Synthesis and self-assembly behavior of thermoresponsive poly(oligo(ethylene glycol) methyl ether methacrylate)-POSS with tunable lower critical solution temperature

This article reports on the synthesis of a novel amphiphilic polyhedral oligomeric silsesquioxane (POSS) end-capped poly(2-(2-methoxyethoxy)ethyl methacrylate)-co-oligo(ethylene glycol) methacrylate) (POSS-P(MEO₂MA-co-OEGMA)). These thermoresponsive organic–inorganic hybrid polymers exhibit critical phase transition temperature in water, which can be finely tuned by changing the feed ratio of OEGMA and MEO₂MA. The lower critical solution temperature (LCST) of POSS-P(MEO₂MA-co-OEGMA) increases from 31 to 59 °C with the increasing of OEGMA content. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies show that these polymers can self-assemble into spherical micelles with the thermosensitive block into the corona and the POSS forming the core, and larger aggregates are formed when the temperature values are above their LCSTs. These thermoresponsive polymers POSS-P(MEO₂MA-co-OEGMA) with self-assembly behavior and tunable tempetature-responsive property have the potential applications in material science and biotechnology.     

The doubly thermo-responsive triblock copolymer nanoparticles prepared through seeded RAFT polymerization

The doubly thermo-responsive triblock copolymer nanoparticles of polystyrene-block-poly(N-isopropylacrylamide)-block-poly[N,N-(dimethylamino) ethyl methacrylate] (PS-b-PNIPAM-b-PDMAEMA) are successfully prepared through the seeded RAFT polymerization in situ by using the PS-b-PNIPAM-TTC diblock copolymer nanoparticles as the seed. The seeded RAFT polymerization undergoes a pseudo-first-order kinetics procedure, and the molecular weight increases with the monomer conversion linearly. The hydrodynamic diameter (D _h) of the triblock copolymer nanoparticles increases with the extension of the PDMAEMA block. In addition, the double thermo-response behavior of the PS-b-PNIPAM-b-PDMAEMA nanoparticles is detected by turbidity analysis, temperature-dependent 1H-NMR analysis, and DLS analysis. The seeded RAFT polymerization is believed as a valid method to prepare triblock copolymer nanoparticles containing two thermo-responsive blocks.     

Thermo- and pH- dual responsive inorganic-organic hybrid hydrogels with tunable luminescence

A thermo- and pH- dual responsive luminescent hydrogel was successfully constructed by coupling dysprosium-containing polyoxometalates Na₉DyW₁₀O₃₆ (DyW₁₀) with the ABA triblock copolymer, where the B block is PEO and the A block is the thermosensitive poly(methoxydi(ethylene glycol) methacrylate-co-N,N-dimethylaminoethyl methacrylate). The complex hybrid underwent a sol-gel phase transition above the lower critical solution temperature (LCST) of the A block. DyW₁₀ was electrostatically encapsulated into the hydrophobic domain of the A block with enhanced photoluminescence. When temperature cooled down, the luminescence could be restored. By addition of acids to protonate the A block, and emission of DyW₁₀ was simultaneously enhanced. Sensitivity of poly(N,N-dimethy laminoethyl methacrylate) (PDMAEMA) to pH also enabled the emission of DyW₁₀/copolymer hydrogel to be reversibly switched by alternating acid/base treatments.     

Phase transition temperature controllable poly(acrylamide-<Emphasis Type="Italic">co</Emphasis>-acrylic acid) nanocomposite physical hydrogels with high strength

Poly(acrylamide-co-acrylic acid) nanocomposite physical (P(AAm-co-AAc)NCP) hydrogels have been prepared through the in situ free radical solution polymerization based on a “single network, dual cross-linkings” strategy. The P(AAm-co-AAc) NCP hydrogels are composed of nanobrushes of P(AAm-co-AAc) chains grafted on the surface of vinylhybrid silica nanoparticles (VSNPs). In the hydrogel system, the VSNPs act as the “analogous chemical cross-linking points” once the hydrogen bonds formed between the P(AAm-co-AAc) chains of the nanobrushes, thus leading to the fabrication of high-strength P(AAm-co-AAc) NCP hydrogels. Compared with conventional thermosensitive P(AAm-co-AAc) hydrogels, the P(AAm-co-AAc) NCP hydrogels have a broader range of phase transition temperature, which can be adjusted by altering the monomer ratio, the VSNPs concentration, the addition of urea and N,N-dimethylacrylamide (DMAAm). At the same time, the mechanical properties of the P(AAm-co-AAc) NCP hydrogels have been improved significantly by the introduction of VSNPs. Furthermore, both the phase transition and the tensile strength of the P(AAm-co-AAc) NCP hydrogels are largely influenced when Fe³⁺ ions are introduced as the ionic crosslinkers into the hydrogel networks.     

