End-group Titration Research Articles

Mechanism Study of the Polymerization of Polyamide 56: Reaction Kinetics and Process Parameters.

Polyamide 56 (PA56) has gained significant attention in the academic field due to its remarkable mechanical and thermal properties as a highly efficient and versatile biobased material. Its superior moisture absorption property also makes it a unique advantage in the realm of fiber textiles. However, despite extensive investigations on PA56's molecular and aggregate state structure, as well as processing modifications, little attention has been paid to its polymerization mechanism. Herein, the influence of temperature and time on PA56's polycondensation reaction is detailed studied by end-group titration and carbon nuclear magnetic resonance (NMR) techniques. The reaction kinetics equations for the pre-polymerization and vacuum melt-polymerization stages of PA56 are established, and possible side reactions during the polycondensation process are analyzed. By optimizing the reaction process based on kinetic characteristics, PA56 resin with superior comprehensive properties (melting temperature of 252.6 °C, degradation temperature of 371.6 °C, and tensile strength of 75MPa) is obtained. The findings provide theoretical support for the industrial production of high-quality biobased PA56.

Hydrolytic Depolymerization of Polyethylene Terephthalate by Reactive Extrusion

Abstract Continuous hydrolytic depolymerization of polyethylene terephthalate (PET) resin at high temperature and pressure was carried out in a co-rotating twin screw extruder. In this novel process, hydrolysis is achieved by injection of saturated steam at high pressure. Optimum conditions occur at relatively low screw speeds and water/PET ratios. Hydrolysis extent was measured using carboxyl end group titration, and by determination of molecular weights using NMR and GPC analysis. Low molecular weight products are obtained at low residence times in the extruder, suggesting high depolymerization rates. This is supported by the results of a simple kinetic model.

Biobased poly(glycerol citrate) synthesis optimization via design of experiments

AbstractNowadays, glycerol polyesters are willingly studied, due to their potential to use in tissue engineering and drug delivery systems. Poly(glycerol citrate) is a quite new material that could have very interesting properties because of the easy formation of three‐dimensional hydrophilic networks. Moreover, both glycerol and citric acid are commonly used chemicals in the food and pharmaceutical industry. They are cheap, well available, and well‐known substances. In this work poly(glycerol citrate) was synthesized in bulk polycondensation with water removal. The polyester structure was widely characterized by FTIR, NMR, GPC, and the end group titration methods. The synthesis procedure was optimized and described via five mathematical models with the use of the design of experiments. The presented method was developed for further industrial use and allows for avoiding gelling phenomena. Based on this work, poly(glycerol citrate) could be obtained with desired properties, moreover, the process is prepared for scaling‐up.

Synthesis of Poly(ethylene glycol) Grafted Polyamidoamine Dendrimer Hydrogels and Their Temperature and pH Sensitive Properties

PEG-based smart hydrogels have excellent properties and are widely used in the drug delivery, tissue engineering and other fields. In this article, a temperature responsive and pH sensitive dual responsive hydrogel which is suitable for water plugging and profile control in the Daqing oil field was prepared via graft copolymerization using polyethylene glycol (Mn = 600, 1000, and 2000) and polyamidoamine (PAMAM) as raw materials. The structure and properties of the products were characterized using infrared, 1H NMR and UV–Vis spectroscopy, end group titration, scanning electron microscopy (SEM) and swelling behavior tests. The influence of the molecular weight of the PEG precursor on the critical phase transition temperature (LCST) and pH sensitivity of the hydrogel were systematically studied. The experimental results showed that when the molecular weight of the PEG precursor was varied in the range of 600–2000, the hydrogel showed obvious temperature sensitivity and the LCST increased from 40 to 50°C. When the pH was in the range of 8–11, the hydrogel exhibited obvious pH sensitivity, swelling under alkaline conditions under acid shrinkage conditions, and the swelling ratio of the hydrogel increased upon increasing the molecular weight of the PEG precursor. The hydrogel was switched at temperatures between 10 and 60°C, pH values between 3 and 11, and the swelling behavior of the hydrogel showed good reversibility for swelling–deswelling, which provides the possibility for water plugging and profile control in an oil field. SEM showed that the hydrogels in their dry state had a spherical structure and as the molecular weight of the PEG precursor increased, the size of the spherical particles decreased and the porosity increased.

