Converting Poly(Methyl Methacrylate) into a Triple-Responsive Polymer

Non-activated Esters as Reactive Handles in Direct Post-Polymerization Modification

Non-activated esters are prominently featured functional groups in polymer science, as ester functional monomers display great structural diversity and excellent compatibility with a wide range of polymerization mechanisms. Yet, their direct use as a reactive handle in post-polymerization modification has been typically avoided due to their low reactivity, which impairs the quantitative conversion typically desired in post-polymerization modification reactions. While activated ester approaches are a well-established alternative, the modification of non-activated esters remains a synthetic and economically valuable opportunity. In this review, we discuss past and recent efforts in the utilization of non-activated ester groups as a reactive handle to facilitate transesterification and aminolysis/amidation reactions, and the potential of the developed methodologies in the context of macromolecular engineering.

Synthesis of functional polyacrylamide (co)polymers by organocatalyzed post-polymerization modification of non-activated esters

The broad application of polyacrylamides (PAMs) has greatly promoted the development of new synthetic methods to prepare PAM-based functional (co)polymers regarding their traditional preparation via the direct polymerization of various acrylamide monomers. Herein, we have explored the post-polymerization modification of the poly(2,2,2-trifluoroethyl acrylate) (PTFEA) homopolymer, a typical non-activated ester, and various amines using the organo-catalytic system involving 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,2,4-triazole (TA). The reaction kinetics (e.g., the optimized reaction solvent, temperature, time, initial molar ratio of amines to esters and the molar ratio of DBU to TA) were carefully studied with the modulus substrate of iso-propylamine as the formed poly(iso-propyl acrylamide) (PNIPAM) representing the most investigated PAM. The full and partial amidation of the esters in PTFEA could be precisely regulated just by controlling the kinetic conditions to give (co)polymers with designable compositions and structures. We have demonstrated that the poly(N-acryloyl pyrrolidine) obtained by the post-polymerization modification of non-activated ester and pyrrolidine exhibited a noticeable phase transition, which confirmed the robustness and versatility of the post-polymerization modification. The described method paves the way for the synthesis of various (co)polymers with amide side chains from readily available polymer precursors.

Maleic and Methacrylic Homopolymers with Pendant Dibutylamine or Dibutylamine Oxide Groups as Kinetic Hydrate Inhibitors

Kinetic hydrate inhibitors (KHIs) are applied in oil and gas fields to prevent gas hydrate formation, most often in cold subsea flow lines. The main component in industrial KHI formulations is a water-soluble polymer with many amphiphilic groups of which the hydrophilic part is most commonly the amide functional group. In the last decade, we have investigated polyamine oxides as alternatives to polyamides due to the strong hydrogen bonding of the amine oxide group. Here, we report the KHI performance of maleic and methacrylic homopolymers with dialkylamine and dialkylamine oxide pendant groups. Performance screening experiments were conducted under high pressure with a Structure II-forming natural gas mixture in steel rocking cells using the slow (1 °C/h) constant cooling test method. Polymers with dibutylamine groups gave much better KHI performance than polymers with dimethylamine or diethylamine groups. Polyamines formed from polymaleic anhydride reacted with 3-(dibutylamino)-1-propylamine (DBAPA) or 2-(dibutylamino)-ethanol (DBAE) gave good water solubility and good KHI performance, probably due to self-ionization between the dibutylamino and carboxylic acid groups. The lack of self-ionization for the methacryl homopolymers of DBAPA and DBAE explains why these polymers are not water-soluble. Oxidation of the maleic or methacryl polyamines to polyamine oxides gave water-soluble polymers with good compatibility with brines (0.5-7.0 wt % NaCl), but only the DBAPA-based polyamine oxides gave improved KHI performance compared to the polyamines. Poly(3-(dibutylamino oxide)-1-propyl methacrylamide) gave a similar performance to commercial N-vinyl pyrrolidone:N-vinyl caprolactam 1:1 copolymer and without a cloud point in deionized water up to +95 °C.

Functional Mesostructured Electrospun Polymer Nonwovens with Supramolecular Nanofibers

Functional, hierarchically mesostructured nonwovens are of fundamental importance because complex fiber morphologies increase the active surface area and functionality allowing for the effective immobilization of metal nanoparticles. Such complex functional fiber morphologies clearly widen the property profile and enable the preparation of more efficient and selective filter media. Here, we demonstrate the realization of hierarchically mesostructured nonwovens with barbed wire-like morphology by combining electrospun polystyrene fibers, decorated with patchy worm-like micelles, with solution-processed supramolecular short fibers composed of 1,3,5-benzenetricarboxamides with peripheral N,N-diisopropylaminoethyl substituents. The worm-like micelles with a patchy microphase-separated corona were prepared by crystallization-driven self-assembly of a polyethylene based triblock terpolymer and deposited on top of the polystyrene fibers by coaxial electrospinning. The micelles were designed in a way that their patches promote the directed self-assembly of the 1,3,5-benzenetricarboxamide and the fixation of the supramolecular nanofibers on the supporting polystyrene fibers. Functionality of the mesostructured nonwoven is provided by the peripheral N,N-diisopropylaminoethyl substituents of the 1,3,5-benzenetricarboxamide and proven by the effective immobilization of individual palladium nanoparticles on the supramolecular nanofibers. The preparation of hierarchically mesostructured nonwovens and their shown functionality demonstrate that such systems are attractive candidates to be used for example in filtration, selective separation and heterogenous catalysis. This article is protected by copyright. All rights reserved.

