Copolymerization of ethylene/α‐olefins over (2‐MeInd)2ZrCl2/MAO and (2‐BzInd)2ZrCl2/MAO systems

Ethylene homopolymerization and ethylene/α‐olefin copolymerization were carried out using unbridged and 2‐alkyl substituted bis(indenyl)zirconium dichloride complexes such as (2‐MeInd)₂ZrCl₂ and (2‐BzInd)₂ZrCl₂. Various concentrations of 1‐hexene, 1‐dodecene, and 1‐octadecene were used in order to find the effect of chain length of α‐olefins on the copolymerization behavior. In ethylene homopolymerization, catalytic activity increased at higher polymerization temperature, and (2‐MeInd)₂ZrCl₂ showed higher activity than (2‐BzInd)₂ZrCl₂. The increase of catalytic activity with addition of comonomer (the synergistic effect) was not observed except in the case of ethylene/1‐hexene copolymerization at 40°C. The monomer reactivity ratios of ethylene increased with the decrease of polymerization temperature, while those of α‐olefin showed the reverse trend. The two catalysts showed similar copolymerization reactivity ratios. (2‐MeInd)₂ZrCl₂ produced the copolymer with higher M_w than (2‐BzInd)₂ZrCl₂. The melting temperature and the crystallinity decreased drastically with the increase of the α‐olefin content but T_m as a function of weight fraction of the α‐olefins showed similar decreasing behavior. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 928–937, 2000     

Gas‐phase ethylene polymerization using zirconocene supported on mesoporous molecular sieves

Mesoporous molecular sieves, with pore diameters of 2.6–25 nm, were impregnated with methylaluminoxane and bis(butylcyclopentadienyl)zirconium dichloride and tested as catalysts for the gas‐phase homopolymerization of ethylene at ethylene pressures of 200 psi and temperatures of 50–100°C and for 1‐hexene/ethylene copolymerization at 70°C. The activities and activity profiles, at constant Zr and Al contents, depended on the pore size of the supports and the polymerization temperature. Maximum activities for both the homopolymerizations and copolymerizations were observed for catalysts made with supports having pore diameters of 2.6 and 5.8 nm. Homopolymerization activities were highest at temperatures of 70–80°C; average homopolymerization and copolymerization activities up to 9000 kg of polyethylene/(mol of Zr h) were obtained. The weight‐average molecular weights (M_w's) were not a function of the support pore size but decreased with increasing reaction temperatures, from about 260,000 at 50°C to about 165,000 at 100°C. The polydispersities were essentially constant at 2.5 ± 0.2 for the homopolymers. M_w's for the 1‐hexene/ethylene copolymers had an average value of 117,000 with an average polydispersity of 2.8. The amount of triisobutyl aluminum added to the reactor significantly affected the activity and activity profiles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1161–1177, 2003     

Influence of support friability and concentration of α‐olefins on gas‐phase ethylene polymerization over polymer‐supported metallocene/methylaluminoxane catalysts

The effects of support friability (Φ) and ethylene/comonomer ratios were investigated over supported metallocene/methylaluminoxane catalysts prepared with nine different porous polymeric supports and various comonomer concentrations with a 2‐L reactor operated in the semibatch gas‐phase mode at 80°C and 1.4 MPa. Φ of the supports was measured with a newly devised method. The performance of the supported catalysts depended on support Φ as follows. The average homopolymerization activities varied from less than 6 t of polyethylene (PE) (mol of Zr)^?1 h^?1 for low‐Φ catalysts to 10–20 t of PE (mol of Zr)^?1 h^?1 for moderate‐Φ catalysts and up to 100 t of PE (mol of Zr)^?1 h^?1 for the high‐Φ catalysts. The presence of 1‐hexene and propylene comonomers increased the activity of the low‐Φ catalysts by up to 20‐fold and 50‐fold, respectively; that is, there were very marked comonomer effects. Activity enhancement by 1‐hexene was less than 3‐fold for the moderate‐Φ catalysts, whereas the high‐Φ catalysts showed little activity enhancement. Sometimes, 1‐hexene even resulted in activity reductions. Very different particle morphologies were obtained with the catalysts of different Φ's. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 514–527, 2007     

