Jorge F. J. Coelho

The quest for sustainable polyesters – insights into the future

Polyesters from renewable resources are an expanding area with a burgeoning scientific activity, nevertheless little has been reviewed about this particular class of polymers. The present appraisal intends to contribute to fill this literature gap by reviewing recent aspects related to the most promising renewable-based polyesters. Emphasis will be placed on bio-based polyesters that, given their comparable properties, may replace polymers derived from fossil fuel feedstock, and on bio-based polyesters with completely innovative properties for novel applications. Furthermore, the sources of renewable monomers will also be reviewed, together with the most relevant eco-friendly synthetic approaches used in polycondensation reactions leading to polyesters.

Biobased polyesters and other polymers from 2,5-furandicarboxylic acid: a tribute to furan excellency

Motivated by the general concern about sustainability and environmental issues, an intense search for renewable-based polymers has grown exponentially in recent years. This search definitely spotlighted polyesters derived from 2,5-furandicarboxylic acid, among other polymers, as some of the most promising, especially due to the resemblance of this renewable monomer to the well-known petroleum-based terephthalic acid, as well as owing to the possibility of preparing innovative materials. The huge number of recent papers and patents about this family of polymers explore aspects as diverse as synthesis with other renewable-based monomers, leading to the preparation of materials with enhanced thermo-mechanical, biodegradability and liquid crystalline properties, among other features. Additional aspects pursued in such studies are innovation in the synthetic approaches or their optimisation, as well as the development of applications for everyday-life objects for example packaging materials, especially bottles, textiles, coating, and toners, among many other uses. Despite this intense activity, little has been reviewed recently about this unique family of polyesters or derived polymers, as the only reviews on the subject date back to the last century. In this perspective, the present review aims at contributing to filling this literature gap, covering recent aspects related with challenges in developing polyesters, polyamides, or other polymers from 2,5-furandicarboxylic acid and their precursors. Emphasis is placed on monomer synthesis, polymerisation reactions, catalysts and applications.

Drug delivery systems: Advanced technologies potentially applicable in personalized treatments

Advanced drug delivery systems (DDS) present indubitable benefits for drug administration. Over the past three decades, new approaches have been suggested for the development of novel carriers for drug delivery. In this review, we describe general concepts and emerging research in this field based on multidisciplinary approaches aimed at creating personalized treatment for a broad range of highly prevalent diseases (e.g., cancer and diabetes). This review is composed of two parts. The first part provides an overview on currently available drug delivery technologies including a brief history on the development of these systems and some of the research strategies applied. The second part provides information about the most advanced drug delivery devices using stimuli-responsive polymers. Their synthesis using controlled-living radical polymerization strategy is described. In a near future it is predictable the appearance of new effective tailor-made DDS, resulting from knowledge of different interdisciplinary sciences, in a perspective of creating personalized medical solutions.

Fabrication and characterisation of PCL and PCL/PLA scaffolds for tissue engineering

Purpose – The main purpose of this research work is to study the effect of poly lactic acid (PLA) addition into poly (e-caprolactone) (PCL) matrices, as well the influence of the mixing process on the morphological, thermal, chemical, mechanical and biological performance of the 3D constructs produced with a novel biomanufacturing device (BioCell Printing). Design/methodology/approach – Two mixing processes are used to prepare PCL/PLA blends, namely melt blending and solvent casting. PCL and PCL/PLA scaffolds are produced via BioCell Printing using a 300-μm nozzle, 0/90° lay down pattern and 350-μm pore size. Several techniques such as scanning electron microscopy (SEM), simultaneous thermal analyzer (STA), nuclear magnetic resonance (NMR), static compression analysis and Alamar BlueTM are used to evaluate scaffolds morphological, thermal, chemical, mechanical and biological properties. Findings – Results show that the addition of PLA to PCL scaffolds strongly improves the biomechanical performance of th...

