Multi-arm star polyisobutylenes

Summary The first synthesis of a multi-arm radial-star polyisobutylene (*-PIB) is described. The synthesis occurred by the addition of excess divinylbenzene (DVB) linking reagent to a living polyisobutylene (PIB) charge i.e., by the arm first method under specific conditions. The radial structure of the *-PIB was proven by determining the molecular weight of a sample by light scattering, then selectively destroying the aromatic polydivinylbenzene (PDVB) core, and finally determining the molecular weight of the surviving alphatic PIB arms. The synthesis strategy, kinetic observations during synthesis, and procedures leading to a representative *-PIB are described. This product whose g/mole with , contained 90.3 mole% (78 wt.%) PIB arms and 9.7 mole% (22 wt.%) aromatic core; thus the number of PIB arms emanating from the core was (number average number of arms)=56 or (weight average number of arms)=110.     

Polymerization of substituted acetylenes by (mesitylene)M(CO)3 (M=W,Mo)

Summary Phenylacetylene could be polymerized by (mesitylene)W(CO)₃ in CCl₄ to give a polymer with 12,000 in ca. 80% yield. UV irradiation was unnecessary unlike the W(CO)₆–CCl₄-h catalyst. The present polymerization did not proceed in toluene. The (mesitylene)W(CO)₃ catalyst afforded high molecular weight polymers from phenylacetylenes bearing bulky substituents (e.g., Me₃Si and CF₃) at the ortho position. The Mo counterpart, (mesitylene)Mo(CO)₃, catalyzed the polymerization of 1-chloro-2-phenylacetylene and 1-chloro-1-octyne to provide high molecular weight polymers . Catalytic amounts of Lewis acids accelerated the polymerization of phenylacetylene by (mesitylene)W(CO)₃, but decreased the polymer molecular weight; this polymerization proceeded not only in CCl₄ but also in toluene.     

The influence of total monomer concentration on the “reactivity” of ω-(p-vinylbenzyl ether) macromonomers of poly(2,6-dimethyl-1,4-phenylene oxide) determined from radiacal copolymerization experiments with butyl methacrylate

Summary The influence of the total monomer concentration on the radical reactivity ratio r₁ of butyl methacrylate (BMA) (M₁)--(p-vinylbenzyl ether) macromonomer of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-VBE) (M₂) monomer pair was investigated. For two different molecular weights of the PPO-VBE macromonomer ( , and ), the determined reactivity ratio r₁ decreases with the increase of the macromonomer concentration. Therefore, the reactivity of the macromonomer, 1/r₁, follows the opposite trend. This dependence is due to micelles formation during copolymerization. This microsegregation process partitionates the comonomer concentrations between the bulk of solvent and around the growing chain and therefore, the experimental r₁ is actually a product of the true reactivity ratio r₁ ⁰ and a partition coefficient k.     

Quantitative aspects of chain extension of telechelics

Summary Quantitative aspects of chain extension of telechelics have been studied. Molecular weight independent characteristic terms were defined and simple expressions were derived for number average extension, , and number average degree of extension, , as a function of number average functionality (¯F_n) of telechelic prepolymers. Analysis of these expressions indicate that _n and ¯DE_n are enormously sensitive to insignificant changes in ¯F_n close to ideal ¯F_n = 2.0. Molecular weight of the extended polymer (¯M_r) has also been calculated considering ¯F_n, number average molecular weight of the prepolymer (¯M_n), and molecular weight of the extender (M_e).     

Syntheses of diblock copolymers: poly(2-methylpropene)-b-poly(α-amino acid)

Summary Diblock copolymer poly (2-methylpropene)-b-poly (-amino acid) was obtained by polymerization of the corresponding N-caboxy anhydride initiated by a poly (2-methylpropene) bearing a terminal amine in dioxane/CH₂Cl₂ mixture. Copolymers were analyzed by FT IR, ¹H and ¹³C NMR. of the -amino acid segment determined by ¹H NMR fits well with those obtained by a theoretical calculation.     

Dilute acid-hydrolized cotton cellulose An electron diffraction study

Summary A comparative morphological investigation by electron diffraction analysis was carried out on samples of cotton cellulose from different stages of dilute-acid-catalysed hydrolytic degradation reactions. Within the range from 13000 (native material) to 500 only a gentle decrease of the relative crystallinity was observed. For below 500 the crystallinity decreases much faster, together with a simultaneous marked increase in paracrystalline lattice distortion and the show up of crystallographic evidence for a new cellulose phase which became better defined as degradation proceeded. A clearly defined parallel can be established between the different kinetic stages of the degradation reaction and the degree-of-polymerization dependence of the morphological features. The resulting evidence is at odds with the traditionally held views about the effects of acid hydrolysis of cellulose on its morphological fine structure.     

