Article pubs.acs.org/Macromolecules
Polypropylene Copolymer Containing Cross-Linkable Antioxidant Moieties with Long-Term Stability under Elevated Temperature Conditions Gang Zhang, Changwoo Nam, and T. C. Mike Chung* Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16801, United States
Linnea Petersson and Henrik Hillborg ABB AB, Corporate Research, Forskargränd 7 72178 Västerås, Sweden ABSTRACT: Despite its commercial success, isotactic polypropylene (PP) is not suitable for the applications that require long-term exposure to high-energy conditions, such as elevated temperatures, UV radiation, or high electric fields, due to the combination of polymer chain oxidative degradation, incompatibility with polar additives (antioxidants, stabilizers, etc.), and low material softening temperature. This paper presents a new solution that can simultaneously address both chemical and physical limitations. The idea is to develop a new PP-HP copolymer that contains some specific hindered phenol (HP) groups, homogeneously distributed along the polymer chain. These PP-bound HP pendant groups can not only effectively protect PP chains from the oxidative degradation but also engage in a facile cross-linking reaction to form a 3-D network structure during the oxidation reaction. One accelerated oxidation test in air at 190−210 °C shows this distinctive advantage. While a commercial PP polymer (containing common antioxidants and stabilizers) degrades within 1 h, a PP-HP copolymer with about 1 mol % (9 wt %) HP groups shows almost no detectable weight loss after 1000 min. In an ASTM endurance test under a targeted application temperature (140 °C in air), the commercial PP shows 1% weight loss within about 10 days. On the other hand, this new PP-HP lasts for 105 days (4 order increase) under the same condition. In the strain−stress curve measurement, the PP-HP film also shows no detectable change in tensile strength and modulus after constant heating the polymer film at 140 °C in air for 1 week. Overall, the experiment results present the potential of expanding PP applications into a much higher temperature range (>140 °C) under oxygen oxidative environments.
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INTRODUCTION Thermal and oxidative stability of polymers has always been a major issue in considering its applications. Most polymer products are added with antioxidants right after polymerization to inhibit their oxidation reaction during melt processes at elevated temperatures and outdoor applications under UV exposure and heat.1−3 As illustrated in Scheme 1, the PP polymer is liable to chain degradation due to the presence of the tertiary proton in every repeating unit, which is relatively labile and is more prone to an oxygen attack. The formed hydroperoxide moiety degrades the polymer chain in forming a terminal aldehyde and unsaturated group as well as regenerating new free radicals. In other words, this is a catalytic reaction mechanism with rapid degradation of the polymer chain.4 Thus, antioxidants (stabilizers), with the ability to donate hydrogen atoms and neutralize the polymeric radicals, are needed, inhibiting (or slowing down) the oxidation−degradation cycles.5 The most common antioxidants used in polyolefin are hindered phenol molecules, including octadecyl-3-(3,5-di-tert© XXXX American Chemical Society
butyl-4-hydroxyphenyl)propionate (Irganox 1076) and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Irganox1010).6,7 However, there are some concerns around using these relatively polar antioxidant molecules, namely due to the incompatibility with a nonpolar semicrystalline PP matrix. It is difficult to achieve a homogeneous mixture and maintain a minimum effective antioxidant concentration throughout the PP matrix.8 As a result, the concentrated antioxidants near the polymer surfaces also accelerate the loss of antioxidant when exposed to solvents, heat, or strong electric fields.9 The research on polymeric antioxidants has recently gained some attention with the objective of addressing common additive loss issues. There are two general functionalization approaches by grafting10−12 the desirable functional group to the polymer Received: June 11, 2017 Revised: August 5, 2017
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DOI: 10.1021/acs.macromol.7b01235 Macromolecules XXXX, XXX, XXX−XXX
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chain or copolymerization13−15 with a comonomer containing the specific functional moiety. The common postpolymerization approach involves rubber materials with unsaturated moieties that are reactive to the functionalization reaction. Some reactive stabilizers were also applied during the grafting reactions.16−18 Several polymeric hindered phenol antioxidants applied to PE and PP polymers were reported by using several grafting reactions.19−21 On the other hand, the direct copolymerization approach to incorporate antioxidant groups to PE and PP by transition metal coordination polymerization mechanism is very rare due to the limitations of catalyst poison and different comonomer reactivity ratios.22,23 There are few reports24−27 discussing PE- and PP-bound hindered phenol antioxidants prepared by metallocene-mediated copolymerization. In our previous work,28 we reported the incorporation of 3,5-bis(tertbutyl)-4-hydroxy antioxidant groups to PP