Copolymerization of propylene with p‐allyltoluene using metallocene catalysts

Copolymerization of propylene with p‐allyltoluene (p‐AT) was performed using two metallocene catalysts, rac‐ethylenebis(indenyl)zirconium dichloride and rac‐dimethylsilylenebis[1‐(2‐methyl‐4‐phenylindenyl)]zirconium dichloride. The effects of the polymerization conditions, such as the amount of p‐AT in the feed and polymerization temperature, on the properties of the copolymers and the activity of the catalysts were investigated. With increasing p‐AT feed, the incorporation of p‐AT increased, but the activity of the metallocene catalyst, the melting temperature (T_m) and the number‐average molecular weight of the copolymers decreased. Higher polymerization temperature tended to enhance the activity of the metallocene catalyst and the incorporation of p‐AT. The copolymers produced using the two metallocene catalysts were characterized with ¹H NMR, ¹³C NMR and differential scanning calorimetry; the results showed that the copolymers had a random structure. Copyright © 2006 Society of Chemical Industry Society of Chemical Industry     

Synthesis and properties of ethylene/styrene copolymers produced by metallocene catalysts

Ethylene/styrene copolymers were synthesized under constant polymerization conditions using six different metallocene catalysts activated with methylaluminoxane. For all the catalysts used, the activity and molecular weight of the copolymers produced decreased with the amount of styrene in the reactor feed, but the styrene content of the copolymers increased. Catalysts with carbon bridges and bulky ligands gave rise to copolymers with higher styrene content. As a result of the increased styrene content of the copolymer, the melting temperature decreased. This effect was ascribed to a decrease in the crystallinity of the copolymers. It was also found that lamellar thickness could be significantly diminished by the incorporation of comonomers. The copolymers showed a broad spectrum of mechanical properties as a function of the comonomer ratio. At low styrene contents, they behaved like typical semicrystalline thermoplastics, and at higher styrene contents, they exhibited the properties typical of elastomers. Of the catalysts tested, [rac‐ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl)]zirconium dichloride emerged as the most promising for the production of ethylene/styrene copolymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3420–3429, 2006     

Influence of supported metallocene catalysts on polymer tacticity

Metallocene catalysts in dissolved form are in most cases unsuitable for the production of polyethylene or polypropylene on an industrial scale. In order to use them in existing technical processes, metallocenes have to be supported. C_s-symmetric zirconocenes show a high activity and no leaching additional triisobutyl aluminum is used as scavenger and MAO-covered silica for heterogenization. The aluminum : zirconium ratio can be reduced to values of 500:1 to get optimal activities. The syndiotacticity of the obtained polypropylene is lower compared with polymers of the homogeneous catalyst and decreases strongly with a thinner propene concentration. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparative effect of metallocene and Ziegler‐Natta polypropylene on the exfoliation of montmorillonite and hectorite clays to obtain nanocomposites

The present study was carried out on the effect of molecular weight and polydispersity of polypropylene (PP) obtained via Ziegler‐Natta or metallocene catalysis on the formation of nanocomposites with montmorillonite and mineral and synthetic hectorite. The formation of the nanocomposites was achieved by the melt‐mix method. X‐ray diffraction, transmission electron microscopy, and analysis of mechanical properties showed that, using PP obtained via metallocene catalysis (polydispersity ～ 2), it is possible to achieve improved formation of nanocomposites compared with PP obtained via Ziegler‐Natta catalysis (polydispersity ～ 4). It was also found that the molecular weight of the PP affects the tendency toward clay exfoliation and consequently the properties of the nanocomposites. Montmorillonite type clay was evaluated at 1%, 3%, and 5% by weight in the nanocomposite. The nanocomposite with 1 wt % clay was found to have better mechanical properties compared with the nanocomposite containing 3 wt % and 5 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 698–706, 2007     

Thermooxidative degradation of isotactic polypropylene prepared on metallocene catalyst and its sorption capacity