New Poly(Methacrylate)s Containing Benzylpiperazine and Methylpiperidine Moieties

The synthess of two new methacrylate esters containing 2-(4-benzyl piperazin-1-yl)-2-oksoethyl and 2-(4-methylpiperidin-1-yl)-2-oksoethyl group are described. The monomers produced from the reaction of corresponding 4-methylpiperidinechloroacetamide and 1-benzylpiperazinechloroacetamide with sodium methacrylate were polymerized in DMSO solution at 65°C using AIBN as an initiator. The monomers and their polymers were characterized by IR, ¹H- and ¹³C-NMR spectroscopy. The glass transition temperature of the polymers were investigated by DSC and the apparent thermal decomposition activation energies (E _d ) were calculated by Ozawa method using the SETARAM Labsys TGA thermobalance. By using gel permeation chromatography, weight average ( ) and number average ( ) molecular weights and polidispersity, indices of the polymers were determined.     

The performance of porous and gauze electrodes in electrolysis with parabolic velocity distribution

An approximate numerical method for the estimation of the velocity exponent in (small-scale) flow-through porous and gauze electrodes is presented. The method can also be employed to determine if a plug-flow or a parabolic-flow model offers a more reliable representation of the experimental behaviour of the electrode.Nomenclature a cross sectional area of the electrode - B integration parameter (Equations 7 and 8) - c exit active ion concentration, its mean measured value in the case of parabolic flow,c _o its inlet value;c _m its mean value; its mean calculated value in the case of parabolic flow;c ^* dimensionless concentration, equal toc/c _o; mean dimensionless concentration, equal to /c _o - F Faraday's constant - i _L mean limiting current density (geometric-area base) - j proportionality factor (Equation 1) - k _m mass transport coefficient, its mean value - L length of the electrode - n number of electrons involved in the electrode reaction - N ionic flux - r radial coordinate - R _E geometric radius - R limiting degree of conversion - s specific surface area of the electrode (surface per volume) - u linear solution velocity; u_o its maximum (centreline) value; its mean value (=u_o/2) - v volumetric flow rate; its mean value - x transform variable forz - z dimensionless radial distance - velocity exponent for mass transport (Equation 1)     

Synthesis of block copolymers of p-methoxystyrene and vinyl ethers by the hydrogen iodide/zinc iodide initiating system

Summary Amphiphilic or polar-nonpolar AB block copolymers of p-methoxystyrene (pMOS) and vinyl ethers (VE; methyl or isobutyl) were synthesized by the sequential living cationic polymerization initiated with the hydrogen iodide/zinc iodide (HI/ZnI₂) system in toluene at -15 and +25 °C. pMOS-VE block copolymers of narrow molecular weight distributions ( = 1.05−1.25; = 6000−16000) were obtained in nearly quantitative blocking efficiency, when methyl or isobutyl VE was polymerized first by HI/ZnI₂, followed by addition of pMOS to the resulting living polymer solutions; an additional amount of ZnI₂ was required to accelerate the second-phase living polymerization of the less reactive styrenic monomer. Similar block polymerizations in an opposite monomer-addition sequence (from pMOS to VE), in contrast, resulted in mixtures of the desired block polymer and homopolymer of pMOS.     

Mass transfer at the electrodes of the ‘falling-film cell’

In the falling-film cell the electrolyte flows as a thin film in the channel between an inclined plane plate and a sheet of expanded metal which work as electrodes. The present work gives the mass transfer coefficients at both electrodes; the experimental variables are the electrolyte flow-rate, the angle of inclination of the channel and the interelectrode distance. The results allow three different flow regimes to be characterized. At low flow rates, there exists a particular regime where capillary effects are present; in this regime the mass transfer coefficient decreases with increasing flow rate, which is interesting from the point of view of possible industrial electrolytic applications.Nomenclature b width of the inclined channel - D diffusion coefficient - d interelectrode distance - e _m mean film thickness - Grashof number, based ond - Grashof number, based onL - ¯k overall mass transfer coefficient, defined by Equation 9 - L electrode length - Q _v volumetric flow rate - volumetric flow rate per unitQ _vl width of channel - Reynolds number - Schmidt number - Sherwood number, based ond - Sherwood number, based onL - mean velocity of the liquid film - inclination angle of the channel with respect to the horizontal - kinematic viscosity of them electrolyte     

Phase transfer catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of a terminating comonomer phenol: 2,4,6-tri-tert-butylphenol or 4-bromo-2,6-di-tert-butylphenol

Summary This paper describes the phase transfer catalyzed (PTC) polymerization of 4-bromo-2,6-dimethylphenol (1) in the presence 2,4,6-tri-tert-butylphenol (2) or 4-bromo-2,6-di-tert-butylphenol (4). The polymerization of 1 in the presence of 2 at a 1/2 molar ratio of 3/1 led to poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with _n of 13400 g/mol at a yield of 85%. In contrast, the polymerization of 1 in the presence of 4 at 1/4 molar ratios of 5/1 and 10/1 did not produce any methanol insoluble PPO fraction when 4 was added at the beginning of the polymerization. However, PPO with _n + 1600 to 2400 g/mol were obtained when 4 was added to the polymerization system after 0.5 h and respectively 2.0 h after the homopolymerization of 1 was started. A radical-anion mechanism is proposed to account for these polymerization results.     

