Hyperbranched Polystyrenes Research Articles

Preparation of Functional Long-Subchain Hyperbranched Polystyrenes via Post-polymerization Modification: Study on the Critical Role of Chemical Stability of Branching Linkage.

Post‐polymerization modification (PPM) is one of the most powerful strategy for preparing polymers with functional groups that cannot be synthesized by direct polymerization. So far, numerous experimental efforts have been devoted to the stability issue of monomer structures during the PPM process, but little attention was paid to chemical linkages. However, for hyperbranched polymers, a minor change of linkage unit could lead to a significant influence on the overall stability and performance of polymer materials. In this work, we investigated the chemical stability of long‐subchain hyperbranched polystyrenes with ester, aryl ether, and carbon‐carbon bonds as branching linkages under a few most popular PPM conditions, including NaOH hydrolysis reaction, TFA‐promoted hydrolysis reaction, BBr3‐catalyzed methoxy‐hydroxyl conversion reaction, and LiAlH4 carbonyl reduction reaction. Related results are summarized into a synthetic route map that can provide practical and intuitive guidance for preparing functional long‐subchain hyperbranched polystyrenes and other type of polymers by PPM for future applications.

Characterization of mixed solutions of hyperbranched and linear polystyrenes by a combination of size‐exclusion chromatography and analytical ultracentrifugation

AbstractSeparation and characterization on mixed solutions of hyperbranched and linear polystyrenes was achieved using size‐exclusion chromatography (SEC) as the first dimension and analytical ultracentrifugation (AUC) as the second dimension. The results show that linear and hyperbranched polystyrenes with similar hydrodynamic sizes (one fraction from SEC) can be separated by AUC according to the molar mass, and the separation efficiency decreases with the increasing of the retention volume in SEC. Moreover, the molar masses determined by AUC are consistent with the values measured by SEC‐refractive index (RI) and SEC‐multi‐angle light scattering (MALS) detection. Furthermore, the result shows that the separation efficiency decreases with the increasing of the subchain length of hyperbranched polystyrenes. Our study lays a solid foundation for future studies to separate polymers with different topologies by a combination of SEC and AUC.

Adhesive Catalyst Immobilization of Palladium Nanoparticles on Cotton and Filter Paper: Applications to Reusable Catalysts for Sequential Catalytic Reactions

AbstractPalladium nanoparticles dispersed in ammonium salts of hyperbranched polystyrenes are adhesively immobilized on the surface of cotton or filter papers by simply heating with dicarboxylic acids or halide anions. The resulting Pd@cotton and Pd@filter paper behave as reusable catalysts; in particular, Pd@filter paper is useful as catalyst for application to sequential cross‐coupling and hydrogenation reactions to produce several different products with just one piece of the paper catalyst.magnified image

Degradation Kinetics of Model Hyperbranched Chains with Uniform Subchains and Controlled Locations of Cleavable Disulfide Linkages

We developed a strategy to make model hyperbranched structure with uniform subchains and controlled locations of cleavable linkages. First, a novel seesaw-type tetrafunctional initiator with one alkyne, one disulfide linkage, and two bromine groups (≡–S–S–(Br)2) was prepared. Using such an initiator, an AB2-type macromonomer (azide∼∼alkyne∼∼azide) with one disulfide linkage at its center was prepared via successive atom transfer radical polymerization (ATRP) and azidation substitution reaction, where ∼∼ represents polystyrene chains. Further interchain “clicking” coupling between the azide and alkyne groups on the macromonomers led to model hyperbranched polystyrenes with uniform subchains and controllablly located cleavable disulfide linkages. The 1H nuclear magnetic resonance spectra, Fourier transform infrared spectroscopy, and size exclusion chromatography with a multiangle laser light scattering detector confirmed the designed degradable hyperbranched structure. Armed with this novel sample, we studi...

Experimental and theoretical studies of scaling of sizes and intrinsic viscosity of hyperbranched chains in good solvents

