Syndiotactic Polystyrene Synthesis using Polymer
17/03/2010 · One-pot synthesis of isotactic-capped syndiotactic polystyrene ..
of isotactic-capped syndiotactic polystyrene.
The occurrence of several peaks in some of the radial distribution function plots suggests the existence of preferred arrangements of POSS moieties. X-ray scattering curves were also obtained, and a new peak due to the POSS moieties was predicted. These curves can be compared with future experiments to determine the accuracy of the force ﬁeld used in this simulation. Mechanical properties, computed using static deformation method, predict that incorporating POSS monomers with T10 and T12 cages containing phenyl groups into polystyrene will result in higher values for the moduli. These results should be compared to both experimental data and simulations based on dynamic method in the future. Trends in the solubility parameters, d, were also predicted and are available for comparison to future experimental studies.
Glass transition temperatures were predicted from speciﬁc volume versus temperature plots. Incorporation of small mole fractions of T8-POSS compounds raised the predicted change in Tg for styrene copolymers, but not for MMA copolymers. Phenyl-substituted T8, T10 and T12-POSS monomers were predicted to substantially raise the Tg of their atactic polystyrene copolymers. The trends in Tg predicted upon incorporating various T8-POSS monomers into styrene copolymers agreed with experimental results. When the POSS substituents were phenyl groups, the Tg increases in styrene copolymers were much larger than when the substituents were alkyl groups. Such R- group compatibility allows the massive pendant POSS moieties to exert larger restrictions on seg- mental motion. When the R groups are alkyl functions, they are less compatible with the styrene polymer’s phenyl rings and pack less efﬁciently. This effect operates to lower Tg, counter- acting the effect of the large pendant masses and volumes of the pendant POSS groups in restricting segmental motion. Therefore, the Tg increases are smaller. PMMA is a polar polymer, and all of the R substituents used (e.g., cyclopentyl, cyclo- hexyl, isobutyl, and phenyl) are nonpolar. Thus, R-group compatibility with the PMMA medium is less than that with polystyrene. Consequently, the Tg values exhibit small decreases or no change upon incorporating 4 or 5 mol % of 1a, 1b, 1c, or 1d (POSS with cyclopentyl, cyclohexyl, iso- butyl, and phenyl groups, respectively) into PMMA.
polymerization of styrene to polystyrene
Synthetic polymers have a limited temperature use range. Hybrid organic/inorganic polymeric materials have been developed to improve material properties. Polymers like polystyrene and polymethyl methacrylate are typically used below their glass transition temperatures (Tg) in their glassy state, where they are hard and brittle. When a polyhedral oligomeric silsesquioxane (POSS) monomer is copo- lymerized into such plastics, their useable tempera- ture range can be increased due to an increase in the Tg or due to a rise in moduli in the rubbery region. Polymer nanocomposites containing POSS have been considered for applications in low dielec- tric constant materials, synthesis of dendrimers, coatings for lithography, materials with increased resistance to oxidation, processing viscosity modiﬁers, and ﬂame retardants.
Numerous experimental studies have been performed on the synthesis and determination of the structural properties of polymers containing POSS. However, few numerical simulations have appeared. Molecular dynamic simulations have been carried out on norbornene/norbornenyl-POSS copolymers. Two recent numerical studies have employed molecular dynamics simulations to investigate the properties of polymer nano- composites containing POSS moieties. Unlike the present study, which deals with copolymers containing chemically bound POSS moieties, these two studies focus on a polymer nanocomposite in which POSS moieties are blended, but not chemically bonded to the polymer matrix. Striolo et al. studied POSS moieties, with either methyl groups or hydrogen atoms as the corner substituents, blended in a polydimethylsiloxane matrix. The other study involved cyclopentyl-substituted POSS dispersed in a polyethylene matrix. Lattice Monte Carlo simulations have been used by Lamm et al. to model polymer POSS nanocomposites by using rigid cubes and bead–spring chains to model the POSS moieties and the polymer backbone, respectively. The effect of introducing 10 mol % of mono-norbornenyl-substituted T8 POSS monomers with seven cyclohexyl or seven cyclopentyl func- tions on the remaining cage Si atoms was analyzed. Wei et al. used molecular dynamics simula- tions to estimate the properties of a polymer nanocomposite containing carbon nanotubes and polyethylene. Molecular dynamics simulations of bulk atactic polystyrene in the vicinity of its Tg have been performed using the united atom model. Mechanical properties of polyethylene were predicted using a molecular mechanics force ﬁeld for the interatomic potential and quasi harmonic lattice dynamics for the vibrational free energy.Raaska et al. conducted molecular mechanics and molecular dynamics simulations on amorphous polystyrenes with different tacticities and estimated their cohesive energies and solubility parameters.A molecular dynamics study of atactic polystyrene was performed to study the X-ray structure factor. An aim of the present work is to predict the effect of small mole fractions of POSS comonomers, incorporated into either polystyrene or polymethyl methacrylate, on the glass transition temperatures, moduli, Poisson’s ratio, X-ray scattering intensity, and solubility parameters. Why does POSS impart these changes? The systems selected, herein, are based on the experimental data available in the literature whenever possible.