Potentiometric determination of the molecular weight of polymers

Summary The determination of acid end-groups of acrylamide and acrylonitrile polymers initiated by cerium (IV)-malonic acid, cerium (IV)-tartaric acid and cerium (IV)-citric acid redox initiators systems was made in aqueous and nonaqueous media potentiometrically. The effect of solvent, titrant and electrode system on the half-neutralization potentials and number-average molecular weights, , were determined potentiometrically and were studied. These values were compared with those obtained by viscosimetric and conductometric methods.     

Synthesis of a perfluorinated azo initiator

Summary A method to determine the recombination/disproportionation rate during the polymerization of styrene is described. In this method, a perfluorinated azo initiator used to prepare a perfluorinated polystyrene was first synthesized. Then, the recombination/disproportionation rate was calculated by comparing the number-average molecular weight and the fluorine content in weight of this resulting polystyrene.     

Influence of molecular weight on the crystallization of poly(vinylidene fluoride)

Five samples of Poly (vinylidene fluoride) with a molecular weight from 45,000 to 260,000 were analyzed by means of FT-IR spectroscopy in order to study the influence of molecular weight on the crystallization process. The spectra of films obtained from methylethylketone solutions revealed the prevalence of form II () in the case of lower and of form III () in the higher molecular weight samples. The amount of form III was found to increase as the Mv decreased and as annealing temperatures increased. The deconvolution technique of vibrational spectra allowed detection of small amounts of other forms accompanying the prevailing one.     

Characterization of metal-ion containing polyesters

Summary The glass transition behavior of poly(diethylene glycol-co-succinic acid) (DEGSA) and its complexes obtained in the reaction with MgO have been investigated. The number average molar mass ( ) of the DEG-SA samples prior to complexation was determined by titration of the terminal COOH groups. The glass transition temperature (T_g) was measured as a function of molar mass and Mg²⁺ ion content. The dependence of T_g on obeyed the Fox-Flory relationship. Addition of increasing amounts of MgO to DEG-SA led to a gradual increase in T_g, and a decrease in the heat capacity change (c_p). This behavior is associated with complex formation between COO^-and Mg²⁺. The decrease in c_p is a result of ion-ion and to a lesser extent ion-dipole interactions which lower chain mobility. The common limiting T_g value for the three DEG-SA samples at an Mg²⁺/COO^- ratio of ca. 0.5 approaches T_g,, which is the corresponding T_g of a polymer of infinite molar mass.     

On the determination of oxygen potentials and O/M ratios in mixed U-Pu oxides by means of solid state galvanic cells

Measurements of oxygen potential on uranium-plutonium mixed oxides by means of solid state galvanic cells are discussed and compared with precedent data. Discrepancies in the values at low temperature (1000 K) as well as in the versusT slopes are found, which disappear when the samples are thermally cycled. An analysis is performed of this effect, showing that the absence of a good homogeneization of the sample in oxygen and/or in plutonium content can give rise to mixed potentials and hence to erroneous results.     

Effect of PVC on low-polar isobutylene polymerization in the presence of BCl3

Summary The isobutylene polymerizations in the presence of BCl₃ were carried out in dichloromethane ([M]=7 mol/l) at-20°C in the presence and absence of PVC. The products of polymerizations in the absence of PVC are oligoisobutylenes with a narrow molecular weight distribution ; their structure was analyzed by ¹H-NMR spectroscopy. In addition to the signals assigned to known unsaturated terminal structures [ 4.62 and 4.82-CH₂C(CH₃)=CH₂, 5.12-CH=C(CH₃)₂], a new intense signal was found at 5.09 ppm and assigned to the structure-CH=C(CH₃)CH₂CH₃. A mixture of isobutylene homopolymers and PVC grafted with isobutylene (approx. 9.5% wt. isobutylene grafted) is formed in the presence of PVC.     

Halato-telechelic polymers

Summary Halato-telechelic polymers (HTP) resulting from the neutralization of carboxy telechelic polymers behave as useful ion-containing model compounds. Carboxy telechelic polybutadiene ( ) neutralized by magnesium methoxide exhibits a secondary relaxation mechanism characteristic of the ionic component. The activation process of this secondary relaxation obeys to an Arrhenius-type dependence and an activation energy of 30.5 Kcal/mole is calculated.     

Raman study of chain deformation in polypropylene

Summary Raman spectroscopy was used to study the transfer of energy that occurs among the internal vibrations of crystalline isotactic polypropylene as it is compressed. The group was found to play a significant role in the subsequent chain deformation.