Effect Of Polymerization Conditions Research Articles

Graft polymerization of vinyl monomers onto nanosized alumina particles

To enhance the interfacial interaction in alumina nanoparticles filled polymer composites, an effective surface modification method was developed by grafting polystyrene and polyacrylamide onto the particles. That is, the alumina surface was firstly treated with silane, followed by radical grafting polymerization in aqueous or non-aqueous systems. Results of infrared spectroscopy and dispersiveness in solvents demonstrated that the desired polymer chains have been covalently bonded to the surface of the alumina particles. They also greatly changed their surface characteristics. In addition, effects of polymerization conditions, including ways of monomer feeding, concentrations of monomer and initiator, and reaction time, on the grafting reaction were presented. It was found that the growing polymer radicals and/or the grafted polymer chains had a blocking effect on the diffusion of radicals or monomers towards the surface of nanoalumina. This was due to the fact that the interaction between the solvent and the grafted polymers was weaker than that between the grafted polymers and the nanoparticles. 2002 Elsevier Science Ltd. All rights reserved.

Polyethylene Made with In Situ Supported Ni-Diimine/SMAO: Replication Phenomenon and Effect of Polymerization Conditions on Polymer Microstructure and Morphology

The catalyst prepared by supporting in situ 1,4-bis(2,6-diisopropylphenyl)acenaphthenediiminenickel(II) dichloride (1) on silica–methylaluminoxane (SMAO) has high activity for ethylene polymerization, although it is less active than the unsupported system 1/MAO. No external alkylaluminum cocatalyst needs to be added to the in situ supported system. Short chain branches are produced without addition of α-olefin comonomer, due to the chain-walking mechanism. Ethylene pressure and polymerization temperature affect the degree of short chain branch formation. At constant ethylene pressure, when the polymerization temperature rises, the short chain branch content also increases. For a given ethylene pressure, there is a threshold polymerization temperature above which polymer particle agglomeration starts to occur. For the conditions investigated herein, from 30 to 50°C the morphology of the polymer particles replicates that of the support. At 55°C, polyethylene starts to become soluble in the reaction medium, and therefore morphological control is gradually lost. Above 70°C, only soluble polymer is produced. Similar results are observed by keeping the temperature constant and changing the ethylene pressure.

The Effect of Polymerization Conditions on the Density and Tg of Bisphenol-A and Hexafluoroisopropylidene-Containing Polybenzoxazines

The volumetric expansion of bisphenol-A and aniline-based benzoxazine (BA-a) has been studied by comparing the room temperature density of the cured BA-a under different polymerization conditions with the amorphous BA-a monomer. The glass transition temperatures (Tg) of BA-a at various degrees of polymerization have been investigated by differential scanning calorimetry (DSC). The degrees of conversion at different polymerization temperatures were compared with the respective glass transition temperatures. It was found that substantial development of Tg occurs at low degrees of conversion. A fluorinated polybenzoxazine was synthesized from the ring-opening polymerization of hexafluoroisopropylidene-containing benzoxazine monomer. The properties of the fluorine-containing polymer were compared to those of nonfluorinated polybenzoxazine. Fluorine incorporation had a profound effect on the glass transition temperature of polybenzoxazine. The thermal stability also improved upon fluorination.

Controllable radical copolymerization of styrene and methyl methacrylate using 1,1,2,2‐tetraphenyl‐1,2‐bis(trimethylsilyloxy) ethane as initiator

AbstractCopolymerization of styrene (St) and methyl methacrylate (MMA) was carried out using 1,1,2,2‐tetraphenyl‐1,2‐bis (trimethylsilyloxy) ethane (TPSE) as initiator; the copolymerization proceeded via a “living” radical mechanism and the polymer molecular weight (Mw) increased with the conversion and polymerization time. The reactivity ratios for TPSE and azobisisobutyronitrile (AIBN) systems calculated by Finemann–Ross method were rSt = 0.216 ± 0.003, rMMA= 0.403 ± 0.01 for the former and rSt= 0.52 ± 0.01, rMMA= 0.46 ± 0.01 for the latter, respectively, and the difference between them and the effect of polymerization conditions on copolymerization are discussed. Thermal analysis proved that the copolymers obtained by TPSE system showed higher sequence regularity than that obtained by the AIBN system, and the sequence regularity increased with the content of styrene in copolymer chain segment. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1474–1482, 2001

