Two-stage Polymerization Process Research Articles

Morphology and properties of PP in-reactor alloys prepared with a MgCl2/TiCl4/diisobutyl phthalate/phosphate tris-methylphenyl ester catalyst system

A series of polypropylene(PP)/poly(ethylene-co-propylene) in-reactor alloys with different ethylene con-tents was prepared through a two-stage polymerization process using a MgCl2/TiCl4/diisobutyl phthalate/phosphate tris-methylphenyl ester catalyst system. The ethylene content, particle shape, fractured surface, and glass-transition temperature(Tg) of the obtained PP in-reactor alloys were characterized by means of nuclear magnetic resonance, scanning electron microscopy(SEM), and dynamic mechanical analysis(DMA). The ethylene content of the PP alloys increased from 2.34% to 26.69% when the propylene/ethylene feed ratio was increased from 66/34 to 54/46(molar ratio). Morevoer, the increment in ethylene content increased the notched Izod impact strength of the resulting PP al-loys. The impact strength of the PP alloy with an ethylene content of 26.69% was 55.8 kJ/m2, which is 12.7 times that of isotactic polypropylene. The results of DMA and SEM analysis reveal that ethylene-propylene random copoly-mer(EPR) in the PP alloy has a low Tg of ca.‒50 °C and a high interface compatibility with the PP matrix. The ex-cellent impact performance of the PP alloy can be attributed to the uniform dispersal of EPR in the alloy particles and PP matrix.

Emulsion Hydrolytic Polymerization of Caprolactam

Emulsion hydrolytic caprolactam polymerization method is proposed as an alternative to existing instrumental-technological solutions to production of fibre-forming polyamide-6 in a melt. The conditions for implementing a single- and a two-stage polymerization process and characteristics of the synthesized polymers are given. It is shown that emulsion polymerization at a temperature below the polymer melting point can be used to produce high-molecular polyamide 6 with a near-equilibrium content of low-molecular compounds.

Effect of phase separation on overall isothermal crystallization kinetics of PP/EPR in‐reactor alloys

AbstractIn the present work, the effect of phase separation on overall isothermal crystallization kinetics of two polypropylene/ethylene‐propylene random copolymer (PP/EPR) in‐reactor alloys was investigated. It is found that at lower crystallization temperatures (Tc), the overall crystallization rate decreases with increasing phase separation temperature (Ts). This is attributed to the lower linear spherulitic growth rate incurred by the lower PP content in the PP‐rich phase at higher Tss. In contrast, at higher Tcs, quenching from a higher Ts to Tc promotes nucleation as a result of more dramatic concentration fluctuation, leading to a faster overall crystallization rate. The overall crystallization rate of the PP/EPR in‐reactor alloy prepared by multi‐stage sequential polymerization process (MSSP) is retarded by increasing phase separation time (ts). However, prolonging phase separation time has little effect on the crystallization rate of the sample prepared by two‐stage polymerization process (TSP). This result can be attributed to the different phase separation rates of these two samples. The SAXS result confirms that at higher Tc, phase separation in the melt before crystallization can retard crystallization, when compared with the directly quenched samples. It is also found that the phase‐separated PP/EPR in‐reactor alloys exhibit a larger long period because of more amorphous phases included between the lamellar crystals. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preparation and characterization of spherical PP/PB alloys with MgCl2-supported Ziegler-Natta catalyst

Polypropylene (PP)/polybutene-1 (PB) alloys within reactor were prepared by MgCl2-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology. First, propylene homo-polymerizations were carried out to form isotactic polypropylene (iPP) particles containing active catalyst. Then, butene-1 was subsequently polymerized to form polybutene-1 phase inside the iPP particles. Finally, iPP/PB alloys with spherical shape and adjustable PB content were synthesized. The catalytic activity and catalytic stereospecificity of the Z-N catalyst in the two-stage polymerization process are discussed. The composition and physical properties of the PP alloys were characterized by FT-IR, 13C-NMR, SEM, DSC and XRD. It was found that the in-reactor PP alloys are mainly composed of PP and PB with a little amount of poly(buteneco-propylene) random copolymers and poly(butene-block-propylene) block copolymers. SEM measurements verified that the PB phases with size in the range of 300–400 nm dispersed in the PP matrix uniformly. The incorporation of PB upon the PP matrix affects the properties of final products greatly.

