Amount Of Cyclic Oligomers Research Articles

Composition of Water-Soluble Substances in Polyamide-6 Produced on a Cascade Polyamide Production Line

Long-term observations of the composition of unextracted granulate and extraction water generated during the industrial process for producing PA-6 on a Polymer Engineering cascade polyamide production line have shown that despite fluctuations in the process parameters for synthesis of PA-6, on this line the amount of cyclic oligomers exceeds the equilibrium value by a factor of 1.6-1.7 and remains practically constant. The amount of residual caprolactam, on the other hand, depends considerably on fluctuation in these parameters, in a number of cases turning out to be less than the equilibrium values as a result of entrainment of its vapor from the polycondensation reactors by the stream of inert gas. From the data obtained, it follows that during the cyclic oligomer extraction process under commercial conditions, cyclic oligomers with n e” 5 are not completely removed. Concentrations of cyclic oligomers in the polymer granulate that are systematically higher than the equilibrium values should be considered as evidence that they are formed in excess in the “oligomer splitting” stage, preceding the actual hydrolytic polymerization of caprolactam, and that they slowly disappear during the latter stage.

Polylactones 60: Comparison of the Reactivity of Bu3SnOEt, Bu2Sn(OEt)2, and BuSn(OEt)3 as Initiators of ϵ‐Caprolactone

Bu3SnOEt, Bu2Sn(OEt)2, and BuSn(OEt)3 were used as initiators of ring‐opening polymerizations of ϵ‐caprolactone conducted in 2 M solutions in chlorobenzene with monomer/functional group ratios of 50/1. Time‐conversion curves were recorded in the temperature range of 30–90°C. The reactivity of the initiators increased with the number of alkoxy groups attached to the tin atom. Analogous results were obtained with Bu3SnOMe and Bu2Sn(OMe)2. MALDI‐TOF mass spectra of the polyesters isolated after 98–99% conversion indicated the presence of small amounts of cyclic oligomers (up to 2000 Da) even at reaction temperatures as low as 30°C. Due to transesterification also broad molecular weight distributions were found.

Synthesis and polymerization of new self‐polymerizable quinoxaline monomers

AbstractExtended self‐polymerizable poly(phenylquinoxaline) monomer mixtures {i.e.,2‐[4‐(4‐hydroxyphenoxy)phenyl]‐3‐phenyl‐6‐chloroquinoxaline and 3‐[4‐(4‐hydroxy phenoxy)phenyl]‐2‐phenyl‐6‐chloroquinoxaline, 2‐[4‐(4‐hydroxyphenoxy)phenyl]‐3‐phenyl‐6‐fluoroquinoxaline and 3‐[4‐(4‐hydroxyphenoxy)phenyl]‐2‐phenyl‐6‐fluoroquinoxaline, and 2‐(4‐fluorophenyl)‐3‐phenyl‐6‐(4‐hydroxyphenoxy)quinoxaline and 3‐(4‐fluorophenyl)‐2‐phenyl‐6‐(4‐hydroxyphenoxy)quinoxaline} more flexible and nucleophilic than a previously reported monomer mixture [i.e., 3‐(4‐hydroxyphenyl)‐2‐phenyl‐6‐fluoroquinoxaline and 2‐(4‐hydroxyphenyl)‐3‐phenyl‐6‐fluoroquinoxaline] were synthesized. The monomer mixtures were then polymerized into high‐molecular‐weight polymers. A sample was obtained, through a chlorine displacement reaction, that was a semicrystalline polymer with an intrinsic viscosity of 1.11 dL/g in m‐cresol at 30 ± 0.1 °C and two melting temperatures at 339 and 377 °C in the first differential scanning calorimetry scan. There was a melting temperature at 328 °C without a detectable glass‐transition temperature (Tg) when the sample was subjected to a second differential scanning calorimetry scan. The samples from fluorine displacement reactions were completely amorphous polymers. They had intrinsic viscosities of 0.53–0.90 dL/g in m‐cresol at 30 ± 0.1 °C and Tg's of 220–224 °C. The polymer samples from fluorine displacement reactions were evaluated with gel permeation chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight analyses, which monitored the existence of certain amounts of cyclic oligomers. The thin films of the polymers had room‐temperature tensile strengths of 97–113 MPa, room‐temperature Young's moduli of 2.30–2.35 GPa, and room‐temperature elongations at break of 40–150%. The melt viscosity decreased from 107 to less than 104 Pa s at 310 °C as the frequency was increased from 10−2 to 102 rad/s. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 78–91, 2005