Using a set of hyperbranched polystyrenes with different overall molar masses but a uniform subchain length or a similar overall molar mass but different subchain lengths, we studied their sizes and hydrodynamic behaviors in toluene (a good solvent) at T = 25 °C by combining experimental (laser light scattering (LLS) and viscometry) and theoretical methods based on a partially permeable sphere model. Our results show that both the average radii of gyration (<R(g)>) and hydrodynamic radius (<R(h)>) are scaled to the weight-average molar mass (M(w)) as <R(g)> ~ <R(h)> ~ M(w)(γ)M(w,s) (φ), with γ = 0.47 ± 0.01 and φ = 0.10 ± 0.01; and their intrinsic viscosity ([η]) quantitatively follow the Mark-Houwink-Sakurada (MHS) equation as [η] = K(η)M(w)(ν)M(w,s)(μ) with K(η) = 2.26 × 10(-5), ν = 0.39 ± 0.01, and μ = 0.31 ± 0.01, revealing that these model chains with long subchains are indeed fractal objects. Further, our theoretical and experimental results broadly agree with each other besides a slight deviation from the MHS equation for short subchains, similar to dendrimers, presumably due to the multi-body hydrodynamic interaction. Moreover, we also find that the average viscometric radius (<R(η)>) determined from intrinsic viscosity is slightly smaller than <R(h)> measured in dynamic LLS and their ratio (<R(η)>/<R(h)>) roughly remains 0.95 ± 0.05, reflecting that linear polymer chains are more draining with a smaller <R(h)> than their hyperbranched counterparts for a given intrinsic viscosity. Our current study of the "defect-free" hyperbranched polymer chains offers a standard model for further theoretical investigation of hydrodynamic behaviors of hyperbranched polymers and other complicated architectures, in a remaining unexploited research field of polymer science.

How Does a Hyperbranched Chain Pass through a Nanopore?

Starting from seesaw-type linear macromonomer azide∼∼alkyne∼∼azide, where “∼∼” represents polystyrene with a controllable length, we successfully obtained two series of narrowly distributed “defect-free” hyperbranched polystyrenes with an identical subchain length but different overall molar masses or with a similar overall molar mass but different subchain lengths. Our ultrafiltration study reveals that the critical flow rate (qc,b) to pull these branched chains through a small cylindrical pore under an elongational flow field depends on both polymerization degrees of the entire chain and the subchain (Nt and Nb) as qc,b ∼ NtγNbφ, where γ and φ are 1.0 and −0.4, different from those predicted values γ = 1/3 and 1/4, and φ = 1/15 and −1/4 for the weak and strong confinements, respectively. Besides the previously improper assumption of each blob as a hard sphere, such discrepancies are also attributed to (1) a smaller scaling exponent between the size and molar mass of the chain squeezed inside the pore be...

Hydrophobicity/hydrophilicity tunable hyperbranched polystyrenes as novel supports for transition-metal nanoparticles

Development of a new preparative procedure for hyperbranched polystyrene having Cl end groups (HPS-Cl) enables to prepare HPS-NR(3)(+)Cl(-), for which the hydrophobicity/hydrophilicity is tunable by the R groups. The resulting ammonium salts behave as a good support of platinum nanoparticles, which is useful for catalytic biphasic hydrogenation of alkenes.

Thermocurable Hyperbranched Polystyrenes for Ultrathin Polymer Dielectrics

Thermocurable hyperbranched polystyrenes were successfully synthesized using atom transfer radical polymerization and exhibited superior ultrathin film formation capabilities in comparison with the linear analogues, as assessed by the minimal film thickness attainable by spin-coating without dewetting. They were suitable as ultrathin film organic dielectrics, with parallel plate specific capacitances as high as ∼680 nF/cm2. Similar to high performance inorganic dielectrics, capacitance measurements pointed to the presence of "dead" interfacial capacitance, which could be accounted for by considering the geometric effect of roughness "incommensurability" between metal electrode and polymer film.

Synthesis and characterization of hyperbranched polystyrene via click reaction of AB2 macromonomer

AbstractWell‐defined hyperbranched polystyrenes have been successfully prepared by polymerization of AB2 macromonomer, polystyrene containing an azide group at its one end and two terminal propargyl groups at the other end via click reaction. For preparation of AB2 macromonomers, an ATRP initiator, bispropargyl 2‐bromosuccinate (BPBS) with two propargyl groups and one bromine group was synthesized by the successive bromination and esterification reaction of L‐aspartic acid. The resulting BPBS initiated the ATRP of St, and subsequently, the terminal bromine groups of (CH≡C)2‐PS‐Brs were substituted by N3 via the reaction with sodium azide resulting the AB2 macromonomer, (CH≡C)2‐PS‐N3 with various molecular weights. All intermediates and the resultant polymers were characterized by GPC, 1H NMR, FTIR, and MALLS methods. The polymerization kinetics study showed fast increase of DP at the initial stage of polymerization and then slow increase of their DP. The final “HyperMacs” have high‐molecular weight up to Mw,MALLS = 340,000 g/mol, their molecular weight distributions were moderately narrow (Mw/Mn = 1.47–1.65). The ratios of [η]H/[η]L of the HyperMacs formed in the polymerization system increased with evolution of polymerization. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 454–462, 2010

