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A novel macromolecular auxiliary antioxidant with polyethylene (PE) as polymer skeleton and phosphites as side groups is prepared based on commercial ethylene‐vinyl acetate (EVA) copolymers and its potential as polyolefin stabilizers is studied in depth. The synthesis approach of this PE‐grafted antioxidant consists of a typical EVA hydrolysis reaction and a two‐step nucleophilic substitution reaction of PCl3, 2,4‐di‐tert‐butylphenol, and the hydrolysis product. Results of the thermogravimetric analysis show that the macromolecular structures endow the as‐synthesized antioxidant with much better thermal stability than that of the commercial antioxidant 168. In addition, antioxidant behaviors of the PE‐grafted antioxidants in polypropylene (PP) matrix are investigated in detail through characterization of the melt flow index of multiple‐extruded stabilized PP as well as the short‐term oxidation induction time test and the long‐term thermo‐oxidative aging test. Results show that even with extremely low content of the effective antioxidant groups, the as‐synthesized macromolecular antioxidant still has excellent antioxygenic properties. [ABSTRACT FROM AUTHOR]

ABSTRACT High melt flow rate (MFR) of polypropylene can improve its processability and its high isotacticity is favor of keeping good mechanical properties of polypropylene. In this study, as a convenient and effective method, the mixture of phosphate and alkoxysilane as mixed external donors for Ziegler-Natta catalyst is used to improve MFR of polypropylene. The MFR of polypropylenes prepared by mixed external donors is three to five time higher than that prepared by dicyclopentyl dimethoxysilane (Donor-D) alone, which is attributed to broad molecular weight distribution and low molecular weight of polypropylene prepared by mixed external donors. In addition, isotacticity and lamella thickness of polypropylene prepared by mixed external donors containing triisopropyl phosphate or phenyl-phosphonic acid dipentyl ester are very close to that prepared by Donor-D, which lead to keep high thermal properties and good mechanical properties for the polypropylenes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44704. [ABSTRACT FROM AUTHOR]

The effects of different mixed external donors on the crystallization behavior and sequence length distribution of polypropylene prepared by MgCl2-supported TiCl4 Ziegler-Natta catalyst were studied through successive self-nucleation and annealing (SSA) technique. The SSA results show that the crystallization ability and the relative contents of long isotactic sequence length gradually increase with the increase of the relative component of Donor-1 (cyclohexylmethyldimethoxysilane, dicyclohexyl(dimethoxy)silane, and dipiperidinedimethoxysilane) in the different mixed external donors when the ratio of the mixed external donors/Ti (Si/Ti) is unchanged. The thickness distribution of lamellar also becomes broader, indicating the sequence length distribution of polypropylene gets broader. The crystallization ability and the relative contents of long isotactic sequence length of polypropylene prepared by the mixed cyclohexylmethyldimethoxysilane and n-propyltriethoxysilane (CN) external donors are lowest. However, the effect of the mixed dicyclohexyl(dimethoxy)silane and n-propyltriethoxysilane (HN) and the mixed dipiperidinedimethoxysilane and n-propyltriethoxysilane (PyN) external donors on the crystallization ability and sequence length of polypropylene are more significantly. Especially, the relative content of long isotactic sequence length increases sharply from 0.2 to 27.5% in the polypropylene chain of sample prepared by the mixed PyN external donors when the proportion of Donor 1 is running up to 90%. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

As the external donor in Ziegler-Natta catalysts have an important influence on the stereo-defects distribution of polypropylene, the effects of the mixed external donors (the mixture of Donor-C (cyclohexylmethyldimethoxysilane) and Donor-N ( n-propyltriethoxysilane) ) on the isotactic sequence length and its distribution of polypropylene prepared by Ziegler-Natta catalyst through propylene bulk polymerization were studied through the Successive self-nucleating and annealing (SSA) and C-NMR techniques. The SSA results showed that the relative contents of the highest isotactic component and the lamellar thickness in the polypropylene chain gradually increased with the increase of the relative component of Donor-C in the C/N mixed external donors, indicating the isotactic sequence length of polypropylene got longer, and the lamellar thickness distribution of polypropylene became broader, revealing the isotactic sequence length distribution of polypropylene got broader. In addition, the C-NMR results showed that the average meso isotactic sequence length ( MSL) of polypropylene gradually increased with the increase of the content of Donor-C in the C/N mixed external donors, which was in good coincident with the results calculated from SSA, showing a good correspondence between the SSA and C-NMR techniques. [ABSTRACT FROM AUTHOR]

