Prevention of polyurethane oxidative degradation with phenolic antioxidants covalently attached to the hard segments: Structure-function relationships (original) (raw)
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Journal of Biomedical Materials Research Part A, 2006
Polyurethane (PU) components of cardiovascular devices are subjected to oxidation-initiated surface degradation, which leads to cracking and ultimately device failure. In the present study, we investigated a novel bromoalkylation chemical strategy to covalently attach the antioxidant, di-tert-butylphenol (DBP), and/or cholesterol (Chol) to the PU urethane nitrogen groups to hypothetically prevent oxidative degradation. These experiments compared PU, PU-DBP, PU-Chol, and PU-Chol-DBP. A series of comparative oxidative degradation studies involved exposing PU samples (modified and unmodified) to H 2 O 2 -CoCl 2 for 15 days at 37°C, to cause accelerated oxidative degradation. The extent and effects of degradation were assessed by attenuated total reflectance Fourier transformation infrared spectroscopy (FTIR), scanning electron microscopy (SEM), surface contact angle measurements, and mechanical testing. Both the Chol and DBP modification conferred signifi-cant resistance to oxidation related changes compared to unmodified PU per FTIR and SEM results. SEM demonstrated cavitation only in unmodified PU. However, contact angle analysis showed significant oxidation-induced changes only in the Chol-modified PU formulations. Most importantly, uniaxial stress-strain testing revealed that only PU-DBP demonstrated bulk elastomeric properties that were minimally affected by oxidation; PU, PU-Chol, PU-Chol-DBP showed marked deterioration of their stressstrain properties following oxidation. In conclusion, these results demonstrate that derivatizing PU with DBP confers significant resistance to oxidative degradation compared with unmodified PU.
Biological stability of polyurethane modified with covalent attachment of di-tert-butyl-phenol
Journal of Biomedical Materials Research Part A, 2007
Polyurethane cardiovascular implants are subject to oxidation initiated surface degradation, which is mediated by monocyte-derived macrophages (MDM); this often leads to surface cracking and device failure. The present studies examined the hypothesis that covalently attaching antioxidant, di-tert-butylphenol (DBP), to the urethane nitrogens of a polyether polyurethane (PU) via bromo-alkylation reactions could prevent this problem. PU was configured with two dosages of DBP, 0.14 mM DBP/g PU of DBP (PU-DBP) and a more highly modified (HM) 0.40 mM DBP/g PU (PU-DBP-HM). THP-1 cells, a human MDM cell line, stimulated with phorbol ester and seeded on PU, PU-DBP, and PU-DBP-HM films were assessed for reactive oxygen species (ROS) production via a fluorescent based dihydrorhodamine-123 assay. Results from these studies showed a significant dose-dependent reduction of ROS levels for THP-1 cells seeded on PU-DBP versus unmodified PU. PU, PU-DBP, or PU-DBP-HM films were implanted into subdermal pouches of Sprague-Dawley rats. Films were explanted after 10 weeks and assessed for oxidative degradation via light and scanning electron microscopy (SEM) and Fourier transformation infrared spectroscopy (FTIR). Light microscopy showed extensive surface cracking, which was confirmed via SEM, on unmodified PU surfaces that was absent in both PU-DBP and PU-DBP-HM explanted films. FTIR analysis showed reduction in oxidation-induced ether crosslinking that was directly related to DBP dosages. It is concluded that modifying PU with the covalent attachment of an antioxidant confers biodegradation resistance in vivo in a dose dependent manner; this effect is likely due to quenching of the ROS generated by the adherent macrophages.
Polymer, 2018
In order to prolong the thermo-oxidative stability of polypropylene and prevent antioxidant loss, this research details an effective approach to prepare polymeric antioxidant via surface functionalization of polypropylene with long-chain macromolecules containing hindered phenolic stabilizers. The polymeric antioxidant (PPNA) is prepared by amide bond formation between phenolic stabilizer containing carboxylic acid moiety and amine functionalized polypropylene (PPNH 2). Test results confirmed surface changes through plasma treatment, amine and antioxidant modification. The resultant PPNH 2 and PPNA exhibit reduced crystallinity while the crystallization temperature shifts toward higher values, suggesting simultaneous effects of steric hindrance and nucleation of long-chain structures. Immobilization of phenolic stabilizer results in improving thermo-oxidative stability of polypropylene.
Macromolecules, 2017
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 10 5 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.
