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.     

Coiling/uncoiling behaviour of sodium polystyrenesulfonate in 2‐ethoxyethanol–water mixed solvent media as probed using viscometry

Precise measurements of the viscosities of solutions of sodium polystyrenesulfonate in water and in 2‐ethoxyethanol–water mixtures containing varying amounts of 2‐ethoxyethanol have been performed at 308.15, 313.15, 318.15 and 323.15 K. The intramolecular contributions to the reduced viscosities of the polyelectrolyte solutions were obtained through isoionic dilution maintaining the total ionic strengths of the solutions at polyelectrolyte concentrations of 0.0033, 0.0054 and 0.0080 eq L^?1 with sodium chloride. The Huggins constants were also obtained from the experimental data. The influences of the medium and the temperature on the intramolecular contributions to the reduced viscosities as well as on the Huggins constants have been interpreted from the points of view of the conformational characteristics and polyelectrolyte–solvent and polyelectrolyte–polyelectrolyte interactions prevailing in the polyelectrolyte solutions under investigation. Polyion chains were found to coil upon addition of 2‐ethoxyethanol to water or upon an increase of temperature. Thermodynamic affinities for polyelectrolyte–solvent and polyelectrolyte–polyelectrolyte interactions were found to depend greatly on the medium. © 2014 Society of Chemical Industry     

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.     

Effect of primary polymer chain rigidity on intramolecular cyclization and intramolecular crosslinking in free‐radical crosslinking monomethacrylate/dimethacrylate copolymerizations

d‐Bornyl methacrylate (BoMA) was chosen as a typical example of bulky monomethacrylate monomers, the polymerization of which led to the formation of a rigid polymer chain. To discuss the effect of primary polymer chain rigidity on intramolecular cyclization, we compared the solution copolymerization results of BoMA with 1 mol % ethylene dimethacrylate (EDMA; n = 1) and poly(ethylene glycol dimethacrylate) [CH₂?C(CH₃)CO(OCH₂CH₂)_nOCOC(CH₃)?CH₂, n = 9 (PEGDMA‐9)] with those of methyl methacrylate (MMA) with 1 mol % EDMA and PEGDMA‐9; the dependence of the weight‐average degree of polymerization on conversion for the former BoMA copolymerization systems was completely opposed to that for the latter MMA systems, and this was a reflection of a reduced occurrence of intramolecular cyclization caused by the rigidity of the primary polymer chain. The effect of primary polymer chain rigidity on intramolecular crosslinking was discussed through a comparison of both BoMA/EDMA and MMA/EDMA copolymerizations. The correlations of the intrinsic viscosity, root‐mean‐square (rms) radius of gyration, and second virial coefficient with the molecular weight were examined for both BoMA/EDMA (90/10) and MMA/EDMA (90/10) copolymerizations in a dilute solution because microgelation was observed in solution MMA/EDMA (90/10) copolymerization as a reflection of a locally extensive occurrence of intramolecular crosslinking. The logarithmic plots of both the intrinsic viscosity and rms radius of gyration versus the molecular weight for MMA/EDMA copolymerization were compared with those for the corresponding BoMA/EDMA copolymerizations. The second virial coefficients were greater than 10^?5 mol cm³ g^?2 for BoMA/EDMA copolymers, even when the conversion was very close to the gel point, whereas they were quite low, that is, less than 10^?5 mol cm³ g^?2, for an MMA/EDMA copolymer obtained at more than 15% conversion. These were ascribed to a suppressed occurrence of intramolecular crosslinking, a reflection of the lessened flexibility of the polymer main chain and a steric effect due to the bulky d‐bornyl groups. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1086–1093, 2004     

Harnessing irreversible thermal strain for shape memory in polymer additive manufacturing

Shape transformation upon annealing of fused filament fabrication additively manufacturing structures is investigated as a one-way shape memory strategy using commodity thermoplastics. Irreversible thermal strain, which is a measurement of shape transformation upon annealing, is shown to depend on both raster angle and layer thickness, both of which are parameters than can be easily adjusted on most FFF printers. We present an algorithm based on our understanding of the underlying micromechanics of the system that allows for input of desired final dimensions and output the necessary print parameters. We also demonstrate that this approach is extensible to other materials and report more complex shape memory geometries. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48239.     