Anionic synthesis of amine ω-terminated β-myrcene polymers

Well-defined amine ω-terminated β-myrcene polymers were synthetized via anionic living polymerization under an inert atmosphere with dropwise addition of equimolar amounts of N-benzylidenetrimethylsilylamine to β-myrcene polymer living chain ends in benzene at 25 °C. Chain coupling and acetophenone polymers were not detected as side products. End-group titration with perchloric acid showed a polymer amination yield of up to 85 % of ω-terminated β-myrcene polymers. The amine ω-terminated β-myrcene polymers were synthesized with a narrow molecular weight distribution (\( \overset{-}{M_w}/\overset{-}{M_n} \) ≈ 1.1) as calculated by GPC analysis using polystyrene standards. Functionalization of the amine group in the polymer chain was corroborated with FTIR, 1H-NMR, and 13C-RMN spectra. A higher yield of the amine ω-terminated β-myrcene polymer was not achieved due to differences in isomer conformation in the β-myrcene polymer.

Investigation of hydrolysis in poly(ethylene terephthalate) by FTIR-ATR

The hydrothermal aging of poly(ethylene terephthalate) (PET) was investigated at 70–95 °C. A new method to investigate the hydrolysis degree of PET by Fourier transform infrared spectroscopy (FTIR) was proposed. The spectra during the hydrothermal aging were measured using attenuated total reflection accessory (ATR). Peak resolving of carbonyl regions was performed, and the ratio of two groups of bands representing carboxylic acids and esters respectively were calculated to show the hydrolysis degree of ester groups in PET. The acid/ester ratio shows exactly the same trend as the average chain scission number per unit mass at various temperatures and thus can be used as a parameter to characterize the hydrolysis and random chain scission of PET. This method related to the hydrolysis mechanism directly, is simple, fast and convenient compared to the traditional methods such as viscometry, end-group titration and size exclusion chromatography (SEC). It may also be useful in hydrolysis characterization of other polyesters.

Biodegradable in situ gelling delivery systems containing pilocarpine as new antiglaucoma formulations: effect of a mercaptoacetic acid/N-isopropylacrylamide molar ratio

Ocular drug delivery is one of the most commonly used treatment modalities in the management of glaucoma. We have recently proposed the use of gelatin and poly(N-isopropylacrylamide) (PNIPAAm) graft copolymers as biodegradable in situ forming delivery systems for the intracameral administration of antiglaucoma medications. In this study, we further investigated the influence of carrier characteristics on drug delivery performance. The carboxyl-terminated PNIPAAm samples with different molecular weights were synthesized by varying the molar ratio of mercaptoacetic acid (MAA)/N-isopropylacrylamide (NIPAAm) from 0.05 to 1.25, and were determined by end-group titration. The preparation of gelatin-g-PNIPAAm (GN) copolymers from these thermoresponsive polymers was achieved using carbodiimide chemistry. Our results showed that the carboxylic end-capped PNIPAAm of high molecular weight may lead to the lower thermal phase transition temperature and slower degradation rate of GN vehicles than its low molecular weight counterparts. With a decreasing MAA/NIPAAm molar ratio, the drug encapsulation efficiency of copolymers was increased due to fast temperature-triggered capture of pilocarpine nitrate. The degradation of the gelatin network could greatly affect the drug release profiles. All of the GN copolymeric carriers demonstrated good corneal endothelial cell and tissue compatibility. It is concluded that different types of GN-based delivery systems exhibit noticeably distinct intraocular pressure-lowering effect and miosis action, thereby reflecting the potential value of a MAA/NIPAAm molar ratio in the development of new antiglaucoma formulations.

Synthesis and characterization of polyisobutylene-b-polyamide multi-block copolymer thermoplastic elastomers

A series of polyisobutylene (PIB)-polyamide (PA) multi-block copolymers was synthesized via an amidation reaction to form novel thermoplastic elastomers (TPEs). A two prepolymer approach was taken in which a difunctional primary-amine-terminated polyisobutylene (NH2-PIB-NH2) was synthesized as the soft block and a difunctional carboxylic acid-terminated polyamide (HO2C-PA-CO2H) was synthesized separately as the hard block. The two prepolymers were reacted in the bulk under nitrogen at 220 °C to form the multiblock copolymer TPEs. Various copolymers were synthesized from combinations of two different PIBs (either 1000 or 2000 g/mol), and four different PAs (PA-11 and PA-6, each at either 1000 or 2000 g/mol). 1H and 13C NMR spectroscopies were used to confirm the structure of the individual prepolymers and the copolymers. Prepolymer molecular weights were determined by gel-permeation chromatography (GPC), end-group titration, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS); the latter also provided confirmation of end-group functionality of prepolymers. For GPC of PA homopolymers and PIB-PA copolymers, trifluoroacetylation of the secondary amide groups of the PA blocks was necessary to obtain solubility of the copolymers in the THF mobile phase. Copolymer number–average molecular weights varied from 8100 to 20,630 g/mol.

