13C n.m.r. study of solvation mechanisms in the radiation-induced polymerization of vinyl ethers

A ¹³C n.m.r. study of the microstructure of ethyl vinyl ether (EVE) and isopropyl vinyl ether (IPVE) polymers prepared under various experimental conditions and using chemical or γ-ray initiation has been made. Long stereo-sequence assignments were conducted for poly EVE allowing determination of the configurational statistic of propagation in the radiation-induced polymerization of EVE in low polar solvents. Stereo-sequence intensities are found in good agreement with the Markovian model. The results are considered as further support for the occurence of a specific interaction between the growing active centres and the polymer chains. In the case of IPVE polymers much more important overlappings of the resonance patterns are observed thus preventing any similar detailed study.     

Plasma‐modified poly(vinyl alcohol) membranes for the dehydrationof ethanol

Non‐porous poly(vinyl alcohol) (PVA) membranes prepared by a cast‐evaporating technique were covered with an allyl alcohol or acrylic acid plasma‐polymerized layer. The wettability and the surface energy, as well as the chemical nature of the deposit, were assigned by X‐ray photoelectron spectroscopy (XPS) and Fourier‐transform infrared spectroscopy (FTIR). The ability of the modified membranes for dehydrating the water/ethanol azeotropic mixture by pervaporation was studied at 25, 40 and 60 °C. The best selectivity (α = 250 at 25 °C) was obtained in the case of the allyl alcohol plasma treatment. The results obtained are discussed on the basis of the hydrophilicity as well as in terms of the weakly crosslinked superficial layer that favoured the membrane swelling. Copyright © 2003 Society of Chemical Industry     

Synthesis of high-molecular weight poly(vinyl alcohol) by low-temperature emulsifier-free emulsion polymerization of vinyl acetate and saponification

High-molecular weight (HMW) poly(vinyl alcohol) (PVA) was prepared via an emulsifier-free emulsion polymerization of vinyl acetate (VAc) using a redox initiation system in low temperatures, and the subsequent saponification with potassium hydroxide in methanol. The effect of the polymerization conditions on the conversion, molecular weight, and branching degree was investigated. PVA with maximum viscosity-average degree of polymerization (DP) of 8270 could be prepared by saponification of poly(vinyl acetate) (PVAc), with DP of 10,660 obtained at temperature of 10°C, monomer concentration of 30%, potassium persulfate molar ratio to monomer of 1/2000, agitation speed of 160 rpm. The conversion was above 90%. From the emulsifier-free emulsion polymerization of VAc in low temperature, PVAc with HMW and high linearity was effectively prepared, which might be useful for the preparation of high-strength and high-modulus PVA fiber. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

非腈复合引发剂用于乙酸乙烯溶液聚合

以生物乙烯法生产的乙酸乙烯为单体、过氧化月桂酰-十二烷基二甲基叔胺为非腈复合引发剂、甲醇为溶剂进行溶液聚合反应的研究。实验考察了反应温度、反应时间、甲醇用量、引发剂用量对反应产物聚合率和聚合度的影响,采用正交试验优化了乙酸乙烯溶液聚合的反应条件,确定反应因素对聚合率和聚合度影响的相对大小。结果表明,最优的乙酸乙烯溶液聚合条件为:反应温度65℃,反应时间3h,甲醇用量10%,引发剂用量0.010%,获得聚乙烯醇产品的聚合度为3776,聚合率为45.29%。直观分析确定影响聚合率的因素主次顺序为引发剂用量> 反应时间> 甲醇用量> 反应温度;影响聚合度的因素主次顺序为甲醇用量 >引发剂用量 >反应温度 >反应时间。     

Nonaqueous polymerization of vinyl chloride: An environmentally friendly process

Poly(vinyl chloride) (PVC) is produced via a nonaqueous polymerization process in which hexane is used as a diluent. This nonaqueous process can lead to significant energy savings, significant reductions in carbon dioxide emissions, and the elimination of wastewater. Various suspending agents have been used to evaluate their effects on the shape and morphology of PVC grains. The nonaqueous process leads to the formation of PVC grains with higher porosity than that of typical suspension PVC. The bulk density is slightly lower than that of suspension PVC, but the thermal stability seems to be similar. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Graft polymerization of vinyl acetate onto silica

