~(13)C-NMR研究聚丁二烯的序列结构

本文采用~13C-NMR方法研究了不同催化体系制备的聚丁二烯。经分析指出,聚丁二烯分子链的三种序列(顺-1,4-序列、反-1,4-序列和1,2-序列)和十七类脂碳碳核为~13C-NNR谱贡献了十六个谱峰。经数据的解析,得到一组计算聚丁二烯脂碳部分各谱峰化学位移的经验参数。在本文条件下,应用该组参数得到的计算值与实验值符合较好。本文确认了聚丁二烯反-1,4-序列第四峰(T_4)的存在。初步研究了聚丁二烯~13℃-NMR谱图的定量处理问题。     

用IR、~1H和~(13)C-NMR研究聚戊二烯-1,3结构

用IR、~1H和~(13)C-NMR方法研究了环烷酸钕催化聚戊二烯-1,3的链节结构和序列分布。结果表明,聚合物含有约70％顺-1,4,25％反-1,2和5％反-1,4结构。确定了计算脂肪碳~(13)C-NMR化学位移的一组经验参数,对各峰做了归属。~(13)C-NMR能很好地辨别顺-1,4,反-1,4和反-1,2等各种结构,发现稀土催化聚戊二烯-1,3单体链节是以头-尾相联,不存在反结,并发现了1,4-1,2联结的序列。     

~(13)C-NMR研究铁系聚丁二烯(顺1,4-1,2)的链结构

前已报道,以高活性铁催化剂可以制得性能良好的含顺-1,4-1,2结构的等二元聚丁二烯。文献已有用~(13)C-NMR研究以钴,钼催化剂合成的这种等二元聚合物的报导。本工作用~(13)C-NMR进行了研究,得到的聚合物的~(13)C-NMR图谱表明,聚合物的脂碳部分共有十一个共振峰,烯碳部分有九个峰。通过改进Furukawa的经验参数,并应用Randall的方法,这些共振峰的归属得到了令人满意的结果。确认该聚合物是双烯和单烯的无规共聚物,但偏离Bernoulli分布,趋向于一级Markov分布。     

~(13)C-NMR研究聚丁二烯长支链支化

本文研究了用不同催化体系制备的聚丁二烯和加氢的聚丁二烯的~(13)C-NMR谱图。结合GPC测定支化度的数据,提出了二种可能的支化结构。以Ni及Co催化体系聚合的试样,支化点可能位于顺-1,4主链双键的α-次甲基上;而由Ni+Mo催化体系聚合的试样,可能为1,2-乙烯基的双键打开接长支链。     

~(13)C-NMR化学位移与聚合物的构象——Ⅰ.1,2-聚丁二烯乙烯基叔碳(-CH=)的~(13)C-NMR谱研究

本文应用半经验方法来解析无规1,2-聚丁二烯乙烯基叔碳(—CH=)的~(13)C-NMR谱图。研究指出只有主链CH与乙烯基叔碳之间的gauche排列和由此产生的屏蔽效应对后者的化学位移的改变作出了贡献。因此,可以直接利用键概率来归属十个五元组立构异构体的排列顺序。由于上述原因,得到了对于无规1,2-聚丁二烯乙烯基叔碳的~(13)C-NMR谱的一种新的归属,并且通过研究全同和间同1,2-聚丁二烯的~(13)C-NMR谱图予以证明。     

~(13)C-NMR研究3,4-聚异戊二烯的序列分布

Fe(acac)_3-Phen-AlEt_3 催化体系可使异戊二烯聚合成以 3,4-链节为主具有一定结晶性能的聚异戊二烯。本文对该聚合物的~(13)C-NMR 谱进行了全分析,研究了序列分布、微观结构。结果表明不同方法求得的微观结构含量很好地一致,说明对~(13)C-NMR 谱峰归属的正确性。并指出顺-1,4/3,4-序列中存在着头-头,尾-尾的连接方式,3,4-嵌段链节不足够长及存在反节可能是结晶度不太高的主要原因。     

聚丁二烯的序列结构

Ⅰ.¹³C-NMR研究聚丁二烯的序列结构 聚丁二烯的链状分子包含三种序列,十七类脂碳碳核。其中包含被遗漏的反1,4-序列的第四碳。在聚丁二烯的¹³C-NMR谱图上确认了与之对应的共振吸收峰,T₄峰。得到了一组经验参数,当用于聚丁二烯的¹³C-NMR谱图(脂碳部分)时,各谱峰化学位移计算值和实验值相一致。但是,与1,2-序列两端的四类碳核:Ca₄, T₄, V₂和V₈相对应之谱峰的化学位移计算值均低于实验值。     