RAFT polymerization of linear ABC triblock copolymer P<Emphasis Type="Italic">t</Emphasis>BA-<Emphasis Type="Italic">b</Emphasis>-PS-<Emphasis Type="Italic">b</Emphasis>-P2VP and regulation of its hierarchical self-assembly structure in solution

Linear ABC triblock copolymer PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ was successfully synthesized by RAFT polymerization. Block copolymer micelles were prepared by the two-step hierarchical self-assembly process. Size exclusion chromatography and ¹H NMR were used to characterize the structure of samples. Morphologies and size of micelles were determined by transmission electron microscope. The results showed that the densely dispersed spherical micelles of PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ were obtained in the first step of the hierarchical self-assembly process. In the second step, core-compartmentalized micelle strings with different lengths and distribution densities were obtained when the primary self-assembled solution was dialyzed in distilled water with pH ≈ 3. When distilled water with pH ≈ 3 was added drop-wise to this solution, uniformly dispersed spherical core-compartmentalized micelles of PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ were prepared. Thus, hierarchical self-assembly structure of linear ABC triblock copolymer was obtained successfully and the preparation of uniformly dispersed spherical micelles of triblock copolymers was realized simply by changing the secondary self-assembly methods.     

Responsive polymer-based multicolor fluorescent probes for temperature and Zn2+ ions in aqueous media

We report on the fabrication of fluorescent and multicolor probes for Zn²⁺ ions and temperature from a mixture of three types of fluorophore-labeled responsive block copolymers in aqueous media. Quinoline-based Zn²⁺-recognizing fluorescent monomer ZQMA, red-emitting rhodamine B-based monomer RhBEA, and blue-emitting coumarin derivative Coum-OH, were synthesized first. A ZQMA-labeled well-defined double hydrophilic block copolymer (DHBC), PEG-b-P(MEO₂MA-co-ZQMA), was synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization of 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA) and ZQMA by utilizing a PEG-based macroRAFT agent. Following similar procedures, PEG-b-P(St-co-RhBEA) amphiphilic diblock copolymer and PEG-b-P(MEO₂MA-co-Coum) DHBC were also synthesized, where P(St-co-RhBEA) was a RhBEA-labeled polystyrene (PS) block. At room temperature in aqueous solution, almost nonfluorescent PEG-b-P(MEO₂MA-co-ZQMA) can effectively bind Zn²⁺ ions, leading to prominent green fluorescence enhancement due to the coordination of ZQMA with Zn²⁺ ions. However, by mixing red-emitting PEG-b-P(St-co-RhBEA) and blue-emitting PEG-b-P(MEO₂MA-co-Coum) with PEG-b-P(MEO₂MA-co-ZQMA) at an appropriate ratio, three color transitions could be observed. In the absence of Zn²⁺ ions, a mixed pink fluorescent originating from Coum and RhBEA was observed; upon the addition of a certain amount of Zn²⁺ ions, the green fluorescence enhanced dramatically, leading to a white fluorescence readout. By further increasing the amount of Zn²⁺ ions, the green fluorescence further enhanced and overwhelmed the blue and red emissions, leading to a green-dominant mixed-fluorescence emission. In addition, upon increasing the temperature, the fluorescence of Coum decreased considerably due to the fluorescence-resonance energy transfer (FRET) between Coum and ZQMA moieties. In this way, a ratiometric fluorescent thermometer can be constructed.     

