EVA-g-VC的结构和动态粘弹性

本文研究了聚乙烯-醋酸乙烯酯(EVA,VAc:14％)与氯乙烯(VC)接枝共聚物(EVA-g-VC)的相结构和分子结构。接枝物EVA-g-VC由游离EVA、均聚PVC和EVA-VC接枝高分子三者组成,EVA呈连续相,PVC呈分散微粒。EVA-g-VC中EVA的含量越高,PVC粒子体积越小。实验结果表明,接枝物中“凝胶”的EVA玻璃化温度,随投料比(VC/EVA)的减小而升高;另外随VC/EVA减小,凝胶中PVC的含量和PVC的分子量也减小。这些结果说明,VC/EVA较小时得到的接枝物中,EVA上VC接枝点的数目较多,而PVC接枝链的长度较短。EVA-VC是不相容两相——EVA和PVC的“粘着剂”,其作用表现在:VC/EVA越小,接枝物中EVA和PVC的玻璃化温度越靠近。     

Monolayers of hydrogen-bonded polymer blends at the air–water interface: poly(vinylacetate)+poly (4-hydroxystyrene)

 The surface pressure (Π) vs surface concentration (Γ_s) curves of the hydrogen-bonded polymer blend poly(vinylacetate)+ poly(4-hydro-xystyrene) (PVAc+P4HS) have been measured at 25 °C onto a water subphase at pH=2.0. While PVAc forms extended monolayers, and the free surface of water is found to be a good solvent for it, P4HS forms compressed monolayers, and the surface is a near Θ-type solvent for it. PVAc and P4HS form miscible non-ideal monolayers until near the collapse pressure through the whole concentration range. The composition dependence of the Π–Γ_s curves is rather complex. Contrary to what might be expected, the addition of PVAc to the blend does not reduce the rigidity of the monolayer until its weight fraction is larger than 0.5. The compressibility data of the P4HS-rich monolayers suggest the existence of a second maximum at high surface coverages, a result already observed in some polysiloxanes. Received: 11 March 1998 Accepted: 7 May 1998     

Polymerization of vinyl compounds in the presence of perfluoroisopropenyl ester

To report a new polymerization reaction phenomenon, this article examines the polymerization of butyl vinyl ether and N‐vinylcarbazole in the presence of 2‐benzoxypentafluoropropene [CF₂?C(CF₃)OCOC₆H₅ or BPFP]. The homopolymer of butyl vinyl ether was produced in the presence of a catalytic amount of BPFP in high yields. N‐Vinylcarbazole, which is a monomer well‐known for producing its homopolymer under cationic polymerization conditions, also yielded its homopolymer in the presence of BPFP. It was concluded that some cationic species would be yielded by the addition of BPFP. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 908–910, 2007.     

Self‐polyaddition of triethylsilyl perfluoroisopropenyl ether

The results on radical self‐polyaddition reactivity of two trialkylsilyl perfluoroisopropenyl ethers, triethysilyl perfluoroisopropenyl ether [CF₂?C(CF₃)OSi(C₂H₅)₃] (FTEE) and dimethylphenylsilyl perfluoroisopropenyl ether [CF₂?C(CF₃)OSi(CH₃)₂C₆H₅] (DMPE), and two perfluoroisopropenyl carboxylates, 2‐butyroxypentafluoropropene [CF₂?C(CF₃)OCOC₃H₇] (BuFPP) and 2‐(methoxyacetoxy)pentafluoropropene [CF₂?C(CF₃)OCOCH₂OCH₃] (MFPP), are described. Radical self‐polyaddition of FTEE afforded a polymer as high as 1.87 × 10⁴ in molecular weight in the presence of radical generators such as benzoyl peroxide and di‐tert‐butyl peroxide. DMPE gave only addition products with initiating radicals. BuFPP and MFPP scarcely yielded even addition products with radical. The mechanism that the self‐polyaddition of FTEE was initiated by the addition of radical onto the perfluoroisopropenyl group followed by a 1,5‐shift to afford a methyl radical that attacked the perfluoroisopropenyl group of another FTEE molecule is proposed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2743–2754, 2003     

A Review of Online Real-Time Process Analyses of Melt-State Polymer Using the Near-Infrared Spectroscopy and Chemometrics

Abstract

This review describes the online process monitoring of the melt-state polymer by near-infrared (NIR) spectroscopy and chemometrics. The spectra of linear low-density polyethylene (LLDPE), random polypropylene (RPP), block polypropylene (BPP), and ethylene-vinylacetate (EVA) copolymer in melt states measured by an online monitoring system with a Fourier transform near-infrared spectrometer are discussed. The calibration models for the density of LLDPE, the content of ethylene copolymers in RPP and BPP, and vinylacetate concentration (VA) in EVA copolymers using partial least squares regression are reported. The continuous monitoring of the LLDPE density at the real plant is described as an example of online monitoring using NIR spectroscopy and chemometrics. For the precise prediction of VA in EVA, a combination method using regression and discrimination was inducted. Three compensation methods for the effect of the temperature change in the RPP and BPP samples are shown. Conventional calibration transfer methods are introduced, and a practical calibration transfer method using two samples and its performance are reported using BPP and RPP spectra. Moreover, the possibility of a calibration correction method using one sample for the realization of long-term traceability is indicated by the example of the relocation.     

