End-group Titration Research Articles

Polymerization of L‐leucineN‐carboxyanhydride with 1,6‐hexanediamine as initiator

AbstractL‐Leucine N‐carboxyanhydride was polymerized in N,N‐dimethylformamide (DMF) or 1,4‐dioxane (DIO) at 25°C with either 1,6‐hexanediamine (1) or its monocarbamate 2 using a constant volume apparatus, initially filled with nitrogen or carbon dioxide. Number average molar masses from amino end group titrations on one hand and from initial monomer/initiator ratios and conversions on the other were practically identical for monomer conversions between 25 and 79%, indicating both the living nature of the polymerization and a participation of all initially present amino groups, despite the fact that polymer precipitation was observed at higher conversions for all systems and an additional precipitation of the carbonate 2 for the system 1/DIO/CO2 at low conversions. Two kinetic stages were observed for the latter system, but three kinetic stages for all other ones. The absence of a rapid initial polymerization period for the system, 1/DIO/CO2 as contrasted to the high initial rates for the systems 1/DMF/CO2 or 1/DMF/N2 points towards a carbamate mechanism in the first case and an amine mechanism in the second. The relation between intrinsic viscosities and number average molar masses of poly(L‐leucine) in trifluoroacetic acid at 25°C was found as [η] = 0,0169 〈Mn0,86 ± 0,04 ml/g.

Biodegradable polymers for use in surgery — poly(ethylene oxide)/poly(ethylene terephthalate) (PEO/PET) copolymers: 2. In vitro degradation

The degradation mechanism of a series of poly(ethylene oxide)/poly(ethylene terephthalate) (PEO/PET) copolymers, synthesized as described in Part 1 1, has been studied in vitro. The need for the development of in vitro test methods for candidate biomaterials is set down. The effect of time, temperature, pH and selected enzymes on the rate and mechanism of degradation is elucidated. The degradation products are identified. The degree of degradation was monitored molecularly by gel permeation chromatography (g.p.c.) and end-group titration techniques. The composition of the copolymers was obtained using infra-red (i.r.) and nuclear magnetic resonance (n.m.r.) spectroscopy. Mass loss and water uptake data are also given. The mechanism of degradation is shown to be by hydrolysis. The effect of ethylene oxide (EO) and 60Co γ-irradiation sterilization on the copolymers was investigated.

The relation between the molecular weight and intrinsic viscosity of polymethyl acrylate

A series of unfractionated and fractionated samples of polymethyl acrylate of different low molecular weights have been prepared by homogeneous solution. polymerization in dimethyl formamide in presence of γ, γ'-azo-(γ-cyano-n-valeric acid) as initiator under a variety of conditions. The number-average molecular weights have been determined by end-group titrations and vapour pressure osmometry. The following [η]-M relationships for polymethyl acrylate have been obtained. [η] = 33.5 x 10−5M0.63 for unfractionated samples in benzene at 25 °C. [η] = 3.89 x 10−5M0.843 for fractionated samples in benzene at 35 °C.

The relation between the molecular weight and intrinsic viscosity of polyvinyl alcohol

A series of unfractionated and fractionated samples of polyvinyl acetate were prepared by homogeneous solution polymerization of vinyl acetate in N,N-dimethylformamide at 90 °C. in presence of γ, γ-azo-(γ-cyano-n-valeric acid) as initiator under a variety of conditions. A portion of each sample was hydrolysed to polyvinyl alcohol. The number average molecular weights have been determined by end-group titrations. The following molecular weight-intrinsic viscosity relationships for polyvinyl alcohol have been obtained. [η] = 33.88 X 10−5M0.716 — for unfractionated samples in water at 30 °C. [η] = 29.51 X 10−5M0.716 — for fractionated samples in water at 30 °C.

