Carbocationic telechelic polymers

Synthesis of PIB prepolymers. fm-Chlorine-telechelic PIB (Mn=4,000 MVf/Mn 1.09) (7), and an allyl-telechelic PIB (Mn=9,500 Mw/Mn 1.14) (7,8) were prepared by living carbocationic polymerizations. The tert-chlorine ended PIB was quantitatively dehydrochlorinated (9) to -C(CH3)=CH2 terminated polymer. Both olefin-telechelic PIBs were then hydroborated and oxidized (10) to prepare the primary hydroxyl termini. The hydroxyl-telechelic polymers were esterified with methacryloyl chloride to methacrylate-telechelic PIBs, MA-PIB-MA (11). 

Living carbocationic polymerization (LCCP) (Faust and Kennedy, 1987 Ivan and Kennedy, 1990 Joseph, 1999) relies on complex ion equilibria, which are normally maintained in the absence of polar solvents and monomers. Only specific polar additives (such as di-tert. butyl pyridine, or N,N-dimethyl acetamide) are compatible with a LCCP, so that the direct copolymerization of monomer containing H bonds is not possible. In the same manner, endquenching reactions with quenchers containing H bonds is not possible, as often only chlorine-telechelic polymers would result. 

A special case of controlled initiation is the inifer method. The word inifer (front initiator transfer agentsl describes compounds that function simultaneously as initiators and as chain transfer agents. The inifer technique provided the first carbocationic route toward the synthesis of telechelic ta. to functional) polymers. 

In recent years, there have been significant developments in the field of living carbocationic polymerization (LCCP) of vinyl monomers, such as isobutylene (IB), styrene and its derivatives, and vinyl ethers, leading to a wide variety of functional polymers (for recent reviews see Refs. 1-4). Due to the attractive properties of polyisobutylene (PIB) available only by carbocationic polymerization, coupling this hydrophobic, thermally, oxidatively, and hydrolytically stable polymer with a low Tg to a variety of other chain segments is expected to result in new useful products. For instance, methacrylate-telechelic PIB (MA-PIB-MA) obtained by LCCP and subsequent chain end derivatization has been successfully used to synthesize novel amphiphilic networks by radical copolymerization of MA-PIB-MA with a variety of monomers, such as N,N-dimethylacrylamide and 2-trimethylsilyloxyethyl methacrylate, a protected 2-hydroxyethyl methacrylate... 

Polystyrene and Derivatives. Telechelic polystyrene, poly(2,4,6-trimethylst5Tene), poly(p-methylstyrene), and poly(p-chlorostyrene) can be prepared by living carbocationic polymerization (269-271) or by inifer method (272). While end-quenching the living carbocationic polsrmerization gave quantitatively polymers with sec-benzylic termini, the diciunyl chloride/BClg inifer system yielded a,with olefine end groups were also prepared by dehydrochlorination (272,273). 

Ivan, B. and Kennedy, J.P. (1990) Living carbocationic polymerization. XXX. One-pot synthesis of allyl-terminated linear and tri-arm star polyisobutylenes, and epoxy- and hydro xy-telechelics thereftom. Journal of Polymer Science Part A Polymer Chemistry, 28,89-104. 

Friedel-Crafts alkylation of various aromatic rings such as benzene, toluene or phenol lead to a variety of diaromatic products (equation 46). Nitration of this telechelic followed by reduction leads to a polymer with terminal amine groups. The phenol-terminated telechelics can be further derivatized as shown in Scheme 47. 57.458 Recently, tertiary esters and ethers were used in conjunction with BCI3 to provide the first example of a living carbocationic polymerization of isobutylene. Scheme 48 shows the polymerization mechanism suggested for initiation with tertiary esters. The resulting polymers are telechelics containing one or two tertiary chlorine chain ends. 

---