Competitive functionalization and chain scission on segmented polymers: chain length and chain length distribution in the reacted polymers

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Abstract

In the functionalization of segmented polymers at every junction site between the segments, chain scission is an unavoidable competitive reaction in most cases. The influence of the process selectivity on the weight and number average numbers of segments in the reacted polymer (Nw and Nn) was thus analysed as a function of the precursor characteristics such as its length (number of segment N0), its polydispersity (monodisperse or most probable distribution), the functionality of the short junction unit between the segments (number of reaction sites f=1 or 2). Simple relations of the type Nw=f(No,w,f,p) where p is the probability of chain scission for an elementary reaction are calculated for finite initial chains.

Introduction

In the course of our work on zwitterionomers [1] we were faced with the synthesis of segmented tertiary amine polymers by quantitative demethylation of a segmented ionene precursor according to the following scheme: where Nu, M+ is a nucleophilic organometallic reagent and PTMO a monodisperse poly(tetramethyleneoxide) segment (Mn×10−3∼2–8). If the dequaternization reaction is not perfectly selective—only N+–CH3 bond breaking—chain scission clearly occurs and may result in a very significant molecular weight decrease. Such a situation is not restricted to the previous case but it may be found or expected in many other chemical modifications of segmented polymers: see for instance the analogous demethylation of segmented polyurethanes zwitterionomers of the methylammoniopropanesulfonate type into the homologous sulfonate anionomers [2].

The main purpose of this communication is to thus analyze the influence of the reaction selectivity on the length (number of segments, N) and on the length distribution of a segmented chain after such a process involving two competitive reactions at every junction between the segments: one without chain scission and the other with chain scission.

Section snippets

Model definition

  • The open chain model consists of N0 monodisperse polymer segments (telechelic polymers of very narrow Poisson distribution may be easily obtained by “living” ionic polymerization for a number of monomers [3], [4], [5], [6]) separated by N0−1 reacting junction units of functionality f, f=1 or 2.

    Classical polycondensation between telechelic polymers [7] of identical length but not necessarily of identical chemical structure corresponds to a functionality f=1. Chain extension of telechelic

Case 1: monodisperse initial chains of functionality f=1

This rather academic case corresponds for instance to a well fractionated segmented precursor.

The statistical weight of a subchain comprising N units in the system after reaction reads:ZN0=1−pN0−1ZN=21−pN−1p+N0−N−11−pN−1p2forN<N0

By normalization, the first moment M1 gives the total amount of segments per initial chain, N0.

The means Nn and Nw are computed from the momentsMi=N=1N0NiZNthroughNn=M1M0andNw=M2M1

Straightforward calculations leads to:Nn=N0N0−1p+1N0N0p+1and:Nw=N0p2−p+21−p1−pN0−1N0p2

Conclusion

Continuously increased interest is currently devoted to functionalized segmented polymers: the very regular distribution of the functional unit along the chain may result in significantly improved or even in new specific properties with respect to those observed in the most usual statistical structures of identical functionalization density where unit distribution is already well known as a major factor of their physical and chemical properties [15]. In some scarce and highly favorable cases,

References (15)

  • R. Jérome et al.

    Progr Polym Sci.

    (1991)
  • Y. Tezuka

    Progr Polym Sci.

    (1992)
  • T. Hashimoto et al.

    Polymer

    (1994)
  • B. Grassl et al.

    Macromolecules

    (1995)
  • J.A. Miller et al.

    J Macromol Sci Phys

    (1983)
  • Nuyken O, Pask S. In: Mark HF, Bikales NM, Overberger CG, Menges G, editors. Encyclopedia of polymer science and...
  • P.V. Van Caeter et al.

    Trends Polym Sci.

    (1995)
There are more references available in the full text version of this article.
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