Synthesis and Characterization of Star Polymer with Comb-like Poly(lauryl methacrylate) Arms by Atom Transfer Radical Polymerization via One-pot ‘Arm-First’ Method

Atom transfer radical polymerization (ATRP) was used to prepare core crosslinked star polymers with comb-like poly (lauryl methacrylate) (LMA) arms by one-pot “arm-first” method, involving the synthesis of comb-like PLMA arms, followed by their crosslinking, using a mixture of LMA monomer and ethylene glycol dimethacrylate (EGDMA) crosslinker. By adjusting the feeding time and level of EGDMA, a series of star-like polymers with various comb-like arms length and number can be obtained. The molecular architecture including radius of gyration (Rg), hydrodynamic radius (Rh) and intrinsic viscosity (η_i) etc. were characterized by a triple-detector gel permeation chromatography (GPC) equipped with a refractive index detector, viscometer detector and a multi-angle static laser light scattering (MALLS) detector. The thermal property and shearing stability of these star-like polymers were also investigated.     

Molecular modeling of polymers. IV. Estimation of glass transition temperatures

A method is described which allows molecular modeling to be combined with a group additive property model to estimate glass transition temperatures of linear polymers. T_g is assumed to be a function of conformational entropy and mass moments of the polymer. These two molecular properties are estimated in terms of the torsion angle units composing the polymer using conformational energy calculations. A “universal” T_g equation is derived using 30 structurally diverse polymers and multidimensional linear regression analysis. “Designer” T_g equations are also derived specifically for acrylate and methacrylate polymers. The work described here demonstrates how molecular modeling can be combined with group additivity theory to yield open-ended models that are not restricted by lack of requisite group additive parameters and take advantage of three-dimensional molecular information.     

Equation of state and the thermodynamic properties of liquid polymers: Application of the Hirai-Eyring model

It is shown that the Hirai-Eyring model for the liquid state is capable of accurately describing the p, V, T behavior of liquid polymers in the temperature range over which measurements are now made, and below. Once the parameter choices necessary to accomplish the fit are made for a particular polymer, the excess thermodynamic functions (differences in properties, liquid less solid) are determined by the same parameters. Above the glass transition temperature T_g the volume, excess enthalpy, and square of the excess entropy are predicted by the model to be essentially linear with temperature, in agreement with experiment. Below T_g, these functions do not remain linear (as is usually assumed in extrapolating the equilibrium behavior to low temperatures), but instead they rapidly approach zero in a continuous way as the temperature is lowered. These remarks apply to glass-forming materials composed of small molecules, as well as to polymers. The “paradox” raised by Kauzmann is thus resolved, and the Gibbs-DiMarzio second-order transition appears to be unnecessary.     

线形、梳形和星形高分子静态和动态性质的模拟

以梳形高分子为纽带,基于粗粒化分子动力学模拟方法,研究了线形、梳形和星形拓扑结构高分子的静态和动态性质,以揭示稀溶液中高分子链行为与链拓扑结构依赖关系的一般性规律.研究结果表明,随着线形-梳形-星形的链拓扑结构转变,回转半径的标度关系由仅依赖分子聚合度转变为同时依赖链聚合度与臂数或侧链数.分析了星形高分子和梳形高分子的静态和动态性质的特征规律.星形高分子的臂数增加使其尺寸迅速减小,形状则由长椭球形转变为类球形,且扩散系数也随之增加;其均方回转半径(〈R_g〉)和扩散系数(D)与分子聚合度(N)及臂数(f)的标度规律为〈R_g〉~N~(0.581)f~(-0.402),D~N~(-0.763)f~(0.227).梳形高分子的静态与动态性质与分子聚合度及侧链数的依赖关系为〈R_g〉~N~(0.597)f~(-0.212)(每个支化点只有一条侧链)和〈R_g〉~N~(0.599)f~(-0.316)(每个支化点有多条侧链).     

