Molecular weight distribution and thermal characterization of polydimethylsilmethylene

1,1,3,3-Tetramethyl-1,3-disilacyclobutane (I) was polymerized under the following conditions with H₂PtCl₆·6H₂O as catalyst: (a) addition of I dropwise to a large excess of catalyst at room temperature, producing [(CH₃)₃SiCH₂(CH₃)₂Si]₂O in 90% yield; (b) polymerization at room temperature in the presence of 10% water with 23 ppm Pt, yielding 9% conversion to low molecular weight polymer after 4 weeks; (c) polymerization in an open vessel (25°C., 7 ppm Pt, M?_n = 1.2 × 10⁵), a closed vessel (100°C., 28 ppm Pt, M?_n = 1.7 × 10⁵), in a closed tube after twice freezing and evacuating (25°C., 23 ppm Pt, M?_n = 2.9 × 10⁵); (d) polymerization in an oxygen atmosphere (25°C., 17 ppm Pt, M?_n = 2.7 × 10⁵). The molecular weight distributions of the polymers with M?_n = 1.2 × 10⁵ and 1.7 × 10⁵ was studied by gel-permeation chromatography. Ratios of M?_w/M?_n are 3.1 and 2.7, respectively. In both cases a long tail of high molecular weight polymer is evident. Interpretation of the molecular weight distributions is qualitatively discussed on the basis of a postulated seven-step mechanism. Water is shown to be a source of chain termination. Evidence is presented for the existance of ?SiOSi? and ?SiOH in the silmethylene polymers. Negligible cyclization occurs. Orders of thermal stability measured by DTA and TGA for polydimethylsilmethylene (A), polydimethylsiloxane (B), and polysiobutylene (C) are: in He, A > B > C; in air, in air, B > C ? A. A fractionally precipitated polydimethylsilmethylene had a weight loss of less than 5% by 600°C. by TGA analysis at 10°C./min. in He.     

One‐pot synthesis of isocyanate and methacrylate multifunctionalized polyisobutylene and polyisobutylene‐based amphiphilic networks

Amphiphilic polymer networks consisting of hydrophilic poly(2‐hydroxyethyl methacrylate) (PHEMA) and hydrophobic polyisobutylene (PIB) chains were synthesized from a cationic copolymer of isobutylene (IB) and 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (IDI) prepared at ?50 °C in dichloromethane in conjunction with SnCl₄. The isocyanate groups of this random copolymer, PIB(NCO)_n, were subsequently transformed in situ to methacrylate (MA) groups in the dibutyltin dilaurate‐catalyzed reaction with 2‐hydroxyethyl methacrylate (HEMA) at 30 °C. The resulting PIB(MA)_n with number–average molecular weight 8200 and average functionality F_n ～ 4 per chain was in situ copolymerized radically with HEMA at 70 °C, giving rise to the amphiphilic networks containing 41 and 67 mol % HEMA. PHEMA–PIB network containing 43 mol % HEMA was also prepared by radical copolymerization of PIB(MA)_n precursor with HEMA using sequential synthesis. An amphiphilic nature of the resulting networks was proved by swelling in both water and n‐heptane. PIB(NCO)_n and PIB(MA)_n were characterized by FTIR spectroscopy, SEC and the latter also by ¹H NMR spectroscopy. Solid state ¹³C NMR spectroscopy was used for characterization of the resulting PHEMA–PIB networks. Whereas single glass‐transition temperature, T_g = ?67.4 °C, was observed for the rubbery crosslinked PIB prepared by reaction of PIB(NCO)_n with water, the PHEMA–PIB networks containing 67 and 41 mol % HEMA showed two T_g's: ?70.4 and 102.7 °C, and ?63 and 107.2 °C, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2891–2900, 2006     

Organometallic polymers. XIV. Copolymerization of vinylcyclopentadienyl manganese tricarbonyl and vinylferrocene with N-vinyl-2-pyrrolidone