Gas‐phase olefin polymerization over supported metallocene/MAO catalysts: influence of support on activity and polydispersity

Three catalysts obtained by supporting bis(n‐butylcyclopentadienyl)zirconium dichloride/methylaluminoxane on: (1) porous crosslinked poly(2‐hydroxyethylmethacrylate‐co‐styrene‐co‐divinylbenzene) particles (CAT1); (2) swellable crosslinked poly(styrene‐co‐divinylbenzene) particles (CAT2); and (3) by evaporating the catalyst precursors solution to dry powder, CAT3 were used in gas‐phase polymerization of ethylene, and ethylene/1‐hexene in a 2 L semi‐batch reactor at 80 °C and 1.4 MPa. The average polymerization activities of the three catalysts were 12.3–15.5, 4.2–10.1, and 14.3–62.9 ton PE (mol Zr h)^?1 respectively. CAT1 and CAT3 produced polyethylenes with a polydispersity range of 2.3–2.7, while that of CAT2 was 3.5–6.4. The supported catalysts produced polyolefin particles with bulk density of 0.36–0.43 g ml^?1, and essentially no fines. Ethylene/1‐hexene co‐polymerization (7 mol m^?3 initial 1‐hexene concentration in the reactor) increased polymerization activities and produced lower‐molar‐mass co‐polymers. At 21 mol m^?3 1‐hexene the polymerization activities decreased, but the relative amount of the low‐molar‐mass co‐polymer for CAT2 increased, leading to higher polydispersity. Copyright © 2006 Society of Chemical Industry     

Comonomer effects in copolymerization of ethylene and 1‐hexene with MgCl2‐supported Ziegler‐Natta catalysts: New evidences from active center concentration and molecular weight distribution

In this article, comonomer effects in copolymerization of ethylene and 1‐hexene with four MgCl₂‐supported Ziegler‐Natta catalysts using either ethylene or 1‐hexene as the main monomer were investigated. It was found that no matter which monomer was used as the main monomer, the polymerization activity was significantly enhanced by introducing small amount of comonomer. In copolymerization with ethylene as the main monomer, the strength of comonomer effects was much stronger in active centers producing low‐molecular‐weight polymer than those producing high‐molecular‐weight polymer. In copolymerization with 1‐hexene as the main monomer, the number of active centers ([C*]/[Ti]) was determined, and the propagation rate constants (k_p) were calculated. Deconvolution of the polymer molecular weight distribution into Flory components were made to study the active center distribution. Introduction of small amount of ethylene caused marked increase in the number of active centers and decrease in average chain propagation rate constant. Introducing internal electron donor in the catalyst enhanced not only the number of active centers but also the chain propagation rate constant. In copolymerization of 1‐hexene with small amount of ethylene, the internal donor weakened the comonomer effects to some extent and changed the distribution of comonomer effects among different types of active centers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41264.     

A new post‐metallocene catalyst for alkene polymerization: copolymerization of ethylene and 1‐hexene with titanium complexes bearing N,N‐dialkylcarbamato ligands

A new type of post‐metallocene polymerization catalyst based on titanium complexes with N,N‐dialkylcarbamato ligands was used to copolymerize ethylene and 1‐hexene. These easy‐to‐synthesize and stable complexes in combination with different organoaluminium co‐catalysts produce random ethylene/1‐hexene copolymers characterized by a broad molecular weight distribution and high 1‐hexene incorporation, as confirmed by SEC, DSC and ¹³C NMR analysis. The influence of the main reaction parameters on the polymerization reactions was studied including the type of catalyst components, solvent, temperature, the ethylene partial pressure and the [Al]/[Ti] ratio in the catalyst. A higher activity and a higher 1‐hexene incorporation were achieved with AlMe₃‐depleted methylalumoxane as co‐catalyst and chlorobenzene as solvent. © 2013 Society of Chemical Industry     

