28 Sep Thermosensitive Polymers as Smart Materials

Thermosensitive polymers are a class of “smart” materials that have the ability to respond to a change in temperature. Such polymers are uncommon as they are soluble in water at low temperature and become non-soluble when increasing the temperature. Because of their change of physical properties triggered by temperature stimulus, thermosensitive polymers are materials of interest in a wide range of applications such as drug delivery, surface coating, films and membranes, actuators or water treatment. The change of thermosensitive polymer physical state occurs at the LCST and depends on the polymer chemical structure and its interaction with water.

SPECIFIC POLYMERS synthesizes a broad array of monomers and polymers of interest in this area.

(Meth)acrylamides

The best-known class of thermosensitive polymers are based on (meth)acrylamide monomers. Among them, N-iso-propylacrylamide (NiPAm) has been the most studied to synthesize Poly(NiPAM) Thermosensitive Polymer (LCST: 32°C). SPECIFIC POLYMERS offers a variety of (meth)acrylamide monomers and corresponding homopolymers that exhibit LCST values in different temperature domains and thus of interest for various applications.

Factors influencing polymer LCST values

LCST values depend on polymer concentration and homopolymer molecular weight. The concentration directly influence polymer-water interactions. Increasing homopolymers molecular weight is in favor of polymer-polymer interaction and thus lead to a decrease of the LCST.

Other factors can have a significant impact on the LCST :

• Chain end functionalized thermosensitive polymers: Hydrophilic functional groups will tend to increase the LCST value. This will be all the more pronounced  for low molecular weight homopolymers. (See examples of chain-ends functional polyNiPAM below).
• Thermosensitive copolymers : Copolymerization of aforementioned monomers with hydrophilic or hydrophobic co-monomers can have significant impact on the LCST value. Hydrophlic co-monomers will increase the LCST and conversely. High ratio of co-monomers can even lead to the loss of thermosensitive properties. (See examples of thermosensitive copolymers below).
• Thermosensitive copolymers architecture : For block polymers, each block conserve its own LCST whereas, for statistical copolymers, resulting LCST value an average value of each corresponding homopolymers.
• Dispersity have an influence on the width of the transition from soluble to insoluble. To reduce polydispersity, Controlled Radical Polymerizations (CRP) can be used.

Thermosensitive copolymers

SPECIFIC POLYMERS can copolymerize aforementioned monomers in order to prepare functional thermosensitive copolymers. As for examples, NiPAM or NnPAM were copolymerized with MAPC₁ leading to thermosensitive copolymers bearing phosphonic acid moieties. Increasing the ratio of phosphonated functional groups came with an increase of the LCST. Such polymers were shown to be of great interest for the treatment of metallic pollution in wastewater. [2][3]