Ambient temperature rapid SARA ATRP of acrylates and methacrylates in alcohol–water solutions mediated by a mixed sulfite/Cu(II)Br2 catalytic system

The new generation of catalytic systems for Controlled/“Living” Radical Polymerization (CLRP) of vinyl monomers should be non-toxic, inexpensive and provide fast polymerizations in environmentally friendly media. Herein, we report the successful ambient temperature ATRP of several vinyl monomers (MA, n-BA, MMA and DMAEMA) catalyzed by inorganic sulfites (Na2S2O4 and Na2S2O5) and small amounts of a Cu(II)Br2/Me6TREN system in alcohol–water mixtures. The controlled character of ATRP of acrylates and methacrylates was confirmed by the linear increase of molecular weights with monomer conversion, narrow molecular weight distributions (Mw/Mn ∼ 1.05) and by reinitiation experiments (copolymerization and chain extension). 1H NMR and MALDI-TOF analyses confirmed the molecular structure and chain-end functionality of the obtained polymers. ATRP of MA using this novel catalytic system in alcohol–water mixtures with multifunctional Br-based initiators provides 4 and 6 arm star polyacrylates in a controlled manner without any observable gel formation. The data presented open up the possibility of using fast ATRP catalyzed by inorganic sulfites (approved by FDA as food and beverage additives) in solvents that are inexpensive, eco-friendly and widely used in chemical industrial processes.

Synthesis of well-defined poly(2-(dimethylamino)ethyl methacrylate) under mild conditions and its co-polymers with cholesterol and PEG using Fe(0)/Cu(II) based SARA ATRP

Atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DMAEMA) with a mixed transition metal catalytic system consisting of Fe(0) and small amounts of CuBr2/PMDETA (N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) in water–isopropanol mixtures at 60 °C and 25 °C is reported and compared with commonly used CuBr/PMDETA-mediated ATRP systems. The obtained kinetics of polymerization showed that, in addition to the environmental attractiveness of this catalytic system, Fe/Cu mixed transition metal mediated ATRP of a DMAEMA monomer provides a significantly improved control of polymer chain growth, forming PDMAEMA of low dispersity values at all conversions. The controlled character of ATRP of DMAEMA was confirmed by the linear increase of molecular weights with monomer conversion, narrow molecular weight distributions, and re-initiation/chain extension experiments. The molecular structure of the obtained polymer(s) was confirmed by 1H nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy. ATRP of DMAEMA was also extended to synthesis of functional bio-relevant polymers with cholesterol and poly(ethylene glycol) segments.

Phosphonium-based ionic liquids as modifiers for biomedical grade poly(vinyl chloride).

This work reports and discusses the influence of four phosphonium-based ionic liquids (PhILs), namely trihexyl(tetradecyl) phosphonium dicyanamide, [P(6,6,6,14)][dca]; trihexyl(tetradecyl) phosphonium bis(trifluoromethylsulfonyl)imide, [P(6,6,6,14)][Tf(2)N]; tetrabutyl phosphonium bromide, [P(4,4,4,4)][Br]; and tetrabutyl phosphonium chloride, [P(4,4,4,4)][Cl], on some of the chemical, physical and biological properties of a biomedical-grade suspension of poly(vinyl chloride) (PVC). The main goal of this work was to evaluate the capacity of these PhILs to modify some of the properties of neat PVC, in particular those that may allow their use as potential alternatives to traditional phthalate-based plasticizers in PVC biomedical applications. PVC films having different PhIL compositions (0, 5, 10 and 20 wt.%) were prepared (by solvent film casting) and characterised by Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, dynamical mechanical thermal analysis, scanning electron microscopy/energy-dispersive X-ray/electron probe microanalysis, X-ray diffraction, transmittance, permeability towards oxygen and carbon dioxide, thermal degradation, contact angle measurement, water and vapour uptake, leachability and biocompatibility (haemolytic potential, thrombogenicity and cytotoxicity). A conventional organic plasticizer (di-isononyl phthalate) was used for comparison purposes. The results obtained showed that it was possible to change the neat PVC hydrophobicity, and consequently its water uptake capacity and plasticizer leachability, just by changing the PhIL employed and its composition. It was also possible to significantly change the thermal and mechanical properties of PVC films by choosing appropriate PhIL cation/anion combinations. However, a specific PhIL may not always be capable of simultaneously keeping and/or improving both physical properties. In addition, ionic halide salts were found to promote PVC dehydrochlorination. Finally, none of the prepared materials presented toxicity against Caco-2 cells, though pure [P(6,6,6,14)][dca] decreased HepG2 cells viability. Moreover, PVC films with [P(6,6,6,14)][dca] and [P(4,4,4,4)][Cl] were found to be haemolytic and thus these PhILs must be avoided as PVC modifiers if biomedical applications are envisaged. In conclusion, from all the PhILs tested, [P(6,6,6,14)][Tf(2)N] showed the most promising results regarding blood compatibility, leaching and permeability to gases of PVC films. The results presented are a strong indicator that adequate PhILs may be successfully employed as PVC multi-functional plasticizers for a wide range of potential applications, including those in the biomedical field.

