Synthesis and polymerization of maleimide-type new macromonomer with polystyrene having controlled chain length

A new reactive and functionalized polystyrene with a maleimide moiety at the one polymer end was synthesized with N-(4-(1-chloroethyl)pheyl)maleimide (CEPMI)/SnCl₄/tetra-butylammonium chloride (TBAC) initiating system. The polymer obtained with the CEPMI/SnCl₄/TBAC initiating system under the condition of [TBAC]/[SnCl₄] = 1 was to be maleimide-type macromonomer with polystyrene having controlled molecular weight of polystyrene (VI). VI could be polymerized with anionic and radical initiators to give new type graft polymer (poly[N-(4-ethylphenyl)maleimide]-graft-polystyrene) with controlled chain length with respect to side chains.     

Concentration dependence of the diffusion coefficient in polymer solution and molecular weight distribution determined by the diffusion method

The effects of the concentration dependence of the diffusion coefficient of a polymer solution (polystyrene in benzene and cyclohexane) in determining molecular weight distribution by the diffusion method are briefly discussed. The value of the ratio D_m0/D_A0 in a good solvent was found to be close to 1.0 for a polydisperse polymer and less than 1.0 for monodisperse polymers. Molecular weight distribution curves of the polydisperse sample were obtained by the diffusion method in cyclohexane and benzene, respectively. The molecular weight distribution curve obtained for the polymer used in benzene solution looked as if the polymer had a narrow molecular weight distribution. The phenomena cited above were interpreted in the light of the concentration dependence of the diffusion coefficient of polymer solutions.     

Cooperative and self-diffusion of polymers in semidilute solutions by dynamic light scattering

The quasielastic light scattering from semidilute solutions of polystyrene in tetrahydrofuran has been measured and we observe two distinct exponential decays separated by several orders of magnitude. The angular dependence of the decay constants is indicative of diffusive processes which we identify with the cooperative diffusion coefficient, D_c and the self diffusion coefficient D_s. It is found that D_c, identified with the fast decay, increases with polystyrene concentration and is independent of molecular weight. However, D_s decreases sharply with concentration and molecular weight. An explanation is given for the light scattering detection of these two diffusion coefficients which is based only on the assumptions inherent in the reptation model. In a limited region of molecular weight and concentration the experimental results appear to be consistent with the predictions of scaling theory.     

Interfacial tension of demixed polymer solutions near the critical temperature: polystyrene + methylcyclohexane

Interfacial tension between demixed solutions of polystyrene + methylcyclohexane has been measured near the critical temperature as a function of temperature using polystyrenes with molecular weights 9000 ～ 1.26 × 10⁶. The critical exponent for the interfacial tension was determined to be about 1.30 for the lower molecular weight systems. However, for higher molecular weights the exponent could not be obtained because the system departed from critical behaviour. Magnitudes of the interfacial tension were proportional to about N^?0.44, where N is the polymerization index. Experimental results were compared with the recently-proposed theories and found to be in qualitative agreement. The tricritical theory of polymer solutions was also compared with the experimental results.     

A Direct GPC Calibration for Low Molecular Weight Polybutadiene,Employing Dual Detectors

Abstract

The calibration of gel permeation chromatograph (GPC) for a given polymer type is usually done by running well-characterized polymer samples of the same type. The available polystyrene and polyglycol standards with molecular weights below 5000 do not give parallel calibration curves, and the points for polystyrene are not on an extension of the higher-molecular-weight portion of the curve. In order to check the calibration in this low molecular-weight region and to establish an independent curve for polybutadiene, a polybutadiene sample prepared by a-methylstyrene tetramer-Na₂ initiation was chromatographed. In doing this, dual detection was used, consisting of a differential refractometer, and an ultraviolet absorption spectrophotometer.

The UV signal from the spectrophotometer was assumed to represent the tetramer portion of the polymer, and its percentage was calculated at each volume increment, using externally determined response factors. This percentage and the tetramer molecular weight gives the molecular weight of the polymer eluting at each volume increment. After correction for the aromatic portion of the polymer, these data and the points obtained with the polybutadiene standards were found to give a reasonable calibration curve for the entire range. The present paper describes the application of this technique to the examination of low molecular-weight polybutadiene.     

