Catalysis of ethylene to linear low‐density polyethylene with iron‐based diimine complex immobilized on calcosilicate and silica‐supported rac‐Et(Ind)2ZrCl2

Iron‐based diimine complex was immobilized on calcosilicate (CAS‐1) to form heterogeneous precatalyst, which oligomerized ethylene to α‐olefins even without the use of aluminum alkyl compounds as activators. The α‐olefins, upon the catalysis of another catalyst, i.e., silica‐supported rac‐Et(Ind)₂ZrCl₂, copolymerized with ethylene to produce linear low‐density polyethylene (LLDPE). The copolymerization reactions could be performed with the addition of triethylaluminum alone because of the introduction of methylaluminoxane to CAS‐1 and silica during the supporting process. In addition to the formation of more α‐olefins with lower molar mass, the layered structure of CAS‐1 acted well in the controlled release of α‐olefins in the copolymerization process. The simultaneous employment of the aforementioned two catalysts hence resulted in high catalytic activities, smooth kinetic process, well‐regulated branching degree, higher molecular weights (M_n), improved thermal stability, and better morphology of the LLDPE obtained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of VB‐a/POSS hybrid monomer and its polymerization of polybenzoxazine/POSS hybrid nanocomposites

A benzoxazine monomer (VB‐a) containing an allyl groups was synthesized through the Mannich condensation of bisphenol A, formaldehyde, and allylamine (bisphenol‐A and allylamine as VB‐a). This monomer was then reacted with polyhedral oligomeric silsesquioxane (POSS) through hydrosilylation, followed by thermal curing to form poly(VB‐a)/POSS hybrid nanocomposites. The curing behavior of the nanocomposites was monitored using Fourier transform infrared spectroscopy (FTIR), and their thermal and morphological properties were investigated through thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and scanning electron microscopy. DMA revealed that the glass transition temperatures of the poly(VB‐a)/POSS nanocomposites were higher than that of the pristine poly(VB‐a), presumably because the POSS cages effectively hindered the motion of the polymer chains. TGA confirmed that the thermal degradation temperatures and char yields of the polybenzoxazines increased after incorporation of the POSS moieties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

In situ copolymerization of ethylene to produce linear low‐density polyethylene by Ti(OBu)4/AlEt3‐MAO/SiO2/Et(Ind)2ZrCl2

Linear low‐density polyethylene (LLDPE) is produced in a reactor from single ethylene feed by combining Ti(OBu)₄/AlEt₃, capable of forming α‐olefins (predominantly 1‐butene), with SiO₂‐supported Et(Ind)₂ZrCl₂ (denoted MAO/SiO₂/Et(Ind)₂ZrCl₂), which is able to copolymerize ethylene and 1‐butene in situ with little interference in the dual‐functional catalytic system. The two catalysts in the dual‐functional catalytic system match well because of the employment of triethylaluminum (AlEt₃) as the single cocatalyst to both Ti(OBu)₄ and MAO/SiO₂/Et(Ind)₂ZrCl₂, exhibiting high polymerization activity and improved properties of the obtained polyethylene. There is a noticeable increment in catalytic activity when the amount of Ti(OBu)₄ in the reactor increases and 1‐butene can be incorporated by about 6.51 mol % in the backbone of polyethylene chains at the highest Ti(OBu)₄ concentration in the feed. The molecular weights (M_w), melting points, and crystallinity of the LLDPE descend as the amount of Ti(OBu)₄ decreases, which is attributed mainly to chain termination and high branching degree, while the molecular weight distribution remains within a narrow range as in the case of metallocene catalysts. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2451–2455, 2004     

