Kinetic and microstructure studies of poly(ethylene-co-p-methylstyrene) copolymers prepared by metallocene catalysts with constrained ligand geometry

This paper discusses the poly(ethylene-co-p-methylstyrene) copolymers prepared by metallocene catalysts, such as Et(Ind)₂ZrCl₂ and [C₅Me₄(SiMe₂N^tBu)]-TiCl₂, with constrained ligand geometry. The copolymerization reaction was examined by comonomer reactivity (reactivity ratio and comonomer conversion versus time), copolymer microstructure (DSC and ¹³C-NMR analyses) and the comparisons between p-methylstyrene and other styrene-derivatives (styrene, o-methylstyrene and m-methylstyrene). The combined experimental results clearly show that p-methylstyrene performs distinctively better than styrene and its derivatives, due to the cationic coordination mechanism and spatially opened catalytic site in metallocene catalysts with constrained ligand geometry. A broad composition range of random poly(ethylene-co-p-methylstyrene)copolymers were prepared with narrow molecular weight and composition distributions. With the increase of p-methylstyrene concentration, poly(ethylene-co-p-ethylstyrene)copolymer shows systematical decrease of melting point and crystallinity and increase of glass transition temperature. At above 10 mol % of p-methylstyrene, the crystallinity of copolymer almost completely disappears. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1017–1029, 1998     

Effect of zinc salts on the spontaneous copolymerization of 4-vinylpyridine with various electron-rich vinyl monomers

The spontaneous copolymerization of 4-vinylpyridine (4-VP) complexed with three different zinc salts (chloride, acetate, and triflate) with various electron-rich vinyl monomers (p-methoxystyrene, MeOSt; p-methylstyrene, MeSt; α-methylstyrene, α-MeSt; p-tert-butylstyrene, BuSt; styrene, St) was investigated in methanol at 75°C. Increasing the zinc salt concentration or the nucleophilicity of the electron-rich monomer increased the copolymer yields. All obtained copolymers are characterized by high molecular weight (10⁵) and broad molecular weight distribution. Both ¹H-NMR and elemental analyses confirmed the almost 1 : 1 copolymer structure. Changing the anion of the zinc salt does not have a considerable effect either on the copolymerization rate or on the molecular weight. The proposed mechanism exhibits the formation of a σ-bond between the β-carbons of the two donor–acceptor monomers. This creates the 1,4-tetramethylene biradical intermediate which can initiate the copolymerization reaction. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2787–2792, 1997     

Synthesis of PP graft copolymers via anionic living graft-from reactions of polypropylene containing reactive p-methylstyrene units

In this article, we discuss a new chemical route for preparing polypropylene (PP) graft copolymers containing a PP backbone and several (polar and nonpolar) polymer side chains, including polybutadiene, polystyrene, poly(p-methylstyrene), poly(methyl methacrylate), and polyacrylonitrile. The new PP graft copolymers had a controlled molecular structure and a known PP molecular weight, graft density, graft length, and narrow molecular weight distribution of the side chains. The chemistry involves an intermediate poly(propylene-co-p-methylstyrene) copolymer containing few p-methylstyrene (p-MS) units. The methyl group in a p-MS unit could be lithiated selectively by alkylithium to form a stable benzylic anion. Because of the insolubility of the PP copolymer at room temperature, the excess alkylithium could be removed completely from the lithiated polymer. By the addition of the anionically polymerizable monomers, including polar and nonpolar monomers, the stable benzylic anions in PP initiated a living anionic graft-from polymerization at ambient temperature to produce PP graft copolymers without any significant side reactions. The side-chain length was basically proportional to the reaction time and monomer concentration. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4176–4183, 1999     

Synthesis of Some New 1,2,4‐Triazole Derivatives by Mitsunobu Chemistry

The reactive 1 : 1 intermediate produced in the reaction between triphenylphosphine and diisopropyl azodicarboxylate has been trapped by isocyanates or isothiocyanates to yield 1,2,4‐triazole derivatives 2 (Scheme 1). The structures of the highly functionalized compounds 2 were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, EI‐MS) and by elemental analyses. A mechanism for this type of cyclization is proposed (Scheme 2).     

