Triazolinedione-'clicked' poly(phosphoester)s : systematic adjustment of thermal properties

The thermal properties of halogen-free flame retardant poly(phosphoester)s from acyclic diene metathesis polycondensation have been optimized by a systematic post-modification using 1,2,4-triazoline- 3,5-dione derivatives. The straightforward modification not only increased their glass transition temperatures significantly but also improved the thermal stability with respect to their char yields

Fourier Transforms of Lorentz Invariant Functions

Fourier transforms of Lorentz invariant functions in Minkowski space, with support on both the timelike and the spacelike domains are performed by means of direct integration. The cases of 1+1 and 1+2 dimensions are worked out in detail, and the results for 1+n dimensions are given.Comment: 15 pages, 1 figur

Main-chain water-soluble polyphosphoesters: multi-functional polymers as degradable PEG-alternatives for biomedical applications

Polyphosphoesters (PPEs) are a class of (bio)degradable polymers with high chemical versatility and functionality. In particular, water-soluble PPEs with the phosphoester group in the polymer backbone are currently discussed as a potential alternative to poly(ethylene glycol) (PEG). Ring-opening polymerization of typically 5-membered cyclic phosphoesters gives straightforward access to various well-defined PPEs. Several PPE candidates have proven their biocompatibility in vitro in terms of cytocompatibility, antifouling properties, “stealth effect”, degradability (hydrolytic and enzymatic), and some promising in vivo results in drug delivery vehicles. The possibility to control the properties with the appropriate tuning of the lateral chain makes PPEs especially appealing. This review summarizes recent developments of such PPEs for biomedical applications, e.g. in protein-polymer conjugates, hydrogels for tissue engineering, or nanocarriers for drug and gene delivery. We summarize the progress made over the years, highlighting the strengths and the shortcomings of PPEs for these applications to date. We critically evaluate the current state of the art, try to assess their potential and to predict future perspectives, shedding light on the pathway that needs to be followed to translate into clinics

Defect engineering of polyethylene-like polyphosphoesters: Solid-state NMR characterization and surface chemistry of anisotropic polymer nanoplatelets

Anisotropic materials with very high aspect ratios, such as nanoplatelets, are an exciting class of materials due to their unique properties based on their unilamellar geometry. Controlling their size and surface-functionality is challenging and has only be achieved in some cases for synthetic polymers. We present a general approach to prepare polymer-nanoplatelets with control over the lateral size and basal functionality, by simple polycondensation of precisely spaced and functional phosphate groups in polyethylene-like polymers. Because of the relatively large size of the phosphate groups, they are expelled from the bulk crystal to the basal surface. This allows to control the chain-folding during crystallization, which we analyzed via solid-state NMR and TEM. Furthermore, we present chemistry “on the surface” of the platelets: the pendant ester group at the phosphate offers the possibility to introduce functional groups accessible for further chemical modification on the crystal surface. This is shown by introducing a 2-acetylthioethyl ester group and subsequently cleaving this 2-acetylthioethyl ester group to the free P–OH. Together, these results render polyethylene-like polyphosphoesters a versatile platform for soft-matter nanoplatelets as functional colloids

Impurity and edge roughness scattering in armchair graphene nanoribbons: Boltzmann approach

The conductivity of armchair graphene nanoribbons in the presence of short-range impurities and edge roughness is studied theoretically using the Boltzmann transport equation for quasi-one-dimensional systems. As the number of occupied subbands increases, the conductivity due to short-range impurities converges towards the two-dimensional case. Calculations of the magnetoconductivity confirm the edge-roughness-induced dips at cyclotron radii close to the ribbon width suggested by the recent quantum simulations

Superbase-enabled anionic polymerization of poly(alkyl cyanoacrylate)s:achieving well-defined structures and controlled molar masses