Biodegradable Polyesters and Polyamides From Difunctionalized Lauric and Coconut Fatty Acids

In this work, a major fatty acid from coconut oil was used as starting material in preparing biodegradable polymers. Thus, polyesters and polyamides from varying proportions of monomers, hydroxy- and amino- derivatives of lauric acid were synthesized. Initially, the derivatives were prepared by regioselective chlorination of lauric acid, in the presence of ferrous ions in strong acid medium. Subsequent hydroxylation and amination procedures yielded the hydroxy- and amino- derivatives of lauric acid. These monomers were polymerized in a reaction tube by simple polycondensation method at 220–230 °C for 6–8 h without catalyst. Molecular weight determination using –COOH by end group titration and gel permeation chromatography (GPC) gave an average molar mass of 3,000–5,000 g mol−1 with n = 15–25 monomer units. Thermal properties such as glass transition (Tg) and decomposition (Td) temperatures were obtained using differential scanning calorimetry (DSC). The same processes of synthesis and determinations above were applied to coconut fatty acids, derived from saponification of coconut oil, and resulted to very similar conclusions. A quick biodegradation assay against fungus Aspergillus niger UPCC 4219 showed that the polymers prepared are more biodegradable than conventional plastics such as polypropylene, poly(ethyleneterepthalate) and poly(tetrafluoroethylene) but not as biodegradable as cellulosic (newsprint) paper.

Milled Wood Lignin: A Linear Oligomer

The degree of polymerization (DP) of softwood and hardwood milled wood lignin samples and their branching degrees were quantitatively evaluated by a novel end-group titration approach composed of QQ-HSQC, (31)P NMR, and DFRC coupled with (31)P NMR analysis techniques. The DP of lignin can be calculated when the C9 formula, the amounts of phenolic groups, pinoresinol (β-β), diphenylethane (β-1), and phenolic diphenyl (5-5') lignin subunits have been determined. Data on the degree of polymerization of lignin obtained by NMR techniques were not affected by supramolecular aggregation processes. (31)P NMR analysis coupled with DFRC and QQ-HSQC allowed a detailed evaluation of the occurrence of condensed units in lignin and showed the terminal nature of diphenyl ether and diphenyl subunits. The resulting data unequivocally show that milled wood lignin is a linear oligomer.

Preparation and characterization of star-shaped nylon 6 with high flowability

Three kinds of star-shaped nylon 6 samples with different branched-chain length were prepared by the hydrolytic polymerization of e-caprolactam using trimesinic acid as trifunctional reactant. The structure of prepared star-shaped nylons was characterized by infrared spectroscopy and 1H-NMR. Compared with linear-chain nylon 6, star-shaped nylons with the equivalent molecular weight present higher melt flow indices and lower relative viscosities due to decreased molecular dimensions and reduced hydrogen bond interactions between neighboring molecules. The molecular weights of the products were determined by end-group titration and 1H-NMR, and the molecular weight distributions (MWDs) were evaluated by gel permeation chromatography. The results show that the molecular weight decreased and the MWD narrowed as the concentration of trimesinic acid increased. Wide-angle X-ray diffraction patterns of star-shaped and linear-chain nylons show that increasing the concentration of trimesinic acid leads to good symmetry and high crystallizability, but this also degrades crystal perfection as observed using a polarized optical microscope. The viscosity of nylon 6 can be significantly reduced while maintaining its mechanical performance through the use of star-branching and an appropriate concentration of trimesinic acid.

Hydrolytic and thermal degradation of PET fibers and PET granule: The effects of crystallization, temperature, and humidity

AbstractThe main purpose of this research work was to illustrate the extent of hydrolytic degradation of PET caused by warm water and also to separate the influence of moisture, temperature, and orientation in the degradation process. To achieve this purpose, thermal and hydrolytic degradation of PET (Partly Oriented Yarn (POY), Fully Drawn Yarn (FDY) and granule) at temperatures above and below glass transition temperature (Tg) were carried out using a water bath and an electrical oven. Technical methods such as determination of the moisture content, viscometric analysis, carboxylic end group titration, and X‐ray diffraction were used to analyze the degradation of PET. The results obtained from different analysis show that the major portion of degradation is carried out by both moisture and heat mutually rather than their entirely individual that have a minor effect. Degradation at lower temperatures from Tg were less prominent and was increased noticeably above Tg. Crystallinity plays a significant role in preventing hydrolytic degradation as the extent of degradation was increased from FDY to granule to POY. X‐ray diffraction analysis showed that crystallinity was increased from POY to granule to FDY. Determination of intrinsic viscosity, molecular weight based on viscosity (Mv), chain scissions, and carboxylic end group analysis were the main quantities for the degradation measurement. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Study of hygrothermal ageing of glass fibre reinforced PET composites