Behavior of poly(ethylene‐co‐olefin) polymers as elastomeric materials

The properties of two new ethylene‐α‐olefin copolymers, namely, ethylene–1‐hexene copolymer (EHC) and ethylene–1‐octadecene copolymers (EOC), synthesized via metallocene catalysts were evaluated. The copolymerization was carried out in an autoclave reactor with Et(Indenyl)₂ZrCl₂/methylaluminoxane as a catalyst system. These single‐site catalysts (metallocene type) allow one to obtain very homogeneous copolymers with excellent control of the molecular weight distribution and proportion of comonomer incorporation. So, copolymers with 18 mol % comonomer in the case of EHC and 12 mol % for EOC were shaped, and activities around 100,000 kg of polymer mol^?1 of Zr bar^?1 h^?1 were reached. The properties of these copolymers were compared with other commercial elastomers, such as ethylene–propylene copolymers synthesized by Ziegler–Natta catalysts and an ethylene–octene copolymer obtained via metallocene catalysts. The results show that these new copolymers, in particular, EOC, had excellent elastomeric properties. Furthermore, they had a relatively low viscosity, which implied a good response during processing. Moreover, the effectiveness of these copolymers as impact modifiers for polyolefins was also studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3008–3015, 2004     

Ethylene/1‐hexene copolymerization with supported Ziegler–Natta catalysts prepared by immobilizing TiCl3(OAr) onto MgCl2

Five titanium complexes TiCl₃(OAr) (Ar = C₆H₅? , 2,6‐Me₂C₆H₃? , 2,6‐i‐Pr₂C₆H₃? , 2,6‐t‐Bu₂C₆H₃? , 4‐Me‐2,6‐t‐Bu₂C₆H₃? ) were immobilized, respectively, on MgCl₂ in semibatch reaction to form supported catalysts for olefin polymerization. Comparing with the catalysts prepared by immobilizing TiCl₃(OAr) onto MgCl₂ in batch reaction, the catalysts prepared by semibatch reaction have lower titanium content and higher ArO/Ti ratio. The aryloxy‐containing catalysts studied in this work showed higher ethylene/1‐hexene copolymerization activity and higher 1‐hexene incorporation rate than the blank catalyst when activated by triisobutylaluminum. Similar effects of the aryloxy ligand were observed when the copolymerization is conducted in the presence of hydrogen. Introducing aryloxy ligand in the catalysts either by semibatch or batch reaction caused similar effects of enhancing copolymerization activity and α‐olefin incorporation rate. Mechanism of the effects of aryloxy ligand has been discussed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41329.     

Preparation of ethylene/1‐octene copolymers from ethylene stock with tandem catalytic system

Tandem catalysis offers a novel synthetic route to the production of linear low‐density polyethylene. This article reports the use of homogeneous tandem catalytic systems for the synthesis of ethylene/1‐octene copolymers from ethylene stock as the sole monomer. The reported catalytic systems involving a highly selective, bis(diphenylphosphino)cyclohexylamine/Cr(acac)₃/methylaluminoxane (MAO) catalytic systems for the synthesis of 1‐hexene and 1‐octene, and a copolymerization metallocene catalyst, rac‐Et(Ind)₂ZrCl₂/MAO for the synthesis of ethylene/1‐octene copolymer. Analysis by means of DSC, GPC, and ¹³C‐NMR suggests that copolymers of 1‐hexene and ethylene and copolymers of 1‐octene and ethylene are produced with significant selectivity towards 1‐hexene and 1‐octene as comonomers incorporated into the polymer backbone respectively. We have demonstrated that, by the simple manipulation of the catalyst molar ratio and polymerization conditions, a series of branched polyethylenes with melting temperatures of 101.1–134.1°C and density of 0.922–0.950 g cm^?3 can be efficiently produced. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

(Co)polymerization of ethylene via nonmetallocene catalysts with diphenyl phosphoroso schiff‐base ligand

