Showing papers in "Polymer Bulletin in 1990"

Reactivity in radical polymerization of N -substituted maleimides and thermal stability of the resulting polymers

Abstract: The effect ofN-substituents on the radical polymerization ofN-substituted maleimides (RMI) was investigated. The polymerization reactivities, i.e. yield and molecular weight of the polymers, were found to change depending on the structure of theN-substituents. The poly(RMI)s bearing a bulkyN-substituent were confirmed to be semiflexible poly(substituted methylene)s which were soluble in many organic solvents, but did not melt below their decomposition temperatures. From thermogravimetric analysis determined in a nitrogen stream, no weight-loss of poly(RMI) was observed at temperature below 300°C, and the maximum decomposition temperature was 400–440°C, except forN-tert-alkyl substituted derivatives which decomposed at 240–280°C via a two-step reaction.

Chain transfer activity of some activated allylic compounds

Abstract: Various olefins that are activated towards free radical addition and contain a homolytic leaving group in the allylic position are effective chain transfer agents in free radical polymerizations of methyl methacrylate and other monomers These allylic compounds include bromides, phosphonates, stannanes, thioethers, sulfoxides, and sulfones Allylic silanes and chlorides, however, do not posess significant chain transfer activity Suitable activating substituents towards radical addition are phenyl, ethoxycarbonyl, cyano, and acetoxy Several of the compounds have an advantage over thiols in that they do not contain sulfur

Synthesis of ?simple graft? poly(isoprene-g-styrene) by anionic polymerization

Abstract: The synthesis of a well-defined near-monodisperse polyisoprene-graft-polystyrene copomymer having a single, centrally located graft site is described. The method utilized to prepare this structure involved capping “living” polystyryllithium anions by reaction with methyltriclorosilanne, followed by addition of a slight stoichiometric excess of polyisoprenyllithium. After linking, the residual polyisoprene arms were removed by fractionation to yield the pure graft copolymer.

Living cationic polymerization of styrene by the 1-phenylethyl chloride/tin tetrachloride initiating system in the presence of tetra-n-butylammonium chloride

Abstract: An initiating system, consisting of 1-phenylethyl chloride, tin tetrachloride, and tetra-n-butylammonium chloride [CH3CH(Ph)C1/SnCl4/nBu4NCl], led to living cationic polymerization of styrene in CH2Cl2 solvent at-15°C; typically, CH3CH(Ph)Cl/SnCl4/nBu4NCl=20/100/40 mM for 10 M of styrene The living nature of the process was confirmed by an increase in the number-average molecular weight (\(\bar M_n \)) of the polymers in direct proportion to monomer conversion and its continuation on supplying a fresh feed of styrene after the polymerization; the observed \(\bar M_n \) was close to the calculated value assuming that one molecule of CH3CH(Ph)Cl yields one living polymer Throughout these reactions, the polymer's molecular weight distribution (MWD) stayed very narrow (\(\bar M_w /\bar M_n \leqslant 11\)), though slightly broadening after the second monomer addition In the absence of nBu4NCl, the CH3CH(Ph)Cl/SnCl4 system yielded polystyrene with a bimodal MWD where the lower polymer fraction alone was apparently of a long lifetime Styrene polymerization with the H2O/SnCl4 system was also examined, both with and without added nBu4NCl, and a long-lived propagating species was obtained in the presence of nBu4NCl

Comprehensive characterization of superabsorbent polymer hydrogels

Abstract: An approach to the quantitative description of superabsorbent polymer hydrogels is examplified by partially hydrolyzed polyacrylamide gels obtained by three-dimensional radical copolymerization or radiation cross-linking of the polymer. The modified swelling theory has been used to develop a system of experimental and computational methods for the evaluation of the supergels network parameters. The possibility of applying these methods to the analysis of the network formation process is also discussed.

Synthesis of functional polyesters derived from serine

Abstract: Functional polyesters, bearing lateral amino group, derived from racemic or optically active serine have been prepared by anionic polymerization of N-tritylated serine β-lactones. Polymers with molecular weights up to 30000 have been obtained. Removal of protective group leads to polyserine-ester.