Reactive melt blending of PS‐POSS hybrid nanocomposites

Hybrid nanocomposites of polystyrene (PS) and methacryl phenyl polyhedral oligomeric silsesquioxane (POSS) were synthesized by reactive melt blending in the mixing chamber of a torque rheometer using dicumyl peroxide (DCP) as a free radical initiator and styrene monomer as a chain transfer agent. The effects of mixing intensity and composition on the molecular structure and morphology of the PS‐POSS hybrid nanocomposites were investigated. The degree of POSS hybridization (α_POSS) was found to increase with the POSS content, DCP/POSS ratio, and rotor speed. For the PS‐POSS materials processed in the absence of styrene monomer, an increase in the α_POSS led to a reduction in the molecular weight by PS chain scission, as a consequence of the free radical initiation. On the other hand, the use of styrene monomer as a chain transfer agent reduces the steric hindrance in the hybridization reaction between POSS and PS, enhancing the degree of POSS hybridization and avoiding PS degradation. The PS‐POSS morphology consists of nanoscale POSS clusters and particles and microscale crystalline POSS aggregates. PS‐POSS with higher α_POSS values and lower amounts of nonbound POSS showed improved POSS dispersion, characterized by smaller interfacial thickness (t) and greater Porod inhomogeneity lengths (l_p). The processing‐molecular structure–morphology correlations analyzed in this study allow the POSS dispersion level in the PS‐POSS materials to be tuned by controlling the reactive melt blending through the choice of the processing conditions. These insights are very useful for the development of PS‐POSS materials with optimized performance. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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     

Nano‐sized silica supported Me2Si(Ind)2ZrCl2/MAO catalyst for ethylene polymerization

Nano‐sized and micro‐sized silica particles were used to support a zirconocene catalyst [racemic‐dimethylsilbis(1‐indenyl)zirconium dichloride], with methylaluminoxane as a cocatalyst. The resulting catalyst was used to catalyze the polymerization of ethylene in the temperature range of 40–70°C. Polyethylene samples produced were characterized with scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Nano‐sized catalyst exhibited better ethylene polymerization activity than micro‐sized catalyst. At the optimum temperature of 60°C, nano‐sized catalyst's activity was two times the micro‐sized catalyst's activity. Polymers obtained with nano‐sized catalyst had higher molecular weight (based on GPC measurements) and higher crystallinity (based on XRD and DSC measurements) than those obtained with micro‐sized catalyst. The better performances of nano‐sized catalyst were attributed to its large external surface area and its absence of internal diffusion resistance. SEM indicated that polymer morphology contained discrete tiny particles with thin long fiberous interlamellar links. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of poly(HEMA‐co‐MMA)‐g‐POSS nanocomposites by combination of reversible addition fragmentation chain transfer polymerization and click chemistry

New hybrid poly(hydroxyethyl methacrylate‐co‐methyl methacrylate)‐g‐polyhedral oligosilsesquioxane [poly(HEMA‐co‐MMA)‐g‐POSS] nanocomposites were synthesized by the combination of reversible addition fragmentation chain transfer (RAFT) polymerization and click chemistry using a grafting to protocol. Initially, the random copolymer poly(HEMA‐co‐MMA) was prepared by RAFT polymerization of HEMA and MMA. Alkynyl side groups were introduced onto the polymeric backbones by esterification reaction between 4‐pentynoic acid and the hydroxyl groups on poly(HEMA‐co‐MMA). Azide‐substituted POSS (POSS? N₃) was prepared by the reaction of chloropropyl‐heptaisobutyl‐substituted POSS with NaN₃. The click reaction of poly(HEMA‐co‐MMA)‐alkyne and POSS? N₃ using CuBr/PMDEATA as a catalyst afforded poly(HEMA‐co‐MMA)‐g‐POSS. The structure of the organic/inorganic hybrid material was investigated by Fourier transformed infrared, ¹H‐NMR, and ²⁹Si‐NMR. The elemental mapping analysis of the hybrid using X‐ray photoelectron spectroscopy and EDX also suggest the formation of poly(HEMA‐co‐MMA)‐anchored POSS nanocomposites. The XRD spectrum of the nanocomposites gives evidence that the incorporation of POSS moiety leads to a hybrid physical structure. The morphological feature of the hybrid nanocomposites as captured by field emission scanning electron microscopy and transmission electron microscopic analyses indicate that a thick layer of polymer brushes was immobilized on the POSS cubic nanostructures. The gel permeation chromatography analysis of poly(HEMA‐co‐MMA) and poly(HEMA‐co‐MMA)‐g‐POSS further suggests the preparation of nanocomposites by the combination of RAFT and click chemistry. The thermogravimetric analysis revealed that the thermal property of the poly(HEMA‐co‐MMA) copolymer was significantly improved by the inclusion of POSS in the copolymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

POSS改性负载型Ziegler-Natta催化剂及其乙烯/1-己烯共聚反应

采用具有开放型骨架结构的大孔SiO₂（Macro-SiO₂）与MgCl₂形成复合载体,同时引入聚倍半硅氧烷（POSS）形成具有空间分隔作用的POSS/MgCl₂纳米团聚体,负载TiCl₄后制备得到改性Ziegler-Natta催化剂。采用红外分析、热重分析、CO低温吸附红外、扫描电镜、粒径分析等手段对POSS改性前后催化剂的结构进行表征,发现POSS的引入能诱导MgCl₂形成更多Mg_4c²⁺缺陷位点,并促进了Lewis酸性位点的形成,有利于TiCl₄有效活性中心的负载。乙烯/1-己烯共聚结果表明,POSS改性催化剂活性较高,最高可达1.03×10⁶ g?（mol?h）^-1,同时具有更高的共聚能力,共聚产物中共聚单体摩尔分数可达3.79%,且聚合产物具有较窄的分子量分布（MWD=3~6）。     

溶剂对rac-Et[Ind]_2ZrCl_2/MMAO催化体系催化乙烯-降冰片烯共聚合的影响

采用乙基桥连二茚基二茚基二氯化锆(rac-Et[Ind]2ZrCl2)/MMAO催化体系催化乙烯/降冰片烯共聚合,比较了甲苯、苯、正己烷、环己烷及其混合溶剂作为反应介质对共聚合活性及共聚物结构的影响。通过差示扫描量热分析(DSC)对共聚产物进行了热力学性质的表征。结果表明,聚合活性和产品的玻璃化转变温度(Tg)在不同溶剂体系中有着显著的差异,在相同聚合条件下,当甲苯/苯体积比为80/20时,聚活活性达到最高,但产品的Tg和降冰片烯的插入率较低。     

POSS/PMMA纳米复合材料的制备及性能研究

采用八乙烯基倍半硅氧烷(OV-POSS)通过原位聚合法制备了具有交联网状结构的POSS/PMMA纳米复合材料。通过FT-IR、DSC等方法对纳米复合材料的结构和性能进行了表征。结果表明,通过原位聚合法制备的POSS/PMMA纳米复合材料具有交联网状结构,POSS的引入能明显改善材料介电性能和热学性能,但当OV-POSS含量较高时,热学性能有所下降。当POSS的用量为0.6%时,POSS/PMMA纳米复合材料的介电常数从2.91降低至2.77,介电损耗从0.0088降低至0.0039,复合材料的Tg也上升了。     

Preparation and characterization of amphiphilic block copolymer of polyacrylonitrile‐block‐poly(ethylene oxide)

The synthesis of polyacrylonitrile‐block‐poly(ethylene oxide) (PAN‐b‐PEO) diblock copolymers is conducted by sequential initiation and Ce(IV) redox polymerization using amino‐alcohol as the parent compound. In the first step, amino‐alcohol potassium with a protected amine group initiates the polymerization of ethylene oxide (EO) to yield poly(ethylene oxide) (PEO) with an amine end group (PEO‐NH₂), which is used to synthesize a PAN‐b‐PEO diblock copolymer with Ce(IV) that takes place in the redox initiation system. A PAN‐poly(ethylene glycol)‐PAN (PAN‐PEG‐PAN) triblock copolymer is prepared by the same redox system consisting of ceric ions and PEG in an aqueous medium. The structure of the copolymer is characterized in detail by GPC, IR, ¹H‐NMR, DSC, and X‐ray diffraction. The propagation of the PAN chain is dependent on the molecular weight and concentration of the PEO prepolymer. The crystallization of the PAN and PEO block is discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1753–1759, 2003     

Preparation and characterization of ethylene vinyl acetate copolymer/montmorillonite nanocomposite

