Summary: The end coupling of living PSLi chains in hydrocarbon media by the addition of monoalkylbromides has been examined. A very selective PS–PS coupling reaction was obtained with neo‐pentylbromide (94%) at a ratio of PSLi/alkylbromide equal to 1 while the secondary and tertiary bromine derivatives yield only very limited coupling. The coupling mechanism is likely to involve a lithium‐bromine interchange at the PS chain end, generating polystyryl‐bromide which then reacts selectively with the remaining polystyryllithium chains.
Here, we show that a poly(ethylene oxide) polymer can be physically cross‐linked with silicate nanoparticles (Laponite) to yield highly extensible, bio‐nanocomposite fibers that, upon pulling, stretch to extreme lengths and crystallize polymer chains. We find that both, nanometer structures and mechanical properties of the fibers respond to mechanical deformation by exhibiting strain‐induced crystallization and high elongation. We explore the structural characteristics using X‐ray scattering and the mechanical properties of the dried fibers made from hydrogels in order to determine feasibility for eventual biomedical use and to map out directions for further materials development.
This work focused on the synthesis and aqueous self‐assembly of a series of novel hyperbranched star copolymers with a hyperbranched poly[3‐ethyl‐3‐(hydroxymethyl)oxetane] (HBPO) core and many linear poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) arms. The copolymers can synchronously form unimolecular micelles (around 10 nm) and large multimolecular micelles (around 100 nm) in water at room temperature. TEM measurements have provided direct evidence that the large micelles are a kind of multimicelle aggregates (MMAs) with the basic building units of unimolecular micelles. It is the first demonstration of the self‐assembly mechanism for the large multimolecular micelles generated from the solution self‐assembly of hyperbranched copolymers.
A solution processible polymer—poly(3,3‴‐didodecylquaterthiophene) (PQT‐12) is investigated at the liquid/solid interface using the scanning tunneling microscopy (STM). Two‐dimensional ordered films made up of self‐assembled domains, with dimensions of 100 nm × 50 nm adsorbed on highly oriented pyrolytic graphite (HOPG) were formed. These domains consist of parallel lamellar polymer chains, with the alkyl chains forming interdigitated structures, along with U‐shaped and closed ring segments of the polymer chains. A polymer chain packing model is proposed herein, which attempts to propose a correlation between the packing of long chains and charge mobilities. These STM results could help in understanding the relationship between the extended conjugation and molecular organization of the PQT‐12 chains.
A novel poly(aryleneethynylene), in which the main chain and the tetrathiafulvalene (TTF) side chains are coplanar, has been prepared and characterized. The polymer can self‐assemble in tetrahydrofuran (THF) and the π‐extended coplanar backbones adopt good face‐to‐face stacking, which is confirmed by X‐ray diffraction (XRD) analysis. Cyclic voltammetry has revealed that the polymer has reversible electroactive properties. The optical bandgap deduced by UV‐vis absorption spectroscopy and the electrochemical bandgap are 2.03 and 2.14 eV. The conductivities of the powder and the realigning solid of the polymer are 6 × 10−8 and 4 × 10−6 S cm−1.
A facile approach to polymer nanocomposites with single‐wall carbon nanotubes and cationic polymers is reported. The composite material was synthesized by producing carboxylic acid groups at the nanotube termini followed by a reaction with poly(allylamine) in water. Fourier transform infrared spectral and thermogravimetric analyses corroborate that the poly(allylamine) chains were wrapped on the surface of the carbon nanotubes. The scanning electron microscopic (SEM) image shows that the nanotubes were dispersed with little aggregation, thus, strongly suggesting that the poly(allylamine) chains have covered the single‐wall carbon nanotubes, which was further evidenced by transmission electron microscopy. The composites are soluble in water, and this solubilization process opens up new opportunities in the solution chemistry on pristine nanotubes.
Poly(vinyl acetate) (PVAc) nanogels are synthesized by a radical crosslinking copolymerization (RCC) in solution of vinyl acetate and divinyl adipate (DVA) or 2,4,6‐tris(allyloxy)‐1,3,5‐triazine (TAT) as the crosslinker, in the presence of a xanthate as a reversible chain transfer agent. Higher concentrations of crosslinker and lower concentrations of xanthate produce PVAc nanogels of higher molar masses, for a given concentration of xanthate and for a fixed concentration of crosslinker, respectively. The xanthate end‐groups allow for the synthesis of ‘second generation’ nanogels through a subsequent RCC from precursors. The chemical cleavage of the crosslinks yields individual poly(vinyl alcohol) chains, which attests that the length of the constitutive chains is controlled by the xanthate.
Properties characteristic of the size, shape, and orientation as well as the rigidity of PMMA end‐grafted to an amorphous silica surface are calculated by use of fully atomistic molecular dynamics simulations with MMA as explicit solvent. Both the number of grafted chains and their tacticity is varied. Firstly, properties of one atactic end‐grafted chain are compared to those of the same chain without any surface being present. Secondly one, two, and four atactic grafted chains are evaluated to study the influence of grafting density (at low surface occupancy) and thirdly, results of single grafted iso‐, syndio‐, and atactic chains, respectively, are compared to elucidate the influence of tacticity. Additionally, the used force field is validated by calculation of the diffusion coefficient of solvent molecules.
