The theta temperature of star polymers

We use equations derived from the blob theory to calculate the blob size and the theta temperature of star polymers. In contrast to the case of linear polymers these two parameters are calculated to depend on molecular mass for star polymers. For a given star polymer the theta temperature can be lower or higher than that of the corresponding linear polymer depending on the number and length of its branches. The results are compared with the blob model of Daoud and Cotton for star polymers. Experimental results obtained in the course of this study confirm our calculations.     

Synthesis and characterization of shell-cross-linked polymer networks and large-core star polymers: Effect of the volume of the cross-linking mixture

Group transfer polymerization and sequential addition of monomer and cross-linker were employed for the preparation of two new polymer structures, one of a polymer network and the other of a star polymer. The synthesis was completed in two steps, involving the synthesis of linear methyl methacrylate (MMA) arms of degree of polymerization of 20, followed by their cross-linking using a mixture of MMA monomer and ethylene glycol dimethacrylate (EGDMA) cross-linker. In this study, the volume of the cross-linking mixture was varied systematically. Furthermore, two mixture compositions were employed, involving MMA:EGDMA molar ratios of 1:1 and 3:1, leading to two series of polymeric materials. It was found that at a given cross-linking mixture composition, a larger volume of the cross-linking mixture favored the formation of polymer networks, whereas a smaller volume favored the formation of star polymers. The linear precursors, the star polymers and the extractables from the polymer networks were characterized by gel permeation chromatography in tetrahydrofuran (THF). The absolute weight-average molecular weight, the number of arms and the hydrodynamic radii of the star polymers, as determined using static and dynamic light scattering in THF, respectively, and their average radii as determined by atomic force microscopy, increased as the volume of the cross-linking mixture increased. The gravimetrically measured degrees of swelling in THF, the network sol fraction and the percentage of branched polymer in the sol fraction decreased as the volume of the cross-linking mixture increased.     

Anomalous solubility parameter and probe dependency of polymer-polymer interaction parameter in inverse gas chromatography

Inverse gas chromatography (IGC) has been widely used to measure the Flory-Huggins interaction parameters, χ, between two polymers. For over two decades studies have shown the polymer-polymer interaction parameter to be probe dependent. This study found that the solubility parameters of miscible polymer blends measured by IGC were lower than the volume average values of the components. This led to the conclusion that when specific interactions occur between two polymers the probes have less probability to contact the functional groups of the polymers, leading to a lower apparent solubility parameter. Using the solubility parameter model this deviation was shown to cause the probe dependency. Two methods were proposed to test the miscibility. One was to examine the deviation of the specific retention volume from the weight average rule. The other was to plot ?₂?₃RT(χ₂₃/V₂) vs. the solubility parameters of probes. For miscible blends a linear trend with negative slope was observed. The slope was proportional to the deviation of solubility parameter of the polymer mixtures from the volume average, which could be used as a measurement for miscibility.     

Synthesis of heteroarm star polymers comprising poly(4-methylphenyl vinyl sulfoxide) segment by living anionic polymerization

<正>A series of 3-arm ABC and AA'B and 4-arm ABCD,AA'BC and AA′A″B heteroarm star polymers comprising one poly(4-methylphenyl vinyl sulfoxide) segment and other segments such as polystyrene,poly(α-methylstyrene), poly(4-methoxystyrene) and poly(4-trimethylsilylstyrene) were synthesized by living anionic polymerization based on diphenylethylene(DPE) chemistry.The DPE-functionalized polymers were synthesized by iterative methodology,and the objective star polymers were prepared by two distinct methodologies based on anionic polymerization using DPE-functionalized polymers.The first methodology involves an addition reaction of living anionic polymer with excess DPE-functionalized polymer and a subsequent living anionic polymerization of 4-methylphenyl vinyl sulfoxide(MePVSO) initiated from the in situ formed polymer anion with two or three polymer segments.The second methodology comprises an addition reaction of DPE-functionalized polymer with excess sec-BuLi and a following anionic polymerization of MePVSO initiated from the in situ formed polymer anion and 3-methyl-1,1-diphenylpentyl anion as well.Both approaches could afford the target heteroarm star polymers with predetermined molecular weight,narrow molecular weight distribution (M_w/M_n1.03) and desired composition,evidenced by SEC,~1H-NMR and SLS analyses.These polymers can be used as model polymers to investigate structure-property relationships in heteroarm star polymers.     