The synthesis of high molecular weight polybutene-1 catalyzed by Cp??Ti(OBz)3/MAO

A new stereoregular polybutene-1 was synthesized with a novel catalyst precursor η5-pentamethyl cyclopentadienyl titanium tribenzyloxide (Cp★Ti(OBz)3) and methylaluminoxane (MAO). The effects of polymerization conditions on the catalytic activity, molecular weight and stereoregularity of the products were investigated in detail. It was found the catalyst exhibited highest activity of 91.2 kgPB mol Ti−1 h−1 at T = 30 °C, Al/Ti = 200. The catalytic activity and molecular weight were sensitive to the Al/Ti (mole/mole), polymerization temperature; they also depended on the Ti concentration. The molecular weight of the products increased with decreasing temperature. The structure and properties of the polybutene-1 were characterized by 13C NMR, GPC, DSC and WAXD. The result showed the microstructure of polybutene-1 extracted by boiling heptane was stereoregular, whereas the ether-soluble fraction was atactic. The molecular weight of polybutene-1 was over one million g mol−1 and its molecular weight distribution ( M w/ M n) was from 1.1 to 1.2. © 2001 Society of Chemical Industry

Features of Preparing the Butyl Acrylate–Acrylonitrile Copolymer by Radiation-Induced Emulsion Polymerization

Some specific features of the radiation-induced emulsion copolymerization of butyl acrylate and acrylonitrile and radiation-induced crosslinking of the resulting copolymer in the latex form were studied. The effect of polymerization conditions on the polymerization rate and the molecular mass of the polymer was determined. The copolymer was shown to undergo efficient crosslinking in the latex form by the action of γ-radiation. The radiation-chemical yield of crosslinking sites (G) and the average molecular mass (Mc) of chain segments between two adjacent network junctions were determined.

Effect of polymerization conditions on the microstructure of a liquid crystalline copolyester

Effect of polymerization conditions on the microstructure of a liquid crystalline copolyester

Effect of Low-Temperature Solution Polymerization Conditions of Acrylonitrile on the Molecular Characteristics of Polyacrylonitrile

Acrylonitrile (AN) was solution-polymerized in dimethyl sulfoxide (DMSO) and tertiary butyl alcohol (TBA) at 30,40 and 50°C using a low temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN), and effects of polymerization conditions were investigated in terms of molecular structures of polyacrylonitrile (PAN). Low polymerization temperature by adopting ADMVN proved to be successful in obtaining PAN of high molecular weight with smaller temperature rise during polymerization. Through a polymerization of AN in DMSO at 30°C, PAN having weight-average molecular weight (M w ) of 931,000 was obtained, whose polydispersity index of 1.89. For the same polymerization conditions, DMSO was slightly superior to TBA in increasing molecular weight of PAN. In addition, DMSO was superior to TBA in diminishing molecular structural defects such as enaminonitrile structure in PAN polymerized, indicating that differences in polymerization and termination rates due to a different polymerization mechanisms using two polymerization solvents. The M w , linearity, molecular structural regularity, and whiteness were higher with PAN polymerized at lower temperatures.

Studies of crosslinked styrene-alkyl acrylate copolymers for oil absorbency application. II. Effects of polymerization conditions on oil absorbency

Crosslinked styrene–acrylate copolymers were synthesized and evaluated by swelling properties for oil-absorbency application. The effect of various polymerization conditions (crosslinking agent concentration, initiator concentration, monomer concentration, and polymerization temperature) were studied through oil-absorption tests using kerosene oil. The oil absorbency was influenced mainly by the degree of crosslinking and the hydrophobicity of the copolymer units. The effect of moisture and the types of acrylate were also investigated. The copolymer with a longer alkyl acrylate had higher oil absorbency in the order of stearyl acrylate (SA) > lauryl acrylate (LA) > 2-ethylhexyl acrylate (EHA). The oil absorbency of the lauryl methacrylate (LMA) copolymer was higher than that of the LA copolymer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 914–920, 2000

Preparation of polytetrahydrofuran monomethacrylate macromonomers by cationic ring-opening polymerization of tetrahydrofuran