Reactive antioxidants for peroxide crosslinked polyethylene
Polymer Degradation and Stability, 2017
Three synthesised reactive (graftable) antioxidants, r-AO, with hindered phenol and hindered amine antioxidant functions, were examined for their grafting efficiency in polyethylene and their retention and stabilising performance in peroxide-crosslinked polyethylene pipe material. Their level of grafting in uncrosslinked high density polyethylene, HDPE, and the extent of their retention in highly peroxidecrosslinked HDPE (PEX a) material (both laboratory prepared samples and PEX a pipes produced by commercial processes) were determined after stringent solvent extraction methodologies. The uniformity of distribution of the r-AOs in the PEX a pipes (across the length and thickness of the pipes) were examined using infrared-microscopy and compared with similarly produced PEX a pipes containing commercial antioxidants having the same antioxidant functions. The extent of interference of the graftable hindered phenol and hindered amine antioxidants with the peroxide crosslinking process in the PEX a materials was assessed by comparing the level of crosslinking achieved against analogously prepared samples containing a conventional hindered phenol antioxidant (Irganox 1076). The results obtained showed that the presence of the graftable (r-AOs) antioxidants did not affect the level of crosslinking of the PEX a pipes which remained high (>85%) and that they were retained to a very high extent in the PEX a material after solvent extraction, and are very uniformly distributed across the length and thickness of PEX a pipes. The long-term stabilising performance of the graftable r-AOs in the PEX a material (in both laboratory prepared samples and in peroxide crosslinked pipes produced by commercial processes) was also examined using complimentary methods: oxidative induction time (OIT) before and after solvent extraction, physical embrittlement following oven ageing at 125 o C, as well as by a hydrostatic pressure tests conducted (with water inside and air outside) at 115 o C and 2.5 MPa pressure. The stabilising efficacy of the r-AOs was compared with that of conventionally stabilised PEX a material containing analogous antioxidant functions produced in the same way. The level of retention (in the pipes) of the graftable antioxidants and their long-term stabilising performance was shown to be significantly higher than that of the conventional AOs under all the test conditions used here.
Chlorine dioxide resistance of different phenolic antioxidants in polyethylene
Polymer Degradation and Stability, 2015
A series of polyethylene tape samples containing 8 different phenolic antioxidants (concentration ¼ 0.1 ± 0.01 wt.%) were exposed to water containing 10 ppm chlorine dioxide buffered to pH ¼ 6.8 at 70 C for different periods of time. The degradation rate and depletion time of the antioxidants in the polyethylene were obtained by oxidation induction time measurements using DSC. The majority of the tape samples (6 out of 8) showed a simple behaviour: the rate of antioxidant loss decreased and the antioxidant depletion time increased in linear fashion with increasing initial molar concentration of phenolic groups in the polymer. The tape that contained Hostanox O3 had a high initial phenolic concentration but it exhibited a short antioxidant depletion time due to the limited solubility of this antioxidant in polyethylene. Tapes containing Irganox 1330 and Cyanox 1790 showed antioxidant depletion times that were almost twice that of the other antioxidants with the same initial molar concentration of phenolic groups.
An Antioxidant Bioinspired Phenolic Polymer for Efficient Stabilization of Polyethylene
2014
The synthesis, structural characterization and properties of a new bioinspired phenolic polymer (polyCAME) produced by oxidative polymerization of caffeic acid methyl ester (CAME) with horseradish peroxidase (HRP)-H 2 O 2 is reported as a new sustainable stabilizer toward polyethylene (PE) thermal and photo-oxidative degradation. PolyCAME exhibits high stability toward decarboxylation and oxidative degradation during the thermal processes associated with PE film preparation. Characterization of PE films by thermal methods, photo-oxidative treatments combined with chemiluminescence, and FTIR spectroscopy and mechanical tests indicate a significant effect of polyCAME on PE durability. Data from antioxidant capacity tests suggest that the protective effects of polyCAME are due to the potent scavenging activity on aggressive OH radicals, the efficient H-atom donor properties inducing free radical quenching, and the ferric ion reducing ability. PolyCAME is thus proposed as a novel easily accessible, eco-friendly, and biocompatible biomaterial for a sustainable approach to the stabilization of PE films in packaging and other applications.
Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2019
In vitro oxidative stability of two siloxane poly(urethane urea)s synthesized using 4,4 0-methylenediphenyl diisocyanate (in SiPUU-1) and Isophorone diisocyanate (in SiPUU-2) linked soft segment was evaluated using 20% H 2 O 2 and 0.1 mol/L CoCl 2 solution at 37 C under 150% strain. Commercially available siloxane polyurethane (Elast-Eon™ 2A) and polyether polyurethane (ChronoThane P™ 80A) were used as negative and positive controls, respectively. ChronoSil™ 80A was included as another commercially available polycarbonate polyurethane. Scanning electron microscopic (SEM) examinations, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and molecular weight reduction revealed the extensive degradation of ChronoThane P™ 80A after 90 days while SiPUU-1, SiPUU-2 and Elast-Eon™ 2A showed no noticeable surface degradation. ChronoSil™ 80A showed degradation in both soft and hard segments. Tensile testing was carried out only on unstrained polyurethanes for 90 days. ChronoThane P™ 80A showed 35% loss in ultimate tensile strength and it was only 13-14% for SiPUU-1 and Elast-Eon™ 2A. However, the tensile strength of ChronoSil™ 80A was not significantly affected. The results of this study proved that SiPUU-1 possess oxidative stability comparable with Elast-Eon™ 2A.