Binary Initiator System Research Articles

Preparation and Application of Zwitterion Modified Starch Catalyzed by HRP‐ACAC Binary System

AbstractEnzymatic modification, compared with traditional starch (St) chemical modification methods, avoids using toxic solvents and toxic catalysts. The horseradish peroxidase (HRP), being the most commonly employed natural green initiator, has found extensive application in starch grafting modification as a substitute for chemical initiators. HRP‐catalyzed grafting of starch with vinyl zwitterionic monomers has not been reported. Here, modified starch (St‐PSBMA) is first synthesized by grafting zwitterionic sulfobetaine [2‐(Methacryloyloxy)ethyl]dimethyl‐(3‐sulfopropyl) (SBMA) onto starch by HRP/Acetylacetone(ACAC) binary initiation system catalyzed. The modified starch‐based hydrogel is then prepared by the repeated freeze‐thaw method. Compared with native starch‐based hydrogels, which bind water molecules only through hydrogen bonding, the ability of modified starch‐based hydrogels to bind water molecules is enhanced by ionic solvation. The modified starch hydrogels also have excellent antiprotein adsorption and antibacterial properties due to the presence of a strong hydration layer. The modified starch‐based hydrogel also has excellent sensitivity and stability when used as a sensor for detecting joint motion. The binary HRP initiating system, employed in this study instead of the traditional three‐component HRP initiating system, offers a novel and promising approach for grafting modification of starch without the need for strong oxidant hydrogen peroxide.

Improved silane grafting of high-density polyethylene in the melt by using a binary initiator and the properties of silane-crosslinked products

This work aimed at finding optimum conditions for producing high-density polyethylene (HDPE) with improved silane grafting while maintaining the overall process efficiency. The silane-grafted product was then crosslinked utilizing water as the crosslinking agent. The properties of the samples before and after silane curing were analyzed using differential scanning calorimetry, thermogravimetric analysis, heat distortion temperature, and tensile testing. In the work, vinyltrimethoxysilane-grafted HDPE has been prepared in the melt by reactive extrusion. The effects of single and binary initiator systems, and of extrusion conditions, on silane grafting and undesirable PE self-crosslinking have been investigated. The use of binary initiators (i.e. benzoyl and dicumyl peroxide mixture) successfully led to an HDPE with improved level of grafting and diminished amount of gel from crosslinking side reaction. Results of the swelling factor, in combination with the gel content of the silane-cured products, showed that different crosslink network structures (loose or tight networks) formed during the progress of the crosslink reaction. A tight network was formed after the maximum swelling factor was reached. The structure of the crosslink network affected the tensile and heat aging properties of the materials greatly. The samples of tight networks were able to withstand the high heat of 132 °C which is close to the melting temperature of HDPE. Only 10 % reduction in tensile properties was observed for the crosslinked samples after heat aging.

Effects of molecular weight on thermal responsive property of pegylated poly-l-glutamates

We investigated the ring opening polymerization (ROP) of di- and tri-ethylene glycol monomethyl ether functionalized L-glutamate N-carboxyanhydrides (NCAs) using hexamethyldisilazane (HMDS) as primary initiator and 1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD) as co-initiator. The binary initiator system afforded a living ROP for these pegylated NCAs, and a series of homopolypeptides with controlled molecular weight (MW) and low polydispersity were obtained. We then systematically studied the helical content and clouding point (CP) dependence on polypeptide MW using circular dichroism (CD) spectroscopy and turbidity measurements, respectively. We found that the helical content of both homopolypeptides increased with MW, but the triethylene glycol functionalized poly-L-glutamate (poly-L-EG3Glu) intended to form more stable α-helical structure than diethylene glycol functionalized counterpart (poly-L-EG2Glu) at similar MW. Accordingly, the CP of poly-L-EG2Glu with known end group has strong dependence on its helical content, which is essentially determined by MW. Our results suggested that the thermal responsive properties of these unique pegylated poly-L-glutamates not only rely on their chemical structure but also on their secondary structures, which is different from conventional thermal responsive polymers.

