Crosslinking of PET through solid state functionalization with alkoxysilane derivatives

A new way for crosslinking poly(ethylene terephthalate) (PET) films and fibers is described using solid state functionalization of the PET end groups (alcohol and acid) with two reagents, respectively, 3-isocyanatopropyltriethoxysilane (IPTESI) or/and 3-glycidoxypropyltrimethoxysilane (GOPTMSI). This functionalization is then followed by hydrolysis-condensation reactions of PET-alkoxysilane end groups leading to the PET crosslinking.First of all, the functionalization reactions were investigated on model compounds by ¹H NMR spectroscopy in a range of temperature 80-160 °C. Furthermore, the diffusion of reagents in solid PET, depending on the initial degree of PET crystallinity, was characterized in the same temperature range through the variation of sample mass. On the other hand, this method allowed us to determine the diffusion coefficients and the solubility of the reagents in solid PET at different temperatures and initial crystallinity degrees.End groups functionalized PET films and fibers by alkoxysilane were then crosslinked by immersion of the samples in hot water. The crosslinking density was characterized by measuring the insoluble fraction of PET in good solvent constituted by a mixture of trifluoroacetic acid and dichloromethane (50/50 vol.). An insoluble fraction close to 70% was obtained by the functionalization treatment of amorphous PET film (8% crystallinity) by a mixture of GOPTMSI + IPTESI (50/50 M) at 155 °C for 1 h followed by hydrolysis-condensation reactions at 80 °C for 72 h. Thermomechanical and thermal properties of films and fibers were observed and found to be considerably enhanced in comparison to the untreated samples. The tensile properties of these partially crosslinked samples were maintained up to 320 °C.     

Zinc chloride/acetamide deep eutectic solvent-mediated fractionation of lignin produces high- and low-molecular-weight fillers for phenol-formaldehyde resins

Lignin readily dissolves in a deep eutectic solvent (DES) composed of ZnCl₂/acetamide 1:3 M ratio in concentrations up to 16.7 wt %, and upon addition of water, two fractions were obtained; one composed of lignin with low-molecular weight that remained dissolved in the DES/water mixture, whereas the other fraction of lignin with higher molecular weight (regenerated lignin, RL) was regenerated by precipitation. Both the RL fraction and the whole solution of lignin in DES were used to replace part of phenol (20 wt %) in the condensation of phenol and formaldehyde to introduce biomass in the resulting resins. The lignin treatment that produced the higher yield of RL consisted of lignin/DES ratio of 1:10 (w/w) stirred for 4 h at 100 °C. By using ¹³C NMR spectroscopy, a preferential cleavage of the S unit of lignin during DES treatment was identified. The modified phenol-formaldehyde resin (RLPF) containing the RL exhibited higher bonding strength (1.28 ± 0.16 MPa) and shorter Sunshine gel time (557 s) than PF (587 s), showing that the RL helps to improve the polycondensation process. The resin modified with the whole solution of lignin in DES exhibited the shortest Sunshine gel time due to the effect of zinc(II) accelerating the curing process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48385.     

Towards molecular sieve inorganic catalysts that are akin to enzymes: studies of a selective cyclo-dimerization over ferrierite at ambient temperature

The solid-acid (Brønsted)-catalyzed cyclo-dimerization of 3-hydroxy-3-methylbutan-2-one (HMB) over a synthetic ferrierite molecular sieve is reported. HMB is a stable liquid at ambient temperatures but in acidic solutions it readily undergoes reaction to generate a variety of products. However, in the acidic molecular sieve catalyst studied here, only one product – the cyclic dimer (proven by in situ solid state ¹³C NMR and other evidence) – is observed, together with some unreacted HMB. A plausible, proton-catalyzed mechanism is proposed, and prompts comparison between the cyclo-dimerization of HMB within ferrierite and the mode of action of certain enzymes.     

