Acta Polymerica最新文献

A new kink diamine, bis[4-(4-aminophenoxy)phenyl]diphenylmethane (BAPDM), bearing diphenylmethylene linkage was reacted with various aromatic dianhydrides to prepare the corresponding new polyimides via the poly(amic acid) precursors and thermal or chemical imidization. The poly(amic acid)s were produced with moderate to high inherent viscosities of 0.96–1.68 dl g^–1. All the poly(amic acid)s films could be obtained by solution-cast from N,N-dimethylacetamide (DMAc) solutions and thermally converted into transparent, flexible, and tough polyimide films. The wide-angle X-ray diffraction diagrams revealed that all the polyimides showed amorphous character. These polyimide films had a tensile strength of range 75–147 MPa and tensile modulus of 2.4–3.0 GPa. Polymers PI-3, PI-5 and PI-6 showed excellent solubility in a variety of solvents such as N-methyl-2-pyrrolidinone (NMP), DMAc, N,N-dimethylformamide (DMF), dimethyl sulfoxide, γ-butyrolactone, pyridine, cyclohexanone and tetrahydrofuran. These polyimides had glass transition temperatures between 248–331°C. The thermogravimetric analysis revealed that these polyimides exhibited good thermal stability with polymer decomposition temperature in excess of 500°C in nitrogen and air atmosphere. They had 10% weight loss temperatures in the range of 542–564°C and 549–572°C in nitrogen and air, respectively.

An explanation of the varying (ultra)drawability of semicrystalline polymers is proposed, based on NMR evidence of α_c-relaxation-associated helical jumps and chain diffusion through the crystallites of polyethylene and several similarly “α_c-mobile” polymers; these include isotactic polypropylene, poly(ethylene oxide), poly(oxymethylene), poly(tetrafluoroethylene), poly(vinyl alcohol), and several others. The chain motions provide a mechanism by which hot drawing of these polymers can extend an initially formed fiber morphology by an order of magnitude to draw ratios > 30, without melting. A second class of polymers, including nylons, poly(ethylene terephthalate), syndiotactic polypropylene, isotactic polystyrene, and isotactic poly(1-butene) (form I) lack a crystalline α-relaxation and the associated chain mobility. Therefore, these polymers are “crystal fixed” and drawability is limited to draw ratios < 14, arising mostly from break-up of crystalline lamellae and deformation of the amorphous regions. On this basis, we can explain which polymers are drawable to high draw ratios, given a sufficiently low level of entanglement. The motion through the crystallites is thermally activated and the applied stress only biases the direction of the jumps; this explains the crucial role of temperature and rate in tensile drawing and solid-state extrusion processes. The behavior of the crystal-fixed, poorly drawable polymers strongly suggests that melting, straight chain pull-out, and sliding on crystal planes are not significantly operative during ultradrawing, and that weak intermolecular forces are not a sufficient condition for ultradeformation. Various stages of drawing are distinguished and other models of ultradrawability are discussed critically.

A systematic study, devoted to analyzing the effect of various parameters in the synthesis of furanic aliphatic polyamide by interfacial polycondensation of 2,2′-bis(5-chloroformyl 2-furyl)propane with hexamethylene diamine, is described. The effects of the organic solvent, temperature and phase transfer catalyst type, as well as monomer and sodium hydroxyde concentrations are discussed. The inherent viscosity of the polyamide obtained is higher than those reported in the literature for furanic aliphatic polyamides synthesized from furan-2,5-dicarboxylic acid.

Using different porogens and crosslinkers for 3-O-methacryloyl-1,2;5,6-di-O-isopropylidene-α-D-glucofuranose, porous polymer beads having surface areas of up to 300 m²g^–1 were synthesized by suspension polymerization. After subsequent removal of the protecting groups, a hydrophilic sugar-containing resin was obtained. In the case when the initial polymer had only very small pores, after hydrolysis, an almost non-porous resin was recovered. With initially large pores, the pore structure of the resin remained unchanged. For resins with medium pore sizes, the pore volume and surface area of the unprotected resin were dependent of the degree of hydrolysis. In fact a linear relationship between surface area and degree of hydrolysis could be observed. Furthermore, this relationship was reversible, i. e. after reprotection of partly or fully hydrolyzed resins, the original pore structure of the protected polymer could be recovered. Depending on the degree of hydrolysis, porous resins of various hydrophilicity, containing reactive hydroxyl groups suitable for further derivatization have been synthesized.

