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The present study provides a state of the art on methods for evaluating active chain density of rubbers from swelling experiments. This review focuses more particularly on the effects of components that are known to limit the swelling, and which typically results in an overestimation of the active chain density. These components are commonly considered as insoluble. Different corrections dealing with the two principal insoluble components, namely zinc oxide (Zn0) and carbon black (CB) filler, are thoroughly investigated. A comparative study on the same natural rubber (NR), either filled and unfilled, vulcanized with three different vulcanization systems, is performed to evaluate the relevance of each predictive approach. The results obtained highlight their respective limitations. In particular, it is shown that the swelling ratio of unfilled and filled natural rubbers are linearly related, suggesting that fillers have no significant effect on the overall number of cross‐links formed during vulcanization. As a result, we propose a unified approach for correcting the ZnO content for unfilled NR and both the ZnO and CB contents for filled NR. By comparing with results issued from uniaxial tensile tests, it is shown that the use of a mechanical response is a relevant alternative for determining the active chain density. [ABSTRACT FROM AUTHOR]

Nanogels are nanostructures with dimensions within the nanoscale, composed of crosslinked polymers through their functional groups. Nanogels can display sensitiveness to stimuli, such as pH or temperature. This characteristic has been used in the design of new platforms for the transport and release of active ingredients. Biopolymer‐based nanogels are of great interest due to their biodegradability, biocompatibility, nontoxicity, and among others. In this project, pH‐responsive nanogels are synthesized through a novel methodology, using two polysaccharides classified as safe, biocompatible, and easily accessible materials, i.e., chitosan (CS) and maltodextrin (MD). A reductive amination reaction between CS and partially oxidized MDs allows to synthesized MD/CS nanogels with sizes ranging from 90 ± 5 to 194 ± 40 nm and with a colloidal stability up to 7 weeks. It is found that the variation of nanogels size and charge depends on CS concentration, molecular weight, and pH, as well as on the % oxidation of the MD. As evidence of nanogels pH‐responsiveness, an increase of size and ζ‐potential is observed by decreasing the pH. This size increase is attributed to the swelling of the nanogels upon a change in pH. Finally, doxorubicin is encapsulated in MD/CS nanogels, with a loading capacity up to 57%. [ABSTRACT FROM AUTHOR]

Statistical copolymerization of a monovinyl with a divinylmonomerleads to macroscopic gels, microgels, or soluble branched copolymers,depending on the precise reaction conditions. This approach is widelyused for the manufacture of soft contact lenses and also to preparevarious biomedical hydrogels for the separation and purification ofproteins, DNA, etc. According to Flory–Stockmayer theory, gelationshould occur in such copolymerizations if there is more than 0.50fully reacted divinyl comonomer per primary chain. However, many experimentalstudies indicate significant deviations from this classical theory,which are generally believed to be due to wastage of the divinyl comonomervia intramolecular cyclization. Unfortunately, experimental verificationof this side reaction has proven elusive for the past seven decades.In the present study, we use a disulfide-based cleavable bifunctionalcomonomer to undertake the first experimental quantification of theextent of intramolecular cyclization in nonlinear methacrylic copolymersusing 1H NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The kinetics of swelling of a series of six near-monodisperse, lightly cross-linked poly(2-vinylpyridine) latexes with mean diameters ranging from 380 to 1010 nm has been investigated by the pH jump method using a commercial stopped-flow instrument. These pH-responsive particles become substantially protonated at around pH 4.1, which leads to a rapid latex-to-microgel transition within a time scale of tens of milliseconds. The characteristic swelling time correlates linearly with the mean particle diameter, as predicted by the Tanaka equation. However, faster swelling is observed in the presence of added salt. This is contrary to the theory developed by Tanaka, which assumes that the relaxation of the polymer chains is the rate-limiting step. An alternative viewpoint, in which infusion of solvent determines the characteristic swelling time, satisfactorily explains the experimental observations and collapses most of the data, except for the largest microgels. This discrepancy is suggested to be due to the inaccurate sizing of these micrometer-sized swollen microgels by dynamic light scattering.