Thermal Oxidation Products of Nylon 6 Determined by MALDI‐TOF Mass Spectrometry

Matrix‐assisted laser desorption ionisation (MALDI) mass spectrometry was used, in an attempt to find firm evidence for the structure of the species produced in the thermal oxidative degradation of Nylon 6 (Ny6), at 250°C in air. The MALDI spectra of the products showed the presence of polymer chains containing aldehydes, amides, methyl and N‐formamide terminal groups. The aldehydes undergo further oxidation to produce carboxylic end groups. The formation of azomethines, from the further reaction of aldehydes with amino‐terminated Ny6 chains, is also supported by the appearance of specific peaks in the MALDI spectra.     

Essential role of chain ends in the nylon‐6/poly(ethylene terephthalate) exchange

A combination of NMR and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF) techniques were suitable tools for examining the exchange reactions that occur during the melt‐mixing of nylon‐6 and poly(ethylene terephthalate) (Ny6/PET) blends in the presence of p‐toluene sulfonic acid (TsOH) at 285 °C. Some researchers believe that TsOH is an efficient catalyst for the amide–ester exchange reactions in PET/Ny6 and PET/nylon‐66 blends in the molten state. Instead, we have found that TsOH is able to react in the molten state with PET, yielding PET oligomers terminated with carboxyl groups. Because the latter oligomers can quickly react with Ny6 producing a Ny6/PET copolymer, the role of TsOH in the melt‐mixing process is not that of a catalyst but of a reactant. Our study allowed the structural identification of the Ny6/PET copolyesteramide produced in the exchange as a function of melt‐mixing time. The results revealed the essential role of carboxyl end groups in the exchange reaction between Ny6 and PET and allowed a detailed mechanism for this reaction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2778–2793, 2003     

Influence of chain end groups on the matrix-assisted laser desorption/ionization spectra of polymer blends

The positive ion matrix-assisted laser desorption/ionization (MALDI) spectrum of an equimolar blend of Nylon 6 (Ny6) and hydroxyl-terminated polybutyleneterephthalate (PBT) shows a surprisingly strong imbalance between the two components. Since the average molar masses and the polydispersions of the two polymers are comparable, it follows that the efficiency of MALDI is quite different for the two components of the blend. This finding prompted us to a more detailed study, and to synthesize Ny6 and PBT samples terminated with different end groups, in order to analyze their blends by MALDI. The negative ion MALDI spectra of the mixtures investigated show that PBT samples do not yield signals, so that only Ny6 peaks appear in these spectra. By comparing positive and negative ion MALDI spectra of mixtures of Ny6 terminated with various end groups, it was found that the peak intensity depends on the nature of the end groups. The results reported in the present study may help to clarify some fundamental aspects of the mechanisms of ion formation, when MALDI mass spectrometry is applied to macromolecules. End group ionization efficiency appears to be the most important parameter in determining the relative intensity of peaks in the MALDI spectra of the polymer blends investigated. End-group-dependent ionization is the key to the rationalization of the relative peak intensities in MALDI spectra of polymer mixtures.     

Photo-oxidation products of polyetherimide ULTEM determined by MALDI-TOF-MS. Kinetics and mechanisms

Poly 2,2-bis4-(3,4-dicarboxyphenoxy) phenylpropane dianhydride-1,3-phenylendiamine copolymer (ULTEM) was subjected to photo aging in the attempt to find evidence on the structure of the species formed in the oxidative degradation. The oxidation was followed as a function of the exposure time by MALDI and SEC/MALDI techniques. The SEC curves showed extensive degradation, with the formation of low molar mass oligomers having different end groups. Valuable structural information on the photo-oxidized ULTEM species was extracted from the MALDI spectra of the photo-oxidized ULTEM. These showed the presence of polymer chains containing acetophenone, phenyl acetic acid, phenols, benzoic acid, phthalic anhydride and phthalic acid end groups. The mechanisms accounting for the formation of photo-oxidation products involve several simultaneous reactions: (1) photo-cleavage of methyl groups of the N-methyl phthalimide terminal units; (2) photoxidative degradation of the isopropylidene bridge of BPA units; (3) photo-oxidation of phthalimide units to phthalic anhydride end groups: (4) hydrolysis of phthalic anhydride end groups. The kinetic behaviour of all the species detected is in agreement with the predictions of the reaction mechanisms hypothesized.     

