A Comparison of Three Different Biodegradable Aliphatic Oligoesters (PGA,PLLA, and PCL) with Similar Linear Alkyl End Groups by DSC and SAXS

The biodegradable aliphatic oligoesters polyglycolide (PGA), poly(L-lactide) (PLLA), and poly(?-caprolactone) (PCL) with similar number-average molecular weight M_n values but different linear alkyl end groups [CH₃?[CH₂?CH₂]_m?CH₂?] were compared in terms of their physical properties, parameters such as melting temperature (T_m), crystallinity (x_i), long period (L), and lamella thickness (D). They were analyzed by DSC and SAXS. The effect of a longer and nonpolar alkyl end group such as docosyl [CH₃?[CH₂?CH₂]₁₀?CH₂?] on the long period (L) was more evident for PCL because it was the most nonpolar species in the family of oligoesters analyzed.     

X-ray scattering from the long spacing of completely crystalline oligoethylene glycol di-n-alkyl ethers

Completely crystalline samples of oligoethylene glycol di-n-alkyl ethers, H(CH₂)_nO-(CH₂CH₂O)_m(CH₂)_nH, where m is 9 or 15 and n is in the range 12-18, were orientated in capillaries by slow crystallization in a temperature gradient. X-ray scattering from the long spacings of the oriented samples, rotated continuously through 360°, was concentrated on the equator of a Debye–Scherrer photograph and many orders of reflection could be seen (e.g., up to order 30). The intensities of these reflections were analyzed by use of a model electron density distribution through the layer structure. Thus it was shown that the central oxyethylene block, in helical conformation, is oriented normal to the layer end plane, while the end alkyl bolcks, in planar zigzag conformation, are tilted relative to the layer end plane at an angle in the range 70°–64°.     

Maximum tensile properties of oriented polyethylene,achieved by uniaxial drawing of solution‐grown crystal mats: Effects of molecular weight and molecular weight distribution

The effects of molecular weight (MW) and MW distribution on the maximum tensile properties of polyethylene (PE), achieved by the uniaxial drawing of solution‐grown crystal (SGC) mats, were studied. The linear‐PE samples used had wide ranges of weight‐average (M_w = 1.5–65 × 10⁵) and number‐average MWs (M_n = 2.0–100 × 10⁴), and MW distribution (M_w/M_n = 2.3–14). The SGC mats of these samples were drawn by a two‐stage draw technique, which consists of a first‐stage solid‐state coextrusion followed by a second‐stage tensile drawing, under controlled conditions. The optimum temperature for the second‐stage draw and the resulting maximum‐achieved total draw ratio (DR_t) increased with the MW. For a given PE, both the tensile modulus and strength increased steadily with the DR_t and reached constant values that are characteristic for the sample MW. The tensile modulus at a given DR_t was not significantly affected by the MW in the lower DR_t range (DR_t < 50). However, both the maximum achieved tensile modulus (80–225 GPa) and strength (1.0–5.6 GPa), as well as those at higher DR_ts > 50, were significantly higher for a higher MW. Although the maximum modulus reached 225 ± 5 for M_n ≥ 4 × 10⁵, the maximum strength continued to increase with M_n even for M_n > 4 × 10⁵, showing that strength is more strongly dependent on the M_n, even at higher M_n. Furthermore, it was found that each of the maximum tensile modulus and strength achieved could be expressed by a unique function of the M_n, independently of the wide variations of the sample MW and MW distribution. These results provide an experimental evidence that the M_n has a crucial effect on the tensile properties of extremely drawn and chain‐extended PE fibers, because the structural continuity along the fiber axis increases with the chain length, and hence with the M_n. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 153–161, 2006     

Determination of ketorolac enantiomers in plasma using enantioselective liquid chromatography. Application to pharmacokinetic studies

Summary Residual synthetic adsorbent, cross-linked polystyrene, used in drug purification has been analyzed quantitatively by Curie-point pyrolysis gas chromatography. The peaks of intact polystyrene adsorbent in the pyrogram were used as key peaks for quantitative measurement of residues of the adsorbent in vitamin B₁ and streptomycin sulfate. It was shown that them-ethylstyrene orp-ethylstyrene peaks in the pyrolyzates were suitable for determination of polystyrene adsorbent content. The levels of residual adsorbent in the drugs were found to be <0.1 %, the value stipulated by the International Conference on Harmonization (ICH). In quantitative evaluation of an adsorbent content of 0.1 % the precision was 3.6 % and 2.7 % for vitamin B₁ and streptomycin sulfate, respectively.     