polymer. The resulting copolymers, with a controlled quantity of antioxidant groups homogeneously distributed in the PP matrix, showed advantages of high antioxidant protection over conventional PP organic antioxidants and stabilizers, including hindered phenols and hindered amines. So far, most experimental results in polymeric antioxidants have been focused on the issues of antioxidant compatibility, migration, and oxidative stability. There is no report investigating the antioxidant groups that can also serve as cross-linking agents to provide physical (structural) integrity of polyolefin products under elevated temperature conditions. Although isotactic polypropylene commercial polymers usually exhibit a melting peak at around 165 °C, the broad melting endotherm starts at as low as 70 °C because a broad crystal size distribution. The commercial PP products gradually lose their mechanical strength (due to softening) at a relatively low temperature. The general recommended application temperature is below 100 °C. The cross-linking network structure in the polymer matrix is known to provide advantages of increasing mechanical strength, temperature stability, and resistance to solvents, creep, and stress-cracking.29−33 Crosslinked polyethylene is used everywhere today in water piping and high-voltage electrical cables.34 However, unlike PE, PP cannot be effectively cross-linked in the industry due to the lack of a suitable cross-linking method. The normal approach in the crosslinking PE industry involves high-energy irradiation (γ-rays and electron beams),35−38 peroxide-induced radical reactions,39−43
and silane-moisture cure mechanism.44−46 Most of these methods are not suitable in the PP case due to the prompt degradation of the PP backbone under free radical conditions.47−50 Also, the catalyst will be poisoned during the transition-metal-mediated copolymerization with cross-linkable silane comonomers.22 Several years ago, we introduced an effective self-cross-linking method for both PE and PP polymers, without any external reagent or forming byproduct.51,52 The chemistry involves a monoenchainment of butenylstyrene (BSt) comonomers during the metallocene-mediated copolymerization to form PE-co-BSt or PP-co-BSt copolymers with high molecular weight and narrow molecular weight and composition distributions. The resulting pendant styrene groups, homogeneously distributed along the polymer chain, involve a thermalinduced [2 + 4] cycloaddition reaction to form the corresponding PP or PE network. Most importantly, this selfcross-linking reaction does not affect the polymer backbone and semicrystalline morphology. As will be discussed, another effective self-cross-linking mechanism is applied to the current PP-HP copolymer containing a specific (cross-linkable hindered phenol) antioxidant moiety.
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EXPERIMENTAL SECTION
Materials. All O2 and moisture sensitive manipulations were carried out inside an argon-filled Vacuum Atmosphere drybox. rac-Me2Si[2-Me4-Ph(Ind)]2ZrCl2 catalyst was prepared using the published procedures.53 MAO (10 wt % methylaluminoxane in toluene), chlorotrimethylsilane, triethylamine, 10-undecen-1-ol (Sigma-Aldrich), 1-(3(dimethylamino)propyl)-3-ethylcarbodiimide, 4-N,N-dimethylaminopyridine, calcium hydride (VWR Scientific), 3,5-bis(tert-butyl)4-hydroxyphenylpropionic acid (Ciba), and propylene (Matheson Gas) were used as received. Toluene (Wiley Organics) and xylene (Alfa Aesar) were distilled over sodium benzophenone under argon. Two commercial PP polymers, including Daploy (general-purpose grade) with 210 min. Considering the same linear hindered phenol moiety in both PPHP and the commercial general-purpose PP, the PP-bound HP groups with homogeneous distribution in PP matrix offer much higher antioxidant performance. Endurance under Elevated Operation Temperatures. Polymer aging and endurance time under certain operational conditions are essential information in considering polymer applications. As discussed, it is highly desirable to broaden the PP application temperature and maintain constant performance for a long period time. With the newly developed PP-HP polymer, we are very curious to know what the new operational window is and what the endurance time is at an operational temperature
Figure 3. Gel content test of PP-HP (1 mol % HP) copolymer with different heating conditions. Gel content is the insoluble portion after refluxing in xylene for 2 h. (a) Gel content as a function of temperature (heating at different temperatures for 24 h under air condition). (b) Gel content versus different times (heating treatment at 210 °C under air condition).
at 210 °C. The protection time is just enough for melt processing. The capacitor-grade Borclean PP shows slightly better endurance, about 300 min at 190 °C, but only 20 min at 210 °C. On the other hand, the PP-HP-1 copolymer with 1 mol % (9 wt %) HP content shows a dramatic increase in thermo-oxidative stability. After constant heating at 190 °C in air for 1000 min, the PP-HP-1 copolymer exhibits no detectable weight loss. At 210 °C, the weight loss of PP-HP copolymer is also negligible. F
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Figure 4. TGA curve comparison of a commercial PP (Borclean) and two PP-HP copolymers with 1 and 2 mol % HP group contents under air condition.
