Aliphatic‐Aromatic Hyperbranched Polyesters by Polycondensation of Potassium 3,5‐Bis(bromomethyl)benzoate: Formation of Cyclic Structures

Aliphatic‐aromatic hyperbranched polyesters of reasonable degrees of branching (DB's) but of relatively low molar masses were prepared from 3,5‐bis(bromomethyl)benzoic acid ( 2a ). 2a was synthesized by radical bromination of 3,5‐dimethylbenzoic acid. The polymerization of 2a and that of the potassium salt of 2a ( 2K ), both carried out in the presence of a potassium monocarboxylate (RCOOK), led to directly derivatized polyesters. Polyesters bearing free ? CH₂Br groups were obtained by polymerization of 2K alone or in the presence of 2,4,6‐tris(bromomethyl)mesitylene (TBMM) or by polymerization of 2a in the presence of RCOOK provided that 1 ≤ [RCOOK]/[ 2a ] < 2. These polyesters were later derivatized by reaction with RCOOK. In all cases, RCOOK can be chosen in order to introduce, in the polyesters, reactive functional groups such as unsaturated (double or triple bond) and hydroxy ones. The NMR analysis of polymers has shown that a cyclic dimer (C₂) was formed in most cases. Its amount depends on the process of polymerization and on the experimental conditions. The of polyesters was found to be correlated with the amount of C₂. The MALDI‐TOF analysis of polymers confirmed the formation of cycles and showed that both the polymerization of 2K in the presence of TBMM and that of 2a in the presence of some particular RCOOK's led to the formation of acyclic macromolecules.

Expanded aromatic region of the ¹H NMR spectrum of a polymer showing the six characteristic resonances H, H, H, H, H and H of the cyclic dimer C₂.     

Thermodynamics of depolymerization of biotechnological poly[(R)-3-hydroxybutyrate] with formation of (R,R,R)-4,8,12-trimethyl-1,5,9-trioxadodeca-2,6,10-trione and of its polymerization with ring-opening to highly isotactic poly[(R)-3-hydroxybutyrate] from 0 to 500 K at standard pressure

In adiabatic vacuum and dynamic calorimeters the temperature dependence of the heat capacity C of (R,R,R-4,8,12-trimethyl-1,5,9-trioxadodeca-2,6,10-trione a twelve-membered cyclic trilactone), biotechnological poly[(R)-3-hydroxybutyrate] and highly isotactic poly[(R)-3-hydroxybutyrate] was studied between 5 K and 500 K; temperatures and enthalpies of melting of the above mentioned substances were measured. In a calorimeter with a static bomb and an isothermal shield the energy of combustion of the same substances was measured. From the results the thermodynamic functions C (T), H⁰(T) ? H⁰ (0), S⁰ (T), G⁰ (T) ? H⁰ (0) were calculated in the range of 0 K to 500 K and thermochemical parameters ΔH, ΔH, ΔS, ΔG were estimated at T = 298,15 K and standard pressure. The thermodynamic parameters of depolymerization of the biotechnological polymer to the 12-membered trilactone ΔH, ΔS ΔG and of the polymerization of the monomer formed in the highly isotactic poly[(R)-3-hydroxybutyrate] ΔH, ΔS, ΔG were calculated for 0 K to 500 K.     

Swelling,Elasticity and Spatial Inhomogeneity of Poly(N,N‐dimethylacrylamide) Hydrogels Formed at Various Polymer Concentrations

