用~1H-和~(13)C-NMR方法研究聚对苯二甲酸乙二酯/聚一氧基苯甲酸酯共聚酯的序列分布

测定了PET/30PHB和PET/60PHB共聚酯的高分辨~1H和~(13)C谱,并采用INEPT方法和部分弛豫FT技术确定了季碳吸收峰,对NMR谱进行了归属.应用我们先前提出的方法对共聚酯的序列分布进行了表征.结果表明,两种共聚酯的无规度B_q值均小于1,序列分布不象Jackson等认为的那样为完全无规的.此外,文中还指出,某些研究者套用Flory公式判别PET/PHB共聚酯是否为无规的不妥之处.     

聚对苯二甲酸乙二酯(PET)/聚对乙酰氧基甲酸(PHB)共聚酯及同类共聚物序列分布表征的数学统计

 由聚对苯二甲酸乙二酯(PET)和对-乙酰氧基苯甲酸制得的PET/PHB共聚酯代表了一类序列结构较一般二元共聚物复杂的共聚体系.在揭示了这类共聚物与序列分布有关的诸概率参数中只有一个是独立的之后,定义了参数B_q来描述此类共聚物的无规度.并指出,共聚物B_q=b时的序列分布,可以从一般二元共聚物无规度B=b时的序列结构加以推断.     

聚对苯二甲酸乙二酯(PET)/聚对乙酰氧基甲酸(PHB)共聚酯及同类共聚物序列分布表征的数学统计

由聚对苯二甲酸乙二酯(PET)和对-乙酰氧基苯甲酸制得的PET/PHB共聚酯代表了一类序列结构较一般二元共聚物复杂的共聚体系.在揭示了这类共聚物与序列分布有关的诸概率参数中只有一个是独立的之后,定义了参数B_q来描述此类共聚物的无规度.并指出,共聚物B_q=b时的序列分布,可以从一般二元共聚物无规度B=b时的序列结构加以推断.     

对羟基苯甲酸(PHB)聚对苯二甲酸乙二酯(PET)液晶共聚酯和聚对苯二甲酸乙二酯共混物的酯交换表征

在温度280℃附近对含有液晶共聚酯P-Hydroxy Benzoic Acid/Poly(-Ethylene Terephthalate-)PHB/PET和Poly(-Ethylene Terephthalate-)PET的共混样品进行热处理时,发现共混物的熔点随热处理的时间增加而不断降低,热处理温度越高,相同时间内共混物熔点下降程度越大;而具有相同热历史的纯PET样品熔点几乎保持不变.通过NMR方法证实了PHB/PET-TET共混物熔点随热处理时间下降是由于PHB/PET和PET之间发生了酯交换反应.所以可根据共混物的宏观热性质和PHB/PET序列结构变化表征PHB/PET和PET共混物之间的酯交换程度.     

BF分子X1Σ＋, A1P和B1Σ＋态的势能函数

使用SAC/SAC-CI和D95＋＋, 6-311＋＋g, 6-311＋＋g**及D95(d)基组, 分别对BF分子的基态X¹Σ^＋、第一简并激发态A¹Π和第二激发态B¹Σ^＋的平衡结构和谐振频率进行优化计算. 对所有计算结果进行比较, 得出6-311＋＋g**基组为最优基组. 运用6-311＋＋g**基组和SAC方法对基态X¹Σ^＋, SAC-CI方法对激发态A¹Π和B¹Σ^＋进行单点能扫描计算, 并用正规方程组拟合Murrell-Sorbie函数, 得到相应电子态的势能函数解析式, 由得到的势能函数计算了与X¹Σ^＋, A¹Π和B¹Σ^＋态相对应的光谱常数, 结果与实验数据较为一致.     

烷烃客体分子(CnHm, n≤6, m≤14)在51262和51264水笼中的稳定性与拉曼光谱的密度泛函理论计算

可燃冰矿藏中气体成分非常复杂,通过谱学分析对水合物样品成分进行指认具有重要意义.基于B97-D/6-311++G（2d,2p）的密度泛函理论（DFT）计算,我们系统地探索了构成水合物的两种标准水笼（5¹²6²和5¹²6⁴）包络十八种不同烷烃客体分子的稳定性. 从计算结果可以看出,除了3-甲基戊烷和2,3-二甲基丁烷两个烷烃客体分子,其它16个烷烃客体分子都可以被容纳在5¹²6²笼中;但是与5¹²6²笼不同,十八种烷烃客体分子都可以被容纳在尺寸较大的5¹²6⁴笼中. 同时,我们也模拟了五种直链烷烃和四种环状烷烃在5¹²6²和5¹²6⁴笼中相应的谱学特征,从拉曼谱图上可以看出,随着碳原子数量的增多,直链烷烃客体分子C―H键伸缩振动区的多数拉曼谱带向高波数移动,而环状烷烃客体分子C―H键伸缩振动区的拉曼谱带则向低波数移动. 这些结果为实验上通过拉曼谱测量指认水合物矿藏的成分提供理论参考.     