In the present study a population balance approach is described to follow the time evolution of bivariate molecular weight‐long chain branching (MW‐LCB) distributions in high pressure low density polyethylene autoclaves. The model formulation is based on a sectional grid method, the so‐called fixed pivot technique (FPT). According to this method, the ‘live’ and ‘dead’ polymer chain populations are assigned to a selected number of discrete points. Then, the resulting dynamic discrete‐continuous molar species equations for ‘live’ and ‘dead’ polymer chains are solved at the specified grid points. It is shown that a very good agreement exists between theoretical results and experimental data which proves the capability of the FPT method in calculating the joint MW‐LCB distribution for branched polymers.
A novel top‐surface imaging process was successfully established using selective chemisorption of amine‐functionalized poly(dimethyl siloxane) onto the carboxylic groups formed on the surface of diazoketo‐functionalized polymer film by UV light irradiation. The chemisorbed poly(dimethyl siloxane) worked as an efficient etch mask for the subsequent oxygen plasma etching process for pattern generation. High‐resolution patterns were resolved with the new imaging process.
A dramatic increase in the photostability of a blue‐light‐emitting polymer, poly(9,9‐dioctylfluorene), was achieved by the addition of 5–10 nm gold nanoparticles. The optical absorption band of the gold nanoparticles was tuned to resonate the triplet exciton ground state bandgap energy of the polymer. Photo‐oxidation rate of poly(9,9‐dioctylfluorene) was effectively reduced by doping the polymer with very small amounts (≈10−6–10−5 volume fraction) of the gold nanoparticles.
Retarded photo‐oxidation in PDOF nanocomposite films with various doped gold nanoparticles. 相似文献
Structured hybrid nanoparticles were synthesized via surface‐initiated atom transfer radical polymerization of MMA from ordered mesoporous silica (OMS) nanoparticles with various morphologies. The design of the OMS particles was adjusted to target either spherical core‐shell or cylindrical morphologies with a mean diameter below 400 nm. The polymer growth via ATRP from the silica surface was well‐controlled as demonstrated by the macromolecular characteristics of the grafted chains. Original hybrid multilayered nanoparticles composed of either a dense silica core or hollow core; an inner OMS shell showing radial orientation of the mesopores and an outer PMMA shell with controlled thickness were successfully prepared.
Summary: A comparison between the crystal structure of isotactic cis‐1,4‐poly(1,3‐pentadiene) previously predicted by molecular mechanics calculations and that successively determined by other authors by experimental data is reported. The agreement between the two structures is very good as far as the space group, the unit cell parameters and the conformation of the polymer chain are concerned. The mode of packing of the chains proposed in the experimental crystal structure is very similar to that found as relative minimum in the previous energy calculations. The coexistence, in different amounts, of these two modes of packing is suggested by the analysis of the simulated X‐ray spectra and by the results of new energy calculations.
A mode of packing of chains of isotactic cis‐1,4‐poly(1,3‐pentadiene). 相似文献
Spherical single‐chain‐particles of poly(N‐isopropylacrylamide) were prepared in aqueous solution above the lower critical solution temperature upon the addition of sodium dodecyl sulfate. The size of the single‐chain‐particles was investigated by means of transmission electron microscopy and viscosity measurements of the corresponding solutions, indicating the absence of inter‐chain entanglements among the single‐chain‐particles.
Schematic of the preparation of PNIPAM single‐chain‐globules in solution. 相似文献
A series of size‐controlled, cyclic poly(tetrahydrofuran)s ( of 4 400–8 600) that consist exclusively of the monomer, i.e., oxytetramethylene, unit ( I ) have been prepared in high yield through the metathesis polymer cyclization of a telechelic precursor having allyl groups, 1 , in the presence of a Grubbs catalyst, and the subsequent hydrogenation of the linking, i.e., 2‐butenoxy, unit in the presence of an Adams' catalyst (PtO2). A remarkable topology effect has subsequently been observed upon the isothermal crystallization of these two model polymers, showing distinctive spherulite growth rates and spherulite morphologies in comparison with the relevant linear poly(tetrahydrofuran) counterpart that has ethoxy end groups ( II ).
A PTFE film surface was modified using a combined plasma/ozone‐activated process. The modified PTFE film was further reacted with 2‐bromoisobutyryl bromide to incorporate ATRP initiators in the film surface. Surface‐initiated ATRP on PTFE films was performed using sodium styrene sulfate as a monomer. The poly(sodium styrene sulfate) chain length grafted onto PTFE film surfaces increased with increasing reaction time. Analysis using X‐ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and a contact angle analyzer gave evidence of the success of the PTFE surface modifications.
Biotinylated gradient glycopolymers have been synthesized via RAFT copolymerization of an acrylamide derivative of galactose with N‐acryloylmorpholine in the presence of a biotin CTA. The polymerization was controlled with a linear increase in molecular weights up to 80% conversion. Copolymer chains have a gradient microstructure with an increasing proportion of galactose units towards the ω chain end. The presence of the biotin ligand at the α end of the chains was confirmed by 1H NMR and MALDI‐ToF MS. This strategy based on the use of a biotin‐CTA instead of a post‐polymerization labelling of the chains resulted in a high percentage of α‐functionalized chains (92–95%). Such α‐end‐functionalized glycopolymer chains may interact with streptavidin‐modified surfaces.