N-Vinyl-2-pyrrolidone(I) has been copolymerized with vinylferrocene(II) and vinylcyclopentadienyl manganese tricarbonyl(III) in degassed benzene solutions with the use of azobisisobutyronitrile (AIBN) as the initiator. The polymerizations proceed smoothly, and the relative reactivity ratios were determined as r₁ = 0.66, r₂ = 0.40 (for copolymerization of I with II, M₁ defined as II) and r₁ = 0.14 and r₂ = 0.09 (for copolymerization of I with III, M₁ defined as III). These copolymers were soluble in benzene, THF, chloroform, CCl₄, and DMF. Molecular weights were determined by viscosity and gel-permeation chromatography studies (universal calibration technique.) The copolymers exhibited values of M?_n between 5 × 10³ and 10 × 10³ and M?_w between 7 × 10³ and 17 × 10³ with M?_w/M?_n < 2. Upon heating to 260°C under N₂, copolymers of III underwent gas evolution and weight loss. The weight loss was enhanced at 300°C, and the polymers became in creasingly insoluble. Copolymers of vinylferrocene were oxidized to polyferricinium salts upon treatment with dichlorodicyanoquinone (DDQ) or o-chloranil (o-CA) in benzene. Each unit of quinone incorporated into the polysalts had been reduced to its radical anion. The ratio of ferrocene to ferricinium units in the polysalts was determined. The polysalts did not melt at 360°C and were readily soluble only in DMF.     

Synthesis of thermally-induced phase separating polymer with well-defined polymer structure by living cationic polymerization. I. Synthesis of poly(vinyl ether)s with oxyethylene units in the pendant and its phase separation behavior in aqueous solution

Living cationic polymerization of alkoxyethyl vinyl ether [CH₂?CHOCH₂CH₂OR; R: CH₃ (MOVE), C₂H₅ (EOVE)] and related vinyl ethers with oxyethylene units in the pendant was achieved by 1-(isobutoxy)ethyl acetate ( 1 )/Et_1.5AlCl_1.5 initiating system in the presence of an added base (ethyl acetate or THF) in toluene at 0°C. The polymers had a very narrow molecular weight distribution (M?_w/M?_n = 1.1–1.2) and the M?_n proportionally increased with the progress of the polymerization reaction. On the other hand, the polymerization by 1 /EtAlCl₂ initiating system in the presence of ethyl acetate, which produces living polymer of isobutyl vinyl ether, yielded the nonliving polymer. When an aqueous solution of the polymers thus obtained was heated, the phase separation phenomenon was clearly observed in each polymer at a definite critical temperature (T_ps). For example, T_ps was 70°C for poly(MOVE), and 20°C for poly(EOVE) (1 wt % aqueous solution, M?_n ～ 2 × 10⁴). The phase separation for each case was quite sensitive (ΔT_ps = 0.3–0.5°C) and reversible on heating and cooling. The T_ps or ΔT_ps was clearly dependent not only on the structure of polymer side chains (oxyethylene chain length and ω-alkyl group), but also on the molecular weight (M?_n = 5 × 10³-7 × 10⁴) and its distribution. © 1992 John Wiley & Sons, Inc.     

Multi-arm Star Polyisobutylenes. V. Characterization of Multi-arm Polyisobutylene Stars by Viscometry,Pour Points,Electron Microscopy,and Ultrasonic Shear Degradation

Abstract

Structure/property relationship of multi-arm star polyisobutylenes [?-(PIB) _n s] were characterized by a variety of techniques, including vis-cometry, pour points, electron microscopy, and ultrasonic degradation. The intrinsic viscosity of ?-(PIB) _n s changes very little with temperature in the 30 to 100°C range, whereas that of linear PIBs of the same molecular weight increases strongly with temperature. Kinematic viscosity measurements of select ?-(PIB) _n s gave viscosity indices in excess of 130. The viscosity of ?-(PIB) _n s is mainly determined by the molecular weight of the arms and much less by the number of arms or overall molecular weights. Electron microscopy of ?-(PIB) _n s indicates a compact spherical morphology, a conclusion that was substantiated by radius of gyration measurements. Pour points of ?-(PIB) _n s are ?27°C. Ultrasonic studies gave insight into the mechanism of shear degradation of ?-(PIB) _n s. These characteristics render ?-(PIB) _n s of interest as rheology control additives for motor oils.     