The sorption capacity and resistance to thermooxidative degradation are comparatively studied for isotactic polypropylene (PP) produced in the medium of the liquid monomer on homogeneous metallocene catalytic systems and on a heterogeneous titanium–magnesium catalyst. These polymers are characterized by different sorption capacities with respect to the phenyl‐β‐naphthylamine antioxidant and different induction periods of oxidation by molecular oxygen. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 808–811, 2006     

聚丙烯纤维接枝苯乙烯的研究

采用化学接枝法以苯乙烯(St)为接枝单体、过氧化苯甲酰(BPO)为引发剂,1,2-二乙烯苯(DVB)为交联剂、甲醇和正辛醇为溶剂,对聚丙烯(PP)纤维进行接枝改性。研究了原料配比和反应条件对其接枝的影响。结果表明,PP纤维上接枝St,适宜的原料配比和操作条件为:St质量与PP体积比(St/PP)为4,BPO质量与St体积比(BPO/St)为0.025,DVB与St体积比(DVB/St)为0.025,溶剂与St体积比为5,浸渍24～30h,在85℃恒温水浴中反应6～8h。在较佳条件下可得到导入率为110%-160%的接枝纤维。     

Propylene polymerization using combined syndio‐ and isospecific metallocene catalysts supported on silica/MAO

Syndiotactic and isotactic polypropylene were produced using the metallocene compounds Ph₂C(Flu)(Cp)ZrCl₂ and SiMe₂(2‐Me,4‐Ph‐Ind)₂ZrCl₂ in homogeneous system and supported on silica/MAO. These catalysts were evaluated either isolated or as a binary system. In the latter case, the iso‐ and syndiospecific metallocene complexes were immobilized together during the preparation of the supported catalyst. In a further experimental set, the syndio‐ and isospecific isolated heterogeneous catalysts were mixed at the moment of propylene polymerization. The polypropylenes obtained were evaluated using differential scanning calorimetry. The catalytic activities were also investigated. At all the studied polymerization temperatures, the results showed that the binary catalyst produced polypropylenes with lower melting temperatures in comparison with those obtained when the mixture of isolated supported syndio‐ and isospecific catalysts was employed. Moreover, the activation energies for the polymerization of all catalysts systems were calculated, resulting in a lower value for the binary system when compared to that employing the catalyst mixture and to both the isolated supported metallocene catalysts. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 628–637, 2006     

Toughening of polypropylene with styrene/ethylene‐butylene/styrene tri‐block copolymer: Effects of reactive and nonreactive compatibilization

The effects of compatibilization on the toughening of polypropylene (PP) by melt blending with styrene/ethylene‐butylene/styrene tri‐block copolymer (SEBS) in a twin‐screw extruder were investigated. The compatibilizers used were SEBS functionalized with maleic anhydride (SEBS‐g‐MA), PP functionalized with acrylic acid (PP‐g‐AA), and bifunctional compound p‐phenylenediamine (PPD). The effects of the compatibilization were evaluated through the mechanical properties as well as through the determination of the phase morphology of the blends by scanning electron microscopy. Reactive compatibilized blends show up to a 30‐fold increase in impact strength compared with neat PP; likely the result of the reaction of the bifunctional compound (PPD) with the acid acrylic and maleic anhydride groups, this increase in strength rendered both morphological and mechanical stability to these blends. The addition of PPD to the blends significantly changed their phase morphologies, leading to larger average diameters of the dispersed particles, probably as a result of the morphological stabilization at the initial processing steps during extrusion, with the occurrence of chemical reactions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3466–3479, 2002     

Direct synthesis of fibrous high molecular weight polyethylene using vanadium catalysts supported on an SiO2 ionic liquid system

Polyethylene of fibrous morphology was obtained using Cp₂VCl₂ and VCl₂(salenCl₂) catalysts activated by AlEt₂Cl and AlEtCl₂ and heterogenized on a supported ionic liquid system prepared with SiO₂ and 1‐(3‐triethoxysilyl)propyl‐3‐methylimidazolium chloroaluminate. The fibre length ranges from 15 to 60 µm, depending on the reaction conditions. The polyethylene is characterized by a high molecular weight ((1.1–2.4) × 10⁶ g mol^?1) and a narrow molecular weight distribution (1.4–2.5). It is a linear polymer, properly without branching. The DSC method reveals characteristic changes in melting temperature and crystallinity degree between the first and second scan heating cycles (141 °C and 136 °C, 71% and 46%, respectively). The wide angle X‐ray spectroscopy and Fourier transform infrared spectroscopy methods give crystallinity degree values of 40% and 41%–51%. The influence of type of catalyst precursor, alkylaluminium activator, catalyst/activator molar ratio, reaction time and temperature is discussed. © 2015 Society of Chemical Industry     

