Cyclic Polystyrene Research Articles

Preparation, Characterization, and Nanophase-Separated Structure of Catenated Polystyrene−Polyisoprene

A catenated copolymer consisting of cyclic polystyrene (PS) with short poly(2-isopropenylnaphthalene) (PIPN) segments and cyclic polyisoprene (PI) were prepared by living anionic polymerization. The molecular weight of catenated copolymer is 37 kDa. Naphthalene side groups attached to the PIPN segments in the cyclic P(IPN-b-S) were radical-anionized by a reaction with potassium in THF, and telechelic PI was successfully cyclized by a pair of coupled reactions at two close radical-anionized sites on the cyclic chain under dilute conditions. Formation of the catenated copolymer consisting of cyclic P(IPN-b-S) and cyclic PI was confirmed by size-exclusion chromatography using a UV detector with a wavelength of 320 nm for preferential detection of naphthalene moieties. After isolation of the catenated copolymer by fractionation, it was confirmed by transmission electron microscopy that the topologically linked polymers exhibit a nanophase-separated structure in bulk.

Access to cyclic polystyrenes via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and click chemistry

The coupling of the reversible addition fragmentation chain transfer (RAFT) polymerization technique with the copper-catalyzed Huisgen 1,3-dipolar cycloaddition (“click chemistry”) as a simple and effective way to generate polystyrene (PS) macrocycles is presented. The novel strategy entails the synthesis of linear PS backbones followed by endgroup modification to facilitate click chemistry for the formation of ring shaped polymers. An azido group modified 4-cyanopentanoic acid dithiobenzoate is employed as the chain transfer agent in the RAFT mediated polymerization of styrene to form PS with Mn from 2000gmol−1 to 6000gmol−1 and PDI<1.2. To facilitate the cyclization of the polystyrene chains by click coupling, the thiocarbonylthio endgroup is removed and concomitantly replaced by an alkyne bearing function. This is carried out via the radical decomposition of excess azobis(4-cyano valeric acid) (ACVA) modified with an alkyne endgroup in the presence of the thiocarbonylthio-capped PS. The successful click endgroup modifications of several polystyrenes along with the results from the cyclization of a PS with Mn=4300gmol−1 are discussed in detail. This improved method avoids the presence of thiocarbonylthio functions in the macrocycle, thus considerably increasing the chemical stability of these polymers.

Tadpole‐shaped amphiphilic copolymers prepared via RAFT polymerization and click reaction

AbstractThe tadpole‐shaped amphiphilic copolymers with cyclic polystyrene as the head and a linear poly(N‐isopropylacrylamide) as the tail have been successfully synthesized by combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and “click” reaction. The synthesis involves two main steps: (1) preparation of a linear acetylene‐terminated PNIPAAM‐b‐PS with a side azido group anchored at the junction between two blocks; (2) intramolecular cyclization reaction to produce the cyclic PS block using “click” chemistry under high dilution. The structures, molecular weights, and molecular weight distributions of the resulted intermediates and the target polymers were characterized by their 1H NMR, FTIR, and gel permeation chromatography. The difference of surface property between tadpole‐shaped polymer and its linear precursor was observed, and the water contact angles on the former surface are larger than that of the latter surface. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2390–2401, 2008

Interdiffusion of Cyclic Polystyrene Whose Molecular Weight is Larger than the Critical Entanglement Molecular Weight

Interdiffusion of cyclic polystyrene (c-hPS) / cyclic deuterated polystyrene (c-dPS) laminated film whose molecular weights are ca.50 k was examined by neutron reflectivity and dynamic secondary ion mass spectroscopy. It has been found that time evolution of the interfacial thicknesses of (c-hPS/c-dPS) multi-layer films are similar to those of the corresponding linear hPS/linear dPS (l-hPS/l-dPS) bilayer films at short time region. However, at the annealing time longer than 5×103 s, the interfacial thicknesses of (c-hPS/c-dPS) multi-layer films are evidently larger than those of the (l-hPS/l-dPS) films at each observing time. These results can be explained in terms of the less entanglement nature of cyclic polymers than that of the linear ones.

