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High Molecular Weight Poly(butylene succinate-co-butylene furandicarboxylate) Copolyesters: From Catalyzed Polycondensation Reaction to Thermomechanical Properties

Novel potentially biobased aliphatic-aromatic copolyesters poly(butylene succinate-co-butylene furandicarboxylate) (PBSFs) in full composition range were successfully synthesized from 2,5-furandicarboxylic acid (FA), succinic acid (SA), and 1,4-butanediol (BDO) via an esterification and polycondensation process using tetrabutyl titanate (TBT) or TBT/La(acac)(3) as catalyst. The copolyesters were characterized by size exclusion chromatography (SEC), Fourier transform infrared (FTIR), (1)H NMR, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and their tensile properties were also evaluated. The weight average molecular weight (M(w)) ranges from 39,000 to 89,000 g/mol. The copolyesters are random copolymers whose composition is well controlled by the feed ratio of the diacid monomers. PBSFs have excellent thermal stability. The glass transition temperature (T(g)) increases continuously with φ(BF) and agrees well with the Fox equation. The crystallizability and T(m) decrease with increasing butylene furandicarboxylate (BF) unit content (φ(BF)) from 0 to 40 mol %, but rise again at φ(BF) of 50-100 mol %. Consequently, the tensile modulus and strength decrease, and the elongation at break increases with φ(BF) in the range of 0-40 mol %. At higher φ(BF), the modulus and strength increase and the ultimate elongation decreases. Thus, depending on φ(BF), the structure and properties of PBSFs can be tuned ranging from crystalline polymers possessing good tensile modulus (360-1800 MPa) and strength (20-35 MPa) to nearly amorphous polymer of low T(g) and high elongation (~600%), and therefore they may find applications in thermoplastics as well as elastomers or impact modifiers.

Perspectives On: Criteria for Complex Evaluation of the Morphology and Alignment of Electrospun Polymer Nanofibers

Electrospinning is a promising method for producing polymer materials composed of micro- and nanosized fibers. This method allows the preparation of random and aligned fibers of different morphologies, such as cylindrical or ribbon-shapes, defect-free or with defects, and with or without pores or porous. The increasing number of studies on electrospinning requires a set of criteria for more complex evaluation of the fiber morphology and the topology of these polymer materials to be established. The main characteristics necessary for a complex evaluation of the morphology of electrospun micro- and nanofibers have been systematized in this paper. Examples of characterization of the morphology and of the alignment of various micro- and nanofibers are given.

Polylactide Stereocomplex-Based Electrospun Materials Possessing Surface with Antibacterial and Hemostatic Properties

Novel fibrous materials of stereocomplex between high-molecular-weight poly(d- or l-)lactide (HMPDLA or HMPLLA) and diblock copolymers consisting of poly(l- or d-)lactide and poly(N,N-dimethylamino-2-ethyl methacrylate) blocks, respectively (PLLA-block-PDMAEMA or PDLA-block-PDMAEMA), were prepared by solution electrospinning. Fibers with mean diameters ranging from 1400 to 1700 nm were obtained. The stereocomplex formation was evidenced by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. Annealing at 100 degrees C for 8 h resulted in the appearance of crystalline peaks at 2theta values of 12, 21, and 24 degrees for PLA stereocomplex. X-ray photoelectron spectroscopy (XPS) analyses revealed the gradient composition of the fibers with a surface enriched in tertiary amino groups from PDMAEMA blocks. The availability of tertiary amino groups imparts hemostatic and antibacterial properties to the stereocomplex fibrous materials, as indicated by the performed tests on blood cells and on pathogenic microorganisms.

Preparation of Polyelectrolyte-Containing Nanofibers by Electrospinning in the Presence of a Non-Ionogenic Water-Soluble Polymer

The first successful preparation of nanofibers of a polyampholyte (N-carboxyethylchitosan) by electrospinning was achieved by adding a non-ionogenic water-soluble polymer to the spinning solution. Using this approach, other polyelectrolytes, poly(2-acryloylamido-2-methylpropanesulphonic acid) (PAMPS), and copolymers of 2-acryloylamido-2-methylpropane-sulphonic acid (AMPS) and acrylic acid [P(AMPS-co-AA)] were also electrospun into nanofibers. The non-ionogenic water-soluble polymers were polyacrylamide (PAAm) and poly(vinyl alcohol) (PVA). The average diameters of the electrospun nanofibers were in the range 50-260nm. The average diameter of the nanofibers significantly decreased with increasing polyelectrolyte content. The electrospun nanofibers were crosslinked by heat treatment at 100, 120 or 150°C for the N-carboxyethylchitosan/PAAm pair and at 90°C in the case of P(AMPS-co-AA)/PVA. The presence of an ionizable low-molecular-weight compound (7-iodo-8-hydroxyquinoline-5-sulphonic acid, SQ) led to a more than two-fold decrease in the diameter of the nanofibers and to the appearance of defects. The SQ-containing nanofibers showed antimicrobial activity against pathogenic microorganisms.

Biobased Polyesters with Composition-Dependent Thermomechanical Properties: Synthesis and Characterization of Poly(butylene succinate-co-butylene azelate)

Environmentally friendly poly(butylenesuccinate-co-butyleneazelate) (P(BS-co-BAz)s) aliphatic copolyesters with composition-dependent thermomechanical properties were synthesized from succinic acid (SuA), 1,4-butanediol (BDO), and dimethylazelate (DMAz) through a two-step polycondensation reaction. The molar SuA/AzA ratio was varied from 4:1 to 1:4, and the chemical structure and molecular characteristics of resulting (co)polyesters were characterized by NMR and SEC, whereas thermal properties and crystallinity were studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analyses (DMTA), and X-ray diffraction (XRD). A good agreement between theoretical and experimental SuA/AzA molar ratios in the copolyesters was achieved, together with the recovery of semicrystalline random copolymers of uniform composition along the chains. NMR, DSC, DMTA, and XRD results show that depending on their composition the P(BS-co-BAz) copolyesters might find applications from elastomers to high-impact thermoplastics.

