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Highly branched polyethylene (HBPE) was developed into practical application as highly efficient sorbent material for oil‐spill cleanup and oil/water separation. To obtain large‐scale production of HBPE, a thermal stable Ni(II)‐α‐diimine catalyst for ethylene polymerization in our previous work has been employed to prepare the polyolefin material in a 10‐liter polymerization reactor with a high activity (>106 gPE/mol[Ni] h). The structure, molecular weight and distribution, thermal and mechanical properties were systematically characterized by NMR, ATR‐FTIR, GPC, DSC, DMA, and TGA, respectively. Through simple but feasible cross‐linking process, the HBPE‐based oil‐absorption materials with contact angles up to 111.5° were directly applied into absorption test using various oil and pure hydrocarbons. Reusability and recovery of the absorption materials and oil or solvents were probed by drying or using the distillation method. Oil/water separation was made to determine the hydrophobic and oleophilic nature of this material. Flory‐Rehner polymer swelling theory is employed to study the structure–property relationship via determining the network structure including cross‐linking density ρc and average molecular weight Mc between two cross‐links. The mixture of sorbent material after absorbing oil was regarded as crude oil component to simulate oil refinery process by thermogravimetric analysis, providing an alternative approach for oil‐collection. [ABSTRACT FROM AUTHOR]

Propylene slurry polymerization with a MgCl2-supported Ziegler-Natta catalyst containing internal electron donor was conducted after different durations of pre-contact of the catalyst with triethylaluminum cocatalyst. The number of active centers ([C*]/[Ti]) was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and measuring sulfur content in the polymer. The pre-contact treatment caused selective deactivation of a part of active centers with low stereoselectivity and much lower activity in the initial stage of polymerization as compared with the polymerization run without the pre-contact stage. The active center concentration and polymerization activity decreased with prolonging of the pre-contact stage. The proportion of stereoselective active centers was increased by prolonging the pre-contact stage, so the isotacticity of produced polypropylene was enhanced. Release of active centers through catalyst particle fragmentation was significantly retarded, and the polymerization rate curve changed from decay type to induction type by the precontact treatment. In the induction period both non-stereoselective and stereoselective active centers were released and activated, resulting in gradual reduction of the polymer's isotacticity in the first 5–10 min of polymerization. Selective deactivation of non-stereoselective active centers also took place in propylene polymerization using the catalyst without pre-contacting with the cocatalyst. In this case, the polymerization rate decayed with time after a short induction period of 2–5 min. Over reduction of the active center precursors with low stereoselectivity by triethylaluminum was considered as the reason for their deactivation during the pre-contact or the polymerization processes. [ABSTRACT FROM AUTHOR]

ABSTRACT A precisely sequenced ethylene-propylene (EP) fully alternating copolymer was synthesized via trans-1,4-polymerization of isoprene catalyzed by Ziegler-Natta catalyst followed by hydrogenation. This EP copolymer was used as model polymer for studying structure-property relationship. An ethylene-propylene random copolymer (ethylene-propylene rubber [EPR]) with similar ethylene content was also prepared for comparison, and the effect of comonomer sequence distribution on properties was investigated. The copolymer chain structures were monitored by 1H and 13C NMR and Fourier translation infrared. Differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and tensile tests were employed to determine the thermal and mechanical properties. The fully alternating copolymer EP gives a more precise glass transition comparing than EPR. Further understanding on thermal properties and aggregation behavior of ethylene-propylene copolymers is made possible by this comparative study. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45816. [ABSTRACT FROM AUTHOR]

Significance We report on a novel atmosphere-switching polymerization process (ASPP) that produces advanced polyolefin materials with high performance in a single polymerization reactor through unique monomer feeding policies. In the ASPP, each polymer particle is exposed to 'atmosphere A' and 'atmosphere B' in an alternating manner and time and again. As a result, 'polymer A' and 'polymer B' are formed within the polymer particle in an alternating manner and time and again too. Two types of polypropylene (PP) in-reactor alloys are prepared: impact polypropylene copolymers (IPCs) with an exceptional stiffness-toughness balance and soft polypropylene alloys (SPPs) with well-defined, high-rubber content sticking-free particles. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4468-4473, 2013 [ABSTRACT FROM AUTHOR]