Hygrothermal ageing has been investigated on glass fibre reinforced polyethylene terephthalate (PET) composites using complementary techniques and a multiscale approach in order to identify the different steps of the material's degradation. For early ageing times ( t < 6 h), DMTA tests give evidence of the plasticisation of the PET matrix. GPC measurements and acid end group titration show that the chemical degradation step of the composites occurs immediately and that the main degradation mechanism is random chain scission. The changes in morphology resulting from hydrolysis, investigated through DSC and SAXS experiments, reveal a decrease in the long period that may result from the diffusion of oligomers out of the spherulites. The water uptake for long ageing times is attributed to an interfacial debonding which induces an osmotic pressure in this area. Photomechanical measurements highlight the development of microcracks within the aged material that induced an increase in the variation of material volume.

Synthesis and Characterization of Star‐Branched Nylon 12

AbstractLinear and star‐branched polyamide 12 were prepared in the presence of mono‐ and multifunctional acid agents. Molecular masses and molecular mass distributions are discussed according to our model recently presented and are compared with the data obtained by Flory's model. End group titration and SEC data are discussed. Oligomerisation data confirm the general validity of our model.

Study of interphase in glass fiber–reinforced poly(butylene terephthalate) composites

AbstractIt is well known that application of a coupling agent to a glass fiber surface will improve fiber/matrix adhesion in composites. However, on commercial glass fibers the coupling agent forms only a small fraction of the coating, the larger part being a mixture of processing aids whose contribution to composite properties is not well defined. The interfacial region of the composite will therefore be affected by the coating composition but also by the chemical reactions involved in the vicinity of the fiber and inside the surrounding matrix. The main feature of this study consists in dividing the interface region into two separate regions: the fiber/sizing interphase and the sizing/matrix interphase. A wide range of techniques was used, including mechanical and thermomechanical tests, infrared spectroscopy, gel permeation chromatography, carboxyl end group titrations, extraction rate measurements, and viscosity analysis. Experiments were performed on poly(butylene terephthalate) composites and results indicate that the adhesion improvement is due to the presence of a short chain coupling agent and of a polyfunctional additive, which may react both with the coupling agent and the matrix. According to the nature of this additive, it may be possible to soften the interphase and then to increase the composite impact strength.

End group modification of polyamide-6 in supercritical and subcritical fluids: Part 3: Amine end group modification with diketene and diketene acetone adduct in CO 2

In this paper the modification of the amine end groups of polyamide-6 (PA-6) granules with diketene and the diketene acetone adduct in supercritical and subcritical CO 2 is described. The modified polyamide samples were characterised by end group titrations, viscosity measurements and FTIR spectroscopy. The aim of the modification of the amine end groups of PA-6 was to obtain a polyamide with an amine end group content of around 10 mmol/kg PA-6, which is known to exhibit a satisfactory melt stability. It was expected that the end group modification could be achieved without changing other properties of the polymer, since in supercritical CO 2, relatively mild reaction conditions can be applied. Indeed, chain scission can be avoided, but unfortunately, the described modification resulted in coloured PA-6 granules. By comparing the current results with our earlier data on amine end group modification in supercritical CO 2 it is learnt that 1,2-epoxybutane is the preferred blocking agent.

End group modification of polyamide-6 in supercritical and subcritical fluids: Part 2: Amine and carboxylic acid end group modification with 1,2-epoxybutane

The amine and carboxylic acid end groups of polyamide 6 (PA-6) granules were blocked with 1,2-epoxybutane in supercritical or subcritical fluids. The fluids were mixtures of either propane or CO 2 with 10 mol% 1,4-dioxane. Temperatures of 50–140 °C and pressures of 70–80 bars were applied. The reactions were followed in time. The modified polyamide samples were analysed by carboxylic acid end group titrations, by FTIR spectroscopy, by solution and melt viscosity measurements, by DSC and SEC/DV. End group concentrations, relative viscosities and molecular weight distributions (MWD) of modified samples were compared with corresponding values of unmodified PA-6. It was found that better blocking of the end groups was obtained with increasing reaction temperature. However, after modification, at higher temperatures, a decrease in relative viscosity was found. SEC measurements showed that this decrease in relative viscosity not necessarily implies that chain scission had occurred, but that it must be the result of a different interaction of the modified polymer end groups with the solvent. Best results were obtained for PA-6 modified at 100 °C in propane/1,4-dioxane: an improved melt stability was obtained without discolouration of the PA-6 granules or a change in molecular weight, due to the blocking of the amine end groups but leaving the majority of the carboxylic acid end groups unblocked.

