We recently reported cationic cyclopolymerization of o-vinylbenzaldehydes initiated by boron trifluoride to generate acid-sensitive poly(o-(α-alkyl)vinylbenzaldehyde). Herein we report preparation of core-shell microcapsules (μCs) using flow-focusing microfluidic techniques with shells composed of poly(o-(α-methyl)vinylbenzaldehyde) (PMVB) that release their payload in response to dilute aqueous acid solution. Release profiles of encapsulated fluorescein isothiocyanate-labeled dextran from μCs are controlled by varying the proton concentration and shell-wall thickness. SEM studies indicate that the system's unique reversible release mechanism involves porosity changes in the shell wall due to microcrack formation.

Transient electronics are designed to operate for programmed life times and then degrade leaving little to no trace behind. The initial work on transient electronics has been focused on biomedical applications in which the electronics are implanted, but eventually degrade and resorb into the body after the treatment is complete [1]. Biomedical transient electronics typically use a water soluble substrate, such as silk that slowly degrades as water diffuses into the substrate. However, the ability to more precisely program the lifetime of electronics and utilize other degradation stimuli would enable new applications in a variety of industries. Essential to this effort is the development of a new class of degradable substrates that can be triggered to degrade by exposure to a variety of environmental stimuli (e.g., mechanical stress, UV light, pH). In this study, we present a photodegradable transient substrate made of cyclic poly(phthalaldehyde) (PPA) doped with a photo-acid generator (PAG). Exposing the substrate to UV light generates acid through reaction of the PAG which then promotes the cleavage of the acetal backbone of PPA, leading to rapid fi lm degradation. We monitored the degradation of the fi lm using dynamic mechanical analysis and Fourier transform infrared spectroscopy. Results demonstrate that the polymer degrades into monomer and that the degradation rate is controlled by varying the concentration of PAG and the intensity of the UV source. In addition, electronic transistors, diodes, and resistors were fabricated from magnesium and silicon nanomembranes using our newly designed substrate. A combination of transfer-printing and electron-beam evaporation were used to demonstrate lithographic compatibility. We demonstrate electronic transience of a Mg resistor in as fast as 20 minutes with substantial physical degradation in 72 hours. REFERENCE [1] Hwang, S.-W., et. al. Science. 2012, 337, 1640.

Triggerable transient electronics are demonstrated with the use of a metastable poly(phthalaldehyde) polymer substrate and encapsulant. The rate of degradation is controlled by the concentration of the photo-acid generator and UV irradiance. This work expands on the materials that can be used for transient electronics by demonstrating transience in response to a preselected trigger without the need for solution-based degradation.

The cationic cyclopolymerization of o-vinylbenzaldehydes initiated by boron trifluoride is described. Unlike the incomplete conversion of o-vinylbenzaldehyde (1) at 0 °C, α-methyl-substituted monomers (2) and (3) undergo cyclopolymerizations with complete conversions at -78 °C. On the other hand, α-phenyl-substituted monomer (4) generated indenyl alcohol (7) when subjected to cationic polymerization conditions. The proposed mechanism for o-(α-methyl)vinylbenzaldehyde polymerization explains the importance of reaction temperature for polymer formation. Resulting amorphous poly(o-(α-methyl)vinylbenzaldehyde (10) exhibited good thermal stability (Tonset = 340 °C) with a Tg of 153 °C. Polymer (10) is a brittle and glassy plastic with a storage modulus (E') of 3 × 108 Pa and elongation at break of ∼3%.

Synthesis and morphological characterization are reported for a series of 13 precision branched polyethylene structures, the branch being placed on every 39th carbon and varying in size from methyl to pentadecyl group. A recently established synthetic scheme for preparation of the symmetrical alpha,omega-diene monomer was employed to increase the number of methylene carbons between the branch points from 20 to 38, yielding polymers with 5.26 mol % alpha-olefin incorporation. The morphology of these polymers was investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAX])), and transmission electron microscopy (TEM). Methyl branching significantly reduces the melting point and single crystal lamellae thickness of unbranched polyethylene. On the other hand, all further branches from ethyl to pentadecyl produce polymers that have similar melting points and single crystal lamellae thicknesses. A dear change in the morphology of both solution and melt-grown crystals of these polymers was observed from a situation where the methyl branch is incorporated in the polymer's unit cell to one where branches of greater mass are mostly expelled from the unit cell.