Mechanical and chemical analysis of plasma and ultraviolet–ozone surface treatments for thermal bonding of polymeric microfluidic devices

Here we have demonstrated that radio frequency plasma and ultraviolet-ozone (UVO) surface modifications are effective treatments for enabling the thermal bonding of polymeric microfluidic chips at temperatures below the T(g) (glass transition temperature) of the polymer. The effects of UVO and plasma treatments on the surface properties of a cyclic polyolefin and polystyrene were examined with X-ray photoelectron spectroscopy (XPS), contact angle measurements, atomic force microscopy (AFM) surface roughness measurements and surface adhesion measurements with AFM force-distance data. Three-point bending tests using a dynamic mechanical analyzer (DMA) were used to characterize the bond strength of thermally sealed polymer parts and the cross-sections of the bonded microchannels were evaluated with scanning electron microscopy (SEM). The experimental results demonstrated that plasma and UVO surface treatments cause changes in the chemical and physical characteristics of the polymer surfaces, resulting in a decrease in T(g) at the surface, and thus allowing the microfluidic chips to be effectively bonded at temperatures lower than the T(g) of the bulk polymer without losing the intended channel geometry.

Synthesis of Monocyclic and Linear Polystyrene Using the Reversible Coupling/Cleavage of Thiol/Disulfide Groups

By carefully controlling the concentration of α,ω-thiol polystyrene in solution, we achieved formation of unique monocyclic polystyrene chains (i.e., polymer chains with only one disulfide linkage). The presence of cyclic polystyrene was confirmed by its lower than expected molecular weight due to a lower hydrodynamic volume and loss of thiol groups as detected by using Ellman's reagent. The α,ω-thiol polystyrene was synthesized by polymerizing styrene in the presence of a difunctional RAFT agent and subsequent conversion of the dithioester end groups to thiols via the addition of hexylamine. Oxidation gave either monocyclic polymer chains (i.e., with only one disulfide linkage) or linear multiblock polymers with many disulfide linkages depending on the concentration of polymer used with greater chance of cyclization in more dilute solutions. At high polymer concentrations, linear multiblock polymers were formed. To control the MWD of these linear multiblocks, monofunctional X−PSTY (X = PhCH2C(S)−S−) was ...

Chain dimension of cyclic polymers in solutions

Telechelic polystyrenes (PSs) were synthesized and cyclized by end-to-end ring closure reaction under extremely diluted condition. Cyclic PSs were isolated from coupling products by GPC fractionation and precipitational fractionation, and 4 cyclic polymers, whose molecular weights Mw are covering the range 20k⩽Mw⩽600k, were prepared. It was confirmed that all cyclic polymers have high purity (over 95%) by HPLC. Their radii of gyration Rg were determined in benzene-d6 (good solvent) and cyclohexane-d12 (theta solvent) by small-angle neutron scattering and light scattering. It was found that Rg of cyclic polymer can be scaled with Mw as Rg∝Mw0.6 in benzene-d6 and as Rg∝Mw0.5 in cyclohexane-d12, both exponents being the same as for linear counterparts. However, experimentally determined contraction ratio, Rg(cyclic)/Rg(linear), is smaller than the theoretical predictions.

Comparison of Interdiffusion Behavior between Cyclic and Linear Polystyrenes with High Molecular Weights

Comparison of Interdiffusion Behavior between Cyclic and Linear Polystyrenes with High Molecular Weights

Polystyrene freeze-dried from dilute solution: Tg depression and residual solvent effects

The calorimetric glass transition temperature, Tg, was measured for both linear and cyclic polystyrenes freeze-dried from dilute solutions of 0.10, 0.05, and 0.02% of polymer by weight in benzene. Upon freeze-drying, Tg was found to be depressed by 4–15K depending on the sample, solvent concentration, and freezing conditions. Annealing under vacuum at moderate temperatures, from 40 to 140°C and 0.05Torr, resulted in the shift of Tg back towards its bulk value and was accompanied by a decrease in sample weight. The data is consistent with the observed weight loss being due to residual solvent. The amount of residual solvent is a strong function of the annealing temperature and the initial freeze-drying solution concentration; exposure to vacuum at temperatures far below Tg is generally insufficient for residual solvent removal.

Preparation and Characterization of Cyclic Polystyrenes

Macrocyclic polystyrenes with various molecular weight were prepared by the reaction of linear polystyrene having two end vinyl groups and potassium naphthalenide as a coupling agent. Intermolecular side reactions produced higher molecular weight polycondensates and undesirable chain termination reactions also produced linear precursors in addition to the designed molecules. In order to isolate cyclic polymers from the ring closure reaction mixtures, preparative size exclusion chromatography (SEC) method was employed. The purity of SEC-fractionated cyclic polystyrenes was rigorously examined by liquid chromatography at the critical condition (LCCC) and interaction chromatography (IC). After SEC-fractionation, we obtained large amount of highly pure cyclic polymers, though high molecular weight cyclic polymers contain very small amount of linear precursor (<5%). The purity and isotope effect on reversed-phase liquid chromatography (RPLC) were also rigorously investigated by preparing a deuterated cyclic polystyrene.

