The "Grafting from" method refers to the use of active sites on the substrate surface to initiate in situ polymerization of monomers, which describes the use of surface-attached or self-assembled initiator molecules to grow polymer chains from the substrate surface, which sometimes Known as "surface-initiated polymerization". Alfa Chemistry can use the "Grafting from" method to add a thin layer of polymer brush to a solid surface, which determines the surface properties.
Introduction to The Method
In the "Grafting from" approach, the macromolecular backbone is chemically modified to introduce active sites capable of eliciting function. The initiation site can be introduced by copolymerization, can be introduced in a post-polymerization reaction, or can already be part of the polymer.
The "Grafting from" method is virtually molecularly exact in terms of controlling the density and thickness of the grafted brush. On the substrate surface, a self-assembled monolayer containing an initiator is first immobilized. These monolayers can be immobilized on practically any surface with a sufficient anchoring function, such as glass with silanes and gold, or plasma-oxidized polymers with Si/SiO2 and thiols. The initiator, catalyst, and monomers are then combined together on the surface to graft the polymer chains. In general, the conformations of polymer chains grafted on the substrate surface can be classified into four categories. "Pancakes", "Mushrooms", "Brushes" and "Highly stretched brushes".
Fig 1. Schematic of the conformations that polymer chains grafted onto a surface may adopt, as classified based on the polymer chain configuration in relation to the surface and as constrained by the polymer graft density. (Hedayati M, et al. 2019)
Controlled Polymerization Method for "Grafting from" Method
"Grafting from" reactions have been carried out from polyethylene, polyvinyl chloride and polyisobutylene. Different techniques such as anionic grafting, cationic grafting, atom transfer radical polymerization and free radical polymerization have been used to synthesize "Grafting from" copolymers. To achieve maximum control over brush density, polydispersity, and composition, while allowing block copolymer formation on the surface, there is a great need for controlled and living polymerization. Below are the different types of controlled aggregation methods we use for the "Grafting from" method.
| Controlled Polymerization Method | Description |
|---|
| Atom Transfer Radical Polymerization | ATRP is also recognized as a powerful controlled/living radical polymerization (CRP) method. Surface-initiated atom transfer radical polymerization (SI-ATRP) was established on this foundation. The versatility of SI-ATRP as a grafting method stems from its ability to precisely control and tune the structure and properties of the prepared hybrid materials. Methyl methacrylate (MMA) is considered to be one of the most promising monomers for the formation of polymer brushes via SI-ATRP. |
| Nitroxide - Mediated Polymerization | NMP is another living polymerization technique based on reversible end-capping of living chain terminal radicals with nitroxide leaving groups. Polysaccharide-based comb copolymers were prepared earlier using the NMP process to study cellulose grafting chemistry. |
| Reversible Addition - Fragmentation Chain Transfer Polymerization | RAFT polymerization differs from all other CRP methods in that it can be operated with a variety of monomers under various reaction conditions, due to its controlled molecular weight polymers and very narrow polydispersity. RAFT also provides access to functional polymers, cyclic polymers, gradient copolymers, block polymers, and star polymers. For other common biomedical materials such as PVC, RAFT combined with a "grafting-from" approach is also a useful technique. |
| Ring-Opening Metathesis Polymerization | ROMP is a variant of olefin metathesis that uses strained cyclic olefins to produce stereoregular and monodisperse polymers and copolymers. ROMPs of strained cyclic monomers, especially functionalized norbornene, have recently drawn attention to the modification of polymeric biomaterials to confer useful properties. |
| Other Techniques | There are several other types of CRP that can be used in "grafting" methods, such as living cationic polymerization (LCP) and living anionic polymerization (LAP). |
Fig 2. Strategies of polymer grafting: "grafting from".
Reference
- Hedayati M, et al. (2019). "The Quest for Blood-Compatible Materials: Recent Advances and Future Technologies." Mater. Sci. Eng. R Rep. 138: 118-152.
