PREPARATION OF POLY (LACTIC ACID)THROUGH THIONYL CHLORIDE ACTIVATED POLYCONDENSATION

A two-step process was used to synthesize the high molecular weight poly (lactic acid) using thionyl chloride as an activator for the polycondensation of prepolymer of lactic acid. The products were characterized by GPC, DSC, and 1H-NMR. Poly (L-lactic acid) (PLLA) with molecular weight Mw: 32875 was obtained when thionyl chloride was used, while low molecular weight PLLA Mw: 7350 was yielded without thionyl chloride. Effects of the concentration of thionyl chloride, polymerization time and bases on the molecular weight of poly (lactic acid) were investigated. In DSC scans the glass transition temperatures (Tg) of the resulting polymers varied from 25.3 to 57.6℃, and the Tg of poly(L-lactic acid) was higher than that of poly (D,L-lactic acid) (PDLLA). The melting points of poly (L-lactic acid) and poly (D, L-lactic acid) could not be found unless the polymers were obtained by thionyl chloride activator.

Kinetics and Mechanism of Oxidation of Lactic Acid by Dihydroxyditelluratoargentate(Ⅲ) in Alkaline Medium

The kinetics of the oxidation of lactic acid(Lac) by dihydroxyditelluratoargentate(Ⅲ)[abbreviated as DDA of Ag(Ⅲ)] anions was studied in an aqueous alkaline medium by conventional spectrophotometry in a temperature range of 25- 40 ℃ . The order of the redox reaction of lactic acid and DDA was found to be first order. The rates increased with the increase in and decreased with the increase in . No free radical was detected. In the view of this the dihydroxymonotelluratoargentate(Ⅲ) species(DMA) is assumed to be the active species. A plausible mechanism involving a two electron transfer is proposed, and the rate \{equation\} derived from the mechanism can be used to explain all the experimental results. The activation parameters(25 ℃) and the rate constants of the rate determining step along with the preequilibrium constants at different temperatures were evaluated.

Can Classic Avrami Theory Describe the Isothermal Crystallization Kinetics for Stereocomplex Poly(lactic acid)?

Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to offer quantitative analyses of crystallization kinetic parameters for enantiomeric poly（lactic acid） （PLA） blends may, however, lead to contradictory conclusions. As revealed by this study, during the characterization of isothermal melt and cold crystallization for stereocomplex PLA containing equal-weight poly（L-lactic acid） and poly（D-lactic acid）, the kinetic parameters yielded by Avrami equation are not in line with the classic crystallization hypotheses or the direct morphological observations. The underlying mechanisms, to some extent, lie in the generation of stereocomplex crystals （SCs） during the cooling/heating which affects the subsequent crystallization dynamics. The huge gap between the melting enthalpies of 100% crystalline SCs （142 J/g） and homo-crystals （HCs, 93 J/g） is most likely responsible for the confusing kinetic parameters acquired from the deduction of Avrami equation, which is based on the integration of enthalpies as a function of crystallization time. This prompts for great care that the classic Avrami equation is not applicable to accurately describe the crystallization kinetics of stereocomplex PLA, given the generation of SCs prior to crystallization and the coexistence of HCs and SCs during crystallization.

Kinetic Study of Esterification of Lactic Acid with Isobutanol and n-Butanol Catalyzed by Ion-exchange Resins

The esterification reactions of lactic acid with isobutanol and n-butanol have been studied in the presence of acid ion-exchange resin Weblyst D009. The influences of catalyst loading, stirrer speed, catalyst particle size, initial reactant molar ratio and temperature on the reaction rate have been examined. Experimental kinetic data were correlated by using the pseudo-homogeneous, Langnluir-Hinshelwood and Eley-Rideal models. Nonideality of the liquid phase was taken into account by using activities instead of molar fractions. The activity coefficients were calculated according to the group contribution method UNIFAC. Provided that the nonideality of the liquid is taken into account, the esterification kinetics of lactic acid with isobutanol and n-butanol catalyzed by the acid ion-exchange resin can be described using all threemodels with reasonable errors.