The phase behavior of binary blends of poly(cyclohexyl methacrylate-co-methyl methacrylate) (P(CHMA-co-MMA)) copolymers with poly(α-methylstyrene) (PAMS) and poly(p-methylstyrene) (PPMS) has been determined experimentally and compared to that of the P(CHMA-co-MMA)/PS system. The enthalpic and entropic parts of the segmental interaction parameter for each binary monomer pair involved have been determined from a fit of the lower critical solution temperature (LCST) behavior of these systems, with the aid of Flory-Huggins (FH) theory which incorporates temperature dependent interaction parameters. The results reveal that the strength of the interaction with the copolymer P(CHMA-co-MMA) decreases in the following order: PAMS > PS > PPMS. These differences are also illustrated in the glass transition (T_g)-composition curves of the above systems as well as in analog calorimetry results and scanning electron microscopy (SEM) studies. Good agreement is obtained when various theoretical miscibility windows for binary blends of copolymers involving CHMA, MMA and styrene derivatives are compared to experimental data. Thus it is shown that the subtle difference of monomer structures is captured to a good degree by the segmental interaction parameters derived from phase behavior.

Two copolymers of poly(p-phenylenevinylene) (PPV) containing low levels (0.8 and 3.6 mole %) of the 2,3,5,6-tetramethyl-1,4-phenylenevinylene (TMPV) units were prepared via the sulfonium salt precursor route. The luminescence properties of the two copolymers were studied in detail mainly for photoluminescence (PL) and electroluminescence (EL) characteristics in comparison with those of PPV itself. Inclusion of low levels of TMPV units improves EL efficiency by more than 10 times when a single layer device was constructed using ITO coated glass anode and aluminum metal cathode. This was explained by the possible partial disruption of main chain π-conjugation by the TMPV units which force its phenylene or vinylene structure to twist out of the coplanar structure in order to avoid of the steric repulsion between the methyl and vinyl protons in the TMPV units. The UV-vis, PL and EL spectra of the copolymers support this supposition.

Formation of the polycation/dye complexes by the interaction between polycations with (N,N-dimethyl-2-hydroxypropylene ammonium chloride) units in the main chain and three anionic dyes with two, three and six sulfonic groups (Crystal Ponceau 6R, Ponceau 4R and Direct Red 80) confirmed the chromotropic properties of these polycations and gave information on the influence of the polycation and the dye structure on the stability of the polycation/dye complex. The interaction between polycations and dyes and the stoichiometry of the polycation/dye complexes were followed by UV-VIS spectrophotometry and viscometry. The presence of the nonpolar side chains in polycation structure did not increase the ability to bind these dyes. The stability of the polycation/dye complexes increased with the increase of the content of quaternary ammonium salt groups in the main chain and with the increase of the sulfonic group number of the dye.

It is an open question whether the slow regions or the fast regions of dynamic glass transition heterogeneity display the continuous part of a cell structure. Recent multidimensional NMR experiments of the Spiess group [U. Tracht et al., Phys. Rev. Lett. 1998, 81, 2727] could determine the characteristic length for poly(vinyl acetate), 3 ± 1 nanometers, but could not decide this question. This paper tries to resolve this question with the aid of a model published in this journal 20 years ago. The phenomenological treatment leads to a Levy distribution for the spectral density of volume fluctuation. The connection between mobility and local density by means of free volume identifies the preponderating component of the Levy distribution with a Glarum defect. This implies that far below the crossover region the continuous part has the lower mobility. Other arguments supporting this picture are collected. The model gives also the size distribution of cooperatively rearranging regions (CRRs) as a function of temperature.

Reverse atom transfer radical polymerization of styrene in the presence of a conventional radical initiator (benzoylperoxide, BPO) in bulk was successfully implemented via a new polymerization procedure. The system first reacts at 70°C for ten hours, then polymerizes at 110°C, which results in a well-controlled radical polymerization with high initiation efficiency and narrow molecular weight distribution of the resulting polymer, i. e., the polydispersity is as low as M_w/M_n = 1.32. The initiation mechanism of BPO is different from that of AIBN because there is redox reaction between BPO and Cu^I generated from the reaction of radicals with Cu^II. The initiation mechanism of BPO/Cu^IICl₂/bpy is deduced through the experimental data. The molecular weight of the resultant polymer is in agreement with the theoretical value calculated in accordance with the aforementioned mechanism.

The syntheses and electropolymerization of 3-alkylthiophene functionalized with terminal 1,2-diol group as well as its protected forms were described. It was found that, in spite of the nucleophilic nature of diol function, the thiophene derivative bearing free dihydroxy group exhibits a rather good polymerizability in nitrobenzene and can be electropolymerized to form a stable conducting polymer film with more extended π-electron system than those from its protected forms. Using a two-probe method, the conductivity measurements on oxidized films of the obtained polymers give values in the range of 10^–3–10^–2 S cm^–1. The reactivity of the pendant diol groups of the resulting polymers to attach biomolecules was examined by using redox active 2-aminoethylferrocenylmethylether as a model compound. It was confirmed that by using the well-established two-step procedure developed for the immobilization of proteins to polysaccharides, (primary) amino compounds can be easily bound onto the new polymers without the loss of their electroactivity. Therefore, as the most used functional group for the covalent immobilization of enzymes, vicinal dihydroxy group was incorporated into conjugated polymer systems and a new type of conducting carrier materials developed.