One‐Pot Three‐Component Synthesis of Highly Functionalized 2,3‐Dihydro‐1,3‐dioxo‐1H,5H‐pyrazolo[1,2‐a][1,2,4]triazoles

The reactive 1 : 1 zwitterionic intermediate formed by the addition of isocyanides to dialkyl acetylenedicarboxylates was trapped with 4‐arylurazoles to produce the highly functionalized pyrazolo[1,2‐a][1,2,4]triazoles 5 in good yields (Table). The structures of the products 5a – h were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR), by EI‐MS, and elemental analysis. A possible mechanism for this reaction is proposed (Scheme).     

Design and Theoretical Study of Nickel Catalysts for Syndiotactic Polyolefins

A nickel catalyst was nodeled with ligand L^2,[NH=CH-CH=CH-0]^-,which should have potential use as a syndiotactic plyolefin catalyst,and the reaction mechanism was studied by theoretical calculations using the density functinal method at the B3LYP/LANL2MB level.The mechanism involves the formation of the intermediate [NiL^2Me]^ ,in which the metal occupies a T-shaped geometry.This intermediate has two possible structures with the methyl group trans either to the oxygen or to the nitrogen atom of L^2.The results show that both structures can lead to the desired product via similar reaction paths,A and B.Thus,the polymerization could be considered as taking place either with the alkyl group occupying the position trans to the Ni-0 or trans to the Ni-N bond in the catalyst.The polymerization process thus favors the catalysis of syndiotactic polyolefins.The syndiotactic synthesis effects could also be enhanced by varations in the ligand substituents.From energy considerations,we can conclude that it is more favorable for the methyl ttrans-O position to form a complex than to occupy the trans-N position.From bond length considerations,it is also more favoured for ethene to occupy the trans-O position than to occupy the trans-N position.     

Preparing a functionalized thermoplastic elastomer: Chlorination and synthesis of poly(p-methylstyrene)-block-polyisoprene-block-poly(p-methylstyrene)

A poly(p-methylstyrene)-block-polyisoprene-block-poly(p-methyl styrene) thermoplastic elastomer was synthesized via anionic polymerization using n-butyllithium as an initiator. The sequential method used for the synthesis has resulted in a nearly monodispersed polymer with a polydispersity of 1.02. Chlorination of such formed copolymer using aqueous sodium hypochlorite was then conducted in a variety of solvents. At a 6.9 mol ratio of sodium hypochlorite to monomer unit, chlorination occurred via a substitution reaction instead of an addition reaction, regardless of the type of solvent used. Nevertheless, the location at which the chlorine was incorporated into the polymer varied with the type of solvent used. The chlorination occurred primarily in the two poly(p-methylstyrene) end blocks when conducted in n-hexane solvent. However, only the polyisoprene middle block was chlorinated in chloroform. All three blocks could be chlorinated when the reaction was carried out in methylene chloride. The microstructure of the chlorinated molecules were analyzed using ¹H-NMR and ¹³C-NMR, and the degree of chlorination varied from 7 to 50% of constituting monomer units. A significantly higher degree of chlorination occurred when the reaction was conducted in methylene chloride due to its high dielectric constant. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2969–2980, 1997     

Kinetics and mechanism of reactions between aromatic olefins and hydroxyl radicals

The rates of the reactions of hydroxyl radicals (OH) with styrene, α-methylstyrene, and β-methylstyrene have been measured by irradiating mixtures of these aromatic olefins and NO in an environmental chamber at 298 K. Experimental conditions were used whereby the competition of ozone with OH in oxidizing the hydrocarbons could be considered negligible. The rate constant values, obtained by a relative method using isooctane as reference hydrocarbon, are: styrene (5.3 ± 0.5) × 10^?11 cm³/molec·s, α-methylstyrene (5.3 ± 0.6) × 10^?11 cm³/molec·s, and β-methylstyrene (6.0 ± 0.6) × 10^?11 cm³/molec·s. A simplified kinetic treatment of the experimental data shows that styrene and β-methylstyrene are stoichiometrically converted to benzaldehyde, suggesting that OH attack occurs only on the aliphatic moiety of the aromatic olefins. Benzaldehyde was observed to undergo consecutive oxidation by OH, and its maximum formation yield was about 60%. A reaction mechanism is proposed where the primary rate-determining OH attack leads to the formation of 1-hydroxy-2-phenyl-2-ethenyl radicals, from which benzaldehyde is formed through fast intermediate reactions.     