Effects of concentration and pH on the thermosensitive behavior of a graft copolymer with polyimide backbone and poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylamino-2-ethyl methacrylate) side chains

Aqueous solutions of the graft copolymer with a polyimide backbone and poly(N,N-dimethylamino-2-ethyl methacrylate) side chains with a molecular mass of M = 4.7 × 10⁵ and a grafting density of side chains of 0.44 are investigated by light scattering and turbidimetry. Solutions are studied in a wide concentration range of 0.0008–0.0250 g/cm³ at рН values varying from 2 to 12 for each concentration. The temperature dependences of optical transmission, scattered light intensity, and hydrodynamic radii of scattering objects are obtained. It is shown that the copolymer is thermosensitive only at pH > 8.0. A decrease in acidity of the medium at a fixed concentration of the copolymer is accompanied by a decline in temperatures corresponding to the onset and end of phase separation Т ₁ and Т ₂, leading to the narrowing of this interval. At constant рН values, temperatures Т ₁ and Т ₂ rise with solution dilution, while the phase transition interval becomes wider.     

High performance bio-based polyurethane elastomers: Effect of different soft and hard segments

In this work, a series of high performance bio-based polyurethanes(bio-PUs) were synthesized from polylactide(PLA)-based diols, different diisocyanates(TDI, MDI, HDI, IPDI) and chain extender 1,4-butanediol, in which different soft and hard segments are used to adjust their transition temperatures and mechanical properties. Poly(lactide-co-caprolactone)copolymer diols(co-PLAols) instead of PLA diols as the soft segment improved the thermal stability and mechanical properties of the synthesized bio-PUs. Among them, MDI-based bio-PUs have the highest T_g(43.8 °C), tensile strength(23.5 MPa) and modulus(380.8 MPa), while HDI-based bio-PUs have the lowest T_g(21.4 °C) and highest elongation at break(580%). Especially, the bio-PUs synthesized from co-PLAols and MDI demonstrate better mechanical properties,closed to petroleum-based commodities. Furthermore, the obtained bio-PUs display good shape memory properties at body temperature and cytocompatibility. Therefore, these bio-PUs are promising for applications in biomedical fields.     

Biodegradable poly(butylene succinate-<Emphasis Type="Italic">co</Emphasis>-butylene dimerized fatty acid)s: Synthesis,crystallization, mechanical properties,and rheology

Poly(butylene succinate-co-butylene dimerized fatty acid) (P(BS-co-BDFA)) copolyesters were synthesized from succinic acid (SA) and dimerized fatty acid (DFA) with 1,4-butanediol (BDO) through a two-step process of esterification and polycondensation. The polyester compositions and physical properties of copolyesters were investigated by GPC, ¹H NMR and ¹³C NMR, DSC, WAXD, DMA, TGA, tensile and rheology test. The melting temperature (T_m), and crystallization temperature (T_c) decreased gradually as the content of DFA monomer increased. P(BS-co-BDFA) copolyesters showed the same crystal structure as the PBS homopolyester. Besides, TGA results indicated that P(BS-co-BDFA)s were of higher thermal stabilities. Moreover, it was found that the synthesized P(BS-co-BDFA)s showed the maximum elongation at break (591%) as the DFA contents were 10 mol%. Rheology analysis indicated that the viscoelastic behavior of the polyesters greatly depended on the molecular weight of polyesters.     

Miniemulsion cross-linking: A convenient route to hollow polymeric nanocapsule with a liquid core

Miniemulsion stabilized by poly(2-(dimethylamino) ethyl methacrylate)-block-poly(butyl methylacrylate) (PDMAEMA-b-PBMA) diblock copolymers has been used as liquid templates for the synthesis of polymer nanocapsules via quaternization cross-linking of PDMAEMA segments of the copolymer by 1,2-bis(2-iodoethoxy)ethane (BIEE) crosslinkers. PDMAEMA-b-PBMAs here as a stabilizer in miniemulsion with different molecular weights led to a size variation in diameters of nanocapsules, demonstrating the capsules have potential design capability of this technique. The solution behavior of the capsules has been also investigated in this paper.     

Adjustable crystalline stereocomplexes from enantiopure gradient polycarbonates

Stereoselective interaction was observed in the mixture of enantiopure gradient polycarbonate (denoted as PCOPC-g-PCPC, originated from the enantioselective terpolymerization of CO₂, 3,4-epoxytetrahydrofuran (COPO) and cyclopentene oxide (CPO)) and various isotactic polycarbonates with opposite configuration in chloroform solution. The resultant crystalline stereocomplexes exhibit enhanced thermal stability and new crystalline behaviors, significantly distinct from their parent polymers. It was found that the cocrystallization selectively occurred between (R)-PCOPC (CO₂/COPO copolymer) and (S)-PCOPC-enriched segment in the gradient terpolymer (S)-PCOPC-g-PCPC, while (R)-PCPC (CO₂/CPO copolymer) selectively complexed with (S)-PCPC-enriched segment. No stereocomplexation was observed between (S)-PCOPC-g-PCPC and (S)-PCOPC or (S)-PCPC. This study is beneficial to finding new routes to prepare various semicrystalline materials having a wide variety of physical properties and degradability.     

