Influence of synthesis conditions on molecular weight as well as mechanical and thermal properties of poly(hexamethylene 2,5-furanate)

Poly(hexamethylene 2,5-furanate) (PHF) was obtained by melt polycondensation. The process was carried out at temperatures of 230, 235 and 240 ° C. It has been shown that the selection of the optimal parameters of the synthesis process leads to the obtaining of biomaterials of high molecular weight, and thus better mechanical and thermal properties. The relationship between the molecular weight and the mobility of polymer chains, and consequently the temperature of phase changes and mechanical properties, was determined.

Sustainable polyesters via direct functionalization of lignocellulosic sugars

The development of sustainable plastics from abundant renewable feedstocks has been limited by the complexity and efficiency of their production as well as their lack of competitive material properties. Here, we demonstrate the direct transformation of the hemicellulosic fraction of non-edible biomass into a diester plastic precursor at 83% yield (95% from commercial xylose) during integrated plant fractionation with glyoxylic acid. Melt polycondensation of the resulting xylose-based diester with a range of aliphatic diols led to high-molecular weight amorphous polyesters with combined high glass transition temperatures, tough mechanical properties, and strong gas barriers, which could be processed by injection-molding, thermoforming, and 3D-printing. These polyesters could then be chemically recycled from mixed plastic waste streams or digested under biologically relevant conditions. The transformation’s simplicity led to projected costs that were competitive with fossil alternatives and significantly reduced associated greenhouse gas emissions, especially if glyoxylic acid was sourced from CO2.

Synthesis and study of oligohexamethyleneguanidine hydroiodide as a radiopaque substance

Diagnosis of complex injuries, such as splinter fractures and wounds, skull injuries accompanied by internal injuries that are inaccessible to visual control, presents the greatest difficulties during X-ray examination. Therefore, it is relevant to develop a drug that can help localize the site of a pathological lesion with high accuracy, relying only on the results of an X-ray study, which is possible when a reference point (substance) is applied to the patient’s skin. A radiopaque contrast compound based on an iodinated polymeric matrix with iodine as the contrasting component and polyguanidine as the carrier has been proposed to be used as a reference point substance. The choice of this class of polymers stemmed from the fact that a positive charge is localized to a greater extent on the carbon atom of the guanidine group, which allows loading iodine anions into it. Protonation of pure guanidine with hydroiodic acid has helped obtain guanidine hydroiodide. This finding was confirmed by IR spectroscopy methods (a decrease in the intensity of bands in the region of 1,380, 880 cm−1 in comparison with guanidine, as well as broadening of the band of stretching vibrations of amino groups characteristic of guanidine salts) and X-ray phase analysis. Polyhexamethylene guanidine hydroiodide was synthesized based on hexamethylenediamine and iodine-containing guanidine salt using melt polycondensation. The results show that the aqueous solutions of samples under study absorb X-radiation and are the X-ray-positive substances (exposure radiation dosage E = 0.04 mSV).

Synthesis of a Bio-based and Biodegradable Poly(ethylene-co-isosorbide [2,2'-bithiophene]-5,5'-dicarboxylate) with enhanced Thermal and Degradability Properties

In this investigation, a synthetic biopolymer prepared from bithiophene monomer, isosorbide and ethylene glycol, was synthesized through melt polycondensation. The result showed the polyesters to possess promising thermal and mechanical properties. The bithiophene monomer, [2,2'-bithiophene]-5,5'-dicarboxylicacid acid, was synthesized from a palladium-catalyzed, phosphine ligand-free direct coupling protocol, using polyethylene glycol palladium (Pd/PEG) as catalyst. The procedure was found effective at polymerizing the bithiophene monomer with isosorbide and glycol. The bithiophene polyester displayed several intriguing properties among good thermal resistance, crystallinity and high tensile modulus. Additionally, the bithiophene monomer coupled to isosorbide enhanced the polyester with a comparatively high glass transition temperature. Films cast out these polyesters display excellent oxygen and water barrier properties, and were interestingly superior to those of poly(ethylene terephthalate). Moreover, the novel polyester also has good soil degradability properties.

Preparation of Bisphenol-A and Polydimethylsiloxane (PDMS) Block Copolycarbonates by Melt Polycondensation: Effects of PDMS Chain Length on Conversion and Miscibility

This study aimed to improve polydimethylsiloxane (PDMS) conversion in the preparation of polycarbonate (PC)–polydimethylsiloxane (PDMS) copolymer through melt polycondensation. We examined the transesterification process of PDMS with diphenyl carbonate (DPC) and its copolymerization products with bisphenol-A (BPA) for different chain lengths of PDMS. The key factors affecting PDMS conversion were investigated. Results showed that long-chain PDMS required a higher critical transesterification level (38.6%) to improve miscibility with DPC. During polycondensation, side reactions were more prone to occur when the equilibrium transesterification level of long-chain PDMS was lower. PDMS conversion was also lower when more short-chain PDMS was fed. Increasing the chain length of PDMS also reduced PDMS conversion. Notably, increasing the amount of KOH can significantly improve PDMS conversion throughout the polycondensation stage by increasing the equilibrium transesterification level of long-chain PDMS, thereby inhibiting the occurrence of side reactions.

