End-group Determination Research Articles

RAFT Polymerization with Phthalimidomethyl Trithiocarbonates or Xanthates. On the Origin of Bimodal Molecular Weight Distributions in Living Radical Polymerization

Phthalimidomethyl trithiocarbonate reversible addition−fragmentation chain transfer (RAFT) agents are effective in imparting living characteristics to radical polymerizations of butyl acrylate (BA) and N-isopropylacrylamide (NIPAM) and provide a route to end-functional polymers with predictable molecular weight and narrow molecular weight distributions (e.g., number-average molecular weight for PBA (M̄n) = 21 300 and polydispersity (M̄w/M̄n) = 1.1 at 96% conversion). End group determination suggests that bimodal molecular weight distributions and long chain branches in PBA arise by copolymerization of a PBA macromonomer formed by backbiting β-scission. The S-phthalimidomethyl xanthates provide good control over polymerizations of the less-activated monomers N-vinylpyrrolidone (NVP) and vinyl acetate (VAc). In the case of PBA with a trithiocarbonate end or PVAc with a xanthate end, the C−S bond to the thiocarbonylthio end group can be homolyzed by thermolysis at >180 °C leaving the phthalimidomethyl end group and the ester side groups intact providing macromonomers, with ω end group −CH2−C(CO2C4H9)(CH2) or −CH2−C(O2CCH3)(CH2) respectively, as the main products.

A simple method for determining protic end-groups of synthetic polymers by 1H NMR spectroscopy

A simple method for the determination of protic end-groups (–XH) in synthetic polymers involves in situ derivatization with trichloroacetyl isocyanate (TAI) in an NMR tube and observation of the imidic hydrogens of the derivatized products [–X–C(O)–N H–COCCl 3] by 1H NMR spectroscopy. In this paper, we report that the method is effective for the quantitative determination of hydroxy, primary amino and carboxy end-groups of polymers with M ¯ n < 50 , 000 g mol − 1 . It may also be applied to detect chain ends in higher molecular weight polymers. The signals for the imidic (and, in the case of amines, amidic) hydrogens appear in a region ( δ 7.5–11) that is clear of other signals in the case of most aliphatic polymers and many aromatic polymers such as polystyrene and poly(ethylene terephthalate). The method has been applied in the characterization of polymers formed by conventional and living radical polymerization (RAFT, ATRP, NMP), to end functional poly(ethylene oxide) and to polyethylene- block-poly(ethylene oxide). The method appears less effective in the case of sulfanyl end-groups. The chemical shift of the imidic hydrogen shows remarkable sensitivity to the microenvironment of chain end. Thus, the imidic hydrogens of TAI derivatized polyethylene- block-poly(ethylene oxide) [PE-(EO) m OC(O)N HC(O)CCl 3] are at least partially resolved for m=0, 1, 2, 3 and ≧4 in the 400 MHz 1H NMR spectrum. It is also sensitive to the chain end tacticity of, for example, amino-end-functional polystyrenes and thus to the relative configuration of groups removed from the chain-end by two or more monomer units. TAI derivatization also facilitates analysis of amine functional polymers by gel permeation chromatography (GPC) which is often rendered difficult by specific interactions between the amine group and the GPC column packing.

Determination of silanol end groups in polysiloxanes obtained from dimethyldichlorosilane hydrolysate (DDSH)

Dimethyldichlorosilane hydrolysate, DDSH, the linear part of which contains SiOH end groups, can be used in the preparation of difunctionally terminated (any end groups other than SiOH) polysiloxanes via equilibration polymerisations. In such a case, the problem arises: as to whether the obtained functionalised polymers also contain silanol end groups. To the best of our knowledge, the only direct and the most precise analytical procedure to clarify this question is the Karl Fischer titration/determination of SiOH groups. This determination was performed on a model system consisting of trimethylsilyl terminated polysiloxanes, and it was shown that the obtained polymers contained no SiOH groups.

Reaction kinetics study of asymmetric polymer–polymer interface

In this study, the reaction kinetics of asymmetric polymer–polymer interface was experimentally and theoretically studied. A new rheological method correlating the change of rheological property of reactive system with the conversion of the in situ formed copolymers was applied to study the reaction kinetics of PBT/epoxy reactive system. Then, the new method was proved to be useful by comparing its results with that obtained from the conventional endgroup determination method. Moreover, the conversion of PBT/epoxy reactive system from rheological method could be well fitted by the numerical analysis, from which the kinetic constant and the diffusion constant of epoxy in PBT could be determined simultaneously.