An application of an homogenization method to a model of diffusion in glassy polymers

The sorption of gases in polymers below their glass-transition temperature T_g is known in many cases to be described by the “dual sorption” theory, according to which the gas is held in accordance with both the Langmuir and Henry's laws. Based on this theory, expressions for the “effective diffusion coefficient” in the glassy polymers have been obtained by investigators in the past, notably by Paul and Koros.² The present analysis regards the glassy polymers as inhomogeneous with regions on which the gas sorption follows the Langmuir law. Assuming that the linear dimensions of these regions, which are often referred to as “microvoids” (although they are not space filled by vacuum), are small compared to the macroscopic length of interest but large compared to the mean free path of the penetrant gas molecules, we derive a rigorous relation between the average flux and the concentration gradient in the polymer and show that this relation can be expressed in terms of an “effective diffusion coefficient” D_eff which depends on the details of the microstructure, i.e., the size, shape and spatial distribution of the “microvoids.” This expression for D_eff is shown to reduce to that of Paul and Koros² in two situations: (1) when the “voids” consist of slabs running parallel to the concentration gradient, and (2) when the “voids” are spherical and the temperature of the polymer is not too different from T_g. The results of the present study lead to an alternative procedure for interpreting the experimental data on sorption and permeation which may have some advantages over the procedure currently employed. Finally, the analysis presented here is also applicable to polymers containing adsorptive fillers.     

The Role of Self‐Dilution in Step‐Growth Polymerizations

In step‐growth polymerizations, the molar concentration of reactive linear species (oligomers and polymers) decreases with higher conversions and finally reaches zero at 100% conversion. This self‐dilution favors cyclization at the expense of chain‐growth. Cyclization reduces the average lengths of the linear species, and thus, induces a kind of “self‐acceleration”. Both effects together overcompensate the decreasing cyclization tendency resulting from increasing chain lengths. This influence of the self‐dilution is also operating in the case of “ab_n” monomers, so that at 100% conversion (defined for the “a” functional groups) all hyperbranched polymers will have a cyclic core. With modifications, the “law of self‐dilution” also applies to “a₂ + b₃” or “a₂ + b₄” polycondensations. Furthermore, the “law of self‐dilution” is valid for both kinetically‐ and thermodynamically‐controlled polycondensations.

     

Facile Synthesis of Well‐Defined Branched Sulfur‐Containing Copolymers: One‐Pot Copolymerization of Carbonyl Sulfide and Epoxide

Topological polymers possess many advantages over linear polymers. However, when it comes to the poly(monothiocarbonate)s, no topological polymers have been reported. Described herein is a facile and efficient approach for synthesizing well‐defined branched poly(monothiocarbonate)s in a “grafting through” manner by copolymerizing carbonyl sulfide (COS) with epichlorohydrin (ECH), where the side‐chain forms in situ. The lengths of the side‐chains are tunable based on reaction temperatures. More importantly, enhancement in thermal properties of the branched copolymer was observed, as the T_g value increased by 22 °C, compared to the linear analogues. When chiral ECH was utilized, semicrystalline branched poly(monothiocarbonate)s were accessible with a T_m value of 112 °C, which is 40 °C higher than that of the corresponding linear poly(monothiocarbonate)s. The strategy presented herein for synthesizing branched polymers provides efficient and concise access to topological polymers.     

Facile Synthesis of Well-Defined Branched Sulfur-Containing Copolymers: One-Pot Copolymerization of Carbonyl Sulfide and Epoxide

Topological polymers possess many advantages over linear polymers. However, when it comes to the poly(monothiocarbonate)s, no topological polymers have been reported. Described herein is a facile and efficient approach for synthesizing well-defined branched poly(monothiocarbonate)s in a “grafting through” manner by copolymerizing carbonyl sulfide (COS) with epichlorohydrin (ECH), where the side-chain forms in situ. The lengths of the side-chains are tunable based on reaction temperatures. More importantly, enhancement in thermal properties of the branched copolymer was observed, as the T_g value increased by 22 °C, compared to the linear analogues. When chiral ECH was utilized, semicrystalline branched poly(monothiocarbonate)s were accessible with a T_m value of 112 °C, which is 40 °C higher than that of the corresponding linear poly(monothiocarbonate)s. The strategy presented herein for synthesizing branched polymers provides efficient and concise access to topological polymers.     