Potassium enolates of N,N‐dialkylamides as initiators of anionic polymerization

AbstractStable potassium enolates of N,N‐diethylacetamide [α‐potassio‐N,N‐diethylacetamide (1)], N,N‐diethylpropionamide [α‐potassio‐N,N‐diethylpropionamide (2)], and N,N‐diethylisobutyramide [α‐potassio‐N,N‐diethylisobutyramide (3)] were prepared by the proton abstraction of the corresponding N,N‐diethylamides with diphenylmethylpotassium (Ph2CHK) or potassium naphthalenide in THF. The relative nucleophilicity of 1–3 was estimated to be in the order of 1 < 3 < 2 from the results of the alkylation reaction with methyl iodide. N,N‐diethylacetamide transferred its α‐proton to 2 quantitatively in THF at 0 °C, whereas no reaction occurred between N,N‐diethylisobutyramide and 2; this indicated the relative basicity to be 1 < 2 ∼ 3. Anionic polymerizations of N,N‐diethylacrylamide (DEA) and methyl methacrylate were quantitatively initiated with 2 in THF at −78 °C, whereas the initiation efficiencies of 2 for styrene and 2‐vinylpyridine were about 2 and 67%, respectively. The initiation of DEA with 1–3 at −78 or 0 °C in THF gave poly (DEA)s having broad molecular weight distributions (MWDs; Mw/Mn = 2) and ill‐controlled molecular weights. In contrast, poly(DEA)s of narrow MWDs (Mw/Mn < 1.2) and predicted Mn's were obtained with 2 in the presence of diethylzinc (Et2Zn) at −78 °C, whereas the initiations with 1/Et2Zn and 3/Et2Zn at −78 °C resulted in poor control of the molecular weights. At the higher temperature of 0 °C, all the binary initiator systems (1–3/Et2Zn) induced controlled polymerizations of DEA in terms of the conversion, molecular weight, and MWD. The poly(DEA)s produced with 1–3/Et2Zn at 0 °C showed mr‐rich configurations (mr = 76–89%), as observed for the poly(DEA) generated with Ph2CHK/Et2Zn. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1260–1271, 2007

Anionic polymerization of N,N-dimethylacrylamide with thienyllithium and synthesis of block co-polymers of isobutylene and N,N-dimethylacrylamide by site transformation of chain ends

The anionic polymerization of N,N-dimethylacrylamide (DMAAm) was carried out in THF with a binary initiator system prepared from thienyllithium and the Lewis acids triethylaluminium (Et3Al), diethylzinc (Et2Zn) or triethylborane (Et3B). Polymerizations proceeded in a homogeneous manner and gave polymers having controlled molecular weights. However, in presence of alkoxides the polymerization resulted in polymers insoluble in THF, even when using Et3Al. A synthetic route for the synthesis of polyisobutylene-b-PDMAAm was developed by combining living carbocationic and anionic polymerizations. Thiophene end-capped polyisobutylene (PIB-T), prepared by cationic polymerization, was metalated with n-butyllithium in THF at −40°C. The resulting stable macrocarbanion (PIB-T−, Li+), in conjunction with Lewis acids, was used to initiate the living anionic polymerization of DMAAm, resulting in a new amphiphilic block co-polymer PIB-b-PDMAAm. The molecular structure was characterized by size exclusion and adsorption chromatography and NMR, and the micellisation in aqueous solution was characterized by fluorometry and dynamic light scattering.

Synthesis and Characterization of a Diblock Copolymer of Methyl Methacrylate and Vinyl Acetate by Successive Photo-Induced Charge Transfer Polymerization Using Ethanolamine as the Parent Compound

A diblock copolymer consisting of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) with hydroxyl group at one end is prepared by successive charge transfer polymerization (CTP) under UV irradiation at room temperature using ethanolamine and benzophenone as a binary initiation system. The diblock copolymer PMMA-b-PVAc could be selectively hydrolyzed to the block copolymer of poly(methyl methacrylate) and poly(vinyl alcohol) (PVA) using sodium ethoxide as the catalyst. Both copolymers, PMMA-b-PVAc and PMMA-b-PVA, are characterized in detail by means of FTIR and 1 H NMR spectroscopy, and GPC. The effect of the solvent on CTP and the kinetics of CTP are discussed.

Continuous production of solid polystyrene in back‐mixed and linear‐flow reactors