End group modification of polyamide-6 in supercritical and subcritical fluids: Part 1: Amine end group modification with succinic anhydride

The amine end groups of polyamide 6 (PA-6) granules were blocked with succinic anhydride (SA) in supercritical or subcritical fluids. The fluids were mixtures of either propane or CO 2 with 10 mol% 1,4-dioxane. Temperatures of 50–140 °C and pressures of 70–80 bars were applied. The reactions were followed in time. The modified polyamide samples were analysed by amine end group titrations, by NMR and FTIR spectroscopy, by solution and melt viscosity measurements and by SEC/DV. Sorption measurements were performed to determine the uptake by the PA-6 granules of either CO 2, CO 2/1,4-dioxane saturated with SA, or CO 2 saturated with SA. End group concentrations, relative viscosities and molecular weight distributions of modified samples were compared with corresponding values of unmodified PA-6. It was found that better blocking of the end groups was obtained with increasing reaction temperature. However, at 140 °C the granules discoloured and for PA-6 modified in supercritical CO 2/1,4-dioxane, a decreased molecular weight was found. Optimum results were obtained at 100 °C in propane/1,4-dioxane: a decrease in amine end groups provided a better melt stability without discolouration or a change in molecular weight.

Determination of the molecular weight and other physicochemical properties of poly(bubylene glycol) 1000 by gradient RPHPLC and measurement of the ELSD, UV, and fluorescence responses

Molecular weight and other physicochemical data for poly(butylene glycol) 1000 (PBG 1000) have been determined by use of a new, highly efficient, gradient reversed-phase high-performance liquid-chromatographic (RPHPLC) procedure. Separation of the native material or its α, ω-bis(1-naphthylurethane) derivative was achieved on a C18 stationary phase with a ternary acetonitrile-water-tetrahydrofuran mobile phase. Detection was achieved by measurement of the signal response from evaporative light scattering (ELSD), UV, and fluorescence (FD) detection. Proof that all the oligomers contained in the sample had been separated by the method was obtained by liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry (LC-ESI-TOFMS). It was also confirmed by this technique that di(butylene glycol) is the lowest homologue in the sample. Although the dimer was also observable in the HPLC-UV trace of the PBG 1000 α, ω-bis(1-naphthylurethane) derivative, it was obviously too valatile to be seen in the ELSD trace; tri(butylene glycol) was, nevertheless, still recognizable with sufficient signal intensity. Because all the homologues were separated to baseline, the method was used to calculate the number- and weight-average molecular weights,M n andM w, both from peak areas and from peak heights. The best fit to data obtained from end-group titration were obtained from calculations based on the HPLC-UV response;M n values of 948 and 937 were obtained from peak heights and areas, respectively.M n andM w values calculated from the ELSD trace obtained from native PBG 1000 were substantially (ca 10%) lower that those calculated from the UV trace obtained from the α, ω-bis(1-naphthylurethane) derivative. Similar differences were also discovered by comparing theM n andM w values obtained from UV and FD-values were approximately 20% higher for FD. When the retention times of individual oligomers, from either ELSD of the native sample or from UV-FD of the α,ω-bis(1-naphthylurethane) derivative, were plotted against the number of repeat units,P, the ELSD curve approaches the UV-FD curve at values ofP of approximately 60. This observation can be explained by the pronounced contribution of the hydrophobic end-groups to the overall retention of PBG 1000; the effect of this decreases with increasing chain length and becomes nearly independent ofP only for a very high degree of polymerization.

Hydrolytic Depolymerization of Polyethylene Terephthalate by Reactive Extrusion

Abstract Continuous hydrolytic depolymerization of polyethylene terephthalate (PET) resin at high temperature and pressure was carried out in a co-rotating twin screw extruder. In this novel process, hydrolysis is achieved by injection of saturated steam at high pressure. Optimum conditions occur at relatively low screw speeds and water/PET ratios. Hydrolysis extent was measured using carboxyl end group titration, and by determination of molecular weights using NMR and GPC analysis. Low molecular weight products are obtained at low residence times in the extruder, suggesting high depolymerization rates. This is supported by the results of a simple kinetic model.