Association in Aqueous Solutions of a Thermoresponsive PVCL-g-C₁₁EO₄₂ Copolymer

Abstract

Thermoresponsive associations in aqueous solution of poly(N-vinylcaprolactam) chains grafted with ω-methoxy poly(ethylene oxide) undecyl α-methacrylate (PVCL-g-C11EO42) at different copolymer concentrations have been investigated with the aid of various experimental methods. Turbidity measurements reveal that the cloud point (CP) decreases with increasing polymer concentration, and this effect is more pronounced in the semidilute concentration regime. Small-angle neutron scattering (SANS) results at large scattering wavevectors suggest a gradual conformational transition from random coils to contracted coils in the dilute concentration regime as the temperature rises. The rheological experiments disclose a strong temperature-induced contraction of the molecules in the dilute concentration regime, and the results in the semidilute regime indicate that the polymer chains are unentangled even at high concentrations. Dynamic light scattering results on solutions at temperatures up to the CP show the existence of a bimodal relaxation process; one mode is associated with the diffusion of individual polymer coils, or small clusters of molecules, and the other one is ascribed to interchain aggregation and the formation of aggregates at higher concentrations. At low concentrations, the intrachain species exhibit a temperature-induced compression, whereas at higher concentrations a temperature rise generates intermolecular aggregates. At a low constant temperature, an increase in polymer concentration leads to poorer thermodynamic conditions of the system, and shrinkage of the polymer coils is observed. At temperatures slightly above CP, the decay of the correlation function is characterized by a narrow unimodal relaxation mode. At this stage, most of the intrachain structures have been consumed in the formation of more compact particles.

First investigation of modified poly(2-vinyl-4,4-dimethylazlactone)s as kinetic hydrate inhibitors

“…The temperature at which the first sign of haze in the solution was observed was determined as the cloud point (T Cl ). (Kjøniksen, et al, 2005). The test was repeated for reproducibility.…”

Temperature-induced intermicellization and contraction in aqueous mixtures of sodium dodecyl sulfate and an amphiphilic diblock copolymer

“…The measured signal S from the cloud point analyzer can empirically be related to the turbidity τ , which was determined from measurements of the transmittance on a standard spectrophotometer in a 1 cm cuvette, using the empirical expression τ = (−1/L) ln(I t /I 0 ), where L is the light path length of the cuvette, I t is the transmitted light intensity, and I 0 is the incident light intensity. A direct relationship between the calculated turbidity from the spectrophotometer experiments and S from the cloud point analyzer is found [7] to be τ = 9.0 × 10 −9 S 3.751 . All data from the cloud point analyzer will be presented in terms of turbidity.…”

“…The specifications of this instrument and the procedure for the determination of turbidities have been described previously [7]. The measured signal S from the cloud point analyzer can empirically be related to the turbidity τ , which was determined from measurements of the transmittance on a standard spectrophotometer in a 1 cm cuvette, using the empirical expression τ = (−1/L) ln(I t /I 0 ), where L is the light path length of the cuvette, I t is the transmitted light intensity, and I 0 is the incident light intensity.…”

“…The self-assembly and association of amphiphilic block copolymers in aqueous media have received considerable attention due to the high potential for biomedical and pharmaceutical applications [1][2][3][4][5][6][7][8][9]. Poly(N-isopropylacrylamide) (PNIPAAM) often constitutes the hydrophobic block in this type of copolymer.…”

Schizophrenic micellization in aqueous solutions of the pH- and temperature responsive pentablock terpolymer PDEAEMAx-b-PNIPAAMy-b-PEGz-b-PNIPAAMy-b-PDEAEMAx

“…A detailed description of the equipment and determination of turbidities have been given elsewhere [28]. The apparatus utilizes a scanning diffusive technique to characterize phase changes of the sample.…”