Simulação numérica aplicada para avaliar o efeito da pré-polimerização no comportamento de reatores tubulares

O presente estudo utiliza um modelo matemático fenomenológico para simular um sistema de polimerização contínuo em dois estágios. Este sistema é composto por um reator contínuo tipo tanque agitado (CSTR), para pré-polimerização do monômero (primeiro estágio), associado em série a um reator tubular para conduzir a reação até elevados valores de conversão (segundo estágio). Um modelo detalhado, considerando variações axiais e radiais, assim como operação não-isotérmica, foi utilizado para simular o comportamento do reator tubular em diferentes situações. Um modelo de caracterização também foi desenvolvido para fornecer estimativas do peso molecular médio e do índice de polidispersão do polímero. Os resultados mostram que reações de polimerização conduzidas em sistemas contínuos de dois estágios fornecem um polímero com propriedades menos heterogêneas do que um polímero obtido em um sistema reacional composto por apenas um reator tubular. Além disso, quanto maior a viscosidade da mistura reacional alimentada ao reator tubular, mais homogêneo é o polímero obtido.

Thermoresponsive nanostructured poly(N-isopropylacrylamide) hydrogels made via inverse microemulsion polymerization

The synthesis of nanostructured poly(N-isopropylacrylamide) (polyNIPA) hydrogels by a two-stage polymerization process is reported here. The process involves the synthesis of slightly crosslinked polyNIPA nanoparticles by inverse (w/o) microemulsion polymerization; then, these particles are dried, cleaned and dispersed in an aqueous solution of NIPA and a crosslinking agent (N,N-methylene-bis-acrylamide or NMBA) and polymerized to produce the nanostructured hydrogels. Their swelling and de-swelling kinetics, volume phase transition temperatures (T VPT) and mechanical properties at the equilibrium swollen state are investigated as a function of the weight ratio of polyNIPA particles to monomer (NIPA). The nanostructured gels exhibit larger equilibrium water uptake, faster swelling and de-swelling rates and similar T VPT than those of the conventional ones; moreover, the elastic and Young moduli are larger than those of the conventional hydrogels at similar swelling ratios. The fast swelling and de-swelling kinetics are explained in terms of the controlled inhomogeneities introduced by the method of synthesis.

Polymerizable Living Free Radical Initiators as a Platform To Synthesize Functional Networks

Photopolymerizations of multifunctional monomers afford spatial and temporal control of cross-linked network formation whereas living radical polymerizations provide a means to synthesize well-defined architectures from monovinyl monomers. By combination of these technologies in a two-stage polymerization process, a novel method is developed to synthesize functional polymer networks, and supporting results are provided for preparing controlled polymer grafts within photo-cross-linked networks. To demonstrate the concept of internal grafting, an alkoxyamine living radical initiator (for nitroxide-mediated polymerization, NMP) and a tertiary bromide initiator (for atom-transfer radical polymerization, ATRP) were functionalized with a methacrylate group and either was copolymerized with mono- and divinyl methacrylic monomers during the initial network formation step. Activation of the living radical initiators within styrene-swollen networks resulted in controlled molecular weight polystyrene grafts covalently bound to the photo-cross-linked methacrylic networks. To demonstrate the applicability of this technology for synthesizing functional networks, hydrogels with nitroxide groups were first photopolymerized, and different concentrations of acetoacetoxy, (i.e., ketoester) functionality were subsequently grafted within the loosely cross-linked networks. When the grafted networks were swollen in aqueous solutions containing Fe3+, the cations coordinated with the grafted ketoester moieties. In general, this robust technology could be applied to a wide array of monomers and functional groups to control the chemical, physical, and mechanical properties of the final grafted network for application in sensors, catalysis, separations, and combinatorial chemistry platforms.

Control of particle morphology and film structures of carboxylated poly ( n butylacrylate)/poly (methyl methacrylate) composite latex particles

Particles with a soft (s) core of poly ( n-butyl acrylate)/poly (methyl methacrylate) (PBA/PMMA) copolymer and a hard (h) shell of PMMA were synthesized via a two-stage polymerization process. Two synthesis parameters were investigated: (i) the phase ratio of the core and the shell; and (ii) the compatibility of the two phases. The s/h phase ratio was varied from 100:0 to 0:100. The compatibility between the two phases was changed by (i) using acrylic acid (AA); (ii) by using pure PBA as core material; and (iii) by cross-linking the shell. Particle morphology was characterized by atomic force microscopy (AFM) on freeze-dried and on tempered single particles. The degree of coverage was found to depend on the shell content and the phase compatibility. The results are in good agreement with findings from transmission electron microscopy and solid state NMR given in Acta Polymerica [50 (1999) 347]. The experimental results are compared to predictions from simulation work on the particle morphology based on thermodynamic and kinetic considerations. The second part of the paper focuses on the phase distribution and the film morphology of films formed by the structured particles. Phase distribution at the surfaces, degree of film formation and the phase distribution in the bulk are characterized by AFM, cross-correlated and compared to the findings regarding particle structure in the first part of the paper. This approach is to our knowledge unique regarding its completeness and new in its methodology. The microscopic results concerning the bulk, the single particle and the surface properties are correlated to macroscopic properties like the minimum film forming temperature, pendulum hardness and gloss.