The free‐radical graft polymerization of vinyl acetate onto nonporous silica particles was studied experimentally. The grafting procedure consisted of surface activation with vinyltrimethoxysilane, followed by free‐radical graft polymerization of vinyl acetate in ethyl acetate with 2,2′‐azobis(2,4‐dimethylpentanenitrile) initiator. Initial monomer concentration was varied from 10 to 40% by volume and the reaction was spanned from 50 to 70°C. The resulting grafted polymer, which was stable over a wide range of pH levels, consisted of polymer chains that are terminally and covalently bonded to the silica substrate. The experimental polymerization rate order, with respect to monomer concentration, ranged from 1.61 to 2.00, consistent with the kinetic order for the high polymerization regime. The corresponding rate order for polymer grafting varied from 1.24 to 1.43. The polymer graft yield increased with both initial monomer concentration and reaction temperature, and the polymer‐grafted surface became more hydrophobic with increasing polymer graft yield. The present study suggests that a denser grafted polymer phase of shorter chains was created upon increasing temperature. On the other hand, both polymer chain length and polymer graft density increased with initial monomer concentration. Atomic force microscopy–determined topology of the polymer‐grafted surface revealed a distribution of surface clusters and surface elevations consistent with the expected broad molecular‐weight distribution for free‐radical polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 300–310, 2003     

Thermal characterization of poly(vinyl chloride) samples prepared by living radical polymerization: Comparison with poly(vinyl chloride) prepared by free radical polymerization

Poly(vinyl chloride) (PVC) samples were synthesized by a living radical polymerization (LRP) method and compared with commercial PVC prepared by the conventional free radical polymerization (FRP). The differences were assessed, for the first time, in terms of viscosimetry parameters and thermal analysis. The LRP method used to prepare the PVC‐LRP samples is the only one available to obtain this polymer free of structural defects, being of commercial interest in a view of preparing a new generation of PVC‐based polymer with outstanding performance. The polymerization temperature selected (35°C) to prepare the LRP samples is currently used in the industry to prepare PVC‐FRP grades with moderate to high molecular weight. Since the thermal stability is a direct consequence of the polymer structure, this study is of vital importance to understand the potential of new PVC‐LRP. The thermoanalytical measurements demonstrate an enhanced thermal stability of PVC‐LRP when compared with its FRP counterpart. The PVC‐LRP sample with very low molecular weight reveals a higher thermal stability than the most stable PVC‐FRP sample. It is the first report dealing with thermal analysis of PVC prepared by LRP. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Bulk polymerization of vinyl chloride with half-titanocene/MAO catalyst

Bulk polymerization of vinyl chloride (VC) with Cp^∗Ti(OPh)₃/MAO catalyst was investigated. The bulk polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst proceeded to give poly(vinyl chloride) (PVC) with high molecular weight in good yields. The M_n of the polymer increased in direct proportion to polymer yields and the line passed through the origin. The M_w/M_n of the polymer decreased with an increase of polymer yield. The GPC elution curves were unimodal and the whole curves shifted clearly to the higher molecular weight as a function of reaction time. This indicates that the control of molecular weight can be achieved in the polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst even in bulk. The structure of PVC obtained from the bulk polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst consists of a regular structure. The thermal stability of the polymer obtained with Cp^∗Ti(OPh)/MAO catalyst was higher than that of PVC obtained from radical polymerization and depended on the molecular weight of the polymer. In contrast to that, the initial decomposition temperature of the polymer obtained from a radical polymerization did not depend on the molecular weight. We presumed that the decomposition of the polymer obtained with Cp^∗Ti(OPh)₃/MAO catalyst initiated at the chain end.     