聚丙烯纤维共辐射接枝苯乙烯的研究

以60Co γ射线为辐射源,在氮气保护下对聚丙烯(PP)纤维和苯乙烯-二乙烯苯在甲醇介质中进行共辐射接枝。结果表明,当接枝液中苯乙烯质量分数为20％-30％,辐射总剂量为25-50 kGy时,PP纤维的接枝率高。二乙烯苯相对苯乙烯的质量分数为2％时,纤维的接枝率和玻璃化转变温度最高,分别为701％和161.5℃。接枝反应离开辐射源后存在一定程度的后效应,放置一定时间和接枝液中加入适量无机酸均可有效提高PP纤维的接枝率。在相同条件下,用乙醇替代甲醇可以达到相近的接枝率。     

Synthesis and characterization of solid‐phase graft copolymer of polypropylene with styrene and maleic anhydride

Polypropylene (PP) was modified by solid‐phase graft copolymerization with maleic anhydride (MAH) and styrene (St), using benzoyl peroxide as the initiator and xylene as the interfacial agent. Effects of various factors such as monomer concentration, monomer ratio, initiator concentration on grafting percentage, and acid value were investigated. The graft copolymer was characterized by Fourier transform infrared, pyrolysis gas chromatography—mass spectroscopy, and dynamic mechanical analysis, and the intrinsic viscosity of the extractive from the reaction product was investigated. The results showed that the grafting percentage and acid value of the graft copolymer of PP with two monomers (MAH and St) were considerably higher than those of the graft copolymer of PP with MAH alone. The graft segments were shown to be the copolymer of St and MAH with a substantial molecular weight. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2482–2487, 2000     

高分子量无规聚丙烯的表征及其硫化性能研究

用五甲基环戊二烯三苄氧基钛与甲基铝氧烷催化体系合成出高分子量弹性聚丙烯（El-APP)。用核磁共振碳谱、差示扫描量热法、动态力学分析等测试表明,该产物为高分子量规聚丙烯（APP）,呈现橡胶的动态力学行为,并具有良好热稳定性。El-APP的拉伸强度为2．8MPa,伸长率高达2200％,具有良好弹性。采用过氧化物对其进行硫化研究,结果表明,El-APP正硫化较短,无硫化返原现象,硫化之后拉伸强度提高,永久变形大幅下降。     

Effect of unsaturated chain end‐group on thermal oxidative behavior of polypropylene

In order to clarify the influences of unsaturated chain end‐groups on the oxidative degradation of isotactic polypropylene (iPP), values of activation energy (ΔE) for the oxidative degradation reactions of Ziegler‐catalyzed iPP (ZiPP) and metallocene‐catalyzed iPP (MiPP) having similar tacticity were evaluated by the temperature dependence of the oxidation induction time as determined by thermogravimetric analysis over the range 130–145 °C. The correlation between the content of unsaturated chain end‐groups and the change of ΔE was also studied. The results obtained indicated that the unsaturated chain end‐groups strongly influenced the rate of iPP degradation. Moreover, on addition of oligomer‐like MiPP having unsaturated chain end‐groups, the ΔE value of ZiPP became lower, suggesting that iPP having unsaturated chain end‐groups served as an infectious agent of the degradation. Copyright © 2007 Society of Chemical Industry     

Morphology,crystallization, and thermal behavior of isotactic polypropylene/propylene‐g‐styrene blends

