On the mechanism of oxidation process initiation by the N-hydroxyphthalimide-cobalt (II) acetate system

The effect of the structure of radical catalysts, N-hydroxyphthalimides (NHPI), on the oxidation process initiation in the presence of cobalt (II) acetate is studied. It is shown that the magnitude of the synergic effect of the system NHPI-Co(OAc)₂ depends on the structure of NHPI molecule. The proposed mechanism is confirmed according to which of the NHPI molecules in the inner sphere of the metal are catalytically active.     

Influence of microstructure on the hydrodynamic behavior of poly-α-methylstyrene

The theta temperature of poly-α-methylstyrene in cyclohexane has been found to vary with the stereostructure of the polymer. The observed values range from 305.5°K. for highly syndiotactic material (0.95 syndiotactic diads) to 310.0°K. for anio ically polymerized samples (0.67 syndiotactic diads). Results indicate that the unperturbed dimensions of the polymer increase with increasing isotacticity of the chain, whereas the entropy parameter ψ₁, measured in cyclohexane, decreased as the structure became more isotactic. Measurements of the second virial coefficient in toluene showed an increasing interaction with the solvent as the polymer became more syndiotactic.     

Stereoregularity of poly(methyl methacrylate) prepared by aqueous polymerization and catalyzed by corundum

The aqueous polymerization of methyl methacrylate was carried out in the absence and in presence of corundum or carborundum at 25 and 80°C. In the absence of corundum and carborundum, it has been found that rising the polymerization temperature from 25 to 80°C resulted in changing the tacticity of the obtained polymers. At 25°C the isotactic triad was 26% while the heterotactic triad was 33.5% and the syndiotactic one was 40.5%. Increasing the polymerization temperature to 80°C resulted in a decrease of the isotactic structure to 0% and increased the heterotactic structure and syndiotactic structure to 48 and 52% respectively. Polymerizing at 25°C in presence of corundum (0.5 g) an increase in the syndiotactic triad took place from 40.5 to 50.7% while the isotactic triad decreased from 26 to 22.2% and the heterotactic structure decreased from 33.5 to 27%. Raising the polymerization temperature to 80°C in the presence of the same amount of corundum resulted in an increase in both the isotactic and heterotactic triads to 35 and 32.7%, respectively. Polymerizing at 80°C in presence of corundum (0.5 g) resulted in nearly an equal percentage of each triad 33%.     

Thermal and dynamic mechanical relaxation behavior of stereoregular poly(2-hydroxyethyl methacrylate)

Thermal, dynamic mechanical, and dielectric relaxation techniques were used to determine the relaxation behavior of isotactic and syndiotactic poly(2-hydroxyethyl methacrylate) (pHEMA). Activation energies E_a were determined for the dielectric γ relaxation and compared with those of poly(2-methoxyethyl methacrylate) (pMEMA) to determine the influence of hydrogen bonding on side-chain relaxation processes. No difference in E_a was observed between syndiotactic pHEMA and atactic (predominantly syndiotactic) pMEMA. Isotactic pHEMA, however, had E_a + 1 kcal/mole higher than that of syndiotactic pHEMA. This was attributed to improved side-chain packing in the isotactic polymer.     

甲基丙烯酸甲酯原子转移自由基聚合等规度研究

在0～100℃温度范围内,由原子转移自由基聚合方法,采用助催化和非助催化体系,引发甲基丙烯酸甲酯聚合,利用¹³CNMR测定聚甲基丙烯酸甲酯的等规度.发现原子转移自由基聚合仍以间同立构为主,随着聚合温度的升高间同立构等规度降低,与通常自由基聚合对有规立构控制特征相似.助催化剂异丙醇铝和活性端羰基配位,对聚合物的立构规整性有一定的影响.     

