Factors affecting product distributions in ethylene/styrene copolymerization by (aryloxo)(cyclopentadienyl)titanium complexes‐MAO catalyst systems

Ethylene/styrene copolymerizations using Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) [Cp′ = Cp* (C₅Me₅, 1 ), 1,2,4‐Me₃C₅H₂ ( 2 ), tert‐BuC₅H₄ ( 3 )]‐MAO catalyst systems were explored under various conditions. Complexes 2 and 3 exhibited both high catalytic activities (activity: 504–6810 kg‐polymer/mol‐Ti h) and efficient styrene incorporations at 25, 40°C (ethylene 6 atm), affording relatively high molecular weight poly (ethylene‐co‐styrene)s with unimodal molecular weight distributions as well as with uniform styrene distributions (M_w = 6.12–13.6 × 10⁴, M_w/M_n = 1.50–1.71, styrene 31.7–51.9 mol %). By‐productions of syndiotactic polystyrene (SPS) were observed, when the copolymerizations by 1 – 3 ‐MAO catalyst systems were performed at 55, 70 °C (ethylene 6 atm, SPS 9.0–68.9 wt %); the ratios of the copolymer/SPS were affected by the polymerization temperature, the [styrene]/[ethylene] feed molar ratios in the reaction mixture, and by both the cyclopentadienyl fragment (Cp′) and anionic ancillary donor ligand (L) in Cp′TiCl₂(L) (L = Cl, O‐2,6‐ⁱPr₂C₆H₃ or N=C^tBu₂) employed. Co‐presence of the catalytically‐active species for both the copolymerization and the homopolymerization was thus suggested even in the presence of ethylene; the ratios were influenced by various factors (catalyst precursors, temperature, styrene/ethylene feed molar ratio, etc.). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4162–4174, 2008     

Synthesis,Characterization, and Thermal Behavior of Carboranyl–Styrene Decorated Octasilsesquioxanes: Influence of the Carborane Clusters on Photoluminescence

Novel polyhedral oligomeric silsesquioxanes (POSS) or octasilsesquioxanes with carboranyl–styrene fragments attached to each corner are described. These compounds have been synthesized by olefin‐metathesis reactions between octavinylsilsesquioxane and carboranyl–styrene compounds that possess different substituents (Ph, Me, or H). In all cases, these reactions, which were catalyzed by the Grubbs catalyst, are highly regioselective and yield exclusively the E isomers. The existence of the carborane cage in the POSS structure induces a remarkable thermal stability in these compounds. After combustion at 1000 °C, these carboranyl–POSS compounds exhibit a mass loss lower than 10 %. The UV/Vis absorption data of these carboranyl–POSS compounds shows a slight bathochromic shift with respect to the carboranyl–styrene monomers, with an absorption maximum around 262 nm. Nevertheless, important differences in the emission spectra of the carboranyl–POSS compounds with regard to their carboranyl–styrene precursors are observed; the phenyl‐o‐carborane‐containing POSS compound exhibits the highest fluorescence intensity (Φ_F=44 %), whereas for the POSS compound bearing the methyl substituent, and for the unsubstituted o‐carborane clusters, the fluorescence intensity is much lower (Φ_F=9 and 2 %, respectively). This is precisely the reverse of what occurs with the monomers, in which the unsubstituted o‐carboranyl–styrene compound exhibits the highest Φ_F, and a quenching of the fluorescence is observed in the phenyl‐o‐carboranyl–styrene compound. In addition, a large red shift of around 100 nm is observed for the POSS compounds with respect to their precursors. These experimental results can only be accounted for by the spatial ordering induced by the POSS core that eases interactions, which otherwise would not occur. These results have been confirmed by time‐dependent density functional theory (TDDFT) calculations that exclude a photoinduced electron transfer (PET) process in the POSS compounds.     

Metallocene-catalyzed ethene/styrene co- and terpolymerization with olefinic termonomers