Highly efficient synthesis of cylindrical polymer brushes with various side chains via click grafting-onto approach

Though much attention has been paid to synthesis of cylindrical polymer brushes, it is still not easy to prepare well-defined brushes by a general approach. Herein, well-defined cylindrical polymer brushes with various side chains were synthesized via grafting-onto approach by CuAAC click chemistry. Narrowly dispersed polymer backbones functionalized with azide groups were obtained by post-modification of poly(glycidyl methacrylate) (PGMA) which was prepared by reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerization. The alkyne-terminated side chains, polystyrene, polyacrylates, polymethacrylates and poly(N-alkyl acrylamide)s, were synthesized by RAFT mediated radical polymerization with alkyne-containing chain transfer agents (CTAs). The CuAAC reactions between the backbone and side chain polymers were conducted with an equivalent feed of alkyne-terminated side chains and azide groups under mild conditions. Influences of reaction conditions and chemical composition of polymer side chains on grafting efficiency and molecular weight distribution of the polymer brushes were investigated. It is demonstrated that the side chains of polystyrene, polyacrylates and poly(N-alkyl acylamide)s were grafted at a density above 85% while that of polymethacrylates decreased to ca. 50%. The polymer brushes synthesized under the optimized reaction conditions had well-defined chemical composition and narrow distribution of molecular weight, and their wormlike morphology was visualized by atomic force microscopy (AFM).     

The effect of molecular weight on the fatigue behavior of polystyrene

Significant improvements in the fatigue life of polystyrene can be realized by increase in molecular weight. In this investigation, samples of polystyrene of varying molecular weight were subject to alternating cycles of axial tension and compression at a test speed of 1600 rpm. One set of fatigue tests was made on samples machined from commercial whole polymer rod. A second set of samples was prepared from a PS standard having an average molecular weight of 160,000 and a narrow molecular weight distribution. A third set of samples had a high average molecular weight of 860,000. For a whole polymer, the S–log N curves tended to have the same general shape as for metals, and the endurance limit appeared to be about 1400 psi. The test results show that the average fatigue life, at any given stress amplitude, is significantly increased by increase in molecular weight. For example, the average life of the high molecular weight standard at any given stress level was found to be more than tenfold that of the low molecular weight standard.     

Influence of molecular weight of polymer matrix on the structure and rheological properties of graphene oxide/polydimethylsiloxane composites

The structure and rheological properties of graphene oxide (GO)/polydimethylsiloxane (PDMS) composites are examined as the molecular weight of PDMS and concentration of GO are varied. Clusters formed by GO sheets get smaller and disperse better with increasing molecular weight of PDMS, which results in the higher critical concentration to form network (C_cr). Moreover, at GO concentration just above C_cr, the plateau modulus of samples decreases with the molecular weight of PDMS. During shear experiments, negative normal stress differences (ΔN) are observed in composites with PDMS molecular weight lower than critical entanglement molecular weight (M_c). However, positive ΔN is found in samples with PDMS molecular weight above M_c. It can be concluded that the vorticity alignment of GO clusters induces the negative ΔN based on the optical shear experiments. The possible mechanism for the positive ΔN is also proposed.     

Entanglement interactions in polymers and the chain contour concentration

The plateau region in viscoelastic response is one of several characteristics of concentrated polymer liquids which have been attributed to chain entanglement interactions. The plateau modulus G⁰_N is insensitive to temperature and independent of chain length for long chains. It varies with polymer species in the undiluted state: it also varies with polymer concentration in a manner which is essentially independent of species. We propose here that the species dependence and the concentration dependence are related, and that to a first approximation both are manifestations of a universal law relating a mechanical interaction density, measured by $\text{G}{}^0{}_{\mathrm{N}}\text{kT}$ to the length of uncrossable chain contour per unit volume. Data on many species and concentrations support this proposition and conform reasonably well to a universal power law: G in which v is the number of chains per unit volume, L is the chain contour length, and/is the Kuhn step length of the species.     

Spectroscopic studies of spin-coated dye-in-polymer films. On the relationship between compatibility and aggregation of small molecules in polymer matrices

Dye-in-polymer (DIP) films of various concentrations of I (a p-N,N-dialkyl-aminobenzylidenemalononitrile derivative) in four polymers of different dye-polymer compatibilities have been prepared by spin-coating technique using a wide range of coating speeds (600–8000 rpm). The aggregation of dye molecules in polymer matrix was studied by electronic spectroscopy. The dye-polymer compatibility of various DIP systems was examined by d.s.c. Our results indicate that there exists a staturated concentration of I in each polymer and this saturated concentration decreases as the dye-polymer compatibility decreases, e.g. it decreases from ～20% in poly(vinyl acetate) and in poly(isobutyl methacrylate) to ～10% in styrene/isobutyl methacrylate (8:2) copolymer to ～5% in polystyrene. At dye concentrations lower than this saturated concentration, the degree of dye aggregation is not sensitive to varying spin-coating speeds. At dye concentrations higher than this saturated concentration, the degree of dye aggregation depends on the degree of dye-polymer incompatibility and on the spin-coating speed. The significance of the present work in solvent coating technology of small molecule/polymer systems, in general, will be discussed. Finally, the T_g's of various DIP systems were found not to correlate with the dye concentration (by weight). This is attributable to the strong dye-dye interaction of I inside the polymer matrix.     