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。     

Intramolecular Charge Transfer of 1-Aminoanthraquinone and Ultrafast Solvation Dynamics of Dimethylsulfoxide

The intramolecular charge transfer (ICT) of 1-aminoanthraquinone (AAQ) in the excited state strongly depends on its solvent properties, and the twisted geometry of its amino group has been recommended for the twisted ICT (TICT) state by recent theoretical works. We report the transient Raman spectra of AAQ in a dimethylsulfoxide (DMSO) solution by femtosecond stimulated Raman spectroscopy to provide clear experimental evidence for the TICT state of AAQ. The ultrafast (~110 fs) TICT dynamics of AAQ were observed from the major vibrational modes of AAQ including the ν_C-N + δ_CH and ν_C=O modes. The coherent oscillations in the vibrational bands of AAQ strongly coupled to the nuclear coordinate for the TICT process have been observed, which showed its anharmonic coupling to the low frequency out of the plane deformation modes. The vibrational mode of solvent DMSO, ν_S=O showed a decrease in intensity, especially in the hydrogen-bonded species of DMSO, which clearly shows that the solvation dynamics of DMSO, including hydrogen bonding, are crucial to understanding the reaction dynamics of AAQ with the ultrafast structural changes accompanying the TICT.     

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     

Intramolecular Charge Transfer of Curcumin and Solvation Dynamics of DMSO Probed by Time-Resolved Raman Spectroscopy

Intramolecular charge transfer (ICT) of curcumin in dimethyl sulfoxide (DMSO) solution in the excited state was investigated by femtosecond electronic and vibrational spectroscopy. Excited-state Raman spectra of curcumin in the locally-excited and charge-transferred (CT) state of the S₁ excited state were separated due to high temporal (<50 fs) and spectral (<10 cm⁻¹) resolutions of femtosecond stimulated Raman spectroscopy. The ultrafast (0.6–0.8 ps) ICT and subsequent vibrational relaxation (6–9 ps) in the CT state were ubiquitously observed in the ground- and excited-state vibrational modes of the solute curcumin and the ν_CSC and ν_S=O modes of solvent DMSO. The ICT of curcumin in the excited state was preceded by the disruption of the solvation shells, including the breakage of hydrogen bonding between curcumin and DMSO molecules, which occurs at the ultrafast (20–50 fs) time scales.     

Modeling analysis of chain transfer in reversible addition‐fragmentation chain transfer polymerization

The validity of simplifying the reversible addition‐fragmentation chain transfer (RAFT) polymerization as a degenerative chain transfer process was verified in this work. The simplified chain transfer mechanism enabled the direct modeling investigation of chain transfer coefficient in the RAFT polymerization. It also gave the analytical expressions for concentration, chain length, and polydispersity of various chain species. The comparison between the simulations based on chain transfer mechanism and those from general RAFT mechanism showed that this simplified mechanism can accurately predict RAFT polymerization in the absence of side reactions to adduct radicals other than fragmentation. However, significant errors are introduced at high conversion when side reactions to adduct are present. The chain transfer coefficient of RAFT agent is the key factor in RAFT polymerization. The polydispersity is more sensitive to chain transfer coefficient at low conversion. At high conversion, however, the polydispersity is mainly determined by termination, which can be controlled by RAFT agent concentration and the selection of initiator. At last, an analytical equation is derived to directly estimate chain transfer coefficient of RAFT agent from the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

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。     

Dynamics of inertial dewetting

The dynamics of fast dewetting is considered in both unidirectional and axisymmetric dewetting cases. The analysis provides the front and dewetting velocities along with the wave speed (Froude number larger than 1) based on the momentum and continuity equations. The model does not require any fitting parameter. In the unidirectional case, the present model results are direct, while in the axisymmetric case, a simple trial-and-error procedure is required. Culick’s law (derived for the rupture of soap films and extended to unidirectional fast dewetting velocity by other investigators) is found to be a limiting case for both the dewetting and front velocities at small values of the film thickness for both unidirectional and axisymmetric dewetting geometries. The proposed model results show favorable agreement with published experimental front velocity data at large values of the film thickness.     

可逆/不可逆热致变色Schiff碱配合物的合成与性质

合成了双水杨醛缩对苯二胺（L₁）及其与锌（Ⅱ）的配合物（L₁Zn）和双水杨醛缩间苯二胺（L₂）及其与镍（Ⅱ）的配合物（L₂Ni）,利用核磁共振、红外光谱、紫外-可见光谱、荧光光谱和质谱对4种物质的结构和性质进行了表征。结果表明：两种Schiff碱化合物经二价金属离子配位后其荧光光谱均发生了蓝移现象;热激发实验发现L₁Zn具有可逆热致变色性质,而L₂Ni热致变色不可逆,表明它们是一类新型有机热致变色材料。     

Molecular Dynamics at Extended Timescales

The use of short time trajectory fragments to enhance sampling of kinetics is discussed. It is argued that partitioning of phase space with interfaces that are called milestones and conducting a large number of short time trajectories between these interfaces is a highly efficient and accurate method to calculate thermodynamics and kinetics. The method of Milestoning, which is a theory and an algorithm, enables the rapid calculations of fluxes, stationary distributions, and moments of the mean first passage time. It is based on sub-nanosecond trajectories between cell partitions (milestones) that are defined in coarse space. While the method was applied in the past to highly complex systems, we illustrate it here on a pedagogical two-dimensional system using dividers of Voronoi cells as milestones.