Cationic polymerization of α-methyl styrene from polydienes. II. Tensile properties of poly(butadiene-g-α-methyl styrene) and poly(styrene-b-butadiene-g-α-methyl styrene) copolymers

Tensile properties of poly(butadiene-g-α-methyl styrene) copolymers have been investigated on molded samples. These graft copolymers show thermoplastic elastomer behavior because of their graft copolymer structure. Both modulus and strength increase with increasing α-methyl styrene content and tensile strength is highest at the 45–50% by weight α-methyl styrene level. Tensile strength at elevated test temperatures is considerably higher for these poly(butadiene-g-α-methyl styrene) copolymers than for styrene-butadiene-styrene triblock polymers. This is attributed to the higher glass transition temperature for poly(α-methyl styrene) segments compared to polystyrene segments. The oil acceptance of these graft copolymers appears to depend on the number of loose polybutadiene chain ends. Thus, the tensile strength of oil-extended poly(butadiene-g-α-methyl styrene) copolymers was considerably lower than oil-extended poly(styrene-b-butadiene-g-α-methyl styrene) copolymers even though both copolymers contained equal hard segment contents.     

Miscible blends of poly(styrene-co-acrylonitrile) and poly(α-methyl styrene-co-acrylonitrile) with poly(methyl methacrylate) containing sterically hindered amine group

Poly(methyl methacrylate) containing a small amount of pendant 2,2,6,6-tetramethylpiperidinyl group was found to be miscible with poly(styrene-co-acrylonitrile) and with poly(α-methyl styrene-co-acrylonitrile). The poly(α-methyl styrene-co-acrylonitrile) blends exhibited lower critical solution temperatures. Phase separation of the poly(styrene-co-acrylonitrile) blends could not be induced by heating up to 270°C.     

Rheological behavior and morphology of blends of copolymers of α-methylstyrene-co-acrylate with PVC

The copolymers of poly(α-methyl styrene–methyl acrylate) (PMSMA) and poly(α-methyl styrene–ethyl acrylate) (PMSEA) were synthesized by emulsion polymerization. The compatibility of these copolymers with poly(vinyl chloride) (PVC) was estimated by the solubility parameter method and scanning electron microscopy (SEM). The rheological behavior was investigated by a flow tester. The mechanical properties, rheological behavior, and morphology of these blends show that these copolymers can be used as a processing aid for PVC. © 1996 John Wiley & Sons, Inc.     

HDPE/sPS增容共混复合材料的研究

用2种分子量不同的苯乙烯-(乙烯/丁烯)-苯乙烯三嵌段共聚物(SEBS)和一种苯乙烯-b-乙烯/丁烯((SEB)两嵌段共聚物为增容剂,对高密度聚乙烯(HDPE)/间规聚苯乙烯(sPS),共混物进行增容.采用扫描电镜(SEM)及拉伸试验研究了增容剂的分子量及结构对共混物形态结构及力学性能的影响.结果表明:3种增容剂SEBS (SEB)均可有效地降低sPS分散相的尺寸并增加HDPE/sPS共混物的界面强度,从而提高其力学性能.sPS的掺入可以显著提高HDPE的耐热性能.     

Relaxation process at conductive poly(thiophene) and its poly(alkyl) derivatives : kinetics of electrochemical doping

Summary The kinetics of relaxation i.e. the kinetics of the doping process, have been investigated in poly(thiophene) and its alkyl substituted derivatives poly(3-methyl thiophene) and poly(3-octyl thiophene), by cyclic voltammetry. The polymer films, electrochemically deposited onto platinum and titanium electrodes, relax at various rates, depending on their structure and orientation in relation to the metal surface. The relaxation process is faster in polymers with longer alkyl chains. Received: 18 November 2001/Revised version: 8 February 2002/ Accepted: 12 February 2002     

Investigation on the early and late stage phase-separation dynamics of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) blends through rheological and scattering functions

The phase-separation behavior of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) (PMMA/α-MSAN) blends with two different compositions was studied by time-resolved small angle light scattering (SALS) in the spinodal decomposition (SD) regime from 160 to 210 °C. The rheological function (WLF-like equation) was introduced into the processing of light scattering data. It was found that the WLF-like equation was applicable to describe the temperature dependence of apparent diffusion coefficient D_app and the relaxation time τ of normalized scattering intensity (I(t)−I(0))/(I_m−I(0)) at the early stage of SD, as well as the relaxation time τ of maximum scattering intensity I_m and characteristic scattering vector q_m with I_m at the late stage of SD for PMMA/α-MSAN blends with two different compositions. This is in consistence with the phase-separation behavior of PMMA/SAN reported in our previous paper.     

