New polydimethylsiloxanes with p‐substituted azobenzene side‐groups were synthesized. Thin films and solutions exhibit a photochemical trans‐cis isomerization of the azobenzene groups, followed by their cis‐trans thermal relaxation in the dark. In films, relaxation rates were found to be 100–1 000 times slower than the rates of photoisomerization, the former being very sensitive to the electron‐acceptor character of the substituents. in solution, the rates of cis‐trans relaxation are lower than those obtained for the solid state. This is ascribed to the dipolar intramolecular interactions between cis chromophores, which are favored in solution.
Poly(4‐methyl‐2‐pentyne) (PMP)/TiO2 hybrid nanocomposite membranes have been investigated for natural gas conditioning. Tailor‐made PMP with 35% cis‐content was identified as an attractive material to prepare nanocomposite membranes; it presented good stability towards organic vapors and optimal properties for butane/methane separation. The PMP/TiO2 hybrid nanocomposite membranes presented an improvement of butane permeability and butane/methane selectivity. The addition of TiO2 nanoparticles to the PMP enhanced the selectivity more effectively than fumed‐silica, and it is attractively higher than those currently reported in the open literature.
Maleimido‐terminated PCL (M‐PCL) and alkyne‐terminated PCL (A‐PCL) are prepared by the ring‐opening polymerization of ε‐caprolactone with N‐hydroxyethyl maleimide and 4‐pentyn‐1‐ol as initiators catalyzed by tin(II ) trifluoromethane sulfonate at 25 °C, respectively. A series of saccharide‐terminated PCLs have also been synthesized under mild conditions by two chemical strategies: 1). Michael addition of M‐PCL and amino‐containing maltose, and 2). a ‘click’ reaction of A‐PCL and azide‐containing saccharide. The amphiphilic nature of these maltose‐terminated PCLs make self‐assembly into aggregates in water possible. These aggregates have been characterized by transmission electron microscopy and dynamic light scattering measurements.
A side chain polyrotaxane bearing photoresponsive and nonresponsive recognition sites, i.e., azobenzene (Azo) and heptamethylene (C7) moieties, respectively, linked with a long linker is synthesized. The photoregulated switching of the position of the rotor, i.e., α‐cyclodextrin (α‐CD), in the side chain polyrotaxane is demonstrated by two dimensional rotating frame Overhauser effect spectroscopy and circular dichroism spectroscopy: α‐CD includes the Azo moiety before UV irradiation, whereas α‐CD includes the C7 moiety after trans‐to‐cis photoisomerization of the Azo moieties.
Newly prepared high‐cis poly(2,4‐difluorophenylacetylene) is found to undergo simultaneous cis‐to‐trans isomerization and degradation during aging in THF‐d8 solution exposed to the atmosphere. Partly aged polymers contain two microstructurally differing fractions: deeply isomerized macromolecules of lower MW and microstructurally unperturbed high‐cis macromolecules of higher MW. SEC/DAD provides an unambiguous distinction and UV‐Vis characterization of these fractions. The non‐uniform MW distribution of isomerized and high‐cis macromolecules is assumed to result from acceleration of degradation of polymer chains by simultaneous cis‐to‐trans isomerization.
The homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)3] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)3/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 105 g mol‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)3/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).
Poly(ε‐caprolactone) (PCL)/montmorillonite (MMT) nanocomposites were prepared by in situ ring‐opening polymerization of ε‐caprolactone in the presence of MMT modified by hydroxyl‐group containing alkylammonium cation (Cloisite®30B) in a single mode microwave oven. For the polymerization mixtures, plateaus or exothermal peaks were observed in their temperature‐time profiles and can be attributed to the heat‐generating nature of the ring‐opening polymerization. The morphologies of the nanocomposites showed a predominantly exfoliated structure. The mechanical properties of the nanocomposites were evaluated via dynamic mechanical analysis. Compared with that of the recovered PCL matrix, the mechanical properties of the PCL/Cloisite®30B nanocomposites showed obvious improvement.
A series of supramolecular degradable inclusion complex (IC) films were formed by threading α‐cyclodextrin (α‐CD) molecules over poly(ε‐caprolactone) (PCL) according to the designed ratio of α‐CD–PCL. Due to containing both α‐CD–PCL inclusion crystallites and uncovered PCL crystallites, the resulting supramolecular α‐CD–PCL IC partial films displayed a shape memory effect. The properties of the materials were investigated by 1H NMR, X‐ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and swelling measurement. It was found that the casting temperature and solvent have great influence on the formation and properties of the α‐CD–PCL partial ICs. The modes of complexes on different conditions were proposed. In addition, the introduction of inclusion structure accelerates the degradation of materials strongly.
