Abstract

Four stimuli-responsive polymers of N-isopropylacrylamide (NIPA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and crosslinked derivatives by N,N′-methylene bisacrylamide (MBA) were synthesized: PNA, PAMPSA, PNAM, PAMPSAM. The effect of the cross-linker and methyl sulphonic acid (-CH3-SO3H) group on particle size, aggregation and volume phase transition temperature (VPTT) was investigated. Polymeric particles were synthesized via the surfactant free precipitation polymerization (SFPP) at 70 °C in the presence of cationic initiator 2,2′-azobis[2-methylpropionamidine] dihydrochloride (AMP) system. Chemical composition and morphology of investigated samples were evaluated using ATR-FTIR spectroscopy, 1H-NMR spectrometry and SEM-EDS techniques. The hydrodynamic diameters (HD), zeta potential (ZP), and polydispersity index (PDI) in aqueous dispersions were assessed by dynamic light scattering (DLS) between 18–42 °C. HD values at 18 °C for PNA, PAMPSA, PNAM, PAMPSAM polymers were approx. 32, 730, 715, 665 nm, and ZP values were −1.36, −0.01, 8.90, −0.09 mV, respectively. The VPTT range was observed between 29 and 41 °C. PDI’s for PNA and PNAM were low and varied between 0.276 and 0.460, and between 0.119 and 0.056, respectively. PAMPSA and PAMPSAM were characterized by higher PDI in the range 0.728–0.959 and 0.658–0.836, respectively. The results confirmed the thermal sensitivity of the synthesized polymers and indicated a significant polydispersity and aggregation tendency of the resulting molecules. The conductivity results were applied for the interpretation of the polymerization process.

Highlights

  • Four stimuli-responsive polymers of N-isopropylacrylamide (NIPA) and 2-acrylamido-2methyl-1-propanesulfonic acid (AMPSA) and crosslinked derivatives by N,N0 -methylene bisacrylamide (MBA) were synthesized: PNA, PAMPSA, PNAM, PAMPSAM

  • The polymerization reactions were performed under recurrent experimental conditions, whereas the initiator concentration was adapted to the 1:0.1 molar ratio between monomer and radical

  • The azobis[2-methylpropionamidine] dihydrochloride (AMP) concentration used in the reactions with monomer NIPA was ca. 2.24 M·dm−3 and in reactions with monomer

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Summary

Introduction

Four stimuli-responsive polymers of N-isopropylacrylamide (NIPA) and 2-acrylamido-2methyl-1-propanesulfonic acid (AMPSA) and crosslinked derivatives by N,N0 -methylene bisacrylamide (MBA) were synthesized: PNA, PAMPSA, PNAM, PAMPSAM. PAMPSA and PAMPSAM were characterized by higher PDI in the range 0.728–0.959 and 0.658–0.836, respectively. The results confirmed the thermal sensitivity of the synthesized polymers and indicated a significant polydispersity and aggregation tendency of the resulting molecules. “Stimuli-responsive polymers”, among numerous micropolymers, have received considerable attention from the chemical and pharmaceutical industry. This interest results from their characteristic features, like the ability to change physical or chemical properties under the influence of various external factors: temperature, pH, UV-VIS radiation, biological factors and others; the changes are reversible after the stimulus stops. The mechanism of action of thermally sensitive polymers may be based on the lower critical solubility temperature (LCST)—a parameter characterizing polymers and affecting the possibility of their practical application [5,6]

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