In this article, the effect of diethylaluminum chloride (DEAC) in propylene polymerization with MgCl 2-supported Ziegler-Natta catalyst was studied. Addition of DEAC in the catalyst system caused evident change in catalytic activity and polymer chain structure. The activity decrease in raising DEAC/Ti molar ratio from 0 to 2 is a result of depressed production of isotactic polypropylene chains. The number of active centers in fractions of each polymer sample was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and fractionating the polymer into isotactic, mediumisotactic and atactic fractions. The number of active centers in isotactic fraction ([C i*]/[Ti]) was lowered by increasing DEAC/Ti molar ratio to 2, but further increasing the DEAC/Ti molar ratio to 20 caused marked increase of [C i*]/[Ti]. The number of active centers that produce atactic and medium-isotactic PP chains was less influenced by DEAC in the range of DEAC/Ti = 0–10, but increased when the DEAC/Ti molar ratio was further raised to 20. The propagation rate constant of C i* ( kpi) was evidently increased when DEAC/Ti molar ratio was raised from 0 to 5, but further increase in DEAC/Ti ratio caused gradual decrease in kpi. The complicated effect of DEAC on the polymerization kinetics, catalysis behaviors and polymer structure can be reasonably explained by adsorption of DEAC on the central metal of the active centers or on Mg atoms adjacent to the central metal. [ABSTRACT FROM AUTHOR]

In the present work, the effect of phase separation on overall isothermal crystallization kinetics of two polypropylene/ethylene-propylene random copolymer (PP/EPR) in-reactor alloys was investigated. It is found that at lower crystallization temperatures ( T c), the overall crystallization rate decreases with increasing phase separation temperature ( T s). This is attributed to the lower linear spherulitic growth rate incurred by the lower PP content in the PP-rich phase at higher T ss. In contrast, at higher T cs, quenching from a higher T s to T c promotes nucleation as a result of more dramatic concentration fluctuation, leading to a faster overall crystallization rate. The overall crystallization rate of the PP/EPR in-reactor alloy prepared by multi-stage sequential polymerization process (MSSP) is retarded by increasing phase separation time ( t s). However, prolonging phase separation time has little effect on the crystallization rate of the sample prepared by two-stage polymerization process (TSP). This result can be attributed to the different phase separation rates of these two samples. The SAXS result confirms that at higher T c, phase separation in the melt before crystallization can retard crystallization, when compared with the directly quenched samples. It is also found that the phase-separated PP/EPR in-reactor alloys exhibit a larger long period because of more amorphous phases included between the lamellar crystals. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

The article presents a study on the characterization and fractionation of an ethylene-propylene copolymer that was produced with a MgCl2/SiO2/TiCl4/diester-type Ziegler-Natta catalyst. The researchers used diphenyldimethoxysilane as external donor in the copolymerization. They found that the EP copolymer synthesized by a heterogeneous Ziegler-Natta catalyst system shows intramolecular and intermolecular heterogeneity.

