Bending Behavior of Polymer Films in Strongly Interacting Solvents
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1129-V04-05
Bending Behavior of Polymer Films in Strongly Interacting Solvents Jianxia Zhang and John B. Wiley* Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148 U.S.A. ABSTRACT Several polymers show bending behavior on exposure to selected solvent systems. Either on emersion or evaporation of particular solvents, films can bend or curl within seconds. The response depends on the interaction between polymer chains and solvent molecules as well as the film geometry and surrounding temperature. INTRODUCTION Shape-memory polymers (SMP) have attracted much attention in recent years [1-5]. The driving forces for actuators based on these materials are varied. Examples include structural changes driven via electroactive stimuli [3], optical processes (photomechanics) [6] and variations in pH [7]. Here we investigate a simple mechanical response based on solvent uptake (swelling) and release. Polymer swelling is a well-known process and is dependent on the strong interactions between the polymer chains and a particular solvent [8]. Here we investigate a series of polymer-solvent combinations and study the rapidity of response as well as cycling in these processes. EXPERIMENTAL DETAILS Synthesis. The reagents 4-aminophenol, phenol, 6-chloro-1-hexanol, acryloyl chloride and polyethylene glycol 600 were purchased from Alfa Aesar and tetrabutylammoniumbromide from Sigma-Aldrich. All were used as received. 2,2’-azobisisobutyronitrile (AIBN) was purchased from either Sigma-Aldrich or Fisher Scientific and recrystallized from methanol before use. Synthesis of 4,4’-Dihydroxyazobenzene. 4,4’-Dihydroxyazobenzene was synthesized following the method of Hu et al. [9] 16.232 g (0.149 mol) of 4-aminophenol was dissolved in a mixture of 41 mL water and 41 mL concentrated HCl to form a suspension. And then the mixture was cooled with an ice-water bath with vigorous stirring. The solution of 11.308 g (0.164 mol) of sodium nitrite/35 mL water was added with a dropping funnel. In the mean time, 14.023 g (0.149mol) of phenol was dissolved in 15 g sodium hydroxide/50 mL and cooled to 0oC. Diazotized solution (the first reacted solution) was added to phenol solution dropwise. Then, HCl (12 M) was used to adjust pH to around 1.0. The reaction continued for another 2 hours with stirring. The precipitate was filtered and washed with excess
distilled water until a pH 7 was achieved. The crude product was recrystallized three times with acetone/water. Yield: 6.413 g (20.09%) Synthesis of 4,4’-bis (6-hydroxyhexyloxy)azobenzene. 4,4’-bis (6-hydroxyhexyloxy) azobenzene was synthesized following method of Kumaresan et al. [10]. This reaction was taken under dry nitrogen. 3.032 g (14.15mmol) of 4, 4’-dihydroxyazobenzene, 10.891 g (70.75 mmol) of potassium carbonate and 0.178 g (5% amount to 4,4’-dihydroxyazobenzene) of tetrabutylammoniumbromide were dissolved in 30mL anhydrous Dimethylformamide (DMF). The mixture was heated to 90 °C. 4.253 g (31.13 mmol, 4.15 mL) of 6-chloro-1-hexanol wa
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