Crown Ether Copolymers

Most of the compounds in this class have been prepared from preexisting crown ether units. By far, the most common approach is to use a benzo-substituted crown and an electrophilic condensation polymerization. A patent issued to Takekoshi, Scotia and Webb (General Electric) in 1974 which covered the formation of glyoxal and chloral type copolymers with dibenzo-18-crown-6. The latter were prepared by stirring the crown with an equivalent of chloral in chloroform solution. Boron trifluoride was catalyst in this reaction. The polymer which resulted was obtained in about 95% yield. The reaction is illustrated in Eq. (6.22). 

An alternative copolymerization is illustrated by the method of Blasius. In this preparation, a phenol-formaldehyde (novolac) type system is formed. Monobenzo-18-crown-6, for example, is treated with a phenol (or alkylated aromatic like xylene) and formaldehyde in the presence of acid. As expected for this type of reaction, a highly crosslinked resin results. The method is illustrated in Eq. (6.23). It should also be noted that the additional aromatic can be left out and a crown-formaldehyde copolymer can be prepared in analogy to (6.22).  

A different variety of copolymer has been prepared by Gramain and Frere who treated 1,10-diaza-l 8-crown-6 with the bisglycidyl ether of bisphenol A. The reaction was conducted at reflux in a mixture of THF and methanol. The polymer, illustrated in Eq. (6.24) was formed 83% yield. The polymer was appparently quite stable, surviving aging tests conducted over a two-year period. 

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Although it has been known for many years that ethylene oxide and formaldehyde ean form statistical copolymers, it was not until the interest in crown ethers developed that the potential of macrocyclic formals as complexing agents was recognized. 

It may not be appropriate to compare the thermal stability characteristics of VC/VAc copolymer to that of a VC homopolymer (PVC). The copolymerization would involve different kinetics and mechanism as compared to homopolymerization resulting structurally in quite different polymers. Hence, copolymerization of VC with VAc cannot be regarded as a substitution of chlorines in PVC by acetate groups. To eliminate the possibility of these differences Naqvi [45] substituted chlorines in PVC by acetate groups, using crown ethers (18-crown-6) to solubilize potassium acetate in organic solvents, and studied the thermal stability of the modified PVC. Following is the mechanism of the substitution reaction ... 

Block copolymers of (R,S)-(3-butyrolactone and eCL have been synthesized by combining the anionic ROP of the first monomer with the coordinative ROP of the second one (Scheme 15) [71]. The first step consisted of the synthesis of hydroxy-terminated atactic P(3BL by anionic polymerization initiated by the alkali-metal salt of a hydroxycarboxylic acid complexed with a crown ether. The hydroxyl end group of P(3BL could then be reacted with AlEt3 to form a macroinitiator for the eCL ROP. 

Concerning the synthesis of graft copolymers, Jedlinski et al. have prepared poly(MMA-g-(3BL) copolymers via anionic grafting of 3BL from a modified PMMA backbone [85]. PMMA chains were partially saponified by potassium hydroxide and complexed by 18C6 crown ether so as to act as multifunctional mac-... 

The crown ether adopts a D3d conformation and is coordinated on both faces by NH3 groups from centrosymmetrically related Cu++ complexes. The trans NH3 groups each bind to a crown ether forming long chain copolymers. In addition to the NH3... 

Fig. 6. Isothermal phase transitions from the phase separated to homogeneous state of the aqueous solution of the copolymer containing 11.6 mol % pendant crown ether groups by the addition of (O) potassium and (9) sodium chlorides at 32 °C and 37 °C. Polymer concentration was 1 mass %...

There is only one example that fits into this section and it uses a spectacular way to form the crown ether in the polymer that is worth noting (Scheme 22). In contrast to all other procedures that use crown ethers pre-formed in the monomers, this example by Percec forms the crown ether [13]crown-4 during the polymerization reaction [59]. Cationic cyclocopolymerization of l,2-bis(2-ethenyloxyethoxy)ben-zene 37 with the mesogenic cyano biphenyl unit 38 gave copolymer 39 with a 1 1 ratio of 37 38 displaying a smectic phase. 

Figure 15.10 Schematic representation of a molecular recognition ion gating membrane. The copolymer of thermosensitive polymer fV-isopropylacrylamide, and crown ether polymer, BCAm, is grafted on the pore surface. The membrane senses a specific ion Mn+, by the crown receptor, and closes its pores rapidly.38 (Reprinted with permission from T. Ito et al., J. Am. Chem. Soc. 2002,124,7840—7846. Copyright 2002 American Chemical Society.)...

These two macromonomers were subsequently copolymerized with styrene to yield graft copolymers 84) containing crown ethers in their side chains. 

A method for preparing homopolymers or copolymers of oxiranes by anionic polymerization using s-butyl lithium and triisobutylaluminum but without crown ethers or cryptands during the polymerization process is described. 

The principle of cyclopolymerization has been applied to the synthesis of macrocyclic ether-containing polymers which may simulate the properties of crown ethers. l,2-Bis(ethenyloxy)benzene (a 1,7-diene) and l,2-bis(2-ethenyloxyethoxy)benzene (a 1,13-diene) are typical of the monomers synthesized. Homopolymerization of the 1,7-diene via radical and cationic initiation led to cyclopolymers of different ring sizes homopolymerization of the 1,13-diene led to cyclic polymer only via cationic initiation. Both monomer types were copolymerized with maleic anhydride to yield predominantly alternating copolymers having macro-cyclic ether-containing rings in the polymer backbone. 

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