Model filled polymers. IV, Preparation of conducting composite polymers beads

Abstract: Polyphenylene vinylene (PPV) coated polystyrene (PS) beads which have moderate conductivity when doped were prepared by mixing monodisperse crosslinked PS beads, the surfaces of which had been sulfonated to render them anionic, with cationic PPV precursor polymers. Two different PPV precursor polymers, poly (p-xylylidene tetrathiophenium chloride) and poly (p-xylylene-α-dimethylsulphonium chloride), were employed. Monodisperse crosslinked PS beads were sulfonated in the gas phase using fuming sulfuric acid to yield the surface activated monodisperse polystyrene sulfonic acid (PSSA) beads. Chemical doping with AsF5, of pellets prepared by pressing the coated beads resulted in conductivities as high as 10-1S/cm. The integrity of the polymer beads was determined by Scanning Electron Microscopy (SEM) and arsenic was found throughout the samples by examing fracture surfaces of the pressed coated pellets using EDXS.

Study of the stoichiometric polyelectrolyte complex between chitosan and carboxymethyl cellulose

Abstract: The polyelectrolyte complex (PEC) between chitosan and carboxymethyl cellulose was studied. Turbidimetric measurements revealed that the amount of stoichiometric PEC increased gradually as the solution of one polyelectrolyte was added to the other; the turbidity of the solution reached a maximum for the stoichiometric ratio of the reacting polyelectrolytes in the mixture. At pH 4,0 the composition of the complex is very near to equimolarity. IR spectra and thermal analysis of the PEC exhibited significant differences from those of the 1:1 mixture of the starting polyelectrolytes.

Living cationic polymerization of styrene by the methanesulfonic acid/tin tetrachloride initiating system in the presence of tetra-n-butylammonium chloride

Abstract: Living cationic polymerization of styrene was achieved by the methanesulfonic acid/tin tetrachloride (CH3SO3H/SnCl4) initiating system in the presence of tetra-n-butylammonium chloride (nBu4NCl) in methylene chloride solvent below 0 °C. The typical reagent concentrations of this initiating system were as follows: CH3SO3H/SnCl4/nBu4NCl=20/100/40 mM; [Styrene]0=1.0 M. The number-average molecular weights of the product polymers increased in direct proportion to monomer conversion, and their molecular weight distributions (MWDs) were fairly narrow $$\left( {\bar M_W /\bar M_n \leqslant {\text{1}}{\text{.2}}} \right)$$ throughout the reaction. On addition of a fresh feed of styrene at the end of the polymerization, the added feed was smoothly polymerized at the same rate as in the first stage; the polymer molecular weight further increased in direct proportion to monomer conversion; and their molecular weight distributions stayed narrow $$\left( {\bar M_W /\bar M_n \leqslant {\text{1}}{\text{.2 - 1}}{\text{.3}}} \right)$$ . On the other hand, in the absence of nBu4NCl, the polymerization initiated by CH3SO3H/SnCl4 in CH2Cl2 at -15 °C led to non-living polymers with a broad molecular weight distribution. This indicates that nBu4NCl is essential to this living system.

The localisation model of rubber elasticity. II

Abstract: The effect of the spatial localization of a network chain by surrounding chains is incorporated into the chain probability distribution function and the network free energy is then calculated using the statistical mechanical formalism for constrained systems. In addition to a term having the classical ‘Gaussian’ form, the resulting expression contains another term which depends on both the cross-link density of the network and the plateau modulus of the uncross-linked melt.

Relationships between glass transition temperature and conversion : analyses of limiting cases

Abstract: The Couchman approach to the expression of the compositional variation of glass transition temperature (or the Di-Benedetto equation) can be used to evaluate the effect of molecular weight on Tg for a stepwise linear polymer. An expression for the KL constant in the Fox-Flory equation is proposed. It is also possible to estimate the TgL corresponding to the hypothetical linear structure defined in a three-dimensional network. For different epoxy-diamine systems, we have found a good concordance with the results obtained previously using an additive law.