Synthese de substances macromoleculaires renfermant des motifs monomeres derives de colorants—XIX: Synthese d'oligoethers et d'oligoesters colores par structure

Oligo-oxyethylenes and oligo(oxyethylenes-Co-oxypropylenes) with hydroxy end-groups have been modified by nitration and amination of the end-groups; the modification was partial in some cases and complete in others. Amino end-groups have been diazotized and the oligomers with azo end-groups have been coupled with β oxynaphthic acid and N, N′diethylaniline. Oligomers with chromophoric and hydroxy groups in the chain have been used to prepare polyurethane foams. Structurally coloured polyesters have been synthesized similarly and used to prepare polyurethane elastomers. All these oligomers have been characterized by i.r. and visible spectroscopy, NMR, end-group titration, vapour pressure osmometry and thermal differential analysis.

Synthesis and studies of some organic poly(ammonium phosphate)s, 1

AbstractLong chain organic poly(ammonium phosphate)s (1a–g and 2) were prepared by a precipitation technique by reaction of poly(lithium phosphate) with organic ammonium salts. Their compositions were established by nitrogen and phosphorus analyses and their polymeric nature was confirmed by molecular weight determinations via end group titrations and by the viscosity method. Studies of conductance at different concentrations indicated their polyelectrolytic behaviour. Paper chromatographic studies supplied additional evidence of a long chain polymeric structure, like Graham's salt and poly(lithium phosphate).

Molecular weights and conductance studies of some organic poly(aminiumphosphate)s

Long chain poly(aminiumphosphate)s of general composition (BHPO3)n (where BH = organic cations) were prepared by precipitation technique. The composition was established by the analysis of these derivatives for N and P. The polymeric nature was confirmed by their molecular weight determinations by end group titration and viscosity methods. Conductance studies at different concentrations confirmed their polyelectrolytic behaviour.

Synthese et etude de poly (esters insatures- seq-ethers)—I. Preparation de poly (esters insatures- seq-ethers) par polycondensation en solution

The preparation of ωω′ bisfunctional oligoesters (unsaturated or not) is described. The oligoesters are characterised by NMR, end-group titration and tonometry. Their modification by transformation of acid to acid chloride end-group is reported. Their solution polycondensation with ωω′ dihydroxy polyethers is described. A statistical method has been used to optimize the reaction conditions. The properties of the poly (unsaturated esters-b-ethers) are studied. Examination by thermal differential analysis shows that the two blocks are compatible.

Relationship between molecular weight distribution and flow curves of poly-ϵ-caprolactam

Two series of linear poly-ϵ-caprolactams were synthesized in a range of molecular weights (12,000–42,000) and with different polydispersities ( M w/ M n— 1·55–2·00). Number and weight molecular weights were measured by three methods, viz, end-group titration, solution viscometry and gel permeation chromatography. Melt flow-behaviour was studied with a capillary rheometer and analysed in terms of existing theories of the flow behaviour of polydisperse polymers.

Some properties of poly‐α‐piperidone

AbstractThe high molecular weight polymer of α‐piperidone, which had been unobtainable with the use of alkali metal, trialkyl aluminum, or Grignard reagent as catalyst, was prepared with M–AlEt3, (where M is alkali metal), MAlEt4 or KAlEt3 (piperidone) as catalyst and N‐acyl‐α‐piperidone as initiator. From the determination of the behavior of the solution viscosity of poly‐α‐piperidone in m‐cresol at 30°C. the value of 0.27 for the Huggins constant was obtained. Examination of the correlation between the number‐average molecular weight, determined by endgroup titration, and the intrinsic viscosity gave a somewhat small value for the endgroup COOH. This may be considered due to the consumption of N‐acyl‐α‐piperidone by a propagating polymer in the course of polymerization. The thermal stabilities of the polyamides, nylons 4, 5, and 6, was in the order nylons 6 > 5 > 4 according to differential thermal and thermogravimetric analyses, Poly‐α‐piperidone, which has a reduced viscosity of 0.7, shows a melting point of 270°C.. which was expected from the zigzag pattern of the correlation between melting points and numbers of CH2 groups for polyamino‐acid polymers.

