Thermo- and pH-responsive copolymers based on oligoethyleneglycol methacrylates

Introduction The development of a variety of living and controlled polymerization techniques, such as anionic, radical and cationic polymerizations, has enabled the synthesis of well-defined polymer structures. With these techniques, the polymer length, the architecture as well as the monomer composition and distribution along the backbone can be controlled in an excellent manner. However, the effect of varying molecular structure and composition on the final polymer properties can often not be reliably predicted. To be able to understand the effect of molecular structure on the polymer properties, polymer scientists often prepare libraries of well-defined polymers having systematical changes in, e.g., polymer molecular weight, length and/or architecture to be able to determine (quantitative) structureproperty relationships. The synthesis and screening of such (co)polymer libraries can be accelerated by the use of high-throughput synthesis and screening equipment. In addition, the use of automated parallel synthesis robots increases the comparability of the different copolymers based on the elimination of human errors. Nowadays, the preparation of so-called ‘smart’ materials based on stimuli-responsive polymers attracts a lot of attention. Stimuli-responsive materials can be defined as polymers that undergo a phase transition when an external stimulus is applied. More specifically, polymers exhibiting a lower critical solution temperature (LCST) will be addressed. LCST polymers precipitate from aqueous solution upon heating corresponding to a transition from hydrophilic to hydrophobic. This intriguing behavior results from a delicate balance between hydrophobicity and hydrophylicity within the polymer. As a result, the LCST can be tuned upon incorporation of hydrophobic or hydrophilic comonomers. LCST polymers can be applied as ‘smart’ switchable materials in applications ranging from, e.g., actuators, hydrogels and drug delivery. 19 Besides such thermosensitive polymers, polymers having acidic or basic groups can undergo solubility transitions in aqueous solution upon changes in pH. Furthermore, the combination of thermosensitive and pH-responsive monomers can lead to double-responsive materials that can be addressed by changes in either temperature or pH. In this contribution, the synthesis, structural characterization as well as LCST determination of libraries of oligoethyleneglycol methacrylate (OEGMA) containing (co)polymers is discussed. These libraries include different lengths of OEGMAs as well as different length of the corresponding poly(OEGMA)s. In addition, the combination of OEGMAs with pH sensitive monomers, such as N,N-dimethylaminoethyl methacrylate (DMAEMA), will be reported resulting in double-responsive copolymers.