Cross-linked networks feature exceptional chemical and mechanical resilience but consequently lack recyclability. Vitrimers have emerged as a class of materials that feature the robustness of thermosets and the recyclability of thermoplastics without compromising network integrity. Most examples of vitrimers have involved new polymers with exchangeable bonds within their backbones. In pursuit of a more universal, commercially viable route, we propose a method utilizing commercially available and inexpensive reagents to prepare vitrimers from vinyl monomer-derived prepolymers that contain cross-linkable βketoester functional groups. Controlled radical copolymerization of methyl methracrylate and (2-acetoacetoxy)ethyl methacrylate afforded linear prepolymers that were converted into vitrimers in a single step by treatment with a trifunctional amine. These materials displayed the characteristic features and reprocessability of vitrimers over as many as six (re)processing cycles. Critically, the networks prepared through this process largely retain the chemical and thermal properties of their linear counterparts, suggesting this method holds significant utility as a user-friendly and commercially relevant approach to the rational design of vitrimers with diverse properties.

ABSTRACT:The effect of the chain constraint on the glass-transition temperature of polystyrene (pS) was studied in the context of polymer tethering to curved surfaces. The synthesis and characterization of silica-graft-polystyrene (SiO 2 -g-pS) hybrid nanoparticles is reported. Silica nanoparticles possessing covalently bound pS chains were prepared by the atom transfer radical polymerization of styrene from functionalized colloidal surfaces. These hybrid nanoparticles serve as interesting examples of spherical polymer brushes, as a high density of grafted pS was achieved on the inorganic colloid. The confirmation of a brushlike extension of immobilized chains in a good solvent was obtained with dynamic light scattering in toluene of SiO 2 -g-pS colloids possessing various molar masses of tethered pS. The solid-state morphology of SiO 2 -g-pS ultrathin films was assessed with transmission electron microscopy, and this confirmed that the silica colloids were well-dispersed in a matrix of the tethered polymer. Differential scanning calorimetry was used to study the effects of tethering and chain immobilization on the glass-transition temperature of pS. The measured glass-transition temperature of annealed bulk films of the hybrid nanoparticles was elevated with respect to the value for pure bulk pS. The enhancements ranged from 13 to 2 K for SiO 2 -g-pS brushes possessing tethered pS with number-average molecular weights of 5230 and 32,670 g/mol, respectively.

Hydrophobicity inherently affects a solutes behavior in water, yet how polymer chain hydrophobicity impacts aggregate morphology during solution self-assembly and reorganization is largely overlooked. As polymer and nanoparticle syntheses are easily achieved, the resultant nanoparticle architectures are usually attributed to chain topology and overall degree of polymerization, bypassing how the chains may interact with water during/after self-assembly to elicit morphology changes. Herein, we demonstrate how block copolymer hydrophobicity allows control over aggregate morphology in water and leads to remarkable control over the length of polymeric nanoparticle worms. Polymerization-induced self-assembly facilitated nanoparticle synthesis through simultaneous polymerization, self-assembly, and chain reorganization during a block copolymer chain extension from a hydrophilic poly­( N , N -dimethyl­acrylamide) macro-chain-transfer agent with diacetone acrylamide and N , N -dimethyl­acrylamide. Slight variations in the monomer feed ratio dictated the block copolymer chain composition and were proposed to alter aggregate thermodynamics. Micelles, worms, and vesicles were synthesized, and the highest level of control over worm elongation attained during a polymerization is reported, simply due to the polymer chain hydrophobicity.

Macromolecular stars containing reversible boronic ester linkages were prepared by an arm-first approach by reacting well-defined boronic acid-containing block copolymers with multifunctional 1,2/1,3-diols. Homopolymers of 3-acrylamidophenylboronic acid (APBA) formed macroscopic dynamic-covalent networks when cross-linked with multifunctional diols. On the other hand, adding the diol cross-linkers to block copolymers of poly(N,N-dimethylacrylamide (PDMA))-b-poly(APBA) led to nanosized multiarm stars with boronic ester cores and PDMA coronas. The assembly of the stars under a variety of conditions was considered. The dynamic-covalent nature of the boronic ester cross-links allowed the stars to reconfigure their covalent structure in the presence of monofunctional diols that competed for bonding with the boronic acid component. Therefore, the stars could be induced to dissociate via competitive exchange reactions. The star formation-dissociation process was shown to be repeatable over multiple cycles.

No abstract

Dually responsive poly[(N,N-diethylaminoethyl methacrylate)-b-(N-isopropyl acrylamide)]s (P(DEAEMA-b-NIPAM)s) capable of "schizophrenic" aggregation in aqueous solution were synthesized via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. The nanoassembly morphologies, dictated by the hydrophilic mass fraction, can be controlled by the polymer block lengths, solution pH, and temperature. Both P(DEAEMA 98 -b-NIPAM 209 ) (52.5 wt % NIPAM) and P(DEAEMA 98b-NIPAM 392 ) (70.8 wt % NIPAM) self-assemble into PDEAEMA-core PNIPAM-shell spherical micelles with a hydrodynamic radii (R h ) of 21 and 25 nm, respectively, at temperatures below the lower critical solution temperature of PNIPAM and at solution pH values greater than the pK a of PDEAEMA. The two block copolymers, however, display quite different temperature-responsive behaviors at pH < 7.5. At elevated temperatures (>42 °C) P(DEAEMA 98 -b-NIPAM 209 ) forms spherical micelles (R h =28 nm) with hydrophobic PNIPAM cores stabilized by a hydrophilic PDEAEMA shell. By contrast, P(DEAEMA 98 -b-NIPAM 392 ) assembles into vesicles (R h =99 nm) above 38 °C. The nanostructures were characterized by a combination of dynamic and static light scattering as well as transmission electron microscopy and are being investigated for their potential application as drug delivery vehicles. † Paper number 143 in a series on Water-Soluble Polymers.

The calorimetric glass‐transition temperature (Tg) and transition width were measured over the full composition range for solvent–solvent mixtures of o‐terphenyl with tricresyl phosphate and with dibutyl phthalate and for polymer–solvent mixtures of polystyrene with three dialkyl phthalates. Tg shifted smoothly to higher temperatures with the addition of the component with the higher Tg for both sets of solvent–solvent mixtures. The superposition of the differential scanning calorimetry traces showed almost no composition dependence for the width of the transition region. In contrast, the composition dependence of Tg in polymer–solvent mixtures was different at high and low polymer concentrations, and two distinct Tg's were observed at intermediate compositions. These results were interpreted in terms of the local length scale and associated local composition variations affecting Tg. The possible implications of these results for the dynamics of miscible polymer blends were examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1155–1163, 2004

No abstract