Ethene was co- and terpolymerized with 1-octene and styrene using the methylalumoxane (MAO) activated halfsandwich metallocene Me₂Si(Me₄Cp)(N-t.-butyl)TiCl₂(Cp = cyclopentadienyl, Me = methyl) as catalyst. At temperatures of 40 and 60°C styrene concentration was varied in order to investigate the influence of the comonomers. Despite decreasing the overall activity with respect to ethene/1-octene copolymerization, polymerization activity was found to exibit a relative maximum with increasing styrene concentration. An explanation is given taking two different comonomer effects into account. Low styrene concentration promoted higher 1-octene incorporation compared to ethene/1-octene copolymerization but significantly lowered the molecular weight of the terpolymers. With constant ethene and 1-octene concentration it was possible to produce ethene/1-octene/styrene terpolymers with styrene content varying from 0 to 25 mol % and 1-octene content varying from 8 to 21 mol %. All terpolymers were amorphous. With constant ethene content it was found possible to vary their glass transition temperature with 1-octene/styrene molar ratio incorporated in the terpolymer. ¹³C-NMR spectroscopic microstructure analysis showed that no styrene/1-octene sequences were found in the terpolymer backbone. Furthermore terpolymerizations were conducted successfully incorporating norbornene, 1,5-hexadiene and propene as monomers in terpolymertization with ethene and styrene. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2549–2560, 1997     

Alternating copolymerizations of styrene and acrylic monomers initiated with carbanions in the presence of ZnCl2

On electrochemical initiation of alternating copolymerizations of styrene–acrylonitrile (AN) and styrene–diethyl fumarate (DEF) in the presence of ZnCl₂, radical anions of AN–ZnCl₂ and DEF–ZnCl₂ complexes produced at the cathode were assumed to initiate copolymerization. In analogy with the cathode-initiated copolymerization, the radical anions of AN–ZnCl₂ and DEF–ZnCl₂, generated with the carbanions such as sodium naphthalene, disodium α-methylstyrene tetramer dianion, and butyllithium, were also found to produce alternating copolymers of styrene–AN and styrene–DEF. On the contrary, no polymers were obtained from methyl methacrylate (MMA)–styrene and methacrylonitrile (MAN)–styrene in the presence of ZnCl₂ either with carbanions or by electrochemical reduction. Styrene–MAN–ZnCl₂ yielded an alternating copolymer with carbanions upon introduction of oxygen.     

Copolymerization of ethylene with styrene catalyzed by a linked bis(phenolato) titanium catalyst

Copolymerization of ethylene with styrene, catalyzed by 1,4‐dithiabutanediyl‐linked bis(phenolato) titanium complex and methylaluminoxane, produced exclusively ethylene–styrene copolymers with high activity. Copolymerization parameters were calculated to be r_E = 1.2 for ethylene and r_S = 0.031 for styrene, with r_E r_S = 0.037 indicating preference for alternating copolymerization. The copolymer microstructure can be varied by changing the ratio between the monomers in the copolymerization feed, affording copolymers with styrene content up to 68%. The copolymer microstructure was fully elucidated by ¹³C NMR spectroscopy revealing, in the copolymers with styrene content higher than 50%, the presence of long styrene–styrene homosequences, occasionally interrupted by isolated ethylene units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1908–1913, 2006     

Catalytic systems Me2SiCp*NtBuMX2/(CPh3)(B(C6F5)4) (MTi,XCH3, MZr,XiBu) in copolymerization of ethylene with styrene

Catalytic activity of Me₂SiCp*N^tBuMX₂/(CPh₃)(B(C₆F₅)₄) [MTi, XCH₃ (1); MZr, X=ⁱBu (2)] systems in the ethylene/styrene (E/S) feed was examined. Experimental data revealed high activity for the catalytic system (1) for copolymerization ethylene with styrene, whereas the system with enhanced catalytic activity for ethylene homopolymerization (2) was temporarily blocked in the styrene presence yielding, even at high styrene content, homopolyethylene as the final product. Properties of thus obtained polymers were analyzed. Catalytic system (1) occurred very sensitive to S/E ratio in the comonomers feed. The 10‐fold acceleration for ethylene consumption was shown in two experimental sets conducted at S/E = 1.3 ratio, 1 bar, and 7.5 bar ethylene pressure, respectively. The consequent enhancement in S/E ratio resulted in slowing down both ethylene consumption and catalyst deactivation rates. Atactic polystyrene was formed at high styrene content with the catalyst (1). Catalytic system (1) allowed design of products with the highest styrene content (20 mol %) at low ethylene pressure, moderate temperature, and high S/E ratio. The apparent activation energy estimated from the initial rates of ethylene consumption was 54.6 kJ/mol. Analysis of apparent reactivity factors (r_E = 9 and r_S = 0.04; r_E × r_S = 0.4) and ¹³C‐NMR copolymer spectra revealed an alternating tendency of the comonomers for active center incorporation. DSC measurements showed considerable decrease of melting points and crystallinity even for copolymers with low styrene content. The catalyst produced relatively high–molecular weight copolymers (140–150 kg/mol) even at 80°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1083–1093, 1999     

