New process controls polymer development

The versatility of the RAFT technology provides enormous potential for the design and development of multifunctional polymers that are optimised for performance in a range of application areas that includes: surfactants, coatings, dispersants, nanomaterials, therapeutic or active delivery and personal care. Examples of block copolymer structures with distinctive physical and chemical properties will be presented and the performance attributes of these polymers will be highlighted. The general rules for matching RAFT agents to specific block copolymer compositions will be described and illustrated with a number of examples for accessing various copolymer compositions of relevance to cosmetic based formulations. Of particular interest has been the ability to make hydrophilic-hydrophobic or double hydrophilic block copolymers where the hydrophilic block is composed of unprotected monomers such as acrylic acid or 2-(dimethylamino)ethyl methacrylate. These types of polymers are being developed as new classes of surfactants, film-formers, dispersants and rheology modifiers.

The use of reversible deactivation radical polymerisations (RDRP)1 such as RAFT to generate polymers has given polymer chemists and formulators access to multifunctional polymers to improve the performance of products. RAFT (now referred to as ‘the novel process’) polymerisation is a versatile method for inferring living characteristics to conventional radical polymerisation (RP).2 The method is now well-established for providing control over molecular weight, dispersity, composition and architecture of polymers and offers a convenient route to well-defined, gradient, block and star polymers as well as more complex architectures that include microgels and polymer brushes (Fig. 1).3-8 The process can be applied to most monomers polymerisable by RP; and can also be used to modify polysiloxanes, polyethylene glycol and other condensation based polymers. It is important to select the agent according to the monomers being polymerised and reaction conditions. The substituents of the novel process agents are labelled Z and R (Fig. 3, top). The Z group is responsible for the activation of the C=S double towards radical attack from the initiator or the propagating polymer chain (addition step). The R group should be a good free-radical leaving group (fragmentation step), capable to reinitiate monomer addition through radical polymerisation. Since each addition and fragmentation step results in the formation of the identical novel process endgroup, this process is reversible and ensures the formation of polymer chains with the same length as well as same composition as long as the addition step is faster than the fragmentation step. At the same time, each polymer chain is end-functionalised with both R and Z groups, which facilitates the incorporation of functionality at the chain end. Since the effectiveness of the novel process agents is determined by the substituent R and Z and guidelines for selection have been proposed (Fig. 2 and Fig. 3).4,5 Dithioester and trithiocarbonate novel process agents are good for the polymerisation of more activated monomers (MAM) e.g. methyl methacrylate (MMA), methacrylic acid (MAA), hydroxypropyl methacrylamide (HPMAM), methyl acrylate (MA), acrylic acid (AA), acrylamide (AM), acrylo-nitrile (AN) and styrene (St). Xanthates and dithiocarbamates are suited for the less activated monomers (LAM) e.g vinyl acetate (VAc), N-vinylpyrrolidone (NVP) and N-vinylcarbazole (NVC). Recently, we reported 4-pyridinyl-N-methyldithiocarbamate derivatives that can be switched to allow control of both MAM and LAM.9,10

Discussion