A series of novel nonmetallocene catalysts [N, O, P] with diphenyl phosphoroso ligands were synthesized by the treatment of phthaldialdehyde, substituted phenols, chlorodiphenyl phosphine with metal halides of TiCl₄ and ZrCl₄. The catalyst microstructure was characterized by ¹H NMR and EA. After activated by methylaluminoxane (MAO), these [N, O, P] catalysts were utilized to catalyze the polymerization of ethylene and the copolymerization of ethylene with 1‐octene. The results indicated that the obtained catalysts were highly efficient for ethylene polymerization and ethylene/1‐octene copolymerization. Structures and properties of the obtained polymers were measured by WAXD, DSC, GPC, and ¹³C NMR. The results indicated that polyethylene catalyzed by Cat. 3 possessed the highest weight‐average molecular weight of 1.025 × 10⁶ g/mol and the highest melting point of 136.3°C. The copolymer of ethylene/1‐octene catalyzed by Cat. 1 exhibited the highest 1‐octene incorporation content of 0.63 mol %. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42225.     

Effects of aluminum alkyls on ethylene/1‐hexene polymerization with supported metallocene/MAO catalysts in the gas phase

The effects of aluminum alkyls on the gas‐phase ethylene homopolymerization and ethylene/1‐hexene copolymerization over polymer‐supported metallocene/methylaluminoxane [(n‐BuCp)₂ZrCl₂/MAO] catalysts were investigated. Results with triisobutyl aluminum (TIBA), triethyl aluminum (TEA), and tri‐n‐octyl aluminum (TNOA) showed that both the type and the amount of aluminum alkyl influenced the polymerization activity profiles and to a lesser extent the polymer molar masses. The response to aluminum alkyls depended on the morphology and the Al : Zr ratio of the catalyst. Addition of TIBA and TEA to supported catalysts with Al : Zr >200 reduced the initial activity but at times resulted in higher average activities due to broadening of the kinetic profiles, i.e., alkyls can be used to control the shape of the activity profiles. A catalyst with Al : Zr = 110 exhibited relatively low activity when the amount of TIBA added was <0.4 mmol, but the activity increased fivefold by increasing the TIBA amount to 0.6 mmol. The effectiveness of the aluminum alkyls in inhibiting the initial polymerization activity is in the following order: TEA > TIBA >> TNOA. A 2‐L semibatch reactor, typically run at 80°C and 1.4 MPa ethylene pressure for 1 to 5 h was used for the gas‐phase polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3549–3560, 2004     

Polymerization of olefins and polar monomers catalyzed by bis(imino)Ni(II)/dibutylmagnesium/alkylaluminium halide systems

[Bis(N,N′‐dimesitylimino)acenaphthene]dibromonickel ( 1 ) when activated with diethylaluminium chloride (DEAC) is a very active catalyst for ethylene homopolymerization. The activity (A_E) of 1 /100 DEAC is twenty times greater than that of 1 /100 MAO and of the same order of magnitude as 1 /2000 MAO. In the case of homopolymerization of propylene the highest activity (A_P) was obtained at a ratio of 25/15 for Al_DEAC/Ni. Trialkylaluminium compounds were also found to act as cocatalysts for 1 . The PE synthesized with four different cocatalysts was found by ¹³C NMR to have dissimilar branching distributions. 1 /DEAC shows no activity for the polymerization of proximately substituted polar monomers. The introduction of dibutylmagnesium, (DBM) activates the 1 /DEAC system to copolymerize ethylene and a number of proximately substituted polar monomers. Compared with the 1 /MAO/monomer.AlR₃ catalyst system the former is three times more active for copolymerization of 5‐hexene‐1‐ol or 10‐undecen‐1‐oic acid with ethylene. The activity of copolymerization is 1 /24, 1 /5 and 1 /2 as active as homopolymerization, respectively, in the case of methyl vinyl ketone, vinyl acetate and ?‐caprolactam. In the case of tetrahydrofuran/ethylene, the 1 /MAO catalyst produced copolymers using AlR₃ pretreated THF whereas the 1 /DEAC/DBM catalyst produces homopolyethylene only. No polymerization occurred with an acrylonitrile/ethylene mixture in the presence of 1 /DBM/DEAC catalyst. © 2002 Society of Chemical Industry     