Swelling behavior and mechanical properties of endlinked poly (dimethylsiloxane) networks and randomly crosslinked polyisoprene networks

Measurements of the equilibrium degree of swelling and of the equilibrium modulus were performed on poly(dimethylsiloxane) networks (PDMS) and on polyisoprene vulcanizates. The results support the concept that topological interactions between network chains, e.g. entanglements or the like, have a large influence on the rubber elastic behavior, at least within a certain range of network densities.PDMS networks having network chains of different lengths and varying functionlities of the crosslinks were prepared in bulk by endlinking fractionated ,-divinyl PDMS via multifunctional hydrogen-siloxanes (f=3 to 22). Natural rubber (NR) and synthetic liquid polyisoprene (IR) were cured in bulk with various amounts of dicumyl peroxide to give randomly crosslinked samples.The experimentally determined moduli and degrees of swelling were compared with theoretical predictions based on the phantom network theory and affine network theory, taking into account only chemical crosslinks. The observed discrepancies can be traced back to a contribution of topological interactions (trapped entanglements) to the total effective network density. The modulus and swelling data are consistent, thus ruling out non-equilibrium effects.     

Precise synthesis of thermo-responsive and water-soluble star-branched polymers and star block copolymers by living anionic polymerization

A series of thermo-responsive and water-soluble 4- and 8-arm star-branched poly(2-(2′-methoxyethoxy)ethyl methacrylate) (poly(1)) with well-defined structures were synthesized by living anionic polymerization of 1, followed by a linking reaction with a core compound substituted with either four or eight benzyl bromide moieties. Furthermore, two kinds of sequentially different 4-arm star block copolymers composed of poly(1)-block-poly ((2,2-dimethyl-1,3-dioxolan-4-yl)methyl methacrylate) (poly(4)) were also synthesized by the same linking reaction of the corresponding AB or BA diblock copolymer anion with a core compound substituted with four benzyl bromide moieties. Thus, both well-defined 4-arm (AB)₄ and (BA)₄ star-block copolymers, whose A and B are poly(1) and poly(4) segments, were successfully synthesized. These star-block copolymers were quantitatively converted to the corresponding 4-arm (AC)₄ and (CA)₄ star-block copolymers with the same compositions by hydrolytic acetal cleavage of the poly(4) segment to poly(2,3-dihydroxypropyl methacrylate) (C segment). Poly(1) segments have LCST values and, on the other hand, both water-insoluble poly(4)s and water-soluble poly(2,3-dihydroxypropyl methacrylate)s are non-thermo-responsive segments. The thermo-responsive behavior of the resulting 4- and 8-arm star-branched poly(1) as well as the 4-arm (AB)₄, (BA)₄, (AC)₄, and (CA)₄ star-branched block copolymers has been extensively studied in terms of molecular weight, arm number, composition, and block sequence. As expected, such variables were observed to affect their LCST values. Interestingly, the thermo-responsive behavior of the 4-arm (AC)₄ and (CA)₄ stars was different from that of the block copolymers used as arm segments.     

Highly crosslinked ionic β-cyclodextrin polymers and their interaction with heavy metals

A new aqueous insoluble ionic β-cyclodextrin polymer (PYR) has been synthesized and a potentiometric study of the binary Cu(II)-PYR system is performed to calculate the complexation constants (as logβ in heterogeneous medium). The mathematical processing of the pH-metric data gave the formation constants of Cu(II) complexes and the related species distributions. The model is compatible with the presence of five complex species in the range of pH 2.5–7. Stoichiometry indicates the probable involvement of the alcoholate functionalities of the ligand in the complexation. The capacity of the polymer with respect to metal ions retention is evaluated for both Cu(II) and Cd(II) (chosen as target probes). The possibility to recover the sorbed Cd(II) is also tested by using acidic pH solutions. A complete recovery is obtained and the stability of the polymer is verified over ten steps of retention and desorption. To understand the complexation mechanism involved, two other cyclodextrin-based polymers are synthesized which are characterized by the presence of naphthalic dicarboxylic and carbonate groups as spacers. Their interactions with Cu(II) or Cd(II) are studied. Since the β-cyclodextrin polycarbonate polymer does not have acidic groups on the spacer, it is interesting to compare metal ions retention between this material, which does not present a real cation exchange site, and PYR.     

Synthesis of novel crosslinked sulfonated poly(ether sulfone)s using bisazide and their properties for fuel cell application

Novel crosslinked sulfonated poly(ether sulfone)s (PESs) were prepared by thermal irradiation of the allyl-terminated telechelic sulfone polymers using a bisazide. The sulfonated polymers in different comonomer compositions were fully characterized by ¹H NMR, and the crosslinked structure was also verified by FT-IR spectroscopic analyses. Having both the uniform distribution of the hydrophilic conductive sites and controlled hydrophobic nature by minimized crosslinking over the rigid rod poly(ether sulfone) backbone, the crosslinked polymer membrane (PES-60) offered excellent proton conductivity of 0.79 S cm⁻¹ at 100 °C together with hydrolytic and oxidative stability. In addition, only 17% of methanol permeability of the Nafion^® was observed for the crosslinked PES-60.     

