Direct Polycondensation Of Lactic Acid Research Articles

Functionalized lactic acid macromonomers via polycondensation as an alternative to ring opening polymerization

AbstractEngineered polylactic acid (PLA) nanoparticles synthesized from oligo(lactic acid) macromonomers have been studied over the last decades for controlled drug delivery. These macromonomers are typically produced via ring‐opening polymerization (ROP) of the cyclic dimer lactide, initiated by 2‐hydroxyethyl methacrylate (HEMA). This reaction route, despite leading to well‐defined macromonomers, relies on the production of lactide from lactic acid, which burdens the ROP overall cost for more than 30%. In this work, we report the synthesis of PLA‐based macromonomers by direct polycondensation of lactic acid in the presence of HEMA as a valuable alternative to ROP. In particular, we compare the two processes side by side, focusing on the production of three HEMA‐LAn macromonomers, with n = 2, 4, and 6. Detailed kinetic models are developed for both reaction systems, and the corresponding parameters are estimated by fitting the experimental data. Through these models, the reaction kinetics as well as the time evolution of the entire chain length distributions of the products from polycondensation and ROP could be reliably predicted. This way, we demonstrated that polycondensation is a valuable alternative to ROP only for macromonomers with an average chain length of up to 4 and that ROP remains the main route to longer chains, when a strict control over the chain length distribution is required.

A review on microbial synthesis of lactate-containing polyesters.

Degradable polylactic acids (PLA) have been widely used in agriculture, textile, medicine and degradable plastics industry, and can completely replace petroleum-based plastics in the future. At present, polylactic acid was chemically synthesized by ring-opening polymerisation or the direct polycondensation of lactic acid, which inevitably leads to chemical and heavy metal catalyst pollution. The current research focus has gradually shifted to the development of recombinant industrial strains for the efficiently production of lactate-containing polyesters from renewable resources. This review summarizes various explorations of metabolic pathway optimization and production cost control in the industrialization of lactate-containing polyesters bio-production. In particular, the effects of key enzymes, including CoA transferase, polyhydroxyalkanoate synthase, and their mutants, culture conditions, low-cost carbon sources, and recombinant strains on the yield and composition of lactate-containing polyesters are summarized and discussed. Future prospects and challenges for the industrialization of lactate-containing polyesters are also pointed out.

Synthesis and synthetic mechanism of Polylactic acid

AbstractAt present, Polylactic acid (PLA) is one of the most used biodegradable polyesters. The good properties and its biodegradability make that PLA can replace the fossil fuel derived polymers in different applications. PLA can be synthesized by using different methodologies. Among them, the most widely used forms on an industrial scale are the direct polycondensation of Lactic acid and the ring-opening polymerization of cyclic Lactide. The final properties of the obtained PLA are dependent on the used stereoisomers of the raw materials (Lactic acid and/or Lactide) and the conditions employed to polymerize them. Therefore, the comprehension of the synthetic mechanism of PLA is crucial to control the stereoregularity of PLA, which in turn results in an improvement of the polymer properties. So, distinct mechanisms for the synthesis of PLA by ring-opening polymerization using different catalysts systems (organometallic catalysts, cationic catalyst, organic catalyst, bifunctional catalysts) are examined in this review.

Synthesis and Characterization of Biodegradable Synthetic Thickener from Anionic Triglyceride Polylactic Acid

In this research work, we report the synthesis of novel biodegradable synthetic thickener able to provide good quality prints with reduced wastewater pollution. Biodegradable triglyceride polylactic acid (TGPLA) star polymer hydrogel was prepared via one-pot reaction by direct polycondensation of lactic acid and glycerol. The chemical structure of the produced polymer was determined By Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (1H-NMR), and gel permeation chromatography (GPC). The rheological properties and biodegradation of the novel thickening agent were investigated. The prints quality of the prepared thickening hydrogels increased with increasing lactic acid content, while the apparent viscosity and biodegradation rate increased. Technical evaluation of TGPLA as environmentally friendly thickening agent in printing of different fabrics was studied. In addition, the chemical oxygen demand (COD) and biological oxygen demand (BOD) were described. The use of such thickening composite in printing such variety of fabrics with pigment and different types of dyes including reactive, acid, metal complex, basic, and disperse dyes was described. It was established that the TGPLA composite paste is characterize by a non-Newtonian pseudoplastic performance, and their apparent viscosity increases upon neutralization. Printing pastes are very stable against storing compared to mypro-gum as natural thickener. Printing pastes thickened with TGPLA containing a ratio of 98% of lactic acid and 2% of glycerol; display similar K/S values and colorfastness properties compared to those prints from commercial synthetic thickeners.