Correlation of Morphology Evolution with Superior Mechanical Properties in PA6/PS/PP/SEBS Blends Compatibilized by Multi-phase Compatibilizers

In this study,the maleic anhydride(MAH)and styrene(St)dual monomers grafted polypropylene(PP)and poly[styrene-b-(ethylene-co-butylene)-b-styrene](SEBS),i.e.PP-g-(MAH-co-St)and SEBS-g-(MAH-co-St)are prepared as multi-phase compatibilizers and used to compatibilize the PA6/PS/PP/SEBS(70/10/10/10)model quaternary blends.Both PS and SEBS are encapsulated by the hard shell of PP-g-(MAH-co-St)in the dispersed domains(about 2μm)of the PA6/PS/PP-g-(MAH-co-St)/SEBS(70/10/10/10)quaternary blend.In contrast,inside the dispersed domains(about 1μm)of the PA6/PS/PP/SEBS-g-(MAH-co-St)(70/10/10/10)quaternary blend,the soft SEBS-g-(MAH-co-St)encapsulates both the hard PS and PP phases and separates them.With increasing the content of the compatibilizers equally,the morphology of the PA6/PS/(PP+PP-g-(MAH-co-St))/(SEBS+SEBS-g-(MAH-co-St))(70/10/10/10)quaternary blends evolves from the soft(SEBS+SEBS-g-(MAH-co-St))encapsulating PS and partially encapsulating PP(about 1μm),then to PS exclusively encapsulated by the soft SEBS-g-(MAH-co-St)and then separated by PP-g-(MAH-co-St)inside the smaller domains(about 0.6μm).This morphology evolution has been well predicted by spreading coefficients and explained by the reaction between the matrix PA6 and the compatibilizers.The quaternary blends compatibilized by more compatibilizers exhibit stronger hierarchical interfacial adhesions and smaller dispersed domain,which results in the further improved mechanical properties.Compared to the uncompatibilized blend,the blend with both 10 wt%PP-g-(MAH-co-St)and 10 wt%SEBS-g-(MAH-co-St)has the best mechanical properties with the stress at break,strain at break and impact failure energy improved significantly by 97%,71%and 261%,respectively.There is a strong correlation between the structure and property in the blends.     

Rheological behavior and reversible swelling of pH sensitive poly(acrylamide-<Emphasis Type="Italic">co</Emphasis>-itaconic acid) hydrogels

The study involved preparation of poly(acrylamide-co-itaconic acid) hydrogels by radical cross-linking copolymerization. The copolymer hydrogels were characterized through infrared spectroscopy, thermal analysis, swelling measurements and in oscillatory and steady shear rheology. Results showed that more stable copolymers were formed due to the strong interaction in the hydrogels. These hydrogels have shown substantial percent swelling in water and shrinking in saline solution and acidic buffers. The rheological properties were described by the Herschel-Bulkley and power-law models to explore their non-Newtonian behavior. The results showed that higher itaconic acid content raised the polymer viscosity; the degree of shear-thinning and polymer elasticity (G′) were also increased. The transition from the viscous (G′ < G″) to the predominant viscoelastic behavior (G′ > G″) occurs at a crossover frequency ranged from 17.8 rad/s for polyacrylamide to 15.7, 12.8 and 12.5 rad/s for copolymers.     

Synthesis and characterization of serial random and block-copolymers based on lactide and glycolide

The objective of this study is to investigate the properties of poly(lactide-co-glycolide) with different composition ratios and PLGA-PEG-PLGA copolymers synthesized by ring-opening polymerization method. Their compositions, crystallization properties, thermal and degradation behaviors, hydrophilicity and biocompatibility were studied. Our results demonstrate that poly(lactide-co-glycolide) with a 90% lactide and PLGA-PEG-PLGA show some crystallization properties. While as the decrease of lactide content in polymers, poly(lactide-co-glycolide) become amorphous, whereas, their hydrophilicity have been improved on the contrary. Compared to poly(lactide-co-glycolide), the PLGA-PEG-PLGA copolymer has a better hydrophilicity for the existence of polyethylene glycol block. Furthermore, both these polymers display easy controlled degradation properties and good cell compatibility.     