Liquid crystalline polymers containing mesogenic units based on half-disc and rod-like moieties

Abstract: The synthesis and characterization of the hemiphasmidic monomers 4-{3,4,5-tri-[S(-)-2-methylbutan-1-yloxy] benzoate}-4'-(10-undecenoate)biphenyl (13), 4-[3,4,5-tri-(n-pentan-1-yloxy) benzoate]-4'-(10-undecenoate)biphenyl (14), 4-[3,4,5-tri-(n-dodecan-1-yloxy) benzoate]-4'-(10-undecenoate)biphenyl (15), 4-[3,4,5-tri-(n-dodecan-1-yloxy) benzoate]-4'-(10-undecen-1-yloxy)biphenyl (16) and of the polymethylsiloxanes derived from them (i.e. 17, 18, 19, and 20) are described. Monomers 13 to 16 are only crystalline. Polymer 17 is crystalline, 18 displays an unidentified mesophase, while 19, and 20 exhibit enantiotropic, most probably hexagonal columnar phasmidic mesophases.

Miscible blends of poly(N-vinyl pyrrolidone) with some hydroxyl-containing polymers

Abstract: Poly(N-vinyl pyrrolidone) (PVPr) forms miscible binary blends with poly(hydroxyethyl methacrylate), poly(hydroxypropyl methacrylate) and two styrene/allyl alcohol copolymers, as shown by their glass transition behavior. However, PVPr is immiscible with poly(ethyl methacrylate), poly(n-propyl methacrylate) and polystyrene. The results indicate the importance of hydroxyl groups in achieving miscibility.

A novel technique for preparing organophilic silica by water-in-oil microemulsions

Abstract: A novel technique to prepare ultramicro spherical silica particles containing vinyl groups on their surfaces is presented. This process is a combination of the sol-gel technique and the water-in-oil microemulsion technique in which hydrolysis and condensation of TEOS [Si(OEt)4] and MPS (trimethoxysilylpropylmethacrylate) take place. Spherical silica particles with a size range from 20 to 70 nm were obtained and the surface concentrations of the double bonds per nm2 were from 4 to 7.

Synthesis and characterization of poly(N-tert-alkylmaleimide)s

Abstract: N-tert-Butylmaleimide (tBMI), N-tert-amylmaleimide (tAMI) and N-tert-octylmaleimide (tOMI) were polymerized in the presence of a radical initiator to give high molecular weight polymers. The polymerization reactivity was found to depend on the bulkiness of the N-substituent. From thermogravimetric analysis of the polymers obtained, it was revealed that these polymers thermally decomposed via a two-step mechanism, i.e. elimination of olefins at the first step and decomposition of the resulting N-unsubstituted polymaleimide (poly(MI)) at the second step. The high molecular weight poly(MI) was isolated by thermolysis of poly(tBMI), poly(tAMI) and poly(tOMI) with elimination of isobutene, 2-methyl-1-butene and 2-methyl-2-butene, and 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene, respectively. It was also confirmed that the resulting poly(MI) had excellent thermal stability.

Synthesis and characterization of poly (N-butyl-3,6-carbazolediyl) : a new soluble electroactive material

Abstract: Poly (N-butyl-3,6-carbazolediyl) was synthesized by electrochemcial reduction of the NiBr2, 2,2′bipyridine/3,6 dibromo N-butylcarbazole system in N,N dimethylacetamide. The favorable interactions between solvent and butyl groups lead to the solubilization of the electroactive polymer in organic medium and allowed the determination of macromolecular and structural features by means of classical methods. From 13C NMR investigations it was concluded to a Π conjugation centered on the nitrogen atom of the carbazolic structure.

A new initiating system for the living polymerization of vinyl ethers leading to hydroxy-terminated polymers

Abstract: The reaction of trimethylsilyl iodide (TMSI) with 1,3-dioxolane (DXL) leads to the formation of 1-trimethylsiloxy-4-iodo-3-oxabutane. In combination with tetrabutyl ammonium triflate this compound can be used as an initiator for the polymerization of vinyl ethers. According to a living polymerization mechanism, the polymers are characterized by controlled molecular weights and narrow molecular weight distributions. The trimethylsiloxy head group originating from the initiation reaction is easily transformed into a primary hydroxyl function by hydrolysis.