Adsorption interaction parameter of polyethers in ternary mobile phases: The critical adsorption line

It is shown that in LC of polymers, the interaction parameter in ternary mobile phases can be described by a plane, which is determined by the dependencies in binary mobile phases. Instead of a critical adsorption point, critical conditions are observed along a straight line of composition between the two critical points in binary mobile phases. Consequently, a separation of block copolymers under critical conditions for one block by an adsorption mechanism for the other block can be achieved in ternary mobile phases of different compositions, which allows an adjustment of the retention of the adsorbing block.     

A comparative study of interaction of ibuprofen with biocompatible polymers

In this paper we are reporting the interaction of a non-steroidal anti-inflammatory drug ibuprofen (IBF) with various biocompatible polymers. Being amphiphilic, the drug interacts with the polymers similar to the interaction of surfactants and polymers. Therefore, we have considered the polymer-amphiphile interaction approach using conductimetry. The polymers of different charges (cationic, anionic, and nonionic) have been taken for the study. It was found that the critical aggregation concentration (cac) decreases on increasing the polymer concentrations of cationic as well as nonionic polymers whereas it increases for anionic polymers. The results imply that anionic IBF interacts with cationic and nonionic polymers more strongly as compared to the anionic polymers. A possible anionic-anionic repulsion is responsible for the weak interaction of IBF with anionic polymers. On the other side, the critical micelle concentration (cmc) increases for all polymers which is a usual indication of the interaction between amphiphiles and polymers. Free energies of aggregation (ΔG_agg) and micellization (ΔG_mic) were also computed with the help of degrees of micelle ionization obtained from the specific conductivity - [IBF] isotherms.     

高分子的折叠与聚集

总结了作者有关高分子折叠和聚集方面的工作。最初,作者研究了聚（N-异丙基丙烯酰胺）（PNIPAM）均聚物的折叠或叫做“线团-塌缩球的转变”,然后研究了含有疏水和亲水基团的PNIPAM共聚物的折叠。作者研究了疏水作用和亲水作用对折叠的影响,发现了融化球,有序线团等折叠过程中的中间态。另一方面,作者研究了两亲性高分子在水中的聚集与稳定。作者的结果表明,如果高分子链所形成的稳定聚集体为核-壳结构,则每个亲水基团所占有的面积为一个常数。如聚集体不是核-壳结构,即部分亲水基团分布在聚集体内部,则上述关系不再成立。随亲水基团含量的增加,聚集体将由球状变为超枝化结构。     

Supramolecular main-chain liquid crystalline polymers and networks with competitive hydrogen bonding: networks and linear polymers created from tris- and bis-functionalised pyridyl networking agents

A series of supramolecular polymers and networks with variable liquid crystalline characteristics have been created. These species are formed through the benzoic acid/pyridine hydrogen bonding of a flexible bis-acid and a mixture of a rigid bis-pyridyl and non-mesogenic tris- and bis-pyridyl molecules. The tris networked systems displayed liquid crystalline characteristics up to and including 31.0% netpoint inclusion. Above this concentration, only crystalline and melting behaviours were observed. The bis-containing polymer system displayed liquid crystalline characteristics up to and including 22.5% inclusion. The phenomenon observed in the tris system would seem to be linked to a statistical correlation of hydrogen bond acceptors and donors. The elimination of liquid crystallinity at lower concentrations of the bis-pyridyl dopant could be attributed to the lower melting nature of that species. Smectic phases were found in both series of complexes in loadings up to 10% of the non-liquid crystalline component. There was also no observed phase segregation of the species after multiple heat/cool cycles and extended periods of time in the isotropic state. This would indicate that the thermodynamically more stable mesogenic phase cannot out-compete the non-liquid crystalline network.     

Synthesis and characterization of well-defined poly(tert-butyl acrylate) star polymers

Star polymers with different numbers and lengths of poly(tert-butyl acrylate) (PTBA) arms were obtained via atom transfer radical polymerization. Aliphatic alcohols with different number of hydroxyl groups varying from 3 to 6 and calix[4]arenes based on pyrogallol with 12 and 16 phenol groups were transformed to bromoester derivatives to prepare multifunctional ATRP initiators used as the cores of the stars. The star polymers were characterized by GPC with refractive index, multiangle laser light scattering and viscosimetric detectors. The molar masses of the stars reached 70,000 g/mol and the molar mass dispersities did not exceed 1.2. To elucidate the compact structure of the stars, their true molar masses were determined by GPC with triple detection (RI-MALLS-Visco) and compared with the apparent molar masses obtained from the calibration with linear poly(tert-butyl acrylate) standards. The intrinsic viscosities of the PTBA stars of the same molar mass decreased with the number of star arms but were always lower than the intrinsic viscosities of the analogue linear PTBA polymers. The values of the branching ratio g′ decreased with increasing number of arms indicating more compact structure of stars. The branching ratio g′ was correlated to the empirical predictions.     

