Chain-growth polycondensation: The living polymerization process in polycondensation

Linear Block Copolymer Synthesis

Block copolymers form the basis of the most ubiquitous materials such as thermoplastic elastomers, bridge interphases in polymer blends, and are fundamental for the development of high-performance materials. The driving force to further advance these materials is the accessibility of block copolymers, which have a wide variety in composition, functional group content, and precision of their structure. To advance and broaden the application of block copolymers will depend on the nature of combined segmented blocks, guided through the combination of polymerization techniques to reach a high versatility in block copolymer architecture and function. This review provides the most comprehensive overview of techniques to prepare linear block copolymers and is intended to serve as a guideline on how polymerization techniques can work together to result in desired block combinations. As the review will give an account of the relevant procedures and access areas, the sections will include orthogonal approaches or sequentially combined polymerization techniques, which increases the synthetic options for these materials.

Hierarchical self-assembly of aromatic peptide conjugates into supramolecular polymers: it takes two to tango

Supramolecular polymers are self-assembled materials displaying adaptive and responsive "life-like" behaviour which are often made of aromatic compounds capable of engaging in π-π interactions to form larger assemblies. Major advances have been made recently in controlling their mode of self-assembly, from thermodynamically-controlled isodesmic to kinetically-controlled living polymerization. Dynamic covalent chemistry has been recently implemented to generate dynamic covalent polymers which can be seen as dynamic analogues of biomacromolecules. On the other hand, peptides are readily-available and structurally-rich building blocks that can lead to secondary structures or specific functions. In this context, the past decade has seen intense research activity in studying the behaviour of aromatic-peptide conjugates through supramolecular and/or dynamic covalent chemistries. Herein, we review those impressive key achievements showcasing how aromatic- and peptide-based self-assemblies can be combined using dynamic covalent and/or supramolecular chemistry, and what it brings in terms of the structure, self-assembly pathways, and function of supramolecular and dynamic covalent polymers.

Well-Defined Dual Light- and Thermo-Responsive Rod-Coil Block Copolymers Containing an Azobenzene, MEO2MA and OEGMA

Here we report the dual light- and thermo-responsive behavior of well-defined rod-coil block copolymers composed of an azobenzene unit, 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA) and oligo(ethylene glycol) methacrylate (OEGMA). Azobenzene-containing rigid rod blocks prepared by chain growth condensation polymerization of the azobenzene containing monomer were used as a macroinitiator of atom transfer radical polymerization (ATRP) after attaching an α-bromoisobutyryl group as an end group. Synthesis of well-defined rod-coil block copolymers with different coil block lengths was achieved by copolymerization of MEO₂MA and OEGMA monomers. The synthesized polymers exhibited amphiphilic properties and polymeric micelles were formed in aqueous solution. The light-responsive behaviors of azobenzene moieties, photoisomerization by irradiation of light, and thermo-responsive behaviors of P(MEO₂MA-co-OEGMA) coil blocks, aggregation by increment of temperature over lower critical solution temperature, were investigated. A dual stimuli-responsive behavior of the rod-coil block copolymers was observed when exposed to light and heat.

Dynamics of a Complex Multilayer Polymer Network: Mechanical Relaxation and Energy Transfer

In this paper, we focus on the mechanical relaxation of a multilayer polymer network built by connecting identical layers that have, as underlying topologies, the dual Sierpinski gasket and the regular dendrimer. Additionally, we analyze the dynamics of dipolar energy transfer over a system of chromophores arranged in the form of a multilayer network. Both dynamical processes are studied in the framework of the generalized Gaussian structure (GSS) model. We develop a method whereby the whole eigenvalue spectrum of the connectivity matrix of the multilayer network can be determined iteratively, thereby rendering possible the analysis of the dynamics of networks consisting of a large number of layers. This fact allows us to study in detail the crossover from layer-like behavior to chain-like behavior. Remarkably, we highlight the existence of two bulk-like behaviors. The theoretical findings with respect to the decomposition of the intermediate domain of the relaxation quantities, as well as the chain-like behavior, are well supported by experimental results.

Functional Aromatic Polyamides

We describe herein the state of the art following the last 8 years of research into aromatic polyamides, wholly aromatic polyamides or aramids. These polymers belong to the family of high performance materials because of their exceptional thermal and mechanical behavior. Commercially, they have been transformed into fibers mainly for production of advanced composites, paper, and cut and fire protective garments. Huge research efforts have been carried out to take advantage of the mentioned characteristics in advanced fields related to transport applications, optically active materials, electroactive materials, smart materials, or materials with even better mechanical and thermal behavior.

Structure-controlled polymers prepared by pseudo-living addition-condensation polymerization and their application to light harvesting

An A,B-block amphiphilic polymer and a branched polymer were prepared by using a new type of pseudo-living addition-condensation polymerization. The first polymer showed an interphase photoinduced energy transfer in a micellar system, while the second type showed efficient light-harvesting ability.

Limitations of Using Small Molecules to Identify Catalyst-Transfer Polycondensation Reactions

Catalyst-transfer polycondensation (CTP) is a relatively new method for synthesizing conjugated polymers in a chain-growth fashion using transition metal catalysis. Recent research has focused on screening catalysts to broaden the monomer scope. In this effort, small molecule reactions have played an important role. Specifically, when selective difunctionalization occurs, even with limiting quantities of reaction partner, it suggests an associative intermediate similar to CTP. Several new chain-growth polymerizations have been discovered using this approach. We report herein an attempt to use this method to develop chain-growth conditions for synthesizing poly(2,5-bis(hexyloxy)phenylene ethynylene) via Sonogashira cross-coupling. Hundreds of small molecule experiments were performed and selective difunctionalization was observed with a Buchwald-type precatalyst. Unexpectedly, these same reaction conditions led to a step-growth polymerization. Further investigation revealed that the product ratios in the small molecule reactions were dictated by reactivity differences rather than an associative intermediate. The lessons learned from these studies have broad implications on other small molecule reactions being used to identify new catalysts for CTP.

Controlling molecular weight and polymer architecture during the Passerini three component step-growth polymerization

A new approach to control the molecular weight and polymer architecture using the Passerini three-component step-growth polymerization is described.

Synthesis and physical gelation induced by self-assembly of well-defined poly(arylene ether sulfone)s with various numbers of arms

Synthesis of poly(arylene ether sulfone)s with various numbers of arms by chain-growth polycondensation and physical gelation induced by self-assembly.