Kinetics of uranium sorption from acidic sulphate solutions onto crosslinked polyethyleneimine based resins. 11

Abstract: The kinetics of uranium sorption from acidic sulphate solutions onto weak base resins derived from branched polyethyleneimine have been studied. Finite solution volume method and shrinking core model of Gopala and Gupta for testing film or pore diffusion rate control were used. Remarkably pore diffusion was the rate controlling mechanism for the smaller particle size considered. Stirring rate was found to be negligible on uranium sorption.

Synthesis of α,ω-bis(2,6-dimethylphenol)-poly(2,6-dimethyl-1,4-phenylene oxide) by phase transfer catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of 2,2-di(4-hydroxy-3,5-dimethylphenyl)propane

Abstract: α,ω-Bis(2,6-dimethylphenol)-poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-2OH) was synthesized by the radical-cation phase transfer catalyzed polymerization of 4-bromo-2,6-dimethylphenol (1) in the presence of 2,2-di(4-hydroxy-3,5-dimethylphenyl)propane (2). Copolymerization experiments were performed by a liquid-liquid two phase, benzene/1.5 N NaOH (aq), phase transfer catalyzed reaction with tetrabutylammonium hydrogen sulfate (TBAH) or tricaprylmethyllammonium chloride (Aliquat 336) catalysts. A series of copolymerization experiments were performed with 1/2 molar ratios of 4/1, resulting in PPO-2OH with Mn in the range of 2200–3200 g/mol. Phase transfer catalyzed etherification of the PPO-2OH chain ends with p-chloromethylstyrene was used to synthesize α,ω-bis(vinylbenzyl ether)s of the PPO-2OH (PPO-2VBE). The chain microstructure and the fuctionality of both PPO-2OH and PPO-2VBE was studied by 200 MHz 1H-NMR spectroscopy.

Unsaturated polyesters: 2. Polyester from maleic anhydride and 1,3-propylene glycol

Abstract: The polymerization of maleic anhydride and 1,3-propylene glycol was carried out using p-toluenesulphonic acid as catalyst. The percentage isomerization of maleate to fumarate has been correlated with the extension of polycondensation and the steric hindrance between the condensed functional groups

Studies on the molecular weight dependence of tacticity of anionically prepared PMMAs by on-line GPC/NMR

Abstract: Several PMMA samples prepared in toluene with anionic initiators such as t-C4H9MgBr, n-C4H9MgCl, 1,1-diphenylhexyllithium, t-C4H9Li and t-C4H9Li(n−C4H9)3Al complex were analyzed by the on-line GPC/NMR method using a 500 MHz 1H NMR spectrometer as a real-time detector of GPC. The molecular method for a short time (≤60 min per sample) with a small amount of the sample (≈1 mg). The plots of intensities of the α-methyl proton resonances due to mm- and rr-triads against elution time showed the variation of tacticity with molecular weight of the PMMA. On the basis of the results, the natures of active species in the polymerizations were discussed.

Stereoregular oligomers of methyl methacrylate

Abstract: Packed column SFC has been found suitable for the rapid and detailed analysis of the isotactic and syndiotactic oligomers of MMA, when the temperature gradient technique was applied and the modifier was employed. Oligomer components from trimer to 20-mer separated completely. The heptamer fraction collected three times by SFC gave the 1H NMR spectrum of satisfactorily high S/N ratio; the spectrum agreed well with that of the standard sample. Separation by tacticity as well as by molecular weight was observed for the SFC of a mixture of the isotactic and syndiotactic oligomers. The isotactic oligomers had longer retention time than the syndiotactic oligomers of the corresponding degree of polymerization.

