Polymer-incorporated liposomes were prepared from preformed liposomes and a cholesterol-functionalized poly(acrylic acid) additive via a simple drop-in procedure. These modified liposomes possess surface-active carboxylate groups that can be cross-linked with telechelic 2,2‘-(ethylenedioxy)bis(ethylamine) linkers, resulting in polymer-caged liposomes (PCLs) that are highly stable and have tunable pH-sensitive responses.

Gradient copolymers are prepared from comonomer systems with a range of segregation strengths and homopolymer glass transition temperature (T g) differences to explore the breadths that can be achieved by their single, continuous glass transition regions compared to random and block copolymers. A variety of chain architectures are synthesized using semibatch nitroxide-mediated controlled radical polymerization, including linear gradients, sigmoidal gradients, blocky gradients, and blocky random cases. The derivative of the differential scanning calorimetry heat curve is used to extract T g breadths (ΔT gs). For the first time, these T g breadths are compared against values derived from nanophase separation levels predicted by self-consistent mean-field theory and found to be in good accord. In moderately segregating systems (styrene (S)/n-butyl acrylate and S/tert-butyl acrylate), ΔT g may be tuned dramatically via gradient structure and molecular weight; e.g., a T g breadth exceeding 100 °C, or >65% of the homopolymer T g difference, is obtained with a sigmoidal gradient copolymer of S/n-butyl acrylate. In the very weakly segregating system (S/n-butyl methacrylate), ΔT g remains narrow (<40% of the homopolymer T g difference), regardless of gradient design. In strongly segregating systems (S/4-vinylpyridine and S/4-acetoxystyrene (AS)), ΔT gs are observed spanning 70−80% of the homopolymer T g difference. Small-angle X-ray scattering applied to S/AS materials demonstrates a range of temperature-sensitive scattering intensities consistent with the level of segregation observed through their ΔT gs.

The degree of microphase or nanophase segregation in gradient copolymers with compositions varying across the whole copolymer backbone is studied via low-amplitude oscillatory shear (LAOS) measurements and small-angle X-ray scattering (SAXS). Studies are done as a function of comonomer segregation strength, molecular weight (MW), gradient architecture and temperature. Controlled radical polymerization is used to synthesize strongly segregating styrene/4-acetoxystyrene (S/AS) and the more weakly segregating S/n-butyl acrylate (S/nBA) gradient copolymers. Results are compared to those from S/AS and S/nBA random and block copolymers. The higher MW S/AS gradient copolymer exhibits LAOS behavior similar to the highly microphase segregated S/AS block copolymer, while the lower MW S/AS gradient copolymer exhibits complex, nonterminal behavior indicative of a lower degree of microphase segregation. The S/nBA gradient copolymers demonstrate more liquidlike behavior, with the lower MW sample exhibiting near-Newtonian behavior, indicative of a weakly segregating structure, while the higher MW, steeper gradient sample shows behavior ranging from solidlike to more liquidlike with increasing temperature. With the exception of the lower MW S/nBA case, the gradient copolymers exhibit temperature-dependent LAOS behavior over a wide temperature range, reflecting their temperature-dependent nanodomain composition amplitudes. The S/AS samples have SAXS results consistent with the degree of microphase segregation observed via rheology. Shear alignment studies are done on the higher MW S/AS gradient copolymer, which is the most highly microphase segregated gradient copolymer. Rheology and SAXS provide evidence of shear alignment, despite the gradual variation in composition profile across the nanodomains of such gradient copolymers. A short review of the nomenclature and behavior of linear copolymer architectures is also provided.

Gradient copolymers of exo-5-(benzyloxy)norbornene and exo-5- [(4-tert-butyl)benzyloxy]norbornene were synthesized via ring-opening metathesis polymerization (ROMP). Kinetic studies revealed that the reactivity ratios of both monomers were close to unity. As predicted, this monomer pair did not result in copolymers with significant gradients under batch polymerization conditions. However, semibatch conditions resulted in copolymers with sizable gradients whose shape was independent of the rate of addition. Addition of the monomers simultaneously via a dual and opposite ramping strategy led to a 50/50 copolymer with an exceptionally linear gradient. These gradient copolymers were further functionalized via hydrogenation, bromination, and bromoalkoxylation.