Polytetrahydrofuran monomethacrylate (MA-PTHF) macromonomer was prepared by cationic ring-opening polymerization(CROP) of tetrahydrofuran (THF) using boron trifloride etherate (BF3 · OEt2) as initiator and epichlorohydrin (ECH) as promoter. Two kinds of transfer agents were used: methacrylic acid (represented as TA1), and a mixture of methacrylic acid and sodium methacrylate (represented as TA2). The effects of polymerization conditions on molecular weight and molecular weight distribution of macromonomers were studied in this article, when the composition of reactants was kept constant. Under the same conditions, the molecular weight of macromonomer using TA2 is lower than that using TA1, which indicates that TA2 is more active than TA1. The molecular weight of MA-PTHF macromonomer varies with the polymerization time before transfer agents were added (T1), but molecular weight distribution remains constant. When T1 is limited in 30 min, the apparent number-average molecular weight of MA-PTHF increases significantly with the increase of T1, and ranges from 5000 to 18,000. Hence, the molecular weight of MA-PTHF macromonomer can be controlled by varying T1. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 810–815, 2000

Effect of polymerization conditions on the microstructure of a liquid crystalline copolyester

The melt polycondensation of mixtures of sebacic acid (S), 4,4′-diacetoxybiphenyl (B), and 4-acetoxybenzoic acid (H), carried out for the synthesis of semiflexible liquid–crystalline copolyesters referred to as SBH 1 : 1 : x, has been studied with the aim of clarifying the effect of the reaction conditions on the microstructure and the thermal properties of the products. It has been shown that the segregation of a liquid–crystalline phase within the polymerizing mixture, coupled with the thermodynamic tendency of the two phases to undergo compositional differentiation as polymerization proceeds, is responsible for the formation of blocky, rather than ideally random, copolyesters with poor processibility, when the mole ratio of H to the other two monomers is higher than x ≈ 1.90. The results of this study have shown that this unwanted effect can be considerably limited by carrying out the polycondensation at a relatively high temperature from the very beginning, rather than by the standard technique involving progressive heating of the reaction mixture, thus allowing the production of SBH copolyesters with a higher degree of aromaticity. The results are discussed in terms of the relative rates of the condensation reactions, which are responsible for chain growth, and of the concurrent acidolysis and esterolysis reactions leading to copolyester sequence reorganization. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 141–150, 2000

Polymerization of lactides and lactones: VII. Ring-opening polymerization of lactide by rare earth phenyl compounds

Ring-opening polymerization of D,L-lactide has been initiated with rare earth phenyl compound in bulk and solution. These rare earth phenyl initiators can give high yield and high molecular weight poly(D,L-lactide) (PLA) products. The effects of polymerization conditions, such as reaction time, reaction temperature, monomer/initiator molar ratio on the polymerization have been discussed. The results show that reaction conditions have great influence on the yield and molecular weight of PLA. High molecular weight of PLA is usually obtained in the case of lower M/I molar ratio. The resulting PLA was elaborated in microspheres, and the degradation test in vitro was carried out in pH 7.4 buffer solution at 37°C.

Influence of the catalyst and polymerization conditions on the long‐chain branching of metallocene‐catalyzed polyethenes

A study was made on the effects of polymerization conditions on the long-chain branching, molecular weight, and end-group types of polyethene produced with the metallocene-catalyst systems Et[Ind]2ZrCl2/MAO, Et[IndH4]2ZrCl2/MAO, and (n-BuCp)2ZrCl2/MAO. Long-chain branching in the polyethenes, as measured by dynamic rheometry, depended heavily on the catalyst and polymerization conditions. In a semibatch flow reactor, the level of branching in the polyethenes produced with Et[Ind]2ZrCl2/MAO increased as the ethene concentration decreased or the polymerization time increased. The introduction of hydrogen or comonomer suppressed branching. Under similar polymerization conditions, the two other catalyst systems, (n-BuCp)2ZrCl2/MAO and Et[IndH4]2ZrCl2/MAO, produced linear or only slightly branched polyethene. On the basis of an end-group analysis by FTIR and molecular weight analysis by GPC, we concluded that a chain transfer to ethene was the prevailing termination mechanism with Et[Ind]2ZrCl2/MAO at 80 °C in toluene. For the other catalyst systems, β-H elimination dominated at low ethene concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 376–388, 2000

Influence of the catalyst and polymerization conditions on the long-chain branching of metallocene-catalyzed polyethenes