Comparative Investigations on Optimum Polymerization Conditions for the Synthesis of a Sustainable Poly(Lactic Acid)

The development of synthetic biodegradable polymers using solvent free polymerization has a unique potential to be used as sustainable polymers in biomedical applications. The aim of this work was to synthesize and characterize a sustainable class of poly(lactic acid) (PLA) under different operating conditions via direct polycondensation of lactic acid (LA). Several parameters were tested including the absence of solvents and catalysts on the polymerization, in addition to polymerization temperature and time. Polymerization conditions were evaluated using response surface method (RSM) to optimize the impact of temperature, time, and catalyst. Results showed that molecular weight (Mw) of PLA increased with increasing polymerization time. Highest Mw of 28.4 kD with relatively a broad polydispersity 1.9 was achieved at polymerization temperature 170 °C at 24 h in the free solvent polymerization. This led to a relevant inherent viscosity of 0.37 dl/g. FTIR spectra exhibited a disappearance of the characteristic peak of the hydroxyl group in LA at 3482 cm−1 by increasing the intensity of carbonyl group. The 1H nuclear magnetic resonance (NMR) exhibited the main chain at 5.22 ppm and the signal of methyl proton at 1.61 ppm as well as a signal at 4.33 and 1.5 assigned to the methane proton next to the terminal hydroxyl group and carboxyl group respectively. Meanwhile, the PLA synthesized with a catalyst [Sn(Oct)2] in a free solvent demonstrated comparatively high thermal transition properties of glass transition, melting, and crystallinity temperatures of 48, 106, and 158 °C, respectively. These results are of significant interest to further expand the use of PLA in biomedical applications.

Green polymer chemistry: One-pot, metal-free synthesis of macromonomer via direct polycondensation of lactic acid and its radical polymerization to graft and comb polymers

A new and simple method of one-pot two-stage poly(lactic acid) (PLA) macromonomer synthesis has been developed. The first stage of the reaction is a direct polycondensation of lactic acid (LA) without a catalyst to PLA, and the second stage is a ring-opening addition of PLA to glycidyl methacrylate (GMA) to afford a PLA macromonomer with a methacryloyl polymerizable group (GMA-Macro). Both reactions are performed consecutively in one pot. This method produced GMA-Macro with high functionality in high yields and thus far seems the simplest and probably the cheapest way to prepare PLA macromonomers. Furthermore, the method is metal-free, offering considerable advantages for biomedical and pharmaceutical applications. GMA-Macro has been shown to be useful for the preparation of PLA graft copolymers in solution or in miniemulsion and of PLA comb polymers in solution. LA is a biobased renewable feedstock. Thus, this method provides a good opportunity to conduct ‘green polymer chemistry’.

Scale-Up of Polymerization Process of Biodegradable Polymer Poly(lactic acid) Synthesis Using Direct Polycondensation Method

Environmental problems from petroleum-based plastic wastes have been rapidly increasing in recent years. The alternative solution is focus on the development of environmental friendly plastic derived from renewable resource. Poly(lactic acid) (PLA) is a biodegradable polymer synthesized from biomass having potential to replace the petroleum-based non-degradable polymers utilizations. PLA can be synthesized by two methods: (1) ring-opening of lactide intermediate and (2) direct polycondensation of lactic acid processes. The latter process has advantages on high yields and high purity of polymer products, materials handling and ease of process treatments. The polymerization process of PLA synthesis has been widely studied in a laboratory scale. However, the mass scale production using direct polycondensation of lactic acid has not been reported. We have investigated the kinetics and scale-up process of direct polycondensation method to produce PLA in a pilot scale. The order of reaction is 2 and activation energy of lactic acid to lactic acid oligomers is 61.58 kJ/mol. The pre-polymer was further polymerized in a solid state polymerization (SSP) process. The synthesized PLA from both the laboratory and pilot scales show the comparable properties such as melting temperature and molecular weight. The appearance of synthesized PLA is yellow-white solid powder.