13C n.m.r. relaxation study of poly(aspartic acid)

¹³C n.m.r. relaxation parameters (T₁, line widths and NOE factors) and chemical shifts were measured in dependence on pH for several samples of poly(α-l-Asp) differing in molecular mass and polydispersity, and for samples of poly(α,β-d,l-Asp) differing in molecular mass. Poly(α-l-Asp) dissolved at pH 9 and acidified to pH 6-4 can appear in two different forms, A and B. In n.m.r. spectra these forms differ mainly by the width of the bands of side chain carbons which is larger in form A. Conditions for a reproducible generation of either of the two forms were not found although the effect of molecular mass (3–6 × 10⁴), polydispersity, sample concentration (2.0-0.2 mol l^?1), temperature of dissolution (4°C–37°C), concentration of NaCl (0–4 mol l^?1) or rate of acidification (1 pH unit s^?1 week^?1) and rate of mixing were investigated. The dynamics of poly(α,β-d,l-Asp) is almost unaffected by change of pH. The relaxation parameters of poly(α-l-Asp) at pH 9 and 4 differ more in form A than in form B. Analysis of relaxation data for the methine carbon of poly(α-l-Asp) in form A by means of the isotropic model with a log x² distribution of correlation times yields a correlation time of 1 ns at pH 4. This indicates that the dynamics of the backbone is dominated by rapid segmental motions even at pH 4. The dependence of chemical shifts on pH indicates that the chemical shift values are determined mainly by the ionization of the carboxyl group in the side chain rather than by a conformational transition. The evaluated relaxation parameters suggest, when compared with those of polypeptides with known conformational behaviour, that the two forms of poly(α-l-Asp) differ in conformation (α-helix, β-structure).     

Predicted miscibility of polystyrene and poly(α-methyl styrene) and comparison with experiment

The free energy of mixing of polystyrene with poly(α-methyl styrene) has been calculated using the Flory-Huggins expression and the more recent Flory theory which takes account of free volume effects. The double tangents to the free energy-composition curves were used to define phase separation points and hence the expected phase diagram for the system. Both approaches reproduce the observed behaviour reasonably well but in the latter case this is true only if a semi-empirical entropy parameter is included. The interaction of the polymers with the solvents used to prepare the blends is discussed.     

Miscibility of poly(styrene-co-acrylonitrile) and poly(α-methyl styrene-co-acrylonitrile) with copolymers of methyl methacrylate

Poly(α-methyl styrene-co-acrylonitrile) was found to be miscible with poly(methyl methacrylate-co-ethyl methacrylate) and with poly(methyl methacrylate-co-n-butyl methacrylate). All these blends exhibited lower critical solution temperatures. Poly(styrene-co-acrylonitrile) was also found to be miscible with poly(methyl methacrylate-co-ethyl methacrylate) and with poly(methyl methacrylate-co-n-butyl methacrylate). However, phase separation of these blends could not be induced by heating up to 300°C.     

Miscible blends of poly(styrene-co-acrylonitrile) and poly(α-methyl styrene-co-acrylonitrile) with hydroxyl-containing polymethacrylates

Poly(styrene-co-acrylonitrile)(SAN) and poly(α-methyl styrene-co-acrylonitrile)(MSAN) are miscible with poly(2-hydroxyethyl methacrylate) (PHEMA) and with poly(2-hydroxypropyl methacrylate) (PHPMA). That SAN and MSAN are immiscible with poly(n-propyl methacrylate) and with poly(isopropyl methacrylate) but miscible with PHPMA indicates the enhancement of polymer miscibility due to hydroxyl groups. The miscibility of these blends is explained in terms of recent theories for copolymer/homopolymer blends.     