Isothermal crosslinking studies on polyquinoxalines by dynamic mechanical methods

Torsional braid analysis was used to investigate the crosslinking behavior of linear quinoxaline polymers with and without reactive side groups. The kinetic parameter followed was the glass transition temperature during isothermal exposure in an inert atmosphere. With high molecular weight polyamide-quinoxaline copolymers (PPAQ), an initial decrease in T_g was observed during heat exposure which was followed by a subsequent increase in T_g. This was attributed to simultaneous chain scission and crosslinking reactions. Since the effect of random chain scission on the initial change in T_g of the highest molecular weight polymer samples is much stronger than on low molecular weight analogues, a T_g minimum was observed only on the highest molecular weight polymers. Because of the complexity of the reactions occurring one must consider the activation energies obtained from the Arrhenius plots as “apparent” activation energies. No attempt was made to elucidate the mechanisms of these reactions. It has been shown that isothermal heat exposure of high-temperature aromatic polymers in an inert atmosphere leads to crosslinking. In general, however, linear polymers that have reactive side groups such as methyl or carboxyphenyl groups along the polymer chain crosslink more rapidly than the analogs without these groups.     

Model of sorption of simple molecules in polymers

A model of simple molecule sorption in polymers is proposed which embraces both the glassy and rubbery regions, and incorporates the successful dual-mode model below the glass-transition temperature. Hole filling is shown to be an important sorption mechanism both above and below T_g, although saturation effects do not occur in the rubbery polymer. The model interprets the “dual-mode” Langmuir and Henry's law parameters at the molecular level, and a simple statistical mechanical analysis allows estimation of the parameter values, as well as specifying certain interrelationships between the parameters. Applications of the model to gas solubility data in five polymers are considered [polyethylene (PE), poly(ethylene terephthalate) (PET), polystyrene (PS), polymethacrylate (PMA), poly(vinyl acetate) (PVAc)] and semiquantitative agreement is obtained for PE, PET, and to a lesser extent, PS. For PMA and PVAc, the agreement is qualitative only.     

Spectroscopic Studies on the Simple Rcooh System

The carbonyl stretching vibration of monocarboxylic acid in CCl₄ solution has been investigated. We introduce a new “m-factor” to study the polymerization of this simple RCOOH system. The value of “m-factor” was evaluated and tested in different concentrations and temperatures. Three classes of acid polymers were found as followings: linear dimer in class I (m?2); linear and cyclic dimers in class II (m?4); linear, cyclic dimers, and linear trimer in class III (m?8). A linear relationship between log K₁ and (??1)/(2?+1) was found.     

Etude par pression osmotique de polystyrenes lineaires et ramifies en solution: determination de leurs parametres thermodynamiques

Osmotic pressure measurements have been carried out with moderately concentrated solutions (v₂ ? 0·1 g/cm³) of linear and branched polystyrenes in good and poor solvents at various temperatures. The experimental study of star- and comb-shaped polystyrenes with high segment density leads to the following conclusions: (1) we confirm the lowering of the Flory “theta” temperature of these polymers with respect to that of linear homologues, already found by light scattering technique. (2) We show that, in the low concentration range, the polymer solvent interaction parameter % depends not only upon the polymer concentration but also is a function of the intramolecular volume fraction within the polymer coil: this effect tends to disappear at high concentrations.     