Combination of living anionic polymerization and ATRP via ��click�� chemistry as a versatile route to multiple responsive triblock terpolymers and corresponding hydrogels

A combination of anionic polymerization, atom transfer radical polymerization (ATRP) and ??click?? chemistry was used to construct trishydrophilic ABC triblock terpolymers composed of a pH-sensitive A block, a water-soluble B block and two different thermo-sensitive C blocks without any block sequence limitation problems. First, an azido end-functionalized poly(2-vinylpyridine)-block-poly(ethylene oxide) (P2VP-b-PEO-N₃) diblock copolymer was synthesized by anionic polymerization. In a second step, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methacrylate) (POEGMA) were synthesized via ATRP using an alkyne functionalized initiator. The resulting polymers were attached to the P2VP-b-PEO-N₃ diblock copolymer using the 1,3-dipolar Huisgen cycloaddition (??click?? chemistry). For the ??click?? step, P2VP-b-PEO-N₃ diblock copolymers with either an azidoacetyl or a 2-azidoisobutyryl group were tested. In the latter case, however, a side reaction involving the cleavage of the formed ??click?? product via nucleophilic substitution occurred, preventing a permanent attachment of PDMAEMA or POEGMA to the P2VP-b-PEO-N₃ diblock copolymer. Finally, P2VP-b-PEO-b-POEGMA (with POEGMA=P(MEO₂MA-co-MEO_8.5MA)) and P2VP-b-PEO-b-PDMAEMA triblock terpolymers were successfully synthesized and used to construct stimuli-responsive hydrogels. A concentrated solution of P2VP₅₆-b-PEO₃₇₀-b-P[(MEO₂MA)₈₉-co-(MEO_8.5MA)₇] showed a gel?Csol?Cgel transition at pH?7 upon temperature increase, whereas in the case of P2VP₅₆-b-PEO₃₇₀-b-PDMAEMA₇₀, a gel?Csol or a weak gel?Cstrong gel transition was observed, depending on the applied pH. Finally, the addition of trivalent hexacyanocobaltate(III) ions to the P2VP₅₆-b-PEO₃₇₀-b-PDMAEMA₇₀ solution induced an upper critical solution temperature for the PDMAEMA block, which led to gel formation. This allows for the construction of light-sensitive hydrogels, utilizing the photo-aquation of hexacyanocobaltate(III) ions.     

Simultaneously improving the tensile and impact properties of isotactic polypropylene with the cooperation of <Emphasis Type="Italic">co</Emphasis>-PP and <Emphasis Type="Italic">β</Emphasis>-nucleating agent through pressure vibration injection molding

In this article, crystalline morphology and molecular orientation of isotactic polypropylene (iPP), random copolymerized polypropylene (co-PP) and β-nucleating agent (β-NA) composites prepared by pressure vibration injection molding (PVIM) have been investigated via polarized light microscopy, scanning electron microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Results demonstrated that the interaction between co-PP and iPP molecular chains was beneficial for the mechanical improvement and the introduction of β-NA further improved the toughness of iPP. In addition, after applying the pressure vibration injection molding (PVIM) technology, the shear layer thickness increased remarkably and the tensile strength improved consequently. Thus, the strength and toughness of iPP/co-PP/β-NA composites prepared by PVIM were simultaneously improved compared to those of the pure iPP prepared by conventional injection molding (CIM): the impact toughness was increased by five times and tensile strength was increased by 9 MPa. This work provided a new method to further enhance the properties of iPP/co-PP composites through dynamic processing strategy.     

Glucose-Mediated Insulin Release Carrier

Polyacrylic acid-co-methacrylamidophenylboronic acid) (PAA-co-PMAAPBA) copolymers were prepared using different concentrations of 3-methacrylamidophenylboronic acid (MAAPBA). The release of insulin from the insulin loaded polymer is dependent on the composition between acrylic acid and MAAPBA in the copolymer. With an increase in concentration of 3-methacrylamidophenylboronic acid, the glucose responsive insulin release from polyacrylic acid-co-methacrylamidophenylboronic acid) polymer at the physiological pH of 7.4 was enhanced. The presence of glucose resulted in disintegration of the polymer leading to release of the loaded insulin.     

