Synthesis,characterization and rheological properties of multiblock associative copolymers by RAFT technique

Polymer Bulletin - Preparation of associating multiblock copolymer electrolytes mediated by radical addition–fragmentation chain transfer (RAFT) technique has been evaluated and reported in...     

Synthesis,characterization and rheological properties of three different associative polymers obtained by micellar polymerization

Summary We report the synthesis, characterization and rheological properties in aqueous solutions of three different water-soluble associative polymers (AP’s) (telechelic, multisticker and combined). Polymer chains consisting of water-soluble polyacrylamides, hydrophobically modified with low amounts of N,N-dihexylacrylamide and a linear hydrophobic initiator. These have been prepared via free radical micellar polymerization. We compare the properties of these different polymers, with respect to the localization of the hydrophobic groups, using steady-flow experiments. In the semidiluted regime we clearly differentiate two different zero-shear viscosity (η₀) -vs- concentration (C) behaviors; a first semidiluted regime unentangled, where the viscosity increases strongly and directly with c and a second regime entangled, where the viscosity increases proportionally to C⁴, independently of the localization of the hydrophobic group.     

Concentration effect of <Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide on viscoelastic properties of hydrosoluble thermo-thickening copolymers

In this work, we described the preparation of hydrosolubles thermosensitive copolymers obtained via free radical polymerization in aqueous media. The reactions were carried out under different molar ratio of acrylamide and N-isopropylacrylamide (NIPAM) and are considered [80]/[20], [60]/[40], [50]/[50], [40]/[60] and [20]/[80], respectively. The initial concentration of monomer mixture was kept at 3% (weight) based on the water volume. The polymerizations were performed at 70 °C under mechanical agitation during 7 h and the molar ratio between monomer and initiator (4,4′-azobis cyano pentanoic acid) was kept at 0.07%. The copolymers were characterized and results demonstrated that the monomer concentrations were closed to previously feed to the reaction. The turbidity point rises according to the quantity of poly(acrylamide), PAM, incorporated into the copolymers (composition value). Also, it was observed that the molecular weight of each copolymer decreases when the amount of NIPAM increases. On the other hand, the viscosity of all copolymers growth compared to the increase in the temperature from 25 to 70 °C is observed. Notwithstanding, in the case of copolymer with highest NIPAM concentration (CP5), the viscosity decreases in the temperature range from 60 to 70 °C.     

Synthesis and characterization of telechelic polymers obtained by micellar polymerization

Summary The synthesis, characterization and rheological properties in aqueous solution of two telechelic polymers of different structures and size are reported: they are water soluble polyacrylamides, hydrophobically modified with linear and di-substituted hydrophobic initiators. The polymers were prepared via free radical micellar polymerization. The results of static light scattering (SLS), showed similar weight-average molecular weights (M_w) in all of the synthesized polymers. No signal corresponding to the presence of the hydrophobic group of the initiator could be observed by ¹H NMR; however, the presence of these hydrophobic groups was demonstrated using rheological measurements.     

Impact of additives on the rheological properties of associating water-soluble multiblock polyelectrolytes

The impact of additives on the rheological behavior of four associating water-soluble multiblock polyelectrolytes previously synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization was described. These polyelectrolytes contained different number of blocks ranged from 1 to 7 divided into hydrophilic and hydrophobic. The rheological analyses of polymers were performed at 25°C at a given concentration (0.1–15 wt%) in the presence of sodium chloride (NaCl) 0.1–0.5 M, sodium dodecyl sulfate (SDS) 2–10 mM or a mixture of both. Data demonstrated an increase in the viscosity of macroRAFT (ɳ = 0.002–9 Pa·s) and triblock copolymer-TBC (ɳ = 0.003–0.04 Pa·s) versus the concentration of NaCl. Meanwhile, the viscosity of penta and heptablock copolymer exhibited a diminution whatever the (NaCl) used. Results from the rheological analyses of the associative polyelectrolytes at different (SDS) revealed that the viscosity of macroRAFT and triblock copolymer was kept constant in spite of the increment of the (SDS) while the viscosity of PBC and HBC displayed a pronounced diminution at the lower (SDS). Finally, the results from the rheological analyses of these polyelectrolytes versus a mixture of NaCl-SDS showed a diminution in the viscosity of these solutions at any concentration of additives.