Abstract: A TiCl4/AlCl3/MgCl2 (Cat-B) catalyst containing 5.2wt.% Al was prepared by the reaction of TiCl4 with ethanol adduct of AlCl3/MgCl2 mixture. A TiCl4/MgCl2 catalyst (Cat-A) without doped AlCl3 was also prepared by the same method. Ethylene-1-hexene copolymerization catalyzed by Cat-B in the presence of hydrogen showed slightly higher efficiency and higher 1-hexene incorporation than Cat-A. Comonomer incorporation was markedly increased when the cocatalyst AlEt3 was replaced by Al(i-Bu)3. Adding Ph2Si(OMe)2 as external donor in the catalyst system caused decrease in polymerization activity and 1-hexene incorporation. Each copolymer sample was fractionated into three fractions: n-heptane insoluble fraction (fraction A), n-heptane soluble and n-hexane insoluble fraction (fraction B) and n-hexane soluble fraction (fraction C). In most cases the amount of intermediate fraction (fraction B) was smaller than the other fractions and did not increase as the total 1-hexene content increase, indicating the presence of two classes of copolymer fractions with greatly different comonomer content and clear bimodality of the copolymer composition distribution. Doping AlCl3 in the catalyst, changing cocatalyst and adding external donor mainly changed the weight ratio of fraction A to fraction C, but exerted little influences on their composition. According to the sequence distribution data of the fractions, doping AlCl3 in the catalyst resulted in slight decrease of product of reactivity ratios (r 1 r 2) in both fraction A and fraction C. [Copyright &y& Elsevier]

Abstract: Unbridged bis-substituted-indenyl zirconocene complexes, [(2,4-Me2Ind)2ZrCl2, Met-1; (2,4,6-Me3Ind)2ZrCl2, Met-2], were supported on silica and montmorillonite carriers (resulting in silica-supported catalysts MS-1 and MS-2, and montmorillonite-supported catalyst MT-1). Ethylene polymerization by homogeneous and heterogeneous catalysts showed high activity, affording polyethylenes with high molecular weight. The catalytic activity and the molecular weight of the polymer were improved using the heterogeneous systems. The activities for the ethylene/1-hexene copolymerization by heterogeneous systems were lower than those using homogeneous systems, however, the comonomer was incorporated efficiently into polymer in both the homo- and the heterogeneous systems, and moreover, the microstructure of the copolymer derived from the heterogeneous catalysts showed different characteristics from those resulting from the homogeneous systems. The r E r H values of the heterogeneous catalysts (1.82 for MS-1 and 0.70 for MS-2), are quite different from those of their homogeneous analogues (1.25 for Met-1 and 1.26 for Met-2). [Copyright &y& Elsevier]

Nonbridged bis-substituted indenyl zirconene complexes were used as the catalysts for ethylene/1-hexene copolymerization and propylene polymerization. The complicated “comonomer effect” on the activity of ethylene/1-hexene copolymerization was observed. The effect also worked on the incorporation of comonomer. The number and the position of the substituents were important for the copolymerization behavior and the microstructure of the resultant copolymer as well as for propylene polymerization. [Copyright &y& Elsevier]

Abstract: Polyethylene/montmorillonite (PE/MMT) nanocomposites, one intercalated sample with higher MMT content and one exfoliated sample with lower MMT content, were prepared by in situ polymerization using MMT-supported metallocene as catalyst. Non-isothermal crystallization behaviors of these two nanocomposites were investigated and compared. The exfoliated sample exhibits higher crystallization temperature (T c) than the neat PE, showing nucleation effect of MMT. The intercalated sample has lower T c than the neat PE due to the confinement of MMT. It is observed that the intercalated sample has longer induction period and faster overall crystallization rate, indicating co-existence of suppression and nucleation effects in this sample. The Avrami plots show that the crystal growth of PE in the intercalated sample is two-dimensional, while it is three-dimensional in the exfoliated sample. The crystallization activation energy of the intercalated sample is slightly smaller than that of the exfoliated sample. [Copyright &y& Elsevier]

