几种不可逆加成-断裂型链转移剂在苯乙烯乳液聚合中的研究

研究了基于不可逆加成-断裂链转移机理的3种分子质量调节剂对苯乙烯乳液聚合的影响.主要考察了3种链转移剂对乳液聚合速率、乳胶粒子大小以及聚苯乙烯数均相对分子质量的影响.链转移剂的内在动力学、扩散和自由基解吸附行为决定了其分子质量调节效率、对聚合速率的影响程度和乳胶粒子大小.链转移常数高的α-苯磺酰甲基丙烯酸乙酯使苯乙烯乳液聚合速率下降明显,乳胶粒子粒径分布较宽,且聚合后期不能有效调节聚苯乙烯分子质量 ;而链转移常数相对较小的2,3-二氯丙烯对聚合速率和乳胶粒子粒径的影响轻微,并能全程控制聚苯乙烯分子质量 ;分子质量较大的正十二烷基-2-苯基烯丙基硫则因在乳液体系中的扩散较慢,难以调节聚苯乙烯的分子质量.     

Dynamics of polymer molecules using neutron spin—echo

The dynamics of single polymer chains have been investigated in dilute solution and in the melt using the neutron spin—echo technique. In dilute solution the intramolecular motion is described to a first approximation by that for a Rouse chain incorporating hydrodynamic interactions (Zimm). It is characterised by an inverse correlation time which may be normalised by temperature, solvent viscosity and segment size, and which for long chains varies as Q³ at small scattering angles (Q is the change in wavevector on scattering). At very low Q vectors the predicted ‘universal’ regime is observed, but over most of the accessible range chemical structure also becomes important. For short chains, deviations from this Q³ behaviour are associated with overall molecular diffusion. In the melt, chain entanglements come into play and modify the simple Rouse-type motion. The correlation functions are described by a combination of Rouse motion over short distances and times and a long-time slow-motion predicted by the reptation model of melt dynamics.     

Mechanical behavior of a single polymer chain in a non-solvent

Mechanical properties of a single polystyrene chain in mixtures of dioxane and methanol were measured with AFM. The effect of the solubility of the surrounding liquid on mechanical behavior of a polymer chain was examined. In good and Θ solvents, the force-extension curves exhibit a freely jointed chain (FJC)-like trend with good reproducibility. In a non-solvent, the profile of force-extension curve was dependent on the extension speed: an FJC-like nature emerged at the lower speed of 200 nm/s while saw-toothed curves were obtained at the higher speed of 2000 nm/s. The shape of saw-toothed curves varied from measurement to measurement. A force relaxation was also observed in the non-solvent under a fixed extension distance after 2000 nm/s extension. The mechanical behavior in non-solvents suggests that inhomogeneous deformation of a PS chain occurs due to reduction of the chain mobility.     

Interpenetration of two polymer chain globules

Molecular dynamics was performed in a model system of two chain globules so that a process of the two globules merging was just simulated. It was found that this merging process was recognized as two stages, the wetting stage and the interpenetration stage. The interpenetration does not occur to partially encountered segments of the two globules, even though the chain segments are in the molten state. In the first stage, the touched two globules change their shapes rapidly from a sphere to a half-ball respectively. This obviously shows that the change in shape is mastered by the surface tension. In the second stage, the interpenetration happens to the two-chain sphere with an initial structure of each chain in a half-ball shape. A different molecular mechanism of chain diffusion has been found for this system. It is the chain loop crawling among the globule surface. Characterization of the interpenetration process was carried out by several means of analyzing the trajectory files. It was found that in the interpenetration stage there is a fast evolution and a lentitude period. The interpenetration is a conformational entropy driving process, and takes a half time for the lentitude period, which regards just 15% of total free energy difference.     

A method to determine the relative value of the barriers of carbon chain growth and termination in Fischer-Tropsch synthesis: elementary reaction kinetics for chain growth

A method is established, by which the difference of the reaction activation barriers of carbon chain growth and termination in Fischer-Tropsch (FT) synthesis can be determined from experiments. A FT synthesis is carried out on Fe/Zn catalyst. We apply the method to analyze the experimental result and obtain the difference of reaction activation barriers of carbon chain growth and termination of -olefins on the catalyst.     