Figure 6. Oxidative-induction time results of (a) commercial PP (Daploy), (b) PP (Borclean), and (c) PP blend with PP-HP-1 (PP:PPHP-1 = 10:1 wt ratio).
Figure 8 shows the plots of log (heating rate) vs heating temperature (1/T) under various specific polymer weight loss (conversion) conditions, based on the TGA curves in Figure 7. The slope of each line was used to calculated the activation energy (Ea) of each polymer weight loss (conversion during the polymer chain oxidation and degradation reaction), using the equation in ASTM 1877 test Ea = −(R/b)Δ log β/Δ(1/T), wherein Δ log β/Δ(1/T) = slope of the line obtained in Figure 8, β = heating rate (K/min), T = temperature (K) at constant conversion, gas constant R = 8.314 J/(mol K), and b = 0.457/K on the first iteration. Table 2 summarizes the activation energy (Ea) for both Borclean PP and PP-HP-1 copolymer with various polymer weight loss conditions. In all side-by-side weight loss comparisons, PP-HP-1 polymer shows significantly higher activation energy than Borclean PP, indicating that PP-HP-1 is far more resistant to oxygen oxidation and polymer chain degradation. In the details, it is interesting to note that the different trend in activation energy vs polymer weight loss (Table 2) occurs between two cases. Borclean PP shows a systematical reduction of activation energy (Ea) with the increase of polymer weight loss due to the continuous polymer chain degradation that results in lower polymer molecular weight and higher chain mobility. On the other hand, in the PP-HP-1 case, the initial reduction of activation energy is recovered at a higher conversion level, which may be related to the in situ formation of crosslinkers in the resulting x-PP-HP-1 network.
Figure 5. Isothermal TGA curve comparison at (top) 190 °C and (bottom) 210 °C in air between two commercial PP products and PPHP-1 with 1 mol % HP groups.
>100 °C, which is important in many high-energy applications but not attainable in current PP materials. Thus, the ASTM 1877 method was employed to determine PP-HP endurance time at elevated temperatures in air.60 The failure is defined at 1 wt % polymer weight loss. This method involves a TGA measurement (Figure 7) with various heating rates. For comparison, the high quality capacitor-grade Borclean PP was also examined side-byside as the control runs. G
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Figure 7. TGA curves under various heating rates for (top) PP (Borclean) and (bottom) PP-HP-1.
With the activation energy (Ea), we can estimate the material endurance time under a specific value of conversion and failure temperature, following the ASTM 1877 equation Tf = Ea/ (2.303R[log t f − log{E a /(Rβ)}+ a]), where a is the approximation integral, tf the estimated lifetime, and Tf the failure temperature for a given value of conversion. Figure 9 plots the estimated endurance (lifetime) vs application temperature in air for both commercial Borclean PP and PP-HP-1 with 1 wt % polymer weight loss, assuming this weight loss level is acceptable in the application. It is clear that the PP-HP-1 polymer shows much higher endurance than all commercial PP products in the whole elevated temperature range. The perpendicular line in Figure 9 indicates that the material lifetime for Borclean PP is about 10 days under 140 °C in air. On the other hand, the lifetime of PP-HP-1, under the same condition, is near 105 days. The 4 order increase in endurance is astonishing, which clearly reinforces the idea of PP-bonded HP groups with the combination chemical and physical protections, not only preventing PP chain from thermo-oxidative degradation but also forming a cross-linking (3-D) network structure. The experimental results raise the strong possibility that this new PPHP polymer may address the concern of a thermal and oxidative stability (aging issue) of PP polymer operated at elevated temperature conditions. Mechanical Properties. As discussed, it is essential to maintain the desirable mechanical property during long-term application conditions. The mechanical property is directly
related to the polymer structure (molecular weight, cross-linking density, etc.) and morphology (crystallinity, etc.). Figure 10 compares the strain−stress curves of PP-HP-1 copolymer before and after thermo-oxidative treatment at 140 °C in air for 1 week. Before heating treatment, PP-HP-1 copolymer exhibits tensile strength (21.5 MPa), Young’s modulus (0.7 GPa), and elongation to break (480%). It is interesting to note that comparing with PP homopolymer only 1 mol % incorporation of bulky comonomer units in the PP-HP-1 copolymer, with mild reduction in the crystallinity, has a significant effect on the strain−stress curve with an overall decrease in tensile strength and modulus but increase of PP-HP elongation and toughness. Under 140 °C in air condition, most commercial PP materials lose antioxidants and stabilizers in the early stages of the heating process, and the polymer chains are gradually degraded by oxygen with the reduction of polymer molecular weight and mechanical properties. On the other hand, the PP-HP-1 copolymer shows no detectable change in tensile strength and modulus and a slight reduction in its elongation to break from 470% to 350%. The mechanical property is consistent with the formation of a polymer network in the PP-HP-1 copolymer after the oxidation/coupling reaction of HP moieties (Scheme 3).