Preparation of pH- and reductive-responsive prodrug nanoparticles via polymerization-induced self-assembly

pH- and reductive-responsive prodrug nanoparticles are constructed via a highly efficient strategy, polymerization-induced selfassembly (PISA). First, reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-(diisopropylamino) ethyl methacrylate (DIPEMA) and camptothecin prodrug monomer (CPTM) using biocompatible poly(N-(2-hydroxypropyl) methacrylamide) (PHPMA-CPDB) as the macro RAFT agent is carried out, forming prodrug diblock copolymer PHPMA-P (DIPEMA-co-CPTM). Then, simultaneous fulfillment of polymerization, self-assembly, and drug encapsulation are achieved via RAFT dispersion polymerization of benzyl methacrylate (BzMA) using the PHPMA-P(DIPEMA-co-CPTM) as the macro RAFT agent. The prodrug nanoparticles have three layers, the biocompatible shell (PHPMA), the drug-conjugated middle layer (P(DIPEMA-co-CPTM)) and the PBzMA core, and relatively high concentration (250 mg/g). The prodrug nanoparticles can respond to two stimuli (reductive and acidic conditions). Due to reductive microenvironment of cytosol, the cleavage of the conjugated camptothecin (CPT) within the prodrug nanoparticles could be effectively triggered. pH-Induced hydrophobic/ hydrophilic transition of the PDIPEMA chains results in faster diffusion of GSH into the CPTM units, thus accelerated release of CPT is observed in mild acidic and reductive conditions. Cell viability assays show that the prodrug nanoparticles exhibit well performance of intracellular drug delivery and good anticancer activity.     

Secondary self-assembly behaviors of PEO-<Emphasis Type="Italic">b</Emphasis>-P<Emphasis Type="Italic">t</Emphasis>BA-<Emphasis Type="Italic">b</Emphasis>-PS triblock terpolymers in solution

A series of PEO₄₅-b-PtBA₅₃-b-PS _x (x = 42, 84, 165) triblock terpolymers were synthesized by the atom transfer radical polymerization and characterized by size exclusion chromatography and ¹H NMR. Their self-assemblies were conducted by a two-step hierarchical self-assembly method and a one-step dialysis method and the self-assembly behaviors were investigated. The morphologies, sizes, and size distributions of micelles produced by the self-assembly were determined by transmission electron microscopy and dynamic light scattering. The secondary self-assembled structure of PEO₄₅-b-PtBA₅₃-b-PS _x obtained by the two-step hierarchical self-assembly could be controlled by tuning the length of PS block, the core forming block. The micelles were uniform with diameters of 20–25 nm and their size distributions, except for that of PEO₄₅-b-PtBA₅₃-b-PS₁₆₅, were narrow with particle size distribution indexes ranging from 0.014 to 0.246. The one-step dialysis of the triblock terpolymers produced vesicular micelles with distinct vesicle walls that exhibited similar thicknesses. The vesicles did not show significant aggregation. The size distribution of PEO₄₅-b-PtBA₅₃-b-PS₄₂ vesicle was the narrowest with a particle size distribution index value of 0.135. The PEO₄₅-b-PtBA₅₃-b-PS₁₆₅ vesicles tended to overlap with each other.     

Potential energy surface and proton HFI constants of the cyclopentane radical cation

According to the data of UB3LYP/6-31G* and UMP2/cc-pVTZ calculations, the adiabatic potential energy surface of the cyclopentane radical cation is very intricate and combines six types of stationary structures of C _s and C ₂ symmetry. Ten equivalent C _s structures with the totally symmetric electronic state (C _s (² A′)) correspond to global minima. Conformational transitions between the global minima occur along the inversion and pseudorotation coordinates, for each pair of minima the conformational transition occurring in one stage (through the only transition state). The inversion barrier is ～2 kcal/mol; pseudorotation barriers are ～4–8 kcal/mol. The structure of the potential surface provides the interpretation of the EPR data as a result of dynamic averaging over 20 C _s (² A′) and C ₂ (² A) stationary structures.