Dynamics of Capillary-Viscous Dewetting

Abstract

In this work the kinetics of partial dewetting was investigated for the case where dewetting, driven by capillary forces, is resisted by viscous effects. Both axisymmetric and unidirectional dewetting cases were considered. The analysis extended previous investigations using the Brochard-Wyart and de Gennes (1992) relation, having a cut off of molecular size beyond which the continuum approach is no longer valid, to obtain the dynamic contact angle condition at the receding contact line, and an analogous relation at the advancing contact line at the constant liquid film thickness side. The dynamic contact angle conditions at both sides of the ridge along with the viscous dissipation in the system were considered. A general formulation that can be used for different dynamic contact angle relations was developed. Simplification led to an analytical solution for the dynamic contact angle, size of the dry zone, and width of the ridge. The validity of the approximation was considered. The dynamics of dewetting for the simplified formulation was found to be consistent with the one developed by de Gennes et al. (2010). The dewetting dynamics based on Hoffman, and Brochard-Wyart and de Gennes contact angle relations were together found to yield results in good agreement with available experimental data over the whole viscosity range. The use of the receding contact angle in the model was found to be of primary importance for the case involving contact angle hysteresis.     

Environmental stress cracking and crazing in polymers in terms of irreversible thermodynamics

The processes in environmental stress cracking and crazing in polymers are analysed in terms of the irreversible thermodynamics. The thermodynamic potential of the system composed of the polymer matrix at a flaw tip region and its environmental liquid is constructed as a function of the concentration of the liquid migrated in the matrix and the dilative stress due to stress concentration. A state of the system is represented by a point in the thermodynamic potential diagram. The paths of the state shifts leading to failure in the diagram are governed by the shapes of the thermodynamic potential curves, the liquid concentrations giving the potentials a minimum, the critical concentration and the breakdown concentrations here introduced. Various kinetic data of environmental stress cracking in low density polyethylenes can be understood by the unified picture. The predictions of the theory are also consistent with the reported kinetic nature of crazing.     

扩链剂联用技术对PET扩链反应的影响

通过对PET扩链反应前后的特性粘数 [η]和羧基 [COOH]值的比较 ,讨论了扩链剂联用条件下不同扩链剂种类、用量以及加入方式对于扩链反应的影响。实验结果表明 ,扩链剂联用对于PET树脂增粘是一个良好的方法 ,可使扩链产物的特性粘数由 0 .62dL g增至 1.1dL g ,同时 [COOH]含量降至很低 ;少量荧光剂同时加入显著改善扩链产物的色泽。在一定的联用条件下扩链产物的热稳定性可保持在较好水平。     

Role of chain length in degradation process (chain breakdown)

The role of molecular weight of a chain in the chain breakdown in diluted solution at a constant concentration of chain molecules and constant temperature is discussed theoretically using the methods of the theory of the activated complex and kinetics of cooperative processes. The reaction starts at the certain molecular weight of the chain. The chain breakdown is the flat increasing function of the chain molecular weight. This function has a limit when chain molecular weight approaches infinity. Such dependence is explained by the increase of flexibility (following two theories) and increase of extra entropy of molecules of different sizes (following kinetics of cooperative processes. Unequal reactivity of chemically identical active centers links to the dependence of chain flexibility on the location of the more flexible part (place of reaction) of the chain. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1810–1817, 2002; DOI 10.1002/app.10356     

不可逆示温涂料的发展及应用

分别从功用、发展状况、研制情况及应用情况等方面讲述了国内单、多变色不可逆示温涂料的发展概况。同时以单、多变色不可逆示温涂料在航空发动机表面温度的成功测试案例,讲述了不可逆示温涂料广阔的应用前景。     

Synthesis and properties of a new crosslinkable polymer containing benzoxazine moiety in the main chain

Using difunctional phenolic and amine compounds, a new polymer with benzoxazine groups in the main chain has been synthesized through the Mannich reaction of a phenol, formaldehyde, and an amine. ¹H and ¹³C nuclear magnetic resonance spectroscopies, Fourier transform infrared spectroscopy, size exclusion chromatography, and elemental analysis are used to characterize the resulting polymer. Polymer with molecular weight of approximately 10,000 Da is obtained. The resultant polymer has a moderately broad polydispersity index. The thermal properties of the polymer have also been studied by differential scanning calorimetry and thermogravimetric analysis.     