Continuous dosing of fast initiator during vinyl chloride suspension polymerization: Polymerization rate and PVC properties

Continuous dosing of a fast initiator during the suspension polymerization of vinyl chloride has been carried out in a pilot‐scale reactor. The kinetics course of this polymerization and the particle features of the resulting grains were discussed and compared to the conventional polymerization with the same conversion and maximum reaction rate. It was found for the system used that a suitable dosage trajectory allows the reaction rate to remain constant during polymerization. This decreases the polymerization time up to 53% compared with the conventional suspension polymerization, while the molecular weight distribution and molecular weight of the final grains remained almost unchanged. SEM micrographs revealed that PVC grains prepared using this polymerization process had irregularly shaped, uneven particle surfaces and larger particle sizes. The grains also featured high porosity with loosely aggregated smaller primary particles that led to low levels of residual unreacted monomer. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44079.     

Synthesis of well‐defined poly(vinyl ether)‐based macromonomers having pendant glycerols via living cationic polymerization and their application to the preparation of core−shell polymer particles

A new vinyl ether monomer bearing a glycerol pendant moiety protected with an isopropylidene group (2‐(2,2‐dimethyl‐[1,3]dioxolan‐4‐ylmethoxy)‐ethyl vinyl ether, IpGEVE) was designed as the precursor of a novel type of hydrophilic poly(vinyl ether) containing glycerol pendants. It was found that the polymerization of IpGEVE proceeded in a controlled manner, and the protecting groups of isopropylidene moieties could be cleaved with trifluoroacetic acid. Living cationic polymerization of IpGEVE with an initiator bearing a methacryloyl group (VEM‐HCl) and subsequent deprotection of the pendant isopropylidene groups of the resultant precursor afforded a glycerol‐substituted hydrophilic macromonomer MA‐PGEVE. Nearly monodispersed polymer particles in the submicron size range were successfully obtained via dispersion copolymerization of MA‐PGEVE with styrene.© 2013 Society of Chemical Industry     

Synthesis and characterization of greenish‐blue emitting vinyl copolymer containing pyrene and triarylamine moieties

Two fluorescent monomers N‐phenyl‐N‐(4‐vinylphenyl)pyren‐1‐amine (vinyl‐PyPA) and 1‐vinyl pyrene (VPy) were synthesized in good yields. A series of soluble conductive vinyl copolymers P(PyPA‐co‐VPy) containing vinyl‐PyPA and VPy moieties in different composition ratios were prepared by free radical solution polymerization. These copolymers showed high T_g (190?201 °C) and good thermal stability. The photoluminescence emission maxima of the copolymers were all in the range 474.5?478.5 nm, which was similar to the poly(N‐phenyl‐N‐(4‐vinylphenyl)pyren‐1‐amine) (P(PyPA)) (475 nm) but blue shifted compared with poly(1‐vinyl pyrene) (PVPy) (490.5 nm). The lifetime of the copolymers increased from 10.2 to 29.7 ns with an increase in pyrene content. The copolymers had higher quantum yields (0.51) than those of the homopolymers of P(PyPA) (0.48) and PVPy (0.13). The highest occupied molecular orbital of the copolymers remained relatively unchanged from P(PyPA), while the lowest unoccupied molecular orbital varied from ?2.41 eV to ?2.51 eV with an increase in pyrene ratio in the copolymers. The energy bandgaps of the copolymers (from 2.70 eV to 2.81 eV) were smaller than those of P(PyPA) (2.82 eV) and PVPy (3.47 eV). Two polymer light‐emitting diode (PLED) series were attempted including indium tin oxide (ITO) (fluorocarbon (CFx) treated)/P(PyPA‐co‐VPy)/LiF/Al and ITO(CFx treated)/P(PyPA‐co‐VPy)/1,3,5‐Tri(1‐phenyl‐1H‐benzo[d]imidazol‐2‐yl)phenyl (TPBi)/LiF/Al. The results suggested that the PyPA moiety is hole conducting and the PLEDs can achieve high luminance from 650 to 1150 cd m^?2 (at 100 mA cm^?2) only when an electron injecting layer TPBi is employed. © 2013 Society of Chemical Industry     

Semicontinuous emulsion polymerization of vinyl acetate: Effect of ethoxylation degree of nonionic emulsifiers