The stationary phase capacity concept in elution liquid chromatography

The stationary-phase capacity concepts derived from linear capacity are discussed in connection with the needs of analytical, trace enrichment analysis and preparative chromatography and shown to be unsuited to them. A new concept based on stationary-phase saturation and called “available capacity” is proposed. It generalizes the ion-exchanger exchange capacity to adsorption and partition chromatography when the sampling solvent is the mobile phase. In linear elution chromatography the available capacity is proportional to the solute concentration C_o and to the analytical capacity factor k′ for given C_o and k′ values, it is independent of the nature of the solute. Furthermore, when both the concentrations and the analytical capacity factors (practically, for C_o ≥ 1 M and k′ ≥ 10, respectively) are high, the available capacity reaches a value roughly independent of C_o and k′, called “maximum available capacity” and related only to the number of sites available on the stationary phase. Numerous measurements were made in ion-exchange, adsorption, and reversed-phase chromatography. For solutes having a single polar functional group interacting with the stationary phase, the orders of magnitude of the maximum available capacity are 1.2 mmole g^?1 for a classical silica gel (Partisil 5 μm, 400m^?2 g^?1 with a water content of 2.7%); 1.8 mmole g^?1 for the Lichroprep RP 8 octyl bonded silica (11.6% carbon content); 3.8 mmole g^?1 for an anion exchanger resin of Dowex type.     

星型高分子共混体系的相平衡、相分离和相界面的 统计力学理论

在平均场近似下求得了星型高分子共混体系的混合自由能及其相分离动力学方程。本文的理论结果表明,型高分子共混体系与线型高分子共混体系相比具有更快的相分离速度。而且,因其相界面张力较低,体系较易形成更多的相界面,浓度涨落的临界波矢也更大。除此之外,由于在相同分子量的条件下星型高分子的尺寸要小,因此其相界面更窄,当星型高分子的臂数为1或2时,所有结果均合理地还原到熟知的线型高分子共混体系的结果。因此,本文的结果具有更大的普遍性。     

On pressure dependence of the parameters of the dual-mode sorption model

Sensitivity of the parameters of the dual-mode sorption (DMS) model on the pressure range, in which sorption of gases in polymers have been studied, was analyzed. Different “gas-polymer” systems were considered but the most detailed analysis was performed for sorption of argon and nitrogen in poly[5,5-difluoro-6,6-bis(trifluoromethyl)] norbornene and polysulfone. It was shown that the model parameters depend upon the range of gas pressure studied. Expanding of the pressure range (0-p_i) results in an increase in the Langmuir adsorption capacity C′_H and in reduction of Henry's law solubility coefficient k_D and Langmuir affinity parameter b. These behaviors does not depend on a choice of an experimental apparatus or software and procedure of nonlinear least squares treatment of the data. As statistical analysis indicated, a systematic error of the measurement cannot call forth the observed dependencies of the model parameters. Different physical reasons of these behaviors were considered, among them: the pressure dependence of the affinity parameter, and the dilation of a polymer. The results obtained showed that although the DMS model, as a rule, gives an excellent fit of the experimental curves, and, hence, can be used as a form of compact storage of information on gas sorption in polymers, one should be careful in using it outside the pressure range in which its parameters have been determined. © 1996 John Wiley & Sons, Inc.     

Semi‐rigid polyesters analysed using the “strong‐fragile” concept

Semi‐rigid polyesters from diphenyl dicarbonic acid and some branched propyl and butyl spacers have been investigated using Differential Scanning Calorimetry. From Δc_p at Tg and the determination of the fragility index m, we studied the “strong‐fragile” behaviour of these materials. All the samples appear thermodynamically “strong” and “kinetically” fragile. A comparison of these results with those obtained from glass‐forming liquids leading to linear polymers ‐ such as PET, PCT, PEN or poly‐methyl (α‐n‐alkyl) acrylates ‐ shows that a modification of the polymer rigidity leads to change the fragility index m and the Δc_p at the glass transition.     

