Number-average Molecular Weights Of Polymers Research Articles

Living metathesis polymerization of (p-n-butyl-o,o,m,m-tetrafluorophenyl)acetylene by MoOcl4-n-Bu4Sn-EtOH (1:1:1)

Possibility of living metathesis polymerization by Mo catalysts was examined for (p-n-butyl-o,o,m,m-tetrafluorophenyl)acetylene, which has two fluorine atoms at both ortho positions. The MoOCl4-n-Bu4Sn-EtOH (1:1:1) catalyst yielded a polymer with narrow molecular weight distribution (\(\left( {\bar M_{\text{w}} /\bar M_{\text{n}} = {\text{1}}{\text{.12}}} \right)\)), but the corresponding MoCl5-based catalyst did not formed such a polymer. With the former catalyst, the number-average molecular weight of polymer increased in direct proportion to monomer conversion, while the molecular weight distribution remained narrow; this proves the livingness of the polymerization. The optimal conditions for the living polymerization were [n-Bu4Sn]/[MoOCl4]=∼1.0, [EtOH]/[MoOCl4]=0.5–1.5, and temperature≤30 °C. n-Butyl acetate and acetone as well as EtOH were effective as third catalyst components.

Synthesis and characterization of hydroxy‐terminated poly(alkylene oxides) by condensation polymerization of diols

AbstractAcid‐catalysed condensation polymerization of 1,6‐hexanediol, 1,8‐octanediol and 1,10‐decanediol was carried out in the 150–190°C temperature range in the presence of sulphuric acid or Nafion‐H resin, and the polymerizations were monitored by size‐exclusion chromatography. The products were identified as hydroxy‐terminated poly(alkylene oxides) by 1H and 13C NMR and IR spectroscopy. The polymers were obtained in 66–81% yield from both catalysts in the polymerizations of 1,8‐octanediol and 1,10‐decanediol. With 1,6‐hexanediol the polymer yields were 30 and 42‐56% in the presence of Nafion and sulphuric acid, respectively. These low yields were due to the formation of oxepane as confirmed by gas chromatographic analysis of volatile condensation products. Vapour pressure osmometry showed the number‐average molecular weight of polymers to be in the range 700‐2400, depending on the reaction time and temperature. The hydroxy functionality of the poly(alkylene oxides) was 2.0 as determined by vapour pressure osmometry and 1H NMR spectroscopy.

Use of the fluorescence quantum yield for the determination of the number-average molecular weight of polymers of epicatechin with 4β→8 interflavan bonds

Excitation at 280 nm produces a structureless emission band with a maximum at 321–324 nm for dilute solutions of catechin, epicatechin, and their oligomers in 1,4-dioxane or water. The fluorescence quantum yield, Q, has been measured in these two solvents for five dimers, a trimer, a tetramer, a pentamer, a hexamer, and a polymer in which the monomer units are catechin and/or epicatechin. In a homologous series of monodisperse oligomers in which epicatechin units are connected by interflavan bonds with 4β→8 stereochemistry, Q is found to be inversely proportional to the degree of polymerization. Measurement of Q for a polydisperse sample of this polymer yields the number-average degree of polymerization.

Semi-batch polycondensation: a simplified polymerization model

In a previous paper the N + 1 non-linear differential equations ( N → ∞) which describe unsteady reversible polycondensation in a semi-batch reactor were shown to collapse to a three equation model that is rigorously applicable to non-equilibrium reacting mixtures. The collapsed model is shown to reduce further to a single linear differential equation yielding polymer number average molecular weight directly. Analytic solution for the case of a linear reduction in reactor pressure is presented, and the validity of the unsteady model is discussed.

Techniques of using osmotic membranes to determine the number-average molecular weight of polymers by a dynamic method

Techniques of using osmotic membranes to determine the number-average molecular weight of polymers by a dynamic method

Osmotic method of determining the number-average molecular weight of polymers

Osmotic method of determining the number-average molecular weight of polymers

Ebulliometric Apparatus for Studying Number-Average Molecular Weights of Polymers

Ebulliometric Apparatus for Studying Number-Average Molecular Weights of Polymers

Crosslink density in polybutadiene

AbstractThe crosslink density in polybutadiene has been determined by measurement of the polymer molecular weight by osmometry and the primary chain molecular weight by modifier analysis involving radioactive materials. Since the number of polymer molecules is equal to the number of primary chains less the number of crosslinkages, the experimental measurements may be used to calculated the crosslink density. This method can be used to determine crosslink density at a combination of conversions, modifier loadings, and polymerization temperatures which could not be done by other methods. Branching and cyclic structure forming crosslinks are not measured by this method, the principal assumption of which is that one and only one modifier fragment is attached to each primary chain. Initiation and termination processes tend to reduce the validity of this assumption, but these have been minimized by reduction of the amounts of initiator and found insignificant by comparison of different systems. Modifiers which react with polymer in nonterminal positions also reduce the validity so that primary dodecyl mercaptan was not satisfactory as a modifier in this work, while tertiary alkyl mercaptans were. Also, diisopropyl xanthogen disulfide was not satisfactory because of secondary reactions. The crosslink density of polybutadiene prepared in emulsion decreases with decreasing polymerization temperature. At a given molecular weight, the crosslink density does not appear to be a function of conversion within the range studied. At a given polymerization temperature, increasing polymer number average molecular weight was accompanied by increasing crosslink density although the rate of such increase was smaller at subfreezing polymerization temperatures. These results agree with kinetic theory of crosslinking in emulsion polymerization, but actual values are higher than those obtained in comparable systems by the gel point method.