Rachel K. O'Reilly

Advances and challenges in smart and functional polymer vesicles

Polymer vesicles prepared by self-assembly techniques have attracted increasing scientific interest in recent years. This is as a result of their numerous potential applications such as tunable delivery vehicles, for the templating of biomineralization, as nanoreactors and as scaffolds for biological conjugation. Presented in this review are the recent advances in the preparation and application of ‘smart’ and functional block copolymer vesicles such as those which respond to external stimuli to afford a change in structure, morphology or controlled release event. In this Highlight, we first give an overview of the structure of polymer vesicles, followed by a summary of the methods used for their preparation. We then focus on recently developed intelligent polymer vesicles which can respond to the application of external stimuli such as a change in temperature, pH or redox to afford novel nanomaterials. The potential applications of these materials are explored with specific focus on the functionalization of various domains of the polymer vesicles. Finally, the current limitations in the preparation and application of polymer vesicles are explored as are the challenges facing the development of these nanostructures towards real-world applications.

End group removal and modification of RAFT polymers

This paper describes both well-established routes and recent advances in the end group modification of polymers synthesised by reversible addition–fragmentation chain transfer (RAFT) polymerisation. The lability of the thiocarbonylthio group, which facilitates the RAFT mechanism, allows for ready post-polymerisation functionalisation of RAFT polymers by a number of techniques. In particular, end group thermolysis, radical induced reduction, hetero-Diels–Alder reactions and reaction with nucleophiles are discussed as are the applications and limitations of each method. The versatility of RAFT as a polymerisation tool for the synthesis of polymers with functional end groups for a range of applications is demonstrated.

Anisotropic particles with patchy, multicompartment and Janus architectures: preparation and application

Anisotropic particles, such as patchy, multicompartment and Janus particles, have attracted significant attention in recent years due to their novel morphologies and diverse potential applications. The non-centrosymmetric features of these particles make them a unique class of nano- or micro-colloidal materials. Patchy particles usually have different compositional patches in the corona, whereas multicompartment particles have a multi-phasic anisotropic architecture in the core domain. In contrast, Janus particles, named after the double-faced Roman god, have a strictly biphasic geometry of distinct compositions and properties in the core and/or corona. The term Janus particles, multicompartment particles and patchy particles frequently appears in the literature, however, they are sometimes misused due to their structural similarity. Therefore, in this critical review we classify the key features of these different anisotropic colloidal particles and compare structural properties as well as discuss their preparation and application. This review brings together and highlights the significant advances in the last 2 to 3 years in the fabrication and application of these novel patchy, multicompartment and Janus particles (98 references).

Cylindrical micelles from the living crystallization-driven self-assembly of Poly(lactide)-containing block copolymers

The synthesis and self-assembly of poly(lactide)-b-poly(acrylic acid) and poly(lactide)-b-poly(dimethylaminoethylacrylate) block copolymers by a combination of ring-opening polymerization and reverse-addition fragmentation chain transfer (RAFT) polymerization is reported. Self-assembly of block copolymers containing enantiopure homochiral poly(lactide), PLA, by a simple direct dissolution methodology results in core-crystallization to afford micelles with a cylindrical morphology. Amorphous atactic PLA cores and conditions that did not promote crystallization resulted in spherical micelles. Cylindrical micelles were characterized by transmission electron microscopy (TEM) with cryo-TEM, small angle neutron scattering (SANS) and angular dependent dynamic light scattering (DLS) proving that the cylindrical morphology was persistent in solution. Manipulation of the assembly conditions enabled the length and dispersity of the resultant cylindrical micelles to be controlled.

Stimuli responsive materials

Dramatic developments in the burgeoning field of polymer science are enabling new materials designs, synthetic methods, functional architectures, and applications. Today’s polymers are finding utility in broad areas, ranging from everyday commodity plastics to emerging, specialized, and high-tech materials. Moreover, it is apparent that the continued development of polymeric systems will be facilitated by ever-increasing understanding of advanced polymer synthesis and characterization techniques. This enhanced toolbox and knowledge-base will foster the facile design of next-generation precision materials with predictable and changeable properties. The present themed issue focuses on recent developments in the design of polymers that change properties in response to a single stimulus or multiple stimuli. These so-called ‘smart’ or stimuliresponsive polymers represent a growing cadre of materials that support various applications (e.g., controlled release agents, responsive coatings, and adaptive shape memory materials). Stimuli-responsive materials have benefited from significant advances in polymer science in recent years, and this themed issue highlights several of the fascinating developments that could have a major impact on the implementation of new smart materials. To fully address the field of stimuli responsive polymers, first we must understand the breadth of available stimuli that can induce a desired response, then we must design the polymer functionalities and systems that enable such a response; finally, we must develop methods to characterize the macromolecular changes as a result of that response. As demonstrated in this issue, many of the interesting properties of responsive materials arise from a transition in solubility or conformation of a macromolecule in the presence of a solvent. In this manner, transitions at the molecular level can be amplified to result in a change in nanoscale structure and/or materials properties. Gibson and O’Reilly (DOI: 10.1039/C3CS60035A) overview these transitions in the specific area of thermoresponsive polymers with particular attention to the effect of nanoscale geometry on the resulting change in chain conformation following a temperature change. Sumerlin and co-workers (DOI: 10.1039/ C3CS35499G) also highlight temperatureresponsive polymers with particular emphasis on design parameters that facilitate tuning of the specific transition temperatures. Light-responsive materials have received significant attention, as discussed by Gohy and Zhao (DOI: 10.1039/ C3CS35469E) in a review focused on reversible and irreversible transitions of photoresponsive copolymer micelles. Further, many systems can be designed a Institute for Technical and Macromolecular Chemistry, University of Hamburg, Bundesstrasse 45, D-20146 Hamburg, Germany. E-mail: theato@chemie.uni-hamburg.de b George & Josephine Butler Polymer Research Laboratory, Department of Chemistry, University of Florida, Gainesville, FL 32611, USA. E-mail: sumerlin@chem.ufl.edu c Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK. E-mail: Rachel.OReilly@warwick.ac.uk d Department of Chemical & Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, DE 19716, USA. E-mail: thepps@udel.edu

