Block copolymers of poly(vinyl ethers) and poly(ethylene glycol) by means of the living cationic polymerization of vinyl ethers

Abstract

SummaryIf living poly(vinyl ethers) are terminated with a large excess of methanol, containing aqueous ammonia, well-defined products are obtained. If only a slight excess of methanol is used, aldehydes and coupling products are formed. Sowever, termination with an excess of a hydroxy terminated polymer is cumbersome. According to a given reaction scheme, the termination with methanol in the presence of an anhydrous organic base, should give better results. With two equivalents of triethylamine with respect to the initiator only two equivalents of methanol are needed to give a clean reaction. With this recipe block copolymers of poly(vinyl ether) and poly(ethylene glycol) are prepared.

Near-monodisperse,n-alkyl, end-functionalized poly(methyl vinyl ether)s: Synthesis by living cationic polymerization and solution characterization

“…The water-terminated PMVE bears two characteristic peaks at 9.80 and 2.65 ppm labeled "c" and "d," which are due to the aldehydic proton and to the two protons of the methylene unit next to the aldehyde group. This is consistent with the findings of Loontjens et al, 20 who proposed that the water-terminating agent contributes a hydroxyl group to the polymer end to give a hemiacetal, which is then rapidly transformed to an aldehyde. The methanol-and n-octanol-terminated polymers bear the characteristic acetal proton peak "e" at 4.6 ppm and no trace of an aldehydic signal.…”

“…This has already been observed with water and PEVE. 20 Fig ure 1(b) shows three GPC traces in THF that indicate some dimer formation in the water-terminated polymer and very little dimerization in the ethylene glycol-terminated polymer. In the former case, a small dimer peak was resolved, but in the latter case, the dimers formed a very slight tail to the left of the main polymer peak.…”

“…Acetals are stable at room temperature and neutral pH but are cleaved at higher temperatures or/and low pH to give aldehydes. 19,20 Peaks "f " in PMVEs terminated with n-pentanol or higher agents originate from the methylene protons in the terminating agent.…”

“…First, the end-functionalized polymers formed are unstable to acids. 19,20 Second, the purification procedure to remove the excess of the terminating agent proved rather laborious. Given the high reactivity of the living end of the polymer, one could have attempted to reduce the purification requirements by terminating with stoichiometric amounts of alcohols or carboxylic acids.…”

“…Prior washings with 1% aqueous HCl were avoided because of the lability of the acetal end-groups to acidic conditions. 19,20 The washed polymer solutions were dried under vacuum at room temperature. The dried material was dissolved in 5 mL of tetrahydrofuran, transferred to a dialysis tube (Sigma-Aldrich, MW cutoff 2000), and dialyzed for 1 week against 400 mL tetrahydrofuran to remove the excess carboxylic acids and also the remaining traces of alcohols, particularly the less volatile ones.…”