Synthesis and Characterization of Cross-linked Poly (β-Cyclodextin) Graft Poly(lactic acid) through Direct Polycondensation

1 Results Polylactide or polylactic acid (PLA) and poly(lactic-co-glycolic acid) (PLGA) have been utilized as bioabsorbable materials in the medical and pharmaceutical fields due to their biodegradable and biocompatible properties[1].However,due to its hydrophobicity and free carboxylic group,PLA or PLGA was not suitable for use to encapsulate the protein.Recently,poly (ε-caprolactone) and poly (D,L-lactide) were respectively grafted onto hydrophilic dextrin and gelatin to obtain the amphiphilic biodeg...

Fractionated Crystallization Kinetics and Polymorphic Homocrystalline Structure of Poly(_(L)-lactic acid)/Poly(_(D)-lactic acid)Blends:Effect of Blend Ratio

Stereocomplex(SC)crystallization has been an effective way to improve the physical performances of stereoregular polymers.However,the competition between homo and SC crystallizations can lead to more complicated crystallization kinetics and polymorphic crystalline structure in stereocomplexable polymers,which influences the physical properties of obtained materials.Herein,we select the medium-molecular-weight(MMW)poly(L-lactic acid)/poly(D-lactic acid)(PLLA/PDLA)asymmetric blends with different PDLA fractions(f_(D)=0.01-0.5)as the model system and investigate the effects of f_(D) and crystallization temperature(T_(c))on the crystallization kinetics and polymorphic crystalline structure.We observe the fractionated(i.e.,multistep)crystallization kinetics and the formation of peculiar β-form homocrystals(HCs)in the asymmetric blends under quiescent conditions,which are strongly influenced by both f_(D) and T_(c).Precisely,crystallization of β-form HCs is favorable in the MMW PLLA/PDLA blends with high f_(D)(≥0.2)at a low T_(c)(80-100℃).It is proposed that the formation of metastable β-form HCs is attributed to the conformational matching between β-form HCs and SCs,and the stronger constrain effects of precedingly-formed SCs in the early stage of crystallization.Such effects can also cause the multistep crystallization kinetics of MMW PLLA/PDLA asymmetric blends in the heating process.

Repeated-Batch and Continuous Production of L-Lactic Acid by Rhizopus oryzae Immobilized in Calcium Alginat Beads:ReactorPerformance and Kinetic Model

Repeated-batch and continuous production of L-lactic acid by immobilized Rhizopusoryzae with calcium alginate entrapment method in a three-phase fluidized-bed bioreactor was stud-ied.The operation conditions were optimized.The productivity based on total reactor volume wasabout 3 times higher than that with free cells in a traditional stirred tank bioreactor.A mathemat-ical model was proposed and the model predictions were in good agreement with the experimentaldat.

Effect of DOPO-containing Flame Retardants on Poly（lactic acid）： Non-flammability, Mechanical Properties and Thermal Behaviors

The flame retardancies of three kinds of 9,10-dihydro-9-oxa-10-phosphaphenan-threne 10-oxide（DOPO）- containing flame retardant（A1, A2, A3）/poly（lactic acid）（PLA） composites[PA-n/（Ax-y）, n= 1--12; x= l, 2, 3, denoting three kinds of flame retardants; y= 10%, 20%, 30%, 40%, denoting the mass fraction of Ax] were greatly enhanced by melt blending of flame retardant Ax with PLA, including twin-screw extrusion and injection-molding processes. With only 10%（mass fraction） of Ax added to PLA, good flame retardancy with limiting oxygen index（LOI） values of more than 33% was achieved. As the Ax mass fraction was further increased to 20%, PA-n/（Ax-20%） composites showed much better flame retardancy（LOI~〉35% and UL-94 V-0 rating）. Moreover, the thermal degradation behaviors and mechanical properties of PA-n/（Ax-y） composites were investigated via thermogravimetric analysis（TGA）, differen- tial thermal analysis（DTA）, tensile testing, notched impact-bar testing, and dynamic mechanical analysis（DMA）. TGA results show that PA-n/（Ax-y） composites have slower rate of mass loss and much higher char yield, compared to neat PLA. With the addition of Ax to PLA, the DTA and DMA results indicate slight variations in glass transition tcmpe- ratures（Tg） of PA-n/（Ax-y） composites. Based on TGA results under nonisothermal conditions, the thermal degrada- tion kinetics of PA-n/（Ax-y） composites were studied by KAssinger＇s and Ozawa＇s methods. These thermal degrada- tion dynamic analyses show lower activation energies（EK or Eo） for PA-n/（Ax-y） composites, corresponding to higher mass fractions of Ax（from 10% to 40%）. The PA-n/（Ax-y） composites with good flame retardancy and good mecha- nical properties obtained in this study could be potential candidates for fire- and heat-resistant applications in auto- motive engineering and building fields with more safety and excellent performance.