Morphology and molecular mobility of plasticized polylactic acid studied using solid‐state 13C‐ and 1H‐NMR spectroscopy

MAS ¹³C‐NMR measurements were used for the study of morphology and molecular mobility in amorphous quenched and triacetine‐plasticized PLA samples and PLA samples which underwent cold crystallization during annealing at 80 and 100 °C. The single pulse MAS ¹³C‐NMR spectra indicate that plasticizer promotes cold crystallization which results in the decrease of the temperature of crystallization and formation of more perfect crystalline domains. The T₁(¹³C) spin‐lattice relaxation times show that the presence of plasticizer molecules leads to an increase of local mobility in PLA chains but plasticized PLA after annealing at 100 °C shows more rigid structure. The series of broad line ¹H‐NMR spectra performed at temperatures up to 100 °C provided information on the changes in relaxation processes and morphology of the studied samples. The interpretation of the results obtained using the techniques of NMR spectroscopy were supported by WAXD and DSC measurements. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43517.     

Synthesis and properties of an easy-processable bismaleimide thermoset resin

Reaction of methylenedianiline and maleic anhydride in acetone, followed by cyclodehydration in the presence of acetic anhydride and 1,4-diazabicyclo [2.2.2] octane as a catalyst, affords a mixture of compounds, Desbimid, with maleimide, isomaleimide, and acetamide groups. Dissolution of this mixture in styrene and 2-hydroxyethyl methacrylate results in clear liquid resins. The viscosity of the formulated resins ranges from 100–1700 mPas at 25°C depending on the concentration of Desbimid. These systems can be processed and cured at ambient temperatures until demoulding and postcured at temperatures up to 200 or 250°C. The flexural modulus, flexural strength, and elongation at break of a number of cured formulations are found between 3500–3800 N/mm², 90–115 N/mm², and 2.7–3.5%, respectively.     

Morphological consequences of interchange reactions during solid state copolymerization in poly(ethylene terephthalate) and polycarbonate oligomers

Poly(ethylene terephthalate) (PET) (IV:0.15 dL/g) oligomer was obtained by depolymerisation of high molecular weight PET. Polycarbonate (PC) oligomer (IV: 0.15 dL/g) was synthesized by standard melt polymerization procedure using bisphenol A and diphenyl carbonate in the presence of a basic catalyst. Blends of varying compositions were prepared by melt blending the chemically distinct PET and PC oligomers. The copolymer, poly(ethylene terephthalate-co-bisphenol A carbonate) was synthesized by simultaneous solid state polymerization and ester-carbonate interchange reaction between the oligomers of PET and PC. The reaction was carried out under reduced pressure at temperatures below the melting temperature of the blend samples. DSC and WAXS techniques characterized the structure and morphology of the blends, while ¹NMR spectroscopy was used to monitor the progress of interchange reactions between the oligomers. The studies have indicated the amorphisation of the PET and PC crystalline phases in solid state with the progress of solid-state polymerization and interchange reaction.     

A comparative study of the conformational mobility of octamethyltetrasiloxane and cyclododecane in the solid state

A crystalline mesophase state in which molecules show conformational mobility is discussed for cyclododecane and octamethyltetrasiloxane.¹³C and²⁹Si solid state NMR spectra show changes of the resonance signals which can be explained by changes of the conformation. The transition temperatures in the NMR spectra are correlated with the thermal transitions detected by DSC. Comparisons with the solution spectra give evidence that in case of octamethyltetrasiloxane, the conformational mobility is determined mainly by the molecular packing in the crystal, while packing effects are neglegibly small for cyclododecane. The data are discussed with concern to the corresponding linear chain molecules, i. e. poly(ethylene) and poly(dimethylsiloxane).Herrn Prof. Dr. H. Inagaki zu seinem 60. Geburtstag herzlich gewidmet     

Reverse iodine transfer polymerization of vinyl acetate and vinyl benzoate: synthesis and characterization of homo‐ and copolymers

Homo‐ and copolymers of vinyl esters including vinyl acetate (VAc) and vinyl benzoate (VBz) were synthesized via the reverse iodine transfer radical polymerization technique. Polymerization was carried out in the presence of iodine as the in situ generator of the transfer agent and 2,2′‐azobis(isobutyronitrile) as the initiator at 70 °C. Reverse iodine transfer radical homopolymerization of VAc and VBz led to conversions of 76 and 57%, number‐average molecular weights of 8266 and 9814 g mol^?1 and molecular weight distributions of 1.58 and 1.49, respectively. The microstructure of the synthesized polymers was investigated in detail using gel permeation chromatography, ¹H NMR, ¹³C NMR and distortionless enhancement of polarization transfer (135° decoupler pulse) techniques. Relatively narrow molecular weight distribution and controlled and predictable trend of molecular weight versus conversion were observed for the synthesized polymers, showing that reverse iodine transfer radical homo‐ and copolymerization of VAc and VBz proceeded with controlled characteristics. Results of molecular weight and its distribution along with the ¹H NMR spectra recorded for homo‐ and copolymers indicated that side reactions can occur during the course of polymerization with a significant contribution when VAc, even in a small amount, was present in the reaction mixture. This can result in polymer chains with aldehyde dead end and broadening of the molecular weight distribution. © 2015 Society of Chemical Industry     