Characterization of end groups in nylon 6 by MALDI-TOF mass spectrometry

Four samples of Ny6, each terminated by different end groups, i.e., diamino terminated, monoamino terminated (monocapped), dicarboxyl terminated, and amino-carboxyl terminated, were synthesized and analyzed by MALDI-TOF Mass Spectrometry, in order to accurately characterize their structure by direct identification of mass resolved chains. A self-calibrating method for the MALDI-TOF mass spectra of polymeric samples was used in order to distinguish the end groups existing in the four samples of Ny6. The MALDI-TOF spectra showed the presence of protonated, sodiated, and potassiated ions that were assigned to Ny6 chains containing the expecteted end groups. Furthermore, the MALDI-TOF spectra made possible the simultaneous detection of the cyclic oligomers of Ny6 present in these samples, thus achieving the full structural characterization of the molecular species present in these polyamides. © 1996 John Wiley & Sons, Inc.     

Thermo-oxidative processes in biodegradable poly(butylene succinate)

Aliphatic polyesters have acquired significant interest as environmentally friendly thermoplastics for a wide range of applications, and understanding their degradation behaviour has relevance both for processing and end uses. We have investigated the thermal and thermo-oxidative degradation processes occurring in synthetic and commercial poly(butylene succinate) (PBSu). Thermal oxidation was performed in atmospheric air using extremely thin polymer films at 170 °C for up to 6 h. The oxidized compounds were analyzed by size exclusion chromatography (SEC), NMR spectroscopy, and Mass Spectrometry (MALDI-TOF MS). A measurable reduction of the molar mass of the polyesters was soon apparent, promoting the formation of PBSu oligomers with different end groups. MALDI mass spectrometry combined with the use of extremely thin polyester films provided a virtual magnifying glass to obtain exhaustive information on the structure of the oxidation products. An α-H abstraction mechanism has been unambiguously ascertained to be the primary step in PBSu oxidation. The oxidized polymer chains originating from the decomposition of the hydroperoxide intermediate by radical rearrangement reactions had not been revealed before. The latter products subsequently undergo chain scission processes, which can be accurately traced from the chemical species identified in our work. Thermal degradation experiments were also performed under nitrogen at 240-260 °C. The new species identified in the MALDI spectra support a decomposition pathway taking place through a β-hydrogen-transfer mechanism, followed by the production of succinic anhydride from succinic acid end molecules via a back-biting process.     

Exchange reactions occurring through active chain ends: Melt mixing of nylon 6 and polycarbonate

The chemical reactions occurring in the melt mixing of nylon6/polycarbonate (Ny6/PC) at 240°C were investigated. The reaction of equimolar Ny6/PC blends can be reconciled within the overall scheme of an exchange reaction occurring with the attack of active amino terminals on the inner carbonate groups. We have performed the synthesis of low molecular weight amino-terminated nylon 6 and the effect of the active amino terminal groups on the exchange kinetics was investigated. The exchange reaction yields sizeable amounts of copolymer, in fact after 75 min of melt mixing the (initially equimolar) blend contains 30 mol of unreacted PC and 70 mol of Ny6/PC copolymer (all the Ny6 was therefore incorporated in the copolymer). Trifluoroacetylation of nylon 6 was used to produce CHCl₃-soluble Ny6/PC copolymers, that could be analyzed by NMR. The NMR analysis yielded, beside the copolymer composition, evidence of the presence of urethane units interconnecting the Ny6 and PC blocks. The amount of urethane units increased with the reaction time, indicating a reduction of the block size as a function of the extent of exchange. Our study established the structure of the products formed, provided the materials balance of the process, and investigated some salient kinetic aspects. A thermal degradation study was also performed by thermogravimetry and direct pyrolysis mass spectrometry, to identify the products formed in the thermal treatment of the blends and to investigate the possible role of the inner amide groups in the intermolecular exchange reactions occurring between Ny6 and PC. Our results prove that these reactions occur above 300°C, and that only the cleavage of carbonate groups, by means of Ny6 amino end groups, is actually occurring at 240°C. © 1994 John Wiley & Sons, Inc.     

