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Main observation and conclusion: Styrene polymerization catalyzed by the half‐titanocenes CpTiCl2[1,3‐R2(CH2N)2C=N] (6b: R= 2,6‐Me2C6H3, T4: R = 2,4,6‐Me3C6H2; T5: R = 2,6‐iPr2C6H3) was carried out in the presence of methylaluminoxane (MAO). Compared to the styrene conversion (31%) and syndiospecific index (45%) using reported 6b as precatalyst, T5 bearing ligand with isopropyl substitutes on the N‐aryl‐rings exhibits much higher styrene conversion (61%) and syndiospecific index (99%), indicating that the catalytic behavior could be improved obviously by the introduction of electronic donating and steric bulky substituents. One N atom in imidazolin‐2‐iminato ligand was replaced by O atom, affording half‐titanocenes CpTiCl2[3‐C6H5(CH2N)(CH2O)C=N (T1) and CpTiCl2[2,6‐Me2(C6H3O)(NiPr2)C=N] (T2). Compared to 6b, both higher styrene conversion and syndiospecific index are afforded by using half‐titanocene T1 containing 2‐imino‐3‐phenyloxazolidine ligand. All the results illustrate that both the chemical structure and the nature of substituents of the ligand have obvious influence on the styrene conversion and syndiospecific index in the polymerization of styrene. All the resulting syndiotactic polystyrenes (sPSs) are highly syndiospecific (rrr > 99%). Correspondingly, the sPS prepared using T5/MAO catalytic system exhibits high melting point and narrow molecular weight distribution. The results might show new light on designing more efficient half‐titanocenes for styrene polymerization with both high styrene conversion and high syndiospecific selectivity. [ABSTRACT FROM AUTHOR]

Neodymium complexes containing N-heterocyclic carbene (NHC) ligands, NdCl3[1,3-R2(NCH=)2C:]·THFx(Nd1: R = 2,6-iPr2C6H3, x = 0; Nd2: R = 2,6-Et2C6H3, x = 1; Nd3: R = 2,4,6-Me3C6H2, x = 1) were synthesized and employed as precatalysts for the coordination polymerization of conjugated dienes (butadiene and isoprene). In combination with triisobutylaluminium (TIBA), Nd1 promoted butadiene polymerization to produce extremely high cis-1,4 (up to 99.0%) polybutadienes with high molecular weight (Mw = 250–780 kg·mol−1). The Nd1/TIBA catalytic system also exhibited both high catalytic activity and cis-1,4 selectivity (up to 97.8%) for isoprene polymerization. The catalytic activity, molecular weight and molecular weight distribution of resulting polydienes were directly influenced by Al/Nd molar ratio, aging method, and polymerization temperature. Very interestingly, the high cis-1,4 selectivity of the catalyst towards butadiene and isoprene kept almost unchanged under different reaction conditions. The cis-1,4 polyisoprenes with high molecular weight (Mw = 210–530 kg·mol−1) and narrow molecular weight distribution (Mw/Mn = 1.9–2.7) as well as high cis-1,4 selectivity (~97%) could be synthesized by using the aged Nd1/TIBA catalytic system in the presence of isoprene (100 equivalent to Nd) at low Al/Nd molar ratios of 6–10. Polyisoprenes with low molecular weights (Mw = 12–76 kg·mol−1) and narrow molecular weight distributions (Mw/Mn = 1.7–2.6) were obtained by using Nd2 and Nd3 as precatalysts, indicating that the molecular weight of resulting polyisoprenes can be adjusted by changing the substitutes of ligand in Nd complex. [ABSTRACT FROM AUTHOR]