Abstract: A series of MgCl2/NaCl/ID/TiCl4 type supported catalysts were prepared by comilling NaCl with MgCl2·nEtOH adduct and reacting the mixture with TiCl4 and internal electron donor (ID=di-n-butyl phthalate). Crystallites of NaCl were found in the doped catalysts as revealed by WAXD analysis. The NaCl doped catalysts showed lower catalytic activity and higher isospecificity in catalyzing propylene polymerization. There was a marked change of the molecular weight distribution (MWD) of polymer with NaCl content. Catalyst containing 16mol% NaCl produced PP with much broadened MWD (PDI=13) than the undoped catalyst when TEA was used as the activator, while the TIBA activated catalyst produced PP with much narrower MWD. The changes in catalyst''s active center distribution were studied based on non-linear fitting of the polymer MWD curve by multiple Flory functions. Stereochemical structure of the polymer was studied by thermal analysis. Selective and reversible deactivation of active centers by Cl− from NaCl is proposed to be the main reason for the observed changes in polymerization behaviors and polymer structure caused by doping NaCl in the catalyst. [Copyright &y& Elsevier]

Usinga MgCl2-supported Ziegler–Natta catalyst,a series of polypropylene/poly(ethylene-co-propylene)(PP/EPR) in-reactor alloys with high EPR content (>20 wt %) werepreparedby a periodic switching polymerization process (PSPP) in which themonomer feed was periodically switched between pure propylene andan ethylene/propylene mixture. The change of gas-phase monomer compositionwith time in the PSPP process was investigated. Transition periodswere identified when switching the monomer feed from propylene toethylene/propylene mixture (or vice versa). Because the gas-phaseethylene content in the transition periods was lower than that ofthe monomer mixture feed, copolymer formed in these periods has lowerethylene content than those formed in the steady periods of the copolymerizationstage. As a result, the transition periods led to formation of moresegmented ethylene/propylene copolymer (EPS) and decreased its ethylenecontent. When the switching frequency was altered in an adequate range,the content of EPS in the alloy was increased by increasing the switchingfrequency, and dispersion of the copolymer phase in the PP matrixbecame more uniform. The toughness–stiffness balance of PP/EPRalloy synthesized by PSPP process with adequate switching frequencywas better than the alloy synthesized by a conventional sequentialpolymerization process with only one copolymerization stage. Whenthe switching frequency exceeded a certain limit, the alloy’sEPS content was decreased and its toughness–stiffness balancetended to be worse. [ABSTRACT FROM AUTHOR]

Abstract: Poly(ε-caprolactone) (PCL) was grafted onto multiwalled carbon nanotubes (MWNTs) with high grafting degrees. The surface of MWNTs was first modified by 2-hydroxyethyl benzocyclobutene (BCB-EO) via a [2 + 4] cyclo-addition reaction. Polymerization of ε-caprolactone was conducted in the presence of BCB-EO modified MWNTs and the catalyst stannous octoate. Alternatively, the grafted-BCB-EO first reacted with CpTiCl3 and then the reactant was used to catalyze polymerization of ε-caprolactone. The grafting degrees of PCL prepared from BCB-EO modified MWNTs can reach at least 94%, much higher than those prepared by other two conventional methods. TEM result shows that the morphology and thickness of the grafted PCLs strongly depend on the grafting degree and grafting method. The crystallization and melting behaviors of the MWNTs-grafted PCL were investigated. MWNTs can exert both nucleation and confinement effects on crystallization of the grafted PCL, leading to lower crystallinity but higher crystallization temperature (T c) and melting temperature (T m) of the grafted PCLs. It is found that crystallinity of the grafted PCLs increases with the grafting degree, but T c and T m also depend on the molecular weight. [Copyright &y& Elsevier]

Abstract: Trithiocarbonate group was introduced into the polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymers as the junction of the blocks through RAFT polymerization. Mixed PS and PEO brushes with a V-shape were prepared by anchoring the trithiocarbonate group on the planar gold substrate. The morphology of the V-shaped brushes was characterized by atomic force microscopy (AFM) and the surface composition responsive to solvent treatment was detected by X-ray photoelectron spectroscopy (XPS). Different morphologies were observed for the V-shaped PS-b-PEO brushes, depending on the chain structure and solvent treatment. The highly selective solvent for PEO, ethanol, can intensify or induce microphase separation of the V-shaped brushes, leading to vertical microphase separation. When the V-shaped brushes are treated with the co-solvent, THF, miscible morphology, lateral microphase separation, and vertical microphase separation are observed as the PS block length increases. After treatment with the non-selective poor solvent, cyclohexane, the V-shaped PS106-b-PEO113 brush, exhibits a laterally microphase-separated morphology, but the V-shaped PS52-b-PEO113 and PS253-b-PEO113 brushes are vertically microphase-separated. [Copyright &y& Elsevier]

