丙交酯与碳酸亚乙酯的共聚及性能表征

以丙交酯和碳酸亚乙酯为原料,使用催化剂氯化亚锡在常压氩气保护下引发丙交酯与碳酸亚乙酯开环共聚,得到了不同组成和分子量的聚乳酸-碳酸亚乙酯的共聚物。用FT-IR,1H-NM R,GPC对丙交酯与碳酸亚乙酯共聚物的结构进行了表征。结果表明,氯化亚锡引发丙交酯和碳酸亚乙酯开环共聚得到的是二者的线型无规共聚物,通过GPC和1H-NM R等方法检测得到了共聚物分子量及其组成。     

梳状聚乳酸的制备及其性能研究

以L-乳酸和聚乙烯醇为原料,用1-乙基-(3-二甲氨基丙基)碳二亚胺盐酸盐(EDC· HCL)做催化剂,通过熔融共聚法制备了分子量较大的梳状聚乙烯醇-g-聚乳酸.用红外、核磁对其结构进行了表征;用DSC、TGA表征了材料的热性能;研究了共聚物的接触角、结晶性能以及力学性能.与丙交酯开环聚合相比,本方法反应条件温和,成本较低.所得疏状聚乳酸比纯乳酸直接熔融缩聚产物分子量大大提高,而且材料的韧性得到增强,亲水性改善.     

端氨基聚乙二醇-聚乳酸嵌段共聚物的合成及表征

以聚乙二醇为原料,采用四步反应,合成了二碳酸二叔丁酯单保护的氨基聚乙二醇(BOC-PEG-NH2);并以DOe-PEG-NH2为引发剂,引发丙交酯开环聚合,得到了叔丁氧基酰胺基聚乙二醇-聚乳酸嵌段共聚物(BOC-PEG-PLA).在三氟乙酸二氯甲烷溶液中,脱去保护基团,得到了端氨基聚乙二醇-聚乳酸嵌段共聚物(NH2-PEG-PLA).采用核磁共振氢谱(1H-NMR)、紫外光度仪(UV)表征各聚合物的结构,由凝胶色谱仪(GPC)测定嵌段共聚物的分子量以及分子量分布.结果表明:合成的氨基引发在无催化剂条件下能够引发丙交酯开环聚合,制得分子量高、分子量分布窄的双亲性共聚物.通过三氟乙酸脱保护得到了端氨基聚乙二醇-一聚乳酸(NH2-PEG-PLA),且对分子量没有影响.     

PLLA-PEG-PLLA/Fe_3O_4磁性微球的制备及性能

以聚乙二醇为引发剂,L-丙交酯为单体,开环聚合得到聚乳酸-聚乙二醇三嵌段共聚物(PLLA-PEG-PLLA),采用溶剂挥发法制备了PLLA-PEG-PLLA/Fe_3O_4磁性微球,并通过扫描电镜对其形态进行了表征。利用振动样品磁强计和Tg研究了微球的磁含量和磁性能,结果发现,相同粒径不同磁含量的磁性微球,磁含量越高,升温速率越快,当磁含量为70.57%时,升温速率最快,能达到磁热疗的有效温度42℃。对于磁含量相同,粒径不同的微粒,粒径越小,升温速率越快,粒径约为10μm时升温速率最快。     

乙基纤维素与聚L-乳酸接枝共聚物的合成与表征

以辛酸亚锡为催化剂,乙基纤维素(EC)为接枝骨架,L-丙交酯(L-LA)为接枝单体,在无溶剂条件下本体聚合制备了乙基纤维素-聚L-乳酸接枝共聚物。利用GPC,FTIR,1H NMR对接枝共聚物进行表征。结果表明,L-丙交酯在乙基纤维素残存的羟基上发生开环聚合,将聚乳酸短链引入到乙基纤维素骨架上,所得产物为乙基纤维素与聚L-乳酸接枝共聚物。XRD和偏光显微镜(POM)分析表明,当接枝率大于等于252%时,接枝共聚物开始结晶。     