乳酸菌发酵香菇汁过程中品质变化及动力学模型的建立

利用乳酸菌发酵香菇汁,研究发酵过程中活菌数、理化指标及抗氧化活性的变化规律,并采用Logistic、SGompertz、Boltzmann和DoseResp模型对发酵过程中乳酸菌生长、总酸生成及还原糖消耗进行非线性拟合,建立乳酸菌发酵香菇汁的发酵动力学模型。结果表明,乳酸菌在香菇汁中生长良好,24 h时活菌数最高,为8.95 log CFU/mL;发酵过程中总酸、总酚、总黄酮、可溶性蛋白含量不断升高,最高分别达到6.86 g/L、232.82 mg/L、101.89 mg/L、291.25μg/mL;DPPH自由基、羟自由基和超氧阴离子自由基清除能力较发酵前分别提升了54.46%、26.96%和211.84%。在乳酸菌生长和总酸生成的动力学模型中,均采用Dose Resp模型最佳,R2分别为0.9987和0.9998;Boltzmann模型和Dose Resp模型均可用于定量描述发酵过程中还原糖的消耗情况,两个模型的R2均为0.9996。因此,利用乳酸菌发酵可提升香菇汁品质,所选模型与实验值拟合度较高,能够较好反映乳酸菌发酵香菇汁过程中的动力学特征,为乳酸菌发酵香菇汁的进一步工业化生产提供理论依据。

熔融-固相缩聚法中固相聚合对聚乳酸合成的影响

以L 乳酸单体为原料 ,熔融 -固相缩聚法合成了聚乳酸 ,重点研究了固相聚合的工艺条件。结果表明 ,绝对压力 60Pa ,氯化亚锡为催化剂 ,分段控温 ,可使聚乳酸的粘均分子量提高到固相聚合反应前的 5 3倍。通过对固相聚合产物的结晶度和熔点的分析 ,探讨了固相聚合的机理。

熔融-固相聚合法直接合成聚乳酸的研究

以L_乳酸单体为原料 ,通过熔融 -固相聚合法直接合成聚左旋乳酸 (PLLA) .筛选出SnCl2 为适宜的催化剂进行熔融聚合 ,聚合的最佳工艺条件为 :SnCl2 质量分数为0 .5 % ,180℃、70Pa下反应 10h .以熔融聚合制得的粘均相对分子质量为 5 0 0 0的PLLA为原料 ,于 6 0Pa下 ,以SnCl2 为催化剂进行变温固相聚合 (先在 135℃下反应 5h ,再在15 0℃下反应 10h) ,可使粘均相对分子质量提高到反应前的 5 .3倍 .

聚乳酸-乙醇酸的合成及在药物缓释微球中的应用

采用熔融聚合法直接合成生物降解材料聚乳酸-乙醇酸(PLGA),并以其为载体制备基因重组人干扰素聚乳酸-乙醇酸微球(IFN-α-PLGA-MS)。通过正交试验对干扰素微球的制备工艺进行了优选,同时对微球的性质进行了考察。结果以D,L-乳酸、乙醇酸为原料,氯化亚锡(SnCl2)为催化剂,在165℃、70Pa下熔融聚合10h,PLGA特性粘数[η]最高可达0.2382dL/g,干扰素微球的形态圆整,平均粒径为10.71μm,药物确已被包裹在微球中,微球载药量和包封率分别为8.06%、36.97%,且获得了较满意的干扰素微球制备工艺。