NMR Study of Solid Phloroglucinol

Wide line NMR investigation of solid phloroglucinol has been made over the temperature range 77 °K to 400 °K at the radio frequency 7.5 Mc/s. It has been shown that the second moments (mean square width) of the spectra for the temperatures at which the lattice is effectively rigid, namely below 290 °K are consistent with the assumed model of phloroglucinol, thereby giving an NMR check of the molecular structure of the sample. The rotation of the molecule is observed at all temperatures above 290 °K and the correlation frequencies for molecular reorientation are found to be in excess of 10⁵ Hz. The activation energy is found to be 23.04 kcal/mole.     

NMR-study of structure and dynamics of associates of syndiotactic poly(methyl methacrylate) in toluene

Summary High-resolution ¹H NMR spectra (¹H HR-NMR) of solutions of isotactic (i) and syndiotactic (s) poly(methyl methacrylate) (PMMA) in toluene-d₈ were measured in the concentration range 0.2 to 10% w/v; for solutions of s-PMMA (10% w/v), ¹H NMR spectra with magic angle rotation (MAR-NMR) at various temperatures and ¹³C NMR spectra with strong proton decoupling were also measured. It was found that even in very dilute solutions of s-PMMA in toluene-d₈ a considerable portion (76%) of polymer segments are associated: association is of intramolecular origin and is due to interaction of long syndiotactic sequences. Prom NMR spectra the motion of associated segments appears as isotropic with and effective correlation frequency 10⁶ – 10⁷ Hz. A globular structure of the associates of s-PMMA is proposed.     

Assessment of Lignin Model Quality in Lignin Chemical Shift Assignments – Substituent and Solvent Effects1

Typical solution-state ¹³C NMR spectra of lignins obtained with relatively modern instrumention contain well over 100 signals. The use of classical lignin model compounds is no longer sufficient for accurate interpretation of these spectra. Ultimately, the only valid models for etherified C₉ units in lignin (which account for about 80% of the lignin polymer) must be at least trimeric or tetrameric, depending on the linkages involved. One approach that can be used involves NMR substituent effects. This approach avoids tedious syntheses while retaining the much-needed accuracy of chemical shift correlations between models and natural lignins. Appropriate substituent effects have been calculated by the use of an extensive NMR database of dimeric, trimeric and tetrameric lignin model compounds. Effects related to acetylation and solvent have also been determined. For example, accurate chemical shift data for an underivatized milled-wood lignin (MWL) in DMSO-d₆ can be determined on the basis of the chemical shifts of the corresponding acetylated MWL in acetone-d₆.     

Method to Stop Geopolymer Reaction

The objective of this study was to develop a method to stop geopolymer reaction at early ages so that the molecular structure can be determined and its link to setting behavior probed. Solvent extraction, using a mixture of alcohol and acetone to remove water, was seen to suspend reaction up to at least 53 h, allowing enough time for nuclear magnetic resonance (NMR) tests to determine structure. However, this method caused precipitation of soluble species present at early ages, confounding interpretation of the spectra and thus making it suitable only for mature geopolymers. A combination of water treatment to extract soluble species and solvent treatment to extract water was seen to stop the geopolymer reaction long enough (> 1 week) for NMR tests in specimens with and without calcium.     