The homogeneous neodymium-based catalyst systems containing neodymium carboxylate, isobutyl aluminum compound and chlorinating agent were successfully developed for the coordination polymerizations of butadiene, isoprene and styrene in our laboratory. The catalyst possessed high catalytic activity to butadiene polymerization in hexane, leading to an obvious decrease in the dosage of catalyst to low level, e.g Nd/Bd (molar ratio) was around 35 ppm. Simultaneously, the catalyst exhibited high stereo-selectivity to butadiene polymerization in hexane and polybutadienes with extremely high cis-1,4 configuration of around 99% could be produced under appropriate reaction conditions. Based on our interesting fundamental research works, the continuous butadiene polymerizations were conducted to produce high cis-1,4 polybutadiene in pilot scale in SINOPEC. The industrial equipments (capacity: 30 000 t/a) for production of neodymium butadiene rubber (Nd-BR) were successfully built in SINOPEC in 2012 and the innovation technology has been achieved from fundamental research to industrial application for large scale production of Nd-BR. The Nd-BR products are now commercially available with the trade names of BR Nd40, BR Nd50, BR Nd60 with ML(1+4) 100 °C of 45 ± 5, 55 ± 5, and 63 ± 5, respectively. The excellent properties of these high cis-1,4 Nd-BR products lead to their especially suitable application in green-tire components. [ABSTRACT FROM AUTHOR]

ABSTRACT Cationic polymerizations of isobutylene (IB) with H2O/FeCl3/isopropanol ( iPrOH) initiating system were conducted in nonpolar hydrocarbon media, such as n-hexane or mixed C4 fractions at −40 to 20 °C. This cationic polymerization is a chain-transfer dominated process via highly selective β-proton elimination from CH3 in the growing chain ends, leading to formation of highly reactive polyisobutylenes (HRPIBs) with large contents (> 90 mol %) of exo-olefin end groups (structure A). The content of structure A remained nearly constant at about 97 mol % during polymerization and isomerization via carbenium ion rearrangement could be suppressed in nonpolar media. First-order kinetics with respect to monomer concentration was measured for selective cationic polymerization of IB in the mixed C4 fraction feed at −30 °C and the apparent rate constant for propagation was 0.028 min−1. High polymerization temperature ( Tp) or [FeCl3] accelerate β-proton elimination or isomerizations and simultaneously decrease selectivity of β-proton abstraction from CH3. Molecular weight decreased and molecular weight distribution (MWD) became narrow with increasing Tp or [FeCl3]. To the best of our knowledge, this is the first example to achieve high quality HRPIBs with near 100% of exo-olefin terminals and relatively narrow MWD ( Mw/ Mn = 1.8) by a single-step process in nonpolar hydrocarbon media. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4200-4212 [ABSTRACT FROM AUTHOR]

A novel simple but effective initiating system of HO/AlCl/veratrole (VE) has been developed to synthesize high molecular weight polyisobutylene (PIB) at elevated temperatures via cationic polymerization of isobutylene (IB) in solvent mixture of hexane/methylene dichloride ( n-Hex/CHCl = 2/1, V/V). VE played very important roles in decreasing cationicity of the growing chain ends, suppressing side reactions of chain transfer and termination during polymerization, leading to production of high molecular weight PIBs. PIBs with high yields, having very high weight-average molecular weight ( M) of 1117000 and 370000 g/mol could be synthesized with HO/AlCl/VE initiating system at VE concentration of 5.4 mmol/L at −80 and −60 °C respectively. Molecular weight of PIB increased remarkably with increasing VE concentration. The reaction order with respect to VE concentration was determined to be −3.52 via FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance (ATR) immersion probe. The negative reaction order of VE was consistent with its retarding effect on IB polymerization by interacting with the propagating species. Molecular weight of PIB decreased with increasing polymerization temperature. The activation energy for polymerization degree ( E) could be determined to be around −23 kJ/mol when VE concentration was 5.4 mmol/L or 6.4 mmol/L. [ABSTRACT FROM AUTHOR]

Two pH-responsive amphiphilic diblock copolymers, namely polyisobutylene- block-poly[2-( N, N-dimethylamino) ethyl methacrylate] (PIB- b-PDMAEMA) and polyisobutylene- block-poly(metharylic acid) (PIB- b-PMAA), were synthesized via oxyanion-initiated polymerization, and their multiple self-assembly behaviors have been studied. An exo-olefin-terminated highly reactive polyisobutylene (HRPIB) was first changed to hydroxyl-terminated PIB (PIB-OH) via hydroboration-oxidation of C=C double bond in the chain end, and then reacted with KH to yield a potassium alcoholate of PIB (PIB-OK). PIB-OK was immediately used as a macroinitiator to polymerize DMAEMA monomer, resulting in a cationic diblock copolymer PIB- b-PDMAEMA. With the similar synthesis procedure, the anionic diblock copolymer PIB- b-PMAA could be prepared via a combination of oxyanion-initiated polymerization of tert-butyl methacrylate ( tBMA) and subsequent hydrolysis of tert-butyl ester groups in P tBMA block. The functional PIB and block copolymers have been fully characterized by H-NMR, FT-IR spectroscopy, and gel permeation chromatography (GPC). These samples allowed us to systematically investigate the effects of block composition on the pH responsivity and various self-assembled morphologies of the copolymers in THF/water mixed solvent. Transmission electron microscopy (TEM) images revealed that these diblock copolymers containing small amount of original PIB without exo-olefin-terminated group are able to self-assemble into micelles, vesicles with different particle sizes and cylindrical aggregates, depending on various factors including block copolymer composition, solvent polarity and pH value. [ABSTRACT FROM AUTHOR]