非晶聚对苯二甲酸乙二酯的制备与表征

通过单体酯交换法和聚 2 ,6 萘二甲酸乙二酯 (PEN)与低分子量PET酯交换的方法分别合成了一系列NPA/TPA/EG和IPA/TPA/EG共聚酯 .随着NPA或IPA单元含量的增加 ,等温结晶速度迅速降低 ,共聚物的结晶性降低甚至非晶化 .由NMR分析得知单体酯交换法与聚合物酯交换法得到的共聚酯NPA/TPA/EG序列分布相近 ,链结构都接近完全无规 .由DSC结果分析 ,随共聚单体含量的增加 ,熔点和熔融热降低 ,结晶度也随之降低 .当NPA或IPA含量达到 2 0 %时 ,可以得到非晶的共聚酯 (APET) .本文还对共聚物组成与结晶温度的关系进行了表征     

运用1H-NMR和13C-NMR研究聚对苯二甲酸-2,5-呋喃二甲酸乙二醇共聚酯（PEFT）的序列结构

采用直接酯化法,通过改变对苯二甲酸(PTA)与2,5-呋喃二甲酸(FDCA)的摩尔比,制备了一系列聚对苯二甲酸-2,5-呋喃二甲酸乙二醇共聚酯(PEFT)。运用1H-NMR和13C-NMR测试手段研究PEFT共聚酯的链结构。通过观察PEFT共聚酯链上乙二醇单元中氢原子和碳原子的化学位移及相应的4种信号的强度变化,计算出共聚酯的数均序列长度(L),无规度值(B)和共聚物的组成。通过Yamadera和Murano公式计算所得共聚酯无规度值B均接近于1,说明PEFT共聚酯为无规共聚物;PEF-block-PET嵌段共聚物B为0.577,PEF-blend-PET共混物的B为0;差示扫描量热仪(DSC)测试结果表明,0PEFT共聚酯均有一个玻璃化温度,进一步说明了PEFT共聚酯为无规共聚物。其中PTA∶FDCA的摩尔比为1∶1时,即PEFT-50,B值最大,基于1H-NMR谱图计算得B=1.012,13C-NMR谱图计算得B=1.028。上述结果表明,2,5-呋喃二甲酸与对苯二甲酸在与乙二醇的亲核取代反应中活性相近。     

人宫颈癌细胞(Hela)内的31P核磁共振研究

建立了无损伤性³¹P NMR研究细胞内物质的实验方法, 并对人宫颈癌细胞(Hela)的³¹P NMR谱中含磷小分子代谢物的谱峰进行了分析; 细胞内无机磷(Pi)的化学位移对pH非常敏感, 通过测定其化学位移可间接确定细胞内的pH, Hela细胞内Pi峰的化学位移为5.88±0.01 (n＝3), 计算得到细胞内 pH值为7.05±0.01; 通过测量Hela细胞的³¹P NMR谱中ATP的α磷和β磷及γ磷的化学位移差值, 得出Hela细胞内Mg^2＋与ATP结合的复合物MgATP和整个ATP量的比值, 计算得到Hela细胞内游离Mg^2＋浓度为(253.3±0.13) mmol/L (n＝3), 与其它分析方法相比, ³¹P NMR测定细胞内游离Mg^2＋浓度具有对细胞样品无损伤的优点.     

人宫颈癌细胞(Hela)内的31P核磁共振研究

建立了无损伤性³¹P NMR研究细胞内物质的实验方法, 并对人宫颈癌细胞(Hela)的³¹P NMR谱中含磷小分子代谢物的谱峰进行了分析; 细胞内无机磷(Pi)的化学位移对pH非常敏感, 通过测定其化学位移可间接确定细胞内的pH, Hela细胞内Pi峰的化学位移为5.88±0.01 (n＝3), 计算得到细胞内 pH值为7.05±0.01; 通过测量Hela细胞的³¹P NMR谱中ATP的α磷和β磷及γ磷的化学位移差值, 得出Hela细胞内Mg^2＋与ATP结合的复合物MgATP和整个ATP量的比值, 计算得到Hela细胞内游离Mg^2＋浓度为(253.3±0.13) mmol/L (n＝3), 与其它分析方法相比, ³¹P NMR测定细胞内游离Mg^2＋浓度具有对细胞样品无损伤的优点.     

STUDIES ON THE SEQUENCE STRUCTURE OF TPA/EG/PHB LIQUID CRYSTALLINE COPOLYESTERS

In this paper, the sequence structure of TPA/EG/PHB liquid crystalline copolyesters made from different synthetic methods has been studied by ~1H-NMR with the help of computer program of processing peaks. The results showed that the ether bonds were not observed in TPA./EG/PHB copolyesters and the synthetic process had a great effect on their sequence structure. Under certain conditions, the high,random TPA/EG/PHB copolyesters which were considered to have higher performances than PET/xPHB could be obtained.     