Dimerization of methylstyrenes by acetyl perchlorate and trifluoromethanesulfonic acid

Ring-substituted methylstyrenes (p-, m-, and o-methylstyrenes) in conjunction with acetyl perchlorate (AcClO₄) or trifluoromethanesulfonic acid as catalysts gave their linear unsaturated dimer in high yield in benzene at temperatures from 50 to 70°C. In particular, the yield of o-methylstyrene dimer was as high as 90% in the AcClO₄ catalysis at 50°C. The dimer yield depended on solvent and catalyst. The terminal structures of the dimers and higher oligomers were analyzed by NMR spectroscopy. Oligomers with a cyclic terminal structure increased in the products at higher temperature. The dimer yield was improved by codimerizing p-methylstyrene with less reactive m-methylstyrene or styrene with AcClO₄ catalyst. The dimers obtained partly consisted of linear unsaturated codimers.     

Kinetics of free-radical copolymerization of α-methylstyrene and styrene

The free-radical copolymerization of α-methylstyrene and styrene has been studied in toluene and dimethyl phthalate solutions at 60°C. Gas chromatography was used to monitor the rate of consumption of monomers. For styrene alone, the measured rate of polymerization R_p and M?_n of the polymer coincided with values expected from previous studies by other workers. Solution viscosity η affected R_p and M?_n of styrene homopolymers and copolymers as expected on the basis of an inverse proportionality between η^1/2 and termination rate. The rate of initiation by azobisisobutyronitrile appears to be independent of monomer feed composition in this system. Molecular weights of copolymers can be accounted for by considering combinative termination only. The effects of radical chain transfer are not significant. A theory is proposed in which the rate of termination of copolymer radicals is derived statistically from an ideal free-radical polymerization model. This simple theory accounts quantitatively for R_p and M?_n data reported here and for the results of other workers who have favored more complicated reaction models because of the apparent failure of simple copolymer reactivity ratios to predict polymer composition. This deficiency results from systematic losses of low molecular weight copolymer species in some analyses. Copolymer reactivity ratios derived with the assumption of a simple copolymer model and based on rates of monomer loss can be used to predict R_p values measured in other laboratories without necessity for consideration of depropagation or penultimate unit effects. The 60°C rate constants for propagation and termination in styrene homopolymerization were taken to be 176 and 2.7 × 10⁷ mole/l.-sec, respectively. The corresponding figures for α-methylstyrene are 26 and 8.1 × 10⁸ mole/l.-sec. These constants account for the sluggish copolymerization behavior of the latter monomer and the low molecular weights of its copolymers. The simple reaction scheme proposed here suggests that high molecular weight styrene–α-methylstyrene copolymers can be produced at reasonable rates at 60°C by emulsion polymerization. This is shown to be the case.     

Synthesis of a New Class of Highly Functionalized Phosphorus Ylides Containing Heterocyclic Compounds

The zwitterionic intermediate generated from the reaction of triphenylphosphine with electron deficient acetylenic compounds was trapped by various NH acids. The synthesis resulted in a new class of highly functionalized heterocyclic compounds. Some of the reactions produced E and Z isomers. And the stability and transformation of them were studied by dynamic ¹H NMR and density functional theory (DFT) calculations.     

A field ionization and collisionally activated dissociation/charge stripping study of some [C9H10]+˙ ions

The extent of isomerization of [C₉H₁₀]^+˙ ions, with lifetimes of approximately 10^?11 and 10^?6 s has been investigated using field ionization, collisionally activated dissociation and charge stripping techniques. The [C₉H₁₀]^+˙ ions which were investigated included the molecular ions of α-methylstyrene, β-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, indan, cyclopropylbenzene, allylbenzene and the product of water loss from 3-phenylpropanol. The field ionization spectra of all the C₉H₁₀ hydrocarbons were different indicating that isomerization to a common ion structure had not occurred to a measurable extent for ions with lifetimes of approximately 10^?11 s. Collisionally activated dissociation and charge stripping results indicated that most of the [C₉H₁₀]^+˙ ions continued to maintain unique ion structures (or mixtures of structures) at ion lifetimes of 10^?6 s. Possible exceptions are the [C₉H₁₀]^+˙ ions from allylbenzene and cyclopropylbenzene which gave indistinguishable collisionally activated dissociation and charge stripping spectra.     

