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The crystallization behavior and morphology of polyoxymethylene (POM) and POM with polyamide (PA) were studied by polarized light microscopy (PLM), isothermal and nonisothermal differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The isothermal crystallization kinetics were analyzed with the Avrami equation. Compared with the virgin POM, the addition of PA can reduce the spherulites size and improve the crystallization growth rate and crystallinity ([X.sub.c]) of POM, which demonstrates that the nucleation effect of PA as the high-molecular nucleus is favorable to the mechanical properties and dimension stability of POLYM. ENG. SCI., 45:1174-1179, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION In the mold processing of polymers, crystallization is a universal phenomenon, especially for polymers with regular molecular chains. Differences of crystallinity, crystal structure, and morphology will influence the properties [...]

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]

Novel polyethylene‐based (PE‐based) antioxidants derived from commercially available ethylene‐vinyl acetate copolymer (EVA) with PE as the backbone and hindered phenols as side groups are prepared, and their potential for application as non‐migrating polyolefin stabilizers is investigated. The synthesis route contains the typical hydrolysis of EVA and transesterification reaction between the hydrolysis product and methyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl) propionate. Thermal stabilities of these PE‐based antioxidants (AO‐PE) are studied through thermal analysis under an air atmosphere and shown to be higher than those of antioxidant 1076 and antioxidant 1010 (AO‐1010) due to their macromolecular structures. Antioxidant activities of the AO‐PE are evaluated in polypropylene (PP) by measuring the melt flow index of multiple‐extruded stabilized PP, and the results demonstrate that the antioxidant effectiveness of these antioxidants is strongly related to the molecular weight. [ABSTRACT FROM AUTHOR]

A new synthetic procedure is described for the preparation of dendritic polyethylene brushes with polysiloxane as the main chain, describing for the first time that it is possible to simply and efficiently prepare highly branched architectures for this type of polymer. Furthermore, as a result of the polymer brush architecture, polyethylene acts as the side chains and Si-O-Si as the backbone. The number average molecular weight (Mn) of the polyethylene brushes, which is determined using a multiple angle laser light scattering detector, increases from 5946 to 27 684 g mol-1 while retaining relatively narrow polydispersities (1.5-2.4). The polymer brushes are characterized by solid 29Si NMR and high-temperature ¹H NMR spectra. In addition, X-ray photoelectron spectroscopy and gel permeation chromatography were used to confirm the structure. [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]

Chain-end-functionalized polyethylenes (Cef-PEs: PESSH (Cef1), PESfurfuryl (Cef2), PESNH2 (Cef4), PESNH2•HCl (Cef5), PESCOONa (Cef6), PESCHA(Cef7), PESSO3Na (Cef8), PESOH (Cef9) and PESCOOH (Cef10)) are synthesized by thiol-ene addition of vinyl-terminated polyethylene (v-PE) with 1,2-ethanedithiol, furfurylmercaptan, cysteamine, cysteamine hydrochloride, sodium thioglycolate, L-cysteine hydrochloride, sodium 2-mercaptoethanesulfonate, mercaptoethanol, and thioglycolic acid, respectively. PEStNCO (Cef3) is obtained by subsequent reaction of Cef9 with anhydrous 4,4′-MDI. Cef-PE1-8 are reported for the first time. The conversions of all the reactions are up to 95%-100%. All the Cef-PEs are characterized by NMR, GPC, DSC, FT-IR, and TGA. In the experiments, it is found that alkaline mercaptans and solvents are adverse to the thiol-ene click reactions. [ABSTRACT FROM AUTHOR]

Four novel well-defined polyethylene-bound antioxidants (PE-bound antioxidants) with distinct secondary structures are synthesized via transesterification reactions between methyl 3-(3,5-di- tert-butyl-4-hydroxyphenyl)propionate and hydroxyl-terminated polyethylenes. The results of thermal gravimetric analysis under an air atmosphere demonstrate that the thermal stabilities of PE-bound antioxidants are higher than that of commercial antioxidant Irganox1076 and are strongly related to their chemical structures. Particularly, the most thermally stable PE-bound antioxidant is the one bearing both primary and secondary antioxidant moieties. The antioxidant activities of the PE-bound antioxidants are evaluated in polypropylene by their melt flow index. [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]

A series of star block polymers with a hyperbranched core and 26 arms are successfully synthesized by atom transfer radical polymerization of styrene (St), and poly(ethylene glycol) methyl ether methacrylate from a hyperbranched polystyrene (HBPS) multifunctional initiator. All-solid polymer electrolytes composed of these multiarm star polymers and lithium salts are prepared. The influences of polyoxyethylene (PEO) side-chain length, PEO content, lithium salt concentration and type, and the structure of polymer on ionic conductivity are systematically investigated. The resulting polymer electrolyte with the longest PEO side chains exhibits the best ionic conductive properties. The maximum conductivity is 0.8 × 10−4 S cm−1 at 25°C with EO/Li = 30. All the prepared multiarm star block polymers possess good thermal stability. The mechanical property is greatly improved owing to the existence of polystyrene blocks in the multiarm star polymer molecules, and flexible films can be obtained by solution-casting technique. © 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]