Using apparent molecular weight from SEC in controlled/living polymerization and kinetics of polymerization

Apparent molecular weights from size exclusion chromatography, that is molecular weights relative to standards of a nature different to that of the polymer sample being studied, are frequently used. We use calculations corresponding to realistic cases to provide guidelines for situations when, and to what extent, apparent molecular weights (MWs) can be meaningful. In controlled polymerization, we show how, without due care, use of apparent MW, could lead to the incorrect conclusion that the reaction was not controlled, whereas the true MWs would be close to theoretical values. We show here that the quality of the eluent as a solvent for the standard and the polymer sample is a good indication of the accuracy and the significance of the apparent polydispersity index. Accurate Mark–Houwink–Sakurada parameters are of limited availability, but the data about solvent quality available in handbooks or available from static light scattering measurements. Apparent M_n is of no use in controlled polymerization if simple simulations as performed in this work do not validate their use. The determination of transfer constants by the Mayo plot can be performed using apparent M_n without introducing any significant error, contrary to apparent weight‐average molecular weight M_w or apparent ln number distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 897–911, 2008     

Modellrechnungen von Kraftkonstanten der Tetramethyl-Verbindungen (CH3)4−nM(CD3) n,M=Si,Ge, Sn,Pb

Fromthe experiemntal fundamental vibrational frequencies of (CH₃)₄ M, (CD₃)₄ M and (CH₃)₃ MCD₃,M=Si, Ge, Sn, Pb, and of (CH₃)₂Si(CD₃)₂ and CH₃Si(CD₃)₃ a transferable local symmetry type force field for (CH₃)_4–n M groups has been calculated. Applications involving differentM atoms and numbersn of CH₃ groups are presented.

     

Derivatization of fatty alcohol ethoxylate non‐ionic surfactants using 2‐sulfobenzoic anhydride for characterization by liquid chromatography/mass spectrometry

A derivatization procedure has been developed for the improved characterization of fatty alcohol ethoxylate non‐ionic surfactants by liquid chromatography/mass spectrometry. The end hydroxyl group of each surfactant species was converted into an oxycarbonylbenzene‐2‐sulfonic acid group with 2‐sulfobenzoic anhydride under mild conditions. The produced sulfonic acid group allows all species, including fatty alcohols and those with less than three ethoxylates, to be uniformly ionized by electrospray ionization (ESI) mass spectrometry. Both acid and base can be used as a mobile phase additive for liquid chromatography without affecting M_n and average ethoxylate values, although ion intensities are suppressed during the ESI process. The method was used to analyze seven commercial fatty alcohol ethoxylate non‐ionic surfactants, and the determined M_n and EO values were comparable with the results obtained by NMR. The relative ratio of different fatty alcohol based ethoxylates in a sample can also be determined using the summed mass spectral data. Copyright © 2009 The Dow Chemical Company     

Living polymerization of isobutyl vinyl ether by HI/I2 initiator in polar solvents

This study has shown a nearly perfect living polymerization of isobutyl vinyl ether (IBVE) to proceed not only in nonpolar media (e.g., n-hexane) but in relatively polar CH₂Cl₂ solvent, provided that the HI concentration is sufficiently high. The produced polymers had a nearly monodisperse molecular weight distribution (M _w/M _n ≤ 1.1); the number-average molecular weight (M _n) increased in direct proportion to IBVE conversion and its increase continued on the addition of a fresh feed of the monomer at the end of the polymerization. The use of a more polar medium (PhNO₂/CH₂Cl₂) or a lower HI concentration leads to chain transfer reactions, by promoting the ionic dissociation of the “nondissociated” living propagating species. The successful living polymerization by HI/I₂ in CH₂Cl₂ indicates a very strong interaction between the iodide anion and the growing end.     

Synthesis of poly(p‐phenylene) macromonomers and multiblock copolymers

Rigid‐rod poly(4′‐methyl‐2,5‐benzophenone) macromonomers were synthesized by Ni(0) catalytic coupling of 2,5‐dichloro‐4′‐methylbenzophenone and end‐capping agent 4‐chloro‐4′‐fluorobenzophenone. The macromonomers produced were labile to nucleophilic aromatic substitution. The molecular weight of poly(4′‐methyl‐2,5‐benzophenone) was controlled by varying the amount of the end‐capping agent in the reaction mixture. Glass‐transition temperatures of the macromonomers increased with increasing molecular weight and ranged from 117 to 213 °C. Substitution of the macromonomer end groups was determined to be nearly quantitative by ¹H NMR and gel permeation chromatography. The polymerization of a poly(4′‐methyl‐2,5‐benzophenone) macromonomer [number‐average molecular weight (M_n) = 1.90 × 10³ g/mol; polydispersity (M_w)/M_n = 2.04] with hydroxy end‐capped bisphenol A polyaryletherketone (M_n = 4.50 × 10³ g/mol; M_w/M_n = 1.92) afforded an alternating multiblock copolymer (M_n = 1.95 × 10⁴ g/mol; M_w/M_n = 6.02) that formed flexible, transparent films that could be creased without cracking. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3505–3512, 2001     

