Comb-Like Polymers Pendanted with Elastin-Like Peptides Showing Sharp and Tunable Thermoresponsiveness Through Dynamic Covalent Chemistry Jie Bo, Lei Wang, Wen Li, Xiuqiang Zhang, Afang Zhang Laboratory of Polymer Chemistry, Department of Polymer Materials, College of Materials Science and Engineering, Shanghai University, Nanchen Road 333, Shanghai, 200444, China Correspondence to: Wen Li (E - mail: wli@shu.edu.cn) Received 20 May 2016; accepted 5 July 2016; published online 00 Month 2016 DOI: 10.1002/pola.28228 ABSTRACT: Comb-like polymers carrying two elastin-like poly- peptide (ELP) pendants in each repeat unit were synthesized. The densely attached peptide chains afford these polymers with sharp thermally induced phase transitions, and their lower critical solution temperature (LCST) can be varied with molecu- lar weights, solution pH and salt concentrations. Through ami- no terminals in ELP pendants, oligoethylene glycol (OEG)- based dendrons cored with aldehyde were attached to the pol- ymers through dynamic covalent imines. By virtue of dynamic characteristics of these novel dendronized polymers, their LCSTs can be tuned significantly by dendron coverage to shift from that dominated by ELPs to that dominated by OEG dendrons. Furthermore, dendron coverage can be enhanced obviously by the thermally induced phase transitions or greatly by freezing the polymer aqueous solutions. The work provides a convenient methodology to improve thermoresponsiveness of ELPs through polymer topology and to switch their properties through dynamic covalent chemistry. V C 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 00, 000–000 KEYWORDS: elastin-like peptide; oligoethylene glycol; den- drimer; thermoresponsive polymer; dynamic covalent chemistry INTRODUCTION Thermoresponsive polymers are one of the most important stimuli-responsive materials due to their varies applications in the fields of material science and biolo- gy. 1 These polymers normally display a lower critical solu- tion temperature (LCST) behavior, which determines the soluble and precipitate state of the polymers in aqueous sol- utions. The most studied examples showing LCST behavior are acrylamide, oligoethylene glycol (OEG) and peptide-based polymers. 2 Among them, peptide-based polymers have attracted considerable attention to form one kind of unique smart biomaterials, as they not only show thermoresponsive property but also possess secondary structures which are key issues for bioactivities in living systems. To date, various peptide-based polymers with thermoresponsiveness have been reported, which were mainly constructed through two strategies. One is introduction of linear 3 or dendritic OEG moieties 4 to the side chains of polypeptides. Another is incorporation of thermoresponsive peptide units into the polymer backbone or side chains. 5 As one kind of intriguing thermoresponsive peptides, elastin-based peptides (ELPs) have been intensively investigated to construct peptide- based polymers due to their unusual viscoelasticity, reversible LCST (also called T t ) behavior, and specific ordered folding beyond LCST. 6 ELP-based thermoresponsive polymers have been explored for various applications in bio- materials and bioengineering, such as for creating “smart” surfaces, 7 drug delivery, 8 and tissue engineering. 9 The representative members of ELPs are those based on the pentapeptide VPGVG (V 5 valine, P 5 proline and G 5 glysine) (or its permutations), and the mechanical, conformational and thermoresponsive properties of linear (VPGVG)n have been extensively investigated. 10 It was found that their LCST behavior arises from the hydrophobic dehydration of valine groups, followed by the conformation change from random coil to ordered b-spiral structures, involving mainly type II b-turns. The LCSTs of (VPGVG) n can be modulated by various parameters, including chain length, concentration, pH value, salt and modification of inner or even end groups. 11 Recent- ly, research attention has also been paid to short elastin-like peptides composed of less than 10 repeat units of the penta- peptides, and it was found that these short analogues (even a single VPGVG unit) also exhibit similar inverse-temperature folding transitions as the long analogues. 12 Klok et al. 13 Additional Supporting Information may be found in the online version of this article. V C 2016 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 00, 000–000 1 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE