Synthesis of a thermo- and pH-sensitive comb-type graft copolymer by ionizing radiation
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Synthesis of a thermo- and pH-sensitive comb-type graft copolymer by ionizing radiation Victor H. Pino-Ramos and Emilio Bucio, Departamento de Química de Radiaciones y Radioquímica, Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, CDMX 04510, México Address all correspondence to Victor H. Pino-Ramos at [email protected] (Received 20 June 2018; accepted 6 August 2018)
Abstract A thermo-pH sensitive graft copolymer was successfully obtained by grafting 4-vinylpyridine and N-vinylcaprolactam onto silicone rubber ((SR-g-4VP)-g-NVCL)) in two-step using ionizing radiation as an initiator. Factors such as dose and monomer concentration remarkably affected the grafting yield. Surface grafted films were well characterized by means of infrared-attenuated total reflection, carbon-13 nuclear magnetic resonance, thermogravimetric analysis, and mechanical properties were also studied. Scanning electron microscopy demonstrated that the grafting was superficial; mechanical studies demonstrated that grafting caused loss elongation of SR films. The grafted films showed a critical pH close to physiological pH and a critical temperature (lower critical solution temperature) about 35 °C, therefore, this material presents potential biomedical applications as drug delivery.
Introduction In recent years, the use of thermo and pH-sensitive polymers have been widely recurred to obtain new biomaterials with hydrophilic properties as they contain functional groups that are able to ionize or establish hydrogen bonds in aqueous media. This kind of polymers is frequently used to synthesize biomaterials because of the phase transition that they present, when exposed to changes in their environments.[1,2] However, a pH-sensitive material presents changes on its conformation by ionization/deionization when the pH of medium changes; a thermo-sensitive polymer is a material that undergoes an abrupt change in the swelling degree when temperature of aqueous medium that surrounds it increases. The phase transition in such polymers is known as lower critical solution temperature (LCST).[3–5] A traditional way to synthesize new polymeric materials is through the organic synthesis; however, it takes many years for these materials to have some biomedical applications since they have to demonstrate their biocompatibility; therefore, an interesting alternative to obtain novel polymeric materials with potential applications in the medical field is by the surface modification of commercially available polymers.[6–10] By means of surface modification of polymers, it is possible to get materials with suitable properties according to the purpose for which it is working. Graft copolymerization by ionizing radiation is a well-established technique to produce or modify polymeric materials that combine the chemical and physical properties of both the base polymer and the grafted monomer without the need of a chemical initiator to simultaneously sterilize the material.[6–9,11]
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