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[Abstract] Poly(lactic acid) (PLA) is an attractive candidate for replacing petrochemical polymers because it is fully biodegradable. This study investigated the potential of PLA as a sustainable and environmentally friendly alternative material that can be developed into commercially viable wearable mosquito repellent devices with desirable characteristics. PLA strands containing DEET and IR3535 were prepared by twin screw extrusion compounding and simultaneously functioned as plasticizers for the polymer. The plasticizing effect was investigated by thermal and rheological studies. DSC studies showed that the addition of DEET and IR3535 into PLA strands reduced the glass transition temperature consistent with predictions of the Fox equation, thus proving their efficiency as plasticizers. The rheology of molten samples of neat PLA and PLA/repellents blends, evaluated at 200 °C, was consistent with shear-thinning pseudoplastic behaviour. Raman studies revealed a nonlinear concentration gradient for DEET in the PLA strand, indicating non-Fickian Type II transport controlling the desorption process. Release data obtained at 50 °C showed initial rapid release followed by a slower, near constant rate at longer times. The release rate data were fitted to a novel modification of the Peppas-Sahlin desorption model

Single-walled carbon nanotubes (SWCNTs) are pre-functionalized with a pyridinyl-based dithioester to undergo a hetero Diels-Alder (HDA) reaction with cyclopentadienyl end-capped poly(methyl)methacrylate (Mn = 2700 g mol-1, PDI = 1.14). Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis (EA), and X-ray photoelectron spectroscopy (XPS) evidence the success of the grafting process. The estimated resulting grafting density (from XPS and EA) via the HDA reaction increases by a factor of more than two (0.0774 chains·nm-2 via XPS) compared with typical values obtained via a direct cyclopentadiene driven Diels-Alder conjugation onto non-functional SWCNTs under similar conditions. Cyclopentadienyl end-capped polymer strands react at the surface of pre-functionalized single-walled carbon nanotubes with a pyridine-based dithioester through a hetero Diels-Alder reaction. Elemental analysis and X-ray photoelectron spectroscopy are employed to determine the grafting density. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Without previous modification, single-walled carbon nanotubes (SWCNTs) react as dienophiles in a single-step Diels-Alder [4 + 2] cycloaddition with diene terminal polymer strands. Cyclopentadienyl-capped poly(methyl methacrylate) (Mn = 2900 g mol-1, PDI = 1.2) was grafted onto SWCNTs under mild conditions at ambient temperature as well as at 80 °C in the absence of any catalyst. Thermogravimetric analysis, elemental analysis, and X-ray photoelectron spectroscopy confirm the success of the reaction and allow to estimate the grafting density of the polymer chains on the SWCNTs via the above three independent methods (average grafting density of 0.064 mmol g-1 (0.029 chains nm-2) for samples reacted at ambient temperature and 0.086 mmol g-1 (0.039 chains nm-2) for samples reacted at 80 °C). In addition, high-resolution transmission electron microscopy images confirmed the presence of an amorphous polymer layer (∼3 nm) around the SWCNTs after functionalization. © 2011 American Chemical Society.

Block copolymers in seconds: Catalyst-free, ambient-temperature click conjugation of individual polymer strands becomes possible using novel ATRP-derived cyclopentadienylcapped polymers in an extremely rapid hetero-Diels-Alder cycloaddition with macromolecules equipped with electron-deficient dithioester end groups prepared by the RAFT process. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

The past 5 years have seen a significant increase in the understanding of the fate of so-called mid-chain radicals (MCR), which are formed during the free radical polymerization of monomers that form highly reactive propagating radicals and contain an easily abstractable hydrogen atom. Among these monomers, acrylates are, beside ethylene, among the most promi-nent. Typically, a secondary propagating acrylate-type macro-radical (SPR) can easily transfer its radical functionality via a six-membered transition state to a position within the polymer chain (in a so-called backbiting reaction), creating a tertiary MCR. Alternatively, the radical function can be transferred intramolecularly to any position within the chain (also forming an MCR) or intermolecularly to another polymer strand. This article aims at providing a comprehensive overview of the up-to-date knowledge about the rates at which MCRs are formed, their secondary reactions as well as the consequences of their occurrence under variable reaction conditions. We explore the latest aspects of their detection (via electron spin resonance spectroscopy) as well as the characterization of the polymer structures to which they lead (via high resolution mass spectrometry). The presence of MCRs leads to the formation of branched polymers and the partial formation of polymer networks. They also limit the measurement of kinetic parameters (such as the SPR propagation rate coefficient) with conventional methods. However, their occurrence can also be used as a synthetic handle, for example, the high-temperature preparation of macromonomers. © 2008 Wiley Periodicals, Inc.