Improving lactic acid melt polycondensation: The role of co‐catalyst

A study on lactic acid polycondensation under melt conditions was carried out and a preliminary assessment revealed tin powder as a very good catalyst for poly(lactic acid) (PLA) synthesis by melt polycondensation while confirming previous information on SnCl₂ good performance. However, these catalysts also promoted side reactions leading to racemization and yellowing of the final polymer. The use of p‐toluenesulphonic acid (p‐TSA) or triphenylphosphine (PPh₃) as co‐catalysts proved to be very effective hindering colour formation and allowing synthesizing PLA samples with enhanced properties. The addition of these compounds to neat tin powder increased the PLA optical purity, whereas their addition to SnCl₂ speeded up the polymerization. A significant increase in molecular weight, from 32,500 to 52,000 g mol^?1, was recorded, with the new catalytic system SnCl₂/PPh₃ showing catalytic activity comparable with the one reported in the literature for SnCl₂/p‐TSA. Several characterization techniques were used for assessing polymer samples: the molecular weights were determined by SEC, thermal behavior measured by DSC, and racemization extent calculated from specific rotation measurements. UV/vis spectroscopy was confirmed as a powerful technique for evaluating yellowing of final polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

直接缩聚合成聚乳酸研究进展

聚乳酸是一种性能优良的完全生物降解塑料,产品价格高是其进入市场的重要障碍,通过直接缩聚法有望能合成低 成本的聚乳酸。综述了溶液缩聚及直接熔融缩聚、熔融缩聚-扩链、熔融缩聚-固相聚合合成聚乳酸的研究进展。展望了直接 缩聚法合成聚乳酸的前景。     

聚乳酸熔融缩聚的研究

综述了近年来国内外聚乳酸熔融聚合的研究情况,概述了直接熔融缩聚、熔融-固相和熔融-扩链合成聚乳酸的研究,并研究探讨了熔融聚合中影响聚乳酸相对分子质量的因素。     

缩聚催化剂乙二醇锑的应用

介绍了聚酯缩聚催化剂乙二醇锑在上海石化涤纶部的试用和推广应用过程 ,讲述了乙二醇锑的配制和添加的特点 ,对聚酯生产过程和对聚酯产品的影响 ,以及乙二醇锑的聚酯产品对纺丝后加工性能的影响。     

Melt polycondensation of L‐lactic acid catalyzed by 1,3‐dialkylimidazolium ionic liquids

BACKGROUND: In syntheses of biodegradable and bioresorbable polymers, efficient metal‐free catalysts are very desirable as the resulting products may be more biocompatible. As an attempt to find new metal‐free catalysts, 1,3‐dialkylimidazolium salts, the most commonly used ionic liquids or organic melt salts, were used as single‐component catalysts in the melt polycondensation of L ‐lactic acid for the first time. The resulting poly(L ‐lactic acid) (PLLA) was characterized using gel permeation chromatography, ¹³C NMR, DSC and polarimetry. RESULTS: It has been found that less bulky substituents on the imidazolium ring are conducive to catalytic activity. PLLA with molar mass of about 20 000 g mol^?1 was synthesized at high yield (over 70%) in the presence of various 1,3‐dialkylimidazolium salts. The product exhibits satisfactory color (white to slightly yellow), optical purity (89–95%) and crystallinity (40–55%). A possible catalytic mechanism is proposed. CONCLUSION: As compared with the well‐known binary catalyst system SnCl₂ · 2H₂O/toluene sulfonic acid, the catalysts used in this investigation are better in terms of increasing PLLA yield and preventing discoloration and comparable in terms of racemization. Copyright © 2008 Society of Chemical Industry     

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

Engineered 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-LA_n 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.     

钛酸四乙酯催化酯交换缩聚法合成聚醚型聚氨酯

以钛酸四乙酯(TET)为催化剂,聚四氢呋喃醚二醇(PTMG)和1,6-六亚甲基二氨基甲酸甲酯(HDC)为原料,1,4-丁二醇为扩链剂,酯交换缩聚合成了聚醚型聚氨酯(PEPU)弹性体。以二丁基氧化锡(DBTO)催化合成的PEPU为参考,通过红外光谱(FTIR)、凝胶色谱(GPC)、热重分析(TGA)、力学性能与光学性能测试表征TET的催化效果。通过一系列单因素实验探讨了缩聚温度、缩聚时间、预聚温度、预聚时间对PEPU特性黏度的影响规律。结果表明,TET比DBTO催化制得的PEPU热性能更好,力学性能更优。较佳的制备工艺为:预聚阶段温度为110℃,压力为0.070MPa,时间为20min;160℃下高真空缩聚110min.     