On the interaction of triphenylmethyl salts with α-methylstyrene

The interaction of triphenylmethyl salts with α-methylstyrene and 1,1-diphenylethylene was investigated. With 1,1-diphenylethylene at a monomer-initiator ratio of 2 (room temperature), mainly 1,1,3-triphenyl-3-methyl-indane was isolated, whereas at a ratio of 100 (?10°C), the dimer 1,1,3,3-tetraphenylbutene-1 mainly formed. In both cases no addition of the trityl group was registered. In the interaction of α-methylstyrene with Ph₃C⁺SbCl at a monomer-initiator ratio of 2(room temperature) a pure 1,3,3-trimethyl-1-phenylindane was isolated and no addition of the trityl group to the double bond was recorded. The initiation reaction of α-methylstyrene polymerization by trityl and chlorinated trityl salts was studied at temperatures from ?20 to 0°C and different concentrations. The oligomers obtained with (pCI-C₆H₄)₃C⁺ were investigated by elemental analysis and fluorescence spectroscopy. The presence of Ph₃CH in the reaction mixture was demonstrated by GLC and NMR spectra. The results obtained give evidence that the initiation of α-methylstyrene polymerization involves hydride abstraction from the monomer.     

Copolymerization of methacrylonitrile with p-methylstyrene

Methacrylonitrile was copolymerized with p-methylstyrene in methyl ethyl ketone at 80°C initiated by azobisisobutyronitrile. Monomer reactivity ratios of methacrylonitrile and p-methylstyrene were found to be 0.205 and 0.377, respectively, using the Kelen-Tüdos method. Triad fractions and monomer sequence lengths of three copolymers were determined from ¹³C-NMR spectra and were found to be in good agreement with those calculated from reactivity ratios. © 1994 John Wiley & Sons, Inc.     

Living cationic isomerization polymerization of β-pinene. III. Synthesis of end-functionalized polymers and graft copolymers

α-End-functionalized polymers and macromonomers of β-pinene were synthesized by living cationic isomerization polymerization in CH₂Cl₂ at −40°C initiated with the HCl adducts [ 1; CH₃CH(OCH₂CH₂X)Cl; X = chloride ( 1a ), acetate ( 1b ), and methacrylate ( 1c )] of vinyl ethers carrying pendant substituents X that serve as terminal functionalities. In conjunction with TiCl₃(OiPr) and nBu₄NCl, these functionalized initiators led to living β-pinene polymerization where the carbon–chlorine bond of 1 was activated by TiCl₃(OiPr). Similarly, end-functionalized poly(p-methylstyrene)-block-poly(β-pinene) were also obtained. ¹H-NMR analysis showed that the polymers possess controlled molecular weights (DP _n = [M]₀/[ 1 ]₀) and number-average end functionalities close to unity. The end-functionalized methacrylate-capped macromonomers form 1c were radically copolymerized with methyl methacrylate (MMA) to give graft copolymers carrying poly(β-pinene) or poly(p-methylstyrene)-block-poly(β-pinene) as graft chains attached to a PMMA backbone. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1423–1430, 1997     

Synthesis, structures and membrane properties of siloxane-imide co-polymers produced by aqueous polymerization

We report for the first time, the synthesis of siloxane-imide co-polymers by the reaction of mixtures of 1,4-bis(aminobutyl)tetramethyldisiloxane (ABTMDS) and 1,3-bis(4-aminophenoxy)benzene (TPE-R) with bisphenol A diphthalic anhydride (BPADA) using water as the polymerization solvent. A series of co-polymers were prepared incorporating 10, 20, 40 and 100 mol% of ABTMDS with the aromatic diamine TPE-R as the co-monomer. The synthesized co-polymers showed number average molecular weights in the range of 25,000–60,000. As expected the glass transition temperatures (T_gs) and moduli of the polymers were found to decrease with increasing amounts of the siloxane monomer and the homo-polymer containing only the siloxane diamine showing the lowest T_g (60 °C). The resulting polymers could be solution cast into strong and flexible membranes which showed significant decreases in water absorption and moisture permeability compared to the control polymer without siloxane groups. The polymers were characterized by FTIR, ¹³C and ¹H NMR, GPC, DSC and mechanical properties and structural comparisons were made with similar polymers made by standard solvent synthesis methods. Also cross-linked polymers were prepared by the reaction of ABTMDS with the aromatic homo-polymer control and their membrane properties were compared to those of the water synthesized siloxane co-polymers with a similar siloxane content.     