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)–N H–C(O)CCl 3 from C(O)OH, δ∼8–9 for O–C(O)–N H–C(O)CCl 3 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).

Study on the reaction kinetics between PBT and epoxy by a novel rheological method

In the present study, the reaction kinetics of polybutylene terephthalate (PBT) and epoxy system was studied by a novel rheological method. The reaction process was determined by rheological test and the results showed that there were three stages in the reaction between PBT and epoxy, which were reaction-controlling stage (stage I), reaction-stagnation stage (stage II) and diffusion-controlling stage (stage III). In addition, the stage I was selected to study the reaction kinetics by the rheological method. The results showed that the reaction between PBT and epoxy could be classified as a pseudo-first-order reaction due to the excessive amount of epoxy group. Furthermore, the reaction apparent activation energy of the stage I determined by the rheological method was 143 kJ/mol. To confirm these results, the reaction kinetics was also evaluated by the endgroup determination method, and the results showed that the reaction could also be classified as a pseudo-first-order reaction. Moreover, the apparent activation energy of the reaction was 116 kJ/mol, which was similar to that of the value obtained by the rheological method.

Determination of acid and hydroxyl end-groups in endfunctionalized polystyrenes using 19F NMR

Abstract Carboxyl-terminated polystyrene was esterified with 2,2,2-trifluoroethanol using a carbodiimide-mediated room temperature reaction, and hydroxyl-terminated polystyrene was fluoro-derivatized with trifluoroacetic anhydride. The soformed fluorine-containing esters were then quantitatively determined with 19F NMR, using α,α,α-trifluorotoluene as secondary standard. This provides a technique for the reliable determination of carboxylic acid and hydroxyl groups in small samples of polymers.

Design and synthesis of processible functional copolymers

Novel tailor-made AB, ABAC, and ABAA type heteroaromatic copolymers, in which B represents an N-alkylpyrrole unit, were synthesized via Pd-catalyzed Stille polymerization and characterized by a variety of analytical techniques. MALDI-TOF mass spectrometry allowed the detailed characterization of polymer weight and determination of end groups. By varying the nature of the repeating monomer units and their sequence, copolymers with promising properties for photovoltaic devices could be obtained.

End-group determination of oligosaccharides: a gas chromatography–mass spectrometry/mass spectrometry method for distinguishing between all d-aldohexoses and d-ketohexoses

A method for end-group determination of oligosaccharides is described, which involves conversion of the reducing monosaccharide into a 1-deoxy-1-hydrazinohexitol heptaacetate (aldohexoses) or an epimeric pair of 2-deoxy-2-hydrazinohexitol heptaacetates (2-ketohexoses). Products are linear and unique to each aldohexose or ketohexose. Methods are reported for separation of all stereoisomers of the derivatives on single columns by gas chromatography. Gas chromatography–mass spectrometry/mass spectrometry with electron-impact ionization enabled the 1-deoxy-1-hydrazinohexitol heptaacetates and 2-deoxy-2-hydrazinohexitol heptaacetates to be independently identified in each others presence. Chemical-ionization mass spectrometry/mass spectrometry permitted derivatives to be identified in subpicomolar quantities. The non-acetylated compounds could also be identified as their hydrochlorides by 1H NMR spectroscopy.

Endgroup determination of synthetic polymers by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization (ESI) was performed on a Fourier transform ion cyclotron resonance mass spectrometer for the endgroup and monomer mass determination of three poly(oxyalkylene)s in the mass range of 400–8000 Da. A combined use of the multiple charge states observed with ESI, leads to a threefold increase in accuracy of the endgroup and monomer determination. The improvement is attributed to the increased number of datapoints used for the regression procedure, yielding more accurate results. Endgroup masses are determined with a mass error better than 5 and 75 millimass units for the molecular weight range of 400–4200 and 6200–8000 Da, respectively. A mass error of better than 1 millimass unit was observed for all monomer mass determinations. With ESI, endgroup and monomer masses have been determined for poly(ethylene glycol) oligomers with a mass higher than 8000 Da. This is almost two times higher than observed with matrix-assisted laser desorption/ionization on the same instrument.