聚酯缩聚催化剂用量的控制

缩聚催化剂会对聚酯后加工性能产生不良影响。选择溶解性能好的催化剂 ,降低酯化残存羧基量 ,提高缩聚温度 ,可减少催化剂用量     

Studies on the synthesis and thermal properties of copoly(L‐lactic acid/glycolic acid) by direct melt polycondensation

A two‐step direct copolymerization process of L ‐lactic acid (L ‐LA)/glycolic acid (GA) was developed. The first step was to produce an oligomer of L ‐LA/GA and then the oligomer was polymerized with binary catalyst tin chloride dihydrate/p‐toluenesulfonic acid. In this way, the copoly(L ‐LA/GA) (PLGA), without any organic solvent, was synthesized directly. The thermal properties and solubility in chloroform of PLGA were studied by DSC and NMR. The results showed that the melting point of PLGA decreases with increasing mole fraction of GA units in copolymer. In addition, the melting point of polymer also decreased with increasing degree of racemization of polymer. The solubility of PLGA in chloroform decreased with the increase of the average lengths of the glycolic acid units. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2163–2168, 2004     

Isothermal cold crystallization and melting behaviors of poly(L‐lactic acid)s prepared by melt polycondensation

The isothermal cold crystallization and melting behaviors of poly(L ‐lactic acid)s (PLLAs, weight average molecular weight, M_w, 6000–80,000) prepared via melt polycondensation were studied with differential scanning calorimeter in this work. It is found that the crystallization rate increased with decreasing M_w, reached a maximum at M_w of ca. 21,000 and then decreased again. The crystallinity of PLLA can be controlled in the range 30–50% by crystallization temperature (T_c) and time to fulfill the requirement of subsequent solid state polycondensation. The melting behavior strongly depends on T_c. The samples crystallized at high T_c melted with a single peak but those crystallized at low T_c melted with double peaks. The higher melting point (T_mH) kept almost constant and the lower melting point (T_mL) increased clearly with T_c. But the T_mL changed in jumps and a triple melting peak appeared at the vicinity of a characteristic crystallization temperature T_b, possibly because of a change of crystal structure. The equilibrium melting temperature of PLLA with M_w of 21,300 was extrapolated to be 222°C with nonlinear Hoffman‐Weeks method. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of poly(ester amide)s composed of lactic acid and glycolic acid units by the bulk polycondensation of metal halide salts

Thermal polycondensation of the potassium salt of N‐methylchloroacetyl‐6‐aminohexanoic acid (LAHK) was found to be effective in the preparation of a new poly(ester amide) based on lactic acid units with a high yield and a moderate molecular weight. The reaction started in the solid state and proceeded through the formation of potassium chloride salt as the driving force. The use of a monomer having an amide linkage diminished the secondary reactions previously found in the synthesis of polylactide from 2‐halogenopropionates. The polymerization of potassium salt of N‐chloroacetyl‐6‐aminohexanoic acid (GAHK) took place in a similar temperature range as that of the 2‐chloropropionyl derivative; in this way, it was possible to conduct the copolymerization processes. The polymerization kinetics of LAHK and its mixture with GAHK was studied by Fourier transform infrared spectroscopy. The bulk polycondensation reaction was faster for GAHK than for LAHK, but the kinetic differences were not significant enough to prevent copolymerization at a temperature close to 160°C. Therefore, new degradable materials with tuned properties according to the glycolic acid/lactic acid content were obtained. ¹H‐NMR spectroscopy was useful for following the time evolution of the copolymerization process and for determining the final composition. Calorimetric data showed that all of the samples were thermally stable and that decreases in the melting temperature and enthalpy were observed at intermediate compositions. The existence of an eutectic point became proof that effective copolymerization was achieved in the thermal polycondensation process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43197.     