New unsaturated copolyesters based on 2,5-furandicarboxylic acid and their crosslinked derivatives

The synthesis and characterisation of a novel family of unsaturated polyesters (UPs) and their crosslinked resins (UPRs) based on 2,5-furandicarboxylic acid (FDCA) are reported. Their original features stem from the use of FDCA as the aromatic monomer, and also from the fact that UPs are entirely based on renewable resources, oppositely to most reported materials which are typically based on petrochemicals or instead they are derived from both petrochemicals and a percentage of renewables. Additionally, instead of styrene, 2-hydroxyethylmethacrylate (HEMA) was used as the reactive solvent to obtain the UPRs. These novel resins showed adequate thermal and mechanical behavioural tendencies similar to petrochemical ones, namely high glass transition temperature (up to 104 °C) and good thermal stability (up to 230 °C). These characteristics enhance their prospects of being a successful renewable-based material.

Photocrosslinkable starch-based polymers for ophthalmologic drug delivery

This study focused on the development and characterization of a starch-based polymer with urethane linkages to be used as a controlled drug delivery system for biomedical applications. Starch was modified with 2-isocyanatoethyl methacrylate in order to obtain a polymer containing carbon-carbon double bonds in its structure. This modified starch was then used to produce films by UV irradiation using Irgacure 2959 (CIBA) as the photoinitiator. The modified polymer was characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The swelling capacity, in artificial lachrymal fluid (performed both at room temperature and physiological temperature), and water contact angles measurements were determined. The in vitro biodegradation in artificial lachrymal fluid supplemented with lysozyme was also studied. Scanning electronic microscopy (SEM) was used to characterize the morphology of the materials immediately after synthesis and after biodegradation. Timolol maleate and sodium flurbiprofen were immobilized by adsorption and their in vitro release profiles were followed spectroscopically.

Improvement of the control over SARA ATRP of 2-(diisopropylamino)ethyl methacrylate by slow and continuous addition of sodium dithionite

The kinetics and detailed mechanism of SARA ATRP of 2-(diisopropylamino)ethyl methacrylate (DPA) were investigated. Supplemental activator and reducing agent (SARA) atom transfer radical polymerization (ATRP) using sodium dithionite (Na2S2O4) was used to create well controlled polymers of PDPA. The influence of the initiator, solvent, structure and concentration of the catalyst was studied, and the ratios of Na2S2O4 were adjusted to optimize the polymerization. Well controlled polymers required Na2S2O4 to be slowly and continuously fed to the reaction mixture, with 500 parts per million (ppm) of CuBr2 with tris(2-dimethyamino)amine (Me6TREN) as a ligand. The initial content of Na2S2O4 in the reaction mixture, the feeding rate and the Cu catalyst concentration were optimized to provide polymers with narrow molecular weight distribution (Mw/Mn < 1.15) at high monomer conversion (∼90%). Interestingly, the results revealed that when tris(2-pyridylmethyl)-amine (TPMA) was used as a ligand, the amount of copper required to achieve similar control of the polymerization could be decreased 5 times. This system was successfully extended to the polymerization of oligo(ethylene oxide) methyl ether methacrylate (OEOMA). The high conversion and preservation of the chain-end functionality allows the direct synthesis of POEOMA-b-PDPA block copolymers. The low catalyst concentrations and benign nature of Na2S2O4 make this SARA ATRP method attractive for the synthesis of well controlled water soluble polymers for biomedical applications.