Stefanie N. Guntari

ATRP-mediated continuous assembly of polymers for the preparation of nanoscale films

The continuous assembly of polymers (CAP) via atom transfer radical polymerisation (ATRP) is reported as an efficient approach for the preparation of dense, cross-linked, nanoscale engineered films as surface coatings, hollow capsules and replica particles. These films can be reinitiated to allow the preparation of thicker films without loss of film growth efficiency while maintaining similar film density.

Factors influencing the growth and topography of nanoscale films fabricated by ROMP-mediated continuous assembly of polymers

The continuous assembly of polymers (CAP) mediated via ring-opening metathesis polymerization (ROMP) is demonstrated as a simple and versatile method to fabricate tailored nanostructured thin films. The film thickness and topography were highly dependent upon the variation of different factors that influence the ROMP reaction and mechanism of the assembly process. Herein, we present a detailed investigation of the influence of various parameters on the rate of film formation, the film thickness and the film topography. Whereas the macrocross-linker concentration and molecular weight determined the final film thickness and surface coverage, the initiator concentration and ROMP catalyst activity were found to have a negligible effect on the film properties. Importantly, the minimum amount of polymerizable moieties required in the macrocross-linker to obtain fine control over film thickness and high surface coverage was found to be 7 mol%. The addition of excess ligand (≤100 mM) for the catalyst increased the catalyst lifetime leading to thicker films, although further increases (>100 mM) were found to retard the metathesis reaction. These findings provide valuable insights into the CAPROMP process and will contribute toward developing the next generation of CAP ultrathin films for advanced applications.

Low-Fouling, Biospecific Films Prepared by the Continuous Assembly of Polymers

We report that the continuous assembly of polymers (CAP) approach, mediated by ring-opening metathesis polymerization (ROMP), is a facile and versatile technology to prepare engineered nanocoatings for various biomedical applications. Low-fouling coatings on particles were obtained by the formation of multicompositional, layered films via simple and efficient tandem CAP(ROMP) processes that are analogous to chain extension reactions. In addition, the CAP(ROMP) approach allows for the efficient postfunctionalization of the CAP films with bioactive moieties via cross-metathesis reactions between the surface-immobilized catalysts and symmetrical alkene derivatives. The combined features of the CAP(ROMP) approach (i.e., versatile polymer selection and facile functionalization) allow for the fabrication and surface modification of various types of polymer films, including those with intrinsic protein-repellent properties and selective protein recognition capabilities. This study highlights the various types of advanced coatings and materials that the CAP approach can be used to generate, which may be useful for biomedical applications.

Assembly of Free-Standing Polypeptide Films via the Synergistic Combination of Hyperbranched Macroinitiators, the Grafting-From Approach, and Cross-Chain Termination

Cross-linked polypeptide-based films are fabricated via a novel and robust method employing surface-initiated ring opening polymerization of α-amino acid N-carboxyanhydrides (NCA-ROP). The judicious combination of amine-based hyperbranched macroinitiators and benzyl ester-protected NCA derivatives promotes network formation by cross-chain terminations, which allows the formation of stable cross-linked peptide-based capsules in a one-pot system.

Continuous assembly of polymers via solid phase reactions

The continuous assembly of polymers in the solid state via ring-opening metathesis polymerization (ssCAPROMP) is reported as an effective method for the fabrication of smooth, surface confined, cross-linked nanostructured films. Macrocross-linkers, polymers pre-functionalized with polymerizable pendent groups, were first deposited onto initiator-modified substrates via spin-coating, followed by film cross-linking via ssCAPROMP. The film thickness is tunable by adjusting the reaction time, and multilayered films can be achieved through reinitiation steps, generating complex and unique film architectures with nanometer precision. The technique developed herein allows for controlled and directional growth of cross-linked thin films from the substrate surface in the solid state.

Spatial-controlled nanoengineered films prepared via rapid catalyst induced cross-linking

A new top-down approach to generate stable nanoscale films via catalyst induced cross-linking (CIC) is demonstrated. Polymers with various compositions and bearing pendent norbornene groups (defined as macrocross-linkers) are initially spin-coated onto substrates to form nanometre-thick films; when the films are brought into contact with a catalyst solution, ring-opening metathesis polymerization (ROMP)-mediated cross-linking efficiently occurs to lock the film into place. CIC provides a new paradigm for the fabrication of stable nanoscale films and provides an alternative to traditional methods that use external stimuli (e.g., heat or light) to trigger film cross-linking. The process requires short cross-linking times (<3 min) to generate covalently bonded and stable nanoscale films. This facile nanoengineering approach allows for the creation of complex multi-layered and multi-compositional patterned films, enables excellent control over film properties such as thickness and swellability, and provides access to nanoscale free-standing polymer sheets. To highlight the versatility of the CIC approach, cross-linked, nanostructured and stratified multi-layered films with tunable film thickness were prepared from norbornene functionalised poly(oligo(ethylene glycol) methacrylate), poly(ethylene glycol) and poly(3-hexylthiophene) macrocross-linkers. CIC proceeds at low catalyst concentrations and allows the catalyst solution to be recycled multiple times, as demonstrated through repetition of 10 individual CIC cycles, making the process economical, scalable and applicable to advanced manufacturing techniques. Furthermore, the technique can be used to produce patterned films through selective exposure of specific regions of the polymer film to the catalyst solution. The CIC approach mediated by ROMP is highly efficient, rapid, robust and versatile, providing new opportunities in film assembly, and complementing existing nanoscale film fabrication methodologies.