Effect of oligomers extraction in polycondensation reactions on number and weight average degree of polymerization

doi:10.1016/S0014-3057(02)00060-5

European Polymer Journal

Volume 38, Issue 9, September 2002, Pages 1925-1927

https://doi.org/10.1016/S0014-3057(02)00060-5 Get rights and content

Abstract

In many polycondensation reactions, the isolated polymer does not contain molecules with low degrees of polymerization. The absence of oligomers affects significantly the average degrees of polymerization, the number-average value, $X_{n}$ , in particular. Using the Flory theory of linear polycondensation, formulas have been derived for the calculation of the number-average and weight-average degree of polymerization, $X_{n}$ and $X_{w}$ , respectively, as a function of the extent of reaction, p, and the minimum degree of polymerization of molecules present in the polymer.

Introduction

The kinetics of linear polycondensation reactions can be properly described according to the Flory theory [1]. Based on this theory, the number-average, $X_{n}$ , weight-average, $X_{w}$ , degree of polymerization and distribution function of degrees of polymerization of the final polymer product as a function of the extent of reaction, p, are widely used for polymer characterization. The extent of reaction is simply measured by the amount of the by-product [2], [3], [4], [5] or by calculating $X_{n}$ assuming one type of end groups per chain [6], [7], [8]. At higher polymerization temperatures, however, degradation reactions can change the amount of end groups [9], [10] and affect the $X_{n}$ value calculated only on the basis of p values derived from the number of polymer end groups. In such cases, it is desirable to use also a direct method for $X_{n}$ determination which is independent of the type and amount of end groups. Bulk, melt or solution polycondensation of aromatic polyesters and polyamides yield mostly crystalline, insoluble materials where $X_{n}$ can be assessed only from p calculated from the amount of by-product [11], [12], [13], [14] because direct methods for the determination of the degree of polymerization, using dilute polymer solutions, are not operative. If, in such case, $X_{n}$ and $X_{w}$ are calculated through the p value, the results can be distorted because such procedure does not take into account the fact that, during solution polycondensation, the formed low-molecular-weight oligomers are removed by extraction from the polymer. The aim of this paper is to derive generalized equations for computation of real $X_{n}$ and $X_{w}$ values, taking into account both the p value and the absence of oligomers in the polymer. Such equations are not available in the open literature.

Section snippets

Problem formulation, results and discussion

$X_{n}$ and $X_{w}$ are defined as $X_{n} = ∑_{i=a}^{b} X_{i} N_{i} ∑_{i=a}^{b} N_{i}$ and $X_{w} = ∑ i=a b X_{i} m_{i} ∑_{i=a}^{b} m_{i}$ where X_i is the degree of polymerization of molecules of type i, N_i is the number of molecules of that kind, m_i is their mass fraction, and a and b represent minimum and maximum degrees of polymerization of macromolecules present in the polymer, respectively.

According to the Flory theory, the number of macromolecules of type i, N_i, and their mass fraction m_i are $N_{i} =N[p^{X_{i}−1} (1−p)]$ $m_{i} =X_{i} p^{X_{i}−1} (1−p)^{2}$ respectively; here N is the total

Conclusion

The Flory theory has been used to derive equations for computation of $X_{n}$ and $X_{w}$ values of the final polymer product of a polycondensation which take into account both the extent of reaction p and the extraction of oligomers from polymer. The absence of these components may significantly influence $X_{n}$ and $X_{w}$ . Thus, for precise determination of these molecular characteristics, equations derived in this paper should be employed rather than equations using only the p value for calculation.

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Studies of caprolactam and cyclic oligomer content, molecular weight, and thermal properties during melt post-polycondensation of polycaprolactam in the film state
2023, Polymer
In industrial application of polycaprolactam, the content of caprolactam monomer and oligomers, as well as their average molecular weight are the key factors. In this work, a liquid-chromatography/time-of-flight mass spectrometry (LC-TOF-MS) method and an advanced polymer chromatography/multi-angle laser light scattering/refractive index detector (APC-MALLS-RID) hyphenated technique have been developed as a quantitative analysis method for monomer and cyclic oligomers, and a means of determining the molecular weight of polycaprolactam. The melt post-polycondensation reaction characteristics of polycaprolactam films and the variation in monomers and cyclic oligomers (C2–C7) content have been systematically investigated. The results showed excellent repeatability and stability of quantitative test results on monomers and cyclic oligomers in polycaprolactam. The content of monomers and cyclic oligomers in the polycaprolactam decreased from 10.21% to 1.52% at 260 °C and 50 Pa for 60 min, and the average molecular weight increased from $1.53 \times 10^{4}$ g/mol to $2.36 \times 10^{4}$ g/mol. Additionally, the results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) experiments showed that the thermal stability and crystallization properties of polycaprolactam were improved after the film melt post-polycondensation reaction. Thus, this melt post-polycondensation method can realize the efficient removal of monomers and cyclic oligomers (compared with the traditional hot water extraction method) and afford high-quality polycaprolactam with high average molecular weight.
Facile synthesis of poly (carbonyl urea) oligomer (pcuo) from urea and dipropyl carbonate (dprc) applied as nitrogen slow-release fertilizers
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Short communicationEffect of oligomers extraction in polycondensation reactions on number and weight average degree of polymerization

Abstract

Introduction

Section snippets

Problem formulation, results and discussion

Conclusion

Principles of polymer chemistry

Polym Eng Sci

J Polym Sci Polym Chem

Macromolecules

Macromolecules

J Polym Sci Polym Chem

Macromolecules

Short communication
Effect of oligomers extraction in polycondensation reactions on number and weight average degree of polymerization