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CONCLUSION This paper discusses a novel class of polypropylene (PP-HP) copolymers that may address the major limitation and concern associated with polymer chain degradation and softening under H
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Figure 10. Strain−stress curves of PP-HP-1 copolymer (a) before and (b) after heating at 140 °C in air for 1 week.
contain a high PP backbone and few pendent hindered phenol groups linked with two methylene units (HP), homogeneously distributed along the polymer chain. All experimental results support the oxidation/coupling mechanism of HP moieties that not only offer the effective antioxidant protection of PP chains but also form a cross-linked PP network structure. In other words, instead of weakening mechanical strength in most commercial PP products, PP-HP copolymers become stronger materials upon exposure to high-temperature oxidative conditions. They are suitable for applications that require constant high temperatures (>100 °C) and/or high electric field conditions. This work also opens a new approach in designing new high-temperature polymers.
Figure 8. Log heating rate constant vs inverse temperature kinetics plot for various conversions (weight loss) of (a) PP (Borclean) and (b) PPHP-1.
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Table 2. Activation Energy under Various Polymer Weight Loss (Conversion) for (a) PP (Borclean) and (b) PP-HP-1
AUTHOR INFORMATION
Corresponding Author
activation energy Ea (kJ/mol)
*E-mail
[email protected] (T.C.M.C.).
conversion (%)
PP
PP-HP-1
ORCID
1.0 2.5 5.0 10.0 15.0 20.0
126.8 117.6 104.7 97.0 93.6 91.7
209.1 185.1 163.5 145.8 150.8 171.8
T. C. Mike Chung: 0000-0002-3123-944X Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support of this work through a grant from ABB. REFERENCES
(1) Degradation and Stabilization of Polyolefins; Allen, N. S., Ed.; Applied Science Publishers: London, 1983. (2) Al-Malika, S. Effects of Antioxidants and Stabilization. In Comprehensive Polymer Science; Allen, G., Bevington, J. C., Eds.; Pergamon Press: New York, 1989; Vol. 6, p 539. (3) Emanuel, N. M.; Buchachenco, L. M. Chemical Physics of Polymer Degradation and Stabilization; VNU Science Press: Zeist, Netherlands, 1987. (4) Cook, C. D.; Woodworth, R. C. Oxidation of Hindered Phenols. II. The 2,4,6-Tri-t-butylphenoxy Radical. J. Am. Chem. Soc. 1953, 75, 6242−6244. (5) Tobolsky, A. V.; Norling, P. M.; Frick, N. H.; Yu, H. On the Mechanism of Autoxidation of Three Vinyl Polymers: Polypropylene, Ethylene-Propylene Rubber, and Poly(ethyl acrylate). J. Am. Chem. Soc. 1964, 86, 3925−3930. (6) Scheirs, J.; Pospíšil, J.; O’Connor, M. J.; Bigger, S. W. Polymer Durability; 2009; Chapter 24, pp 359−374. (7) Stillson, G. H.; Sawyer, D. W.; Hunt, C. K. The Hindered Phenols. J. Am. Chem. Soc. 1945, 67, 303−307. (8) Dhawan, A.; Kumar, V.; Parmar, V. S.; Cholli, A. L. Novel Polymeric Antioxidants for Materials. In Antioxidant Polymer: Synthesis, Properties, and Application; Giuseppe, C., Francesca, I., Eds.; John Wiley and Sons: Hoboken, NJ, 2012; pp 385−425.
