Block Copolymers of Methyl Vinyl Ether and Isobutyl Vinyl Ether With Thermo‐Adjustable Amphiphilic Properties

Abstract

The thermo‐adjustable hydrophilic/hydrophobic properties of AB, ABA and BAB block copolymers in which A is poly(methyl vinyl ether) (PMVE) and B is poly(isobutyl vinyl ether) (PIBVE) have been investigated. The block copolymers were prepared by “living” cationic polymerization using sequential addition of monomers. The polymerizations were carried out with the system acetal/trimethylsilyl iodide as initiator and ZnI2 as activator. The initiating system based on diethoxyethane leads to AB block copolymers whereas the initiating system based on tetramethoxypropane leads to ABA or BAB triblock copolymers. Well‐defined block copolymers of different composition with controlled molecular weights up to approx. 10 000 have been prepared. When IBVE is added to living PMVE, PIBVE‐blocks form only in the presence of an additional amount of ZnI2, which is attributed to the fact that part of the ZnI2 is inactive because of complex formation with PMVE. At room temperature, the combination of hydrophilic (PMVE) and hydrophobic (PIBVE) segments provides the copolymers with surfactant properties. Above the lower critical solution temperature (LCST) of PMVE, situated around 36 °C, the PMVE‐blocks become hydrophobic and the amphiphilic nature of the block copolymers is lost. The corresponding changes in hydrophilic/hydrophobic balance have been evaluated by investigation of the emulsifying properties of the block copolymers for water/decane mixtures as a function of the temperature. Below the LCST, the block copolymers have emulsifying properties similar to or better than those of the commercial PEO‐PPO block copolymers (Pluronic®). Either oil‐in‐water or water‐in‐oil emulsions can be obtained, depending on the polymer architecture and the water/decane volume ratio. The emulsifying properties are strongly reduced or completely lost above 40 °C. Emulsions obtained with a PMVE36‐b‐PIBVE54 block copolymer for a water/decane (v/v) ratio of 85/15 remained stable for more than six months.50/50 and a 85/15 water/decane w/o emulsion (15 g/l) with the PMVE36‐b‐PIBVE54 block copolymer at 20 °C.magnified image50/50 and a 85/15 water/decane w/o emulsion (15 g/l) with the PMVE36‐b‐PIBVE54 block copolymer at 20 °C.

Association behavior of thermo-responsive block copolymers based on poly(vinyl ethers)

“…In a previous paper [3], we reported on the living cationic sequential copolymerization of methyl vinyl ether (MVE) and isobutyl vinyl ether (IBVE). The copolymerization was performed by using either a mono-or bifunctional initiating system and by using either MVE or IBVE as the first monomer to be polymerized.…”

“…This technique has been proved to be suitable for the detection of micellization, as exemplified by Armes and others [27] and [30]. The spectrum measured in CDCl 3 shows the characteristic signals of both polymer segments. On the other hand, in D 2 O, which is a non-solvent for PIBVE, PIBVE forms the core of the micelle and the intensity of corresponding signals vanishes in the NMR spectrum.…”

“…The PMVE homopolymer and the PMVE-PIBVE block copolymers with well-defined structures, molecular weights and narrow polydispersities, have been synthesized by 'living' cationic polymerization techniques as described elsewhere [3] and [21]. The polymerizations were carried out with the system acetal/trimethyl silyl iodide as initiator and ZnI 2 as activator.…”

“…This interest is motivated by the potential utilization of these materials for a number of technological applications, such as stimuli-controlled release of drugs [1], stimuli-controlled stabilization of emulsions [2] and [3], thermo-adjustable colloidal stabilization of organic pigments [4], etc. In water, the commonly applied stimuli are pH, ionic strength and temperature.…”

“…The living cationic polymerization of vinyl ethers is now a well-established method for the design of well-defined polymer architectures [21]. In a previous paper, we have reported on the synthesis of a new class of thermo-adjustable polymer surfactants [3]. More precisely, we have combined poly(methyl vinyl ether) (PMVE) blocks with poly(isobutyl vinyl ether) (PIBVE) ones in AB, ABA and BAB structures.…”