Molecular weight distribution in radiation-induced polymerization. I. γ-radiation-induced free-radical polymerization of liquid styrene

The kinetics of γ-radiation-induced free-radical polymerization of styrene were studied over the temperature range 0–50°C at radiation intensities of 9.5 × 10⁴, 3.1 × 10⁵, 4.0 × 10⁵, and 1.0 × 10⁶ rad/hr. The overall rate of polymerization was found to be proportional to the 0.44–0.49 power of radiation intensity, and the overall activation energy for the radiation-induced free-radical polymerization of styrene was 6.0–6.3 kcal/mole. Values of the kinetic constants, k_p²/k_t and k_trm/k_p, were calculated from the overall polymerization rates and the number-average molecular weights. Gelpermeation chromatography was used to determine the number-average molecular weight M?_n, the weight-average molecular weight M?_w, and the polydispersity ratio M?_w/M?_n, of the product polystyrene. The polydispersity ratios of the radiation-polymerized polystyrene were found to lie between 1.80 and 2.00. Significant differences were observed in the polydispersity ratios of chemically initiated and radiation-induced polystyrenes. The radiation chemical yield, G(styrene), was calculated to be 0.5–0.8.     

Synthesis and characterization of two novel star blocks: tCum[poly(isobutylene‐b‐norbornadiene)]3 and tCum[poly(norbornadiene‐b‐isobutylene)]3

Two structurally closely related three‐arm star blocks were synthesized and characterized: tCum(PIB‐b‐PNBD)₃ and tCum(PNBD‐b‐PIB)₃ [where tCum (tricumyl) stands for the phenyl‐1,3,5‐tris(‐2‐propyl) fragment and PIB and PNBD are polyisobutylene and polynorbornadiene, respectively]. The syntheses were accomplished in two stages: (1) the preparation of the first (or inner) block fitted with appropriate chlorine termini capable of initiating the polymerization of the second (or outer) block with TiCl₄ and (2) the mediation of the polymerization of the second block. Therefore, the synthesis of tCum(PIB‐b‐PNBD)₃ was effected with tCum(PIB‐Cl^t)₃ [where Cl^t is tert‐chlorine and number‐average molecular weight (M_n) = 102,000 g/mol] by the use of TiCl₄ and 30/70 CH₃Cl/CHCl₃ solvent mixtures at ?35 °C. PNBD homopolymer contamination formed by chain transfer was removed by selective precipitation. According to gel permeation chromatography, the M_n's of the star blocks were 107,300–109,200 g/mol. NMR spectroscopy (750 MHz) was used to determine structures and molecular weights. Differential scanning calorimetry (DSC) indicated two glass‐transition temperatures (T_g's), one each for the PIB (?65 °C) and PNBD (232 °C) phases. Thermogravimetric analysis thermograms showed 5% weight losses at 293 °C in air and at 352 °C in N₂. The synthesis of tCum(PNBD‐b‐PIB)₃ was achieved by the initiation of isobutylene polymerization with tCum(PNBD‐Cl^sec)₃ (where Cl^sec is sec‐chlorine and M_n = 2900 g/mol) by the use of TiCl₄ in CH₃Cl at ?60 °C. DSC for this star block (M_n = 14,200 g/mol) also showed two T_g's, that is, at ?67 and 228 °C for the PIB and PNBD segments, respectively. It is of interest that the Cl^sec terminus of PNBD, , readily initiated isobutylene polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 740–751, 2003     

Properties of crystallized trans 1,4-polyisoprene

Stirrer crystallization of a trans-1,4-polyisoprene fraction(M?_n = 3 × 10⁵) was carried out from n-butyl acetate and from n-heptane solutions (2% w/v). Fibrous crystals in the ß form were obtained at temperatures of 46-48°C in the two solvents, respectively. At 36-46°C from n-butyl acetate and 25-35°C from n-heptane lamellar crystallization took place leading predominantly to the α form. Melting endotherms and densities for various samples were obtained. The maximum TENDO for α was 74°C and for ß 79°C and the maximum weight fraction crystallinity for ß was 0.78. The stability of performed α nuclei in n-butyl acetate and n-heptane using a fraction with M?_n = 2.5 × 10⁵ was monitored as a function of temperature. The dissolution temperature of fibrous ß-TPI with the maximum TENDO was measured in 13 liquids and the results analyzed in terms of the Flory-Huggins parameter. The heats of fusion for the α and ß forms, obtained by extrapolation of heat of fusion versus change in specific volume, were found to be 8.0 and 10 kJ mol^?1, respectively. The pressure coefficients of the melting temperature were calculated to be 38 and 43 K kbar^?1 and the fold-surface free energies recalculated to be 42 ± 1 and 53 ± 1 erg cm^?2 for the α and ß forms, respectively. The number of monomer units per average noncrystalline chain traverse for the most crystalline fibrous ß-TPI was estimated at 36.     