Ethylene vinyl acetate copolymer (EVA) and monmorillonite (MMT) nanocomposites have been investigated as a function of vinyl acetate content and molecular weight of EVA and types of substituted alkyl ammonium of MMT. It is found that vinyl acetate content and type of substituted alkyl ammonium are important factors for the intercalation behaviour of MMT in MMT/EVA nanocomposite. Maleic anhydride grafted high‐density polyethylene was used as a compatibilizer to improve the intercalation behaviour of MMT. X‐ray diffraction and transmission electron microscopy were used to characterize the intercalation/exfoliation behaviour, and mechanical properties were measured. © 2003 Society of Chemical Industry     

Crystallization of poly(ethylene oxide) embedded with surface‐modified SiO2 nanoparticles

The crystallization of poly(ethylene oxide) (PEO) in the presence of silica nanoparticles (SiO₂ NPs) was investigated in terms of heterogeneous nucleation of SiO₂ NPs using polarizing optical microscopy and differential scanning calorimetry. The content and surface functionality of SiO₂ NPs were considered as the main factors affecting crystallization, and the effect of annealing time and temperature was also examined. The SiO₂ NPs acted as heterogeneous nucleates during the crystallization process, thereby enhancing the nucleation density and limiting the spherulitic growth rate. A kinetics study of non‐isothermal crystallization showed that the crystallization rate of 5 wt% SiO₂/PEO nanocomposite was ca 2.1 times higher than that of neat PEO. In addition, among various surface‐functionalized SiO₂ nanoparticles, alkyl‐chain‐functionalized SiO₂ NPs were favorable for achieving a higher crystallization rate due to the enhanced compatibility between the SiO₂ NPs and PEO chains. © 2012 Society of Chemical Industry     

Ion conduction of poly[methoxy oligo (oxyethylene) propylene] synthesized by the Et(Ind)2ZrCl2-MAO catalyst

Poly[methoxy oligo (oxyethylene) propylene] was synthesized by means of the Et(Ind)₂ZrCl₂-MAO catalyst. The ionic conductivity of poly[methoxy oligo (oxyethylene) propylene] with the lithium salt depends on the content of the lithium salt. The temperature dependence of conductivity was determined and the Vogel–Tammann/Hesser–Fulcher (VTF) plot agreed well with theoretical values, confirming the influence of the polymer segmental motion on conductivity. The ionic conductivity as high as 10^−4.7 s/cm can be obtained at room temperature, and this can be increased one or two orders of magnitude by blending the polyelectrolyte with hydroxyl-containing additives such as tetraethylene glycol. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1397–1400, 1999     

POSS/PMMA纳米复合材料的制备及性能

将笼形纳米粒子八己烯基多面低聚倍半硅氧烷(Oh-POSS)与聚甲基丙烯酸甲酯(PMMA)通过溶液共混法制备无机/有机纳米复合材料.利用FTIR对复合材料的结构进行表征.SEM观察结果显示:当Oh-POSS含量较小时,复合材料薄膜具有较为平整的表面,无机粒子Oh-POSS均匀地分散在PMMA基体之中;随着Oh-POSS含量的增加,Oh-POSS逐步发生聚集现象.TGA、DSC以及拉伸试验结果表明:Oh-POSS含量较低时,Oh-POSS的引入能明显改善材料的热稳定性和力学性能,但当Oh-POSS含量较高时,热学和力学性能下降.     

Synthesis and properties of poly(trimethylene terephthalate‐co‐2‐methyl‐ethylene terephthalate) random copolyesters

