Quantitative description of temperature induced self-aggregation thermograms determined by differential scanning calorimetry

A novel thermodynamic approach for the description of differential scanning calorimetry (DSC) experiments on self-aggregating systems is derived and presented. The method is based on a mass action model where temperature dependence of aggregation numbers is considered. The validity of the model was confirmed by describing the aggregation behavior of poly(ethylene oxide)-poly(propylene oxide) block copolymers, which are well-known to exhibit a strong temperature dependence. The quantitative description of the thermograms could be performed without any discrepancy between calorimetric and van 't Hoff enthalpies, and moreover, the aggregation numbers obtained from the best fit of the DSC experiments are in good agreement with those obtained by light scattering experiments corroborating the assumptions done in the derivation of the new model

Micellar Dynamics in Aqueous Solutions of PEO-PPO-PEO Block Copolymers

The dynamics of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) micelle rearrangements were studied using iodine laser temperature jump experiments with light-scattering detection. Two relaxation processes were detected: the first, fast one was accompanied by an increase in scattered light intensity, while the second, slow process was accompanied by a reduction in light intensity. The Aniansson- Wall theory was used to interpret the experimental results. The equilibrium micelle structures at the start and end points of the temperature jump experiment were used as input for the Aniansson-Wall equations. The solution of these equations agrees qualitatively with experimental data and suggests the mechanisms associated with the two time constants. The first time scale, in the tens of microseconds to about 10 ms range, is attributed to unimer insertion into micelles. The other time scale, in the 1-100 ms range, is associated with the rearrangement of the micelle size distribution. It is shown that the second process is often not observed either because the unimer supply is insufficient or because the micelle number density is not temperature dependent

Thermoresponsive micelles from jeffamine-b-poly(L-glutamic acid) double hydrophilic block copolymers

Double hydrophilic block copolymers (DHBC) consisting of a Jeffamine block, a statistical copolymer based on ethylene oxide and propylene oxide units possessing a lower critical solution temperature (LCST) of 30 degrees C in water, and Poly(L-glutamic acid) as a pH-responsive block were synthesized by ring-opening polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride using an amino-terminated Jeffamine macroinitiator, followed by hydrolysis. This DHBC proved thermoresponsive as evidenced by dynamic light scattering and small-angle neutron scattering experiments. Spherical micelles with a Jeffamine core and a poly(L-glutamic acid) corona were formed above the LCST of Jeffamine. The size. of the core of such micelles decreased with increasing temperature, with complete core dehydration being achieved at 66 degrees C. Such behavior, commonly observed for thermosensitive homopolymers forming mesoglobules, is thus demonstrated here for a DHBC that self-assembles to generate thermoresponsive micelles of high colloidal stability