The formation of polymerizable tubules

We have been investigating the crystallization behavior of the phospholipid amphiphile, 1,2 bis (10, 12-tricosadiynol)-sn-glycero-3-phosphocholine, DC_8,9PC, which forms both vesicles and hollow tubules as well as Langmuir Blodgett monolayers and multilayers. This material has polymerizable diacetylene groups in equivalent positions on the two hydrocarbon tails. The direct crystallization from solution of this amphiphile has been studied using different solvent mixtures and temperatures. The Langmuir Blodgett technique was also used to compress and orient the tubules.     

THEORETICAL ANALYSIS OF KINETICS OF NONISOTHERMAL CRYSTALLIZATION OF POLYMERS

The classical crystallization theories proposed by Avrami, Evans, and Mandelkern wereextended to the nonisothermal situation. The expressions derived from the classical equations canbe expressed in either the differential form or the integral form. A method was provided so as toobtain the parameters characterizing the crystallization rate and mechanism from DSC curves withseveral constant heating or cooling rates. The rate constants of crystallization obtained from bothisothermal and nonisothermal curves of poly(ethylene terephthalate)were compared.     

STRUCTURE EVOLUTION OF POLYMER CHAINS FOR NECKING FORMATION IN HIGH-SPEED FIBER SPINNING PROCESS

Finite element method is used to simulate the high-speed melt spinning process,based on the equation system proposed by Doufas et al.Calculation predicts a neck-like deformation,as well as the related profiles of velocity,diameter, temperature,chain orientation,and crystallinity in the fiber spinning process.Considering combined effects on the process such as flow-induced crystallization,viscoelasticity,filament cooling,air drag,inertia,surface tension and gravity,the simulated material flow behaviors are consistent with those observed for semi-crystalline polymers under various spinning conditions.The structure change of polymer coils in the necking region described by the evolution of conformation tensor is also investigated.Based on the relaxation mechanism of macromolecules in flow field different types of morphology change of polymer chains before and in the neck are proposed,giving a complete prospect of structure evolution and crystallization of semi-crystalline polymer in the high speed fiber spinning process.     

Analysis of Equilibrium and Kinetics of Chromium-Fluoride Complexation from Spectroscopic Data via Chemometrics Methods

IntroductionStudies on reversible kinetic systems are consi-dered as a hotspot of chemical and biochemical kineticresearches[1,2]. Of late, some researches have been fo-cused on the simultaneous optimization of the obverseand reverse rate constants[3,4].H…     

Polymeric pH indicators immobilized PVA membranes for optical sensors of high basicity based on a kinetic process

Two kinds of polymeric pH indicators PPF (phenolphthalein-formaldehyde product) and CPF (o-cresolphthalein-formaldehyde product) immobilized cross-linked poly(vinyl alcohol) membranes (PPF-PVA and CPF-PVA) for optical intermittent determination of high basicity ([OH⁻] = 1-8 M) based on a kinetic process were developed. In our previous work, we had demonstrated that PPF-PVA and CPF-PVA could perform the determination of high pH values from pH 10.0 to 14.0. Here the discoloring kinetic behaviors of PPF-PVA and CPF-PVA were compared with those of free phenolphthalein, o-cresolphthalein and thymolphthalein. Experimental results and theoretical analysis indicated that the response behaviors of the optodes’ membranes in concentrated NaOH solutions were diffusion-independent and still complied with the pseudo-first-order kinetics. In addition, two data analysis methods for determination were presented. One was directly based on the reduced absorbance; the other was based on the discoloring kinetic constant. It was found that the latter could perform a rapid (60 s) and reliable (relative standard deviation: 2.6%) determination for high basicity. These kinds of optodes can be used repeatedly when they are immersed in low-pH solutions to regain the protonated form after each determination.     

Immobilization of α-amylase in vinyl-polymer-based interpenetrating polymer networks

Semi-interpenetrating polymer networks (IPNs) of poly(ethylene glycol), poly(vinyl alcohol) and polyacrylamide were prepared as a support for enzyme immobilization and kinetic studies were performed for the immobilization of -amylase. The effect of IPN composition on the extent of immobilization was investigated and the percentage of relative activity of the immobilized enzyme was evaluated as a function of the chemical architecture of the IPNs, pH and temperature, taking starch as a substrate. The kinetic constants and the maximum reaction velocity were also evaluated. The IPNs were characterized by IR spectral analysis.     