Silica‐supported (nBuCp)2ZrCl2: effect of catalyst active center distribution on ethylene–1‐hexene copolymerization

Metallocenes are a modern innovation in polyolefin catalysis research. Therefore, two supported metallocene catalysts—silica/MAO/(ⁿBuCp)₂ZrCl₂ (Catalyst 1) and silica/ⁿBuSnCl₃/MAO/(ⁿBuCp)₂ZrCl₂ (Catalyst 2), where MAO is methylaluminoxane—were synthesized, and subsequently used to prepare, without separate feeding of MAO, ethylene–1‐hexene Copolymer 1 and Copolymer 2, respectively. Fouling‐free copolymerization, catalyst kinetic stability and production of free‐flowing polymer particles (replicating the catalyst particle size distribution) confirmed the occurrence of heterogeneous catalysis. The catalyst active center distribution was modeled by deconvoluting the measured molecular weight distribution and copolymer composition distribution. Five different active center types were predicted for each catalyst, which was corroborated by successive self‐nucleation and annealing experiments, as well as by an extended X‐ray absorption fine structure spectroscopy report published in the literature. Hence, metallocenes impregnated particularly on an MAO‐pretreated support may be rightly envisioned to comprise an ensemble of isolated single sites that have varying coordination environments. This study shows how the active center distribution and the design of supported MAO anions affect copolymerization activity, polymerization mechanism and the resulting polymer microstructures. Catalyst 2 showed less copolymerization activity than Catalyst 1. Strong chain transfer and positive co‐monomer effect—both by 1‐hexene—were common. Each copolymer demonstrated vinyl, vinylidene and trans‐vinylene end groups, and compositional heterogeneity. All these findings were explained, as appropriate, considering the modeled active center distribution, MAO cage structure repeat units, proposed catalyst surface chemistry, segregation effects and the literature that concerns and supports this study. While doing so, new insights were obtained. Additionally, future research, along the direction of the present work, is recommended. © 2013 Society of Chemical Industry     

Chemical composition distribution study in ethylene/1‐hexene copolymerization to produce LLDPE material using MgCl2‐TiCl4‐based Ziegler‐Natta catalysts

The characteristic features of LLDPE polymerization with ZN catalyst are the time drift effect during polymerization and the bending effect when trying to decrease density of the copolymer by adding more comonomer to the polymerization. The time drift in LLDPE polymerization is revealed by a constant decrease of comonomer incorporation during polymerization time. The bending is revealed by difficulties in lowering the density of LLDPE material below the density of 920 kg/m³. With increasing comonomer content during polymerization, the density does not decrease, but the soluble fraction increases. To try to observe if these phenomena are connected, two types of catalysts, SiO₂ supported and precipitated MgCl₂ ZN catalysts, were studied. A short time (10 min) and an extended time (60 min) copolymerization test series where the polymerizations were performed in the presence of a gradually increasing comonomer amount. Both catalysts show a strong bending when density is presented as a function of 1‐hexene both in 10‐ and 60‐min polymerization, indicating no connection between time drift and bending. The density, melting point, and crystallinity results all indicate that both catalysts are making similar copolymer material with identical chemical composition distribution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ceric ion‐induced graft copolymerization of acrylamide on cationic guar gum at low temperature