Poly(trimethylene terephthalate‐co‐2‐methyl‐ ethylene terephthalate) random copolymers of various compositions were synthesized via traditional two‐step polycondensation by incorporating of 1,2‐propanediol. The molar composition of trimethylene terephthalate and 2‐methyl‐ethylene terephthalate units and chemical structure were confirmed by means of ¹H‐NMR and Fourier transform infrared. The thermal properties of the copolyesters were evaluated by DSC and TGA. As far as the thermal properties is concerned, the main effect of incorporation of 1,2‐propanediol was a lowering in the melting temperature, and an increment of glass transition temperature compared to homopolymer PTT. Due to the effect of the lateral methyl groups in the polymeric chain, the thermal stability is slightly decreased as the amount of the MET units is increased. Furthermore, the crystals of PTT/MET copolyesters were observed by hot‐stage optical polarizing microscopy at the indicated crystallization temperatures. As expected, the incorporation of MET units in the polymer chain of PTT was found to decrease the dimension of the crystals. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Properties of poly(ethylene terephthalate) containing epoxy‐functionalized polyhedral oligomeric silsesquioxane

Poly(ethylene terephthalate) (PET) containing epoxy‐functionalized polyhedral oligomeric silsesquioxane (POSS) was prepared by melt‐mixing and in situ polymerization methods. The melt‐mixed composite showed phase separation while the in situ polymerized composite did not, based on SEM characterization. During melt mixing, the reaction between the epoxy groups of POSS and hydroxyl groups of PET occurred, based on DSC results. DSC results on the in situ polymerization product showed formation of a lower‐melting component compared with PET. The tensile strength and modulus of the melt‐mixed composite fiber decreased compared with those properties of PET, whereas those of the in situ polymerized composite showed slightly higher values than PET despite the relatively small amounts (1 wt%) of POSS used. Dynamic mechanical analysis results showed an increase in storage modulus for the in situ polymerized composite of POSS and PET compared with PET over the temperature range of 40 °C to 140 °C. Copyright © 2004 Society of Chemical Industry     

Photodegradation of ethylene/propylene/polar monomers,co‐, and terpolymers. II. Prepared by Ni catalyst systems

The copolymers of ethylene/propylene as well as their terpolymers with polar monomers were prepared by Ni‐catalyst systems and their photodegradation behavior was studied by Fourier transform infrared spectroscopy. The polar monomers used to synthesize co‐ and terpolymers of ethylene/propylene/polar monomer were 5‐hexen‐1‐ol, 10‐undecen‐1‐ol, acrylamide, methylmethacrylate, acrylonitrile, and methylvinyl ketone. The morphological changes of the irradiated samples were determined by scanning electron microscopy. The photodegradation kinetics has also been studied. The surface damage caused by polychromatic irradiation (λ ≥ 290 nm) at 55 °C in atmospheric air is presented in different micrographs. The rate of photo‐oxidative degradation is very fast in terpolymers containing polar monomers as compared with copolymers and homopolymers. The morphological study of the photodegraded samples showed a very good correlation with the photodegraded results. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1783–1791, 2007     

Study on copolymerization of ethylene/1‐hexene catalyzed by a novel polystyrene‐supported metallocene catalyst

Ethylene/1‐hexene copolymerization was carried out with polystyrene‐supported metallocene catalyst. It was found that the kinetic of the copolymerization was strongly influenced by the steric hindrance of carrier. The influences of 1‐hexene concentration in the feed on catalyst productivity and comonomer reactivity were investigated. The microstructure of resultant copolymer was analyzed by ¹³C NMR. It was found that the different carriers have slight effect on the composite of copolymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1574–1577, 2006     

Synthesis and characterization of a poly(ether–ester) copolymer from poly(2,6 dimethyl‐1,4‐phenylene oxide) and poly(ethylene terephthalate)

A series of poly(ether–ester) copolymers were synthesized from poly(2,6 dimethyl‐1,4‐phenylene oxide) (PPO) and poly(ethylene terephthalate) (PET). The synthesis was carried out by two‐step solution polymerization process. PET oligomers were synthesized via glycolysis and subsequently used in the copolymerization reaction. FTIR spectroscopy analysis shows the coexistence of spectral contributions of PPO and PET on the spectra of their ether–ester copolymers. The composition of the poly(ether–ester)s was calculated via ¹H NMR spectroscopy. A single glass transition temperature was detected for all synthesized poly(ether–ester)s. T_g behavior as a function of poly(ether–ester) composition is well represented by the Gordon‐Taylor equation. The molar masses of the copolymers synthesized were calculated by viscosimetry. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006