Microstructured Polyacrylamide Hydrogels Prepared Via Inverse Microemulsion Polymerization

The synthesis by a two-stage polymerization process of microstructured polyacrylamide hydrogels with large swelling capacity and improved mechanical properties is reported. First, crosslinked polyacrylamide particles of nanosize scale are made by inverse microemulsion polymerization. These particles are then dried and redispersed in an aqueous solution of acrylamide and polymerized in the presence of a crosslinking agent. The microstructured hydrogels, in contrast to transparent conventional polyacrylamide hydrogels, are translucid due to the presence of the dispersed particles. The swelling capacity of these hydrogels increases as the particle content increases and their Young and elastic moduli (at equilibrium swelling) diminish only slightly. Mechanical tests disclose that the microstructured hydrogels have larger Young moduli than conventional hydrogels with an identical degree of swelling.

Molecularly imprinted nanoparticles prepared by core-shell emulsion polymerization

Submicron core-shell polymer particles, with molecularly imprinted shells, were prepared by a two-stage polymerization process. Particles of this type, prepared with a cholesterol-imprinted ethyleneglycol dimethacrylate shell and in the absence of porogen, were found to be 76 nm in diameter with a surface area of 82 m2 g−1. Cholesterol uptake from a 1 mM solution in isohexane was measured at both 10 and 30 mg mL−1, with the imprinted polymer showing considerable binding (up to 57%). Imprinted but not hydrolyzed and hydrolyzed nonimprinted polymers showed very low uptakes (≤4.5%) and a phenol-imprinted polymer showed reduced binding (36%) under the same conditions. Imprinted shells were also prepared over superparamagnetic polymer cores and over magnetite ferrocolloid alone. The cholesterol binding to magnetic particles was very similar to that of equivalent nonmagnetic materials. Magnetic particles could be sedimented in as little as 30 s in a magnetic field. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1851–1859, 2000

Synthesis and properties of poly(ether imide)s derived from 2,7-bis(3,4-dicarboxyphenoxy)naphthalene dianhydride and various aromatic diamines

A naphthalene unit-containing bis(ether anhydride), 2,7-bis(3,4-dicarboxyphenoxy)naphthalene dianhydride, was prepared in three steps starting from the nucleophilic nitrodisplacement reaction of 2,7-dihydroxynaphthalene and 4-nitrophthalonitrile in N,N-dimethylformamide (DMF) solution in the presence of potassium carbonate followed by alkaline hydrolysis of the intermediate bis(ether dinitrile) and subsequent dehydration of the resulting bis(ether diacid). High-molar-mass aromatic poly(ether imide)s were synthesized using a conventional two-stage polymerization process from the bis(ether anhydride) and ten aromatic diamines. The intermediate poly(ether amic acid)s had inherent viscosities of 0.95–2.67 dL/g. The films of poly(ether imide)s derived from two rigid diamines, that is, p-phenylenediamine and benzidine, crystallized and embrittled during the thermal imidization process. The other poly(ether imide)s belonged to amorphous materials and could be fabricated into transparent, flexible, and tough films. These poly(ether imide) films had yield strengths of 91–115 MPa, tensile strengths of 89–136 MPa, elongation to break of 11–45%, and initial moduli of 1.7–2.2 GPa. The Tgs of poly(ether imide)s were recorded in the range of 222–256°C depending on the nature of the diamine moiety. All polymers were thermally stable up to 500°C, with 10% weight loss being recorded above 540°C in air and nitrogen atmospheres. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2281–2287, 1997

Heterogeneous latices as binders in porous particle structures

Heterogeneous carboxylated styrene-butadiene (S/Bu) latices were prepared by a two-stage polymerization process, using three seeds of polystyrene with different molecular weights. The second-stage polymer was a copolymer with a fixed S/Bu-ratio of 1 and a methacrylic acid (MAA) content of either 1 or 10 wt %. It has been found that the morphology of the films made from these latices influenced the modulus in the rubbery region of these films. The heterogeneous latices were used as binders in porous structures based on micron-sized kaolin particles. Such structures are typically employed as paper coatings. Polyester substrates were coated with aqueous suspensions containing the kaolin particles and the heterogeneous latex. The coatings were dried at room temperature, which corresponds to the rubbery region of the latex films. It was found that a higher modulus (which is determined here by the morphology of the latex film) in the rubbery region of the films was associated with coating layers with higher porosity, greater light scattering ability, and higher coating gloss. This is interpreted as being the result of a retarded shrinkage of the coating layers during the drying of these structures due to the increase in modulus of the latex films. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 661–670, 1997