1,2-聚丁二烯~(13)C-NMR弛豫的溶剂效应

本文测定了一系列具有不同微观结构的1,2-聚丁二烯样品在四种溶剂的50.3MHz ~(13)C自旋-晶格弛豫时间(T_1)和核Overhauser效应(NOE)值。并用Schaefer logx~2相关时间分布模型对实验数据进行了拟合。研究了1,2-聚丁二烯在溶液中的~(13)C-NMR弛豫的溶剂效应及其与结构的关系。发现聚合物与溶剂的溶解度参数之差△δ越大,聚合物在溶液中协同链段运动趋向越明显,~(13)C自旋-晶格弛豫速率(1/T_1)越大;1,2-链节较少,分子链较柔顺时,~(13)C-NMR弛豫受溶剂影响较显著。NMR弛豫参数对结构变化的反应在良溶剂中比在不良溶剂中敏感。     

长序列乙烯-丁二烯共聚物的合成

研究了稀土催化剂催化乙烯-丁二烯的共聚合。结果表明,在封管条件下用稀土催化剂可以使乙烯-丁二烯共聚,产生高分子量聚合物。产物的溶液性质表明,不含聚乙烯均聚物,含约8％的聚丁二烯均聚物。DSC、X-射线衍射、电子显微镜和~(13)C-NMR等实验表明,所得聚合物是含长乙烯-乙烯序列的乙烯-丁二烯共聚物,其中聚丁二烯链段的微观结构以顺-1,4构型为主。共聚物中乙烯单元增加,乙烯-乙烯链段的熔点和结晶度增高,晶粒尺寸变大,晶胞参数基本不变。共聚物的力学性能表明,其生胶强度可达20—30kg/cm~2,远比聚丁二烯的强度大。     

~(13)C-NMR研究稀土催化聚戊二烯-1,3的末端链结构

用~(13)C-NMR方法研究了稀土催化聚戊二烯-1,3的末端链结构及聚合温度对聚合物微观结构的影响。结果指出,聚合物的末端活性增长链是以头-尾或尾-头加成生成的anti-和syn-四种 π-烯丙基。聚合温度降低时,顺-1,4含量增加,这可解释为由于 anti-和 syn-异构化的作用。同时解释了反-1,2结构形成的过程。     

A NEW PEAK (T_4) IN THE ~(13)C-NMR SPECTRUM OF POLYBUTADIENE

A new peak at 39.0 ppm in the ~(13)C-NMR spectrum of polybutadiene (PBD) was discovered. This peak is assigned to the fourth peak (T_4) of trans-1,4-sequence marked with an asterisk as shown in Fig. 3 in the text.The occurrence of T_4 carbon nuclei is strongly affected by their neighboring 1,2-units. So long as both contents of trans-1,4- and 1,2-units attain their proper amounts the peak (T_4) with appear in the ~(13)C-NMR spectrum of PBD.     

CARBON-13 NMR STUDY OF MOLECULAR MOTION OF 1, 2-POLYBUTADIENES IN SOLUTION Ⅰ. STRUCTURE DEPENDENCE OF MOLECULAR MOTIOM

Proton decoupled, partially relaxed, Fourier-transform 50.3 MHz carbon-13 NMR in naturalabundance was used to determine spin-lattice times (T_1) and nuclear Overhauser enhancement fac-tors (NOE) of individual carbon of a serics of 1,2-polybutadienes with different structures in solutionin CDCl_2 The structure dependence of molecular metion and the internal motion of vinyl group in1,2-polybutadiene have been studied by nT_1 and NOE values. The nT_1 values of the carbons in cis-1,4-units are the highest and those of the carbons in 1.2-units are the lowest in three types of units in1,2-polybutadiene. The nT_1 values of carbons in the same unit become greater when the adjacent1,2-units are replaced by 1,4-units, and nT_1 values of the carbons in all units decrease sharply withthe increase of content of 1,2-units in the polymers. The fact that nT_1 values of --CH=are larger than those of=CH_2 in vinyl group impliesthat there are complex internal motions of vinyl group. It is shown by calculation that the dominantfactor causing the difference in nT_1 of--CH=and=CH_2 in vinyl group is a swing of vinyl group ina plane peopndicular to the chain backbone.     

A CNDO/S study on the Tn ← T1 absorption spectrum of 1,1′-binaphthyl

CNDO/S calculations demonstrate that changes in the T_n ← T₁ absorption spectrum of 1,1′-binaphthyl in going from rigid to fluid media is consistent with a rotation of the chromophores about the interconnecting bond to a nearly planar trans configuration.     

Cluster self-organization of Na-TR-Ge-O-H (TR = La-Lu, Y, and Sc) germanate systems: Suprapolyhedral precursor clusters and self-assembly of Na2Pr6Ge8O26, Na4Sc2Ge4O13, and Na5ScGe4O12 crystal structures