PET缩聚催化剂的发展及展望

介绍了PET催化剂的发展及现状,简要比较和评价了各种锑系催化剂及应用,对目前国内外较为关注的各种钛系催化剂及应用概况、合成技术等进行了分析和总结,对新型催化剂的发展趋势进行了展望。     

无锑催化剂对PET缩聚反应动力学的影响

用PET缩聚反应动力学方法研究自制无锑催化剂的催化效果,无锑催化剂对缩聚反应速率常数及 反应时间的影响。缩聚反应中,使用无锑催化剂(相对TPA质量分数为0.02％)与常规三氧化二锑催化剂 (相对TPA质量分数为0.04％)相比,缩聚反应速率常数可提高1～2倍以上,反应时间可缩短23～40min。     

新型聚酯缩聚催化剂S-PT评估

在小试装置上 ,通过DMT法、PTA法对聚酯生产所采用的Sb2 O3、Sb(Ac) 3、S 2 4及S PT催化剂进行对比 ,对所得切片进行分析、纺丝并与切片的国家标准进行比较 ,得出的结论是S PT催化剂性能优于其它催化剂     

树脂催化合成无毒增塑剂柠檬酸三辛酯

以树脂作催化剂,合成柠檬酸三辛酯。探讨了催化剂用量、反应温度、酸醇摩尔比和反应时间等因素对酯化反应的影响。结果表明:在150℃,酸醇摩尔比为1∶4.5,催化剂用量为柠檬酸质量的10%,反应1.5 h后,酯化率达到97%以上。催化剂的性能较好,便于与产物分离,可以回收使用。     

锑系催化剂在聚酯缩聚工艺中的应用评价

本文以工业使用的实际经验 ,从反应活性和产品质量两个方面来评价锑系催化剂在聚酯缩聚工艺中的应用。同时 ,也对锑系催化剂的变换工业实验结果进行初步讨论     

Melt polycondensation of L‐lactic acid to poly(L‐lactic acid) with Sn(II) catalysts combined with various metal alkoxides

Melt polycondensation of L ‐lactic acid (LA) was examined in the presence of binary catalyst systems consisting of SnCl₂·2H₂O and metal alkoxides as co‐catalysts. Among the co‐catalysts examined, viz (Al(O ⁱPr)₃,Ti(O ⁱPr)₄,Y(O ⁱPr)₃,Si(OEt)₄ and Ge(OEt)₄), Ge(OEt)₄ was found to be the most effective in enhancing the catalytic activity of Sn(II). With an optimized composition of SnCl₂·2H₂O–Ge(OEt)₄, the molecular weight (M_n) of PLLA reached 40 000 Da in a short reaction time (<15 h) at the optimum reaction conditions of 180 °C and 10 Torr. This catalyst system was also superior to the conventional single metal ion catalysts such as Sn(II) in terms of racemization and discolouration of the resultant polymer. The metal alkoxides, added as co‐catalysts, should work as oxo acids that can effectively control the catalytic activity of Sn(II) ion in the direct polycondensation of LA, in a manner similar to that of proton acids. © 2003 Society of Chemical Industry     

Synthesis and characterization of nanosized polylactic acid/TiO<Subscript>2</Subscript> particle brushes by azeotropic dehydration polycondensation of lactic acid

A method for the synthesis of particle brushes by grafting polylactic acid onto TiO₂ nanoparticle is reported. The efficiency of grafting was enhanced by combining azeotropic separation of water with polycondensation in a single pot. PLA/TiO₂ brushes synthesized with different ratio of lactic acid and TiO₂ were characterized by various techniques such as FT-IR, XRD, TEM, XPS, ¹H and ¹³C NMR. TEM analysis indicates that the sizes of TiO₂ nanoparticles are between 2 and 8 nm. DLS was used to determine overall size of particle brush and average size varied between 59.68–65.83 nm. Zeta potential measurement indicated high stability of water dispersed particles brushes with measured values of ?30.1 to ?37.1 mV for brushes prepared with PLA/TiO₂ ratio of 50:1 and 20:1 respectively. The DSC and TGA analysis showed that PLA/TiO₂ nanocomposites have good thermal stability.

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