Stimuli‐responsive elastomers are smart materials for sensing applications. Natural rubber (NR) is a renewable elastomer with excellent elasticity and fatigue resistance. In this work, a straightforward method for the preparation of pH‐responsive crosslinked materials from NR and poly(4‐vinylpyridine) (P4VP) via free radical crosslinking reaction using benzoyl peroxide (BPO) as an initiator is described. The effects of P4VP and BPO concentrations, reaction time and reaction temperature on immobilization percentage were investigated. It was found that the immobilization percentage reached 90% when using a P4VP concentration of 150 phr and a BPO concentration of 10 phr for 24 h at 90 °C. The pH responsiveness of the crosslinked materials was studied via water swelling, water contact angle and dye release measurements. Unlike unmodified rubber, the P4VP‐crosslinked NR was found to be pH‐responsive in acidic solution. Indigo carmine adsorption studies showed the Langmuir isotherm suggesting monolayer coverage of dye on the rubber surface. The dye could also be released upon increasing the pH of solution above 4. Based on these results, the introduction of pH responsiveness to NR will lead to novel responsive rubber‐based materials that can be used in biomedical and sensing applications. © 2016 Society of Chemical Industry

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Temperature-responsive polymers are smart materials that respond to changes in temperature, making them suitable for a range of applications. We report the synthesis and temperature-responsive behavior of N-vinylcaprolactam-grafted natural rubber. The grafting reaction was carried out using deproteinized natural rubber (DPNR) latex, with 2,2′-azoisobutyronitrile (AIBN) as the free radical initiator. The temperature responsiveness of the graft copolymers was investigated using water swelling and contact angle measurement and compared with that of pure DPNR. The graft copolymer was found to be temperature responsive in the range 32–34 °C, whereas the DPNR was not responsive to temperature. Since the temperature responsiveness of graft copolymer is near the human body temperature, it can be used to fabricate biomedical and sensing materials. Dye adsorption studies revealed the Langmuir isotherm, indicating monolayer coverage. The novel temperature-responsive natural rubber demonstrated in this study has potential uses in a wide range of applications.

We investigated the synthesis of a pH-responsive graft copolymer of natural rubber and 4-vinylpyridine. The grafting reaction was carried out using deproteinized natural rubber (DPNR) latex, with potassium persulfate as a free radical initiator. The pH responsiveness of the graft copolymer was investigated using water swelling and contact angle measurements, and was compared with that of pure DPNR. The graft copolymer was found to become responsive in solution at a pH of around 4. Indigo carmine adsorption studies identified the Langmuir isotherm, suggesting monolayer coverage. The adsorbed indigo carmine, a model anionic drug, and carbon dots, an emerging nanosized fluorophore, could be released from the graft copolymer by lowering the pH of the solution. The graft copolymer was tested as a heavy metal adsorbent, and demonstrated selectivity to copper(II) ions. The graft copolymer of 4-vinylpyridine and DPNR developed in this study is therefore a multifunctional, pH-responsive material with a wide range of potential applications, including sensing and catalysis, as a biomedical material and as an adsorbent.