Graft copolyesters with a PCL backbone and PLLA side chains were successfully prepared in three steps avoiding transesterification. First ε‐caprolactone was polymerised with 1,6‐hexane diol as initiator to obtain hydroxytelechelic oligo(ε‐caprolactone)s. These diols were then subjected—in the second step—to polycondensation with L ‐malic acid yielding in linear poly[oligo(ε‐caprolactone)L ‐malate] having secondary hydroxyl functions in the side chain. For both reactions scandium triflate Sc(OTf)3 was used as a catalyst. In the third step various amounts of L ‐lactide were grafted from the polymer backbone using Zn(oct)2 as catalyst. The successful reaction was confirmed by NMR and SEC (size exclusion chromatography) analysis. Further the thermal properties of the graft copolymers with different graft lengths were determined via differential scanning calorimetry.
Fullerene capped poly(ε‐caprolactone)s (PCLs), namely single‐ and double‐fullerene end‐capped PCLs with different fullerene content, were successfully synthesized. The effect of the fullerene end on the crystallization behavior and mechanical properties of the PCL was studied. The aggregation behavior of the fullerene moieties at the end of the PCL chain was also studied. It was found that the aggregated fullerenes have two kinds of effect on the crystallization behavior of the PCL i.e., confinement effect and nucleating effect. The fullerene content shows a certain balance between the confinement effect and the nucleating effect on the crystallization rate of PCL. It was also found that the mechanical properties of the fullerene end‐capped PCLs are strongly related to the content of fullerene and the mode of end‐capping style: either single or double end‐capping.
Novel fullerene‐ and polyhedral oligomeric silsesquioxane‐ (POSS) double end‐capped poly(ε‐caprolactone) (PCL) were successfully synthesized. The crystallization behavior of the fullerene‐ and POSS‐ double end‐capped PCL and the effect of aggregation of the POSS and fullerene moieties on the crystallization of PCL were thoroughly studied. The aggregation of the fullerene moieties has much larger confinement effect on the crystallization of PCL than that of POSS. The successful incorporation of two nano‐sized objects, that is, fullerene and POSS, into the PCL matrix may introduce their merits, so that PCL can attain multi‐functional properties.
Biodegradable supermacroporous PHEMA cryogels were produced by combining two crosslinkers, poly(ethylene glycol) diacrylate and a newly developed disulfide water soluble crosslinker, N,N′‐bis(methacryloyl)‐L ‐cystine. The biodegradable PHEMA cryogels were prepared with gel fraction yields up to 70% and were characterized by highly interconnected pores of micrometer size and good mechanical stability. When subjected to reductive agents like DTT, the biodegradable PHEMA cryogels disintegrated into small pieces. The rate of disintegration was controlled by the crosslinking density in the cryogels and the DTT concentration.
Random biocompatible/biodegradable poly[propylene‐co‐(ethylene succinate)]s were prepared. Mechanical properties and crystallization rates decreased with propylene succinate content. Glass transition temperatures (Tg) varied between those for the homopolymers. DSC and TMDSC findings showed that multiple melting behaviour of PPESu samples is related to melting–recrystallization–remelting. WAXD observations, eutectic behaviour, and thermodynamic analysis of the equilibrium melting point depression indicated isodimorphic cocrystallization. The copolymers showed enzymatic hydrolysis rates between those of the homopolymers and cytotoxicity/biocompatibility similar to PLA.
The micellization on surfaces of two series of quasi‐diblock copoly(2‐oxazoline)s consisting of 2‐phenyl‐2‐oxazoline (PhOx) segments linked to either 2‐methyl‐2‐oxazoline (MeOx) or 2‐ethyl‐2‐oxazoline (EtOx) segments is investigated in detail. Those micelles are not pre‐existing in the initial ethanol solution but are formed during the spin‐coating process by the evaporation of the solvent inducing the precipitation of the less soluble PhOx segments. The morphology and size of the surface micelles vary according to the fraction of PhOx in the copolymers. Moreover, it is demonstrated that the chemical nature of the more soluble MeOx or EtOx segments also has an influence on the morphology of the resulting surface micelles.