Solution properties of high molecular weight polystyrene

A series of polystyrenes with weight-average molecular weight M?_w up to 1.3 × 10⁷ was prepared by anionic polymerization in tetrahydrofuran (THF). Each sample was characterized by gel-permeation chromatography, light scattering, and viscometry. It was found that each sample had an almost symmetrical and very narrow molecular weight distribution (M?_w/M?_n < 1.07). The mean-square unperturbed radius of gyration 〈S²〉₀ was determined in trans-decalin at 20.4°C as 〈S²〉₀ = 7.8₆ × 10^?18M?_w (cm²). The particle scattering factor was well represented by the Debye equation irrespective of solvent in the range of M?_w < 4 × 10⁶, and only a small deviation was observed in benzene at higher molecular weights. The penetration function Ψ ≡ A₂M²/4π^3/2N_A〈S〉^23/2 was found to approach a relatively low asymptotic value of 0.21–0.23 at molecular weights above 2 × 10⁶ in benzene at 30°C, where A₂ is the second virial coefficient and N_A is Avogrado's number. It was also found that the theta temperature in trans-decalin was affected by the nature of polymer samples. A difference of about 3°C in the theta temperature was observed between two series of anionic polystyrenes, one prepared in THF and the other in benzene, but there was practically no difference in unperturbed chain dimension.     

Effect of the mixture t - BuCl/SnCl4 on the cationic polymerization of isobutylene

The polymerizations of isobutylene initiated with the system tert-butyl chloride (t-BuCl)/SnCl₄ and carried out in CH₂Cl₂ at −20°C and −78°C were investigated. The results obtained demonstrate that the presence of t-BuCl in the polymerizing system gives rise to a PIB product with a distinctly bimodal MWD. The higher-molecular weight (HMW) PIB, M̄_n = 20000, I=M̄_w/M̄_n ∼ 2.5, is the result of existence of the protogenic initiation with residual water in the reaction system. The lower-molecular weight (LMW) PIB, M̄_n < 600, M̄_w/M̄_n ≤ 1.4, is the product of polymerization initiated presumably with a complex t-BuCl-SnCl₄-H₂O. To elucidate the reaction mechanism of the polymerization initiated with the complex, a series of similar isobutylene polymerizations using the initiation system 2,5-dichloro-2,5-dimethylhexane (DDH)/SnCl₄ was run and the oily LMW PIB samples were investigated by ¹H-NMR. A new polymerization mechanism describing the role of DDH and t-BuCl is suggested.     

Thermodynamic Studies of Bi-Univalent Electrolytes. VI. Thermodynamics of Cadmium Acetate from E. M. F. and Calorimetric Measurements

E. M. F. of the Cell, Cd-Hg (2-phase)/CdAc₂(m), Hg₂Ac₂(s)/Hg was measured at 20°, 25°, 30° and 40°C. The standard e. m. f. of the cell, Cd/CdAc₃(m), Hg₂Ac₂(c)/Hg was evaluated as E°=1.1500?11.09×10^?4T+1.06×10^?8T² The thermodynamic data of the reaction, Cd(c) + Hg₂Ac₂(c)=2Hg(l)+Cd⁺⁺(aq)+2Ac^?(aq) at 25°C were estimated as ΔF°=?42,139, ΔH°=?48,698 cal mole^?1 and ΔS°=?22.0 cal deg^?1 mole^?1 at 25°C. The thermodynamic data for the formation of Hg₂Ac₂(s) were evaluated as ΔF_f°=?202.3, ΔH_f°=?154.5 Kcal mole^?1 and S°=72.9 cal deg^?1 mole^?1. From measurements of the heats of solution of CdAc₂·2H₂O in aqueous solution, the relative partial molal enthalpies of cadmium acetate in aqueous solution were estimated.     