尼龙1012的Brill转变

作为一类重要的结晶性聚合物 ,尼龙在加热或冷却过程中的晶型转变 [1,2 ]一直为人们所关注 .其中对尼龙 66的晶型转变研究得最多 [3～ 6 ] .在加热过程中尼龙 66室温下三斜的α晶型转变为高温下的假六方晶型 ,尼龙 66的这一晶型转变称为 Brill转变 [3] .在变温 X射线衍射测试中可明显观察到 Brill转变 :室温下α晶型的两个强的衍射峰随温度升高逐渐靠近 ,并在某一温度下合并为一个峰 ,这一温度称为 Brill转变温度 .近年来研究表明 ,许多脂肪族的尼龙升温时均表现出 Brill转变 ,并且 Brill转变温度随尼龙结晶条件及其结构的不同而不同 [7…     

Thermal,physical and mechanical properties of hydrogenated dimer acid-based Nylon 636/Nylon 66 copolymers

Hydrogenated dimer acid-based Nylon 636/NyIon 66 copolymers were synthesized by in situ polymerization.The effects of Nylon 66 contents on the copolymers were characterized by intrinsic viscosity measurements,attenuated total reflection-Fourier transform infrared spectroscopy,X-ray diffraction,differential scanning calorimetry,tliermogravimetric analysis and mechanical tests.The results showed that incorporation of Nylon 66 into hydrogenated dimer acid-based Nylon had no significant effect on the glass transition or melting temperatures.However,the crystallization temperature,crystallinity degree and the maximum rate of decomposition temperature from derivative thermogravimetry measurements vary.Mechanical testing data revealed that with increasing Nylon 66 concentrations,the tensile strength of copolymers increased,while the elongation at break point and notched izod impact strength decreased.The physical and mechanical properties of HN-40,HN-50 and HN-60 are similar to those of the current PA11,PA1212,and PA1111 Nylon products.     

Crystalline transition in Nylon 10 10

Variable‐temperature X‐ray diffraction was used to monitor the crystalline transition of Nylon 10 10. It could be found that the α‐phase of the sample transforms into a γ‐phase at about 135°C, if the sample is heated from room temperature to a high temperature, which is the so‐called Brill transition of Nylon 10 10. In addition, Nylon 10 10 was found to crystallize directly in a kind of α‐phase from the melt at high temperature, which is much different from the behavior of Nylon 66 and Nylon 10 12. Upon further cooling to room temperature, Nylon 10 10 preserved the α‐phase revealing two peaks in its XRD patterns. However, if the Nylon 10 10 sample with γ‐form was not melted, but immediately cooled from a temperature between T_B and T_m, the reverse transition from γ‐form to α‐form could be observed at about 130°C, indicating reversible Brill transition of Nylon 10 10.     

Effects of gamma and electron beam irradiation on the properties of calendered cord fabrics

The effects of gamma and e-beam irradiation on mechanical and structural properties of nylon 66 (Ny 66), nylon 6 (Ny 6) and poly(ethylene terephthalate) (PET) fabrics used in tyres were investigated. The untreated (greige), treated cords and calendered fabrics were irradiated at different doses. It is found that the effects of high energy irradiation on greige, treated cords and calendered fabrics are similar. No protective effect of compounds used in calendering was observed against radiation-induced oxidative degradation. The deterioration effect of gamma irradiation on mechanical properties is much higher than that of e-beam irradiation for all types of samples. Limiting viscosity numbers of both gamma and e-beam irradiated nylon 6 and nylon 66 cords were found to decrease with increasing dose. It is concluded that PET calendered fabric has higher resistance to ionizing radiation. Ny 6 and Ny 66 calendered fabrics are more sensitive even at low doses. Therefore, the effects of high energy irradiation on tyre cords have to be taken into consideration during tyre design reinforced with particularly Ny fabrics if pre-vulcanization with high energy radiation is to be applied.     

Blends of low-density polyethylene with nylon compatibilized with a sodium-neutralized carboxylate ionomer

An ethylene-methacrylic acid copolymer partially neutralized with sodium (Na-EMAA) was successfully used to compatibilize Nylon 6 (Ny6) and low-density polyethylene (LDPE) blends. The phase morphology and thermal behavior of these blends were investigated over a range of compositions using a variety of analytical techniques. The addition of small amounts (0.5 phr) of Na-EMAA improved the compatibility of Ny6/LDPE blends as evidenced by a significant reduction in dispersed phase sizes. TGA measurements demonstrated an improvement in thermal stability when Na-EMAA was added to either LDPE or Ny6. DSC results of Ny6/Na-EMAA binary blends showed that with increasing Na-EMAA content, the crystallization temperature of Ny6 phase decreased indicating that Na-EMAA retarded crystallization of Ny6. TGA and DSC results indicate that chemical reactions might have taken place between Ny6 and Na-EMAA, a hypothesis confirmed by the Molau test.     