Determination of End Groups in Thermoplastic Addition Polymers by Oligomer Separation and Characterization

Low-molecular-weight fractions have been isolated from polystyrene, poly(vinyl chloride) and high-density polyethylene (HDPE) by fractionation methods. These fractions were subjected to high-performance gel permeation chromatography (HPGPC) to separate individual oligomer species. Repeated injection of fractions and collection of the individual oligomers allowed characterization by nuclear magnetic resonance spectroscopy and mass spectroscopy. Structures for end groups in these oligomers have been deduced, and shown to be consistent with polymerization mechanisms for the formation of each addition polymer. An example of an HPGPC procedure is provided for quantifying the concentration of an oligomer in HDPE by a standard addition method.

Hydrogenation of low‐molar‐mass, OH‐telechelic polybutadienes. II. Nuclear magnetic resonance and infrared spectrometric determination of hydroxyl end groups before and after hydrogenation by diimide

Hydrogenation of low‐molar‐mass, OH‐telechelic polybutadienes. II. Nuclear magnetic resonance and infrared spectrometric determination of hydroxyl end groups before and after hydrogenation by diimide

Hydrogenation of low-molar-mass, OH-telechelic polybutadienes. II. Nuclear magnetic resonance and infrared spectrometric determination of hydroxyl end groups before and after hydrogenation by diimide

1H nuclear magnetic resonance (1H-NMR), 13C-NMR, and infrared spectroscopies were used to determine concentrations (cOH, in mmol/g) of the secondary hydroxyl end groups in the low-molar-mass, OH-telechelic polybutadienes, and their hydrogenated analogs. Mean OH-functionality (fOH ≤ 2), that is, an average number of OH groups per one polymer chain, was calculated from cOH for each sample and each method, and the results were compared with those obtained by a conventional acetic anhydride titration method. It has been found that with molar masses of the samples studied (2310 to 3410 g/mol), the differences between individual spectrometric methods are usually not higher than approximately 10%, which corresponds to an expected relative experimental error. Certain differences in fOH between individual methods are discussed. No systematic change of fOH after virtually total hydrogenation of the olefinic double bonds of the polymeric substrate by diimide was observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3214–3224, 1999

Gel Permeation Chromatography Coupled to Fourier Transform Mass Spectrometry for Polymer Characterization

We report an on-line coupling of gel permeation chromatography (GPC) to Fourier transform mass spectrometry (FTMS) using a modified commercial electrospray ionization (ESI) interface. Selected oligomer profiles for the sodiated (1+ through 5+ charge states) oligomer ions of a narrow-molecular-weight poly(methyl methacrylate) were generated and used for obtaining a calibration curve. Using the MS-generated calibration curve and the refractive index response for quantification, an accurate molecular weight distribution was calculated and showed an excellent agreement with the value specified by the supplier. GPC/ESI/FTMS also allowed for an unequivocal end-group determination and characterization of a secondary distribution due to the formation of cyclic reaction products. We analyzed a glycidyl methacrylate/butyl methacrylate copolymer with a broad molecular weight distribution, where fractionation and high resolving power were required for adequate characterization. Molecular weight distribution data showed the advantage of coupling high-resolution MS and GPC to overcome the difficulty of analyzing polydisperse polymers with MS alone.

Cinétique de polymérisation radicalaire de (méth)acrylates à chaîne latérale fluorée

The radical polymerization of acrylates and methacrylates bearing a perfluorinated chain with an α,ω-bistrichloromethyled or an α,ω-dibenzylic azo initiator is presented. These initiators were synthesized in two or three steps in 40–50% overall yields. Molecular weights of the fluorinated polymers were determined from various methods by taking into account the behavior of these monomers in the termination step (recombination or disproportionation). These methods consisted in the titration of the chlorine content by elemental analysis or from 1H NMR by the determination of the aromatic end-groups. Although the determination of the chlorine content led to a lack of accuracy, the aromatic initiator enabled one to assess the molecular weights of the fluoropolymers produced. From the characteristic kinetic constants, the kinetics of homopolymerization of these methacrylates contributed to a simulation of these reactions which allowed one to compare the theoretical molecular weights to the experimental ones.

