Asymmetrical telechelic

Lou X, Detrembleur C, Jerome R (2002) Living cationic polymerization of 5-valerolactone and synthesis of high molecular weight homopolymer and asymmetric telechelic and block copolymer. Macromolecules 35 1190-1195... 

Poly(a-raethy1styrene- -isobutylene- -a-methyIstyrene) was prepared by the initiation of a-raethylstyrene polymerization from a ditelechelic polyisobutylene containing tert-chlorine end groups. AlEt2Cl was used as coinitiator (177). Poly(isobutylene- -styrene) and poly(isobutylene- -a-raethylstyrene) were prepared by the initiation of styrene and a-raethyIstyrene polymerization from an asymmetric telechelic polyisobutylene, that is, (CH2)2-C=Ch-CH PiB—CH2-C(CH3)2C1 and AlEt2Cl (178). 

The convenient synthesis of a-hydroxyl-co-methoxycarbonyl asymmetric telechelic PIBs has been achieved by the combination of two recently discovered techniques, haloboration-initiation and end capping with 1,1-diphenylethylene followed by end quenching with silyl ketene acetals, 1 -methoxy-1 -trimethylsiloxy-2-methyl-propene (MTSMP), 1-methoxy-1-trimethylsiloxy-propene (MTSP), and 1-methoxy-l-trimethylsiloxy-ethene (MTSE). Nearly quantitative chain end functionalization has been proved by NMR, quantitative NMR, and FT-IR spectroscopy. The methoxycarhonyl end arising by quenching with MTSMP could not be hydrolyzed under either basic or acidic conditions. These methods also failed to yield the acid when the corresponding diisobutylene derivative was used. The sterically less hindered esters, however, readily underwent hydrolysis resulting in the formation of a-hydroxyl-co-carboxyl asymmetric telechelic PIBs. 

Combination of the head and end group control provides a novel synthetic route for the synthesis of a-hydroxyl-co-methoxycarbonyl asymmetric telechelic PIB H0PIBC(R)(R )C00CH3 (a condensation macromonomer). Hydrolysis of the methoxycarbonyl end group results in the formation of a-hydroxyl-co-carboxyl asymmetric telechelic PIB HOPIBC(R)(R )COOH, while ester dcoholysis provides a method for polycondensation reactions of PIB. In the present publication we report the synthesis of these materials. 

Scheme 4. Synthetic strategy for a-hydroxyl-o)-methoxycarbonyl asymmetric telechelic PIBs.

FIGURE 2.1 Various possible architectures for amphiphilic copolymer (a) linear block copolymers with different numbers of A and B blocks, (b) cyclic block copolymers, (c) star block copolymers, (d) graft block copolymers, (e) block copolymers with dendritic or hyper-branched blocks, and (f) semitelechelic polymer (upper), telechelic polymer (middle), and asymmetrical telechelic polymer with different hydrophobic chain ends [9]. 

Pivalactone (a,a-dimethyl-jS-propiolactone) (PVL) can be converted to telechelics and used for the preparation of block copolymers (331,332). An asymmetrical telechelic is prepared from PVL (334) with cyclic amine initiators. These telechelics have a-cycloammonium and a>-carboxyl end groups. 

Problem 12.14 Discuss a possible method of synthesizing an asymmetric telechelic polymer based on polystyrene (DP 50) with a carboxylic group at one end and a hydroxyl group at the other, using combined thiol-ene and CuAAC click reactions. 

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