The well‐known thiol‐ene click reaction is used to polymerize dithiols and diacrylate monomers. Using catalytic amounts of hexylamine, poly(ester‐sulfide)s are synthesized via consecutive Michael additions between 1,4‐butanedithiol and 1,6‐hexanediol diacrylate. The molecular weight of the polymers is controlled by the stoichiometric balance of the reagents and by optimizing reaction time. Maximum conversion is achieved at close to 20 min at room temperature. Thermal characterization of the polymer shows a melting temperature of 53 °C and good thermal stability of up to 200 °C. The poly(β‐thioester) readily degrades when in contact with acetic acid or NaOH solutions, but also degradation under more biological relevant conditions is indicated by partial hydrolysis of the ester linkages in phosphate buffers.
The β-scission rate coefficient of tert-butyl radicals fragmenting off the intermediate resulting from their addition to tert-butyl dithiobenzoate-a reversible addition-fragmentation chain transfer (RAFT) agent-is estimated via the recently introduced electron spin resonance (ESR)-trapping methodology as a function of temperature. The newly introduced ESR-trapping methodology is critically evaluated and found to be reliable. At 20 °C, a fragmentation rate coefficient of close to 0.042 s(-1) is observed, whereas the activation parameters for the fragmentation reaction-determined for the first time-read EA = 82 ± 13.3 kJ mol(-1) and A = (1.4 ± 0.25) × 10(13) s(-1) . The ESR spin-trapping methodology thus efficiently probes the stability of the RAFT adduct radical under conditions relevant for the pre-equilibrium of the RAFT process. It particularly indicates that stable RAFT adduct radicals are indeed formed in early stages of the RAFT poly-merization, at least when dithiobenzoates are employed as controlling agents as stipulated by the so-called slow fragmentation theory. By design of the methodology, the obtained fragmentation rate coefficients represent an upper limit. The ESR spin-trapping methodology is thus seen as a suitable tool for evaluating the fragmentation rate coefficients of a wide range of RAFT adduct radicals.
A facile postmodification strategy for the surface functionalization of nanoparticles is presented based on [2 + 2] photoconjugation with particles made from miniemulsion polymerization of divinylbenzene.
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