Non-Newtonian flow curves including lower and upper Newtonian regions for dilute and moderately concentrated polystyrene solutions

The non-Newtonian viscosity in steady flow was measured for solutions of polystyrene (M?_w/M?_n = 1.1) in diethyl phthalate at 30.0°C. In the moderately concentrated solutions, from 6.03 × 10^?2 to 5.62 × 10^?1g/cm³, the viscosity data modified by frictional parameters fit the Graessley theoretical curve for a narrow distribution polymer. The dilute solutions, from 3.26 × 10^?3 to 1.57 × 10^?2 g/cm³, were nonentangled systems whose non-Newtonian properties could be explained by the excluded volume effect as proposed by Fixman. On the basis of the non-Newtonian data, it was concluded that the solution of 3.30 × 10^?2 g/cm³ was a lower critical entanglement concentration, which was distinguished from the usual higher critical concentration for entanglement. This lower critical concentration was also found in the concentration dependence of the activation energy of flow and the absorbance at 310 nm.     

THERMAL BEHAVIOR AND IONIC CONDUCTIVITY OF POLY[LITHIUM-N(4-SULFO-PHENYL) MALEIMIDE -CO-METHOXY OLIGO(OXYETHYLENE) METHACRYLATE]

Poly[lithium-N(4-sulfophenyl) maleimide -co- methoxy oligo-(oxyethylene) methacrylates] [P(LiSMOE_n)s] with three different oligoether side chains and different salt concentrations were synthesized. The copolyelectrolytes are essentially random in structure, with blocks of methoxy oligo(oxyethylene) meth-acrylate (MOE_nM) recurring sporadically in between the salt units of N(4-sulfophenyl) maleimide. They all show two glass transitions in the temperature range of ?100 to 100°C. The first one below ?30°C is assigned to the oligo(oxyethylene) side chain (T _g1), while the second one located between 20 and 50°C is attributed to the main chain of the polymer host (T _g2). The maximum ionic conductivity of the copolymer electrolytes, 1.6 × 10^?7 S cm^?1 at 25°C, occurs at lithium salt concentration [Li⁺]/[EO] = 2.2 mol%. The ionic conductive behavior of the copolyelectrolytes follows the Vogel-Tammann-Fulcher (VTF) equation. Moreover, a special VTF behavior exists in the copolymers with shorter oligoether side chain and higher salt concentration. Sweep voltammetric results indicate that these copolyelectrolytes have a good electrochemical stability window.     

Optical anisotropy of polyisobutylene: Strain birefringence

Strain birefringence measurements on crosslinked polyisobutylene (butyl rubber) confirm earlier work of Stein and Tobolsky on the linear polymer indicating the optical anisotropy to be much greater than should have been expected from the structural symmetry of the polyisobutylene (PIB) chain. The configuration–optical anisotropy parameter Δa for PIB at 25°C is 4.1(±0.1) × 10^?24 cm³, or about half the value for crosslinked polymethylene, both polymers being undiluted and amorphous. Swelling with cyclohexane, CCl₄, and CBrCl₃ lowers Δa to values of 3.8, 3.4, and 2.8 × 10^?24 cm³, respectively. Contributions from intermolecular correlations in the bulk polymer and from form anisotropy in the diluted systems are small, if not negligible. Temperature coefficients measured isometrically yield d In Δa/dT ≈ 0.2 × 10^?3 deg^?1. Both Δa and its temperature coefficient are much greater than calculated from rotational isomeric state theory assuming additivity of bond polarizabilities. The disparity (more than tenfold for Δa) cannot be relieved by any rational adjustment of the structural parameters. It is suggested that the severe crowding of groups in the PIB chain may affect the anisotropies of group polarizabilities.     