A novel method for determination of polyester end-groups by NMR spectroscopy

An efficient, convenient and quantitative method for characterising polyester end-groups is described. We have found that trichloroacetyl isocyanate (TAI) reacts rapidly and quantitatively with both carboxyl [C(O)OH] and hydroxyl (OH) chain ends to form derivatives that can be readily determined by ¹H NMR spectroscopy. The TAI capped end-groups give rise to characteristic imidic NH resonances in a normally clear region of the ¹H NMR spectrum [δ∼10-11.5 for C(O)-O-C(O)-NH-C(O)CCl₃ from C(O)OH, δ∼8-9 for O-C(O)-NH-C(O)CCl₃ from OH]. The method has been successfully applied to quantitative determination of the end-groups of a wide variety of oligomeric polyesters. It has also been applied to higher molecular weight polyesters including commercial, bottle grade, poly(ethylene terephthalate) (PET) and PET based copolyesters (e.g. PETG).     

The interchange reaction between poly(ethylene terephthalate) and poly(m‐xylylene adipamide)

The interchange reaction in blends of poly(ethylene terephthalate) (PET) and poly(m‐xylylene adipamide) (MXD6) has been characterized in terms of changes observed in spectra obtained with a 600‐MHz ¹H‐NMR. The selective degradation of PET components in the blends was carried out in the NMR tubes prior to evaluation. Results indicate that there is no chemical reaction between the PET and MXD6 in the absence of sodium p‐toluenesulfonate catalyst. The presence of the catalyst activates the interchange reaction between these two resins. A mathematical method was applied to calculate the degree of randomness of PET‐MXD6 copolymer. In addition, the reaction degree was found to be affected by exposure temperature, time, shear rate, and catalyst concentration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Carbon-13 nuclear magnetic resonance analysis of intact oilseeds

High resolution natural abundance¹³C nuclear magnetic resonance (NMR) spectra of intact oilseeds have been obtained by Fourier transform techniques. The spectra can be interpreted in terms of the relative concentrations of the major fatty acids in the oilseed. The¹³C NMR spectra are well resolved despite the fact that¹H NMR spectra of the same seeds are poorly resolved. The difference in resolution can be attributed to the simplicity of the¹³C NMR spectra in which all spin-spin coupling can be removed, in which the separation of lines is increased by a factor of 30, and in which line broadening due to intermolecular dipolar interactions is not important. The¹³C NMR Fourier transform technique is sufficiently sensitive that a high quality spectrum can be obtained from a single soybean, for example, in about 10 minutes. Similar spectra of single seeds can be obtained in comparable times for corn, castor bean, peanut, sunflower seed, and rapeseed. Because the NMR technique is nondestructive, it can be used to select individual oilseeds for use in breeding programs designed to improve oil quality. By employing some special experimental NMR line narrowing techniques, it also appears feasible to obtain moderately well resolved, natural abundance¹³C NMR spectra of the immobile, rigid protein, and carbohydrate components of an intact oilseed, as well as the more mobile oil components.     

Effect of poly(ethylene glycol) on the solid‐state polymerization of poly(ethylene terephthalate)

Poly(ethylene glycol) (PEG) and end‐capped poly(ethylene glycol) (poly(ethylene glycol) dimethyl ether (PEGDME)) of number average molecular weight 1000 g mol^?1 was melt blended with poly(ethylene terephthalate) (PET) oligomer. NMR, DSC and WAXS techniques characterized the structure and morphology of the blends. Both these samples show reduction in T_g and similar crystallization behavior. Solid‐state polymerization (SSP) was performed on these blend samples using Sb₂O₃ as catalyst under reduced pressure at temperatures below the melting point of the samples. Inherent viscosity data indicate that for the blend sample with PEG there is enhancement of SSP rate, while for the sample with PEGDME the SSP rate is suppressed. NMR data showed that PEG is incorporated into the PET chain, while PEGDME does not react with PET. Copyright © 2005 Society of Chemical Industry     

Antiplasticization-based enhancement of poly(ethylene terephthalate) barrier properties

Incorporation of selected low molecular weight diluents (LMWDs) into poly(ethylene terephthalate) (PET) significantly improves oxygen and carbon dioxide barrier properties. A so-called Barrier Improvement Factor (BIF), defined as the ratio of permeability of pure polymer to that of antiplasticized polymer, provides a useful indication of improved barrier properties. The average BIF was found to be 1.20 (±0.02) and 1.34 (±0.03) for O₂ and 1.25 (±0.01) and 1.41 (±0.01) for CO₂ in PET containing - 2.32% phenacetin, or 1.95% acetanilide, respectively. The reduced permeability coefficient in each PET sample is attributed to antiplasticization, and justified by the combination of the effect of reduced free volume and the interaction energies of PET with LMWDs. A more compatible interaction of PET with acetanilide may require higher activation energy for diffusional jump resulting in more reduction in permeability even though both PET-2.32% phenacetin and PET-1.95% acetanilide showed an equal level of reduction in free volume. Solid-state ¹³C cross polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectra verified a reduction in the localized chain mobility of carbonyl carbon of PET in both PET-2.32% phenacetin and PET-1.95% acetanilide. Furthermore, the dynamic mechanical property measurement in the low temperature region verifies that the presence of LMWDs reduced the low temperature β relaxation in PET.     