AbstractA mathematical model has been developed to predict the steady state performance of a continuous bulk styrene polymerization process with catalytic initiation for solid polystyrene. The polymerization section contains one boiling CSTR, followed by multiple linear‐flow reactors. The devolatilization section consists of two polymer pre‐heaters and two high‐solids flashes. The polymer moment equations were solved simultaneously with the reactor modeling equations. The non‐linear algebraic equations were solved by a Newton‐Raphson iteration technique to give the steady‐state styrene monomer weight fraction in a CSTR. The coupled, non‐linear ordinary differential equations were numerically integrated using a single‐step, 4th‐order Runge‐Kutta technique, followed by a multi‐step Adams‐Moulton technique. The resulting computer simulation model is capable of evaluating how the production rate and product quality are affected by feed composition, temperature, initiator type, initiator concentration, and residence time. Several case studies were given for commercially important crystal‐clear and impact‐resistant resins. A binary initiation system gives a good balance of monomer conversion, polymer molecular weights, and rubber grafting compared to a single initiation system. The styrene dimer/trimer occur in low concentrations but can be substantially reduced with a low temperature initiator. The ideal mean residence time is approximately one minute or less in a shell‐and‐tube devolatilization pre‐heater. Low flash chamber vacuum is more effective than high polystyrene melt temperature to reduce the volatile content of the final product. The water injected to the low volatile melt shows promising improvement in the second‐stage polystyrene devolatilization.

Synthesis and characterization of linear ABC triblock copolymer of ethylene oxide, methyl methacrylate, and styrene

A well-defined linear ABC triblock copolymer of ethylene oxide (EO), methyl methacrylate (MMA), and styrene (St) was prepared by sequential living an- ionic and photo-induced charge transfer polymerization (CTP) using p-aminophenol as parent compound. In the first step, the diblock copolymer of PEO-b-PMMA with a protected aniline end group at PEO end was prepared by initiating of phenoxo-anion the polymerization of EO and MMA successively, then the diblock copolymer of PEO- b-PMMA via deprotection of aniline at PEO end constituted a binary initiation system with benzophenone (BP) by charge transfer complex mechanism to initiate the poly- merization of St under UV-irradiation. The GPC and NMR measurements support that in copolymerization, either in the first or second step, neither homopolymer nor side reactions, such as chain transfer or chain termination, was found. The effect of the concentration of PEOa-b-PMMA and St, and the polarity of solvent on the polymeriza- tion rate (Rp) of CTP is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 825- 833, 1999

Controlled Anionic Polymerization of tert-Butyl Acrylate with Diphenylmethyl Anions in the Presence of Dialkylzinc

The anionic polymerization of tert-butyl acrylate (tBA) was carried out with a binary initiator system prepared from diphenylmethyllithium, -potassium, or -cesium (Ph2CHM) and dimethylzinc or diethylzinc in THF at −78 °C. In the absence of dialkylzinc (R2Zn), the poly(tBA)s produced with Ph2CHM possessed ill-controlled molecular weights and broad molecular weight distributions (MWDs). On the other hand, poly(tBA)s having predicted molecular weights based on the molar ratio of monomer to initiators and narrow MWDs (Mw/Mn < 1.15) were obtained in quantitative yields by the initiation with Ph2CHK or Ph2CHCs in the presence of 10−20-fold excess R2Zn, although the polymers obtained with Ph2CHLi/R2Zn still possessed broad MWDs (Mw/Mn = 2). The growing chain end of poly(tBA) associated with cesium counterion is completely stable to reinitiate the further polymerization of tBA in the presence of R2Zn at −78 °C for 1 h, but 56% deactivation occurred after 24 h. It is thus demonstrated that Ph2CHK or Ph2CHCs in conjunction with R2Zn induces the controlled anionic polymerization of tBA in THF at −78 °C. By contrast, addition of R2Zn to the polymerization systems of methyl, ethyl, and isopropyl acrylates showed little effects on the improvement of polymer yields and the molecular weight controls. Well-defined block copolymers, poly(styrene-b-tBA), poly(methyl methacrylate-b-tBA), and poly(tBA-b-N,N-diethylacrylamide), were also anionically prepared by the sequential addition of styrene, methyl methacrylate, or N,N-diethylacrylamide with tBA in the presence of R2Zn.

Calculation of molecular weight distribution in styrene polymerization initiated by a binary initiator system

A computational scheme is presented for the calculation of molecular weight distribution in styrene polymerization initiated by a binary initiator system. In this paper, the method of finite molecular weight moment is presented by calculation of the polymer chain length distribution. This method is compared with the method of integrating an infinite number of polymer population balance equations. The results of the two methods show a reasonably good agreement. It is possible to produce polymer having the same molecular weight distribution.