In an M-T-O model system (M is a polyvalent metal; T = Ge or Si), we consider initial stages of formation of cyclic MT clusters and the mechanism of their modification by T tetrahedra. The polyhedron ratio T/M in clusters increases progressively during modeling from one in M₂T₂ to two (M₂T₂ + 2T = M₂T₄), three (M₂T₂ + 2T₂ = M₂T₆), and four (M₂T₂ + 2T + 2T₂ = M₂T₈). These types of clusters were used to find precursor clusters for T-condensed structures of Na₂Pr₆Ge₈O₂₆, Na₄Sc₂Ge₄O₁₃, and Na₅ScGe₄O₁₂. The TOPOS program package was used to carry out the complete 3D reconstruction of the self-assembly of Na,TR germanates: precursor cluster → primary chain → microlayer → microframework (supraprecursor) → ... framework. In all structures, as previously in six orthotetrahedral Na,TR germanate structures, the basic invariant type of four-polyhedral cyclic precursor cluster M₂T₂ was identified; this cluster is built of TR polyhedra, with CN = 6 or 7, linked via orthotetrahedra. The features of the generation of a Ge radical were considered in the form of a Ge₂O₇ chain and a Ge₄O₁₂ ring in various layers of the Na₂Pr₆Ge₈O₂₆ composite structure, a Ge₄O₁₃ chain in Na₄Sc₂Ge₄O₁₃, and a Ge₁₂O₃₆ ring in the Na₅ScGe₄O₁₂ superionic conductor. Original Russian Text ? G.D. Ilyushin, L.N. Dem’yanets, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 3, pp. 484–496.     

Synthesis and characterization of soft–hard stereoblock polybutadiene with Fe(2‐EHA)3/Al(i‐Bu)3/DEP catalyst system

Stereoblock polybutadiene (PBD) composed of amorphous equibinary cis?1,4/1,2 PBD (e‐PBD, soft) and crystalline syndiotactic 1,2‐PBD (s‐1,2‐PBD, hard) segments is synthesized through one‐pot sequential polymerization with iron(III)2‐ethylhexanoate/triisobutylaluminum/diethyl phosphate [Fe(2‐EHA)₃/Al(i‐Bu)₃/DEP] catalyst system. The first‐stage polymerization of 1,3‐butadiene (BD) is carried out at a low [Al]/[Fe] ratio to give amorphous e‐PBD block, and sequentially, the in situ addition of excessive Al(i‐Bu)₃ and BD to the living polymerization system give rise to a second crystalline s‐1,2‐PBD block. The length of each block is controllable by adjusting cocatalyst and monomer feed ratio. The syndiotactic pentad content is in the range of 63.8–76.6% and increases with the length of s‐1,2‐PBD block. The copolymer exhibits glass transition temperature (T_g) around ?40 °C and melting point (T_m) around 168 °C originating from e‐PBD and s‐1,2‐PBD blocks, respectively. The incompatibility between s‐1,2‐PBD and e‐PBD blocks as well as the crystallization of s‐1,2‐PBD block induce the microphase separation in stereoblock PBD. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1182–1188     

NMR study of molecular reorientations in NH4H2AsO4

Zeeman (T_1Z) and dipolar (T_1D) spin-lattice relaxation times of protons in NH₄H₂AsO₄ were measured as a function of temperature. The existence of a slow motion (τ ≈ 10^?3 see) is established, which is most probably a low frequency hindered reorientation of H₂AsO₄ groups. This motion is slowed down below the Curie point T_c. A sharp increase of the dipolar relaxation rate above T = 314°K indicates the possibility of a new high temperature phase transition in this compound.     

Distinction of the delayed fluorescences S1 → S0 And S2 → S0 of pyrene by selective quenching Of S1 → S0

In the spectrum of the delayed fluorescence (DF) of pyrene, caused by triplet-triplet annihilation T₁ + T₁ → S_n + S_o (n = 1,2), a strong DF S₁ → S_o and a very weak DF S₂ → s₀ are observed. The DF S₁→ S_o is quenched selectively by compounds like N-diethylanine or triethylamine which do not quench T₁ of pyrene.     

Characteristics and formation of [AlO4Al12(OH)24(H2O)12]7+ in electrolysis process

[AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ (Al₁₃) formation in electrolysis process is studied. The results detected by²⁷Al NMR spectroscopy show that high content of Al₁₃ polymer is formed in the partially hydrolyzed aluminum solution prepared by controlled electrolysis process. In the produced electrolyte of total Al concentration ([Al_T]) 2.0 mol · L⁻¹ with a basicity (B = OH/Al molar ratios) of 2.0, the content of Al₁₃ polymer is over 60% of total Al. Dynamic light scattering shows that the size distribution of the final electrolyte solutions ([Al_T] = 2.0 mol · L⁻¹) is trimodal with B = 2.0 and bimodal with B = 2.5. The aggregates of Al₁₃ complexes increase the particle size of partially hydrolyzed aluminum solution.     

FREQUENCY DEPENDENCE OF THE DIELECTRIC RELAXATION OF 1,2-POLYBUTADIENES

The dielectric loss factor and permittivity of a series of 1, 2-polybutadienes with different contents of 1, 2-units and different contents of syndiotactie 1, 2-units were determined over a frequency range from 30Hz to 100KHz at different temperatures. The WLF equation was evaluated for various samples with T_θat 100KHz as a reference temperature and the master curves of various samples have been constructed, which are in accordance with those calculated by Havriliak-Negami equation. The frequency dependence of the dielectric relaxation of 1, 2-polybutadienes was investigated over a frequency range from 10~0 Hz to 10~(12) ZHz in terms of the experimental data and the master curves.