Recent Advances in MALDI Mass Spectrometry of Polymers

Matrix-Assisted Laser Desorption/Ionization (MALDI) allows the identification of repeat units and end groups, the structural analysis of linear and cyclic oligomers, and the estimate of composition and sequence for copolymers. MALDI has also been applied to the measurement of molar mass distributions in polymers and to the study of thermal and oxidative processes in polymers. This paper illustrates the detection of self-association in macromolecules made by coupling MALDI and Size Exclusion Chromatography (SEC), the investigation of polymer oxidation phenomena, and the characterization of copolymers formed in the processing of reactive polymer blends.     

Insight into industrial PLA aging process by complementary use of rheology,HPLC, and MALDI

Nowadays, there is a growing availability of biodegradable industrial materials intended to food contact applications whose service life behavior needs to be further investigated. This article is focused on the degradation of two materials based on polylactic acid. The correlation between the rate of degradation and the amount of trapped degradation products was investigated applying three characterization techniques in parallel, namely rheology, high‐performance liquid chromatography (HPLC), and matrix‐assisted laser desorption/ionization (MALDI). The rate of degradation was studied through the evaluation of their rheological properties and calculation of the number of average molecular weights, and weight‐average molecular weights. Water‐soluble oligomers and lactic acid were quantified by HPLC‐ultraviolet. Changes in cyclic and linear oligomers were monitored by MALDI‐time‐of‐flight mass spectrometry. Specimens of 4‐mm thickness of each biopolymer were subjected to hydrolysis in deionized water up to 6 months at two temperatures, simulating service conditions of food packaging. The diminution in viscosity and consequently in molecular weight distribution (20–60%) showed the degradation of the molecular structure of both polylactic acids. The chain scission was followed through the increasing values of lactic acid and hydrolyzed oligomers (twofold to eightfold), and the predominant signal of the linear oligomers over the cyclic ones with aging. Rheology, HPLC, and MALDI showed to be complementary tools to better understand the changes in the molecular structure. The obtained results showed the necessity of adding suitable stabilizers for each particular food packaging application. Copyright © 2013 John Wiley & Sons, Ltd.     

Degradation of poly(lactic acid) into repolymerizable oligomer using montmorillonite K10 for chemical recycling

The degradation of poly(L-lactic acid) (PLLA) into a repolymerizable oligomer was carried out using a clay catalyst, montmorillonite K10 (MK10), with the objective of developing a chemical recycling process. PLLA having an Mw of 120,000 was degraded by MK10 in toluene at 100 degrees C for 6 h to produce the corresponding linear-type oligomers having a molecular weight of a few hundreds in a yield of greater than 90%. The oligomer was readily polymerized by a conventional chemical catalyst to give a high-molecular-weight PLLA. No isomerization of L-lactic acid occurred during the degradation process using MK10. The MK10 could be repeatedly used at least five times without any significant decrease in its activity. The degradation of PLLA was accelerated by the addition of a small amount of ethanol in toluene using anhydrous MK10 to produce oligomers with ethyl ester end groups.     

Cyclic and telechelic ladder polymers derived from tetrahydroxytetramethylspirobisindane and 1,4‐dicyanotetrafluorobenzene

5,5′,6,6′‐Tetrahydroxy‐3,3,3′,3′‐tetramethylspirobisindane was polycondensed with 1,4‐dicyanotetrafluorobenzene in four different solvents at 70 °C. In dimethylformamide, N‐methylpyrrolidone, and sulfolane exclusively, cyclic polymers were detectable by matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry up to masses around 13,000 Da. In dimethyl sulfoxide, linear byproducts were also found. Higher temperatures caused degradation reactions catalyzed by potassium carbonate. Polycondensations performed with the addition of 4‐tert‐butyl catechol or 2,2′‐dihydroxy binaphthyl yielded linear telechelic oligomers. Equimolar mixtures of linear and cyclic ladder polymers were examined by MALDI‐TOF mass spectra to determine how the end groups and the cyclic structure influenced the signal‐to‐noise ratio. The results suggested a preferential detection of the linear chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5344–5352, 2006     

Synthesis of AB and ABA block copolymers as compatibilizers in nylon 6/polycarbonate blends