The solution polymerization of acrylamide (AM) on cationic guar gum (CGG) under nitrogen atmosphere using ceric ammonium sulfate (CAS) as the initiator has been realized. The effects of monomer concentration and reaction temperature on grafting conversion, grafting ratio, and grafting efficiency (GE) have been studied. The optimal conditions such as 1.3 mol of AM monomer and 2.2 × 10^?4 mol of CAS have been adopted to produce grafted copolymer (CGG1‐g‐PAM) of high GE of more than 95% at 10°C. The rates of polymerization (R_p) and rates of graft copolymerization (R_g) are enhanced with increase in temperature (<35°C).The R_p is enhanced from 0.43 × 10^?4 mol L^?1 s^?1 for GG‐g‐PAM to 2.53 × 10^?4 mol L^?1 s^?1 for CGG1‐g‐PAM (CGG1, degree of substitute (DS) = 0.007), and R_g from 0.42 × 10^?4 to 2.00 × 10^?4 mol L^?1 s^?1 at 10°C. The apparent activation energy is decreased from 32.27 kJ mol^?1 for GG‐g‐PAM to 8.09 kJ mol^?1 for CGG1‐g‐PAM, which indicates CGG has higher reactivity than unmodified GG ranging from 10 to 50°C. Increase of DS of CGG will lead to slow improvement of the polymerization rates and a hypothetical mechanism is put forward. The grafted copolymer has been characterized by infrared spectroscopy, thermal analysis, and scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3715–3722, 2007     

Synthesis of poly(1‐hexene)s end‐functionalized with phenols

Electrophilic alkylations of phenol/2,6‐dimethylphenol were performed with vinylidene‐terminated poly(1‐hexene)s using BF₃·OEt₂ catalyst. Vinylidene‐terminated poly(1‐hexene)s with M_n varying from 400 to 10000 were prepared by bulk polymerization of 1‐hexene at 50 to ?20 °C using Cp₂ZrCl₂/MAO catalysts. The phenol/2,6‐dimethylphenol‐terminated poly(1‐hexene)s was characterized by NMR (¹H, ¹³C), UV, IR and vapor phase osmometer (VPO). The isomer distribution (ortho, para and ortho/para) was determined by ¹³P NMR using a phosphitylating reagent, namely 2‐chloro‐1,3,2‐dioxaphospholane. The number‐average degree of functionality (F_n) >0.9 with >95% para selectivity could be achieved using low‐molecular‐weight oligomers of poly(1‐hexene)s. Copyright © 2005 Society of Chemical Industry     

Synthesis and characterization of homo‐ and copolymers of 3‐(2‐cyano ethoxy)methyl‐ and 3‐[methoxy(triethylenoxy)]methyl‐3′‐methyl‐oxetane

Two oxetane‐derived monomers 3‐(2‐cyanoethoxy)methyl‐ and 3‐(methoxy(triethylenoxy)) methyl‐3′‐methyloxetane were prepared from the reaction of 3‐methyl‐3′‐hydroxymethyloxetane with acrylonitrile and triethylene glycol monomethyl ether, respectively. Their homo‐ and copolyethers were synthesized with BF₃· Et₂O/1,4‐butanediol and trifluoromethane sulfonic acid as initiator through cationic ring‐opening polymerization. The structure of the polymers was characterized by FTIR and¹H NMR. The ratio of two repeating units incorporated into the copolymers is well consistent with the feed ratio. Regarding glass transition temperature (T_g), the DSC data imply that the resulting copolymers have a lower T_g than pure poly(ethylene oxide). Moreover, the TGA measurements reveal that they possess in general a high heat decomposition temperature. The ion conductivity of a sample (P‐AN 20) is 1.07 × 10^?5 S cm^?1 at room temperature and 2.79 × 10^?4 S cm^?1 at 80 °C, thus presenting the potential to meet the practical requirement of lithium ion batteries for polymer electrolytes. Copyright © 2005 Society of Chemical Industry     

Comonomer enhancement effect of 1-hexene in ethylene copolymerization catalyzed over MgCl2/THF/TiCl4 catalysts