Figure 9. Estimated lifetime of (a) Borclean PP and (b) PP-HP-1 with 1 wt % polymer weight loss under various temperature conditions.
elevated temperature conditions and expanding PP applications to higher temperature conditions. These new PP-HP copolymers I
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Applications in Metallized Polymer Film Capacitors. Macromolecules 2015, 48, 2925−2934. (29) Rodriguez-Perez, M. A. Crosslinked polyolefin foams: Production, structure, properties, and applications. Adv. Polym. Sci. 2005, 184, 97−126. (30) Appleby, R. W.; Busfield, W. K. Post-gamma irradiation crosslinking of polyethylene tape by acetylene treatment. J. Mater. Sci. 1994, 29, 227−231. (31) Chodak, I. Properties of crosslinked polyolefin-based materials. Prog. Polym. Sci. 1995, 20, 1165−1199. (32) Zhu, Y. T.; Yoon, H. G.; Suh, K. S. Electrical Properties of Silane Crosslinked Polyethylene in Comparison with DCP Crosslinked Polyethylene. IEEE Trans. Dielectr. Electr. Insul. 1999, 6, 164. (33) Taddei, P.; Affatato, S.; Fagnano, C.; Toni, A. Oxidation in Ultrahigh Molecular Weight Polyethylene and Cross-Linked Polyethylene Acetabular Cups Tested against Roughened Femoral Heads in a Hip Joint Simulator. Biomacromolecules 2006, 7, 1912−1920. (34) Pollet, P.; Liotta, C. L.; Eckert, C. A.; Verma, M.; Nixon, E.; Sivaswamy, S.; Jha, R.; Momin, F.; Gelbaum, L.; Chaudhary, B. I.; Cogen, J. M. Radical-Mediated Graft Modification of Polyethylene Models with Vinyltrimethoxysilane: A Fundamental Study. Ind. Eng. Chem. Res. 2011, 50, 12246−12253. (35) Rijke, A.; Mandelkern, L. Irradiation of Linear Polyethylene. Partitioning between Sol and Gel. Macromolecules 1971, 4, 594−599. (36) Mitsui, H.; Hosoi, F.; Kagiya, T. Acceleration of fluorinecontaining monomer- acetylene system for the r-radiation-induced cross-linking of polyethylene. Polym. J. 1972, 3, 108−110. (37) Oonishi, H.; Kuno, M.; Tsuji, E.; Fujisawa, A. The optimum dose of gamma radiation−heavy doses to low wear polyethylene in total hip prostheses. J. Mater. Sci.: Mater. Med. 1997, 8, 11−18. (38) Shen, F. W.; McKellop, H. A.; Salovey, R. Crosslinking of polyethylene for low wear using radiation and thermal treatments. U.S. Patent 6,228,900, 2001. (39) Miller, A. A. A Kinetic Analysis for the Free-Radical Crosslinking of Saturated Polymers. J. Polym. Sci. 1960, 42, 441−454. (40) Barton, J.; Lazar, M. Interactions of Macroradicals in Polyethylene-Polypropylene Blends. J. Polym. Sci., Part C: Polym. Symp. 1967, 16, 361−368. (41) De Boer, A. P.; Pennings, A. J. Polyethylene networks crosslinked in solution: Preparation, elastic behavior, and oriented crystallization. I. Crosslinking in solution. J. Polym. Sci., Polym. Phys. Ed. 1976, 14, 187− 210. (42) Phillips, P. J.; Lambert, W. S. Regime transitions in a nonreptating polymer: crosslinked linear polyethylene. Macromolecules 1990, 23, 2075−2081. (43) Shen, F. W.; McKellop, H. A.; Salovey, R. Irradiation of chemically crosslinked ultrahigh molecular weight polyethylene. J. Polym. Sci., Part B: Polym. Phys. 1996, 34, 1063−1077. (44) Akutsu, S.; Isaka, T.; Ishioka, M. Process for producing electric conductors coated with crosslinked polyethylene resin. U.S. Patent 4,297,310, 1981. (45) McCormick, J. A.; Royer, J. R.; Hwang, C. R.; Khan, S. A. Tailored rheology of a metallocene polyolefin through silane grafting and subsequent silane crosslinking. J. Polym. Sci., Part B: Polym. Phys. 2000, 38, 2468−2479. (46) Shieh, Y. T.; Chuang, H. C.; Liu, C. M. Water crosslinking reactions of silane-grafted polyolefin blends. J. Appl. Polym. Sci. 2001, 81, 1799−1807. (47) Busfield, W. K.; O’Donnell, J. H. Effects of gamma radiation on the mechanical properties and crystallinity of polypropylene film. Eur. Polym. J. 1979, 15, 379−387. (48) Kunert, K. A.; Soszyńska, H.; Piślewski, N. Structural investigation of chemically crosslinked low density polyethylene. Polymer 1981, 22, 1355−1360. (49) Ruggeri, G.; Aglietto, M.; Petragnani, A.; Ciardelli, F. Some aspects of polypropylene functionalization by free radical reactions. Eur. Polym. J. 1983, 19, 863−866. (50) Lazar, M.; Rado, R.; Rychly, J. Crosslinking of polyolefins. Adv. Polym. Sci. 1990, 95, 149−197.