Dynamic mechanical and dielectric properties of epoxidized SBS triblock copolymer

The morphological and dynamic properties of epoxidized styrene–butadiene–styrene block copolymers were studied and compared with their parent styrene–butadiene–styrene block copolymer (SBS). Two peaks were observed in the mechanical loss (tan δ) curve which can be attributed to segmental motion of epoxidized polybutadiene (EPPB) and polystyrene. Analysis by DSC thermograms also showed the linear increase of glass transition temperature for EPPB domain with the epoxy group content. Phase separated structures of epoxidized SBS as observed by TEM suggests a considerable degree of mixing occurred between phases after 80 mol % of the double bonds in SBS were epoxidized. The interfacial region displays a third peak and causes much steeper drop in modulus at higher temperature than T_g of EPPB. Parallel dielectric relaxation measurements were also made in the frequency range of 30 Hz–1 KHz as a function of temperature. In each dielectric constant (?′) curve, there is a maximum near the T_g of EPPB determined from the dielectric loss tangent curve. The shift in T_g of EPPB versus epoxy group content was consistent with that measured by the thermal and dynamic mechanic analysis. These findings indicated an 8°C shift in glass transition temperature as the epoxy group content in EPPB increased 10%.     

Environmentally benign electrophilic and radical bromination ‘on water’: H2O2-HBr system versus N-bromosuccinimide

A H₂O₂-HBr system and N-bromosuccinimide in an aqueous medium were used as a ‘green’ approach to electrophilic and radical bromination. Several activated and less activated aromatic molecules, phenylsubstituted ketones and styrene were efficiently brominated ‘on water’ using both systems at ambient temperature and without an added metal or acid catalyst, whereas various non-activated toluenes were functionalized at the benzyl position in the presence of visible light as a radical activator. A comparison of reactivity and selectivity of both brominating systems reveals the H₂O₂-HBr system to be more reactive than NBS for benzyl bromination and for the bromination of ketones, while for electrophilic aromatic substitution of methoxy-substituted tetralone it was higher for NBS. Also, higher yields of brominated aromatics were observed when using H₂O₂-HBr ‘on water’. Bromination of styrene reveals that not just the structure of the brominating reagent but the reaction conditions: amount of water, organic solvent, stirring rate and interface structure, play a key role in defining the outcome of bromination (dibromination vs bromohydroxylation). In addition, mild reaction conditions, a straightforward isolation procedure, inexpensive reagents and a lower environment impact make aqueous brominating methods a possible alternative to other reported brominating protocols.     

Solvent effects on the radiation-induced graft polymerization of styrene onto poly(isobutylene oxide)

The graft polymerization of styrene onto preirradiated poly(isobutylene oxide) (PIBO) with methanol and benzene was studied. The order of grafting yield and of the number-average molecular weight of graft chains decrease in the order; undiluted styrene > styrene–methanol (1:1) solution > styrene–benzene (1:1) solution. A kinetic treatment to calculate rate constants from the rate of grafting and the molecular weight of the graft chain was proposed. The propagation rate constant k_p was 0.2–0.3 l./mole-sec and the termination rate constant k_t was 1.0–16.0 l./mole-sec. The ratio k_p/k_t in this heterogeneous system was larger than that in homogeneous system by a factor of about 10⁴–10⁵.     

Determination of coisotacticities of some alternating styrene–acrylic copolymers by NMR spectra

Coisotacticities σ for some alternating copolymers were determined through the analyses of their CH₃O, CH₃ and CH₂ proton NMR spectra; styrene–methyl methacrylate (σ = 0.56), styrene-methyl acrylate (σ = 0.53), styrene–methyl α-chloroacrylate (σ = 0.69), styrene–methacrylonitrile (σ = 0.19), styrene–methacrylamide (σ = 0.16), α-methylstyrene–methyl methacrylate (σ = 0.21), and α-methylstyrene–methyl acrylate (σ = 0.53) were studied. It was found that a terminal model or Bernoullian trial prevails in these complexed copolymerizations with diethylaluminum chloride. The influence of monomer structure on σ values is discussed.     

