用13CNMR研究聚甲基丙烯酸锡酯的立构序列分布

本文测定了自由基型溶液聚合的聚甲基丙烯酸三甲基锡酯(PTMTM),聚甲基丙烯酸三乙基锡酯(PTETM)和聚甲基丙烯酸三丁基锡酯(PTBTM)的¹³C-NMR谱,对其C-2谱扩展分峰,计算立构序列,从定量数据表明,聚合物样品的空间立构富于或稍富于间规立构,随取代基的体积增大而趋于无规分布,作者认为受空间位阻效应和分子内或分子间形成配位键的影响。     

NMR SPECTROSCOPIC STUDY ON COPOLYMER OF ETHYLENE-NORBORNENE

A series of ethylene-norbornene copolymers were synthesised using VO (OEt) Cl_2/Al_2Et_3Cl_3 catalytic system and their structure was characterized by ~1H-NMR, ~1H-~1HCOSY NMR and ~(13)C-NMR. Assignments of NMR spectra were given and discussed indetail.     

Alternierende Copolymerisation von Styrol und Benzylmethacrylat in Gegenwart von Ethylaluminiumsesquichlorid

Zusammenfassung Die alternierende Copolymerisation von Styrol und Benzylmethacrylat in Gegenwart von Ethylaluminiumsesquichlorid als Katalysator zeigt im Anfangsstadium der Reaktion ein vom weiteren Verlauf abweichendes Verhalten. So nehmen die Zusammensetzung und die Grenzviskositäten der Produkte sowie die Reaktionsgeschwindigkeit erst nach der Anfangsphase konstante Werte an.Die¹H-NMR-Spektren von alternierenden und statistischen Copolymeren gleicher Bruttozusammensetzung zeigen deutliche Unterschiede. Das Spektrum des alternierenden Copolymeren bestätigt die alternierende Struktur und spricht gleichzeitig für einen ataktischen Kettenaufbau.

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The alternating copolymerization of styrene and benzylmethacrylate shows a different behaviour at the beginning of the reaction and later on. Thus the composition and the intrinsic viscosity of the products as well as the reaction rate become constant only after the initial stage.The¹H-NMR-spectra of alternating and statistical copolymers with equal composition show distinct differences. The spectrum of the alternating copolymer confirms the alternating structure as well as an atactic chain configuration.

     

聚合温度对聚甲基丙烯酸三丁基锡酯等规度的影响(Ⅰ)

本文测定了0—130℃温度范围内,由~(60)Co-γ射线和两种活性不同的引发剂引发聚合的聚甲基丙烯酸三丁基锡酯的等规度。利用~(13)C-NMR测定聚合物分子链的等规度,如预料的那样,以间同立构为主,并随着聚合温度的升高间同立构等规度降低。作者认为影响聚合物等规度的因素主要是取代基的极性效应。计算出的控制等规度的活化能参数与聚甲基丙烯酸甲酯和聚甲基丙烯酸三甲基锡酯的属同一数量级,可相互比较。     

α－甲基丙烯酸烯丙酯的合成及其自由基、阴离子聚合的研究

合成了α－甲基丙烯酸烯丙酯（ＡＭＡ），并对其自由基、阴离子聚合进行了探讨。结果发现，该单体难以进行选择性自由基聚合，但可用作多种单体自由基聚合的交联剂。用１，１′－二苯基己基锂在ＴＨＦ中引发ＡＭＡ，可顺利地进行α位双键的选择性阴离子聚合，分子量实测值与计算值基本一致。在较低温度下（≤－６０℃），可得窄分布ＰＡＭＡ（Ｍｗ／Ｍｎ＝１．１２～１．１５）。随聚合温度升高，间同和无规聚合物含量分别呈下降和上升趋势。ＧＰＣ、１ＨＮＭＲ及ＦＴＩＲ鉴定表明，用阴离子聚合法可得到溶于多种溶剂、每个重复单元上均定量带有烯丙基双键的窄分布官能性ＰＡＭＡ。     

Polymerization of MMA by oscillating zirconocene catalysts, diastereomeric zirconocene mixtures, and diastereospecific metallocene pairs

Characteristics of methyl methacrylate (MMA) polymerization using oscillating zirconocene catalysts, (2-Ph-Ind)₂ZrX₂ (X = Cl, 1; X = Me, 2), mixtures of rac- and meso-zirconocene diastereomers, (SBI)ZrMe₂ [3, SBI = Me₂Si(Ind)₂] and (EBI)ZrMe₂ [4, EBI = C₂H₄(Ind)₂], as well as diastereospecific metallocene pairs, rac-4/Cp₂ZrMe₂ (5) and rac-4/CGCTiMe₂ [6, CGC = Me₂Si(Me₄C₅)(t-BuN)], are reported. MMA polymerization using the chloride catalyst precursor 1 activated with a large excess of the modified methyl aluminoxane is sluggish, uncontrolled, and produces atactic PMMA. On the other hand, the polymerization by a 2/1 ratio of 2/B(C₆F₅)₃ or 2/Ph₃CB(C₆F₅)₄ is controlled and produces syndiotactic PMMA. Mixtures of diastereomeric ansa-zirconocenes 3 or 4 containing various rac/meso ratios, when activated with B(C₆F₅)₃, yield bimodal PMMA; this behavior is attributed to the meso-diastereomer that, in its pure form, affords bimodal, syndio-rich atactic PMMA. For MMA polymerization using diastereospecific metallocene pairs, rac-4/5 and rac-4/6, the isospecific catalyst site dominates the polymerization events under the conditions employed in this study, and the aspecific and syndiospecific sites are largely nonproductive, thereby forming only highly isotactic PMMA.     