General Polymer Science & Technology
A sudden increase in segmental motion occurs in the glass transition temperature (Tg) region. Changes in both the heat capacity and speciﬁc volume versus temperature take place. The storage modulus drops. As the temperature in- creases above Tg, a pronounced increase in dV/dT (where V is the volume) occurs, caused by the introduction of free volume and driven by segmental motion enhancements. Simulations of the speciﬁc volume versus temperature are used to predict Tg (the temperature where this steep change occurs) for comparison to experimental Tg values. The speciﬁc volumes of pure atactic polystyrene, simulated, herein, at several temperatures using the all-atom model (0.96–1.04 cm3/g), were typically marginally lower than the corresponding simulated values obtained using united- atom model (0.98–1.05 cm3/g).
Figure 4 shows the computed speciﬁc volume versus temperature curves for atactic polystyrene,the styrene copolymers 2d, 5 and 6 (containing 4 mol % of the p-styryl (phenyl) T8, T10, and T12- POSS monomers 1d, 3 and 4, respectively) and the styrene copolymer 2c containing 5 mol % of p- styrylheptaisobutyl(T8)POSS, 1c. The break in the slope for each system locates the predicted Tg. Tables 1 and 2 summarize these predicted Tg values for both the styrene and the methyl metha- crylate copolymers illustrated in Figures 4–7.
Polystyrene with Polystyrenes ..
Polystyrene Polystyrene, atactic | Sigma-Aldrich
Polystyrene - Wikipedia
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Atactic polystyrene ..
Thermal Properties of Atactic and Isotactic Polystyrene
can be used for cross-linking the polystyrene chains to give the polymer used in Solid phase peptide synthesis
Polystyrene: Synthesis, Production and Applications - J. …
A series of well-defined polystyrene--poly(ferrocenylethylmethylsilane) (PS--PFEMS) diblock copolymers was synthesized from styrene and ethylmethylsilaferrocenophane via sequential anionic polymerization.
Questions and Answers - Department of Chemistry
Atactic polystyrene backbone MSD plots are shown in Figure 8. Backbone motion increases with temperature. A sudden increase in the back- bone motion occurs at the glass transition temperature. Figure 9 displays the MSD of the backbone polystyrene carbon atoms for the styrene copolymer 2d (4 mol % of phenyl-substituted T8- POSS monomer 1d). This case is characterized by lower MSD at 450 K (compare Figs. 8 and 9) and has a higher Tg than that for atactic polystyrene (45 K higher, see Table 1). This suggests that the presence of POSS moieties could retard the motion of the polymer backbone. Figure 10 shows the backbone MSD at different temperatures for MMA copolymer 8a (10 mol % of isobutyl-substituted T8-POSS, 7a). Simulations of longer durations are required to observe diffusive behavior at high temperatures.
Session 1: What are some of the polymers that you encounter every day
The simulated solubility parameters (d) and volumetric coefﬁcients of thermal expansion (CTEV)for atactic polystyrene and the styrene/POSS copolymer systems are shown in Table 3. Solubil- ity parameters were determined from the square root of the simulated cohesive energy densities, taking into account the effect of the cut-off dis- tance on the nonbonded potentials. All the pre- dicted solubility parameters for styrene/POSS copolymers (2a–d, 5, and 6) were lower than those for polystyrene. Only the styrene/hepta- phenyl (T8) POSS copolymer 2d gives a d-value comparable to that of atactic polystyrene. This is due to the compatibility between the phenyl rings of styrene monomer units and those on the POSS corners (favorable p-stacking interactions).
Describe their physical properties
Table 5 lists the calculated elastic constants of atactic polystyrene at 500, 400, and 325 K. The tensile modulus decreases with an increase in temperature. The value of the tensile modulus, computed at 325 K, is rv4.3 GPa, and the experimental value is in the range of 3.2 GPa (unoriented case) to 4.2 GPa (oriented monoﬁlament). The use of a dynamic method for determining mechanical properties would give more accurate results, but it involves signiﬁcant additional computational costs, since separate molec- ular dynamics simulations must be performed under certain constraints. Hence, it was not used in the present study. Estimation of mechanical properties through molecular dynamics simula- tions is less accurate for amorphous systems, which might contain large unoccupied regions in the computational cell (e.g., systems in this study), compared to crystalline systems.
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