一种生物可降解材料PDLLA-(MAh-PEG)_n-PDLLA的合成与表征

丙交酯(LA)开环聚合时同时引入功能性单体合成含活性基团的可降解聚合物,是目前对聚乳酸(PLA)类材料进行改性的一个重要研究方向。文中首先以聚乙二醇(PEG)和马来酸酐(MAh)为原料,采用溶液缩聚法制得聚乙二醇与马来酸酐的交替预聚物(MAh-PEG)n;然后以辛酸亚锡为催化剂,(MAh-PEG)n为引发剂,引发D,L-丙交酯(D,L-LA)开环聚合,制得聚(D,L-乳酸)(PDLLA)与(MAh-PEG)n的共聚物PDLLA-(MAh-PEG)n-PDLLA。采用凝胶渗透色谱(GPC)、傅里叶红外(FT-IR)、核磁共振(NMR)等方法对共聚物的结构和性质进行研究。结果发现,随着(MAh-PEG)n用量的增加,共聚物的分子量有所下降。这种聚合物的主链含有不饱和双键和亲水性的链段,预计将成为一种新的生物可降解材料。     

赖氨酸改性聚乳酸/聚乙二醇共聚物的制备及表征

在丙交酯与聚乙二醇开环共聚的基础上进行了二次聚合,利用具有生物相容性的赖氨酸对聚乳酸/聚乙二醇低聚物进行改性,制备出了赖氨酸改性聚乳酸/聚乙二醇共聚物。通过红外光谱、核磁共振谱、X射线衍射分析仪、差示扫描量热仪、凝胶渗透色谱和接触角测量仪分析比较了聚乳酸、聚乳酸/聚乙二醇和赖氨酸改性聚乳酸/聚乙二醇3种聚合物之间存在的差异。结果表明,实验成功合成了赖氨酸改性聚乳酸/聚乙二醇共聚物;赖氨酸(L-lys)的引入使得共聚物的热焓(ΔH)和熔点(T_m)分别由纯PLLA的81.57 J/g和177.34℃降到46.02 J/g和151.34℃,有效地改善了分子链的柔性和结晶度;聚合物的数均相对分子质量(M_n)也由纯PLLA的7.7×10~4降到了3.2×10~4,且相对分子质量分布变宽,但亲水性却得到大幅提高,有望适用于组织工程领域。     

低相对分子质量线型和星形聚乳酸及其共聚物多元醇的合成、结构与性能

利用丙交酯在小分子多元醇链转移剂和辛酸亚锡催化剂的作用下开环聚合或与己内酯共聚,合成了一系列线型和星形聚乳酸和聚(乳酸-co-己内酯)多元醇。获得的聚乳酸和聚(乳酸-co-己内酯)实际相对分子质量接近于理论相对分子质量,且相对分子质量分布较窄。聚合过程研究表明,在多元醇链转移剂下丙交酯开环聚合反应较快,其转化率在10min内达到95%以上,且之后聚乳酸多元醇相对分子质量基本不变。通过差示扫描量热法、热重分析研究了聚乳酸和聚(乳酸-co-己内酯)多元醇的热性能。聚乳酸多元醇的玻璃化转变温度(Tg)随着相对分子质量的增大而升高;己内酯的引入可以有效地降低聚乳酸多元醇的Tg,且提高了聚乳酸多元醇热稳定性。     

共载姜黄素与阿霉素的聚乳酸-聚乙烯亚胺微球的制备及体外评价

以辛酸亚锡(Sn(Oct)2)为催化剂,1,4-丁二醇和丙交酯为原料,开环聚合生成了聚乳酸(PLA),然后用异氟尔酮二异氰酸酯(IPDI)偶联小分子量的聚乙烯亚胺(2 000Da)与PLA,生成了可生物降解的嵌段共聚物聚乳酸-聚乙烯亚胺(PLA-PEI,PEA)。采用水包油包水(W/O/W)乳化溶剂挥发法,制备了共传输阿霉素(DOX)与姜黄素(Cur)的PEA微球联合给药系统。并对PEA/(DOX+Cur)微球进行了表征和考察,包括粒度分布、形貌、载药量、包封率、体外释放和细胞摄取等。通过实验结果可知,PEA微球给药系统有望为肿瘤及其它重大疾病联合治疗提供有意义的思路。     

丙交酯单体的制备及纯化

聚乳酸类高分子因其良好的生物降解性能和力学强度已在生物医用材料方面获得应用，并越来越多地受到人们的关注。聚乳酸及其共聚物可望成为21世纪的通用绿色高分子。其单体制备方法及聚合方法的改进成为当前研究的热点，乳酸直接缩聚不能得到高分子量的产物，高分子量的聚乳酸是通过丙交酯的开环聚合获得，文中就丙交酯类单体的制备及纯化方法的发展现状进行评述。为对此感兴趣的人们的起步研究提供便利。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。