Abstract: Traditional cobalt-zinc double metal cyanide complex [Zn–Co(III)DMCC] catalysts could catalyze the copolymerization of carbon dioxide (CO2) with propylene oxide (PO) to afford poly (propylene carbonate) (PPC) with high productivity. But the molecular weight (MW) of PPC and the polycarbonate selectivity were not satisfied. In this work, by using a nanolamellar Zn–Co(III) DMCC catalyst, the CO2–PO copolymerization was successfully performed to yield PPC with high molecular weight (Mn : 36.5 kg/mol) and high molar fraction of CO2 in the copolymer (: 74.2%) at low polymerization temperatures (40∼80 °C). Improved selectivity (: 72.6%) and productivity of the catalyst (6050 g polymer/g Zn) could be achieved at 60 °C within 10 h. The influences of water content on CO2–PO copolymerization were quantitatively investigated for the first time. It was proposed that trace water in the reaction system not only acted as an efficient chain transfer agent, which decreased MW of the resultant copolymer, but also strongly interacted with zinc site of the catalyst, which led to low productivity of PPC and more amounts of cyclic propylene carbonate (cPC). These conclusions were also supported by the apparent kinetics of CO2–PO copolymerization. ESI-MS results showed that all polymers have two end alkylhydroxyl groups. It was thus proposed that the alkylhydroxyl groups came from the initiation reaction of Zn–OH in the catalyst and the chain transfer reaction by H2O. The proposed mechanism of chain initiation, propagation and chain transfer reaction were proved by the experimental results. [Copyright &y& Elsevier]

Abstract: This paper describes a convenient one-pot terpolymerization of CO2, cyclohexene oxide (CHO) and maleic anhydride (MAH) to afford a poly (ester-carbonate) with a low content of ether units (2.9–4.3 mol%) using a highly active Zn–Co(III) double metal cyanide complex (DMCC) catalyst. Terpolymerization was carried out in tetrahydrofuran (THF) at 75–90 °C and 1.0–4.0 MPa and no cyclic carbonate was observed in NMR spectra. The number-average molecular weight (M n) of the terpolymer was up to 14.1 kg/mol with a narrow molecular weight distribution of 1.4–1.7. The apparent efficiency of the catalyst was up to 12.7 kg polymer/g Zn, representing the highest catalytic activity for terpolymerization of CO2, epoxides and cyclic anhydrides to date. THF dramatically inhibited polyether formation in this terpolymerization owing to its nucleophilicity towards the Zn2+ center of Zn–Co (III) DMCC. This presents the first example of solvent-assisted selectivity for inhibiting ether units in CO2 polymerization catalyzed by a heterogeneous system. Kinetic analyses of MAH/CHO/CO2 terpolymerization (MAH/CHO 0.2) suggested that polyester production was slightly faster than polycarbonate production in the early stage. A mechanism for this terpolymerization catalyzed by Zn–Co (III) DMCC catalyst was proposed. Moreover, addition of small amounts of MAH (MAH/CHO molar ratio ≤0.2) during CO2/CHO copolymerization can improve the thermal properties of the resultant terpolymers. [Copyright &y& Elsevier]