聚苯乙烯结晶及其晶型转化

介绍了等规和间规聚苯乙烯的合成、晶型及晶体结构研究的进展情况。重点对高间规度聚苯乙烯的各晶型及其相互转化进行了综述。     

Thermal properties of some hydrogenated poly(α-methyl styrenes)

The Synthesis of poly(isopropenyl cyclohexane) via the hydrogenation of poly(α-methyl styrene) is described. Depending on the reaction time and catalyst system a homopolymer or a copolymer is obtained. Under the conditions of synthesis both materials are highly syndiotactic. For the pure hydrogenated homopolymer (>99.9%) the glass transition temperature was found to be 185.4°C, about 20°C above T_g of poly(α-ethyl styrene). Contrary to expectations, the glass transitions of the 92/8, 33/67 poly(isopropenyl cyclohexane-co-methyl styrene) and poly(α-methyl styrene) are almost identical, as are the decomposition temperature ranges. Thermal data indicate that the decomposition mechanism of the copolymers and hydrogenated homopolymer is random scission. The thermogravimetric curves also indicate that the copolymers are random. Thus, chain stiffness appears not to increase rapidly with hydrogenation of this highly syndiotactic polymer.     

NMR spectroscopic,osmometric, and viscometric study of association of syndiotactic poly(methyl methacrylate) in dilute solutions

Association of syndiotactic (s) poly(methyl methacrylates) (PMMAs) in toluene, benzene, and acetonitrile has been studied by NMR spectroscopy, osmometry, and viscometry. It was found that in solutions of highly syndiotactic PMMA in toluene, most of the polymer exists in the associated state. Association takes place by means of stereospecific intermolecular and intramolecular interactions of long parallel syndiotactic sequences. The minimum length of syndiotactic sequences necessary for association of s-PMMA in toluene is 7–8 monomer units. Viscosity data indicate that in dilute solutions the associated structures appear as large formations which do not have the character of compact particles. The formation of the aggregates of PMMA is a relatively slow process. A model of the structure of the aggregates of s-PMMA in toluene is proposed. As compared with that in toluene, the tendency to aggregation in benzene and acetonitrile is negligible. Integral parameters currently used for the characterization of polymer-solvent interaction, like “good” or θ solvent, are not suitable for predicting the tendency of s-PMMA to aggregation. The formation of aggregates evidently has some connection with the effect of the solvent upon the conformational structure of syndiotactic sequences.     

Effect of tacticity on permeation properties of poly(methyl methacrylate)

The effect of stereoregularity on gas permeation properties of poly(methyl methacrylate) (PMMA) was investigated. The gas permeability coefficients for He, H₂, O₂, N₂, Ar, CH₄, and CO₂ at 35°C near atmospheric pressure have been measured for three different PMMAs. Apparent diffusion and solubility coefficients were obtained from time lag data, and these were compared with data for a commercial PMMA previously reported. The permeability, solubility, and diffusion coefficients increase as the content of syndiotactic sequences increases. These observations are consistent with more dense packing of the isotactic form in the glassy state that stems in part from its lower glass transition temperature. The transport behavior for a 50:50 isotactic/syndiotactic blend was also studied. These so-called stereocomplexes exhibit permeation behavior comparable to other weakly interacting miscible blend systems.     

Functionalization of syndiotactic polystyrene with succinic anhydride in the presence of aluminum chloride

Syndiotactic polystyrene has been chemically modified with succinic anhydride by use of Friedel-Crafts acylation reaction in the presence of anhydrous aluminum chloride in carbon disulfide. The modified syndiotactic polystyrene containing -COCH₂CH₂COOH fragments in side phenyl rings, named succinoylated syndiotactic polystyrene (s-sPS), was characterized by FTIR and ¹H NMR spectroscopy. The effects of reaction conditions on the degree of succinoylation of s-sPS were investigated. In addition, the effects of incorporation of carboxyl groups into syndiotactic polystyrene on the thermal behavior were studied by differential scanning calorimetry in comparison with pure syndiotactic polystyrene. It was found that the crystallization temperature, melting temperature, and degree of crystallinity of the modified polymer decreased with increasing the degree of succinoylation, while the glass transition temperature increased.     