Homo- and copolymerization of ethylene were performed by using a catalyst system composed of TiCl₄/THF/MgCl₂ complex activated with AlEt₃ at 70°C and 3 atm. To investigate the effect of the compositional difference of the catalyst on the rates of homo- and copolymerization and on the reactivity in ethylene–hexene copolymerization, a series of six catalysts with different compositions (Mg/Ti = 0.4–16.5) were prepared by coprecipitation. The catalytic activity in ethylene polymerization increased sharply with the Mg/Ti ratio from 21 (Mg/Ti = 0.4) to 1477 kg PE/g-Ti h (Mg/Ti = 16.5). The activity in copolymerization with 1-hexene also increased with Mg/Ti ratio. The values of r₁ were 120, regardless of Mg/Ti ratios within the experimental error range. Enhancement of the polymerization rate by the addition of 1-hexene in the reaction medium was observed only for the catalysts of low Mg/Ti ratio. This unusual effect of 1-hexene on the polymerization rate was explained by chemical and physical processes that occurred during polymerization. © 1993 John Wiley & Sons, Inc.     

Isobutylaluminum aryloxides as metallocene activators in Homo‐ and copolymerization of olefins

The article describes that sterically hindered isobutylaluminum aryloxides with bulky ^tBu substituents at 2,6‐ positions of aryl fragment, i.e. (2,6‐di‐^tBu,4‐R‐C₆H₂O)AlⁱBu₂ (R = H ( 1‐DTBP ), Me ( 1‐BHT ), ^tBu ( 1‐TTBP )) and (2,6‐di‐^tBu,4‐R‐C₆H₂O)₂AlⁱBu (R=H( 2‐DTBP ), Me( 2‐BHT )) can serve as cocatalysts for metallocene complexes. Isobutylaluminum aryloxides have been applied for activation of rac‐Et(2‐MeInd)₂ZrMe₂ in homopolymerization of ethylene, propylene, copolymerization of ethylene and propylene, and terpolymerization of ethylene, propylene, and 5‐ethylidene‐2‐norbornene at Al/Zr = 300 mol/mol. The type of R substituent at 4‐position has a significant effect on catalyst activity. The catalytic system with 1‐TTBP showed the highest activity in all homo‐ and copolymerization processes. Diisobutylaluminum aryloxides provide much higher activity to the systems in all polymerization processes and stronger ability for propylene incorporation in copolymer than diaryloxides. The activities of the systems with isobutylaluminum aryloxides are similar or exceed that of the system with MAO as activator as have shown for propylene polymerization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43276.     

Effect of acrylic acid neutralization on ‘livingness’ of poly[styrene‐ran‐(acrylic acid)] macro‐initiators for nitroxide‐mediated polymerization of styrene

BACKGROUND: The effect of acrylic acid neutralization on the degradation of alkoxyamine initiators for nitroxide‐mediated polymerization (NMP) was studied using styrene/acrylic acid and styrene/sodium acrylate random copolymers (20 mol% initial acrylate feed concentration) as macro‐initiators. The random copolymers were re‐initiated with fresh styrene in 1,4‐dioxane at 110 °C at SG1 mediator/BlocBuilder^® unimolecular initiator ratios of 5 and 10 mol%. RESULTS: The value of k_pK (k_p = propagation rate constant, K = equilibrium constant) was not significantly different for styrene/acrylic acid and styrene/sodium acrylate compositions at 110 °C (k_pK = 2.4 × 10^?6–4.6 × 10^?6 s^?1) and agreed closely with that for styrene homopolymerization at the same conditions (k_pK = 2.7 × 10^?6–3.0 × 10^?6 s^?1). All random copolymers had monomodal, narrow molecular weight distributions (polydispersity index M?_w/M?_n = 1.10–1.22) with similar number‐average molecular weights M?_n = 19.3–22.1 kg mol^?1. Re‐initiation of styrene/acrylic acid random copolymers with styrene resulted in block copolymers with broader molecular weight distributions (M?_w/M?_n = 1.37–2.04) compared to chains re‐initiated by styrene/sodium acrylate random copolymers (M?_w/M?_n = 1.33). CONCLUSIONS: Acrylic acid degradation of the alkoxyamines was prevented by neutralization of acrylic acid and allowed more SG1‐terminated chains to re‐initiate the polymerization of a second styrenic block by NMP. Copyright © 2008 Society of Chemical Industry