(η5-Pentamethylcyclopentadienyl)trimethyltitanium as a precursor for the syndiospecific polymerization of styrene

An equimolar mixture of Cp*Ti(CH₃)₃ (2) and Ph₃C⁺[B(C₆F₅)₄]^? (1) forms a highly active and syndioselective catalyst for the polymerization of styrene, producing 96% syndiotactic polystyrene (PS) at an activity of 0.91 × 10⁷ g PS (mol Ti)^?1 (mol styrene)^?1 h^?1. Both activity and syndioselectivity can be increased using tri–isobutylaluminum (TIBA) to scavenge the system. ESR measurements indicate that the polymerization proceeds via titanium(IV) intermediates. Catalysts derived from 2/methylaluminoxane (MAO) as well as Cp*TiCl₃/MAO also function as syndioselective styrene polymerization catalysts, but are less active than the ‘cationic’; system derived from 1 and 2.     

Synthesis of the block copolymer of styrene and 1-butene with a novel supported Ti-catalyst

The present investigation deals with sequential block copolymerization of styrene and 1-butene with a novel MgCl₂-supported TiCl₄ catalyst modified with a rare earth compound NdCl_x(OR)_y (SN-1 catalyst), which was developed in our laboratory. The catalytic activities are 1300–2500 g/g·Ti·h. Analyses of copolymers with solvent extraction, ¹³C-NMR, WAXD, GPC, and DSC was performed. The results indicate that the SN-1 catalyst selectively gave crystalline diblock copolymers of isotactic polystyrene and isotactic poly(1-butene), with the styrene unit content of 30–60 mol %. © 1996 John Wiley & Sons, Inc.     

May Trifluoromethylation and Polymerization of Styrene Occur from a Perfluorinated Persistent Radical (PPFR)?

The radical polymerization of styrene (St) initiated by a trifluoromethyl radical generated from a perfluorinated highly branched persistent radical (PPFR) is presented with an isolated yield above 70 %. The release of ^.CF₃ radical occurred from a temperature above 85 °C. Deeper ¹H and ¹⁹F NMR spectroscopies of the resulting fluorinated polystyrenes (CF₃-PSts) evidenced the presence of both CF₃ end-group of the PSt chain and the trifluoromethylation of the phenyl ring (in meta-position mainly). [PPFR]₀/[St]₀ initial molar ratios of 3:1, 3:10 and 3:100 led to various molar masses ranging from 1750 to 5400 g mol⁻¹ in 70–86 % yields. MALDI-TOF spectrometry of such CF₃-PSts highlighted polymeric distributions which evidenced differences between m/z fragments of 104 and 172 corresponding to styrene and trifluoromethyl styrene units, respectively. Such CF₃-PSt polymers were also compared to conventional PSts produced from the radical polymerization of St initiated by a peroxydicarbonate initiator. A mechanism of the polymerization is presented showing the formation of a trifluoromethyl styrene first, followed by its radical (co)polymerization with styrene. The thermal properties (thermal stability and glass transition temperature, T_g) of these polymers were also compared and revealed a much better thermal stability of the CF₃-PSt (10 % weight loss at 356–376 °C) and a T_g of around 70 °C.     

Preparation of CaCO3/Polystyrene Inorganic/Organic Composite Nanoparticles

CaCO₃/polystyrene inorganic/organic composite nanoparticles (50 nm) with a core/shell structure were synthesized in 80% yield by emulsion polymerization. Nanometer CaCO₃ was pretreated with γ‐methacryloxypropyltrimethoxysilane in order to introduce polymerizable groups onto its surface. Soxhlet extraction experiments have shown that only 4% of total encapsulating polystyrene (PS) was removable when the ratio of CaCO₃ to styrene was relatively low (14.8–29.6%), indicating strong adhesion between CaCO₃ and PS.     

Copolymerization of norbornene and styrene catalyzed by a novel anilido–imino nickel complex/methylaluminoxane system

Copolymerizations of norbornene with styrene were carried out with a catalytic system of anilido–imino nickel complex (ArN?CHC₆H₄NAr)NiBr (Ar = 2,6‐dimethylphenyl) and methylaluminoxane in toluene. The influence of the comonomer feed content and polymerization temperature on the conversion and composition of the copolymers with (ArN?CHC₆H₄NAr)NiBr/methylaluminoxane was investigated. An increase in the initial styrene feed content led to an increase in the incorporated styrene content of the resulting copolymer. The determination of the reactivity ratios showed a much high reactivity for norbornene (reactivity ratio for styrene = 0.26, reactivity ratio for norbornene = 20.78), which was consistent with a coordination mechanism. NMR analysis of the end groups further confirmed that the chain was initiated through a styrene secondary insertion or a norbornene insertion into Ni? H and terminated through β‐H elimination from an inserted styrene unit. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5237–5246, 2006     