Synthesis and characterization of amphiphilic diblock copolymer of polystyrene and polyvinyl alcohol using ethanolamine-benzophenone as photochemical binary initiation system

Amphiphilic diblock copolymers of polyvinyl alcohol (PVA) and polystyrene (PS), which are very difficult to prepare by common polymerization methods, have been obtained by initiation of the polymerization of styrene and vinyl acetate successively, followed by hydrolysis, using the ethanolamine-benzophenone (BP) charge-transfer complex (CTC). The effects of solvents, concentration of monomer, BP, ethanolamine, and PS prepolymer, with a reactive imino group (PSa), on the photo-induced charge- transfer polymerization (CTP) of St and block copolymerization of VAc are discussed. The copolymer of PS-b-PVAc and the hydrolyzed product, PS-b-PVA, were characterized by FTIR, NMR, and GPC in detail. The effect of PS chain length on the crystallization of PVA was described. q 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 109- 115, 1998

Preparation of diblock copolymer of methyl methacrylate and vinyl acetate by successive radical mechanism and selective hydrolysis of the polyvinyl acetate) block

The preparation of a block copolymer of methyl methacrylate (MMA) and vinyl acetate (VAc) (PMMA- b-PVAc) was carried out by successive charge-transfer polymerization (CTP) in aniline—benzophenone as binary initiation system under ultraviolet irradiation; subsequently a block copolymer of PMMA and poly(vinyl alcohol) (PMMA- b-PVA) was derived by selective hydrolysis of PMMA- b-PVAc in ethanolic sodium ethoxide. These copolymers were characterized in detail by means of Fourier transform infra-red and proton nuclear magnetic resonance spectroscopies, and gel permeation chromatography. The solvent polarity exerts an effect on the copolymerization.

Photochemical-induced polymerization kinetics of styrene and methyl methacrylate by initiation of binary system composed of polyethylene oxide with aniline end group and benzophenone

The kinetics of photochemical polymerization of styrene (St) and methyl methacrylate (MMA) using a binary initiation system composed of poly(ethylene oxide) with an aniline end group (PEOa) and benzophenone (BP) was investigated by a modi- fied dilatometer. The effect of the concentration of the monomer, BP and PEOa, and of the molecular weight of PEOa on the polymerization rate (Rp) and conversion of monomers is discussed in detail. The formulas of Rp } (PEOa) 0.38 (St) 0.33 (BP) 0.56 and Rp } (PEOa) 0.36 (MMA) 0.30 (BP) 0.54 using benzene as a solvent are derived when the molecular weight of PEO is 11,000 (PEOa 0 11,000). Compared with the small aminophenol (AP), there existed a critical PEOa concentration to affect the Rp and conversion of the monomers and the critical concentration is strongly dependent on the polarity of the solvents and molecular weight of PEOa. It is confirmed that in the same conditions the solution polymerization behavior of St and MMA initiated by the imino radical of PEO would not be affected by the properties of the second block although PMMA is miscible and PS is immiscible with PEOa in the bulk. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2095-2103, 1997

Dynamics of a CSTR for styrene polymerization initiated by a binary initiator system

AbstractThe steady state and dynamic behavior of a continuous stirred tank reactor has been analyzed for free radical solution polymerization of styrene initiated by a mixture of two initiators having different thermal stabilities. From the steady state analysis of the reactor model with a mean residence time as a bifurcation parameter, four unique regions of steady state solutions are identified in an operating parameter space for a given initiator feed composition. A variety of complex bifurcation behavior such as multiple steady states, Hopf bifurcation and limit cycles have been observed and their stability characteristics have been analyzed. The effects of feed initiator composition and the concentration of the initiator in the feed stream on the reactor dynamics are also presented.

The multiple-component initiator technique for constant-rate free-radical homopolymerization

The multiple initiator method of controlling polymerization at a prescribed rate is studied. A correlation of the auto-acceleration function with the kind and concentration of the initiator is assumed. The equations for the determination of the kind and concentration of the initiator to control polymerization at a constant rate are then derived. Bulk polymerization of methyl methacrylate is chosen for verification. Using the method proposed and binary initiator systems, we determine several sets of initiator pairs and their concentrations for polymerization of methyl methacrylate at rates of 0.1 and 0.2 h −1 for various reaction temperatures. The results indicate that the polymerization rates obtained with the given initiator pairs and concentrations are what we have prescribed.

Physical properties of vinyl chloride‐propylene copolymers

AbstractThe polymerization conditions that control the physical properties of vinyl chloride‐propylene copolymers have been examined, and the interaction between these polymerization conditions and the melt rheology, intrinsic viscosity, and bound propylene level of the copolymer have been quantified into a series of process control relationships. The interaction between primary and secondary suspension systems have been optimized for these copolymers to maximize the resin porosity. Binary initiator systems have been identified to overcome the degradative polymer kinetics associated with propylene comonomer.