Living cationic polymerization of vinyl ether with a cyclic acetal group

The living cationic polymerization of 5‐ethyl‐2‐methyl‐5‐(vinyloxymethyl)‐1,3‐dioxane ( 1 ), a vinyl ether with a cyclic acetal unit, was investigated with various initiating systems in toluene or methylene chloride at 0 to ?30 °C. With initiating systems such as hydrogen chloride (HCl)/zinc chloride (ZnCl₂), isobutyl vinyl ether–acetic acid adduct [CH₃CH(OiBu)OCOCH₃]/tin tetrabromide (SnBr₄)/di‐tert‐butylpyridine (DTBP), and CH₃CH(OiBu)OCOCH₃/ethylaluminum sesquichloride (Et_1.5AlCl_1.5)/ethyl acetate (CH₃COOEt), the number‐average molecular weights (M_n's) of the obtained poly( 1 )s increased in direct proportion to the monomer conversion and produced polymers with relatively narrow molecular weight distributions [MWDs; weight‐average molecular weight/number‐average molecular weight (M_w/M_n) = 1.2–1.3]. To investigate the living nature of the polymerization with CH₃CH(OiBu)OCOCH₃/SnBr₄/DTBP, a second monomer feed was added to the almost polymerized reaction mixture. The added monomer was completely consumed, and the M_n values of the polymers showed a direct increase against the conversion of the added monomer, indicating the formation of a long‐lived propagating species. The glass transition temperature and thermal decomposition temperature of poly( 1 ) (e.g., M_n = 13,600, M_w/M_n = 1.30) were 29 and 308 °C, respectively. The cyclic acetal group in the pendants of the polymer of 1 could be converted to the corresponding two hydroxy groups in a 65% yield by an acid‐catalyzed hydrolysis reaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4855–4866, 2007     

Pyrolysis gas chromatography/mass spectrometry of polyvinylsilanes. Mass spectrometric characteristics of alkanes and alkenes containing two or more triorganosilyl substituents

Pyrolysis gas chromatography/mass Spectrometry was applied to the investigation of homopolymers obtained from trimethyl-, n-pentyldimethyl-, n-octyldimethyl- and trideuteromethyldimethyl-vinylsilanes. The electron impact-induced fragmentation of alkanes, alkenes and alkadienes containing two or more corresponding silyl substituents and resulting from pyrolysis of polymers was elucidated. The most characteristic fragmentation patterns of trimethylsilyl-substituted compounds are due to the loss of HSi(CH₃)₃ and Si(CH₃)₄ from M^+˙, the order of which depends on the presence or absence of a double bond in hydrocarbon chain. The same structural parameter determines the probability of the characteristic decomposition of n-alkyldimethylsilyl-substituted compounds through the loss of alkene and alkyl groups from the molecular ions.     

Intramolecular excited state complexes in trichromophoric model compounds for polyesters derived from 2,6‐naphthalenedicarboxylic acid and aliphatic glycols: experiment,rotational isomeric state model,and molecular dynamics

Steady‐state fluorescence was used to measure the ratio of emission intensities, denoted I_D/I_M, for excited state complexes and excited monomers of five trichromophoric compounds, 2‐naphthyl‐COO‐(CH₂)_m‐OOC‐2,6‐dinaphthyl‐COO‐(CH₂)_m‐OOC‐2‐naphthyl, m = 2–6. The linear aliphatic alcohols H(CH₂)_nOH, n = 1–7, as well as mixtures of ethylene glycol and methanol, were used to change the viscosity of the medium, η. The values of I_D/I_M depend on η and m. A Rotational Isomeric State model and Molecular Dynamics simulations were used for interpretation of the experimental results. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 253–266, 1999     