Multistep DNA‐Templated Reactions for the Synthesis of Functional Sequence Controlled Oligomers

Biomimetic: A strand displacement mechanism was designed to permit DNA-templated synthesis of functional oligomers of arbitrary length (see scheme). Key features of the mechanism are that successive coupling reactions take place in near-identical environments and that purification is only necessary in the last synthesis step.

Biomimetic radical polymerization via cooperative assembly of segregating templates

Segregation and templating approaches have been honed by billions of years of evolution to direct many complex biological processes. Nature uses segregation to improve biochemical control by organizing reactants into defined, well-regulated environments, and the transfer of genetic information is a primary function of templating. The ribosome, wherein messenger RNA is translated into polypeptides, combines both techniques to allow for ideal biopolymer syntheses. Herein is presented a biomimetic segregation/templating approach to synthetic radical polymerization. Polymerization of a nucleobase-containing vinyl monomer in the presence of a complementary block copolymer template of low molecular weight yields high molecular weight (M(w) up to ~400,000 g mol(-1)), extremely low polydispersity (≤1.08) daughter polymers. Control is attained by segregation of propagating radicals in discrete micelle cores (via cooperative assembly of dynamic template polymers). Significantly reduced bimolecular termination, combined with controlled propagation along a defined number of templates, ensures unprecedented control to afford well-defined high molecular weight polymers.

Using Metallo‐Supramolecular Block Copolymers for the Synthesis of Higher Order Nanostructured Assemblies

Many research groups have explored the properties and solution self-assembly of main chain metallo-supramolecular multiblock copolymers. Until recently, these metal complexes have been used to prepare mainly micelle type structures. However, the self-assembly of such copolymers has been exploited further to create more advanced architectures which utilize the reversible supramolecular linkage of their building blocks as a key component in their synthesis. Furthermore, the incorporation of multiple orthogonal interactions and stimuli responsive polymers into their design, enables more precise external control of their properties. This feature article discusses recent developments and provides an insight into their potential exploitation and development for the creation of novel, smart, and responsive nanostructures.

Structural reorganization of cylindrical nanoparticles triggered by polylactide stereocomplexation

Co-crystallization of polymers with different configurations/tacticities provides access to materials with enhanced performance. The stereocomplexation of isotactic poly(L-lactide) and poly(D-lactide) has led to improved properties compared with each homochiral material. Herein, we report the preparation of stereocomplex micelles from a mixture of poly(L-lactide)-b-poly(acrylic acid) and poly(D-lactide)-b-poly(acrylic acid) diblock copolymers in water via crystallization-driven self-assembly. During the formation of these stereocomplex micelles, an unexpected morphological transition results in the formation of dense crystalline spherical micelles rather than cylinders. Furthermore, mixture of cylinders with opposite homochirality in either THF/H2O mixtures or in pure water at 65 °C leads to disassembly into stereocomplexed spherical micelles. Similarly, a transition is also observed in a related PEO-b-PLLA/PEO-b-PDLA system, demonstrating wider applicability. This new mechanism for morphological reorganization, through competitive crystallization and stereocomplexation and without the requirement for an external stimulus, allows for new opportunities in controlled release and delivery applications.

Crystallization-driven sphere-to-rod transition of poly(lactide)-b-poly(acrylic acid) diblock copolymers: mechanism and kinetics

The aqueous crystallization-driven sphere-to-rod transition of poly(lactide)-b-poly(acrylic acid), PLA-b-PAA block copolymers, with a short homochiral PLA core forming block and a 10 times longer (in terms of degree of polymerization) PAA corona forming block is presented. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) is utilized to follow the kinetics of the transition and wide angle X-ray diffraction (WAXD) to confirm the correlation between degree of crystallinity and morphology. Studies at different concentrations and solvent mixtures provide valuable information regarding the nucleation and growth mechanism of the system, showing that the micelle dynamics are a key aspect of the assembly process. Furthermore, the in situ crystallization-driven cylinder formation during the acrylate ester hydrolysis reaction is demonstrated. Finally, we report that the micelle morphology can be switched between cylinders and spheres by facilitating or blocking the crystallization of the core block, demonstrating a simple method to control the morphology of the resultant assembly.