Dynamics and self-organization of catalytic systems

The kinetics of a catalytic reaction is frequently formulated in terms of simple concepts of the Langmuir type. Apart from limitations arising from the non-uniformity of the catalyst's surface and from the coverage dependence of the rate constants, several other complications may come into play. These may arise on the quantum level where energy flow between the various degrees of freedom may cause failure of simple transition state theory, as well as on the continuum level where formulation of rate equations in terms of coupled non-linear differential equations may give rise to a rich scenario of spatio-temporal self-organization, including kinetic oscillations, chaos, and formation of concentration patterns. Several of these phenomena are illustrated by selected examples.     

Kinetics of polymer surface fluorination: Elemental and plasma-enhanced reactions

E.s.c.a. spectra of surface fluorinated polyethylene, poly(vinyl fluoride), and poly(vinylidene fluoride) are reported. Two reaction environments were used in this study: exposure to elemental fluorine and immersion in a glow discharge plasma. The systematic variation of fluorine composition in the polymer phase is shown to have a dramatic effect on the kinetics of the elemental reaction and little effect in the plasma reaction.     

Overall effectiveness factor of heterogeneous-homogeneous chain reactions with one limited species in a catalytic slurry reactor

The analysis of the overall effectiveness factor for the reaction system involving heterogeneous-homogeneous chain reactions at low concentration of one species is studied. A more general theoretical analysis for estimating the overall effectiveness factor of reaction systems which can be a heterogeneous-homogeneous chain reaction system at low concentration of one species in a slurry reactor is presented, incorporating all the transport parameters. The concepts of overall effectiveness factors for reactions have been extended from the traditional heterogeneous reaction system to the heterogeneous-homogeneous chain reaction system. The effects of reaction mechanism and kinetic models on the overall effectiveness factor are also proposed. Comparisons of the overall effectiveness factor for a slurry reactor with or without considering the reaction mechanism are also obtained.     

酶催化反应动力学的荧光法研究进展

介绍了酶催化反应的动力学模型,综述了荧光法在酶催化反应动力学研究中的应用进展,简要分析了存在的问题及研究前景.     

Assessment of the sliding link model of chain entanglement in polymer networks

The stress-strain relations derived from the sliding link model of chain entanglement proposed by Ball et al. (Polymer 1981, 22, 1010) are compared with experimental results. There is good agreement with Ogden's empirical treatment of several results obtained previously from general pure strain tests on rubber vulcanizates. New uniaxial data for random polyisoprene networks at various stages from the gel point indicate that a significant fraction of trapped entanglements does not behave as the sliding links of the model but gives the same contribution to the stress as the chemical cross-links.     

温度对巯基封端液态聚硫橡胶结构的影响

利用凝胶渗透色谱和核磁共振波谱分析,通过研究聚硫橡胶在温度变化时分子结构发生的变化,推断出温度变化时聚硫橡胶链交换反应模式。     

环氧聚合型扩链剂对POM/TPU共混体系的相容作用

使用环氧聚合型扩链剂作为POM/TPU共混物的相容剂,研究其对POM/TPU共混物的流变性能、力学性能、结晶性能和耐热性的影响。结果表明,添加环氧聚合型扩链剂后,POM/TPU共混物的熔体流动速率先升高然后降低;冲击强度提高,断裂伸长率大幅提高;结晶度先升高后降低;热变形温度提高。     

Fast switching ferroelectric liquid crystal side chain polymer

Two products were isolated at a result of esterification of acrylic acid with 4-[4-(n-hydroxyundecanyloxy)phenyl] benzoic acid (5) One is 4-[4-(n-acryloloxy-undecanyloxy)phenyl] benzoic acid (6), and the other is 4-{4-[n-(3-acryloloxy-propionyloxy)undecanyloxy]phenyl}benzoic acid (7) which containts two molecules of acrylic acid. Compound7 is obtained unexpectedly and still unknown in the literature. Its identification is confirmed by the isolation and characterization of the monomer9. The mesogenic monomers8 and9 which were synthesized from 4-hydroxyphenyl 2(S)-[2(S)-methylbutoxylpropionate (4) and the corresponding acrylates6 and7 exhibit the enentiotropic Sc* and S_A phases. The Sc^* phase temperature range is up to 31 °C. The spontaneous polarization and response time for the monomers8 and9 is 97 and 16 nC/cm² as well as 90 and 64 µs respectively. It us the liquid crystal side chain polymer11, not10, which is switchable in the presence of an electric field. The spontaneous polarization of 36 nC/cm² and the response time of 3.1 ms is obtain from the new polyacrylate.