comprehensive study of structure-activity relationship, data from last 5 years has been compiled for photo-curable PU categorized on the basis of solvent as well as acrylate components. In this review a range of parameters including tensile strength, hardness, flexibility, hydrophobicity/hydrophilicity, solvent resistance, storage/young's modulus, shape recovery, viscosity, curing kinetics and thermal stability has been compared against composition.     

Biodegradable Polylactide and Its Nanocomposites: Opening a New Dimension for Plastics and Composites

The academic and industrial aspects of the preparation, characterization, mechanical and materials properties, crystallization behavior, melt rheology, and foam processing of pure polylactide (PLA) and PLA/layered silicate nanocomposites are described in this feature article. Recently, these materials have attracted considerable interest in polymer science research. PLA is linear aliphatic thermoplastic polyester and is made from agricultural products. Hectorite and montmorillonite are among the most commonly used smectite‐type layered silicates for the preparation of nanocomposites. Smectites are a valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity, and transparency in solution. In their pristine form, they are hydrophilic in nature, and this property makes them very difficult to disperse into a polymer matrix. The most common way to overcome this difficulty is to replace interlayer cations with quaternized ammonium or phosphonium cations, preferably with long alkyl chains. In general, polymer/layered silicate nanocomposites are of three different types: (1) intercalated nanocomposites, in which insertion of polymer chains into the layered silicate structure occurs in a crystallographically regular fashion, regardless of polymer to layered silicate ratio, with a repeat distance of few nanometer; (2) flocculated nanocomposites, in which intercalated and stacked silicate layers are sometimes flocculated due to the hydroxylated edge–edge interactions between the silicate layers; (3) exfoliated nanocomposites, in which individual silicate layers are uniformly distributed in the polymer matrix by average distances that totally depend on the layered silicate loading. This new family of composite materials frequently exhibits remarkable improvements in its material properties when compared with those of virgin PLA. Improved properties can include a high storage modulus both in the solid and melt states, increased flexural properties, a decrease in gas permeability, increased heat distortion temperature, an increase in the rate of biodegradability of pure PLA, and so forth.

Illustration of the biodegradability of PLA and various nanocomposites.     

Versatility of potential biomedical use of functional polysuccinates

Polysuccinates with pendant allyl groups (PSAGE) were synthesized by melt copolymerization of succinic anhydride with allyl glycidyl ether and eventually other glycidyl ethers. It was found that PSAGE could be crosslinked by radical copolymerization with methyl methacrylate. Oxidized PSAGE considered as multifunctional epoxy resin was cured with use of glutaric anhydride to form solid material susceptible to hydrolytic degradation to water-soluble non-toxic products. Comb-like amphiphilic polysuccinates containing both pendant poly(oxyethylene) chains and epoxy groups have been synthesized as well and checked for their solubility in water. Properties of PSAGE-type polymers suggests their potential use as biomaterials and polymeric drug carries. Please note, in the print publication of D. Theis, T. Schmidt, K.-F. Arndt, Macromol. Symp. 210 (2004), 465, erroneously the DOI 10.1002/masy.200450651 is repeated. There, the DOI should read: 10.1002/masy.200450652     

Strategies for detecting ecotoxicological effects of biodegradable polymers in agricultural applications

Biodegradable is the long awaited and highly accepted property for materials (polymers) used in agricultural applications. Methods for determining biodegradability and material disintegration are established and already in use for routine analysis. Methods for analysing ecotoxic effects caused by biodegradable materials are neither established nor in routine use. In the past, biotests have been developed and optimised solely for investigations of single chemicals. Such tests are applicable even if they are not validated for the detection of undesired ecotoxicological effects deriving from biodegradation of polymers in soil. Since the biodegradation process does have an influence on the physical, chemical and biological status of the soil matrix, both biotests and chemical analysis are required in many cases. Theory, background data from method development and some results are presented.     