MgCl2/TiCl4/diether is a fifth-generation Ziegler-Natta catalyst for the commercial polymerization of propylene. The outstanding features of this catalyst are the high activity and high isotacticity for propylene polymerization without using an external electron donor. In this study, we explored the copolymerization of propylene and 1-octene with MgCl2/TiCl4/diether catalyst. It was found that MgCl2/TiCl4/diether catalyst showed higher polymerization activity and led to greater 1-octene content incorporation, compared with a fourth-generation Ziegler-Natta catalyst (MgCl2/TiCl4/diester). With an increase in 1-octene incorporation in polypropylene chains, the melting temperature, glass transition temperature and crystallinity of the copolymers decreased distinctly. The microstructures of the copolymers were characterized using 13C NMR spectroscopy, and the copolymer compositions and number-average sequence lengths were calculated from the dyad concentration and distribution. This result is very important for the in-reactor polyolefin alloying process, especially for the case of a single catalyst and two-step (or two-reactor) process. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: An effective route to synthesize the amphiphilic diblock copolymer containing a poly(ε-caprolactone) block and a polyolefin block, such as polyethylene, syndiotactic polystyrene and isotactic polypropylene is discussed in this article. There are two reaction steps including the preparation of polyolefins by the combination of metallocene/methylaluminoxane as catalyst system and various chain transfer agents as well as the subsequent anionic ring-opening polymerization of ε-caprolactone. The molecular structure in terms of composition, molecular weight, molecular weight distribution of the diblock copolymers prepared is controllable by these well-defined reaction mechanisms. The scanning electron microscope (SEM) results showes that the compatibilities of the polyolefins and polycarbonate blends are improved greatly using these amphiphilic diblock copolymers as the polymeric compatilizers. [Copyright &y& Elsevier]

Discusses the effects of co-catalysts on the morphology of isotastic polypropene prepared using metallocene catalyst. Preparation of the isotastic polypropene with good morphology and high bulk density; Proposal of the formation mechanism of active centers; Adjustment of the polymerization conditions to solve the problem of morphology.

Abstract: PP-g-PS copolymers were synthesized with the same polypropylene (PP) backbones and various side chain lengths of PS sequences via reactive comonomer p-allyltoluene (p-AT) by Ziegler–Natta copolymerization and the subsequent living anionic graft-polymerization. 1H NMR characterized that the PP-g-PS copolymer had grafted 3.15 side chains per 1000 carbons in the PP backbones and the length of PS sequences varied in the range of 25.8–309.9 units. PP/PS blends with the PP-g-PS copolymer as compatibilizer (wt. 75/25/5) were prepared and characterized by SEM, WAXD and DMA to investigate the morphologies, crystallinity and glass transition temperatures of the PP/PS blends. All the results pointed out that the average side chain length (GL) of the graft copolymer (GL is from 25.8 to 309.9) made great effects of the PP/PS blends, such as the PS dispersed phase, the crystallinity of the PP component and the two glass transition temperatures of the blends, which showed the same trend with the increase of the GL. Overall, only with a suitable average side chain length, the PP-g-PS copolymer could achieve optimal compatibilizing efficiency of the PP/PS blends. [Copyright &y& Elsevier]

Abstract: The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out with conventional Ziegler–Natta catalyst supported on MgCl2. The effects of the concentration of ADMS in the feed on the polymerization reaction and copolymer properties were investigated. The resulting copolymer PP-co-ADMS was chlorinated to PP–Si–Cl by refluxing the copolymer with SOCl2 in benzene. The chlorinated copolymer was used to initiate ATRP of MMA with CuCl/PMDETA as catalyst to produce graft copolymer PP-g-PMMA, which was characterized with 1H NMR, 13C NMR, GPC and DSC. Polymer blend of iPP/PP-g-PMMA/PMMA was prepared and the results shown that PP-g-PMMA was an effective compatilizer. [Copyright &y& Elsevier]

Isotactic polypropylene (iPP) with narrow molecular mass distribution was freeze-extracted from n-octane solutions with varying concentrations. The recovered samples were characterized by differential scanning calorimetry. It is found that the sample recovered from the very dilute solution exhibits the higher non-isothermal crystallization temperature, faster isothermal crystallization rate, and smaller Avrami index. And there should exist a critical concentration corresponding with the critical overlap concentration proposed by de Gennes in the polymer solutions. In the solution well below the critical concentration, the iPP chains were isolated from each other, resulting in an acceleration of melt crystallization for the recovered samples. It seems that the chain entanglement is a barrier to the melt crystallization of polymer. [Copyright &y& Elsevier]

Nitrogen-doped porous carbon with controllable specific surface area or nitrogen content was prepared from chlorinated polypropylene and nitrogen-containing compounds. The product shows high porosity and regular pore structure. [Display omitted] Here we report a facile method to prepare nitrogen-doped porous carbon with controllable specific surface area and nitrogen content through pretreated chlorinated polypropylene with nitrogen-containing compounds(NCCs). The microstructure and porous textures of the obtained carbons are characterized by BET, SEM, TEM, XRD and Raman, respectively. SEM shows that pore structure can be found in carbon matrix. And with the increase of nitrogen content, more amorphous carbon are observed in Raman spectral. The results show that the specific surface areas are effectively increased from 1000 m2/g to 3269 m2/g when the structure of NCCs have a nitrogen-contained hexatomic ring, and nitrogen content are apparently raised from 1.3 at% to 27.73 at% when the NCCs contain guanidyl structure. Besides, XPS shows that when the nitrogen content is relatively low, nitrogen emerge at carbon matrix mainly in form of pyrrolic-N, and with the increase of nitrogen content, the pyridinic-N become the main structure of nitrogen in carbon. [ABSTRACT FROM AUTHOR]