Computational study of metathesis degradation of rubber. distributions of products for the ethenolysis of 1,4-polyisoprene

The molecular modeling of the product distributions for the ethenolysis of 1,4-polyisoprene at 25 °C using the B3LYP/6-31G(d,p) level of theory reveals that chain–ring and chain–chain equilibria are completely shifted toward the formation of 2-methyl-1,5-hexadiene. The amount of cyclic oligomers at equilibrium with linear molecules is small. The concentration of 2-methyl-1,5-hexadiene at equilibrium with linear isoprene oligomers is of 90 mol%. The value of 1,5-hexadiene at equilibrium with butadiene oligomers for the ethenolysis of 1,4-polybutadiene corresponds to 46 mol%. These results are in agreement with experimental data.

Linear Addition Polymers and Cyclic Oligomers ofN,N-Diglycidyl Aniline and Amines. Uncrosslinked Epoxide-Amine Addition Polymers, 46

The addition polymerization of N,N-diglycidyl aniline (DGA) and disecondary diamines leads to linear addition polymers with molecular weights ranging from 2 500 to 9 100 Da respectively. Their relatively broad molecular weight distribution (M w /M n = 5.5 to 17) is caused by the formation of small amounts of cyclic oligomers. Surprisingly, the addition polymerization of primary monoamines and DGA results in the formation of oligomers only. These oligomers have molecular weights between 684 and 1 165 g.mol -1 . 13 C NMR spectra proof that during addition reaction no side-reaction took place and that the epoxide end groups were completely consumed. Obviously, the addition products mainly consist of cyclic oligomers. In the MALDI-TOF mass spectra cyclic oligomers of repeat units between n = 1 and n = 7 were observed. The kinetics of the addition polymerization can be described by both a formal model and the smallest necessary set of elementary reactions. In order to find the optimum parameters, the set of differential equations was solved numerically by multivariate non-linear regression. The perfect agreement between model calculations and experimental curves allows reliable predictions of the reaction behavior for arbitrary temperature-time profiles.

Electrochemical Polymerization of 1,10-Decanedithiol in CH3CN at Constant Current

Full Paper: The addition polymerization of N,N-diglycidyl aniline (DGA) and disecondary diamines leads to linear addition polymers with molecular weights ranging from 2 500 to 9 100 Da respectively. Their relatively broadmolecular weight distribution (M w /M n = 5.5 to 17) is caused by the formation of small amounts of cyclic oligomers. Surprisingly, the addition polymerization of primary monoamines and DGA results in the formation of oligomers only. These oligomers have molecular weights between 684 and 1 165 g.mol - 1 . 1 3 C NMR spectra proof that during addition reaction no side-reaction took place and that the epoxide end groups were completely consumed. Obviously, the addition products mainly consist of cyclic oligomers. In the MALDI-TOF mass spectra cyclic oligomers of repeat units between n = 1 and n = 7 were observed. The kinetics of the addition polymerization can be described by both a formal model and the smallest necessary set of elementary reactions. In order to find the optimum parameters, the set of differential equations was solved numerically by multivariate non-linear regression. The perfect agreement between model calculations and experimental curves allows reliable predictions of the reaction behavior for arbitrary temperature-time profiles.

Computational Study of Metathesis Degradation of Rubber, 3. Distribution of Cyclic and Linear Oligomers via Intermolecular Degradation of cis-Poly(butadiene)

The molecular modeling of the product distributions for the intermolecular metathesis degradation of cis-poly(butadiene) (cis-PB) in the presence of ethylene as chain-transfer agent (CTA) at 298.15 K using the B3LYP/6-31G (d, p) level of theory reveals that chain–ring and chain-chain equilibria are shifted toward the formation of 1,5-hexadiene. The amount of cyclic oligomers at equilibrium with linear molecules is negligible. The α,ω-vinyl-terminated butadiene oligomers–1,5-hexadiene equilibrium constant depends on the cis/trans isomer ratio in linear butadiene molecules. While the concentration of 1,5-hexadiene at equilibrium with cis-butadiene oligomers is 86 mol-%, this value for trans-butadiene oligomers corresponds to 50 mol-% of 1,5-hexadiene. The results of calculations are in reasonable agreement with recent experimental data on the intermolecular metathesis of 1,4-cis-PB with ethylene using a well-defined ruthenium alkylidene catalyst. The calculations predict that cis-butene as a CTA is more efficient in the metathesis depolymerization of cis-PB compared with ethylene.