Synthesis and characterization of poly(d,l-lactic acid) via enzymatic ring opening polymerization by using free and immobilized lipase

Polylactic acid is an interesting biodegradable and bioabsorbable material, and is produced from lactic acid, either by the direct polycondensation of lactic acid or via the ring-opening polymerization (ROP) of lactide. A future target of it is to improve some of the polyester properties for specific biomedical applications. The biocatalytic ROP of lactide is attractive as a route to polymer synthesis due to its lack of toxic reactants, mild reaction requirements, and recyclability of immobilized enzyme. Therefore, the use of immobilized enzymes is also being investigated.The aim of this work was to develop a methodology to synthesize high molecular weight polylactic acid via enzymatic ROP method using free enzyme and Candida antarctica lipase B (CALB) immobilized onto chitin and chitosan. The efficiency of the two approaches has been compared, with polymerization kinetics and resulting products fully characterized by FT-IR, NMR, DSC, XRD, and TGA analyses.

Star-shaped poly(lactic acid) with carboxylic acid terminal groups via poly-condensation

A series of star-shaped poly(lactic acid)s with carboxylic acid terminal groups have been synthesized by direct poly-condensation of lactic acid in the presence of a poly-carboxylic acid core molecule with triphenylphosphonium trifluoromethanesulfonate (TPP-T) catalyst.These star-polymers had thermal properties not very much different from those of star-shaped poly(lactic acid) with hydroxyl terminal groups and linear poly(lactic acid), irrespective of the structure of the core molecule and number of polymer arms. Solubility and degradability of these star-polymers were, however, greatly enhanced compared to those of star-polymers with hydroxyl terminal groups and increased depending on the number of polymer arms. From the star-shaped polymers, a variety of ammonium salts and the corresponding carboxyamides were successfully prepared.

Effect of metal triflates on direct polycondensation of lactic acid

Various metal triflates were employed for direct polycondensation of lactic acid to afford poly(lactic acid). Screening of the metal triflates was conducted with the polycondensation of lactic acid at 160–180 °C for 16 h under reduced pressure (1.4 kPa) after a pre-dehydration process under an air atmosphere. Examined metal triflates are scandium, yttrium, ytterbium, lanthanum, hafnium, copper, and silver triflates. Polycondensation using scandium triflate afforded poly(lactic acid) with high molecular weights (M n = 4.3 × 104) in a good yields (62%) under the following conditions; catalyst amount = 0.05 mol%, pre-dehydration at 180 °C for 2 h, and polycondensation at 180 °C for 16 h. Active metal triflates coordinated with lactic acid strongly, confirmed by 1H NMR and FT-IR spectroscopy.

Microwave‐Assisted Single‐Step Synthesis of Poly(lactic acid) by Direct Polycondensation of Lactic Acid

AbstractThe microwave‐assisted direct polycondensation of LA to synthesize PLA has been studied. Microwave irradiation strikingly accelerates the polymerization rate of LA compared to conventional heating. By use of a binary catalyst of SnCl2/p‐TsOH, PLA with a $\overline M _{\rm w}$ of 16 000 is obtained within 30 min under a reduced pressure of around 30 mmHg. MALDI‐TOF MS measurements reveal that the PLA formed is mainly composed of linear polymer and macrocyclics.magnified image

Swelling and hydrolytic degradation of poly( d, l-lactic acid) in aqueous solutions

