Programmed photodegradation of polymeric/oligomeric materials derived from renewable bioresources.

Renewable polymeric materials derived from biomass with built-in phototriggers were synthesized and evaluated for degradation under irradiation of UV light. Complete decomposition of the polymeric materials was observed with recovery of the monomer that was used to resynthesize the polymers.

Solvent-responsive self-assembly of amphiphilic invertible polymers determined with SANS.

Amphiphilic invertible polymers (AIPs) are a new class of macromolecules that self-assemble into micellar structures and rapidly change structure in response to changes in solvent polarity. Using small-angle neutron scattering (SANS) data, we obtained a quantitative description of the invertible micellar assemblies (IMAs). The detailed composition and size of the assemblies (including the effect of temperature) were measured in aqueous and toluene polymer solutions. The results show that the invertible macromolecules self-assemble into cylindrical core-shell micellar structures. The composition of the IMAs in aqueous and toluene solutions was used to reveal the inversion mechanism by changing the polarity of the medium. Our experiments demonstrate that AIP unimers self-assemble into IMAs in aqueous solution, predominantly through interactions between the hydrophobic moieties of macromolecules. The hydrophobic effect (or solvophobic interaction) is the major driving force for self-assembly. When the polarity of the environment is changed from polar to nonpolar, poly(ethylene glycol) (PEG) and aliphatic dicarboxylic acid fragments of AIP macromolecules tend to replace each other in the core and the shell of the IMAs. However, neither the interior nor the exterior of the IMAs consists of fragments of a single component of the macromolecule. In aqueous solution, with the temperature increasing from 15 to 35 °C, the IMAs' mixed core from aliphatic dicarboxylic acid and PEG moieties and PEG-based shell change the structure. As a result of the progressive dehydration of the macromolecules, the hydration level (water content) in the micellar core decreases at 25 °C, followed by dehydrated PEG fragments entering the interior of the IMAs when the temperature increases to 35 °C.

Invertible micellar polymer assemblies for delivery of poorly water-soluble drugs.

Strategically designed amphiphilic invertible polymers (AIPs) are capable of (i) self-assembling into invertible micellar assemblies (IMAs) in response to changes in polarity of environment, polymer concentration, and structure, (ii) accommodating (solubilizing) substances that are otherwise insoluble in water, and (iii) inverting their molecular conformation in response to changes in the polarity of the local environment. The unique ability of AIPs to invert the molecular conformation depending on the polarity of the environment can be a decisive factor in establishing the novel stimuli-responsive mechanism of solubilized drug release that is induced just in response to a change in the polarity of the environment. The IMA capability to solubilize lipophilic drugs and deliver and release the cargo molecules by conformational inversion of polymer macromolecules in response to a change of the polarity of the environment was demonstrated by loading IMA with a phytochemical drug, curcumin. It was demonstrated that four sets of micellar vehicles based on different AIPs were capable of delivering the curcumin from water to an organic medium (1-octanol) by means of unique mechanism: AIP conformational inversion in response to changing polarity from polar to nonpolar. The IMAs are shown to be nontoxic against human cells up to a concentration of 10 mg/L. On the other hand, the curcumin-loaded IMAs are cytotoxic to breast carcinoma cells at this concentration, which confirms the potential of IMA-based vehicles in controlled delivery of poorly water-soluble drug candidates and release by means of this novel stimuli-responsive mechanism.