Grafting of single amino-acid units to polyhydroxy polymers

The reaction between N-carboxy anhydrides (NCAs) of amino acids and polymeric alkoxide derivatives of polyhydroxypolymers such as cellulose acetate in solution at ( A/ I) ratios of NCA to alkoxide⩽1 was investigated. Amino-acid derivatives of the polyhydroxypolymers were thus obtained in which essentially single amino-acid units were attached to the polymeric backbone through either their carboxyl or amino group, as seen from end group titrations. NCAs of α-amino acids and N-substituted α- and β-amino acids were used. The reaction at A/ I ratios between 1 and 4, led to the attachment of polypeptide side chains whose DP n was given by A/ I. The percentage terminal amino groups increased on increasing the A/ I ratio above unity. The results obtained may help to elucidate the initiation mechanism of the polymerization of NCAs by alkoxides; this has been a subject of controversy.

Molecular weight determination of polyamides by vapor pressure osmometry

AbstractThe vapor pressure osmometry method for determining the molecular weight of polyamides has been studied by use of the newly developed solvents. Polymers used were polycaprolactams, polyenanthamides, and polypelargonamides. The measurements were carried out with 2,2,3,3‐tetrafluoro‐1‐propanol and 2,2,3,3,4,4,5,5,6,6,7,7‐dodecafluoro‐1‐heptanol as solvents at 50 and 130°C., respectively. Endgroup determinations on samples were also done in m‐cresol by 0.1 N‐hydrochloric acid. Reduced resistance differences (ΔR/C)0 obtained by vapor pressure osmometry at 50°C. were found to be in linear relation with the reciprocal of the number‐average molecular weight determined by endgroup titrations; but anomalous results were obtained when dodecafluoroheptanol was used as the solvent at 130°C.

Studies in condensed phosphates. Part VIII. Complex potassium polymetaphosphates of calcium, zinc, and cadmium

AbstractDerivatives with the formulas [K4Ca(PO3)6]n, and [K4Cd(PO3)6]n have been prepared by heating together mixtures of KH2PO4, CaO, (or ZnO or CdO), and (NH4)2HPO4 in the mole ratio of 4 : 1 : 2 at 800°C. for 1 hr. The number‐average molecular weights of these derivatives have been measured by endgroup titration. Their conductance has been measured in aqueous solution of varying concentration, and their properties compared with those of Graham's salt and its complex derivatives prepared under similar conditions.

Separation of the oligophosphates

Mixtures consisting of orthophosphate, its linear polymers up to and including tridecaphosphate, and three cyclic polymers have been separated by ion-exchange chromatography. One of the cyclic polymers (found in polyphosphate glasses of − n ≅ 10) is probably pentametaphosphate. Its cyclic nature has been demonstrated by end-group titrations and by paper chromatography, but attempts to determine the number of phosphorus atoms in the ring failed because of the very small amount of the compound available. Evidence is presented in support of the common assumption that the linear phosphates above the tetramer are eluted in the sequence of their increasing degree of polymerisation.

Viscometric Studies of Solutions of Sodium Phosphates, Graham Salts and Vanadium-containing Graham Salts

Abstract The intrinsic viscosities of sodium orthophosphates, pyrophosphate, tripolyphosphate and Graham salts of relatively low molecular weight (lower than 10300) were measured. The relation between the intrinsic viscosity at 25.5°C and the average molecular weight measured by the end group titration was [η]=6.9×10−4×M0.61 in a 0.035 n sodium bromide solution, and [η]=0.0348+0.112×10−4×M in a 0.07 n sodium bromide solution. Vanadium-containing Graham salts (sodium vanadate-phosphate copolymers) seemed to be hydrolyzed immediately by the dissolution. The intrinsic viscosity of the solution was much smaller than that of sodium polyphosphate of the corresponding degree of polymerization. The rate of the hydrolysis of branched sodium polyphosphate was proportional to the number of branchings, and the rate constant was 0.39 hr−1 at 25.5°C.

Studies in condensed phosphates. Part II. Viscosities of simple and complex sodium metaphosphate solutions

AbstractThe viscosity‐average molecular weights M̄w of [Na4Ca(PO3)6]n and [Na4Ba(PO3)6]n polymers determined by Staudinger's equation in 0.0035N NaCl solution were found to be lower than their number‐average molecular weights M̄n determined by endgroup titration. The above anomaly has been shown to be owing to the effect of bivalent cations liberated in equilibria of the type: This has been further confirmed by measurments of M̄w by the light scattering method. In aqueous solutions the greater change in viscosity of [Na4Ca(PO3)6]n solution with dilution is also ascribed to the secondary dissociation of the polymeric anions at lower concentrations.