Poly(lactic Acid): A Versatile Biobased Polymer for the Future with Multifunctional Properties—From Monomer Synthesis, Polymerization Techniques and Molecular Weight Increase to PLA Applications

Environmental problems, such as global warming and plastic pollution have forced researchers to investigate alternatives for conventional plastics. Poly(lactic acid) (PLA), one of the well-known eco-friendly biodegradables and biobased polyesters, has been studied extensively and is considered to be a promising substitute to petroleum-based polymers. This review gives an inclusive overview of the current research of lactic acid and lactide dimer techniques along with the production of PLA from its monomers. Melt polycondensation as well as ring opening polymerization techniques are discussed, and the effect of various catalysts and polymerization conditions is thoroughly presented. Reaction mechanisms are also reviewed. However, due to the competitive decomposition reactions, in the most cases low or medium molecular weight (MW) of PLA, not exceeding 20,000–50,000 g/mol, are prepared. For this reason, additional procedures such as solid state polycondensation (SSP) and chain extension (CE) reaching MW ranging from 80,000 up to 250,000 g/mol are extensively investigated here. Lastly, numerous practical applications of PLA in various fields of industry, technical challenges and limitations of PLA use as well as its future perspectives are also reported in this review.

Surface Modification of Poly(l–lactic acid) through Stereocomplexation with Enantiomeric Poly(d–lactic acid) and Its Copolymer

Poly(l–lactic acid) with high molecular weight was used to prepare PLLA films by means of the solvent casting technique. Poly(d–lactic acid) (PDLA) and poly(d–lactic acid–co–glucose) copolymer (PDLAG) with a low molecular weight were synthesized from d–lactic acid and glucose through melt polycondensation. PLLA films were immersed in PDLA or PDLAG solution to prepare surface-modified PLLA films. The modified PLLA film presented stereocomplex crystal (SC) on its surface and homogeneous crystals (HC) in its bulk. The HC structure and surface morphology of modified PLLA films were obviously damaged by PDLA or PDLAG solution. With increasing immersion time, the PLLA films modified by PDLA decreased both the HC and SC structure, while the PLLA films modified by PDLAG increased the SC structure and decreased the HC structure. Hydrophilic glucose residues of PDLAG on the surface would improve the hydrophilicity of surface-modified PLLA films. Moreover, the hydrophilicity of glucose residues and the interaction of glucose residues with lactic acid units could retard HC destruction and SC crystallization, so that PLLA films modified by PDLAG possessed lower melting temperatures of HC and SC, the crystallinity of SC and the water contact angle, compared with PDLAG–modified PLLA films. The SC structure could improve the heat resistance of modified PLLA film, but glucose residues could block crystallization to promote the thermal degradation of PLA materials. The surface modification of PLLA films will improve the thermal stability, hydrophilicity and crystallization properties of PLA materials, which is essential in order to obtain PLA-based biomaterials.

Synthesis and Properties of Thermotropic Copolyesters Based on Poly(ethylene terephthalate) and 4′-Acetoxy-4-biphenyl-carboxylic Acid

A series of novel copolyesters based on polyethylene terephthalate (PET) and 4′-hydroxy-biphenyl-4-carboxylic acid (HBCA) was obtained by melt polycondensation of bis(2-hydroxyethyl) terephthalate and 4’-acetoxybiphenyl-4-carboxylic acid (ABCA) as co-monomers with Sb2O3 as a catalyst. Using this synthetic procedure, a set of copolymers containing 20–80 mol% of HBCA units was prepared. According to NMR spectroscopy, the copolymers were of random composition. Copolyesters comprising 60–80 mol% of HBCA possessed increased heat resistance and formed nematic melts at 270 °C and higher. The liquid crystal (LC) phase formation was accompanied by transition to non-Newtonian characteristics of the melt flow, as well as an equalization of storage and loss moduli values. According to XRD and polarizing microscopy, the LC glassy phase of the copolyesters coexists with crystalline regions of poly-(4’-hydroxy-4-biphenylcarboxylate), non-melting up to 400 °C and above. The mechanical characteristics of these LC copolyesters showed similar or better values than those of well-known LC polymers. These novel copolyesters can be useful in obtaining heat-resistant materials with an ordered structure and, as a consequence, improved performance.

Enzymatic Synthesis of Poly(alkylene succinate)s: Influence of Reaction Conditions

Application of lipases (preferentially Candida antarctica Lipase B, CALB) for melt polycondensation of aliphatic polyesters by transesterification of activated dicarboxylic acids with diols allows to displace toxic metal and metal oxide catalysts. Immobilization of the enzyme enhances the activity and the temperature range of use. The possibility to use enzyme-catalyzed polycondensation in melt is studied and compared to results of polycondensations in solution. The experiments show that CALB successfully catalyzes polycondensation of both, divinyladipate and dimethylsuccinate, respectively, with 1,4-butanediol. NMR spectroscopy, relative molar masses obtained by size exclusion chromatography, MALDI-TOF MS and wide-angle X-ray scattering are employed to compare the influence of synthesis conditions for poly(butylene adipate) (PBA) and poly(butylene succinate) (PBS). It is shown that the enzymatic activity of immobilized CALB deviates and influences the molar mass. CALB-catalyzed polycondensation of PBA in solution for 24 h at 70 °C achieves molar masses of up to Mw~60,000 g/mol, higher than reported previously and comparable to conventional PBA, while melt polycondensation resulted in a moderate decrease of molar mass to Mw~31,000. Enzymatically catalyzed melt polycondensation of PBS yields Mw~23,400 g/mol vs. Mw~40,000 g/mol with titanium(IV)n-butoxide. Melt polycondensation with enzyme catalysis allows to reduce the reaction time from days to 3-4 h.