Butadiene/isoprene copolymers were prepared using the catalyst system V(acac)3‐MAO. The structure of the comonomers is trans‐1,4 and the butadiene and isoprene units are statistically distributed along the polymer chain. The attitude of the butadiene sequences to crystallize in the monoclinic form and to evolve in the hexagonal form is preserved in the copolymer for a certain range of composition. The temperature interval between the two endothermic events is progressively reduced by increasing the isoprene content. The monoclinic/hexagonal transition produces a considerable increase in the lamellar thickness of the polymers. Thermal degradation of the copolymers is influenced by the composition and takes place in two different stages: a series of cyclization and cross‐linking reactions occur before the decomposition step.
Novel proton exchange membranes were solvent‐cast from DMF solutions of the terpolymers poly[(MA‐alt‐S)‐co‐AMPS], containing hydrophobic phenyl and reactive hydrophilic carboxylic and organo‐sulfonic acid fragments with different compositions, and PEGs with different molecular weights and amounts. These membranes were formed as a result of physical (via H‐bonding) and chemical (via PEG) cross‐linking. The structures of membranes were confirmed by FT‐IR and 1H‐ and 13C NMR spectroscopy. Mechanical and thermal properties, swellability, and proton conductivity of these membranes were significantly affected both by the chemical composition of the terpolymers (mainly the AMPS content) and also the cross‐linker (PEG) molecular weight and content in the final form of the membranes. It was concluded that the membranes prepared by using the terpolymer with an AMPS content of 36.84 mol‐% and PEG with a molecular weight of 1 450 and with an initial PEG content of 30 wt.‐% are the most suitable ones for fuel cell applications.
Atomic force microscopy (AFM) was used for modifying the surface structures of poly(ε‐caprolactone) (PCL) thin film. Oriented growth of PCL crystals at a desired area of the film surface was induced by scanning with a strong, normal load. PCL crystals were first grown edge‐on from the induction line and then their orientation changed to flat‐on at a lamellar length. The effects of molecular weight, crystallization temperature, scanning rate, and normal load on the AFM‐tip‐induced crystallization were examined. The growth kinetics of lamellar crystals in the AFM‐tip‐induced crystallization was the same as that in spherulitic crystallization. It was found that the formation of precursors strongly depends on the applied tip load and is facilitated when the applied load is higher than a threshold.
The synthesis and phase behaviour of PB32 is reported. The results indicate that PB32 develops a low‐ordered smectic mesophase of the type SmCalt. The slow formation of such a mesophase allows the quenching of the isotropic melt into an amorphous state so that both amorphous glass and smectic glass can be obtained, which exhibit different glass‐transition temperatures. Mechanical tests indicate that the macromolecular chains in the mesophase of PB32 can be oriented either parallel or perpendicularly in relation to the streching direction, depending on the deformation conditions. Solid‐state 13C NMR spectroscopy results show that the mobility of the chains is rather similar in both phases.
The amphiphilic triblock copolymer PLA‐b‐PLL‐b‐MPEG is prepared in three steps through acylation coupling between the terminal amino groups of PLA‐b‐PZLL‐NH2 and carboxyl‐terminal MPEG, followed by the deprotection of amines. The block copolymers are characterized via FT‐IR, 1H NMR, DSC, GPC, and TEM. TEM analysis shows that the triblock polymers can form polymeric micelles in aqueous solution with a homogeneous spherical morphology. The cytotoxicity assay indicates that the final triblock polymer micelles after deprotection show low cytotoxicity against Bel7402 human hepatoma cells. MPEG and PLL were introduced into the main chain of PLA affording a kind of ideal bioabsorbable polymer materials, which is expected to be useful in drug and gene delivery.
The Ni‐catalyzed polymerization of P3AOTs was studied and compared with the controlled chain‐growth polymerization of P3ATs. By varying the ratio of the initial monomer concentration to the initiator concentration, no linear dependence of the molar mass was observed, revealing that the polymerization does not proceed via a controlled mechanism. This was also confirmed by analyzing the end‐groups of the polymer with MALDI‐TOF mass spectrometry. To acquire more information on the polymerization mechanism, the formation of the actual monomer and the polymerization reaction were studied into more detail. These experiments proved that the polymerization proceeds via a chain‐growth mechanism, although not in a controlled way.