PVC/EVA-g-VC共混物的形态与加工条件和性能的关系

PVC/EVA(-14)及 PVC/EVA(-14)-g-VC的等速升温Brabender塑化曲线上有两个扭矩峰,分别标志着EVA和PVC的塑化,对应着共混形态经历的三个变化:(1)EVA塑化——PVC粉粒破碎;(2)EVA呈连续相——PVC集结粒子解体;(3)EVA呈分散相——PVC初级粒子熔化。聚合投料比(VC/EVA)越小,EVA-g-VC的塑化温度和熔体粘性越高,两个扭矩峰靠得越近。实验结果表明,EVA-g-VC与EVA相比,不仅与PVC有更好的相容性,而且有较好的均匀可混性。冲击强度的测定结果表明:EVA连续网——PVC初级粒子结构具有较高的冲击强度。VC/EVA较小时所得EVA-g-VC改性的PVC可在较宽的加工温度范围保持EVA连续网结构和较高的冲击强度。     

Permeation of water through polar and nonpolar polymers and copolymers: Determination of the concentration‐dependent diffusion coefficient

The diffusion and permeation properties of liquid water through different polar and nonpolar polymers and copolymers were studied with a highly sensitive permeameter. The transient permeation fluxes through the polar polymer films could be fitted well only with an exponential equation for the diffusivity concentration dependence; this empirical exponential equation represented the diffusion plasticization effect of water on the materials. For the hydrophobic polyolefins, this exponential equation was no longer valid, and another form of the equation was empirically found to account for the reduction of the water diffusivity with the extent of the permeation. Such a negative plasticization effect might be attributed to the formation of water clusters in the polyolefins. The values of the diffusion coefficient of water in the dry polar polymers were smaller than those in dry polyolefins, but the opposite behavior was found for the permeability because it was much more favorable for water sorption in the polar polymers than in the hydrophobic polyolefins. For the ethylene–vinylacetate copolymers, the plasticization effect of water on its own diffusion was negative for the sample with a low vinyl acetate (VA) content; it became nil at 19 wt % VA and positive at higher VA contents. This increase in the extent of the water sorption with the increase in the VA content led to a steady increase in the water permeability in the poly(ethylene‐co‐vinylacetate) copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1998–2008, 2000     

Interpenetrating Networks Obtained by Crosslinking in the Vinylacetate (VAc)-Triethoxyvinylsilane (VTES)-Tetraethoxysilane (TEOS) System

In the present work the sol-gel process in the ternary system VAc-VTES-TEOS was approached. The monomer that ensures the crosslinking of the obtained networks is VTES, which could react with VAc by free-radical polymerisation and with TEOS by hydrolysis-polycondensation. The early stage evolution of the process was monitored by gas chromatography coupled with mass spectrometry (GC-MS). The gels obtained were characterised by IR spectroscopy, DTA/TG analysis and DSC measurements. Important differences in the gelling process and in the properties of the obtained gels could be noticed, related to the presence of VAc and VTES in the reaction mixtures. The investigation allowed to establish the compositions and the experimental conditions in which gels with high degree of crosslinking could be obtained.     

Non-aqueous PVAc dispersions prepared in a reactive epoxy functionalized PDMS liquid medium

The system vinyl acetate (VAc)/poly(dimethylsiloxane) diglycidylether (PDMS-DGE) is a typical example of two monomers where both components are polymerizable in a “one-pot” procedure by two distinct reaction mechanisms. Non-aqueous dispersions (NAD) are obtained in a first step by free-radical polymerization of the dispersed VAc-PVAc phase. The study of the reaction kinetics has shown that the polymerization rate is mainly influenced by the partition coefficient of VAc between both phases in presence. The colloidal characteristics of the NAD, such as particle size, stability and viscosity were examined in function of monomer and initiator concentrations. Preliminary UV curing tests of the PDMS-DGE phase in the presence of a cationic photoinitiator have shown that PVAc/PDMS two-phase coatings can be obtained, without any solvent emission.     

Mechanism of spherulitic crystallization as deduced from observations of partially crystallized glassy polystyrene

Thin films of isotactic polystyrene partially crystallized from the glassy state were studied in detail by means of transmission electron microscopy and electron diffraction. Initial nucleation and growth stages of spherulitic fibrils (or lamellae) were illustrated clearly by using novel techniques, such as Au decoration, and novel specimens such as thin films containing holes.

Spherulitic nucleation begins with the crystallization of a liquid-crystal-like nodule or a group of these nodules merging to form a spherulitic center. Fibrils or lamellae grow and fan out from the nucleus by additional incorporation of maturing nodules. Proliferation of fibrils is essentially a space-filling process through the crystallization of uncrystallized nodules or nodules that were left behind by growing fibrils which had initiated earlier. The deduced mechanism of spherulitic crystallization leads directly to the formation of interlamellar links between neighboring fibrils. However, no extended-chain-type interlamellar links were revealed by Au decoration.

The application of the mechanism of spherulitic crystallization from the glass to that from the melt is also suggested; it is based primarily on recent studies which show remarkable similarities between structures existing in the glassy and the melt states prior to crystallization.