聚乳酸的直接合成及其红霉素肺靶向药物微球的应用

以DL-乳酸为原料,通过熔融聚合法直接合成外消旋聚乳酸(PDLLA)。以SnCl2为催化剂,用量0.5%(质量),在170℃、70Pa下反应10h,获得了粘均分子量为4100的PDLLA,将其应用于红霉素肺靶向微球的载体。用正交试验确定了红霉素-聚乳酸微球(ERY-PDLLA-MS)最佳成型工艺条件,用DSC和SEM表征其成球性能。微球体外缓释半衰期为28h,175h后累积释药百分率约为80%。注射微球混悬剂的兔肺组织中药物含量为普通市售红霉素注射剂的6倍,达到了肺靶向的目的。

熔融缩聚合成聚L-乳酸的研究

以L-乳酸为原料,通过熔融缩聚法合成了聚乳酸(PLLA).考察了预聚条件、催化剂种类和用量、催化剂溶解程度、聚合温度及时间对聚乳酸分子量的影响.采用FTIR和1H-NMR分析聚合物结构,GPC测定分子量分布.研究表明,等摩尔量的氯化亚锡(SnC l2)和对甲苯磺酸(TSA)组成的复合催化剂效果最好,SnC l2的用量为预聚物(OLLA)的0.4%为宜;预聚过程和催化剂在OLLA中的充分溶解对提高聚合物分子量具有重要意义;合适的聚合温度约为165℃;在发生爬杆现象前,随反应时间的增加,聚乳酸分子量增加.在优化的工艺条件下,可以在较短时间(8 h)内获得分子量为65000左右的聚乳酸.

熔融聚合法直接合成聚乳酸的研究

以Ｌ一乳酸单体为原料,系统地研究了熔融聚合法直接合成聚乳酸的最佳工艺条件,即:选择氯化亚锡为催化剂,用量０．５ｗｔ%,在聚合温度１８０℃、绝对压力７０Ｐａ下反应１０ｈ,可获得较高分子量的聚乳酸。

熔融共聚法用外消旋乳酸直接合成聚乙醇酸-乳酸及其表征

以乙醇酸(GA)、廉价的外消旋乳酸(D,L-LA)为原料,以氯化亚锡(质量分数0.5％)为催化剂,在165℃、70 Pa下熔融聚合10 h,通过熔融共聚法直接合成了不同配比的系列生物降解材料聚乙醇酸-乳酸(PGLA),用凝胶渗透色谱、傅里叶变换红外光谱、核磁共振氢谱、差示扫描量热分析、X射线衍射等系统地对其进行了表征。当n(GA):n(D,L-LA)=1:1,直接熔融聚合法获得的D,L-PGLA 50／50的重均相对分子质量为24 300,比相同条件下合成的L-PGLA 50／50的18 000要高。

乳酸直接聚合的热力学、动力学研究

以乳酸单体为原料 ,在无催化剂存在和常压下直接缩聚合成聚乳酸 ,并研究了乳酸直接聚合的动力学 ,结合其热力学的分析 ,指出提高真空度脱除水分、控制合适的温度、选择合适的催化剂是获得高分子量聚乳酸的关键 。

无毒催化剂催化合成外消旋聚乳酸及其在药物缓释微球中的应用

以D,L 乳酸单体为原料,使用人体营养添加剂如乳酸锌、乳酸钙、乙酸锌、硫酸锌、牛磺酸等作为无毒催化剂,通过熔融聚合直接合成低分子量的生物降解材料外消旋聚乳酸(PDLLA),粘均分子量接近4000。以PDLLA为载体,应用于制备抗菌药物环丙沙星聚乳酸微球,用DSC和SEM表征其成球性能,载药微球体外缓释半衰期为31.9h,53.2h后累积释药百分率约为84.0%,具有明显的缓释作用。

聚乳酸合成研究进展

针对直接法和二步法合成聚乳酸的共性,从单体纯度、催化剂选择到共沸脱水、微波辅助、超临界流体介质,以及到固相聚合、反应挤出、扩链等各个方面,对近年来聚乳酸合成研究的新进展进行了综述,指出各种新方法、新技术的复合应用是提高聚乳酸分子量、降低其成本的关键。

聚L-乳酸的固态缩聚

采用熔融 /固态缩聚方法制备了聚L 乳酸。考察了不同催化剂、反应温度、反应时间和预聚物颗粒大小对固态缩聚反应速度的影响。结果表明 ,利用真空干燥箱 ,在适宜的反应条件下反应 ,有利于最终聚合物分子量的控制。