Cellulose–polyacrylonitrile blends, 1: thermodynamic interaction parameters and phase diagram in dimethylacetamide–LiCl

The phase diagram of ternary mixtures composed of cellulose, polyacrylonitrile and dimethylacetamide–7% LiCl was determined at room temperature. Homogeneous solutions were observed at low polymer concentrations. Two demixing areas were experimentally evidenced when the concentration increased: the first corresponds to an equilibrium between isotropic phases, while the second represents the coexistence of a cellulose mesophase with an isotropic phase. The diagram is discussed in terms of the interaction parameters, determined via light scattering.     

Hydrophilic,cationic large‐core star polymers and polymer networks: Synthesis and physicochemical characterization

Group transfer polymerization was used to prepare hydrophilic, cationic large‐core star polymers (LCSPs) and networks of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) and ethylene glycol dimethacrylate (EGDMA) in a two‐step procedure involving the synthesis of linear DMAEMA arms, followed by their crosslinking using a mixture of DMAEMA monomer and EGDMA crosslinker. The degree of polymerization of the linear chains prepared in the first step was kept constant, while the composition of the crosslinking mixture was varied systematically at a constant amount of crosslinker. The monomer/crosslinker molar ratio determined whether LCSPs or polymer networks would be produced. In particular, a high monomer/crosslinker molar ratio led to the formation of networks, whereas LCSPs were formed when a low monomer/crosslinker molar ratio was used. The absolute weight‐average molecular weight of the LCSPs was determined using static light scattering, whereas their hydrodynamic radii and radii of gyration were determined using dynamic light scattering and small‐angle neutron scattering, respectively. The sol fraction extracted from the networks decreased as the monomer/crosslinker molar ratio increased. The degrees of swelling of all of the networks were measured as a function of pH and were found to increase below pH 7. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3958–3969, 2008     

Lyotropic liquid crystalline phase behavior of amphiphilic monomers and polymers having a rod-like hydrophobic moiety

Distinct changes in the lyotropic mesophase behaviour of nonionic polyethyleneglycol containing amphiphiles are observed, when rigid, rod-like molecular units are introduced into the hydrophobic part of these amphiphiles, or when the amphiphiles are added as side chains to poly(methylhydrogene siloxane), yielding amphiphilic side chain polymers. Low molar mass amphiphiles with a dominating rigid, rod-like hydrophobic unit form planar-like micelles which aggregate into lamellar mesophases. Compared with their corresponding low molar mass amphiphiles, amphiphilic side chain polymers show a distinct stabilization of mesophases composed of anisometric micelles, i.e. hexagonal H₁-phases (built up by rod shaped micelles), and lamellar L -phases (built up by planarshaped micelles). In addition, several of the polymeric amphiphiles exhibit the formation of a lyotropic nematic N_c-phase regime. Optically isotropic I₁-phases composed of approximately spherical-like micelles are, on the other hand, disfavoured by the polymerfixation. Investigations of monodisperse amphiphilic side chain oligomers reveal a linear relationship between the thermal stability of the individual mesophases and the logarithm of the degree of polymerization. Changes in mesophase behaviour, due to the introduction of rigid, rod-like molecular units into the hydrophobic part of the low molar mass amphiphiles, are ascribed to packing restraints of the amphiphiles in the micelles. Alterations in mesophase behaviour which occur as a consequence of polymerfixation are discussed in terms of changes in micellar kinetics, packing restraints, and changes in the interaction between adjacent hydrophobic layers of neighbouring micelles.     

Prediction of maxima and minima in the curve of total sorption parameter in ternary polymer systems. Influence of ternary interaction parameter

Flory-Huggins theory modified by Pouchly has been applied to predict maxima and minima in the curve of total sorption in ternary polymer systems formed by a polymer and two liquids. In this work, different diagrams based on experimental magnitudes easily obtained such as the difference in affinities of liquids, solvents and non solvents, and the solvent molar volume ratio. Total sorption parameter has been considered to be the decisive magnitude to define extrema conditions in both cosolvent and cononsolvent ternary polymer systems. The theoretical prediction is not altered by the inclusion of ternary interactions. Different examples of ternary systems dealing with vinyl polymers and polydimethyl siloxane have been used to test the above formalism.