Abstract: The morphology of two polypropylene/poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys prepared by multi-stage sequential polymerization (MSSP) and two-stage polymerization (TSP) processes, respectively, was investigated. It is observed that the alloy prepared by MSSP (sample 1) exhibits lower phase separation temperature than the alloy prepared by TSP (sample 2), probably due to the higher content of PP segments in the blocky copolymer fractions of sample 1. Two thermal treatments were applied to the samples: (1) The samples were directly quenched from 230°C to 132°C for isothermal crystallization; (2) The samples were firstly held at 160°C for 60min for phase separation and then cooled to 132°C for crystallization. It is found that both microstructure and thermal treatment affect the morphology of the alloys, and the differences in morphology are interpreted in terms of phase diagram. For sample 1 and for the samples subjected to phase separation prior to crystallization, the EPR-rich phase contains more PP and thus is more viscous, which leads to more inclusion of the EPR-rich phase into the spherulites. A coarse spherulitic structure is formed due to crystallization of PP in the included EPR-rich phase. More included EPR-rich phase and its stronger crystallizability can further lead to the narrower boundaries and formation of connections between the adjacent spherulites. [Copyright &y& Elsevier]

The novel cyclic trithiocarbonate was synthesized by dialkylation of trithiocarbonate anion with 2,2′-bis(bromomethyl)biphenyl in a two-phase system using an onium salt as a phase-transfer agent. Styrene polymerization was carried out in the presence of cyclic trithiocarbonate (CTTC). CTTC undergoes ring opening-polymerization and the incorporated trithiocarbonate moiety derived from CTTC performs as the reversible addition-fragmentation chain transfer (RAFT) agent. Through this mechanism, multiblock polystyrenes containing various narrow polydispersity blocks can be prepared. [ABSTRACT FROM AUTHOR]

Abstract: Polyethylene/montmorillonite (PE/MMT) nanocomposites with different dispersion states of MMT were prepared by in situ polymerization. Isothermal crystallization of the intercalated nanocomposite, in which the PE chains were confined in the MMT layers, was studied and was compared with that of the exfoliated nanocomposite. It is observed that the intercalated sample has longer induction period, longer crystallization half time and larger crystallization activation energy than the exfoliated sample, showing that crystallization of PE is retarded due to confinement of the MMT layers. Analysis of crystallization kinetics shows that Avrami exponent (n) increases gradually with crystallization temperature. However, the maximal value of n is 2.0 for the intercalated sample, but it can reach 3.0 for the exfoliated sample. It is inferred that the stems of the PE crystals confined in the MMT layers are parallel to the MMT layers. The Hoffman–Weeks extrapolation method cannot be applied in the intercalated sample because of the small lateral surface of the PE crystals. Based on the depression of the melting temperature, the specific free energy of the PE/MMT interface was estimated, which is about 1.0mJ/cm2, much smaller than the free energy of the lateral surface of PE crystals. This is attributed to the origin of the strong nucleation effect of MMT. [Copyright &y& Elsevier]

Poly(vinyl chloride) (PVC) was prepared using a titanium complex with an anionic oxygen tripod ligand [CpCo{P(O)(OEt)2}3]− () as catalyst and methyl aluminoxane (MAO) as cocatalyst. The polymerization behavior was compared with that of pentamethyl cyclopentadienyl titanium trichloride (Me5CpTiCl3). It is observed that LOEtTiCl3 can polymerize vinyl chloride with activity comparable to that of Me5CpTiCl3. The PVC samples prepared with LOEtTiCl3/MAO exhibit bimodal molecular weight distribution and the fraction of high molecular weight peak decreases with polymerization temperature. The microstructure and thermal decomposition of the PVC obtained were studied. Five types of structural defect were detected by 1H-NMR. Only saturated structural defects are found at low polymerization temperature, but at high polymerization temperature unsaturated structural defects, possibly resulting from dehydrochlorination of the saturated structural defects, appear as well. No head-to-head structural defect is observed. 13C-NMR shows that the PVC prepared by LOEtTiCl3 has an atactic stereostructure. Compared with the PVC from radical polymerization and anionic polymerization, the PVC samples prepared with LOEtTiCl3 show improved thermal stability. [Copyright &y& Elsevier]