On the theoretical strength of gelspun/hotdrawn ultra-high molecular weight polyethylene fibres

Abstract: The fraction of load carrying chains in various gelspun/hotdrawn ultra high molecular weight polyethylene (UHMWPE) fibres was evaluated on the basis of a recent morphological model A linear relation was found between the strength of the fibre and the fraction of load carrying chains, calculated by this method By extrapolation of this relation to a fraction of load carrying chains of unity, a theoretical strength of 30±3 GPa was estimated for polyethylene

Molecular Engineering of Liquid Crystalline Polymers by Living Polymerization. 7. Influence of Copolymer Composition on the Phase Behavior pf Poly(11-((4-cyano-4'Biphenyl)oxy)undecanyl Vinyl Ether-co-2-((4-Cyano-4'- Biphenyl)oxy)ethyl Vinyl Ether)

Abstract: : This paper describes the synthesis of poly 11-4-cyano-4 '-biphenyl) oxyundecanyl vinyl ether-co-2-(4-cyano-4'biphenyl)oxyethyl vinyl ether A/B poly(6-11)-co-(6-2)A/B where A/B refers to the molar ratio between the monomers 6-11 and 6-2, with number average molecular weights above 15, by living cationic polymerization. The phase behavior of the resulting copolymers was discussed as a function of copolymer composition. Within this range of molecular weights, in the first heating scan poly(6-11) exhibits a melting and an enantiotropic s(A) phase, while poly(6-2) only a glass transition temperature. Depending on composition, poly(6-11-CO6-2)A/B either display an enantiotropic nematic, enantiotropic s(A) or both enantiotropic nematic and anantiotropic s(A) phases.

Curing of epoxy resins with dicyandiamide : reaction behaviour of glycidyl ethers

Abstract: Etude par chromatographie HPLC des produits obtenus par reaction du phenyl glycidyl ether et d'une resine (DGEBA) avec le dicyandiamide dans le DMF en presence d'un accelerateur (N,N-dimethyl benzylamine). Influence de la temperature et du solvant

Characterization of surfaces of carbon fibres by scanning tunneling microscopy

Abstract: The experimental results obtained by scanning tunneling microscopy (STM) studies of different carbon fibres are presented and discussed The comparative analysis of the STM images at scales from hundreds of nanometers down to atomic scale reveals the differences of surface features for carbon fibres processed from different precursors, polyacrylonitrile fibres and pitch The high temperature treatment of carbon fibres — the so-called graphitization process — as used to improve the stress modulus induces drastically increased ordering phenomena at the atomic level Structural information obtained by STM on the surface of the fibres as well as in their cross sectional areas is discussed in comparison with known results of diffraction studies STM appears to be the new powerfull technique for the detailed structural studies of surfaces of carbon fibres The perspectives of these studies are under discussion

Synthesis and characterization of poly(N-tert-alkylmaleimide)s: 1. Radical polymerization of N-tert-butylmaleimide leading to a less-flexible poly(substituted methylene)

Abstract: Cinetique de la polymerisation radicalaire en solution du N-t-butyl maleimide; discussion de l'effet du groupe t-butyl sur la reactivite du monomere. Etude par viscosimetrie et diffusion lumineuse de la rigidite du polymere en solution et de son influence sur la polymerisabilite du monomere

Further studies on the high-speed gel-spinning of ultra-high molecular weight polyethylene

Abstract: The high-speed spinning technique has been applied to very elastic solutions of ultra-high molecular weight polyethylene in paraffin oil in an attempt to produce a strong fiber in a one-step process. At a winding speed of 4000 m/min a fiber was produced with a tensile strength of 2.3 GPa, a Young's modulus of 46 GPa and a elongation at break of 6.5%. This fiber could not be hot drawn anymore. At a winding speed of only 1 m/min the same solution yielded after spinning and hot drawing a fiber with a tensile strength of 7.2 GPa.

Ionic conductivity and morphology of complexes formed by polyurethanes and lithium perchlorate

Abstract: Segmented polyether urethane (SEU) and urethaneurea (SEUU) were synthesized using ABA type triblock copolymer as a prepolymer, where A stands for poly(oxyethylene) and B stands for poly(oxytetramethylene). Lithium perchlorate was dissolved in SEU or SEUU to prepare LiC104 complexes (SEU/LiC104 and SEUU/LiC104) in film form. The highest conductivities observed here were 5.13x10-6 S cm-1 at 30°C and 3.34x10-5 S cm-1 at 50°C for LiC104/SEUU (oxyethylene-units content, 31 mol%). The ionic conductivity of these complexes was found to show the Arrhenius type temperature dependency. The effect of lithium perchlorate dissolution on the morphology of SEU and SEUU were also discussed.