The Efficiency of Polymer Fractionation at Lower Critical Solution Temperatures

The efficiency of a single fractionation step (i.e. of the partition of a given polymer sample between the coexisting phases which form when its solution demixes) is governed by the variation of the mass ratio of the individual P-mers with chain length. These dependences have been measured for the system dimethoxymethane/diethylether/ polystyrene which exhibits lower critical solution temperatures by means of the Baker-Williams method and by means of g.p.c. Their comparison with the results of previous investigation on systems showing upper critical solution temperatures reveals no thermodynamic differences in the aptitude of upper and lower critical solution temperatures for fractionation from dilute solutions. The extension of the molecular weight distribution into the low molecular weight region by the addition of oligomer, answered the question whether the monomer concentration in the coexisting phases is practically identical, as predicted by classical theories, or larger by a factor of nearly ten in the polymer-rich phase, as extrapolated from the information concerning the polymer. The direct observation yields intermediate values which demonstrate that the variation of the logarithm of the partition coefficient with the degree of polymerisation P cannot be represented by a linear function with sufficient accuracy when a broader range of molecular weights is considered; in this case it is necessary to replace P by P^2/3.     

Interdiffusion and marker movements in concentrated polymer-polymer diffusion couples

Intrinsic and interdiffusion coefficients of binary polymer-polymer diffusion couples with initially large concentration gradients are markedly dependent on concentration, even when the polymers differ only in molecular weight. Assuming local thermal equilibrium of vacancies (or free volume) within the couple leads to different intrinsic diffusion coefficients for the two polymer species and to net vacancy fluxes. These fluxes should produce movement of inert markers in the couple relative to a point far from the initial interface. That such marker movements and vacancy fluxes actually occur is demonstrated by experiments in which the motion of 20 nm diameter Au islands is monitored by Rutherford backscattering spectrometry. The markers which are initially at the interface between thin films of monodisperse polystyrene (one 2 × 10⁷M_w and the other 1.1 × 10⁵M_w) are progressively displaced toward the lower molecular weight side of the couple. As expected the marker displacement is proportional to the square root of time at the diffusion temperature.     

Direct synthesis of polymer-grafted inorganic hybrids via reversible chain transfer catalyzed polymerization

In this work, a new simple and robust method for preparation of polymer-grafted inorganic hybrids through “grafting to” reaction is presented. Polymer chains were synthesized by reversible chain transfer catalyzed polymerization (RTCP) are capped with iodine according to the RTCP mechanism. The obtained iodine-capped polymer chains can react irreversibly with the hydroxyl groups available on the surface of inorganic materials through a nucleophilic substitution (SN) reaction. In this method, there is no need to modify the surface of inorganic materials or to functionalize polymer chains prior to the “grafting to” reaction. RTCP produced polystyrenes with different molecular weights, e.g., 4,000, 6,000, and 8,000 g/mol, and silica nanoparticles were employed as the polymer and inorganic materials, respectively. The resulting hybrids were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, and transmission electron microscopy techniques. According to the results, graft density decreased by increasing the polystyrene molecular weight. Additionally, the rheological studies of prepared polystyrene nanocomposites containing 2 wt % of the produced hybrids confirmed the better dispersion of the modified hybrids in the polystyrene matrix. The glass transition temperature (T _g) of the polystyrene nanocomposites was driven by differential scanning calorimeter technique. Analysis of nanocomposites’ T _g results revealed that increment of the grafted polymer molecular weight of hybrids increased the glass transition temperature of the prepared nanocomposites due to improvement of the dispersion level.     

Living radical dispersion photopolymerization of styrene by a reversible addition-fragmentation chain transfer (RAFT) agent

In this study, an addition-fragmentation chain transfer agent bearing dithioester group is synthesized and applied to conventional dispersion photopolymerization of styrene in ethanol medium in the presence of poly(N-vinylpyrrolidone) stabilizer with varying amounts of the RAFT agent and optionally with conventional initiator, azobisisobutyronitril (AIBN) at various temperatures. Monomer conversion, molecular weight evolution, polydispersity index (PDI), and final particle sizes are measured. The PDI of the formed polymer is between 1.5 and 2.5 in the presence of RAFT agent. Higher concentration of RAFT agent or elevated temperature leads to the acceleration of the polymerization rate resulting in fast conversion, and reducing molecular weight and PDI. Stable polystyrene beads above 1 μm in diameter are successfully prepared by means of RAFT method applied in dispersion polymerization. The weight average particle sizes are between 1.08 and 2.04 μm, and the uniformity (D_w/D_n) is ranged from 1.26 to 2.51.     