A study was made on the effects of polymerization conditions on the long-chain branching, molecular weight, and end-group types of polyethene produced with the metallocene-catalyst systems Et[Ind]2ZrCl2/MAO, Et[IndH4]2ZrCl2/MAO, and (n-BuCp)2ZrCl2/MAO. Long-chain branching in the polyethenes, as measured by dynamic rheometry, depended heavily on the catalyst and polymerization conditions. In a semibatch flow reactor, the level of branching in the polyethenes produced with Et[Ind]2ZrCl2/MAO increased as the ethene concentration decreased or the polymerization time increased. The introduction of hydrogen or comonomer suppressed branching. Under similar polymerization conditions, the two other catalyst systems, (n-BuCp)2ZrCl2/MAO and Et[IndH4]2ZrCl2/MAO, produced linear or only slightly branched polyethene. On the basis of an end-group analysis by FTIR and molecular weight analysis by GPC, we concluded that a chain transfer to ethene was the prevailing termination mechanism with Et[Ind]2ZrCl2/MAO at 80 °C in toluene. For the other catalyst systems, β-H elimination dominated at low ethene concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 376–388, 2000

Syndiospecific polymerization of styrene based on dichlorobis(1,3-diketonato)titanium/methylaluminoxane catalyst system: effects of substituents on catalyst activity

Dichlorobis(substituted-1,3-diketonato)titanium complexes 4a–e have been synthesized and were combined with methylaluminoxane as cocatalyst to be employed in the polymerization of styrene. The polystyrenes produced have high syndiotacticities of 94.0–98.2%. The substituents at either 2- or 1,3-positions of 1,3-diketones can noticeably influence catalyst activities. The catalytic activities of 4a–c bearing 2-substituents and 4e bearing 1,3-diphenyl groups are tenfold higher than that of 4d bearing 1,3-dimethyl groups. The effects of polymerization conditions on the catalyst activities and the syndiotacticities of the polystyrene produced have been examined. © 2000 Society of Chemical Industry

Effects of ethylene polymerization conditions on the activity of SiO2-supported zirconocene and on polymer properties

The effects of polymerization conditions were evaluated on the production of polyethylene by silica-supported (n-BuCp)2ZrCl2 grafted under optimized conditions and cocatalyzed by methylaluminoxane (MAO). The Al : Zr molar ratio, reaction temperature, monomer pressure, and the age and concentration of the catalyst were systematically varied. Most reactions were performed in toluene. Hexane, with the addition of triisobutilaluminum (TIBA) to MAO, was also tested as a polymerization solvent for both homogeneous and heterogeneous catalyst systems. Polymerization reactions in hexane showed their highest activities with MAO : TIBA ratios of 3 : 1 and 1 : 1 for the homogeneous and supported systems, respectively. Catalyst activity increased continuously as Al : Zr molar ratios increased from 0 to 2000, and remained constant up to 5000. The highest activity was observed at 333 K. High monomer pressures (≈ 4 atm) appeared to stabilize active species during polymerization, producing polyethylenes with high molecular weight (≈ 3 × 105 g mol−1). Catalyst concentration had no significant effect on polymerization activity or polymer properties. Catalyst aging under inert atmosphere was evaluated over 6 months; a pronounced reduction in catalyst activity [from 20 to 13 × 105 g PE (mol Zr h)−1] was observed only after the first two days following preparation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1987–1996, 1999

Synthesis and properties of unsaturated polyoxyethylene and its graft copolymers with styrene

The unsaturated polyoxyethylene (PEO) was synthesized by copolymerization of ethylene oxide with allyl glycidyl ether in toluene using bimetallic-oxo-alkoxide as a catalyst. The effects of polymerization conditions on conversion and intrinsic viscosity of the copolymer were studied. The unsaturated copolymer was characterized with infrared spectra, 1H NMR, and wide-angle X-ray diffraction. The relationship between crystallinity of the copolymers and conductivity of their LiClO4 complexes were investigated. The copolymer with ∼ 65 wt % PEO content exhibits a room temperature conductivity of 1 × 10−4 S cm−1 at a molar ratio of EO/Li = 20. The unsaturated PEO was graft-copolymerized with styrene using 2,2′-azobis(isobutyronitrile) as initiator in toluene, with grafting efficiency ∼ 50%. The purified graft copolymer was characterized with infrared spectra, 1H NMR, and wide-angle X-ray diffraction, and was shown to have good emulsifying properties and a phase-transfer catalytic property. LiClO4 complex of the graft copolymer with 70 wt % PEO content exhibits a room temperature conductivity approaching 1 × 10−4 S cm−1 at molar ratio of EO/Li = 20/1. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2417–2425, 1998