Studies in condensed phosphates. Part I. Sodium metaphosphates and their derivatives with calcium, barium, and zinc salts

AbstractDerivatives with the formulas [Na4Ca(PO3)6]n, [Na4Ba(PO3)6]n, and [Na4Zn(PO3)6]n have been prepared by heating together mixtures of NaH2PO4.2H2O, CaO (or Ba(OH)2.‐8H2O or ZnO), and (NH4)2HPO4 in the molar ratios of 4:1:2 at 700 and 800°C. for 1 hr. The number‐average molecular weights of these derivatives have been measured by the endgroup titration method. Their conductance has been measured in aqueous solution of varying concentration, and their properties compared with those of Graham's salt (NaPO3)n prepared under similar conditions.

The relationship between the molecular weight and intrinsic viscosity of polystyrene

AbstractThe polymerization of styrene using γ,γ′‐azo (γ‐cyano‐n‐valeric acid) as initiator was studied at 100°C. in DMF solution.It has been shown that the rate of polymerization is proportional to the square root of the initiator concentration and 3/2 power of the monomer concentration. The chain‐transfer constant for styrene radicals and dimethylformamide has been determined at 100°C., with the result Cs = 1.08 · 10−4.Several samples of polystyrene of low molecular weights (below the osmotic pressure range) were prepared under a variety of conditions in the presence of this initiator. Their molecular weights were determined by viscosity and end group titrations, both for fractionated and unfractionated samples. The results are compared with those obtained by other workers.

Effect of low-frequency ultrasonic waves on aqueous solutions of condensed phosphates

High-molecular metaphosphate undergoes a true fission when aqueous solutions are subjected to the action of ultrasonic waves of low frequency. There is a marked decrease in the viscosity which is permanent, and diminution in the end-group titration. The fission of the molecule is attended by a slight increase in the conductivity of the solution. There is also an increase in the pH. Practically the same amount of phosphate dialyzed out of the control and the irradiated solutions, indicating that, under the conditions of irradiation employed, low-molecular dialyzable compounds are not formed in significant quantities. The rate of degradation of metaphosphates increases with the increase in the weight-average molecular weight. Pyrophosphate, tri- and tetrapolyphosphates, and tri- and tetrametaphosphates do not undergo any significant degradative changes during ultrasonic irradiation. Estimation of orthophosphate by the isobutyl alcohol extraction method indicates that low-frequency ultrasonic irradiation does not split orthophosphate from metaphosphate.

A non‐hydrolytic polymerization of ϵ‐caprolactam. The polymerization initiated by hydrogen chloride

AbstractSome experiments are described which show that the polymerization of ϵ‐caprolactam (CL) can be accomplished by heating the lactam under anhydrous conditions in the presence of hydrogen chloride or of salts of strong acids and ammonia or amines at temperatures of 220–260°C. To study this type of polymerization more closely, two series of kinetic experiments with the sytem CL–HCl hae been performed (254°C.; initial molar ratios of HCl to CL, 0.025 and 0.0125). The progress of the reaction, characterized by the degree of conversion (determined by extraction of the unconverted lactam with water), is compared with the polymerization of CL initiated by corresponding amounts of water or of ϵ‐aminocaproic acid. The products obtained have been characterized by endgroup titration values and intrinsic viscosity. Some additional data have been obtained by chromatography and IR investigations. The titrations show that the molecules bear an amino group at one end of the chain; the nature of the other endgroup is still obscure. Reaction constants calculated for an uncatalyzed additon of CL to amino groups prove to be of about the same magnitude as those of the water‐initiated polymerization without additional HCl. At the same time some kinetic experiments with the system CLH2OHCl are presented. Both systems have some striking features in common. The catalytic effect of the HCl present in this system can be attributed to the rapid formation of amino groups in the very first moments of the reaction, thus leading to an enhanced rate of polymerization by addition of CL to amino groups.