Synthesis and Characterization of Macrocyclic Vinyl‐Aromatic Polymers.

AbstractSummary: Matching macrocyclic and linear polystyrenes (PS) were synthesized by the initiation of styrene with 2,7‐dimethyl‐3,6‐diphenyloctane dianion lithium salt followed by high dilution coupling with 1,4‐bis(bromomethyl)benzene or protonation. Liquid chromatography at the critical condition shows the presence of less than 4% of linear PS impurities in the fractionated cycles. SEC studies confirm that the ratios of apparent MWs of cyclic and linear PS increase from about 0.7 to more than 0.9 as MWs decrease. Fluorescence studies show that the monomer emissions at 285 nm strongly increase with decreasing MW whereas those of the linear polymers are not significantly affected. This may be due in part to the increased rigidity of the smaller cycles that decreases the rate of radiation‐less deactivation.Dependence of 〈G〉 on number average MW.magnified imageDependence of 〈G〉 on number average MW.

Chain length dependence of the thermodynamic properties of linear and cyclic alkanes and polymers

The specific heat capacity was measured with step-scan differential scanning calorimetry for linear alkanes from pentane (C(5)H(12)) to nonadecane (C(19)H(40)), for several cyclic alkanes, for linear and cyclic polyethylenes, and for a linear and a cyclic polystyrene. For the linear alkanes, the specific heat capacity in the equilibrium liquid state decreases as chain length increases; above a carbon number N of 10 (decane) the specific heat asymptotes to a constant value. For the cyclic alkanes, the heat capacity in the equilibrium liquid state is lower than that of the corresponding linear chains and increases with increasing chain length. At high enough molecular weights, the heat capacities of cyclic and linear molecules are expected to be equal, and this is found to be the case for the polyethylenes and polystyrenes studied. In addition, the thermal properties of the solid-liquid and the solid-solid transitions are examined for the linear and cyclic alkanes; solid-solid transitions are observed only in the odd-numbered alkanes. The thermal expansion coefficients and the specific volumes of the linear and cyclic alkanes are also calculated from literature data and compared with the trends in the specific heats.

Control of the Morphology of Linear and Cyclic PS-b-PI Block Copolymer Micelles via PS Addition

We have studied the effect of polystyrene (PS) homopolymer addition on the morphology of self-assembled block copolymer micelles made from linear or cyclic poly(styrene-b-isoprene), PS-b-PI, in a selective solvent for the PI block (heptane). Both copolymers have the same composition: the degree of polymerization is 290 for the PS block, and 110 for the PI block, and we focused on the influence of the addition of small amounts of PS homopolymer on the micellar morphology. For the copolymer concentrations considered, the linear copolymer self-organizes into spherical micelles while the cyclic copolymer forms cylindrical micelles. PS and PI chains constitute the core and the corona of these micelles, respectively, due to the different affinity of the blocks for heptane. Consequently, the PS homopolymer added is "solubilized" into the micellar core. Dynamic light scattering (DLS) data combined with atomic force microscopy (AFM) results show that the addition of PS homopolymer induces a drastic change in the micellar organization. Indeed, a morphological transition, from spheres to cylinders for the linear copolymer, and from cylinders to vesicles for the cyclic copolymer, is observed. These results highlight the fact that a small incorporation of PS homopolymer is clearly sufficient to modify the morphology (size and shape) of the micelles. This approach could be a key parameter for the design/control of micelles for specific applications in nanotechnology.

Preparation of mechanically cross-linked poly(vinyl alcohol)

A novel cyclic macromonomer based on a cyclic polystyrene was prepared. Its radical copolymerization with vinyl acetate was carried out to give a mechanically cross-linked poly(vinyl acetate) which was converted to a mechanically cross-linked poly(vinyl alcohol) with high swellability.

Local segmental relaxation in bidisperse polystyrenes

AbstractDynamic mechanical results are reported for segmental relaxation of monodisperse polystyrenes (PSs) with molecular weights of 0.7, 3, 18, and 104 kg/mol and bidisperse PSs created from blending pairs of these materials. The data for the monodisperse polymers confirm previous findings; namely, there is an increase in the glass‐transition temperature normalized temperature dependence of the segmental relaxation times (fragility) with increasing molecular weight, along with a breakdown of the correlation between the fragility and the breadth of the relaxation function. For both the monodisperse and bidisperse PSs, the glass‐transition temperature is a single function of the average number of chain ends, independent of the nature of the molecular weight distribution. It is also found that these materials exhibit fragilities that uniquely depend on the number‐average molecular weight, that is, on the concentration of chain ends. In blends with linear PS, cyclic PS with a low molecular weight behaves as a high polymer, similar to its neat behavior, reflecting the overriding importance of chain ends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2604–2611, 2004

Preparation of Mechanically Cross-Linked Polystyrenes

This paper reports preparation of mechanically cross-linked polystyrenes using cyclic macromonomer as a nonbonding cross-linking agent. Emulsion and thermal self-initiated copolymerizations of styrene with a well-defined cyclic macromonomer based on a cyclic polystyrene were carried out to obtain mechanically cross-linked polystyrenes with high swellability. Mechanically cross-linked chloromethylated polystyrene was prepared by thermal self-initiated terpolymerization of the cyclic macromonomer, styrene, and 4-vinylbenzyl chloride.