The Polymerization of Free Enols with Electron-Deficient Comonomers

Abstract

The balance between kinetics and thermodynamics is illustrated herein by the first direct polymerization of vinyl alcohol, the thermodynamically unstable tautomer of acetaldehyde, at a rate faster than it can tautomerize. Vinyl alcohol was formed through the acid catalyzed hydrolysis of ketene methyl vinyl acetal. With excess water present, the kinetics of tautomerization first order dependence upon vinyl alcohol (k_obs = 2.73 × 10^?4 s^?1). Under water starved conditions, however, the kinetics now show a zero order dependence upon the concentration of vinyl alcohol (k_obs = 3.5 × 10^?6 M/s). Under these latter conditions, the half life of vinyl alcohol is nearly 24 hours at room temperature. Although cationic and homo free radical polymerization of vinyl alcohol failed, we found that this meta-stable species could be quantitatively polymerized in a copolymerization (AIBN, hυ, -10 to 25°C) with maleic anhydride. The k_obs for copolymerization was found to be 4.41 × 10^?4 sec^?1 at ?10°C. Since the rate of polymerization is far greater than that of tautomerization under these conditions (ca. 30 times faster at ?10°C), there is no significant increase in acetaldehyde concentration during polymerization.     

Synthetic thermally reversible gel systems. III

Polyacrylylglycinamide (PAG) and its thermally reversible aqueous gels have been investigated and comparisons made with gelatin. For unfractionated PAG homopolymers in 2M NaCNS at 25°C, the Mark-Houwink-Sakurada equation is [η] = 1.16 × 10^?3 M?_n^0.52. The Huggins k′ value is found to be about 0.9 and the Flory-Huggins polymer-solvent interaction parameter, 0.49. A theoretically calculated value of K_θ is very close to the experimental one and it is for this reason and the observed μ and M?_n exponent values that 2M NaCNS at 25°C approaches being a θ solvent for PAG. A thermodynamic approach based on equilibrium swelling and modulus measurements indicates that a single thermally reversible crosslink in a gelatin gel involves numerous peptide backbone units, whereas in PAG gels a crosslink perhaps involves only one residue from each of two chains. These results complement the very high exothermic heat of gelation crosslinking, δH_c, for gelatin compared to PAG. ΔH_c has been measured on PAG samples of different DP and found to be independent of chain length. Similar measurements on acrylylglycinamide copolymers and terpolymers containing basic and acidic groups produce no change in δH_c so that coulombic forces do not appear to be significant. Data are also included relating to the density of PAG, its glass transition and thermal decomposition temperature, the tensile modulus of equilibrium-swelled PAG films in water and the chain-transfer constant of methanol with the acrylylglycinamide free radical.     

Studies on some radical transfer reactions by entrapping the radicals as polymer end groups. I. Reaction of hydroxyl radicals with amines

The reaction of OH radicals with a number of amines has been studied by entrapping the resultant radicals as polymer end groups which have been detected and estimated by the sensitive dye partition technique. Expressions have been developed relating the average amounts of end groups per polymer molecule to the rate constant of the radical transfer reaction, the rate constants determined for reaction with n-butyl, n-hexyl, and n-octyl amine being 1.00 × 10¹⁰, 1.31 × 10¹⁰, and 1.46 × 10¹⁰ mol^?1 L s^?1, respectively, at 25°C. The order of reactivity for amines of different classes has been found to be as primary < secondary > tertiary, the rate constants for reaction with n-butyl, dibutyl, and tributyl amine being 1.00 × 10¹⁰, 1.81 × 10¹⁰, and 1.67 × 10¹⁰ mol^?1 L s^?1, respectively, at 25°C. The change in the reactivity of the amine with chain length and amine class has been explained by activation and deactivation of the CH₂ group from which H abstraction by OH radicals occurs, respectively, by the alkyl group and by the protonated amino nitrogen under the acidic condition of the medium. Between pH 1.00 and 2.17, the rate of the reaction with n-butyl amine remains practically unchanged, but from pH 2.20 to 2.72 the rate constant increases with increasing pH, indicating that deprotonation of the positively charged nitrogen starts at about pH 2.20. The method is simple and accurate and can be applied to detect and estimate very reactive radicals.     