Abstract: Cationic polymerizations of p-methylstyrene (pMS) with H2O/AlCl3/triphenylamine (TPA) or triethylamine (TEA) initiating system were carried out in mixed solvents of n-hexane and dichloromethane at −80 ∼ −50 °C. The effects of TPA or TEA concentration, solvent polarity, polymerization temperature and time on monomer conversion, number-average molecular weight (M n ), molecular weight distribution (MWD, M w /M n ), stereoregulatity and crystallinity of poly(p-methylstyrene) (PpMS) were investigated. The stereospecific cationic polymerization of p-methylstyrene could be achieved and high molecular weight (M n  = 116,000 ∼ 436,000 g mol−1) polymers with isotactic-rich segments (more than 75% of meso dyad) along macromolecular chains could be successfully synthesized. A possible mechanism for stereospecific cationic polymerization of pMS was proposed. The propagation proceeded via the dominant back-side attack and insertion of monomer from the growing ion paired species. The steric course of propagation was mainly determined by the tightness of the growing ion paired species and steric hindrance in counteranion. The resulting isotactic-rich PpMS could form crystal morphology with 10 ∼ 30 μm in size by flow-induced crystallization under pressure at 180 °C. A possible model for the aligning mechanism was sketched to describe crystallization and to explain the multi-melting peaks and lower glass transition temperatures of PpMS. This is the first example of stereospecific cationic polymerization of p-methylstyrene to get crystallizable polymers with such high molecular weights and isotacticity. [Copyright &y& Elsevier]

The copolymerization of 4-vinylbenzyl chloride (VBC) and vinyl acetate (VAC) was carried out in toluene at 75°C via radical polymerization using 2,2′-azo-bis-(isobutyronitrile) (AIBN) as an initiator. The random copolymers of poly(4-vinylbenzyl chloride- co-vinyl acetate) (P(VBC- co-VAC)) with number average molecular weight ( M) from 2000 to 6900, relatively narrow molecular weight distribution (MWD, M/ M ca. 2.0) and with different copolymer composition of 4-vinylbenzyl chloride (VBC) from 17 mol% to 62 mol% could be obtained. The P(VBC- co-VAC) copolymers with an average number of 7 to 13 initiating sites of benzyl chloride per macromolecule could be used for the cationic polymerization of isobutylene (IB). The cationic polymerizations of IB were further conducted by using P(VBC- co-VAC) copolymers as macroinitiators in conjunction with TiCl at −40°C in CHCl. The effects of VBC/TiCl (molar ratio) on monomer conversion, M and MWD of the resultant copolymers were investigated under 3 sets of conditions. It is found that P(VBC- co-VAC)- g-PIB copolymers with relatively narrow MWD ( M/ M ca. 2.0) and with terminal tert-chlorine functional groups in branched PIB chains could be successfully synthesized when VBC/TiCl (molar ratio) was set in the range from 0.10 to 1.12. The unimodal GPC curve of the P(VBC- co-VAC)- g-PIB copolymers by RI detector was almost in harmony with the GPC curve by UV detector. The TEM image of the P(VBC- co-VAC)- g-PIB copolymer stained by RuO indicated that the copolymer formed a two-phase morphology with P(VBC- co-VAC)-rich domains of 20-100 nm in size tethered by PIB branch segments. [ABSTRACT FROM AUTHOR]

FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance (ATR) immersion probe was utilized to study in situ the copolymerization of butadiene (Bd) and isoprene (Ip) with neodymium-based catalyst in hexane. The relationship between the signal intensity of monomer and its concentration was investigated. The kinetic study of copolymerization of Bd and Ip was further conducted, and the monomer reactivity ratios were determined via in situ ATR FTIR. The signal band at 1010 cm was assigned to wagging vibration of Bd and its intensity was proportional to Bd concentration ([Bd]) in the range of 0.46-3.88 mol·L. The signal bands at 890 and 989 cm were assigned to wagging vibration of Ip and the signal intensity was also proportional to Ip concentration ([Ip]) in the range of 0.08-4.73 mol·L at 890 cm and 0.08−7.49 mol·L at 989 cm, respectively. Thus the signal band at 1010 cm was chosen to monitor Bd concentration and bands at 989 and 890 cm to monitor Ip concentration during the copolymerization, respectively. It was demonstrated that the conversions of Bd and Ip calculated from FTIR data agreed very well with those obtained gravimetrically. The polymerization rates were first order with respect to both [Bd] and [Ip], respectively at different polymerization temperatures. The apparent propagation activation energy for Bd and Ip could be determined to be 54.4 kJ·mol and 57.7 kJ·mol, respectively. The monomer reactivity ratios were calculated to be 1.08 for Bd ( r) and 0.48 for IP ( r) based on FTIR data. The Bd-Ip copolymer products with random sequence could be obtained with only one glass transition temperature. [ABSTRACT FROM AUTHOR]

The highly reactive polyisobutylenes (PIBs) with α-double bonds (87.5 mol%) or tert-chloro (tert-Cl) groups (95 mol%) could be prepared via the cationic polymerization of isobutylene (IB) coinitiated by BF3 or TiCl4 respectively. The Friedel-Crafts alkylation of diphenylamine (DPA) with the highly reactive PIB with α-double bonds was further conducted under different conditions, such as at different alkylation temperature, in the mixed solvents of CH2Cl2/n-hexane with different solvent polarity and at DPA concentration ([DPA]). The resultant PIBs with sec-arylamino terminal groups were characterized by GPC with RI/UV dual detectors and 1H-NMR spectrum. The experimental results indicated that alkylation efficiency increased with increases in reaction temperature, solvent polarity and [DPA]. The 77 mol% of sec-arylamino terminated PIBs could be obtained in 10/90 (V/V) mixture of nHex/CH2Cl2 with [DPA]/[PIB] of 3.0 at 60°C for 45 h. Moreover, the alkylation of DPA with highly reactive PIBs with mainly tert-Cl terminal groups was also carried out in 10/90 (V/V) mixture of CH2Cl2/nHex with [DPA]/[PIB] = 3.0 at 60°C for 45 h, and almost monoalkylation with 100 mol% sec-arylamino terminal groups could be achieved. These results will help further explorations of the molecular engineering via combination of cationic polymerization with alkylation. [ABSTRACT FROM AUTHOR]

Abstract: Cationic polymerization of isobutylene (IB) in a mixture of methylene dichloride (CH2Cl2) and n-hexane (n-Hex) was conducted by using H2O as initiator, TiCl4 as co-initiator in the presence of strong external electron pair donor (ED), such as pyridine (Py), dimethylacetamide (DMA) or triethylamine (TEA). The effects of ED concentration, TiCl4 concentration, solvent polarity, polymerization temperature (T) and time on IB polymerization, molecular weight (MW) and molecular weight distribution (MWD, Mw/Mn) of polyisobutylene (PIB) products were investigated. The relative amount of polymer formed via uncontrolled initiation by conventional active species (I) decreased with increasing the solvent polarity, TiCl4 concentration and ED concentration in the polymerization. The desirable polymerization of IB with apparent absence of chain transfer reactions could be obtained by H2O/TiCl4 initiating system in the presence of ED under the appropriate reaction conditions. The external electron pair donors and TiCl4 did specially play important and effective roles on polymerization. [Copyright &y& Elsevier]

