Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking

In this study, six-arm star-shaped poly(<i>N</i>-vinylcaprolactam) (PNVCL) polymers prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization were subjected to aminolysis reaction using hexylamine. Chemically crosslinked gels or highly end-functionalized star pol...

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Autores principales:	Norma A. Cortez-Lemus, Eduardo Hermosillo-Ochoa, Ángel Licea-Claverie
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	aminolysis star polymers poly(<i>N</i>-vinylcaprolactam) end-group functionality chain-end functionalization RAFT Organic chemistry QD241-441
Acceso en línea:	https://doaj.org/article/54a31f56413a445c8abdd980e6fe663e
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spelling	oai:doaj.org-article:54a31f56413a445c8abdd980e6fe663e2021-11-11T18:43:36ZEffective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking10.3390/polym132136772073-4360https://doaj.org/article/54a31f56413a445c8abdd980e6fe663e2021-10-01T00:00:00Zhttps://www.mdpi.com/2073-4360/13/21/3677https://doaj.org/toc/2073-4360In this study, six-arm star-shaped poly(<i>N</i>-vinylcaprolactam) (PNVCL) polymers prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization were subjected to aminolysis reaction using hexylamine. Chemically crosslinked gels or highly end-functionalized star polymers can be obtained depending mainly on the type of solvent used during the transformation of the RAFT functional group. An increase in the viscosity of the solution was observed when the aminolysis was carried out in THF. In contrast, when the reaction was conducted in dichloromethane, chain-end thiol (PNVCL)<sub>6</sub> star polymers could be obtained. Moreover, when purified (PNVCL-SH)<sub>6</sub> star polymers are in contact with THF, the gelation occurs in just a few minutes, with an obvious increase in viscosity, to form physical gels that become chemically crosslinked gels after 12 h. Interestingly, when purified (PNVCL-SH)<sub>6</sub> star polymers were stirred in distilled water, even at high aqueous solution concentration (40 mg/mL), there was no increase in the viscosity or gelation, and no evident gels were observed. The analysis of the hydrodynamic diameter (<i>D<sub>h</sub></i>) by dynamic light scattering (DLS) did not detect quantifiable change even after 4 days of stirring in water. On the other hand, the thiol groups in the (PNVCL-SH)<sub>6</sub> star polymers were easily transformed into trithiocarbonate groups by addition of CS<sub>2</sub> followed by benzyl bromide as demonstrated by UV-Vis spectroscopical analysis and GPC. After the modification, the (PNVCL)<sub>6</sub> star polymers exhibit an intense yellow color typical of the absorption band of trithiocarbonate group at 308 nm. To further demonstrate the highly effective new trithiocarbonate end-functionality, the PNVCL polymers were successfully chain extended with <i>N</i>-isopropylacrylamide (NIPAM) to form six-arm star-shaped PNIPAM-<i>b</i>-PNVCL block copolymers. Moreover, the terminal thiol end-functionality in the (PNVCL-SH)<sub>6</sub> star polymers was linked via disulfide bond formation to <span style="font-variant: small-caps;">l</span>-cysteine to further demonstrate its reactivity. Zeta potential analysis shows the pH-responsive behavior of these star polymers due to <span style="font-variant: small-caps;">l</span>-cysteine end-functionalization. By this using methodology and properly selecting the solvent, various environment-sensitive star polymers with different end-groups could be easily accessible.Norma A. Cortez-LemusEduardo Hermosillo-OchoaÁngel Licea-ClaverieMDPI AGarticleaminolysisstar polymerspoly(<i>N</i>-vinylcaprolactam)end-group functionalitychain-end functionalizationRAFTOrganic chemistryQD241-441ENPolymers, Vol 13, Iss 3677, p 3677 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	aminolysis star polymers poly(<i>N</i>-vinylcaprolactam) end-group functionality chain-end functionalization RAFT Organic chemistry QD241-441
spellingShingle	aminolysis star polymers poly(<i>N</i>-vinylcaprolactam) end-group functionality chain-end functionalization RAFT Organic chemistry QD241-441 Norma A. Cortez-Lemus Eduardo Hermosillo-Ochoa Ángel Licea-Claverie Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking
description	In this study, six-arm star-shaped poly(<i>N</i>-vinylcaprolactam) (PNVCL) polymers prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization were subjected to aminolysis reaction using hexylamine. Chemically crosslinked gels or highly end-functionalized star polymers can be obtained depending mainly on the type of solvent used during the transformation of the RAFT functional group. An increase in the viscosity of the solution was observed when the aminolysis was carried out in THF. In contrast, when the reaction was conducted in dichloromethane, chain-end thiol (PNVCL)<sub>6</sub> star polymers could be obtained. Moreover, when purified (PNVCL-SH)<sub>6</sub> star polymers are in contact with THF, the gelation occurs in just a few minutes, with an obvious increase in viscosity, to form physical gels that become chemically crosslinked gels after 12 h. Interestingly, when purified (PNVCL-SH)<sub>6</sub> star polymers were stirred in distilled water, even at high aqueous solution concentration (40 mg/mL), there was no increase in the viscosity or gelation, and no evident gels were observed. The analysis of the hydrodynamic diameter (<i>D<sub>h</sub></i>) by dynamic light scattering (DLS) did not detect quantifiable change even after 4 days of stirring in water. On the other hand, the thiol groups in the (PNVCL-SH)<sub>6</sub> star polymers were easily transformed into trithiocarbonate groups by addition of CS<sub>2</sub> followed by benzyl bromide as demonstrated by UV-Vis spectroscopical analysis and GPC. After the modification, the (PNVCL)<sub>6</sub> star polymers exhibit an intense yellow color typical of the absorption band of trithiocarbonate group at 308 nm. To further demonstrate the highly effective new trithiocarbonate end-functionality, the PNVCL polymers were successfully chain extended with <i>N</i>-isopropylacrylamide (NIPAM) to form six-arm star-shaped PNIPAM-<i>b</i>-PNVCL block copolymers. Moreover, the terminal thiol end-functionality in the (PNVCL-SH)<sub>6</sub> star polymers was linked via disulfide bond formation to <span style="font-variant: small-caps;">l</span>-cysteine to further demonstrate its reactivity. Zeta potential analysis shows the pH-responsive behavior of these star polymers due to <span style="font-variant: small-caps;">l</span>-cysteine end-functionalization. By this using methodology and properly selecting the solvent, various environment-sensitive star polymers with different end-groups could be easily accessible.
format	article
author	Norma A. Cortez-Lemus Eduardo Hermosillo-Ochoa Ángel Licea-Claverie
author_facet	Norma A. Cortez-Lemus Eduardo Hermosillo-Ochoa Ángel Licea-Claverie
author_sort	Norma A. Cortez-Lemus
title	Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking
title_short	Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking
title_full	Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking
title_fullStr	Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking
title_full_unstemmed	Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking
title_sort	effective end-group modification of star-shaped pnvcl from xanthate to trithiocarbonate avoiding chemical crosslinking
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/54a31f56413a445c8abdd980e6fe663e
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Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking

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