(9) Yang, C. Z.; Yaniger, S. I.; Jordan, V. C.; Klein, D. J.; Bittner, G. D. Most Plastic Products Release Estrogenic Chemicals: A Potential Health Problem that Can Be Solved. Environm. Health Persp. 2011, 119, 989− 996. (10) Barnard, D.; Dawes, K.; Mente, P. G. In Proceedings of the International Rubber Conference 1975, Kuala Lumpur; 1975, Vol. 1, p 215. (11) de Jonge, C. R. H. I.; Hoentjen, G.; Ershov, V. V.; Nikiforov, G. A. Antioxidative properties of phenylsubstituted phenols, 6. Synergism of chemically bonded phenylsubstituted phenolic antioxidants and βactivated thioethers. Makromol. Chem. 1979, 180, 1077−1080. (12) Saltman, W. M.; Auerbach, M. Polymeric Compositions. U.S. Patent 3,985,709, 1976. (13) Boffa, L. S.; Novak, B. M. Copolymerization of Polar Monomers with Olefins Using Transition-Metal Complexes. Chem. Rev. 2000, 100, 1479−1494. (14) Wilén, C. E.; Auer, M.; Strandén, J.; Näsman, J. H.; Rotzinger, B.; Steinmann, A.; King, R. E.; Zweifel, H.; Drewes, R. Synthesis of Novel Hindered Amine Light Stabilizers (HALS) and Their Copolymerization with Ethylene or Propylene over Both Soluble and Supported Metallocene Catalyst Systems. Macromolecules 2000, 33, 5011−5026. (15) Menichetti, S.; Viglianisi, C.; Liguori, F.; Cogliati, C.; Boragno, L.; Stagnaro, P.; Losio, S.; Sacchi, M. C. Ethylene-based copolymers with tunable content of polymerizable hindered phenols as nonreleasing macromolecular additives. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 6393−6406. (16) Hanauer, R. H.; Willette, G. L. Polymeric Antioxidant Viscosity Index Improvers. U.S. Patent 4,098,709, 1978. (17) Willette, G. L.; Hanauer, R. H. Polymers containing anti-oxidant functionality. U.S. Patent 4,096,319, 1978. (18) Pesetskii, S. S.; Jurkowski, B.; Krivoguz, Y. M.; Olkhov, Y. A. Solubility of additives: Grafting of itaconic acid onto LDPE by reactive extrusion. II. Effect of stabilizers. J. Appl. Polym. Sci. 2001, 81, 3439− 3448. (19) Boragno, L.; Stagnaro, P.; Losio, S.; Sacchi, M. C.; Menichetti, S.; Viglianisi, C.; Piergiovanni, L.; Limbo, S. LDPE-Based Blends and Films Stabilized with Nonreleasing Polymeric Antioxidants for Safer Food Packaging. J. Appl. Polym. Sci. 2012, 124, 3912−3920. (20) Li, C. Q.; Wang, J.; Ning, M. M.; Zhang, H. P. Synthesis and Antioxidant Activities in Polyolefin of Dendritic Antioxidants with Hindered Phenolic Groups and Tertiary Amine. J. Appl. Polym. Sci. 2012, 124, 4127−4135. (21) Xie, H.; Li, H. Q.; Lai, X. J.; Wu, W. J.; Zeng, X. R. Synthesis and antioxidative properties of a star-shaped macromolecular antioxidant based on β-cyclodextrin. Mater. Lett. 2015, 151, 72−74. (22) Chung, T. C. Functionalization of Polyolefins; Academic Press: London, 2002. (23) Chung, T. C. Synthesis of functional polyolefin copolymers with graft and block structures. Prog. Polym. Sci. 2002, 27, 39−85. (24) Wilén, C. E.; Näsman, J. H. Polar Activation in Copolymerization of Propylene and 6-tert-Butyl-[2-(1,1-dimethylhept-6-enyl)]-4-methylphenol