Determination of End Groups of Synthetic Polymers by Matrix-Assisted Laser Desorption/Ionization: High-Energy Collision-Induced Dissociation

Matrix-assisted laser desorption/ionization has been combined with high-energy collision-induced dissociation for the analysis of poly(ethylene glycols) with butanoyl, benzoyl and acetyl end groups, using novel technology comprising a magnetic-sector mass spectrometer and ion buncher with an in-line quadratic-field ion mirror. High-energy (>8 keV) collision-induced dissociation facilitated unambiguous end-group determination of these polymers, providing masses of end groups and structural information. The high-energy collision-induced dissociation also provided information regarding repeat units.

Accurate end group determination of low molecular weight polymers by electrospray ionization time-of-flight mass spectrometry

A method is described for the identification of monomers and end groups in low molecular weight synthetic polymers using electrospray ionization and an orthogonal accelerated time-of-flight mass spectrometer. Thanks to the high mass accuracy the elemental composition of the monomer and end group of an unknown alkylated poly(ethylene oxide) was determined with an error of 1 mDa. The present method compares well with literature data for polymer characterization by Fourier transform ion cyclotron resonance mass spectrometry and might be a simple alternative provided that the inherent lower resolution is not critical.

Polymer Analysis by Liquid Chromatography/Electrospray Ionization Time-of-Flight Mass Spectrometry

Hyphenation of liquid chromatography (LC) techniques with electrospray ionization (ESI) orthogonal acceleration time-of-flight (oa-TOF) mass spectrometry (MS) provides both MS-based structural information and LC-based quantitative data in polymer analysis. In one experimental setup, three different LC modes are interfaced with MS: size-exclusion chromatography (SEC/MS), gradient polymer elution chromatography (GPEC/MS), and liquid chromatography at the critical point of adsorption (LCCC/MS). In SEC/MS, both absolute mass calibration of the SEC column based on the polymer itself and determination of monomers and end groups from the mass spectra are achieved. GPEC/MS shows detailed chemical heterogeneity of the polymer and the chemical composition distribution within oligomer groups. In LCCC/MS, the retention behavior is primarily governed by chemical heterogeneities, such as different end group functionalities, and quantitative end group calculations can be easily made. The potential of these methods and the benefit of time-of-flight analyzers in polymer analysis are discussed using SEC/MS of a polydisperse poly(methyl methacrylate) sample, GPEC/MS of dipropoxylated bisphenol A/adipic acid polyester resin, LCCC/MS of alkylated poly(ethylene glycol), and LCCC/MS of terephthalic acid/neopentyl glycol polyester resin.

Polymer Analysis by Micro-Scale Size-Exclusion Chromatography/MALDI Time-of-Flight Mass Spectrometry with a Robotic Interface

Polydisperse synthetic polymers cannot be characterized reliably by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI MS) alone. Coupling of size-exclusion chromatography (SEC) with MALDI MS provides both absolute mass calibration of the SEC column based on the polymer itself and determination of monomers and end groups from the mass spectra. Now a micro-scale SEC (μSEC) system has been developed in which the MALDI matrix solution is coaxially added to the column effluent and directly spotted onto the MALDI targets in a robotic interface. Each spot corresponds with a 10-s elution window from the μSEC column, thus yielding a narrow polymer distribution which is amenable to characterization by MALDI MS. This μSEC/MALDI MS system is less laborious and time-consuming and features very low solvent consumption and reduced solvent emission during the evaporation step as compared to the conventional-sized SEC/fraction collector systems applied in the past. The performance is demonstrated by the characterization of a polybisphenol A carbonate and a complex dipropoxylated bisphenol A/adipic acid/isophthalic acid copolyester resin.

RNA analysis. Size and 3' end group determination.

The most commonly used method to analyze the quality of RNA is electro-phoresis in agarose gels. The distance an RNA molecule moves in a gel is dependent both on its mol wt and its conformation. Hence, to accurately compare RNAs across virus groups or to determine their size, it is crucial to completely denature the sample. Formaldehyde was the first denaturant to be used for this purpose () and is still a popular choice. Other reagents that denature but do not degrade RNA include formamide, which destroys base pairing, and glyoxal (ethanedial). Glyoxalation introduces an additional ring into guanosine residues, which then sterically hinders GC-pair formation. The first method described here incorporates formaldehyde in the gel and is adapted from Lehrach et al. (). The second approach, which is based on the method of McMaster and Carmichael (), uses glyoxal to denature the sample prior to loading it onto a nondenaturing gel. The latter technique has the advantage of allowing native (nondenatured) RNA to be run on the same gel as denatured RNA.