Synthesis and properties of unsaturated polyoxyethylene and its graft copolymers with styrene

The unsaturated polyoxyethylene (PEO) was synthesized by copolymerization of ethylene oxide with allyl glycidyl ether in toluene using bimetallic-oxo-alkoxide as a catalyst. The effects of polymerization conditions on conversion and intrinsic viscosity of the copolymer were studied. The unsaturated copolymer was characterized with infrared spectra, 1 H NMR, and wide-angle X-ray diffraction. The relationship between crystallinity of the copolymers and conductivity of their LiClO 4 complexes were investigated. The copolymer with ∼ 65 wt % PEO content exhibits a room temperature conductivity of × 10 -4 S cm 1 at a molar ratio of EO/Li = 20. The unsaturated PEO was graft-copolymerized with styrene using 2,2'-azobis(isobutyronitrile) as initiator in toluene, with grafting efficiency ∼ 50%. The purified graft copolymer was characterized with infrared spectra, 1 H NMR, and wide-angle X-ray diffraction, and was shown to have good emulsifying properties and a phase-transfer catalytic property. LiClO 4 complex of the graft copolymer with 70 wt % PEO content exhibits a room temperature conductivity approaching 1 × 10 4 S cm 1 at molar ratio of EO/Li = 20/1.

Low temperature suspension polymerization of vinyl acetate using 2,2′-azobis(2,4-dimethylvaleronitrile) for the preparation of high molecular weight poly(vinyl alcohol) with high yield

To obtain high molecular weight (HMW) poly(vinyl acetate) (PVAc) with high conversion and high linearity for a precursor of HMW poly(vinyl alcohol) (PVA), vinyl acetate (VAc) was suspension-poly-merized using a low-temperature initiator, 2,2′-azobis (2,4-dimethyl-valeronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior and molecular structures of PVAc and PVA prepared by saponifying PVAc were investigated. On the whole, the experimental results well corres-ponded to the theoretically predicted tendencies. Suspension polymerization was slightly inferior to bulk polymerization in increasing molecular weight of PVA. In contrast, the former was absolutely superior to the latter in increasing conversion of the polymer, which indicated that the suspension polymerization rate of VAc was faster than the bulk one. These effects could be explained by a kinetic order of ADMVN concentration calculated by initial-rate method and an activation energy difference of polymerization obtained from the Arrhenius plot. Suspension polymerization at 30 °C by adopting ADMVN proved to be successful in obtaining PVA of HMW (number-average degree of polymerization (P n)): (4200–5800) and of high yield (ultimate conversion of VAc into PVAc: 85–95%) with diminishing heat generated during polymerization. In the case of bulk polymerization of VAc at the same conditions, maximum P n and conversion of 5200–6200 and 20–30% was obtained, respectively. The P n, lightness, and syndiotacticity were higher with PVA prepared from PVAc polymerized at lower temperatures.

Molecular imprint polymers as highly selective stationary phases for open tubular liquid chromatography and capillary electrochromatography.

Chiral separations employing molecular imprint polymer (MIP) stationary phases in both open tubular liquid chromatography (OT-LC) and capillary electrochromatography (OT-CEC) are demonstrated. MIPs are highly crosslinked polymers containing spatial and functionality memory of template molecules which provide a higher degree of selectivity when used as stationary phases for chromatographic separations. Thin films of molecular imprinted polymers bonded to the inner walls of 25 microm ID fused-silica capillaries were prepared using an in situ polymerization technique developed in our laboratory that allows the use of conventional fused-silica capillaries with polyimide outer coatings. The success rate in preparing such open tubular columns was about 70%. Methacrylic acid and 2-vinyl pyridine were chosen as functional monomers, and either ethylene dimethacrylate or trimethylol propane trimethacrylate was used as the crosslinker. Toluene was employed as the porogen. Effects of polymerization conditions on column preparation and chromatographic performance were studied. Enantiomeric separations of D- and L-dansyl phenylalanines were achieved in both OT-LC and OT-CEC modes with good selectivity and efficiencies. Both types of separations may be performed on the same column using a single commercial instrument.