Multifunctional linear methacrylate copolymer polyenes having pendant vinyl groups: Synthesis and photoinduced thiol–ene crosslinking polyaddition

UV‐induced thiol‐ene crosslinked films composed of linear methacrylate copolymers having pendant enes (MCPenes) are reported. An approach involving a combination of controlled radical polymerization to synthesize well‐controlled pendant hydroxyl containing copolymers (MCP_OHs) with the following facile carbodiimide coupling of the formed MCP_OHs with enes allows for the synthesis of well‐controlled MCPenes with narrow molecular weight distribution. The density of the pendant enes in MCPenes are easily modulated by varying monomer ratios in the feed. Under UV irradiation, the resulting MCPenes undergo thiol‐ene polyaddition reactions with polythiols to form crosslinked films with a uniform network. The results from thermal and mechanical analysis suggest these properties are tuned by adjusting the densities of pendant enes in MCPenes and the amount of thiols in the reactive mixtures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 572–581     

New Types of Planar Chiral [2.2]Paracyclophanes and Construction of One‐Handed Double Helices

New types of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes were synthesized from racemic 4,12‐dihydroxy[2.2]paracyclophane as the starting compound. Regioselective dibromination and transformation afforded a series of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes, which can be used as chiral building blocks. In this study, left‐ and right‐handed double helical structures were constructed via chemoselective Sonogashira–Hagihara coupling. The double helical compounds were excellent circularly polarized luminescence (CPL) emitters with large molar extinction coefficients, good photoluminescence quantum efficiencies, and large CPL dissymmetry factors.     

Chlorosulfonyl styrene–divinylbenzene copolymer characteristics as a function of chlorosulfonation and chlorination reaction parameters

Chlorosulfonyl substituted styrene–divinylbenzene copolymer is a highly reactive intermediate used in organic synthesis. It is obtained in three steps: (1) the polymeric support in the form of spherical beads is prepared by free radical polymerization of styrene; (2) the divinylbenzene mixture and the aromatic styrene groups of the obtained copolymer are sulfonated with chlorosulfonic acid in dichloroethane and (3) this is followed by chlorination of the sulfonyl groups with PCl₅/POCl₃ mixture. Chemical analysis shows that chlorosulfonation leads to both sulfonyl and chlorosulfonyl products in which content and ratio vary as a function of reaction parameters: maximum total group content of 5.1 meq/g is reached after 3 hr reaction, at 40°C with styrene to a chlorosulfonic acid molar ratio of 12.4:1. In the chlorination reaction, sulfonyl to chlorosulfonyl conversion is also observed to vary as a function of time and chlorinating mixture composition: 99.6 mol% conversion degree is attained after 2 hr reaction with styrene/PCl₅/POCl₃ in a molar ratio of 1:4:23. © 1997 John Wiley & Sons, Ltd.     

Grafting of styrene onto low molecular weight polymers and copolymers of butadiene

The grafting of styrene onto low molecular weight polybutadienes and butadiene–styrene co-polymers was studied. A mathematical method was used for the design of experiments and for the determination of the optimum grafting conditions with respect to the conversion of styrene and the efficiency of grafting. The reaction parameters were temperature (65–105°C), time (2–10 hr), concentration of the initiator, polymer to monomer ratio (10/90–90/10) and dilution by solvent (toluene). The optimum grafting conditions were chosen under which 50–60 wt-% of styrene was grafted onto backbone polymer at a high conversion of the monomer. It was found that the reactions producing graft copolymer prevailed over the styrene homopolymerization when the temperatures employed were lower (65–85°C), and the reaction time (8–10 hr), backbone polymer/monomer ratio, and the dilution by solvent were higher. The efficiency, density, and degree of grafting were found to increase with the increase in the molecular weight of the backbone polymer. The efficiencies and densities of grafting onto low molecular weight polybutedienes were higher than those of grafting onto low molecular weight butadiene–styrene copolymers. Grafting efficiencies and grafting densities were in the ranges 37.8–61.6 wt % and 0.06–0.26, respectively, in the studied range of number-average molecular weights (M?_n = 2400–6000).     

The solubility of light fullerenes in styrene over the temperature range 20–80°C

The temperature dependence (over the range 20–80°C) of the solubility of light fullerenes (C₆₀ and C₇₀) and a mixture of fullerenes (60 wt % C₆₀, 39 wt % C₇₀, and 1 wt % C_76–90) in styrene was studied. The corresponding solubility polytherms are given and characterized.