A 1H nuclear magnetic relaxation study of the mechanism and solvent dependence of the motion of predominantly syndiotactic poly(methyl methacrylate) in dilute solution

¹H spin-lattice and spin-spin relaxation times have been measured for individual groups of nuclei in predominantly syndiotactic poly(methyl methacrylate) in dilute solution. The rate of backbone motion is affected by the viscosity and thermodynamic quality of the solvent, whereas the rate of α-methyl internal rotation is less affected by solvent. The relaxation times have been analysed in terms of backbone conformational transitions and methyl rotation.     

Miscibility of poly(styrene-co-acrylonitrile) and poly(α-methyl styrene-co-acrylonitrile) with polymethacrylates containing sterically hindered amine groups

Sterically hindered amine groups were incorporated into poly(methy1 methacrylate) and poly(ethy1 methacrylate) by copolymerizing 2,2,6,6 tetramethylpiperidinyl methacrylate (TPMA) with MMA and EMA. The replacement of the pendant alkyl groups of the polymethacrylates by SHA groups reduced their miscibility with poly(styrene-co-acrylonitrile) (SAN) and with poly(α-methyl styrene-co-acrylonitrile) (MSAN). The cloud points of the miscible blends indicated that the effective interaction parameter B of a blend became less negative with increasing TPMA content in the copolymer, and B was more negative for SAN blend than for a corresponding MSAN blend.     

Phase equilibria in quasi-binary poly(α-methylstyrene) solutions

Upper (UCST) and lower (LCST) critical solution temperatures have been measured for poly(α-methyl styrene) in four solvents. The extent of solvent—polymer interaction was found to be reflected in the miscibility range exhibited by these systems. The data could be described by theoretical curves derived using the Patterson—Delmas theory, if an arbitrary selection of the reference temperature was made for each quasi-binary system. Curves showing the relative contributions of the cohesive energy and free volume contribution to the polymer—solvent interaction parameter were also derived from this theory; these illustrated that while the free volume factors predominated at the LCST, the cohesive energy contribution could still play a significant role.     

Permeability of synthetic poly(α-amino acid) membranes to oxygen dissolved in water

Membranes of synthetic poly(α-amino acids), namely, poly(γ-methyl L -glutamate) (PMLG), poly(γ-benzyl L -glutamate) (PBLG), poly(L -glutamic acid) (PLGA), poly(L -methionine) (PLM), and poly(N^?-carbobenzoxy-L -lysine) (PCLL), were prepared and their permeabilities of oxygen dissolved in water were measured in the 8–50°C temperature range using an oxygen electrode. Permeation curves for the poly(α-amino acid) membranes did not approach steady-state currents because of membrane degradation. To eliminate this, the membranes were laminated between polystyrene membranes; thus, the poly(α-amino acid) membranes came in direct contact with neither cathode surface nor electrolyte solution. No effect of membrane thickness on the permeability was observed. The Arrhenius plots of permeability coefficients for PCLL appear to change slope at about 22°C. This is consistent with the diffusion of oxygen in PCLL through the side-chain regions between helices. Comparisons between the permeability of oxygen dissolved in water and permeability of gaseous oxygen obtained by the high-vacuum method and between the activation energy of permeation of dissolved oxygen and that of gaseous oxygen were made in order to elucidate the effect of water on the oxygen permeation of each polymer. The permeability of the poly(α-amino acid) membranes to dissolved oxygen appears to depend on the properties of the side chains of the polymers.     

Dynamics of molecular chains. Ultrasonic relaxation of monosubstituted polystyrenes

The ultrasonic attenuation of polystyrene derivatives: o-(CH₃, Cl, Br), m-(Br), p-(Br) and α-methyl, has been investigated as a function of temperature and frequency. At least two relaxation processes were needed to account for the ultrasonic spectra and the related thermodynamic parameters have been calculated. The position and steric hindrance of the substituent have no significant effect on the activation energy but affect the enthalpy difference corresponding to the highest frequency relaxation process. The results obtained permit comparison of the intramolecular mobility of the monosubstituted polystyrenes with that of polystyrene. Poly(α-methylstyrene) behaves very much like polystyrene. Intramolecular mobility appears higher in poly(m-bromostyrene) than in p- or o-substituted polymers. Finally, the shift of the ultrasonic spectra of o-substituted polystyrenes to low frequencies is all the stronger as the substituent is bulky.     