Syntheses and characterization of poly (tetrahydrofuran) polyols with multifunctional oxocarbenium perchlorates as initiator

New oxocarbenium perchlorates, [(C2H5)(4-n)C(CH2OCH2CH2CO+ClO)n, n = 3, 4] were synthesized and used in the preparation of poly (tetrahydrofuran) (PTHF) polyols. The structures of PTHF polyols and corresponding hydrolysis products were determined by 1H-NMR and FTIR. GPC curves showed that the amount of cyclic oligomers was negligible. The polymerization process was followed by gas chromatography. Kinetic studies showed no termination reaction. The mechanism of the polymerization was discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3391–3399, 1999

Syntheses and characterization of poly (tetrahydrofuran) polyols with multifunctional oxocarbenium perchlorates as initiator

New oxocarbenium perchlorates, [(C2H5)(4-n)C(CH2OCH2CH2CO+ClO)n, n = 3, 4] were synthesized and used in the preparation of poly (tetrahydrofuran) (PTHF) polyols. The structures of PTHF polyols and corresponding hydrolysis products were determined by 1H-NMR and FTIR. GPC curves showed that the amount of cyclic oligomers was negligible. The polymerization process was followed by gas chromatography. Kinetic studies showed no termination reaction. The mechanism of the polymerization was discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3391–3399, 1999

Mechanism of Octamethylcyclotetrasiloxane Polymerization in the Presence of Siloxanediols

Polymerization of hexamethylcyclotrisiloxane (D 3 ) in CH 2 Cl 2 at 30°C, initiated by triflic acid (TfOH) was studied in the presence of siloxanediols (HD 2 OH or HD x OH) which polycondense giving water, or in the presence of water alone for comparison. D represents a siloxane unit OSiMe 2 . In the second case, the relative amounts of cyclic oligomers (D 6 , D 9 ) and of linear high polymer (HP) vary strongly with the molar ratio r = [H 2 O]/[TfOH]. When r increases from 1 to 100 (in homogeneous phase), D 9 /D 6 increases from 0.2 to 2 and D 6 /HP decreases from 1 to 0.3. The large decrease of D 6 amount and the increase in D 9 /D 6 are attributed to the suppression of their formation through oxonium ions and to their exclusive formation, for r > 100, by cyclization of silanol-esters, which is more rapid for HD 9 OTf than for HD 6 OTf. For polymerization of D 3 in the presence of HD 2 OH, there is a fast and limited ring-opening of D 3 (about 10% conversion over 6min) at the beginning, without formation of cyclics (D 6 , D 9 , etc). Then reaction with D 3 stops. Polymerization of HD 2 OH takes place simultaneously, at the same rate as in the absence of D 3 , with slow formation of high polymer. At the end of the polycondensation (after, eg, 4 h) D 3 polymerization starts again, giving D 6 , D 9 , etc, and HP. The inhibition period for D 3 is attributed to the complexation of triflic acid hydrates by silanol groups. These activated silanol groups do not react with D 3 . A comparison of D 3 polymerization with the addition of water, HD 2 OH or HD 15 OH leads to the conclusion that when r is not too large, propagation involves silylester end-groups, but that for large r ratios (100 or higher), it probably occurs mainly on silanol groups reacting with an activated monomer.

On the formation of permethylcyclopolysilanes in the w�rtz-type reaction of Me2SiCl2: The influence of solvent and complexing agent

Permethylcyclopolysilanes are most often prepared by Wurtz-type coupling of Me2SiCl2 with Na K alloy in THI: When nonpolar solvents like benzene were used, only linear polysilanes (Me2Si)n were produced, but the addition of a catalytic amount of crown ether 18-crown-6 was found to increase significantly the amount of cyclic oligomers. The ratio of (Me2Si)6 to (Me2Si)5 decreased from 18:1 to 6:1 in the presence of crown ether in a typical synthesis in THF. An explanation based on solvated electron theory has been proposed.