Glass transition behavior of hyper-branched polystyrenes

Hyper-branched polystyrenes (HBPS) were synthesized. The bulk glass transition temperature (Tg) measured by differential scanning calorimetry (DSC) for two kinds of HBPS with an equivalent Mw, which were fractionated from different lots, were different, being respectively higher and lower than that of the corresponding linear polystyrene (PS). Infrared spectroscopy revealed that the Tg of HBPS increased with an increasing extent of intramolecular cross-linking, or cyclization, in the molecule. The segmental dynamics of HBPS was examined by dynamic mechanical analysis. The relaxation temperature for the segmental motion in HBPS was consistent with the DSC results. The fragility index was always lower for HBPS than for the linear PS, regardless of its primary structure and chain end chemistry. This would indicate that the segmental motion for HBPS is less cooperative than that of the linear PS, probably due to a lack of intermolecular chain entanglements in HBPS.

Degree of branching of hyperbranched polystyrenes via a controlled radical mechanism of an inimer: Determination by a kinetic approach

AbstractWe studied, with a kinetic approach, the living nature and degree of branching (DB) of the formation of hyperbranched polystyrene by the free‐radical photopolymerization of 2‐(N,N‐diethyldithiocarbamyl)methylstyrene in benzene. The free‐radical polymerization proceeded with a living radical mechanism. Subsequently, we treated the kinetics of the initiation and propagation steps of the active A* and B* (side‐group) sites with model compounds. The degradation rates of two types of dithiocarbamate groups at the A and B sites agreed well with theoretical trends for CS bond dissociation energies predicted by the density functional theory for model compounds. The reactivity of the initiating B* groups was greater than that of the propagating A* groups. DB of the hyperbranched polymers was estimated to be 0.31 with both reaction rates in terms of Müller's equation. This result supported the DB value (0.39) estimated from NMR data. The hyperbranched molecules obtained in this work were not perfectly dendritic but had somewhat defective structures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1810–1815, 2005

Nanopattern formation on polymer substrate using star-hyperbranched nanospheres

Hyperbranched polystyrenes (PS) were prepared by living radical photopolymerization of 4-vinylbenzyl N, N-diethyldithiocarbamate as an inimer under UV irradiation. These hyperbranched PS exhibited large amounts of photofunctional dithiocarbamate groups on their outside surfaces. Subsequently, we derived the star-hyperbranched copolymers by grafting from hyperbranched macroinitiator with t-butyl methacrylate. We obtained poly(methacrylic acid) star-hyperbranched PS nanospheres by hydrolysis of poly( t-butyl methacrylate) grafted chains. We studied in detail two-dimensional nanopattern formation on poly(4-vinylpyridine) (P4VP) or partially quaternized P4VP substrate using such nanospheres by electrostatic interaction.

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Polymer architecture plays an important role in the solution, rheological, mechanical and processing behavior. In this series of two papers, we explore the role of branching, especially branch density, on the conformation and rheology of homopolymers. A series of model star-core hyperbranched polystyrenes (HBPS) with branch functionality, f, ranging from approximately 15 to 55, and branch molecular weight Mbr of 5, 10, 20, and 50 kg/mol are synthesized and characterized via triple detection SEC3 for the molecular weight, polydispersity, intrinsic viscosity, and radius of gyration. Compared to linear polymers and symmetric stars with three and eight arms of the same total molecular weight, these polymers exhibit considerably lower radius of gyration, Mark−Houwink exponent, and intrinsic viscosity. The hydrodynamic radii of HBPS with the highest branch density (f ≈ 50) are only about half the corresponding values of linear polymers of the same molecular weight, whereas this ratio is equal to 0.8 for symmetric stars. Our measurements suggest that HBPS have a very compact shape, high segmental density, and a starlike architecture. HBPS with branches shorter than the characteristic critical molecular weight exhibit a linear dependence of zero-shear viscosity on molecular weight, suggesting a lack of entanglements, and further indicating the starlike nature of the HBPS. Study of the rheology and flow birefringence of model polystyrenes will be presented in the following publication in this journal (Macromolecules 2003, 36, 407).