Piezoelectricity in oriented films of poly(γ-benzyl-L-glutamate)

Oriented films of poly(γ-benzyl L -glutamate) (PBLG) were prepared by two methods. Films of PBLG cast from chloroform solutions were elongated by rolling at 70°C. A solution of PBLG in methylene bromide was placed in a magnetic field of about 7000 gauss and the solvent was slowly evaporated for a few days until an oriented film was obtained. The real and imaginary components of the complex piezoelectric strainconstant d₂₅^* = d₂₅′ ? jd₂₅″ were determined over the temperature range from ?180°C to +180°C at a frequency of 20 Hz. The constants showed dispersions at about 20°C and about 100°C, where dynamic viscoelastic dispersions were also observed. Degree of crystallinity X_c and degree of orientation II_a of crystallites were determined from x-ray diffraction diagrams. The product X_cII_α and the value of d₂₅′ at room temperature were found to be linearly related, and both showed a maximum at an elongation ratio of 1.5 (the ratio of the final to initial length) for roll-oriented films and at an initial solution concentration of 15% by weight for magnetically oriented films. The largest values of d₂₅′ were approximately 2 × 10^?12 and 4 × 10^?12 coulomb/newton, respectively, at room temperature.     

Synthesis of polyisobutylene with arylamino terminal group by combination of cationic polymerization with alkylation

The controlled cationic polymerization of isobutylene (IB) initiated by H₂O as initiator and TiCl₄ as coinitiator was carried out in n‐Hexane/CH₂Cl₂ (60/40, v/v) mixture at −40 °C in the presence of N,N‐dimethylacetamide (DMA). Polyisobutylene (PIB) with nearly theoretical molecular weight (M_n = 1.0 × 10⁴ g/mol), polydispersity (M_w/M_n) of 1.5 and high content (87.3%) of reactive end groups (tert‐Chlorine and α‐double bond) was obtained. The Friedel‐Crafts alkylation of triphenylamine (TPA) with the above reactive PIB was further conducted at different reactions, such as [TPA]/[PIB], solvent polarity, alkylation temperature, and time. The resultant PIBs with arylamino terminal group were characterized by ¹H NMR, UV, and GPC with RI/UV dual detectors. The experimental results indicate that alkylation efficiency (A_eff) increased with increases in [TPA]/[PIB], reaction temperature, and reaction time and with a decrease in solvent polarity. The alkylation efficiency could reach 81.0% at 60/40(v/v) mixture of n‐Hex/CH₂Cl₂ with [TPA]/[PIB] of 4.49 at 50 °C for 54 h. Interestingly, the synthesis of PIB with arylamino terminal group could also be achieved in one pot by combination of the cationic polymerization of IB initiated by H₂O/TiCl₄/DMA system with the successive alkylation by further introduction of TPA. Mono‐, di‐ or tri‐alkylation occurred experimentally with different molar ratio of [TPA]/[PIB]. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 936–946, 2008     

Polymerization kinetics of rac‐lactide initiated with alcohol/stannous octoate using in situ attenuated total reflectance‐fourier transform infrared spectroscopy: An initiator study

rac‐Lactide polymerization kinetics in THF at 72 °C were monitored in real‐time using mid‐infrared ATR‐FTIR spectroscopy, with diamond composite insertion probe and light conduit technology. Monomer concentration as a function of time was acquired using the 1240 cm^?1 resonance associated with the ? CO? O? C? stretch. Polymerizations were initiated with either n‐propanol (PrOH), ethylene glycol (EG), trimethylol propane (TMP), or pentaerythritol (PENTA) with the coinitiator stannous octoate (Sn(Oct)₂). Polymerizations were found to be reversible at high monomer conversions, with a residual monomer concentration at 72 °C (345 K) of 0.081 M. The polymerizations were internally first‐order with respect to monomer, indicating a constant concentration of propagating centers. For a typical reaction with [rac‐LA]₀ = 1.0 M, [PENTA]₀ = 1.3 × 10^?2 M, and [Sn(Oct)₂] = 2.5 × 10^?2 M, the first‐order rate constant, k_app was measured as 1.8 × 10^?4 s^?1. First‐order rate constants were determined to be independent of polymer architecture (i.e., initiator functionality) and proportional to [Sn(Oct)₂] for [Sn(Oct)₂]₀/[ROH]₀ ? 1, where [ROH]₀ represents the initial concentration of initiating hydroxyl groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 797–803, 2009