Hyperbranched cyclic and multicyclic polymers by “a2+b4” polycondensations

At first, theoretical aspects of “a₂+b₄” polycondensations (meaning polycondensations of difunctional and tetrafunctional monomers) are discussed and compared with what is known about “a₂+b₃” polycondensations. The following review of experimental results is subdivided into three sections. First, syntheses of hyperbranched polyethers and polyesters by polycondensations based on equimolar feed ratios will be reported. Second, kinetically controlled (i.e., irreversible) syntheses of multicyclic polymers using equifunctional feed ratios (i.e., a₂/b₄ ratios of 2:1) will be described. In the third section, syntheses of multicyclic polymers via thermodynamically controlled (reversible) “a₂+b₄” polycondensations will be discussed. Characteristic for these polycondensations are again equifunctional feed ratios and metal alkoxides as “a₂” or “b₄” monomers, which catalyze rapid equilibration reactions. Finally, potential applications of the new polymers will shortly be mentioned. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1971–1987, 2009     

Linear polymers of vinyl aryl monomers containing another unsaturated group

The synthesis and the anionic polymerization of representative substituted styrenes, CH₂?CH? C₆H₄R′, where R′ is an ethylenic or acetylenic group attached directly or indirectly to the benzene ring, to linear polymers is described. In contrast, crosslinked polymers were obtained when radical and cationic initiators were used. The unpolymerized, unsaturated bonds in R′ in the resulting linear polymers were shown to be present by infrared spectroscopic methods and by the following post-reactions of these bonds: (1) the thermal- and radical-initiated crosslinking of the linear polymers through the unsaturated bonds in R′; (2) the post-bromination of these unsaturated bonds; (3) the post-copolymerization of these unsaturated bonds with vinyl monomers; and (4) the reaction of decaborane with the acetylenic bonds. The anionic copolymerizations of methyl methacrylate, acrylonitrile, and styrene with these monomers were performed and confirmed their behavior as substituted styrenes. Block copolymerizations with styrene and methyl methacrylate were also performed and the expected results obtained. Post-bromination of the linear polymers afforded self-extinguishing polymers. The linear polymers and copolymers may be classified as “self-reactive” polymers which yield thermosetting polystyrenes.     

Cationic star polymer siRNA transfectants interconnected with a piperazine-based cationic cross-linker

Cationic star polymers of 2-(dimethylamino)ethyl methacrylate (DMAEMA) were prepared via the “arm-first” method under group transfer polymerization (GTP) conditions, and were interconnected using a novel, hydrophilic, positively ionizable dimethacrylate cross-linker which is essentially the cyclic dimer of DMAEMA, thus ensuring that the building units of the arms and the core of the star polymers were identical. After their physicochemical characterization, these star-like polyamines were evaluated for their ability to transfer small interfering RNA (siRNA) to murine myoblast cells. Suppression efficiency was found to increase with polymer loading and star branch size, attaining sufficiently high values, comparable to that observed with standard non-viral siRNA transfection systems, while cytotoxicity was kept reasonably low.     

Characterization of hydrophilic networks synthesized by group transfer polymerization

Group transfer polymerization was used to synthesize several series of hydrophilic random and model networks. Cationic random networks were prepared both in bulk and in tetrahydrofuran (THF) using a monofunctional initiator and simultaneous polymerization of monomer and branch units, while a bifanctional initiator was employed in THF for the synthesis of model networks comprising basic or acidic chains. Upon polymerization of the monomer, the latter initiator gives linear polymer chains with two “living” ends, which are subsequently interconnected to a polymer network by the addition of a branch unit. Homopolymer network star polymers were also synthesized in THF by a one‐pot procedure. The synthesis involved the use of a monofunctional initiator and the four‐step addition of the following reagents: (i) monomer, to give linear homopolymers; (ii) branch unit, to form “arm‐first” star polymers; (iii) monomer, to form secondary arms and give “in‐out” star polymers; and, finally (iv) branch unit again, to interconnect the “in‐out” stars to networks. Different networks were prepared for which the degree of polymerization (DP) of the linear chains between junction points was varied systematically. For all networks synthesized, the linear segments, the “arm‐first” and the “in‐out” stars were characterized in terms of their molecular weight (MW) and molecular weight distribution (MWD) using gel permeation chromatography (GPC). The degrees of swelling of both the random and model networks in water were measured and the effects of DP, pH, and monomer type were investigated.