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 2. Linear Viscoelasticity and Flow Birefringence

In the preceding publication, we showed that the hyperbranched polystyrenes (HBPS) synthesized as part of this study may be viewed as starlike molecules with a high branch density, which are either unentangled or weakly entangled. In this paper, the role of architecture, especially the branch density, on the rheological and orientation behavior is investigated using simultaneous, quantitative stress and flow birefringence measurements in the melt state. Linear PS and eight-arm symmetric PS stars follow the stress−optical rule (SOR) over a wide dynamic range, with the stress−optical coefficient (C) governed by the arm molecular weight. When the branch density is “moderate” (greater than ∼20 arms), there is only a hint of nonterminal behavior in the viscoelastic moduli, while the C drops by 30% compared to a star with eight arms of comparable length. When the branch density is “high” (∼50 arms), and the arms are unentangled, the nonterminal behavior in G* is clearly apparent, and there is a dramatic breakdo...

Kinetics of Hyperbranched Polystyrenes by Free Radical Polymerization of Photofunctional Inimer

Kinetics of Hyperbranched Polystyrenes by Free Radical Polymerization of Photofunctional Inimer

Architecture and solution properties of hyperbranched polymers via the living radical mechanism

A novel route to hyperbranched polystyrenes (PSs) from N,N-diethylaminodithiocarbamoylmethylstyrene (DTCS) as an inimer by one-pot photopolymerization is presented. This polymerization proceeded by the self-addition living radical mechanism. Branched PSs were also prepared by living radical copolymerization of DTCS with styrene under UV irradiation. Two monomers (DTCS and styrene) showed equal reactivity towards both propagating species and the copolymer composition was the same as the comonomer composition. Both branching and the chain length of hyperbranched molecules could be controlled statistically by the feed monomer ratios. Hyperbranched poly(ethyl methacrylate)s (PEMAs) were also prepared by the self-addition living radical polymerization of 2-(N,N-diethylaminodithiocarbamoyl)ethyl methacrylate (DTCM). Copolymerizations of DTCS with maleic anhydride (MA) were carried out under UV irradiation. These reactivities showed strong alternation and the propagating copolymer radicals always proceeded with homopolymerization of 1 : 1 complexes formed between the donor and acceptor monomers. These hyperbranched polymers exhibited large amounts of photofunctional carbamate (DC) groups on the peripheral surface. Subsequently, amphiphilic hyperbranched-graft copolymers were derived by grafting from a hyperbranched PS macro-initiator with 1-vinyl-2-pyrrolidinone. These graft-hyperbranched copolymers were soluble in water and methanol. The dilute solution properties of such hyperbranched polymers were studied in detail.

Unusual contributions of molecular architecture to rheology and flow birefringence in hyperbranched polystyrene melts

AbstractWith the increase in sophisticated synthesis methods, it appears that polymer architecture may be a tunable property. Therefore, the role of architecture in rheological and processing properties has received renewed attention, mainly because of dendrimer synthesis and metallocene‐catalyst technology. Linear polymers and hyperbranched polymers represent two ends of branching complexity. Some previous studies have suggested that hyperbranched polymers may behave like unentangled polymers, whereas others have proposed that they exhibit the properties of soft colloids. In an effort to compare the responses of linear and hyperbranched polymers, we synthesized starlike hyperbranched polystyrenes (HBPSs) of various branch lengths and numbers of branches. The HBPSs used in this study were unentangled or weakly entangled, allowing us to study the effect of branch density more readily. Two linear polystyrene (L‐PS) melts and two HBPSs were studied. Using a custom‐built rheooptical apparatus, we characterized the rheology and flow birefringence of these materials. To our knowledge, these are the first flow birefringence measurements on highly branched polymer melts. Our results suggest that the flow behavior of HBPS is significantly different from that of L‐PS: (1) HBPS shows nonterminal behavior in the low‐frequency rheological response; (2) when the stress‐optical rule (SOR) holds, the stress‐optical coefficient of HBPS is much lower than those of analogous linear polymers; and (3) when the branch density is high and the branch length is sufficiently low, the SOR fails for these homopolymer melts. A significant increase in the birefringence for a given amount of stress in the low‐frequency region suggests that there may be a soft core in these materials due to the strong preferential radial orientation of chain segments near the center of a molecule versus those near the periphery. The predominantly elastic response of the soft structures may be responsible for the enhanced form birefringence. Our preliminary results indicate that these materials may exhibit both polymeric and soft‐colloid natures. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2562–2571, 2001

Synthesis of hyperbranched polymers by self-addition free radical vinyl polymerization of photo functional styrene

The hyperbranched polystyrenes are prepared by the self-addition free radical vinyl polymerization of N,N-diethylaminodithiocarbamoylmethyletyrene (DTCS). DTCS monomers play an important role in this polymerization system as an inimer that is capable of initiating living radical polymerization of the vinyl group. The compact nature of the hyperbranched macromolecules is demonstrated by viscosity measurements compared to the linear analogues.