Tuning of the surface biological behavior of poly(L-lactide)-based electrospun materials by polyelectrolyte complex formation.

Poly(L-lactide) (PLLA) and poly(L-lactide)/poly(ethylene glycol) (PLLA/PEG) electrospun fibrous materials coated with a polyelectrolyte complex (PEC) were prepared. This was achieved by consecutive deposition of a layer of N-carboxyethylchitosan (CECh) and a layer of a double hydrophilic block copolymer, poly(ethylene oxide)-b-quaternized poly[2-(dimethylamino)ethyl methacrylate] (PEO-b-PDMAEMAQ100), resulting in PEC formation between the two polyelectrolytes on the surface. Noteworthy, to improve the water wettability of the electrospun PLLA fibrous materials, that is, to enable more uniform deposition of the polyelectrolyte partners, water/ethanol mixed solvent was used for preparation of CECh and PEO-b-PDMAEMAQ100 solutions. The formation of PEC-based coating was demonstrated by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The PEC formation allows targeted modification of the biological behavior of the electrospun materials as evidenced by the performed tests in respect to blood cells and pathogenic microorganisms. In contrast to the pristine mats, the novel PEC-coated mats exhibit hemostatic properties and reduce the adhesion of pathogenic microorganisms.

Poly(L-lactide) and poly(butylene succinate) immiscible blends: from electrospinning to biologically active materials.

For the first time the preparation of defect-free fibers from immiscible blends of high molar mass poly(lactic acid) (PLA) and poly(butylene succinate) (PBS) in the whole range of the polyester weight ratios is shown. Electrospinning using the solvent-nonsolvent approach proved most appropriate. Moreover, electrospinning revealed crucial for the obtaining of PLA/PBS materials maintaining integrity. DSC and XRD analyses attested for a plasticizing effect and for increased PLA crystallinity at PBS addition to PLA. The mechanical properties of the PLA/PBS mats were controlled by the alignment of the fibers and changed from plastic to brittle materials upon increasing the PBS content. Drug loading and tests against pathogenic microorganisms suggested that the obtained mats can find application as antibacterial fibrous materials.

Modification of the Adhesive Properties of Silicone-Based Coatings by Block Copolymers

The improvement of the (bio)adhesive properties of elastomeric polydimethylsiloxane (PDMS) coatings is reported. This is achieved by a surface modification consisting of the incorporation of block copolymers containing a PDMS block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) block in a PDMS matrix, followed by matrix cross-linking and immersion of the obtained materials in water. Contact angle measurements (CA), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) showed the presence of the PDMAEMA block at the surface, drastic morphology changes, and improved adhesion properties after immersion in water. Finally, underwater bioadhesion tests show that mussels adhere only to block copolymer-filled coatings and after immersion in water, i.e., when the PDMAEMA blocks have been brought to the coating surface. These observations highlight the significant role of hydrophilic groups in the surface modification of silicone coatings.

Preparation of narrowly dispersed stereocomplex nanocrystals: a step towards all-poly(lactic acid) nanocomposites

Stereocomplexed polylactide-based nanocrystals were designed through a two-stage procedure comprising (i) the stereocomplexation of enantiomeric polylactide-based triblock copolymers and (ii) their selective recovery after acid-hydrolysis of the amorphous blocks. A “one-pot” synthetic process to prepare two enantiomeric P(D,D-LA)-b-P(rac-LA)-b-P(D,D-LA) and P(L,L-LA)-b-P(rac-LA)-b-P(L,L-LA) triblock copolymers of n = 10 100 g mol−1 and Đ = 1.10–1.11 was developed via a two-step ring-opening polymerization. The triblock copolymers were then subjected to stereocomplexation of the enantiomeric blocks followed by acidic hydrolysis of the amorphous racemic blocks to obtain uniform in size stereocomplex nanocrystals (scNCs) consisting solely of near-perfect stereocomplex. Hydrolysis conditions were optimized based on DSC analyses and the scNC crystal structure was confirmed by XRD. The morphology of sc-b-P(rac-LA)-b-sc and scNCs was studied by peak-force tapping atomic force microscopy, allowing simultaneous topography and adhesion mapping image analyses. The results clearly evidence the recovery of narrowly dispersed low-adhesive spherical nanoparticles with an average diameter of 15 ± 4 nm with concentration-controlled shape and size. Such unprecedented all-PLA stereocomplexed nanocrystals might find applications as renewable nanofillers in all-PLA nanocomposites.

Multiresponsive Shape Memory Blends and Nanocomposites Based on Starch

Smart multiresponsive bionanocomposites with both humidity- and thermally activated shape-memory effects, based on blends of ethylene-vinyl acetate (EVA) and thermoplastic starch (TPS) are designed. Thermo- and humidity-mechanical cyclic experiments are performed in order to demonstrate the humidity- as well as thermally activated shape memory properties of the starch-based materials. In particular, the induced-crystallization is used in order to thermally activate the EVA shape memory response. The shape memory results of both blends and their nanocomposites reflect the excellent ability to both humidity- and thermally activated recover of the initial shape with values higher than 80 and 90%, respectively.