Polymerization of cyclic acetals. II. Synthesis of amphiphilic block copolymers

The sequential copolymerization of 1,3,6-trioxacyclooctane (TOC) and 1,3-dioxolane (DOL) (B) with various vinyl monomers (A) was investigated. Under appropriate conditions amphiphilic block copolymers of the type AB and ABA were formed. The reaction mixtures and the isolated polymers were analyzed by GPC (double detection—IR and UV at 254 nm), IR, ¹H-, and ¹³C-NMR spectroscopy. Block copolymers with chosen molecular weights and low polydispersity could be obtained only by sequential copolymerization of p-methoxystyrene on “living” TOC. In the polymerization of DOL with α-methylstyrene and i-butyl vinyl ether (IBVE) transfer reactions take place to a larger degree.     

Model compounds and 13C NMR increments for the characterization of maleic anhydride-grafted polyolefins

A set of model compounds that mimic the graft sites of maleic anhydride (MA) functionalized polyolefins was synthesized and characterized with NMR spectroscopy. The acquired carbon nuclear magnetic resonance data were used to deduce chemical-shift increments for the prediction of ¹³C chemical shifts of MA functionalized polyolefins. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4368–4385, 1999     

Polar‐Functionalized,Crosslinkable, Self‐Healing,and Photoresponsive Polyolefins

The nonpolar nature of polyolefins is one of their biggest limitations. Now, an efficient route to generate polar‐functionalized, crosslinkable, self‐healing, photoresponsive polyolefins with thermoplastic, elastomeric, and thermosetting properties is reported. Tunable amounts of carboxylic acid and a cyclic comonomer are installed onto polyolefins by palladium‐catalyzed terpolymerization reactions. The incorporated carboxylic acid unit can alter the surface properties of polyolefins. The subsequently introduced Fe³⁺/citric acid combination induces dynamic crosslinking and enables self‐healing. Under UV light irradiation, citric acid reduces Fe³⁺ to Fe²⁺ and decreases the crosslinking density. The Fe²⁺ moiety can be easily oxidized back to Fe³⁺, making the process reversible at the expense of citric acid. The incorporated cyclic comonomer modulates the crystallinity of polyolefins, provides elastic properties, and installs carbon–carbon double bonds for sulfur‐induced vulcanization.     

Kinetic and mechanistic studies of the copolymerization of bis-4-substituted-1,2,4-triazoline-3,5-diones with styrenes

Highly reactive 4-substituted-1,2,4-triazoline-3,5-diones (TDs) have been studied extensively as dienophiles, but little work has been done on their role as enophiles and particularly on their use as propagating species in polymerization studies. The copolymerization between bis-4-substituted-1,2,4-triazoline-3,5-diones (bis-TDs) and styrene has been reported. The purpose of the present work was to synthesize new copolymers derived from a variety of substituted styrenes and bis-TDs and to study the mechanism and kinetics of this novel polymerization. Three bis-TDs were prepared: 3,3′-dimethyl-4,4′-bis[3,5-dioxo-1,2,4-triazoline-4-yl] biphenyl (8), t-1,4-bis[3,5-dioxo-1,2,4-triazoline-4-yl] methyl cyclohexane (9), and 4,4′-bis[3,5-dioxo-1,2,4-triazoline-4-yl] phenyl ether (10). Their structures were fully established by spectroscopic studies, elemental analyses, and indirectly, their quantitative ene reactions with 2,3-dimethyl-2-butene. Copolymerization between bis-TDs and substituted styrenes was carried out in dimethylformamide (DMF), tetrahydrofuran (THF), or dichloroethane (DCE). Polymers formed were characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and viscometry. Molecular weights of polymers range from 5000 to 16,000 in most cases. They were stable up to 250°C and higher. Polymers derived from bis-TDs and p-t-butylstyrene, α-methylstyrene, p-nitrostyrene, and p-acetoxystyrene contained only Diels-Alder-ene (DAe) repeating units, whereas those derived from styrene, p-chlorostyrene, p-bromostyrene, p-methylstyrene, p-methoxystyrene, and 4-vinylbiphenyl contained both DAe and double Diels-Alder (dDA) repeating units. A kinetic study of the copolymerization of 4,4′-bis-(3,5-dioxo-1,2,4-triazoline-4-yl) phenyl ether with α-methylstyrene, p-t-butylstyrene, styrene, p-chlorostyrene, and p-nitrostyrene in DCE was carried out; the copolymerization rate constants were 60.9, 49.8, 8.4, 5.5, and 0.8 (1 mol^?1s), respectively.