Living cationic polymerization of 2‐adamantyl vinyl ether

Living cationic polymerization of 2‐adamantyl vinyl ether (2‐vinyloxytricyclo[3.3.1.1]^3,7decane; 2‐AdVE) was achieved with the CH₃CH(OiBu)OCOCH₃/ethylaluminum sesquichloride/ethyl acetate [CH₃CH(OiBu)OCOCH₃/Et_1.5AlCl_1.5/CH₃COOEt] initiating system in toluene at 0 °C. The number‐average molecular weights (M_n's) of the obtained poly(2‐AdVE)s increased in direct proportion to monomer conversion and produced the polymers with narrow molecular weight distributions (MWDs) (M_w/M_n = ～1.1). When a second monomer feed was added to the almost polymerized reaction mixture, the added monomer was completely consumed and the M_n's of the polymers showed a direct increase against conversion of the added monomer. Block and statistical copolymerization of 2‐AdVE with n‐butyl vinyl ether (CH₂?CH? O? CH₂ CH₂CH₂CH₃; NBVE) were possible via living process based on the same initiating system to give the corresponding copolymers with narrow MWDs. Grass transition temperature (T_g) and thermal decomposition temperature (T_d) of the poly(2‐AdVE) (e.g., M_n = 22,000, M_w/M_n = 1.17) were 178 and 323 °C, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1629–1637, 2008     

Self-assembly of the pre-formed inclusion complexes between cyclodextrins and alkanethiols on gold electrodes

A new kind of self-assembled monolayer (SAM) formed in aqueous solution through the pre-formed inclusion complexes (abbreviated CD · C_n) between α, β-cyclodextrins (CDs) and alkanethiols (CH₃(CH₂)_n−1)SH, n = 10, 14 and 18) was prepared successfully on gold electrodes. High-resolution ¹H NMR was used to confirm the formation of CD · C_n. X-ray photoelectron spectroscopy, cyclic voltammetry and chronoamperometry were used to characterize the resulting SAMs (denoted as M_CD·Cn). It was found that M_CD·Cn were more stable against repeated potential cycling in 0.5 M H₂SO₄ than SAMs of CH₃(CH₂)_n−1SH (denoted as M_Cn), with a relative sequence of M_β−CD·Cn > M_α−CD·Cn > M_Cn. In addition, an order of blocking the electron transfer between gold electrodes and redox couples (both Fe(CN)³₆ and Ru(NH₃)³⁴₆) in solution, M_CD·C10 > M_CD·C14 > M_CD·C18, was observed. A plausible explanation is provided to elucidate some of the observations.     

Synthesis and reactions of cysteine‐based telechelic polymers

The radical polyaddition of N‐4‐vinylbenzoyl‐L ‐cysteine methyl ester (VCM) was carried out in the presence of 2,2′‐azobisisobutyronitrile (AIBN, 3 mol %) as an initiator in dimethyl formamide (DMF) with monomer concentrations of 0.5 and 1.0 M at 60 °C for 20 h under nitrogen atmosphere to afford the corresponding polymers [poly(VCM), PVCM] with number‐average molecular weights (M_n)'s of 5300 and 18,000 in 92 and 95% yields, respectively. The obtained polymers had a heterotelechelic structure with thiol and olefin end moieties. The radical polymerization of methyl methacrylate and trityl methacrylate was carried out in the presence of PVCM with AIBN (3 mol %) as an initiator in DMF at 60 °C for 20 h to afford the block copolymers with M_n values in the range of 13,000–26,800 in good yields. PVCM [M_n = 18,000; polydispersity (M_w/M_n) = 1.56] was treated with 4 equiv of NaOH aq. (1.0 M) to afford the polymer having carboxyl groups in the side chain with a M_n of 17,300 and M_w/M_n of 1.88 in 95% yield and was also oxidized to polysulfoxide and polysulfone with 4 equiv of H₂O₂ per sulfide unit in CH₂Cl₂ (1.0 M) for 20 h. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 23–31, 2001     

Viscosity–molecular weight relationship for fractionated poly(ethylene terephthalate)

Poly(ethylene terephthalate) was separated into 12 fractions of equal size by a stepwise increase in the amount of solvent in the two-phase liquid fractionation system of phenol-tetrachloroethane (PTCE) (1:1) and n-heptane. Various molecular weight parameters of the fractions were measured by osmotic pressure and gel-permeation chromatography. Intrinsic viscosity-molecular weight plots were made for three different solvents at 25°C. Mark-Houwink constants for viscosity-average molecular weight were measured and gave values of K of 2.50, 2.37, and 2.25 × 10^?4 dl/g and values of a of 0.73 for 1:1 PTCE, 3:2 PTCE, and o-chlorophenol, respectively. A comparison with the literature values for this polyester was made, and application of the Mark-Houwink equation to the determination of number-average (M _n) and weight-average (M _w) molecular weight of whole polymers is considered.     