Poly(vinyl acetate) latices were prepared in the presence of an ammonium persulfate initiator, 10–50 mol of an ethoxylated nonylphenol nonionic emulsifier, and a poly(vinyl alcohol) colloid stabilizer by applying semicontinuous emulsion polymerization (delayed monomer and initiator addition process) in a laboratory scale similar to industrial practice. Two approaches were applied: the molar concentration of the nonionic emulsifier was kept constant and the weight ratios in the polymerization recipe varied or the weight ratios were kept constant. The effects of the change in the ethoxylation degree of the emulsifier to the final latex viscosity, average polymer molecular weight, polymer grafting degree, surface tension of the latex, and the surface free energy of the dried films were investigated. It was determined that the resultant latex viscosity decreases and the viscosity‐average polymer molecular weight increases with increase of the nonionic emulsifier ethoxylation degree. The increase of the ethoxylation degree does not seriously affect the surface tension of the resultant latex or the surface free energy of the dried poly(vinyl acetate) films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 844–851, 2002     

Dehydrochlorination of poly(vinyl chloride) modified with titanium dioxide/poly(ethylene oxide) based paint photocatalysts

The dehydrochlorination of poly(vinyl chloride) (PVC) film samples modified with titanium dioxide (TiO₂)/poly(ethylene oxide) (PEO) based paint photocatalysts [the addition of methyl linoleate (ML) or methyl oleate (MO)] was performed. After 24 h of UV photoirradiation, the sample with TiO₂/PEO showed that there existed a structure with the longest polyene length, whereas that with TiO₂/PEO/ML contained the most polyene structures. The chloroform‐soluble fraction of the sample with TiO₂/PEO contained a poly(vinyl alcohol) (PVA) structure instead of a polyene one and showed a novel method of PVA production via PVC photodegradation. The molecular weight curve of the fraction shifted slightly to a lower molecular weight compared to that without the photocatalyst; this showed that slight polymer chain scission occurred. The ¹H‐NMR and ¹³C‐NMR spectra showed that the content of PVA units was about 20%, and the PVA sequence was blocky. The fraction of the sample with TiO₂/PEO/ML contained the highest methyl group content; this showed that the branch degree was highest as was the polyene content. These highest contents were due to the existence of the grafted ML. Pyrolysis gas chromatography/mass spectroscopy measurements suggested that there existed more polyene and graft units in the chloroform‐insoluble fractions of the samples with TiO₂/PEO, TiO₂/PEO/ML, and TiO₂/PEO/MO, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40760.     

An investigation of precipitation polymerization in liquid vinyl chloride by photon correlation spectroscopy

Simultaneous photon correlation spectroscopy and light transmittance measurements were used to follow changes in the particle size and particle number density of poly(vinyl chloride) (PVC) particles which phase separated in liquid vinyl chloride (VCM) during the early stages of bulk polymerization. The scope and limitations of these techniques for studying dynamic systems are discussed. The nature and extent of interaction forces are deduced from experimental data together with a proposed mechanism for the colloidal stability of PVC gel particles in liquid VCM.     

Ring‐opening metathesis polymerization of dicyclopentadiene catalyzed by titanium tetrachloride adduct complexes with oxygen‐containing ligands

Ring‐opening metathesis polymerization of dicyclopentadiene catalyzed by TiCl₄ · 2L/CH₃Li system [where L is tetrahydropyran (1), dioxane, 2,5‐dimethylfuran, or tetrahydrofurfyl alcohol] is reported. The obtained polymer was characterized by IR and ¹H‐NMR. These catalytic systems effectively promoted the polymerization reaction. Seven influencing factors are discussed. When the aging temperature was 0°C, the aging time was 90 min, the polymerization temperature was 60°C, Li/Ti was 1.5–2, and the monomer/catalyst molar ratio ranged between 30 and 50, the polymerization reaction catalyzed by complex 1 yielded better results within a shorter period of time. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 662–666, 2001     

An experimental investigation of poly(vinyl chloride) emulsion polymerization: Effect of initiator and emulsifier concentrations on polymerization kinetics and product particle size