Photoinitiated polymerization of N-vinylcarbazole in the presence of azobisisobutyronitrile

Azobisisobutyronitrile is a photosensitizer of the polymerization of N-vinylcarbazole in benzene solution at λ = 365 nm. At low concentrations of initiator, a low molecular weight polymer is the dominant product, but, as the initiator concentration is raised, this is replaced progressively by a high molecular weight fraction. Kinetic mechanisms compatible with the experimental observations are proposed and indicate that the high and low molecular weight fractions are formed distinctively through the intermediacy of radical and cationic species, respectively arising from the quenching by the initiator of the first excited singlet and triplet states of the monomer.     

Light scattering characterisation of polymers II. Analyses of high molecular weight polystyrene

For light scattering analysis of an extremely high molecular weight polymer with large size in solution, use of mixtures of a given polymer with its low molecular weight homologue is described to have great advantages. With such bimodal mixtures as test samples, one can alter the unknown form of the angular variations of scattered lights to a form to be expected and widen the range of the linearity with sin² (ø/2), where ø is the scattering angle. According to the considerations, a sample of linear polystyrene was successfully analysed on a commercial apparatus, Fica 50 to have the weight-average molecular weight of 27 million.     

Comparison of the hole pressure and exit pressure methods for measuring polymer melt normal stresses

There has been considerable controversy over whether one can extract the primary normal stress difference (N₁) for polymer melts from hole pressure (P_H) and exit pressure (P_ex) data. In this paper values of P_H and P_ex are obtained for three polymer melts in the same slit-die apparatus under the same operating conditions. It is found that there is a good correlation between values of N₁ obtained by means of a cone-and-plate rheometer and those obtained by means of P_H data and the Higashitani-Pritchard theory. On the other hand, values of N₁ obtained by means of P_ex data for polystyrene were two to five times higher than those obtained by means of the cone-and-plate device. For the lower molecular weight low density polyethylene (LDPE) sample, values of P_ex were found to be both positive and negative. For the higher molecular weight LDPE sample, values of P_ex were found not to increase monotonically with with σ_w. Hence, it was difficult to obtain unequivocal values of N₁ for LDPE.     

Temperature drop turbidimetry as a means for the rapid determination of the polydispersities of polymers: Polystyrene

The molecular weight distributions of fractionated and unfractionated polystyrene samples were determined from turbidimetric data obtained by controlled precipitation from dilute solutions in cyclohexanol by cooling from 90 to 20°C. Estimates of the distributions were obtained by calibration of the temperatures of onset of precipitation and the weight average molecular weight of the polymer in solution, as suggested by Shultz,¹ and correcting for the concentration change on precipitation.     

Effects of functional groups on the thermal properties of modified polystyrene

Polystyrene is, after polyolefins, the most widespread polymer in both industry and everyday life, successfully replacing some raw natural materials. In this study, the chemical modification of polystyrenes of different molecular weights was performed with various functional group modifiers (epichlorohydrin, maleic anhydride, and acetic anhydride) in one stage and in the medium of the cationic catalyst BF₃·O(C₂H₅)₂ according to previous studies. The concentration of the functional groups bonded to the aromatic ring of the polymer as a result of the chemical modification of polystyrenes of different molecular weights depended on the molecular weight of the polymer, and more functional groups were bonded to lower molecular weight polystyrene. The effects of the functional groups bonded to the structure of the polymer on the thermal properties of modified polystyrene were investigated. The polystyrene that was modified by maleic anhydride was more stable against thermal destruction at high temperatures. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2549–2553, 2007     

Gel permeation chromatography: universal calibration for rigid rod and random coil polymers

The g.p.c. behaviour of poly (γ-benzyl-l-glutamate) (PBLG) samples, polystyrene standards and poly(2-vinyl pyridine) has been examined in N,N-dimethylacetamide (DMA) at 80°C. Solution viscosity measurements show that DMA is a good solvent for the flexible random coil polystyrene and that it promotes a helical rigid-rod shaped PBLG. Comparison of polystyrene and poly (2-vinyl pyridine) confirms that polystyrene separates strictly according to steric exclusion and that polymer/gel interactions are not involved. A PBLG calibration curve predicted from the polystyrene calibration by the [η] M universal calibration procedure was used to calculate average molecular weight and M_peak data from the PBLG chromatograms. The calculated $\text{M}\text{?}{}_{\mathrm{v}}$ values are in good agreement with experimental data. Plots of log [η] M_peak against retention volume for PBLG and polystyrene were coincident. These results suggest that the product [η] M is a valid universal calibration parameter for PBLG and polystyrene which have significantly different shapes. Comparison of theoretical equations relating the diameter of polystyrene hydrodynamic spheres to the half-length of PBLG helices suggests that the parallel-plane model may be a useful mathematical representation of pore geometry.