High molecular weight methyl ester of microbial poly(β,l-malic acid): Synthesis and crystallization

High molecular weight poly(α-methyl β,l-malate) (M_n ∼ 25,000, PD ∼ 1.7) was prepared from microbial poly(β,l-malic acid) (M_n ∼ 29,000, PD ∼ 1.3) by methylation with diazomethane in dry acetone without substantial cleavage of the polyester main chain. The thermal properties of this poly(malate) were assessed and its crystal structure was preliminary examined. Two crystal forms were identified by X-ray diffraction, their occurrence being dependent on crystallization conditions. The kinetics of nonisothermal and isothermal crystallizations from the melt were studied and modelled using the Avrami approach. Results were compared to those recently reported by us for low molecular weight poly(α-methyl β,l-malate) (M_n ∼ 3000, PD ∼ 1.3).     

Polarization of excimer emission in solution

Polarization of fluorescent emission of excimer structures for polystyrene and poly (α-methyl styrene) has been examined in cyclohexane solution. No depolarization was observed resulting in the conclusion that energy migration does not take place under the experimental conditions studied.     

Periodic organosilica hollow nanospheres as anode materials for lithium ion rechargeable batteries

Polymeric micelles with core-shell-corona architecture have been found to be the efficient colloidal templates for synthesis of periodic organosilica hollow nanospheres over a broad pH range from acidic to alkaline media. In alkaline medium, poly (styrene-b-[3-(methacryloylamino)propyl] trimethylammonium chloride-b-ethylene oxide) (PS-PMAPTAC-PEO) micelles yield benzene-silica hollow nanospheres with molecular scale periodicity of benzene groups in the shell domain of hollow particles. Whereas, an acidic medium (pH 4) produces diverse hollow particles with benzene, ethylene, and a mixture of ethylene and dipropyldisulfide bridging functionalities using poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) micelles. These hollow particles were thoroughly characterized by powder X-ray diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TG/DTA), Fourier transformation infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), magic angle spinning-nuclear magnetic resonance ((29)Si MAS NMR and (13)CP-MAS NMR), Raman spectroscopy, and nitrogen adsorption/desorption analyses. The benzene-silica hollow nanospheres with molecular scale periodicity in the shell domain exhibit higher cycling performance of up to 300 cycles in lithium ion rechargeable batteries compared with micron-sized dense benzene-silica particles.     

Study of solution properties of poly(α-methyl styrene) in various solvents by dilute-solution viscometry

The values of Mark–Houwink–Sakurada constants were determined for poly(α-methyl styrene) (PαMs) of high and low molecular weights in a variety of solvents by a new approach, which requires only polydisperse samples. The results are in accord with those reported in the literature. In addition, the present work reports the values of the Flory interaction parameter for PαMs in 13 solvents of distinct solvent power at various temperatures. Three refined methods pertaining to both polar and nonpolar solvents were applied to estimate the solubility parameter (δ₂) of PαMs resulting in δ₂ = 18.75 ± 0.15 (J/mL)^1/2 at 30°C. Finally, the scatter data of the Huggins coefficient over a range of expansion factors varying from 0.7 to 2.6 seem to conform better to a newly proposed empirical equation than to the contemporary model after Imai. © 1993 John Wiley & Sons, Inc.     

Dielectric properties of poly(α-methyl α-n-propyl-β-propiolactone)/poly(vinyl chloride) blends

The dielectric properties of miscible blends of poly(vinyl chloride) (PVC) and poly(α-methyl-α-n-propy-β-propiolae-tone) (PMPPL) have been investigated at different temperatures above and below T_g. The results were analyzed using the Cole-Cole representation and lead to the conclusion that this mixture does not exhibit micro-scale heterogeneities. Dielectric constant and dielectric loss master curves were constructed using the stress relaxation shift factors determined previously; the same shift factors could be used for the homopolymers and their blends. Similarities between the dielectric master curves and the stress relaxation master curves of PVC, PMPPL, and their blends, are also discussed.