Investigation of Temperature Sensitivity Behaviors of Water Soluble Polyacrylamides Erdal Ug ˘uzdog ˘an, 1 Emir Baki Denkbas , 2 Osman Sermet Kabasakal 3 1 Chemical Engineering Department, Pamukkale University, Kinikli 20070, Denizli, Turkey 2 Chemistry Department, Hacettepe University, Beytepe 06800, Ankara, Turkey 3 Chemical Engineering Department, Eskisehir Osmangazi University, Meselik Campus 26480, Eskisehir, Turkey Correspondence to: O. S. Kabasakal (E-mail: osk@ogu.edu.tr) ABSTRACT: Temperature sensitive polymers with a lower critical solution temperature (LCST) are used in a variety of industries such as the pharmaceutical, cosmetic, food, and paint. These polymers are generally of the poly(N-alkylacrylamide) type, of which poly(N- isopropylacrylamide) (PNIPA) is the most commonly used. More novel poly(N-alkylacrylamide)s have also been the subject of much attention recently. In this study, N-alkylacrylamides containing different alkyl groups were synthesized by nucleophylic substitution reactions of various amines with acryloyl chloride. They were polymerized using the solution polymerization method, and the tem- perature sensitivities of the polymers were investigated. For this purpose, three monomers, N,N-diethylacrylamide, N-cyclopropylacry- lamide, and 4-piperidineethanolacrylamide, were synthesized using diethylamine, cyclopropylamine, and 4-piperidineethanol, as the amines, respectively. The obtained polymers, poly(N,N-diethylacrylamide) (PDEA), poly(N-cyclopropylacrylamide) (PCPA), and poly(4-piperidineethanolacrylamide) (PPEA), were found to be thermoresponsive, particularly PPEA is a potential novel material that can be utilized as an alternative to the common temperature sensitive polymers. The effects of several conditions on the LCST and the critical flocculation temperature (CFT) of the polymers were also investigated. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000–000, 2012 KEYWORDS: lower critical solution temperature; critical flocculation temperature; stimuli-sensitive polymers; water-soluble polymers; solution properties Received 20 April 2011; accepted 1 May 2012; published online 00 Month 2012 DOI: 10.1002/app.38008 INTRODUCTION Temperature-responsive water-soluble polymers that are exten- sively used as additives by pharmaceutical, cosmetic, food, and paint industries are of great scientific and technological impor- tance. These polymers are soluble in water at low temperatures but become insoluble as the temperature rises above the lower critical solution temperature (LCST). This feature has led to applications in bioengineering 1–5 and nanotechnology 6–8 and provides superiority to the future applications in the area of biosensors and membranes. Drug delivery systems, 9,10 human gene delivery vectors, 11,12 biocatalysts, 13,14 super absorbents, 15,16 the separation and purification of metal ions, 17,18 and biomole- cules 19,20 are among the most important fields in which temper- ature sensitive polymers are used. The phase separation behavior of the aqueous solutions of tem- perature-sensitive polymers is generally associated with the tem- perature dependency of hydrogen bonding and hydrophobic interactions, 21–23 but the mechanisms of this behavior have not been fully examined. Generally, poly(N-alkylacrylamide)s have temperature sensitivity properties. Poly(N-isopropylacrylamide) (PNIPA) that has been extensively studied as a thermo-respon- sive homopolymer, has a repeat unit that consists of hydrophilic (amide) and hydrophobic (isopropyl) groups. The LCST for lin- ear forms of PNIPA is about 32  C 24,25 in water, being close to the human body temperature that is 37  C. This value might restrict the usage of PNIPA in biomedical and biotechnological applications such as improving new controlled drug releasing systems and the use of polymeric-based materials as micro car- riers in enzymes. Both rapid changes in the application fields of temperature-sensitive polymers and the diversity of these appli- cations require synthesis of novel polymers with different LCST values. Therefore, the synthesis of temperature sensitive poly- meric materials having different LCST values has been exten- sively studied. These researches have been focused on two areas. One of them is about getting the LCST of known temperature sensitive polymers (i.e., PNIPA) to a specific value by chemical modification and the second area is synthesizing a novel V C 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2012, DOI: 10.1002/APP.38008 1