Application of high-resolution, two-dimensional 1H and 13C nuclear magnetic resonance techniques to the characterization of lipid oxidation products in autoxidized linoleoyl/linolenoylglycerols

Subjection of polyunsaturated fatty acid (PUFA)-rich culinary oils to standard frying episodes generates a range of lipid oxidation products (LOP), including saturated and α,β-unsaturated aldehydes which arise from the thermally induced fragmentation of conjugated hydroperoxydiene precursors. Since such LOP are damaging to human health, we have employed high-resolution, two-dimensional ¹H-¹H relayed coherence transfer, ¹H-¹H total correlation, ¹H-¹³C heteronuclear multiple quantum correlation, and ¹H-¹H J-resolved nuclear magnetic resonance (NMR) spectroscopic techniques to further elucidate the molecular structures of these components present in (i) a model linoleoylglycerol compound (1,3-dilinolein) allowed to autoxidize at ambient temperature and (ii) PUFA-rich culinary oils subjected to repeated frying episodes. The above techniques readily facilitate the resolution of selected vinylic and aldehydic resonances of LOP which appear as complex overlapping patterns in conventional one-dimensional spectra, particularly when employed in combination with solvent-induced spectral shift modifications. Hence, much useful multi-component information regarding the identity and/or classification of glycerol-bound conjugated hydroperoxydiene and hydroxydiene adducts, and saturated and α,β-unsaturated aldehydes, present in autoxidized PUFA matrices is provided by these NMR methods. Such molecular information is of much value to researchers investigating the deleterious health effects of LOP available in the diet.     

Co γ-irradiation-initiated RAFT polymerization of VAc at room temperature

In this work, the reversible addition-fragmentation chain transfer (RAFT) polymerization of vinyl acetate (VAc) was successfully performed at room temperature using ⁶⁰Co γ-irradiation as the initiation source. Under the dose rate of 10 Gy/min irradiation, the polymerization proceeded smoothly and converted approximately 90% of the monomer within 7 h. The molecular weight distribution (M_w/M_n) remained narrow (M_w/M_n < 1.35) up to 90% conversion. Compared to AIBN-initiated RAFT polymerization at 60 °C, ⁶⁰Co γ-irradiation-initiated RAFT polymerization is a technique that can better control the molecular weight, especially at high conversion. The ¹H NMR spectra and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry confirmed that most of the chain ends of poly(VAc) (PVAc) from γ-irradiated RAFT polymerization were living and can be reactivated for chain-extension reactions. The microstructures of PVAc from ⁶⁰Co γ-irradiated RAFT polymerization (almost head-to-tail addition) and AIBN-initiated RAFT polymerization (5% tail-to-tail addition) were different, as revealed by the ¹³C NMR spectra. For the first time, ⁶⁰Co γ-irradiation was used as an initiation source for RAFT polymerization of VAc at room temperature.     

Highly functionalized polystyrene by direct metalation—carboxylation

Summary Polystyrene was directly metalated using 1:1 mixture of n-butyllithium (n-BuLi) and potassium-t-butoxide (t-BuOK) in cyclohexane/hexanes at ambient temperature. The metalated polymer on reaction with solid carbon dioxide followed by a metal-proton exchange gave a carboxylated polymer containing 6.38–6.57 mmol acid/g polymer which corresponds to the introduction of carboxyl groups on 94–97% of the repeat units of polystyrene.Based on ¹³C nMR spectra meta, para and ortho aromatic ring substitution was proposed. No detectable backbone carboxylation occurs. the distribution of carboxylated sites on the aromatic ring: 9% ortho, 58% meta and 33% para. Quantitative ¹³C NMR analyses indicates essentially quantitative functionalization.