over a Racemic [1,1′-(Dimethylsilylene)bis(.eta.5−4,5,6,7tetrahydro-1-indenyl)]zirconium Dichloride/MAO Catalyst System. Macromolecules 1994, 27, 4051−4057. (25) Wilén, C. E.; Luttikhedde, H.; Hjertberg, T.; Näsman, J. H. Copolymerization of Ethylene and 6-tert-Butyl-2-(1,1-dimethylhept-6enyl)-4-methylphenol over Three Different Metallocene−Alumoxane Catalyst Systems. Macromolecules 1996, 29, 8569−8575. (26) Auer, M.; Nicolas, R.; Rosling, A.; Wilén, C. E. Synthesis of Noveldl-α-Tocopherol-Based and Sterically-Hindered-Phenol-Based Monomers and Their Utilization in Copolymerizations over Metallocene/ MAO Catalyst Systems. A Strategy to Remove Concerns about Additive Compatibility and Migration. Macromolecules 2003, 36, 8346−8352. (27) Zhang, Y. J.; Li, H. Y.; Zhang, Y.; Li, Q.; Ma, Z.; Dong, J. Y.; Hu, Y. L. Synthesis and Properties of Polyethylene-Bound Antioxidants. Macromol. Chem. Phys. 2014, 215, 763−775. (28) Zhang, G.; Li, H. X.; Antensteiner, M.; Chung, T. C. Synthesis of Functional Polypropylene Containing Hindered Phenol Stabilizers and J
DOI: 10.1021/acs.macromol.7b01235 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules (51) Lin, W. T.; Shao, Z.; Dong, J. Y.; Chung, T. C. Cross-Linked Polypropylene Prepared by PP Copolymers Containing Flexible Styrene Groups. Macromolecules 2009, 42, 3750−3754. (52) Yuan, X. P.; Chung, T. C. Cross-linking Effect on Dielectric Properties of Polypropylene Thin Films and Applications in Electric Energy Storage. Appl. Phys. Lett. 2011, 98, 062901−062903. (53) Spaleck, W.; Kueber, F.; Winter, A.; Rohrmann, J.; Bachmann, B.; Antberg, M.; Dolle, V.; Paulus, E. F. The Influence of Aromatic Substituents on the Polymerization Behavior of Bridged Zirconocene Catalysts. Organometallics 1994, 13, 954−963. (54) Gloger, D.; Paavilainen, J. New Way to Produce Polypropylene Grade in A Sequential Process. International Patent Application WO 2011/080152 A1. (55) Brandrup, J.; Immergut, E. H. Polymer Handbook, 3rd ed.; WileyInterscience: New York, 1989; p VII-7. (56) Scheirs, J.; Pospisil, J.; O’Connor, M. J.; Bigger, S. W. Characterization of Conversion Products Formed During Degradation of Processing Antioxidants. In Polymer Durability: Degradation, Stabilization and Lifetime Prediction; ACS Advances in Chemistry Series 249; American Chemical Society: Washington, DC, 1996; pp 360−374. (57) Neises, B.; Steglich, W. Simple Method for the Esterification of Carboxylic Acids. Angew. Chem., Int. Ed. Engl. 1978, 17 (7), 522−524. (58) Viebke, J.; Gedde, U. W. Assessment of Lifetime of Hot-water Polyethylene Pipes Based on Oxidation Induction Time Data. Polym. Eng. Sci. 1998, 38, 1244−1250. (59) Standard Test Method for Oxidative-Induction Time of Polyolefins by Differential Scanning Calorimetry. ASTM D3895-14. (60) Standard Practice for Calculating Thermal Endurance of Materials from Thermogravimetric Decomposition Data, ASTM E1877-15.
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