Telechelic ionomers

Telechelic Ionomers. Low molecular weight polymers terminated by acid groups have been treated with metal bases to give ionomers in which the cations can be considered as connecting links in the backbones (67—71). The viscoelastic behavior of concentrated solutions has been linked to the neutralizing cation. 

Figure 10.16 A schematic representation of the morphology of a telechelic ionomer where (1) represents the ion-containing core, (2) an immobilised interfacial layer and (3) a phase containing network chains, dangling chains and free chains [153]...

The most important ionic groups are carboxylates and sulfonates, but other groups like ammonium have also been reported. " Special classes of ionomers are zwitterionic ionomers, which contain both cationic and anionic groups, as well as ionomers with regular architectures like block ionomers, mono- or telechelic ionomers, star ionomers, or ionenes, which have regularly spaced ionic groups. ... 

Small domains of high electronic density have been imaged in halato-telechelic ionomers by Scanning Transmission Electron Microscopy (STEM) using the technique of atomic number or Z-contrast. The possibility that these are ionic domains is evaluated and the morphology compared with that derived from recent SAXS experiments. 

A specialty class of carboxyl containing elastomers are the telechelic ionomers. In these systems the carboxyl functionality terminates both ends of the polymer chain. Such polymers range in molecular weight from 1500 to about 6000. These materials can be prepared via several synthetic routes involving anionic or free radical initiated polymeri-zation(32-34). Recently, telechelic sulfonate ionomers of poly-isobutylene have been synthesized(35). These systems offer an unusual opportunity to assess the influence of chain length, chain architecture, cation type, and the Influence of polar additives on ionomer properties. 

Stieber, F. and Eicke, H.-F. (1996) Solution of telechelic ionomers in a water/AOT/oU (w/o) microemulsion A static and dynamic light scattering study. Colloid Polym. Sci., 274, 826-835. 

More recently, in addition to random ionomers, telechelic ionomers in which ionic groups are located only at the chain end(s) became available and were used for the study of polyelectrolyte behavior [26-29]. Discussion was made from the point of view that the behavior of telechelic ionomers in nonaqueous solutions is basically similar to that of polyelectrolytes in aqueous/nonaqueous solutions (including random ionomers in nonaqueous solutions). Also, the study of fundamental aspects of polyelectrolytes was made possible because of the simplicity of the structure of telechelic ionomers. For example, telechelic ionomers with only one ionic group at the chain end can be used to study the role of intermolecular interactions, since there is no intramolecular electrostatic interaction available for this type of ionomer [27]. Due to space limitations, this chapter will only cover polyelectrolyte behavior of random ionomers in polar solvents. Some results on telechelic ionomers can be found elsewhere [26-29]. 

Random ionomers having very small ion contents (e.g., 0.3 mol% for a 400,000 molecular weight PS) and telechelic ionomers show some deviations from the behavior noted herein. Although these deviations are of interest in studies of the essential features of polyelectrolyte behavior of ionic polymer solutions, we have limited our discussion to typical random ionomers (having an ion content of over 1.0 mol%). 

Hara M, Wu J, Jerome RJ, Granville M. Salt-free polyelectrolyte behavior of halato-telechelic ionomers in polar solvent. Macromolecules 1988 21 3330-3331. 

Kupperblatt G. A comparison of the polyelectrolyte behavior of random and telechelic ionomers in solution. Ph.D. dissertation, Rutgers University, New Brunswick, NJ, 1995. 

Interesting polymeric materials such as thermoplastic elastomers based on PIB, associative amphiphiles based on poly(vinyl ethylene) (PVE), and telechelic ionomers have been prepared by cationic polymerization. A major drawback of cationic polymerization is the fact that in order to avoid termination and chain transfer reactions, the whole procedure has to take place at very low temperatures from -80 °C down to-100°G. 

Telechelic ionomers are a special class of ionic polymers in which the charged groups are situated exclusively at the chain ends (see Telechelic Polymers (85,86)) Accordingly, their solid-state structure is characterized by self-assembly of the chain ends into ion multiplets or ionic clusters. Because of this defined... 

Fig. 11. Structure of the anionic spin probe K-TEMPO and schematic structures of telechelic ionomers. Solid lines denote polystsrene blocks, while dotted lines denote poly-isoprene blocks.

Fig. 12. Ionic clusters in telechelic ionomers based on diblock copolsmiers (see also Fig. 11). (a) Spin probes attached to ionic clusters located at the interface between the polystsrrene (PS) and polyisoprene (PI) microphases. The inset shows the CW ESR spectrum for PS-Q-PI, where Q is a quaternary ammonium group. The fast component (arrows) was assigned to probes in the PI microphase, (b) The distribution of ionic clusters in monoionic diblock copolymers suggested by DEER experiments, (c) The distribution of ionic clusters in zwit-terionic diblock copolymers suggested by DEER experiments.

Another technique that makes use of the tuneability of SR sources is x-ray absorption spectroscopy (xas) (2). This is relatively rarely used in pol5uner research. One of the few examples found in the literature deals with halato-telechelic ionomers (40). These are short linear chains selectively terminated by a metal car-boxylate or sulfonate ionic group. The local order of these groups could be determined by using extended x-ray absorption spectroscopy (exafs). More work using this technique applied to ionomer morphology is reported (41). 

Figure 2. (a) Ring opening polymerization of trimethylene carbonate initiated from butane diol and catalyzedfrom stannous octanoate. (b) Three different telechelic ionomers, anionomer, cationomer and zwitterionomer. 

Loveday D et al (1997) Investigation of the structure and proptalies of polyisobutylene-based telechelic ionomers of narrow molecular weight dis tribution.2. Mechanical. J Appl Polym Sci... 

A special class of ionomers in which the functional groups are situated at chain ends are telechelic ionomers. The technique used for their synthesis... 

In this study, (o- and a,o)-carboxylic add-functional PLA were synthesized using a chemical recycling process with reagents from renewable resources. The chemical reQrcling process involves a transesterificafion reaction between commerdal PLA and monomers containing hydroxyl groups [9]. The functionalized PLA was nmtralized with metal acetates of various valencies (Na lT, K, Ca, TsP, Y ). This proach produced PLA-based telechelic ionomers. The effect of ion concentration, metal cation valency and the location of the ioiuc moieties on the thermal and mechanical properties of the PLA ionomer are discussed in this paper. 

The T , of the oo- and a,(o-(metal carboxylate) PLAs increased with q/a, see Figure 6. The increase in T is believed to be due to nucleation of the PLA by the ionic groups, and that effect was more apparent in the oo-telechelic ionomer. For the a,(o-(metal carboxylate) PLA, the Zn and Y species did not exhibit a melting endotherm. The heat of fusion of co-(metal carboxylate) PLA increased slightly compared to the parent carboxylic acid-functionalized PLA. However, the heat of fusion for the o,(o-(metal carboxylate) PLA deereased, which suggests that crystallization is suppressed by the metal carboxylate groups when situated on both ends of the chains. This may be a kinetic effect, due to the inereased viscosity of the o,(o-telechelic ionomer. 

The ion concentration and the choice of the coimter-ion affected the thermal behavior of the PLA ionomers. The Tg of the PLA ionomers was dependent on the strength of the ionic interactions, q/a. The location of the metal carboxylates on the PLA backbone had different effects on crystallization, fn the case of the o)-(metal carboxylate) PLA, crystallization was promoted by a higher ion concentration. However, for the a,o)-telechelic ionomers, higher ion concentration hindered crystallization, probably due to the higher melt viscosity. 

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