New biodegradable polymers for delivery of bioactive agents

Biodegradable, thermosensitive triblock copolymer, PLGA-PEG-PLGA, can be easily fabricated into drug-loaded microspheres or injectable in situ hydrogel system for protein or water-insoluble drugs without use of organic solvent. Aqueous-based microsphere exhibited continuous release of intact insulin in vitro for 3 weeks while the microspheres prepared using dichloromethane showed initial burst and incomplete release. Confocal miscoscopy images of microspheres corroborated the release pattern. Next study with an injectable in situ hydrogel (ReGel^TM) exhibited zero-order insulin release in vitro and sustained plasma insulin level for 2 weeks in vivo upon single subcutaneous injection in SD rats.     

An important biodegradable polymer – polylactone-family polymer

Systemic investigation on the synthesis and properties of aliphatic polylactones were carried out. And various materials were obtained with different degradation rates and mechanical properties. Two in vivo experiments were presented in this study to envision the biomedical applications of this kind of aliphatic polylactones.     

An investigation of the condensation kinetics in poly(ester-amide) and poly(ester-sulphide) preparation

Synthetic processes leading to hydrophilic biodegradable polymers for bio-inspired applications were investigated from a kinetic point of view. In accordance with the reported mechanism of ester aminolysis, polycondensation reactions of α-amino-ω-esters, diesters, and diamines resulted markedly dependent on the basicity of the alkoxide leaving-group, being relatively fast for penthachlorophenate monomers. Furthermore, experimental data concerning the homopolycondensation of penthachlorophenyl α-amino-ω-oligo(ethyleneglycol) succinates of different degree of oligomerization clearly showed the existence of concurrent first and second-order processes, which were attributed to the intramolecular cyclization and intermolecular polycondensation reaction, respectively. In contrast to theoretical predictions based on the collision theory, however, minor incidence of the cyclization reaction was shown by the shortest monomers, thus suggesting a significant kinetic effect due to steric hindrance and solvent-reagent interactions. Analysis of the base-catalyzed Michael-type addition of α,ω-oligo(oxyethylene)dithiols to methyl (meth)acrylate allowed for the optimization of the relevant polymerization process involving hydrophilic diacrylates. Interestingly, very low reaction rates were determined for methacrylic components, supposedly because of steric and electronic factors connected to the presence of the α-methyl group. Minor effects on the reaction rate were also induced by solvent polarity and catalyst nature.     

Polycaprolactone based biodegradable polyurethanes

Two series of segmented polyurethanes were prepared with systematic variation in soft and hard segment length. The soft segment was constituted by polycaprolactone (PCL) blocks of molecular masses 530 or 2000 and the hard segment (HS) by urethane blocks, in a concentration that varied from 12% to 44% in weight of the whole polyurethane. Morphological analyses indicated that the amount of crystallinity of copolymers was strongly dependent on the PCL molar mass and hard segment content. The copolymers with longer PCL soft segments (Mn=2000) were semicrystalline, but those with shorter PCL segment (Mn=530) were unable to crystallize. The primary factor affectingthe biodegradability of copolymers as evaluated by Sturm tests was the extent of the phase separation, and that the segmental blending of the less biodegradable polyurethane (HS) blocks with PCL in the amorphous phase had a critical unfavorable consequence, which may be attributed to the size of the accessible area by microorganisms.     

Polymeric nanoparticles based on polylactide and related copolymers

The preparation of nanoparticle suspensions was carried out by using commercial biodegradable polymers as poly(d,l-lactide), poly(d,l-lactide-co-glycolide) and poly(d,l-lactide-co-ϵ-caprolactone). The method of preparation was based on the controlled addition of polymer organic solution to an aqueous phase containing dispersing agents. Poly(ethylene glycol) (10, 20, and 35 kDa grade), Tween 20, and Pluronic F-127 were used as dispersing agents in the aqueous phase. Content and type of both polymeric matrix and dispersing agent resulted of paramount relevance for the attainment of monodispersed nanoparticles with average diameter of about 130 nm. The addition of a steric stabilizer allowed for nanoparticle purification and isolation while preventing their agglomeration. The best results were obtained by using 35 kDa grade poly(ethylene glycol) as dispersing agent and either mannitol or glycidylisopropylidenglyceryl-β-cyclo-dextrin as steric stabilizer. The adopted procedure afforded biodegradable nanoparticle suspensions that could be used for the incapsulation and intravenous administration of biologically active proteins and oligopeptides.