This article proposes the first report on the synthesis of nanometric crosslinked polynorbornene particles by ring‐opening metathesis polymerization in dispersion using ruthenium‐based complex (PCy3)2Cl2RuCHPh as initiator. Stable but raspberry‐shaped particles were obtained. In this study, a particular attention was paid to the influence of the crosslinker nature and addition mode on reaction kinetics and morphology of the latex particles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Controlled-release systems have attracted much interest in biomedical applications, being able to reduce the toxicity of active pharmaceutical ingredients (APIs) by targeting their therapeutic action in the diseased tissues. These systems allow the use of new performance-active molecules, while overcoming secondary-effect issues. Several strategies have been developed to synthesize such materials: i) the extension of API release, ii) the increase of the circulating half-lives of drugs, and iii) the targeting of specific diseased areas in the organism.[1] A large range of techniques are used to focus the action of a drug, from the grafting of specific cell receptors onto carriers, to the development of environmentally responsive systems.[2]Among stimuli-responsive systems, thermally sensitive particles are widely used, [3] since thermal variations are easy to control and to apply both in vitro and in vivo. Each thermosensitive polymer has a critical temperature from which morphological changes can be observed. This can be attributed to solubility variations [4] (LCST: lower critical solubilization temperature, UCST: upper critical solubilization temperature), sol-gel transitions [5] (polymers designed with an amphiphilic balance) or changes of the chain mobility [6] (T g : glass transition). To date, most of the thermoresponsive polymers used for drug delivery have been focused on LCST control and amphiphilic balance. Controlled-release systems based on macromolecule chain mobility have been hardly or even never investigated, especially polymers exhibiting a T g above the body temperature requiring external stimuli to release the drug.Herein, we report the development of a new concept of thermoresponsive particles based on the original combination of two stimuli-responsive polymers organized in single submicron particles (200-500 nm) and their use as drug-delivery systems. Such particles exhibit a core-shell structure with a polynorbornene (PNB) core grafted with poly(ethylene oxide) (PEO). PNB is proposed to induce a T g effect, whereas the PEO chains exhibit an LCST behaviour. PNB is a non-cytotoxic polymer, [7] whose T g ranges from 35 to 45 8C depending on the chain length.[8] PEO is well known in the field of biomedical applications for it prevents drug-delivery systems from being recognized by the immune system, therefore enlarging the circulating half-lives.[9] PEO is soluble in water at room temperature (RT) and has a LCST~90 8C or more depending also on the chain length.[10] However, it has been proved that the PEO chains LCST slightly decreases when grafted onto a surface.[11]The case of hydrogels and interpenetrated networks (IPNs) has been already reported; however, the combination of two thermoresponsive polymers, respectively responsible for a T g and a LCST effect, has never been applied to the synthesis of sequential controlled drug-delivery systems. To date, low-T g hydrophilic segments allow rearrangements of polymer chains resulting in easier penetration of the physiological medium into the ...
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