INFLUENCE OF THERMAL TREATMENTS ON THE POLYMORPHISM IN STEREOIRREGULAR ISOTACTIC POLYPROPYLENE: EFFECT OF STEREO-DEFECT DISTRIBUTION

The influence of cooling rate from the melt on the polymorphism and crystallinity is investigated as a function of isotacticity and stereo-defect distribution in polypropylenes. Detailed analysis of wide angle x-ray diffraction patterns shows that crystallinity in the materials used is nearly independent of the experimental cooling rates (0.5–40°C/min). At high cooling rates, the materials exist mainly in the α-phase, whereas the amount of the γ-phase increases at the lower cooling rates. With an increasing amount of stereo-defects, this cooling-rate dependence of the polymorphism is enhanced. The effect of different stereo-defect distributions, as observed in metallocene-(random) and Ziegler–Natta (blocklike) derived isotactic polypropylenes, was investigated. The formation of the γ-phase is more prevalent in materials with a random defect distribution compared to the materials in which the stereo-defects have a blocklike distribution. The crystallinity decreases more rapidly as a function of the tacticity in the random defect-distributed materials.     

Stereospecific radical polymerization of optically active (S)-N-(2-hydroxy-1-phenylethyl) methacrylamide catalyzed by Lewis acids

The effects of Lewis acids, namely, rare earth metal trifluoromethanesulfonates, on the radical polymerization of (S)-N-(2-hydroxy-1-phenylethyl) methacrylamide were examined under various conditions. In the absence of Lewis acids, syndiotactic-rich polymers (r = 84%) were obtained, whereas in the presence of a catalytic amount of Lewis acids, the polymerization proceeded in an isotactic-specific manner (m up to 64%). Polymerization solvents strongly influenced the effect of the Lewis acids. The polymerization in n-butyl alcohol showed the highest isotactic selectivity, whereas the polymerization in DMSO showed no isotacticity-enhancing effect. Further increases in the Lewis acid concentration and the polymerization temperature did not produce clear effects on the tacticity of the polymers. The interaction between the monomer and Lewis acids was investigated, and the plausible mechanism of stereocontrol in the radical polymerization of (S)-HPEMA was analyzed based on the Lewis acid-monomer interaction.     

Stereocontrol during photo-initiated controlled/living radical polymerization of acrylamide in the presence of Lewis acids

Poly(acrylamide) (PAM) with controlled molecular weight and tacticity was prepared by UV-irradiation-initiated controlled/living radical polymerization in the presence of dibenzyl trithiocarbonate (DBTTC) and Y(OTf)₃. The rapid and facile photo-initiated controlled/living polymerization at ambient temperature led to controlled molecular weight and narrow polydispersity (M_w/M_n = 1.12-1.24) of PAM. The coordination of Y(OTf)₃ with the last two amide groups in the growing chain radical effectively enhanced isotacticity of PAM. The isotactic sequence of dyads (m), triads (mm) and pentads (mmmm) in PAM were 70.32%, 50.95%, and 29.97%, respectively, which were determined by the resonance of methine (CH) groups in PAM under ¹³C NMR experiment. Factors affecting stereocontrol during the polymerization were studied, including the type of Lewis acids, concentration of Y(OTf)₃, and monomer conversion. It is intriguing that the meso tacticity increased gradually with chain propagation and quite higher isotacticity (m = 93.01%, mm = 86.57%) was obtained in the later polymerization stage (conversion 65-85%).     

SUPPORTED CATALYST WITHOUT EXTERNAL ELECTRON DONOR FOR PROPYLENE POLYMERIZATION Ⅱ. TACTICITY DISTRIBUTION AND MICROSTRUCTURE OF POLYPROPYLENE*

Propylene was polymerized with a novel supported Ziegler-Natta catalystcontaining 2,2-di-iso-butyl-1,3-dimethoxy-propane (DIBDMP) as internal donor and in theabsence of external donor. The tacticity distribution of polypropylene was obtained by usingtemperature rising elution fractionation (TREF) technique and microstructure of fractionswas studied with ~(13)C-NMR. Compared with the catalyst without electron donor, this cat-alyst gives a considerably narrower tacticity distribution. Fractionation data demonstratethat DIBDMP shows better performance than aromatic diester DNBP (di-n-butyl phtha-late). Chemically inverted propylene units and less stereoblockiness are found in the firstfraction. Possible reasons for these were presented.