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Polymers: Making New Materials
Published in Richard J. Sundberg, The Chemical Century, 2017
One of the main uses for poly(vinyl acetate) is for hydrolytic conversion to the water soluble polymer poly(vinyl alcohol), which is a surfactant and emulsifier. Vinyl alcohol is not a stable chemical entity, so it cannot be polymerized directly. Copolymerization of vinyl acetate with acrylic acid introduces anionic substitutents and the copolymer finds application in paper coating. Hydrophobic groups can be introduced by copolymerization with a long-chain α-olefin or lauryl vinyl ether. These materials give surfactants with high activity and increased viscosity. Copolymers with ethylene, vinyl chloride and methyl methacrylate are also manufactured. Poly(vinyl acetate) is also used as an adhesive. Poly(vinyl acetate) is also used in manufacture of controlled-release tablets and capsules, often in a mixture with poly(N-vinylpyrrolidone), which is known as povidone. The matrix or coating of the tablet or capsule slowly disintegrates as the polymer dissolves in aqueous media, allowing the active ingredient to diffuse out.17
Intelligent Scaffold–Mediated Enhancement of the Viability and Functionality of Transplanted Pancreatic Islets to Cure Diabetes Mellitus
Published in Gilson Khang, Handbook of Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine, 2017
Min Jun Kim, Hae Hyun Hwang, Dong Yun Lee
PVA is different from most vinyl polymers in that it is not just polymerized by the corresponding monomer. The monomer, vinyl alcohol, is unstable and tautomerizes to an acetaldehyde. After first polymerizing vinyl acetate, polyvinyl acetate groups are hydrolyzed to form vinyl alcohol groups.120 The polymerized PVA polymer is water soluble and thermoplastic. Because of the thermoplastic property, PVA undergoes gelation in aqueous solution to form various structures by microcrystallization through freeze-thaw processes. The gelation step of PVA involves repeated cycles of freezing at −80°C for 24 h and then rapidly thawing in 37°C medium for a few seconds.133,134 Therefore, when applied to corresponding materials, encapsulation is mainly used for macrocapsules because of its ability to reduce cellular damage.115,116 In addition, macroencapsulation using PVA results in higher physical strength and elastic character. In this regard, PVA modification has been used for the macroencapsulation of pancreatic islets.135 The first PVA-encapsulated islet cells were reported in 1992 from the Kyoto group. They designed a tube type of PVA modification with mesh reinforcement. PVA-islet macroencapsulation is processed by the interactions of the thiol-alkyl side chains with the isolated islets. PVA-modified islets can avoid the immune response, thus preventing a major factor in hyperacute rejection. Moreover, PVA hydrogel shows a very low permeability toward immunoglobulin G (Ig G),136 and its insulin content and secretion are better than in the untreated islet group.137 Thus, PVA polymers can used to avoid the host immune response and provide appropriate treatment for type 1 diabetes mellitus.
Polymers in Special Uses
Published in Manas Chanda, Plastics Technology Handbook, 2017
Poly(ethylene-co-vinyl alcohol) is a thermoplastic used extensively in laminates for food containers due to its excellent film forming and oxygen barrier properties. Limited evidence for the disappearance of the polymer was provided [121]. Whether or not the copolymer is biodegradable is apparently related to the size and distribution of the ethylene blocks.
Flurbiprofen-loaded interpenetrating polymer network beads based on alginate, polyvinyl alcohol and methylcellulose: design, characterization and in-vitro evaluation
Published in Journal of Biomaterials Science, Polymer Edition, 2020
On the other hand, methylcellulose (MC) is also a natural water-soluble carbohydrate polymer [23] and can be chemically crosslinked with a dialdehyde in the presence of a strong acid to form a hydrogel [32]. On the other hand, poly(vinyl alcohol) (PVA) is widely used in drug delivery systems due to its hydrophilic nature, biocompatibility, biodegradability, perfect chemical resistance, permeability and physical properties [33].
Porous solid carbon source-supported denitrification in simulated mariculture wastewater
Published in Environmental Technology, 2021
Hua Li, Qingsong Liu, Hongbiao Dong, Yafei Duan, Ziming Zhou, Jiasong Zhang
Poly(vinyl alcohol) (PVA) is a water-soluble material containing large amounts of hydroxyl groups. PVA has been widely applied because it has many advantages such as low cost, non-toxicity, biocompatibility, high durability and chemical stability [17]. Some investigations have been carried out on its application in the fields of separation processes, wound dressing and microorganism immobilization [18].