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Amphiphilic block and “blocklike” copolymers based on polyisobornyl acrylate and polyacrylic acid were used as stabilizers for hydrophilic titanium dioxide and hydrophobic copper phthalocyanine pigments. As reflected by the dispersion stabilities and electrokinetic sonic amplitude ESA measurements, the molecular architecture of the copolymer is of great importance for its interaction with the pigment surface. It was observed that irrespective of polymer composition, blocklike copolymers exhibit lower stabilization ability and quite different adsorption behavior in comparison to block copolymers with sharp block boundaries. Models for the adsorption behavior of both block and blocklike copolymers are proposed.

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.

A dual initiator (4-hydroxy-butyl-2-bromoisobutyrate), that is, a molecule containing two functional groups capable of initiating two polymerizations occurring by different mechanisms, has been prepared. It has been used for the sequential two-step synthesis of well-defined block copolymers of polystyrene (PS) and poly(tetrahydrofuran) (PTHF) by atom transfer radical polymerization (ATRP) and cationic ring-opening polymerization (CROP). This dual initiator contains a bromoisobutyrate group, which is an efficient initiator for the ATRP of styrene in combination with the Cu(0)/Cu(II)/N,N,N',N",N"-pentamethyldiethylenetriamine catalyst system. In this way, PS with hydroxyl groups (PS-OH) is formed. The in situ reaction of the hydroxyl groups originating from the dual initiator with trifluoromethane sulfonic anhydride gives a triflate ester initiating group for the CROP of tetrahydrofuran (THF), leading to PTHF with a tertiary bromide end group (PTHF-Br). PS-OH and PTHF-Br homopolymers have been applied as macroinitiators for the CROP of THF and the ATRP of styrene, respectively. PS-OH, used as a macroinitiator, results in a mixture of the block copolymer and remaining macroinitiator. With PTHF-Br as a macroinitiator for the ATRP of styrene, well-defined PTHF-b-PS block copolymers can be prepared. The efficiency of PS-OH or PTHF-Br as a macroinitiator has been investigated with matrix-assisted laser desorption/ionization time-of-flight spectroscopy, gel permeation chromatography, and NMR. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3206–3217, 2003

Copolymers with both pH- and thermo-responsiveness were synthesized by free radical copolymerization of N-vinylcaprolactam with small amounts of acrylic acid. The copolymers have been prepared in various solvents and characterized by gel permeation chromatography, Fourier-transform infrared (FTIR) spectroscopy and titration. The phase separation behaviour of these copolymers was studied in water and buffered solutions at a variety of pH values and temperatures by means of attenuated total reflectance FTIR and cloud-point measurements. The aqueous solutions of the copolymers showed a temperature, pH and molecular weight dependent phase-separation behaviour. Copyright © 2003 Society of Chemical Industry

Thermo-responsive graft copolymers have been synthesized based on a poly(N-vinylcaprolactam) (PVCL) backbone and either hydrophilic poly(ethylene oxide) (PEO) or hydrophobic poly(tetrahydrofuran) (PTHF) side chains. The phase separation behavior of the graft polymers in water was studied by transmittance measurements and compared to that of the corresponding swollen segmented polymer networks and aqueous solutions of both polymers. The influence of the concentration and length of the grafts on the cloud point temperature (TCP) has been demonstrated. PVCL-g-PTHF copolymers have been synthesized by using the macromonomer technique, i.e. the radical copolymerization of VCL with a PTHF macromonomer. A special feature of these amphiphilic graft copolymers is their ability to stabilize aqueous emulsions below the TCP and to suddenly break them above the TCP. PVCL-g-PEO copolymers were prepared by a grafting onto method. First, succinimide groups were introduced in the backbone, to which amino terminated PEO chains were grafted in the second step. This leads to di-hydrophilic copolymers that become amphiphilic after heating their aqueous solutions above the TCP.

A new type of ‘intelligent’ hydrogels has been developed in the form of organic/inorganic hybrid materials by making use of the sol-gel technology. Poly(N-vinylcaprolactam) (PVCL) has been incorporated in these materials for its thermo-responsive properties. The synthesis of the hybrid hydrogels was achieved by the in situ formation of an inorganic silica phase in the presence of an aqueous solution of high molecular weight PVCL. This methodology results in the preparation of micro-heterogeneous systems in which silica particles of nanometer dimensions act as physical cross-links for the PVCL molecules. Hydrogen bonds between the remaining non-condensed silanol groups and the PVCL carbonyl functions, together with physical entanglements, are responsible for the strong interactions between the organic and inorganic phases. Stress-strain tests on highly swollen materials demonstrated that the unique structure of these thermo-responsive hybrid hydrogels improves the mechanical stability to a great extent as compared to conventional hydrogels. Transmission measurements demonstrate that the presence of the inorganic phase does not influence the cloud point temperatures of PVCL significantly. On the other hand, the response of the reinforced hybrid hydrogels to temperature becomes less pronounced for increasing silica fractions. The reversibility of the swelling/deswelling process has been demonstrated by swelling experiments as a function of temperature. PVCL/SiO2 hybrid hydrogels.