Effects of concentration changes in initiator species Na₂SO₃, (NH₄)₂S₂O₈ and CuSO₄, and emulsifier, ammonium stearate, on poly(vinyl chloride) (PVC) emulsion polymerization kinetics and on product particle size were experimentally investigated. It was observed that to obtain industrially significant rates and overall conversions, not only an optimum concentration ratio of Na₂SO₃/(NH₄)₂S₂O₈/CuSO ₄ must be used, but also the concentrations of these species must be above certain limits. Increasing the concentration of the emulsifier used did not influence the rate of polymerization, but led to increases in limiting conversions. Product particle size analyses indicate that average particle size is independent of initiator concentration and rate of initiation. An increase in the emulsifier concentration on the other hand appears to lead to an increase in number of particles in the system and thus promotes smaller particle sizes.     

In-situ polymerization of n-butyl acrylate in poly(vinyl chloride)

The in situ polymerization of n-butyl acrylate with poly(vinyl chloride) has been studied. Butyl acrylate was polymerized using a peroxydicarbonate initiator and a thiol chain transfer agent in the presence of poly (vinyl chloride) beads suspended in water. The products were examined, after pressing into sheets, for optical clarity and by dynamic mechanical analysis. It was found that if 10% butyl acrylate was peesent in the mixture homogeneous blends were formed but if 15% or more butyl acrylate was present two phase mixtures were formed. If homogeneous blends prepared as above were reswollen in butyl acrylate, and the latter then polymerized, homogeneous blends containing more poly(butyl acrylate) could be prepared. The interaction parameters between both poly(vinyl chloride' and poly(butyl acrylate) and butyl acrylate were estimated by inverse gas chromatography. Using these and an estimate of the polymer/polymer interaction parameter the three component phase diagram could be qualitatively explained.     

Solid‐state characterization and the thermal properties of stereoregular poly(vinyl chloride) prepared by urea clathrate polymerization

The solid‐state characterization of highly stereoregular poly(vinyl chloride) (PVC) prepared by urea clathrate polymerization was carried out by using various instrumental analyses. The structural differences of PVC appeared most remarkably in solubility to organic solvents, IR, WAXD, and solid‐state ¹³C‐NMR spectra. The value of the glass transition temperature (T_g) was about 90°C, not as high as expected, although its detection was quite difficult. The thermal stability was poor, as evidenced by the easy discoloration of this polymer by heat treatment, which was related to the absence of a termination reaction. Dynamic ESR spectra in the solid state clearly indicate that the radical formation occurs at such a low temperature as 160°C in the initial degradation stage. The degradation characteristics of urea clathrate PVC were critically discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2820–2825, 1999     

Influences of some polymerization conditions on particle properties of suspension poly(vinyl chloride) resin

Effects of polymerization temperature, conversions, and nonionic surfactant on the particle properties of suspension poly(vinyl chloride) (PVC) resins were investigated. It was shown that polymerization temperature has no significant influences on the mean particle size of PVC resin, and that the cold plasticiser absorption (CPA) of resin decreases linearly with the increase of polymerization temperature. Agglomeration of VCM droplets finishes before 20% conversion, and the mean particle size keeps almost constant at later stages of the polymerization process, but the CPA continues decreasing with the increase of conversion. Scanning Electron Microscopy (SEM) micrographs show that the degree of agglomeration of primary particles increases with polymerization temperature and conversion. Addition of nonionic surfactant to the VCM suspension system, as a secondary suspending agent, has a great influence on the particle properties of PVC resin. The particle size and CPA increase as the concentration of nonionic surfactant increases. The nonionic surfactant with a greater HLB value is more effective in raising the mean particle size, but is less effective in raising the CPA. It is considered that the added nonionic surfactant would be absorbed faster on the VCM/water interface than the poly(vinyl alcohol) (PVA), which was used as the primary suspending agent. Because the colloid protection ability of the nonionic surfactant is less than that of PVA, droplets become less resistant to coalescence, and the mean particle size of the final PVC resin increases consequently. The increase of porosity is caused by the combined effects of increased coalescence of VCM droplets and the nonionic surfactant's steric effect inside the droplets. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1544–1552, 2002