Abstract: Cationic polymerization of styrene was conducted with 1-chloro-1-phenylethane (SCl)/AlCl3/phenyl methyl ether (PME) initiating system in hexane/CH2Cl2 (60/40, v/v) at −80 °C. The kinetics for cationic polymerization of styrene was investigated by in-situ ATR-FTIR spectroscopy. The isotactic-rich polystyrene (iPS) with m dyad of 81%, mm triad of 63% and mmmm pentad of 50% could be synthesized. Small amounts of crystalline regions in iPS formed after flow-induced crystallization and the crystallinity increased with increasing the molecular weight of iPS. Furthermore, the long-chain branched isotactic-rich polystyrene (biPS) with around 12 times higher molecular weight than that of corresponding iPS could be synthesized via cationic polymerization of styrene by introducing a small amount of isoprene (Ip) as a comonomer and branching sites as well. The possible mechanism for long-chain branching formation via intermolecular alkylation reaction by using Ip structural units along polymer chain as branching sites was proposed. The nucleation rate of biPS could be greatly enhanced with increasing the content of branching sites, leading to an obvious increase in crystallinity. The multi-melting temperatures from 140 °C to 237 °C were observed in DSC curves of these PS products. The tensile strength of commercial atactic polystyrene could be improved remarkably from 41.4 MPa to 55.7 MPa by adding 16.7% of biPS. [Copyright &y& Elsevier]

Grafting single end-tethered polymer chains on the surface of graphene is a conventional way to modify the surface properties of graphene oxide. However, grafting arc-like macromolecular bridges on graphene surfaces has been barely reported. Herein, a novel arc-like polydimethylsiloxane (PDMS) macromolecular bridges grafted graphene sheets (GO -g-Arc PDMS) was successfully synthesized via a confined interface reaction at 90 °C. Both the hydrophilic α- and ω-amino groups of linear hydrophobic NH 2 -PDMS-NH 2 macromolecular chains rapidly reacted with epoxy and carboxyl groups on the surfaces of graphene oxide in water suspension to form arc-like PDMS macromolecular bridges on graphene sheets. The grafting density of arc-like PDMS bridges on graphene sheets can reach up to 0.80 mmol g −1 or 1.32 arc-like bridges per nm 2 by this confined interface reaction. The water contact angle (WCA) of the hybrid membrane could be increased with increasing both the grafting density and content of covalent arc-like bridges architecture. The superhydrophobic hybrid membrane with a WCA of 153.4° was prepared by grinding of the above arc-like PDMS bridges grafted graphene hybrid, dispersing in ethanol and filtrating by organic filter membrane. This superhydrophobic hybrid membrane shows good self-cleaning and complete oil-water separation properties, which provides potential applications in anticontamination coating and oil-water separation. To the best of our knowledge, this is the first report on the synthesis of functional hybrid membranes by grafting arc-like PDMS macromolecular bridges on graphene sheets via a confined interface reaction. [ABSTRACT FROM AUTHOR]

Thesynthesis of well-defined graft copolymers of poly(γ-benzyl-l-glutamate)-g- polytetrahydrofuran, PBLG-g-PTHF, has been achieved via controlled termination ofliving PTHF branch chains with −NH– functional groupsalong PBLG macromolecular backbone. The PBLG backbone with differentmolecular weights (Mn= 2000–45000g·mol–1) were prepared by anionic ring-openingpolymerization of γ-benzyl-l-glutamate N-carboxyanhydrade (BLG-NCA). Living PTHF chains with predictablechain length (Mn= 720–7000 g·mol–1) were prepared by living cationic ring-opening polymerizationof THF with methyl triflate (MeOTf) as an initiator. The graftingefficiency (GE) of living PTHF chainsonto PBLG backbone via controlled termination reached to near 100%.The grafting density (GD) along PBLG backboneand average number of PTHF branches (Nb,PTHF) in PBLG-g-PTHF graft copolymers could be mediatedby changing the molar ratio of living PTHF chains to −NH–functional groups. Circular dichroism (CD) and FTIR spectra show thatsome of the graft copolymers maintain α-helical structure fromPBLG, and the strength of CD signals for α-helical structureof the graft copolymers also decreased with increasing GD. The crystallization degree and spherulitic growth rateof the PBLG-g-PTHF graft copolymers decreased withincreasing GD. The obvious phase separationand reticular state of aggregation morphology in PBLG-g-PTHF graft copolymers could be observed. PBLG-g-PTHF graft copolymers have no cytotoxicity and even conducive forcell survival. These graft copolymers had extremely low bibulous rate,and all the water absorption ratios were kept around 1.02 to maintainthe shape and dimensional stability. [ABSTRACT FROM AUTHOR]