Vibrational assignments for the CCL stretching region of the Raman spectrum of poly(vinyl chloride)

It is shown that, by assuming that each of the peaks resolved in the CCl stretching region of the Raman spectra of a series of poly(vinyl chloride) gels can be associated with a definite triad structure, most of the peaks can he assigned to syndiotactic, isotactic, or heterotactic triad configurations without reference to the spectra of model compounds or to vibrational calculations. The results are in general agreement with most previous assignments except for the assignment of the peak at 646 cm^–1. Previously this was assigned to syndiotactic material, but it is here assigned to a structure consisting of consecutive syndiotactic, isotactic, and syndiotactic placements in a conformation not very distorted from the planar zigzag conformation.     

X-ray diffraction and infrared studies on annealed highly syndiotactic poly(vinyl chloride)

X-ray diffraction scans and infrared absorption spectra for the C-CI stretching region were obtained for a highly syndiotactic poly(vinyl chloride) (PVC) sample made by the urea clathrate method. When the polymer was annealed at a series of increasing temperatures up to 180°C, x-ray diffraction measurements showed that the crystallinity increases steadily with annealing temperature. Even at 50°C an increase above the original value of 63% was detectable and by 180°C it had reached 70% with a further increase to 78% after cooling to ambient temperature. There is a concurrent significant increase in the lateral crystallite dimensions. However, the infrared spectrum did not change, in agreement with the recent prediction of Moore and Krimm that there is no observable band splitting from interchain interaction in crystalline regions, thus indicating that these C-CI bands cannot be used as a measure of crystallinity. The results from computer curve fitting of the spectra suggest that at least 85% of the polymer consists of long planar syndiotactic sequences and there is therefore substantial order along the chain direction. A mechanism for the increase in crystallinity on annealing, involving the lateral ordering of these regular chains, is discussed. Furthermore, as the temperature is raised some amorphous material is converted to a nematic phase, and this may crystallize during the subsequent cooling.     

硫氰基/有机铜锂体系引发MMA阴离子聚合研究

采用有机锂为引发剂,以甲基丙烯酸酯（MMA）类为单体进行阴离子聚合,其副反应较严重,因为在此类单体分子中存在卢碳和羰基碳两个亲核点,引发剂进攻羰基碳则会使链终止,在聚合过程中发生各种副反应,以碱金属（Li,Na,K）为反离子的有机碳负离子化合物,其亲核性较强,倾向于进攻羰基碳,因此甲基丙烯酸酯类单体的阴离子聚合除了采用较大立体阻碍引发剂外。     

茂金属催化丙烯间规聚合的研究进展

间规聚丙烯的结构独特新颖,具有良好的透明性、透气性以及耐辐射性等性能。由间规聚丙烯制成的共混材料,在医疗产品、包装和汽车配件等方面具有巨大的潜在用途。要得到性能优异的商品化间规聚丙烯,就需要在催化剂的选择性、催化剂负载化和聚合工艺等方面做深入研究。本文综述了间规选择性茂金属催化剂及其聚丙烯产品的研发进展,着重介绍了间规选择性茂金属催化剂的发展及其影响催化性能的因素,同时涉及间规聚丙烯的生产工艺以及间规聚丙烯产品的加工应用等方面。     

Thermogravimetric investigations of carbonaceous materials—Syndiotactic polystyrene systems

A system of a syndiotactic polystyrene (s-PS)-carbonaceous material, obtained as a result of syndiotactic polymerisation of styrene in the presence of carbonaceous materials of organic origin of different degree of coalification before and after their ammoxidation, was studied. The initial materials were plum stone waste, brown coal and hard coal. The interactions between the system components were studied by the method of differential scanning calorimetry (DSC). It has been found that the type of the carbonaceous material used determines the thermal effects of the phase transitions in s-PS (detected on thermograms) and the melting point of s-PS. It has been shown that on melting of the syndiotactic polystyrene in the presence of the carbonaceous materials containing a relatively large number of oxide groups, the polymer oxidation reactions occur. This effect does not occur when carbonaceous materials with preliminary ammoxidation are applied.     

Synthesis of a novel syndiotactic poly(macromonomer) consisting of styrene‐terminated polyisoprene macromonomers using half‐titanocene catalysts

Homopolymerization of a styrene‐terminated polyisoprene macromonomer (SIPM) by half‐titanocene catalysts in combination with methylaluminoxane (MAO) was investigated. Polymerization of the SIPM with CpTiCl₃‐MAO as the catalyst was found to proceed readily to give a high molecular weight polymer. ¹H and ¹³C NMR spectra of the poly(SIPM) after ozonolysis of the isoprene side chain revealed that poly(SIPM) is a highly syndiotactic polymer. Syndiotactic poly(SIPM) is soluble in usual solvents in spite of having highly syndiotactic sequences on its main chain and a considerable degree of polymerization.     