Nylon 6 (Ny6) and Bisphenol A polycarbonate (PC) are immiscible and form biphasic blends. To improve the compatibility of Ny6 and PC several ABA and AB Ny6/PC block copolymers were synthesized, and their compatibilizing behavior on the blends were tested. Block copolymers were prepared by reacting monoamino- or diamino-terminated Ny6 homopolymers with high molecular weight PC at 130°C in anhydrous DMSO. The reaction of diamino- and monoamino-terminated Ny6 with polycarbonate produces block copolymers of the type PC-Ny6-PC (ABA) and PC-Ny6 (AB), respectively, plus a certain amount of unconverted PC degradated to lower molecular weights. To separate the block copolymer from the unconverted PC, a selective fractionation with tetrahydrofuran (THF) and trifluoroethanol (TFE) was carried out. Three different fractions were obtained: THF-soluble fraction, TFE-soluble fraction, and the TFE-insoluble fraction. The scanning electron microscopy (SEM) analysis of a 75/25 (wt/wt) Ny6/PC blend added with 2% of ABA or AB block copolymers, showed the presence of smaller PC particles more adherent to the polyamide matrix, with respect to the same blend nonadded, which is clearly biphasic. The size of the PC particles decreases from ABA to AB compatibilized blends and the adhesion with the matrix is increases in the same way. © 1996 John Wiley & Sons, Inc.     

Preparation of telechelic oligomers by controlled thermal degradation of isotactic poly(1-butene) and poly(propylene-ran-1-butene)

It was found that telechelic isotactic oligo(1-butene) and telechelic oligo(propylene-ran-1-butene) could be isolated as nonvolatile oligomers from polymer residues resulting from the thermal degradation of isotactic poly(1-butene) and poly(propylene-ran-1-butene), respectively. Their structures were determined by ¹H and ¹³C NMR with attention being paid to their reactive end groups. The maximum average number of terminal vinylidene groups per molecule (f_TVD) was 1.8, indicating that about 80 mol% were α,ω-diene oligomers having two terminal vinylidene groups. This useful new telechelic oligomer had a lower polydispersity than the original polymer, in spite of its lower molecular weight and T_m. The composition of end groups of nonvolatile oligomers obtained by thermal degradation of poly(propylene-ran-1-butene) could be explained by the differences in bond dissociation energy and activation energy of elementary reactions during thermal degradation, based on the monomer composition of the original polymer.     

Application of isotopic labeling,and gas chromatography mass spectrometry,to understanding degradation products and pathways in the thermal-oxidative aging of Nylon 6.6

Nylon 6.6 containing ¹³C isotopic labels at specific positions along the macromolecular backbone has been subjected to extensive thermal-oxidative aging at 138 °C for time periods up to 243 days. In complementary experiments, unlabeled Nylon 6.6 was subjected to the same aging conditions under an atmosphere of ¹⁸O₂. Volatile organic degradation products were analyzed by cryofocusing gas chromatography mass spectrometry (cryo-GC/MS) to identify the isotopic labeling. The labeling results, combined with basic considerations of free radical reaction chemistry, provided insights to the origin of degradation species, with respect to the macromolecular structure. A number of inferences on chemical mechanisms were drawn, based on 1) the presence (or absence) of the isotopic labels in the various products, 2) the location of the isotope within the product molecule, and 3) the relative abundance of products as indicated by large differences in peak intensities in the gas chromatogram. The overall degradation results can be understood in terms of free radical pathways originating from initial attacks on three different positions along the nylon chain which include hydrogen abstraction from: the (CH₂) group adjacent to the nitrogen atom, at the (CH₂) adjacent the carbonyl group, and direct radical attack on the carbonyl. Understanding the pathways which lead to Nylon 6.6 degradation ultimately provides new insight into changes that can be leveraged to detect and reduce early aging and minimize problems associated with material degradation.     

Synthesis and Enzymatic Degradation of Nylon 66 Copolymers with Poly(Ethyleneglycol)s

Abstract

Nylon 66 (N66) copolymers were prepared by melt polycondensation of adipic acid and hexamethylenediamine with 5–80 mol% poly(ethylene glycol) (PEG), where the molecular weight (MW) of PEG was 200–1000. The reduced specific viscosity of the copolymers was increased by the copolymerization. The crystallinity and melting temperature (T _m) of N66 components decreased with increasing PEG content, but T _m depression of copolymers at the same mole content decreased with increasing MW of PEG, suggesting that the copolymer structures are not of the random type but of the block type at the higher MW of PEG. The water absorption increased with increasing PEG content, and its increase was much higher at the higher MW of PEG. The enzymatic degradation was estimated by the weight loss of copolymer films in the buffer solution with and without a lipase at 37°C. The weight loss was enhanced appreciably by the presence of a lipase, and increased abruptly at higher PEG content, which was correlated to water absorption and the concentration of ester linkages. The enzymatic degradation of these N66 copolymers was much higher than that of previously reported PET copolymers with PEG. The abrupt increase of weight loss by alkali hydrolysis was fairly comparable to that of water absorption.