Tor Kit Goh

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.

Bromoisobutyramide as an Intermolecular Surface Binder for the Preparation of Free‐standing Biopolymer Assemblies

Bromoisobutyramide (BrIBAM)-modified silica templates facilitate the formation of bio-functional thin films made of a range of biopolymers (e.g., polypeptides, nucleic acids or polysaccharides). Upon template removal, non-covalent free-standing biopolymeric assemblies (e.g., hollow capsules or replicated spheres and fibers) are formed without the need for covalent cross-linking.

Highly efficient synthesis of low polydispersity core cross-linked star polymers by Ru-catalyzed living radical polymerization.

The efficient formation of low polydispersity core cross-linked star (CCS) polymers via controlled/living radical polymerization (LRP) and the arm-first approach was found to be dependent on the mediating catalyst system. The Ru catalyst, Ru(Ind)Cl(PPh₃)₂ Cat. 1, and tertiary amine co-catalyst were used to synthesize highly living poly(methyl methacrylate) (PMMA) macroinitiators, which were then linked together with ethylene glycol dimethacrylate (EGDMA) to form PMMA(arm)PEGDMA(core) CCS polymers. The quantitative and near-quantitative synthesis of CCS polymers were observed for low to moderate molecular weight macroinitiators (M(n) =  8 and 20 kDa), respectively. Lower conversions were observed for high-molecular weight macroinitiators (M(n)  ≥  60 kDa). Overall, an improvement of between 10 and 20% was observed when comparing the Cat. 1 system to a conventional Cu-catalyzed system. This significant improvement in macroinitiator-to-star conversion is explained in the context of catalyst system selection and CCS polymer formation.

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.

1,1‐Diphenyl Ethylene‐Mediated Radical Polymerisation: A General Non‐Metal‐Based Technique For The Synthesis Of Precise Core Cross‐Linked Star Polymers

This communication details the successful synthesis of low polydispersity core cross-linked star (CCS) polymers via DPE-mediated polymerisation. We demonstrate the ability to produce poly(methyl methacrylate) and poly(acrylonitrile) CCS polymers that are currently inaccessible via the two most common non-metal-based controlled radical polymerisation techniques (NMP and RAFT polymerisations).

PMMA Star-Like Polymers via One-Pot Conventional Free-Radical Copolymerization

Poly(methyl methacrylate)-based star-like polymers (SLPs) were synthesized by a one-pot conventional free-radical copolymerization. Two aryl ester-based cross-linkers, bisphenol A dimethacrylate and 1,4-bis(methacryloxy)benzene, were found to induce SLP formation by reactivity control when copolymerized with methyl methacrylate. The formulation domain diagrams for these systems were established and high monomer concentrations (up to 70 wt-%) were achievable without the occurrence of macrogelation. Kinetic experiments confirmed that the SLP formation occurs via a pseudo two-step mechanism. Parallel plate rheological analysis of the SLP solutions demonstrated that these polymers had low viscosities, typically several orders of magnitude lower than the analogous linear polymer solution.

Development of amphiphilic multi-star polymers with highly grafted pyrene connectors as unimolecular encapsulation devices

Complex and hierarchically structured unimolecular polymeric architectures provide unique opportunities for self-assembly, encapsulation, segregation and recognition. Herein, we report the synthesis of unimolecular anisotropic and amphiphilic multi-star architectures consisting of multiple discrete core cross-linked star (CCS) polymers covalently tethered together through highly grafted polymeric connectors. These multi-star architectures, referred to as di-star and tri-star polymers, were prepared via a combination of atom transfer radical polymerisation (ATRP) and a copper-catalysed azide-alkyne cycloaddition (CuAAC) grafting-to approach. Initially, poly(tert-butyl methacrylate) (PtBMA)-based multi-star polymers with polyalkyne linear connectors were prepared via ATRP and the arm-first approach. Following isolation of the individual di-star and tri-star polymers, an azido-pyrene derivative was grafted onto the connectors via click chemistry with grafting efficiencies of 88 and 84%, respectively. Subsequently, hydrolysis of the PtBMA star arms provided amphiphilic poly(methacrylic acid) (PMAA)-based multi-stars with pyrene grafted connectors. The ability of the unimolecular di-star polymer to sequester and stabilise hydrophobic guests in aqueous solutions via π–π stacking interactions was investigated through the encapsulation of the anticancer drug pirarubicin. UV measurements provided loading capabilities of ca. 135 molecules of pirarubicin per di-star polymer (ca. 12 wt%).

Synthesis of Anisotropic, Amphiphilic Grafted Multi-Star Polymers and Investigation of their Self-Assembling Characteristics

Herein, we report the synthesis of amphiphilic multi-star architectures consisting of discrete poly(methacrylic acid)-based core cross-linked star polymers joined together by polystyrene-grafted linear connectors by a combination of atom transfer radical polymerisation of protected macroinitiator precursors and a copper-catalysed azide-alkyne cycloaddition grafting-to approach. The anisotropic multi-star architectures, which were obtained as individual di- and tri-star polymers with segregated hydrophobic and hydrophilic domains, undergo aggregation in apolar solvents resulting in the formation of large nanometre-scale vesicles. The self-assembling behaviour of these large amphiphilic multi-star polymers (Mw = 869–1097 kDa) was studied using dynamic light scattering, transmission electron microscopy, and atomic force microscopy.