Dual roles of alkyl alcohols as syndiotactic‐specificity inducers and accelerators in the radical polymerization of N‐isopropylacrylamide and some properties of syndiotactic poly(N‐isopropylacrylamide)

The effects of simple alkyl alcohols on the radical polymerization of N‐isopropylacrylamide in toluene at low temperatures were investigated. We succeeded in the induction of syndiotactic specificity and the acceleration of polymerization reactions at the same time by adding simple alkyl alcohols such as 3‐methyl‐3‐pentanol (3Me3PenOH) to N‐isopropylacrylamide polymerizations. The dyad syndiotacticity increased with a decrease in the temperature and an increase in the bulkiness of the added alcohol and reached up to 71% at ?60 °C in the presence of 3Me3PenOH. With the assistance of NMR analysis, it was revealed that the alcohol compounds played dual roles in this polymerization system; an alcohol compound coordinating to the N? H proton induced syndiotactic specificity, and that hydrogen‐bonded to the C?O oxygen accelerated the polymerization reaction. The effect of syndiotacticity on the properties of poly(N‐isopropylacrylamide)s was also examined in some detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4450–4460, 2006     

磁场对聚合物立体构型影响的研究(Ⅰ)——聚甲基丙烯酸甲酯

本文研究了在甲基丙烯酸甲酯聚合过程中,磁场对产物中间同立构含量的影响。间同立构含量的测定是采用红外光谱定量法。实验结果表明: (1)聚甲基丙烯酸甲酯的间同立构百分含量S%值随磁场强度的增加按指数关系增加。 (2)聚甲基丙烯酸甲酯的玻璃化温度随磁场强度的增加而增加。 (3)聚甲基丙烯酸甲酯的平均分子量随磁场强度的增加,也按指数关系增加。 (4)通过公式计算了聚甲基丙烯酸甲酯分子链中能连续出现N个间同立构链节的组成几率F_N值。     

用新型茂钛催化剂制备的苯乙烯/丁二烯嵌段共聚物的结构表征

用CpTi(OBz)3/MAO催化体系合成的苯乙烯／丁二烯嵌段共聚合产物经丁酮、甲苯、四氢呋喃、氯仿连续抽提,并用已烷对丁酮的可溶级分进行再抽提;不同级分分别用GPC、^13C -NMR、DSC和WAXD等手段进行分析和表征。发现嵌段共聚物主要存在于氯仿可溶级分中,丁酮可溶级分基本上是无规聚苯乙烯和聚丁二烯组成的混合物（己烷可溶级分为聚丁二烯,不溶级分为无规模聚乙烯）。GPS谱图表明该嵌段共聚反应具有单催化活性中心的聚合特征,^13C-NMR谱图显示该嵌段共聚物分子链由间规聚苯乙链段和聚丁二烯链段组成,WAXD图谱显示嵌段共聚物有较高的结晶度。     

Preparation and (13C)NMR spectroscopy of stereoregular poly(methacrylic acid)

Several procedures for synthesis of stereoregular poly(methacrylic acid) have been examined and the polymer characterized by (¹³C)NMR. Using d⁶ DMSO as solvent for spectroscopy gives better spectra than those previously obtained using aqueous solutions and stereochemical splittings can be resolved in the methyl signals. Free-radical polymerization in toluene solution is a Bernouilli process giving mainly heterotactic/syndiotactic polymer. Polymers produced with free-radical initiation in aqueous solution have a higher, and pH dependent, content of syndiotactic triads. A previously described procedure for producing regular polymers by hydrolysis of poly(trimethylsilyl methacrylate) requires modification to produce isotactic contents of above 90% and does not give truly syndiotactic polymer. In contrast, polymerization with γ-radiation can produce polymers with close to 90% of syndiotactic triads.