Crystallization of poly(N-methyldodecano-12-lactam) in blends with poly(styrene-stat-acrylic acid)

Crystallization behaviour of blends of poly(N-methyldodecano-12-lactam) (PMDL) with statistical copolymer poly(styrene-stat-acrylic acid) (PSAA) has been studied by the DSC and WAXD methods. The blend films prepared from dioxane solutions were crystallized at laboratory temperature for five days. Approximate crystallinities of as-prepared neat lower- PMDL 5 and higher-molecular weight PMDL 45 were 28% and 19%, respectively. With increasing PSAA content in the blends the crystallinities decreased sharply. The melting point of the primary crystalline structure of PMDL showed a decreasing dependence on PSAA content in the blends, confirming miscibility of the PMDL-PSAA pair. Recrystallization was strongly suppressed in the blends. The lower-melting endotherm appearing at about 10-15 °C above the crystallization temperature was attributed to melting to less perfect structures formed during secondary crystallization. In neat PMDL, the extent of secondary crystallization was approximately 5-10%. In the blends containing 20% PSAA approximate relative proportion of secondary crystallites on total crystallinity was 40% and 60% for the blends with PMDL 5 and PMDL 45, respectively. WAXD measurements did not reveal any change in crystal modification on blending. Increased T_g in blends of flexible PMDL cannot play a significant role in suppression of primary in favour of secondary crystallization. This was attributed to low mobility of PMDL chains due to dilution effect and specific interactions with the amorphous copolymer component, and, in case of the higher-molecular-weight PMDL, a greater involvement of entanglements. Higher T_g of blends was involved in retardation of non-isothermal crystallization on cooling and subsequent cold crystallization.     

A competitive particle nucleation mechanism in the polymerization of homogenized styrene emulsions

The effects of concentrations of surfactant (sodium lauryl sulfate [SLS]) and initiator (sodium persulfate [SPS]) on the polymerization of homogenized styrene emulsions, stabilized by SLS/lauryl methacrylate (LMA) or SLS/stearyl methacrylate (SMA), were studied. The rate of polymerization increases with increasing [SLS] or [SPS]. In addition to monomer droplet nucleation, the formation of particle nuclei in the aqueous phase (homogeneous nucleation) plays a crucial role in the polymerization kinetics. In comparison with the LMA containing polymerization system, monomer droplet nucleation becomes more important when the more hydrophobic SMA was used as the costabilizer. Furthermore, the degree of homogeneous nucleation increases with increasing [SPS].     

CF3C(O)F水合作用的热力学和动力学理论研究

由于氟氟烃（CFCs）对大气臭氧层有破坏作用，人们拟以另外的化合物来代替它，CF3CX2H（X＝H，CI，F）可能是一类合适的取代物．但人们对它及其反应产物对大气的影响还不清楚.CFaC（0）F是CFaCX。H大气光氧化过程的终产物之一[1－3］，其在大气中的后继反应行为将直接关系到CF2     

Synthesis and crystallization behaviors of poly(styrene-b-isoprene-b-ε-caprolactone) triblock copolymers

The triblock copolymers, poly(styrene-b-isoprene-b-ε-caprolactone)s (PS-b-PI-b-PCL) have been synthesized successfully by combination of anionic polymerization and ring-opening polymerization. Diblock copolymer capped with hydroxyl group, PS-b-PI-OH was synthesized by sequential anionic polymerization of styrene and isoprene and following end-capping reaction of EO, and then it was used as macro initiator in the ring-opening polymerization of CL. The results of DSC and WAXD show big effect of amorphous PS-b-PI on the thermal behaviors of PCL block in the triblock copolymers and the lower degree of crystalline in the triblock copolymer with higher molecular weight of PS-b-PI was observed. The real-time observation on the polarized optical microscopy shows the spherulite growth rates of PCL₂₇, PCL₃₂₈ and PS-b-PI-b-PCL₃₄₄ are 0.71, 0.46 and 0.07 μm s⁻¹, respectively. The atomic force microscopy (AFM) images of the PS₉₀-b-PI₆₆-b-PCL₂₈ show the columns morphology formed by it’s self-assembling.