Optical microscopy, differential scanning calorimetry, and small angle X‐ray scattering techniques were used to study the influence of the crystallization conditions on morphology and thermal behavior of samples of binary blends constituted of isotactic polypropylene (iPP) and a novel graft copolymer of unsaturated propylene with styrene (uPP‐g‐PS) isothermally crystallized from melt, at relatively low undercooling, in a range of crystallization temperatures of the iPP phase. It was shown that, irrespective of composition, no fall in the crystallinity index of the iPP phase was observed. Notwithstanding, spherulitic texture and thermal behavior of the iPP phase in the iPP/uPP‐g‐PS materials were strongly modified by the presence of copolymer. Surprisingly, iPP spherulites crystallized from the blends showed size and regularity higher than that exhibited by plain iPP spherulites. Moreover, the amount of amorphous material located in the interspherulitic amorphous regions decreased with increasing crystallization temperature, and for a given crystallization temperature, with increasing uPP‐g‐PS content. Also, relevant thermodynamic parameters, related to the crystallization process of the iPP phase from iPP/uPP‐g‐PS melts, were found, composition dependent. The equilibrium melting temperature and the surface free energy of folding of the iPP lamellar crystals grown in the presence of uPP‐g‐PS content up to 5% (wt/wt) were, in fact, respectively slightly lower and higher than that found for the lamellar crystals of plain iPP. By further increase of the copolymer content, both the equilibrium melting temperature and surface free energy of folding values were, on the contrary, depressed dramatically. The obtained results were accounted for by assuming that the iPP crystallization process from iPP/uPP‐g‐PS melts could occur through molecular fractionation inducing a combination of morphological and thermodynamic effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2286–2298, 2001     

Effects of molecular weight and molecular weight distribution on creep properties of polypropylene homopolymer

The molecular weights of the industrial-grade isotactic polypropylene (i-PP) homopolymers samples were determined by the melt-state rheological method and effects of molecular weight and molecular weight distribution on solid and melt state creep properties were investigated in detail. The melt-state creep test results showed that the creep resistance of the samples increased by M_w due to the increased chain entanglements, while variations in the polydispersity index (PDI) values did not cause a considerable change in the creep strain values. Moreover, the solid-state creep test results showed that creep strain values increased by M_w and PDI due to the decreasing amount of crystalline structure in the polymer. The results also showed that the amount of crystalline segment was more effective than chain entanglements that were caused by long polymer chains on the creep resistance of the polymers. Modeling the solid-state viscoelastic structure of the samples by the Burger model revealed that the weight of the viscous strain in the total creep strain increased with M_w and PDI, which meant that the differences in the creep strain values of the samples would be more pronounced at extended periods of time.     

Morphology,crystallization, and thermal behavior of isotactic polypropylene/polystyrene blends: Effects of the addition of a graft copolymer of propylene with styrene

Optical microscopy, differential scanning calorimetry, and small‐angle X‐ray scattering techniques were used to study the influence of crystallization conditions on the morphology and thermal behavior of samples of ternary blends constituted by isotactic polypropylene (iPP), atactic polystyrene (aPS), and a novel graft copolymer of unsaturated propylene with styrene (uPP‐g‐PS) with the purpose of assessing the uPP‐g‐PS capability to act as a compatibilizer for iPP/aPS materials. It was shown that the presence of the uPP‐g‐PS copolymer affects the interfacial tension between the iPP and aPS phases in the melt state, with the aPS particle size and the particle‐size distribution being, in fact, strongly modified. In samples of iPP/aPS/uPP‐g‐PS blends, isothermally crystallized from the melt at a relatively low undercooling in a range of the crystallization temperature of the iPP phase, the addition of the uPP‐g‐PS copolymer induced a drastic change both in the aPS mode and the state of dispersion and in the iPP spherulitic texture and inner structure of the spherulite fibrils. In particular, the phase structure developed in the iPP/aPS/uPP‐g‐PS materials was characterized by a crystalline lamellar thickness of the iPP phase comparable to that shown by the plain iPP. The extent of the induced modifications, that is, the degree of compatibilization achieved, resulted in a combined effect of composition and undercooling. Also, relevant thermodynamic parameters of the iPP phase, such as the equilibrium melting temperature (T_m) and the folding surface free energy (ς_e) of the lamellar crystals, were found to be influenced by the presence of the uPP‐g‐PS copolymer. A linear decrease of the T_m and ς_e values with increasing uPP‐g‐PS content was, in fact, observed. Such results have been accounted for by an increase of the presence of defects along the iPP crystallizable sequences and by the very irregular and perturbed surface of the crystals with increasing copolymer content. The observed decrease in T_m values revealed, moreover, that, in the iPP/aPS/uPP‐g‐PS blends, the iPP crystal growth occurs under comparatively lower undercooling, in line with higher crystalline lamellar thickness shown by SAXS investigation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1429–1442, 1999     