The morphology of ADMET-synthesized polyethylene with n-butyl branches precisely spaced on every 39th carbon (EH39) was studied in comparison with an ethylene/1-hexene addition copolymer possessing the same branching probability, the goal being to elucidate the effect of the intramolecular sequence length heterogeneity on the lamella crystal thickness and its distribution: EH39 was found to have an orthorhombic crystalline polymorphism, which is normal for commercialized polyethylenes and different from that of the other ADMET polyethylenes with shorter CH(2) spacing (C15, C21). EH39 exhibits a narrow lamella thickness distribution; the average thickness (l(c,av)) corresponds exactly to the space length between two consecutive branches, suggesting the complete exclusion of n-butyl branches from the crystal stem. The average thickness, l(c,av). mentioned above is also coincident with that obtained from WAXS and SAXS. On the other hand, the 1-hexene copolymer forms much thicker lamellae and a-broader thickness distribution than ADMET polyethylene. Here, the average thickness l(c,av). determined by TEM observation of the copolymer is 1.5 times larger than that calculated from the most probable ethylene sequence length obtained from (13)C NMR, or for a theoretical ethylene sequence length distribution, indicating that the lamellae are composed predominantly of the sparsely branched longer ethylene sequences' that are statistically included. The intramolecular sequence distribution is considered significant to determine the lamella thickness and thickness distribution for short chain-branched polyethylenes with a narrow intermolecular chemical composition distribution.

A symmetrical α,ω-diene monomer with a 36 methylene run length was synthesized and polymerized, and the unsaturated polymer was hydrogenated to generate precision polyethylene possessing a butyl branch on every 75th carbon (74 methylenes between branch points). The precision polymer sharply melts at 104 °C and exhibits the typical orthorhombic unit cell structure with two characteristic wide-angle X-ray diffraction (WAXD) crystalline peaks observed at 21.5° and 24.0°, corresponding to reflection planes (110) and (200), respectively.

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTReducing Branch Frequency in Precision PolyethyleneFabio Zuluaga†, Bora İnci‡, Yoshinobu Nozue§, Satoru Hosoda§, and Kenneth B. Wagener*‡View Author Information† Departamento de Química, Universidad del Valle, AA 25360, Cali, Colombia‡ Center for Macromolecular Science and Engineering, The George and Josephine Butler Polymer Research Laboratory, Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200§ Petrochemicals Research Laboratory, Sumitomo Chemical Company, Kitasode 2-1, Sodegaura, Chiba 299-0295, Japan*Corresponding author. E-mail: [email protected]Cite this: Macromolecules 2009, 42, 14, 4953–4955Publication Date (Web):June 24, 2009Publication History Received24 April 2009Revised10 June 2009Published online24 June 2009Published inissue 28 July 2009https://doi.org/10.1021/ma9009005Copyright © 2009 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1207Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Condensation,Monomers,Nucleic acid structure,Polyethylene,Polymers Get e-Alerts

Metathesis polycondensation chemistry has been employed to control the crystalline morphology of a series of 11 precision-branched polyethylene structures, the branch being placed on each 21st carbon and ranging in size from a methyl group to an adamantyl group. The crystalline unit cell is shifted from orthorhombic to triclinic, depending upon the nature of the precision branch. Further, the branch can be positioned either in the crystalline phase or in the amorphous phase of polyethylene, a morphology change dictated by the size of the precision branch. This level of morphology control is accomplished using step polymerization chemistry to produce polyethylene rather than conventional chain polymerization techniques. Doing so requires the synthesis of a series of unique symmetrical diene monomers incorporating the branch in question, followed by ADMET polymerization and hydrogenation to yield the precision-branched polyethylene under study. Exhaustive structure characterization of all reaction intermediates as well as the precision polymers themselves is presented. A clear change in morphology was observed for such polymers, where small branches (methyl and ethyl) are included in the unit cell, while branches equal to or greater in mass than propyl are excluded from the crystal. When the branch is excluded from the unit cell, all such polyethylene polymers possess essentially the same melting temperature, regardless of the size of the branch, even for the adamantyl branch.

Novel, segmented non-chain extended polyureas were synthesized. Soft segments (SS) were based on poly(tetramethylene glycol) (PTMO) (average molecular weight 1000 or 2000g/mol) and hard segments (HS) were based on a single molecule of a diisocyanate, which was either 1,6-hexamethylene diisocyanate (HDI), 1,4-phenylene diisocyanate (pPDI) or 1,4-trans-cyclohexyl diisocyanate (CHDI). An increase in the SS molecular weight was found to lead to an increased formation of SS crystallites below 0°C, which increased the low temperature modulus. Both 1K and 2K PTMO-based polyureas showed a microphase separated morphology, where the HS formed thread-like, crystalline structures that were dispersed in the continuous SS matrix. Upon deformation, the HS were found to breakdown into distinctly smaller threads, which oriented along the direction of the strain; this effect was found to be partially reversible and time dependent. Both the 1K and 2K polyureas based on HDI HS were found to be thermally stable and potentially melt-processible.

: Metastable polymeric materials were synthesized, formulated with additives and microcapsules, and then processed into films that served as substrates on which electronic devices were fabricated. New to this effort was the intentional development of depackaging cascades -- the rational design of materials that depolymerize on exposure to specific stimuli. In particular, we investigated acid-sensitive, depolymerizable poly(phthalaldehyde) (PPA), and thermally- and base-sensitive poly(olefin sulfone) (POS) polymers. Conditions for film preparation and fabrication of transient electronics on robust PPA and POS films were optimized. Three degradation triggers -- direct activation by photoacid generation, thermal activation, and mechanical rupture of acid-filled microcapsules -- were investigated.