Synthesis and structural study of copolymers of l-lactic acid and bis(2-hydroxyethyl terephthalate)

Poly(ethylene terephthalate)-poly(lactic acid) (PET-PLLA) copolyesters were synthesized by the melt reaction of bis(2-hydroxyethyl terephthalate) (BHET) with l-lactic acid oligomers (OLLA) in the presence of SnCl₂, H₂O-p-toluene sulfonic acid, H₂O catalytic system. The ¹H and ¹³C NMR studies confirm the incorporation of lactate units in PET chains after reaction. Copolyesters containing nearly equimolar terephthalate/lactate ratio are not completely random and present some block-copolymer character, while the microstructure of PET-rich copolyesters is a random one. Due to a longer PET sequence length, the latter exhibit a melting point close to 210 °C while the other ones are amorphous. SEC/MALDI-TOF MS off-line coupling was used to obtain the absolute average molar masses of the copolyesters. The results indicate that the conventional polystyrene calibration method leads to a strong overestimation of PET-PLLA molar masses, while the determined by NMR is much closer to the SEC/MALDI value.     

Poly(ethylene terephthalate) copolyesters derived from (2S,3S)‐2,3‐dimethoxy‐1,4‐butanediol

Novel poly(ethylene terephthalate) (PET) copolyesters, abbreviated PEDMBT, containing optically active (2S,3S)‐2,3‐dimethoxy‐1,4‐butanediol (DMBD) as the second comonomer were investigated. Copolymers with ethylene glycol to DMBD ratios between 95/5 and 50/50 as well as the two parent homopolymers, PET and PDMBT, were prepared by a two‐step melt polycondensation. The resulting copolymers were found to approximately have the composition of the polymerization reaction feed and a random microstructure. Polymer intrinsic viscosities varied from 0.4 to 0.6 dL g^?1 with weight‐average molecular weights ranging from 16,000 to 44,000. PEDMBT copolyesters were distinguished in being much more soluble than PET and showing an increasing affinity for water with the content in dimethoxy groups. According to the asymmetric constitution of DMBD, they displayed optical activity in solution. Both melting and glass‐transition temperatures of the copolyesters were observed to steadily decrease with the content in DMBD. PEDMBTs were found to be crystalline for contents in DMBD up to 30 mol %. Both powder and fiber X‐ray diffraction revealed that the same crystalline structure is shared by PET and the crystalline copolyesters. The homopolyester PDMBT resulted in becoming a polymer with a crystallinity comparable to PET but with a significantly different crystalline structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3250–3262, 2001     

STUDIES ON THERMOTROPIC LIQUID CRYSTALLINE COPOLYESTERS——POLY (ARYLENE TEREPHTHALATE-CO-BUTYLENE TEREPHTHALATE)

A series of copolyesters based on bis(4-hydroxybutyl) terephthalate, terephthaloyl chloride andvarious aromatic diols (i.e. hydroquinone, chlorohydroquinone, bromohydroquinone or dihydroxybi-phenyl) was prepared. ~1H-NMR studies revealed that the monomer units had microstructures closeto random distribution in the chains. The copolymers showed composition-dependent liquid crystal-line properties as verified by visual observation of stir opalescence, polarizing microscope, DSC andX-ray diffration. The copolyesters with aromatic diol contents over a certain extent (for chloro-hydroquinone m≥0.33) were thermotropic with wide liquid crystalline temperature ranges. Theintroduction of chlorohydroquinone into the copolyesters could gradually destroy the crystallinityof the polymers but retain the liquid crystalline characteristics.     

NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

The rα stucture of 1,6,6aλ4 trithiapentalene and 1,6-dioxa-6aλ4-thiapentalene. A 1H-NMR study in the nematic phase including 13C- satellites in natural abundance

The ¹H-NMR spectra of 1,6,6aλ⁴-trithiapentalene and l,6-dioxa-6aλ⁴-thiapentalene in nematic phases have been recorded and analyzed. The ¹³C-¹H dipole-dipole couplings were obtained from the ¹³C satellites in natural abundance. Contributions from the harmonic vibrations to the dipole-dipole couplings have been calculated. The vibration-corrected dipole-dipole couplings yielded the r_α structure in accordance with a rigid C_ZV symmetry of the molecules. No evidence for a rapid valence tautonierization in the molecules was found.     

NMR (1H, 13C, 29Si) study of some allylhalogenosilanes

¹H, ¹³C and ²⁹Si NMR spectra of the allylchlorosilanes (CH₂CH-CH₂-)_xSiCl_4?x and of triallylbromosilane have been analysed. Results are discussed in terms of inductive and steric effects and of contributions of diamagnetic anisotropy. There is no conclusive evidence for (p-d)π conjugation.