Poly(alkyl cyanoacrylate)s (PACAs) find extensive use as adhesives in engineering and medicine. However, their high reactivity often leads to wide molar mass dispersity and uncontrolled chain-end functionalities. Achieving precise polymer structures is crucial, particularly for medical applications to prevent oligomer toxicity. The conventional anionic polymerization of cyanoacrylates initiated by water results in high molar mass dispersities (Ð) and low end-group functionalities. Nonetheless, under specific conditions, anionic polymerization holds the potential for controlling the molar mass and Ð of PACAs. Here, we demonstrate the synthesis of well-defined PACAs by employing minute quantities (1%) of superbases to activate a functional thiophenol (PhSH) initiator. This strategy enables the attainment of adjustable molecular weights (Mn &gt; 20 kg mol−1) and moderate dispersities (Ð &lt; 1.4) for homopolymers and block copolymers. The selective initiation by thiophenol is confirmed through 1H DOSY NMR analysis. Furthermore, the controlled homo- and copolymerization of ACA derivatives highlights the remarkable performance of the superbase in conjunction with PhSH.</p

The microstructure of polyphosphoesters controls polymer hydrolysis kinetics from minutes to years

The stability and degradation rates of polymers in aqueous media are critical factors for their biomedical applications, as they must remain intact for a specific period of time before degrading or degrading on-demand to prevent potential accumulation and harmful effects. Polyphosphoesters (PPEs) are highly compatible with biological systems, and the ester bonds in the backbone allow for hydrolytic degradation. In this study, we have demonstrated that the degradation rate of various PPEs can be precisely controlled by minor modifications to the side-chain and the binding pattern around the phosphorous center in the polymer backbone. We synthesized a systematic library of water-soluble PPEs using ring-opening polymerization, resulting in polyphosphates and in-chain or side-chain polyphosphonates. Specifically, we investigated the degradation rates of side-chain polyphosphonates with different side-chain structures (methyl, ethyl, allyl, iso- or n-propyl) at pH = 8 and pH = 11. Our results indicate that the degradation mechanism is influenced by the type and size of the side-chain, as well as the pH. At pH = 11, hydrophilicity is a key factor, while at pH = 8, electron density on the phosphorus is crucial, leading to a random chain scission or a backbiting mechanism. We also observed that changing the binding pattern of the phosphorus or incorporating additional “breaking points” allowed us to tune the half-life times of the polymer from less than a day to several years. This study highlights the versatile stability of water-soluble PPEs, making them a promising option for various applications that require different hydrolysis rates, such as tissue regrowth.</p

Interfaces Within Graphene Nanoribbons

We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, in contrast to the behavior of the much studied electron gas waveguides. In the curved nanoribbons, the conductance is very sensitive to details such as whether regions of a semiconducting armchair nanoribbon are included in the curved structure -- such regions strongly suppress the conductance. Surprisingly, this suppression is not due to the band gap of the semiconducting nanoribbon, but is linked to the valley degree of freedom. Though we study these effects in the simplest contexts, they can be expected to occur for more complicated structures, and we show results for rings as well. We conclude that experience from electron gas waveguides does not carry over to graphene nanostructures. The interior interfaces causing extra scattering result from the extra effective degrees of freedom of the graphene structure, namely the valley and sublattice pseudospins.Comment: 19 pages, published version, several references added, small changes to conclusion

Collisions between equal sized ice grain agglomerates

Following the recent insight in the material structure of comets, protoplanetesimals are assumed to have low densities and to be highly porous agglomerates. It is still unclear if planetesimals can be formed from these objects by collisional growth. Therefore, it is important to study numerically the collisional outcome from low velocity impacts of equal sized porous agglomerates which are too large to be examined in a laboratory experiment. We use the Lagrangian particle method Smooth Particle Hydrodynamics to solve the equations that describe the dynamics of elastic and plastic bodies. Additionally, to account for the influence of porosity, we follow a previous developed equation of state and certain relations between the material strength and the relative density. Collisional growth seems possible for rather low collision velocities and particular material strengths. The remnants of collisions with impact parameters that are larger than 50% of the radius of the colliding objects tend to rotate. For small impact parameters, the colliding objects are effectively slowed down without a prominent compaction of the porous structure, which probably increases the possibility for growth. The protoplanetesimals, however, do not stick together for the most part of the employed material strengths. An important issue in subsequent studies has to be the influence of rotation to collisional growth. Moreover, for realistic simulations of protoplanetesimals it is crucial to know the correct material parameters in more detail.Comment: 7 pages, 11 figures, accepted by A&