Preparation of macromonomers by copolymerization of methyl acrylate dimer involving β fragmentation

The unsaturated dimer of methyl acrylate [CH₂C(CO₂CH₃)CH₂CH₂CO₂CH₃, or MAD] was copolymerized with various monomers to prepare copolymers bearing the ω-unsaturated end group [CH₂C(CO₂CH₃)CH₂ ] arising from β fragmentation of the MAD propagating radical. Copolymerizations of MAD with cyclohexyl and n-butyl acrylate resulted in copolymers with ω-unsaturated end groups, and increasing the temperature up to 180 °C resulted in an increase in the rate of β fragmentation of MAD radicals relative to propagation. Only a small amount of unsaturated end groups was introduced by copolymerization with ethyl methacrylate (EMA), and the EMA content in the copolymer increased with temperature. These findings could be explained by the reversible addition of the poly(EMA) radical to MAD. The copolymerization with ethyl α-ethyl acrylate (EEA) did yield a copolymer containing unsaturated end groups with MAD units as part of the main chain, although the steric hindrance of the ethyl group suppressed homopropagation and crosspropagation of EEA, resulting in low polymerization rates. Therefore, the copolymerization of MAD with acrylic esters at high temperatures was noted as a convenient route for obtaining acrylate–MAD copolymers bearing unsaturated end groups at the ω end (macromonomer). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 597–607, 2004     

Living carbocationic polymerization. IV. Living polymerization of isobutylene

Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate-BCl₃ complexes under conventional laboratory conditions in various solvents from ?10 to ?50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear M _n versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. DP _n obeys [IB]/[CH₃COOR^t · BCl₃]. Molecular weight distributions (MWD) are very narrow in homogeneous systems (M _w/M _n = 1.2–1.3) whereas somewhat broader values are obtained when the polymer precipitates out of solution (M _w/M _n = 1.4–3.0). The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at ?10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester. BCl₃ complexes most likely proceeds by a two-component group transfer polymerization.     

Study of the end‐group contribution to ToF‐SIMS and G‐SIMS spectra of poly (lactic acid) using deuterium labelling

In this study, polymeric (MW 50 000) and oligomeric (MW 2000) poly (lactic acid) (PLA), both with and without end‐group deuterium exchange, were analysed using static secondary ion mass spectrometry (SSIMS) to investigate the contribution of end‐group‐derived secondary ions to the SSIMS spectra. By monitoring the SSIMS intensities between the non‐deuterated and deuterated PLA, it is evident that the only significant end‐group‐derived secondary ions are [nM + H]⁺ (n > 1) and C₄H₉O₂⁺. The gentle‐SIMS (G‐SIMS) methodology was employed to establish that deuterated fragments were produced through low energy processes and were not the result of substantial rearrangements. It was noted that end‐group‐derived secondary ions had higher G‐SIMS intensities for oligomeric PLA than polymeric PLA, showing that these secondary ions are simple fragment products that are not the result of rearrangement or degraded product ions. Copyright © 2007 John Wiley & Sons, Ltd.     

Rapid and accurate determination of trace volatile sulfur compounds in human halitosis by an adaptable active sampling system coupling with gas chromatography

Halitosis with the main components of trace volatile sulfur compounds widely affects the quality of life. In this study, an adaptable active sampling system with two sample‐collection modes of direct injection and solid‐phase microextraction was developed for the rapid and precise determination of trace volatile sulfur compounds in human halitosis coupled with gas chromatography–flame photometric detection. The active sampling system was well designed and produced for efficiently sampling and precisely determining trace volatile targets in halitosis under the optimized sampling and detection conditions. The analytical method established was successfully applied for the determination of trace targets in halitosis. The limits of detection of H₂S, CH₃SH, and CH₃SCH₃ by direct injection were 0.0140–23.0 μg/L with good recoveries ranging from 82.2 to 118% and satisfactory relative standard deviations of 0.4–9.5% (n = 3), respectively. The limit of detections of CH₃SH and CH₃SCH₃ by solid‐phase microextraction were 2.03 and 0.186 × 10^?3 μg/L with good recoveries ranging from 98.3 to 108% and relative standard deviations of 5.9–9.0% (n = 3). Trace volatile targets in positive real samples could be actually found and quantified by combination of direct injection and solid‐phase microextraction. This method was reliable and efficient for the determination of trace volatile sulfur compounds in halitosis.