Block Copolymers of Styrene and Stearyl Methacrylate. Synthesis and Micellization Properties in Selective Solvents

Facile preparation of hyperbranched glycopolymers via an AB3* inimer promoted by a hydroxy/cerium(iv) redox process

The facile preparation of hyperbranched glycopolymers was performed without protecting group chemistry, where the methyl-6-O-methacryloyl-α-d-glucoside (6-O-MMAGlc) monomer was adopted as an AB₃*-type inimer.

Impact of chain microstructure on solution and thin film self-assembly of PCHD-based semi-flexible/flexible diblock copolymers

Self-assembly of semi-flexible/flexible block copolymers in a selective solvent is examined using a set of diblock copolymers where the chain microstructure of the semi-flexible block is manipulated in order to tune chain stiffness. Conceptually, the reduced conformational space of the semi-flexible block is anticipated to alter the way the chains pack, potentially changing the structure of self-assembled aggregates in comparison to flexible diblock copolymer analogs. Semi-flexible/flexible diblock copolymers comprised of poly(styrene)-block-poly(1,3-cyclohexadiene) (PS-b-PCHD) having systematic changes in chain microstructure, as captured by the ratio of 1,4/1,2-linkages between cyclohexenyl repeat units, and molecular weight of the PCHD blocks were synthesized using anionic polymerization. These diblocks were dissolved in tetrahydrofuran (THF), which is a preferential solvent for PS, and the structures formed were examined using laser light scattering and complementary imaging techniques. Results show that PS-b-PCHD copolymers with a chain microstructure of 90% 1,4/10% 1,2 linkages between cyclohexenyl repeat units (referred to simply as 90/10) are able to micellize, forming spherical structures, while diblocks of 70/30 and 50/50 1,4-to-1,2 ratios remain as single chains and ill-defined aggregates, respectively, when dissolved in THF. With inferences drawn from simple structural models, we speculate that this self-assembly behavior arises due to the change in the chain configuration with increasing content of 1,2-links in the backbone. This renders the chain with higher 1,2 content incapable of swelling in response to solvent and unable to pack into well-defined self-assembled structures.

Soft-patchy nanoparticles: modeling and self-organization

We consider a novel class of patchy particles inspired by polymer-based complex units where the limited valence in bonding is accompanied by soft interactions and incessant fluctuations of the patch positions, possibly leading to reversible modifications of the patch number and size. We introduce a simple model that takes into account the aforementioned features and we focus on the role played by the patch flexibility on the self-organization of our patchy units in the bulk, with particular attention to the connectivity properties and the morphology of the aggregated networks.

A microfluidic platform for integrated synthesis and dynamic light scattering measurement of block copolymer micelles

Microfluidic devices were developed that integrate the synthesis of well defined block copolymers and dynamic light scattering (DLS) measurement of their micelle formation. These metal devices were designed to operate in contact with organic solvents and elevated temperatures for long periods, and thus were capable of continuous in-channel atom transfer radical polymerization (ATRP) of styrene and (meth)acrylate homopolymers and block copolymers. These devices were equipped with a miniaturized fiber optic DLS probe that included several technology improvements, including a measurement volume of only 4 microlitres, simple alignment, and reduced multiple scattering. To demonstrate the integrated measurement, poly(methyl methacrylate-b-lauryl methacrylate) and poly(methyl methacrylate-b-octadecyl methacrylate) block copolymers were processed on the device with a selective solvent, dodecane, to induce micelle formation. The in situ DLS measurements yielded the size and aggregation behavior of the micelles. For example, the block copolymer solutions formed discrete micelles (D(H) approximately = 25 nm) when the corona block was sufficiently long (f(MMA) < 0.51), but the micelles aggregated when this block was short. This study demonstrates the utility of these new devices for screening the solution behavior of custom synthesized polymeric surfactants and additives.

Novel Thermoresponsive and pH-Responsive Aggregates from Self-Assembly of Triblock Copolymer PSMA-b-PNIPAAm-b-PSMA

A series of novel triblock copolymers of poly(stearyl methacrylate)-b-poly(N-isopropylacrylamide)-b-poly(stearyl methacrylate) (PSMA-b-PNIPAAm-b-PSMA) with different molecular weights was synthesized through carboxyl-terminated trithiocarbonates as a highly efficient RAFT agent via reversible addition-fragmentation chain transfer (RAFT) polymerization. The resultant polymers were characterized by 1H NMR, FT-IR spectroscopy, and GPC. By varying the organic solvent used in the self-assembly procedure and adjusting the copolymer composition, multiple morphologies ranging from vesicles and core-shell spherical aggregates with different dimensions to pearl-necklace-like aggregates were obtained. The aggregates showed thermoresponsive and pH-responsive properties through the lower critical solution temperature (LCST) of PNIPAAm and the two carboxyl end groups of the copolymer.

APPLICATION OF MICROTHERMAL ANALYSIS AND PULSED FORCE MICROSCOPY TO CHARACTERIZE NANOSTRUCTURED POLYMER

In this investigation, we present the first results of Microthermal analysis (MicroTA) and Pulsed-Force-Mode (PFM) scanning force microscopy employed for visualization and characterization of nanostructured side-chain crystalline polymeric material. PFM was employed to clearly visualize the interesting self-organizing characteristics and the intimate contact of crystalline order as well as amorphous disorder in such polymer. As the sample was heated above the melting point, the well-defined crystalline regions observed at lower temperature no longer exist, and diffused melt boundaries are clearly observed using PFM. The nanophase separated system undergoes a sharp change in its adhesion and stiffness properties with temperature below and above the crystal melting point. Local thermal analyses using MicroTA exhibit consistent rapid crystal melting curves and its lateral homogeneity.