Metal-Containing initiator Systems. XXXVI. Synthesis of Block Copolymer of Methyl Acrylate and α-Methylbenzyl Methacrylate with Binary Initiator System of Cobaltocene and Bis(ethyl acetoacetato)copper(II)

Abstract Polymerizations of methyl acrylate (MA) and (DL)-α-methyl-benzyl methacrylate (MBMA) with binary initiator system of cobaltocene [Co(C5H5)2] and bis(ethyl acetoacetato)copper(II) [Cu(eacac)2] were studied in acetonitrile at 25°C. The molecular weight of the polymers obtained by MA was found to increase with time in the early stage of polymerization. Although MBMA was also polymerized by this system, asymmetric selective polymerization was not induced in the presence of (-)-sparteine. The synthesis of the block copolymer of MA and MBMA was attempted by using this initiator system. The block copolymer was obtained in 90% yield in the polymerization of MBMA with a polymer radical which prepared from MA with this system for 1 day. The yield of the block copolymer depended on the prepolymeriza-tion time of MA by this system. The resulting block copolymer was characterized by IR, 1H-NMR, and gel-permeation chromatography.

Metal‐containing initiator systems, 35. Synthesis of block copolymers by using the binary initiator system cobaltocene/bis(ethyl acetoacetato)copper(II)

AbstractPolymerization of methyl methacrylate (MMA) with the binary initiator system cobalt‐ocene (Co(C5H5)2)/bis(ethyl acetoacetato)copper(II)(Cu(eacac)2), was studied kinetically at 25°C in acetonitrile. The relationship between yield and molecular weight of the resulting poly(MMA) was suggestive of a living polymerization character in this system. The synthesis of block copolymers of MMA with styrene (St) was attempted by adding St as the second monomer to the polymerization system of MMA. The block copolymer was formed in a yield of 20% when MMA was polymerized for 1 day, while the yield went up to 80% when the MMA polymerization was carried out for 3 days. The resulting block copolymer was characterized by IR spectroscopy and gel‐permeation chromatography.

Metal‐containing initiator systems, 34. Polymerization of vinyl monomers initiated by the binary system cobaltocene/bis(ethyl acetoacetato)copper (II)

AbstractThe effect of some metallocenes such as ferrocene (Fe(C5H5)2), nickelocene (Ni(C5H5)2), and cobaltocene (Co(C5H5)2), on the vinyl polymerization initiated with bis(ethyl acetoacetato)‐copper(II) (Cu(eacac)2) was investigated. Co(C5H5)2 was found to exert a markedly accelerating effect on the polymerization of methyl methacrylate (MMA) with Cu(eacac)2. The polymerization of MMA with the system Co(C5H5)2/Cu(eacac)2 at 50°C was found to be fairly affected by the solvent used. The results of copolymerization of MMA with styrene (St) and the effect of hydroquinone (HQ) on the polymerization of MMA with Co(C5H5)2/Cu(eacac)2 showed that the polymerization proceeds via a radical mechanism. The polymerization of MMA with Co(C5H5)2/Cu(eacac)2 was studied kinetically in acetone. The overall activation energy of the polymerization was calculated to be 86,3 kJ/mol (20,6 kcal/mol). This value was somewhat higher than that (17,6 kcal/mol) obtained for the polymerization of MMA with Cu(eacac)2 alone. The polymerization rate (Rp) is represented by the following equation: Rp = k[Co(C5H5)2]0,5 [Cu(eacac)2]0,2 [MMA]1,3. The high order in monomer concentration suggests a participation of the monomer in the initiation process of this polymerization. This is supported by the examination of the ESR spectrum of the system Co(C5H5)2/Cu(eacac)2/MMA/acetone, where reduction of Cu(II) to Cu(I) occurs. To elucidate the initiation mechanism, the spin trapping technique was applied to the system Co(C5H5)2/Cu(eacac)2/methyl acrylate. From these results, an initiation mechanism for the binary initiator system Co(C5H5)2/Cu(eacac)2 is proposed and discussed.

Polymerization of Vinyl Monomers with Binary Initiator System of N-Chlorosuccinimide and Lewis Acids

Abstract The polymerization of vinyl monomers with a binary system composed of N-chlorosuccinimide (NCS) and some Lewis acids was investigated by means of kinetic and spectral determinations. It was found that the NCS-ZnCl2 system was the most effective as an initiator of radical polymerization of methyl methacrylate, and this polymerization was initiated by a radical produced via the reaction of NCS and ZnCl2, and terminated bimolecularly. By applying a spin trapping technique to the reaction of NCS with ZnCl2, it was shown that the initiating radical was N-succinimidyl radical which was obtained through a homolysis at the N-Cl bond.