Polymersomes: Soft Nanoparticles from Miktoarm Stars for Applications in Drug Delivery

Self-assembly of amphiphilic macromolecules has provided an advantageous platform to address significant issues in a variety of areas, including biology. Such soft nanoparticles with a hydrophobic core and hydrophilic corona, referred to as micelles, have been extensively investigated for delivering lipophilic therapeutics by physical encapsulation. Polymeric vesicles or polymersomes with similarities in morphology to liposomes continue to play an essential role in understanding the behavior of cell membranes and, in addition, have offered opportunities in designing smart nanoformulations. With the evolution in synthetic methodologies to macromolecular precursors, the construction of such assemblies can now be modulated to tailor their properties to match desired needs. This review brings into focus the current state-of-the-art in the design of polymersomes using amphiphilic miktoarm star polymers through a detailed analysis of the synthesis of miktoarm star polymers with tuned lengths of varied polymeric arms, their self-assembly, and applications in drug delivery.

Hierarchical Superstructures by Combining Crystallization-Driven and Molecular Self-Assembly

Combining the unique corona structure of worm-like patchy micelles immobilized on a polymer fiber with the molecular self-assembly of 1,3,5-benzenetricarboxamides (BTAs) leads to hierarchical superstructures with a fir-tree-like morphology. For this purpose, worm-like patchy micelles bearing pendant, functional tertiary amino groups in one of the corona patches were prepared by crystallization-driven self-assembly and immobilized on a supporting polystyrene fiber by coaxial electrospinning. The obtained patchy fibers were then immersed in an aqueous solution of a tertiary amino-functionalized BTA to induce patch-mediated molecular self-assembly to well-defined fir-tree-like superstructures upon solvent evaporation. Interestingly, defined superstructures are obtained only if the pendant functional groups in the surface patches match with the peripheral substituents of the BTA, which is attributed to a local increase in BTA concentration at the polymer fibers' surface.

Thermoresponsive Polymers Based on Tertiary Amine Moieties

Thermoresponsive polymers exhibiting unique reversible phase transition properties in aqueous solution in response to temperature stimuli have been extensively investigated. In the past two decades, thermoresponsive polymers based on tertiary amine moieties have achieved considerable progress and become an important family of thermoresponsive polymers, including tertiary amine functionalized poly((meth)acrylamide)s, poly((meth)acrylate)s, poly(styrene)s, poly(vinyl alcohol)s, and poly(ethylene oxide)s, which exhibit lower critical solution temperature and/or upper critical solution temperature in water or aliphatic alcohols. Their phase transition behavior can be modulated by the solution pH and CO₂ due to the protonation of tertiary amine moieties in acidic condition and deprotonation in alkaline condition and the charged ammonium bicarbonate formed by the tertiary amine moieties and CO₂ . The aim of this review is to summarize the recent progress in the thermoresponsive polymers based on tertiary amine moieties.

Patchy Micelles with a Crystalline Core: Self-Assembly Concepts, Properties, and Applications

Crystallization-driven self-assembly (CDSA) of block copolymers bearing one crystallizable block has emerged to be a powerful and highly relevant method for the production of one- and two-dimensional micellar assemblies with controlled length, shape, and corona chemistries. This gives access to a multitude of potential applications, from hierarchical self-assembly to complex superstructures, catalysis, sensing, nanomedicine, nanoelectronics, and surface functionalization. Related to these applications, patchy crystalline-core micelles, with their unique, nanometer-sized, alternating corona segmentation, are highly interesting, as this feature provides striking advantages concerning interfacial activity, functionalization, and confinement effects. Hence, this review aims to provide an overview of the current state of the art with respect to self-assembly concepts, properties, and applications of patchy micelles with crystalline cores formed by CDSA. We have also included a more general discussion on the CDSA process and highlight block-type co-micelles as a special type of patchy micelle, due to similarities of the corona structure if the size of the blocks is well below 100 nm.

Stoichiometric Control over Partial Transesterification of Polyacrylate Homopolymers as Platform for Functional Copolyacrylates

Only recently, post-polymerization modification reactions of unactivated polyacrylates have been emerging as an attractive alternative to utilizing reactive monomers, enabling the synthetic upcycling of these widely applied polymers. Within this contribution, the triazabicyclodecene-catalyzed transesterification of polyacrylates is reported, including the reaction kinetics and the broad scope for macromolecular design of functional copolyacrylates. More specifically, the transesterification is performed under equilibrium conditions with a set of primary alcohols whereby the reaction kinetics and the obtained conversion as a function of stoichiometric excess of alcohol are evaluated. The results show that the obtained conversion is dependent on the polarity of the solvent and of the alcohol. Through this approach, the transesterification degree can be accurately controlled by stoichiometry, enabling the precise modulation of the macromolecular structure. Finally, the utility of this approach is demonstrated to incorporate functional side chains that are incompatible with radical polymerization, to facilitate Diels-Alder and thiol-ene reactions, enabling access to a broad range of functional materials from simple polyacrylate homopolymer precursors.

Converting Poly(Methyl Methacrylate) into a Triple-Responsive Polymer

Multiresponsive polymers that can respond to several external stimuli are promising materials for a manifold of applications. Herein, a facile method for the synthesis of triple-responsive (pH, temperature, CO2 ) poly(N,N-diethylaminoethyl methacrylamide) by a post-polymerization amidation of poly(methyl methacrylate) (PMMA) is presented. Combined with trivalent counterions ([Fe(CN)6 ]3- ) both an upper and lower critical solution temperature (UCST/LCST)-type phase behavior can be realized at pH 8 and 9. PMMA and PMMA-based block copolymers are readily accessible by living anionic and controlled radical polymerization techniques, which opens access to various responsive polymer architectures based on the developed functionalization method. This method can also be applied on melt-processed bulk PMMA samples to introduce functional, responsive moieties at the PMMA surface.