Low molecular weight poly(lactic acid) was synthesized by direct polycondensation of lactic acid. The oligomers were characterized by viscometry, light scattering, and gel permeation chromatography (GPC). The swelling behaviour of tablets made of the above polymer immersed in buffer solutions at 37 °C was studied. In the same experiments, the hydrolytic stability of d, l-PLA was assessed by measuring the weight loss after drying the tablets. In order to inhibit any degradation due to bacteria, formaldehyde was added in the solution as biostatic factor. The effect of an incorporated drug on the swelling behaviour of d, l-PLA tablets was also considered. It was found that the incorporation of drug in d, l-PLA tablets increases their swelling index, probably due to the creation of additional porosity in the specimens or other interaction between drug and polymeric matrix.

Roles of silica gel in polycondensation of lactic acid in organic solvent

Poly(lactic acid) is among the most important biodegradable, biocompatible polymers. To explore the feasibility of making poly(lactic acid) through potentially more selective enzymatic methods, the lipase-catalyzed direct polycondensation of lactic acid in organic solvents was investigated. At 37 degrees C the reaction was found to favor nonpolar solvents with larger log P values and smaller log S(w/o values. The addition of silica gel appeared to greatly enhance the lactic acid conversion (up to 98%) and the lipase stability under the reaction condition. However, upon further investigations, the silica gel itself was found to catalyze the polycondensation, in addition to the role of water removal. The conversion catalyzed by silica gel alone was actually higher than that by silica gel + lipase (or lipase alone). Up to 93% conversion of the acid functional group (or about 99.5% conversion of lactic acid monomer) was obtained in 120 h with silica gel as the catalyst. The finding is especially significant for interpreting (or reconsidering) the results of many presumably enzyme-catalyzed organic-phase reactions in the presence of silica gel.

Synthesis of High-Molecular-Weight Poly(L-lactic acid) by Direct Polycondensation

To prepare poly(lactic acid) (PLA) with improved mechanical properties, high-molecular-weight poly(L-lactic acid) (PLLA) was synthesized by the direct polycondensation of lactic acid in solution phase. During polymerization, the molecular weight of PLA was influenced by the water content present in the solution; thus, the experimental apparatus was designed to remove the water efficiently and this study was focused on the optimization of the polymerization conditions such as polymerization time, solvent, and kinds of catalyst, etc. Additionally, to search for a good catalyst in the polymerization, the mixed oxide catalysts were synthesized by sol–gel method and it was characterized by XRD and BET. The results show that the Mv of PLA obtained was about 33 000, when 0.2 wt.-% of SnCl2 · 2H2O was used as a catalyst in the polymerization. The DSC study shows that the thermal properties of PLA such as Tg and Tm were influenced by the kind of solvent as well as the molecular weight of PLA. The effect of various kinds of stannous compounds on the molecular weight of PLA synthesized in solution polymerization with molecular sieve.

Syntheses and application of polylactides

Polylactides can be prepared by direct polycondensation of lactic acid, or better, by ring-opening polymerization of cyclic dilactides (usually called lactides). These lactides exist in the form of four stereoisomers two of which ( l, l- and rac. - d, l-) are technically produced in large quantities. These lactides can by polymerized via four different classes of initiators and reaction mechanisms. The characteristics mechanistic and preparative features of the cationic polymerization, anionic polymerization and of the coordination–insertion mechanism are described. Furthermore, copolymerizations of lactides with glycolide or ε-caprolactone and their analytical problems are discussed. Finally, a new type of wound dressing based on transparent are resorbable films of copolylactides is mentioned.

Synthesis of Poly(lactic acid) by Direct Polycondensation of Lactic Acid Using 1,1′-Carbonyldiimidazole, N,N,N′,N′-Tetramethylchloroformamidinium Chloride, and N,N′-Dicyclohexylcarbodiimide as Condensing Agents

Synthesis of Poly(lactic acid) by Direct Polycondensation of Lactic Acid Using 1,1′-Carbonyldiimidazole, N , N , N ′, N ′-Tetramethylchloroformamidinium Chloride, and N , N ′-Dicyclohexylcarbodiimide as Condensing Agents