The production of ethene/propene/5-ethylidene-2-norbornene terpolymers using metallocene catalysts: Polymerization,characterization and properties of the metallocene EPDM

Metallocene catalysts Et(Ind)₂ZrCl₂/MAO and Et(Ind)₂HfCl₂/MAO were used in ethene/propene copolymerization and in ethene/propene/5-ethylidene-2-norbornene (E/P/ENB) terpolymerization. The copolymerization activity of the Et(Ind)₂ZrCl₂/MAO system was 20 × 10³ kg_polym/mol_Mt *h, the Et(Ind)₂HfCl₂/MAO yielding 5 × 10³ kg_polym/mol_Mt *h. The polymerization activity decreased with diene addition, but this effect was significant only at very large diene feeds. The catalysts incorporated diene readily. Materials with an ethene content of 55 to 70 mol % and an ENB content of 2 to 16 mol % were produced. Et(Ind)₂HfCl₂ produced a considerably higher molar mass material than the Et(Ind)₂ZrCl₂ catalyst. The molar mass distributions were narrow. Copolymers and terpolymers with up to 3 mol % ENB content had some crystallinity. Copolymer T_gs were between −59°C and −55°C. The terpolymer glass transition temperature rose 1.5°C per wt % of ENB in the polymer. Polymer characteristics reported include composition, molar mass distribution, melt flow rate, density, and thermal behavior. The dynamic mechanical and rheological properties of the materials in comparison with commercial E/P/ENB terpolymers are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 35–44, 1997     

Full‐range kinetic study on bulk syndiotactic polymerization of styrene with homogeneous metallocene catalysis

By choosing a proper agitator and reinforcing its stirring shear, powdery syndiotactic polystyrene (sPS) is prepared in a bulk precipitation process with two homogeneous metallocene catalyst systems [Cp*TiX₃/MAO/TIBA (X = Cl or OPhOMe)]. A full‐range kinetics study of the heterogeneous polymerization is performed in detail to produce this kind of powdery sPS in an industrial process. A typical curve of conversion versus time takes an S shape and an obvious acceleration phenomenon occurs in the middle stage of the polymerization, although the polymer–monomer gel is avoided. The viscous‐average molecular weight of sPS goes through a peculiar increasing–decreasing–increasing change during the bulk polymerization process. These phenomena are viewed in terms of the two‐phase polymerization mechanism and the overheating in particles during polymerization. The influence of the metallocene catalyst type and concentration, MAO/Ti ratio, triisobutyl aluminum (TIBA)/Ti ratio, and polymerization temperature on the polymerization kinetics are investigated. TIBA has dual effects on the polymerization. A small amount of TIBA in the catalyst system promotes polymerization, but more TIBA leads to a low molecular weight sPS. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2635–2643, 2002     

Radiation‐induced graft copolymerization of 2‐vinylpyridine and styrene onto isotactic polypropylene fiber

Isotactic polypropylene fiber (IPP) was graft‐copolymerized using 2‐vinyl pyridine (2‐VP) and styrene (sty) as the monomers by the mutual irradiation method in air. The percentage of grafting was determined as a function of various reaction parameters and it was found that the maximum grafting of 2‐VP (114%) and sty (76%) was obtained at an optimum dose of 1.08 × 10⁴ and 0.64 × 10⁴ Gy using 1.8 × 10⁻² mol of 2‐VP and 4.3 × 10⁻² mol of sty, respectively. The graft copolymers were characterized by differential scanning calorimetric analysis and isolation of the grafted chains from the grafted iPP samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2959–2969, 1999