Sequential living cationic polymerizations

A macromonomer made of a block copolymer of p-MeS and P-pinene was also prepared by sequential living cationic polymerization of both monomers under the same experimental conditions. The first block had 12 p-MeS units and the second had 11 p-pinene units as evaluated by NMR spectroscopy. 

B. Block Copolymers by Sequential Living Cationic Polymerization... 

A large variety of AB- and ABA-type block copolymers have been prepared from vinyl ethers via sequential living cationic polymerizations. For example, as shown in Scheme 2 (A), isobutyl vinyl ether (IBVE) is first polymerized with the HI/ZnI2 or HCl/ZnCl2 initiating system, and from the resulting living polymer, the second monomer, 2-acetoxyethyl vinyl... 

Scheme 2 Examples of the synthesis of AB-block copolymers by sequential living cationic polymerization [80,87].

As seen in Scheme 2 (A), the most of the syntheses have been carried out with the HI/I2 and HX/ZnX2 (X = halogen) initiating systems, because these systems can effectively polymerize a large variety of vinyl ethers, including those with pendant functions, into well-defined living polymers [1]. In this way, the sequential living cationic polymerizations of two vinyl ethers are mostly "reversible i.e., both A - B and B - A polymerization sequences are operable. This is in sharp contrast to the block copolymerization of a vinyl ether with a styrene derivative or isobutylene (see below), where such reversibility often fails to work. 

In general, styrene and its substituted derivatives are less reactive than vinyl ethers in cationic polymerization, although the reactivity depends considerably on the nature of the substituents. This in turn requires some care in synthesizing block copolymers of styrene derivatives by sequential living cationic polymerization. For example, styrene-methyl... 

Three arm amphiphilic star-block copolymers of isobutyl vinyl ether (IBVE) and 2-hydroxyethyl vinyl ethers were also prepared by Higashimura et al. [23]. The synthetic strategy involved the sequential living cationic polymerization of IBVE and 2-acetoxyethyl vinyl ether, initiated by the trifunctional initiator system composed of tris(trifluoroacetate) and ethylaluminum dichloride, with excess of 1,4-dioxane as a carbocation-stabilizing Lewis base (Scheme 8). 

As we have already reported, sequential living cationic polymerizations of functionalized vinyl ethers (8) readily give amphiphilic block copolymers (17). Such sequential living polymers are equally applicable to the star polymer synthesis. A typical example utilizes an AB living block copolymer ( ) that consists of 2-(acetoxy)ethyl vinyl ether and IBVE (10 and 30 units per chain, respectively). The... 

Sequential living cationic polymerization is primarily used to prepare block copolymers containing a vinyl ether block, or polyisobutylene [18-20]. It can also be coupled with other techniques [18,20]. However, the range of monomers that may be polymerized by this method is comparatively limited and consequently living cationic polymerization is only used in prescribed circumstances. 

Linear amphiphilic polymers with carboxyl groups were also available via sequential cationic polymerization of a fimctional vinyl ether and an alkyl derivative [6]. The sequential living cationic polymerization of diethyl 2-(vinyloxy)ethylmalonate [VOEM CHf=CHOCH2CH2CH(COOCH2CH3)2]... 

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