Effects of freeze-drying on the glass temperature of cyclic polystyrenes

The calorimetric glass temperature was measured for three cyclic polystyrenes with apparent molecular weights ranging from 4.0×10 3 to 195.5×10 3 g/mol for both bulk material and for samples freeze-dried from dilute solution. Freeze-drying from dilute solution was found to reduce the glass temperature by 7–14 K depending on the sample. These T g depressions are 5–12 K greater than those found previously for freeze-dried linear polystyrene. Annealing at 403.2 and 443.2 K (130 and 170 °C) resulted in recovery of the T g back to the bulk value with the time scales depending on both temperature and the magnitude of the T g reduction; the low apparent activation energy dependence of the recovery of T g precludes its being due to viscous flow.

Effect of cyclic chain architecture on properties of dilute solutions of polyethylene from molecular dynamics simulations

We have used molecular dynamics methods to investigate the effects of cyclic chain architecture on the properties of dilute solutions. In order to include solvent effects in estimating these properties, we use a van der Waals scaling factor determined for each solvent by matching to the theta condition. We predict that the theta temperature (θ) of cyclic PE (c-PE) is ∼10% lower than for the linear case (l-PE). This can be compared to the experimental results for polystyrene (PS), where θ for cyclic PS is 2% lower. For conditions corresponding to n-pentane solvent, we predict that 〈Rg2〉cyclic/〈Rg2〉linear is 0.59 for all temperatures above 350 K. The deviation from the ratio of 0.50–0.53 expected from analytic theory is due to the competition between chain stiffness and excluded volume effects. To calculate the intrinsic viscosity of c-PE and l-PE we extended the Bloomfield–Zimm type theory to include chain stiffness corrections. We find that for the theta temperature, the ratio of viscosities for c-PE and l-PE is 0.71, which is 7% higher than the value of 0.66 from the freely jointed chain model. This difference is caused by the larger value of 〈Rg2〉cyclic/〈Rg2〉linear from the simulations.

From “Sunflower-like” Assemblies toward Giant Wormlike Micelles

One of the most interesting and fascinating solution properties of block copolymers is their ability to self-assemble into micelles, lamellar aggregates, and vesicles. Such organized structures have made diblock copolymers of great importance in nanotechnology applications.1-11 For instance, the spontaneously formed vesicles in water are potentially useful as vehicles for delivering drugs and as biomimetic models of biological cells. We show here for the first time that the cyclization of a linear copolymer chain induces a remarkable change in the micellar morphology. This result is highlighted in the case of linear and cyclic polystyrene−polyisoprene (PS−PI) diblock copolymers having exactly the same molar weight and dispersed in a selective solvent for PI. The micelles arising from linear diblock copolymers exhibit a monodisperse spherical shape (50 nm in diameter) whereas those formed from cyclic copolymers are long (>1 μm) cylindrical (wormlike) objects resulting from the unidirectional self-assembly ...

Synthesis of high‐molecular‐weight cyclic and multicyclic polystyrenes

AbstractDifferent cyclic architectures were prepared by combination of living anionic polymerization and coupling reactions. Well‐defined macrocyclic polystyrenes were obtained by reaction of a two‐ended living precursor dianion with an electrophile compound. Two types of coupling agent (diethylenic and dihalogeno compounds) were used and their influence on the cyclization yield was studied. Cyclization with a diethylenic product is preferred as it generates a macrocycle with two living centers and is able to react with a (multifunctional) nucleophile leading to more complex architecture. Cyclic polystyrenes with two attached linear branches were obtained by consecutive coupling of monofunctional and difunctional living chains with DDPE (1,3‐bis(phenyl‐ethylenyl)benzene). High molar mass multicyclic polystyrene was prepared by reaction of living macrocycles with poly(chloromethylstyrene). Size exclusion chromatography and matrix‐assisted laser desorption ionization time of flight (MALDI‐TOF) mass spectrometry analyses have confirmed the high efficiency of these coupling reactions. Copyright © 2003 John Wiley &amp; Sons, Ltd.