Summary: The equilibrium swelling degree, modulus of elasticity and the spatial inhomogeneity of poly(N,N‐dimethylacrylamide) (PDMAAm) hydrogels were investigated over the entire range of the initial monomer concentration. The degree of dilution of the networks after their preparation was denoted by ν, the volume fraction of crosslinked polymer after the gel preparation. The linear swelling ratio of the gels increased linearly with increasing ν. Depending on the value of ν, three different gel regimes were observed: (1) For ν < 0.3, increasing ν decreases the extent of cyclization during crosslinking so that the effective crosslink density of gels increases with rising ν. (2) For 0.3 < ν < 0.7, increasing ν reduces the accessibility of the pendant vinyl groups during crosslinking due to steric hindrance at high polymer concentrations. As a result, the effective crosslink density of gels decreases with increasing ν. (3) For ν > 0.7, the modulus of elasticity increases sharply with increasing ν due to the increasing extent of chain entanglements in this high concentration regime. Static light scattering measurements on the gels show that the degree of spatial gel inhomogeneity in PDMAAm gels attains a maximum value at ν = 0.06. The appearance of a maximum as well as the ν‐dependence of scattered light intensities from gels was successfully reproduced by the theory proposed by Panyukov and Rabin.

Effective crosslink density ν_e of the hydrogels shown as a function of ν.     

Anionic Ring‐Opening Polymerization of Propylene Oxide in the Presence of Phosphonium Catalysts at Various Temperatures

Anionic ring‐opening polymerization of propylene oxide in the presence of a potassium alkoxide initiator was accelerated by the addition of the bulky phosphonium salts tetrakis[cyclohexyl(methyl)amino]phosphonium‐, tetrakis[propyl(methyl)amino]phosphonium‐, and tetrakis[octyl(methyl)amino]phosphonium‐tetrafluoroborate. Dipropylene glycol (DPG) was partially deprotonated (5%) and used as initiator. The delocalization of the positive charge over five atoms promoted the formation of a separated ion‐pair, thus enhancing nucleophilicity and reactivity. The polymerization behavior of the counterions at varied temperatures was studied. Characterization of poly(propylene oxide)s by means of ¹H NMR spectroscopy, size exclusion chromatography (SEC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) showed low polydispersities and the absence of by‐products and impurities. The degree of polymerization (DP _n) for the polymers was in the range of 8–60 (M _n = 630–3 620 g · mol^?1) and M _w/M _n obtained was 1.03–1.35 and 1.11–1.32 for MALDI‐TOF‐MS and SEC, respectively. Values calculated from the titration of hydroxyl groups (OHV) showed good agreement. Determination of the total degree of unsaturation in the range 13–60 mmol · kg^?1 indicated larger amounts with decreasing polymerization rates and increasing polymerization temperatures.

The phosphonium salts Cy₄PBF, Pr₄PBF, and Oc₄PBF.     

Water‐Soluble Conjugated Polyelectrolyte‐Based Fluorescence Enzyme Coupling Protocol for Continuous and Sensitive β‐Galactosidase Detection

A simple, rapid, continuous and homogeneous fluorescent assay for β‐galactosidase was developed, combining an enzyme‐coupled reaction and signal amplification property of conjugated polyelectrolytes (CPs). The procedure is based on a sequence of two coupled biocatalytic steps in which the β‐galactosidase hydrolyzes its substrate to a phenol derivative followed by conversion to quinone (secondary product) with fluorescence quenching ability by the tyrosinase. The fluorescence of PFP?SO is efficiently quenched by the quinone via an electron transfer process. The limit of detection (LOD) of this assay is less than 0.0005 U · mL^?1, which is better than that of electrochemical method and is comparable to that of most sensitive chemiluminescent techniques. In principle, this sensor mechanism will extend the application window of CPs for wide‐spectrum enzyme detections. This “mix‐and‐detect” approach could be expanded to a high‐throughput manner.

     

Thermal degradation of polymers in the melt, 2. Kinetic approach to the formation of volatile oligomers by thermal degradation of polyisobutylene

The thermal degradation of polyisobutylene is characterized by kinetics consisting of four types of intramolecular hydrogen abstraction (back-biting) of primary (p) and tertiary (t) terminal macroradicals (R and R) and the successive β scission at the inner position of the main chain. This reaction affords four types of terminal monoolefins in the volatile oligomers. Assuming the reaction occurs competitively under a steady state regarding the on-chain macroradicals, the composition of the monoolefins are represented as the rate ratios of the respective back-biting processes. The rate ratio between the abstractions of different types of hydrogens (CH₂ and CH₃) from the same type of macroradicals is expressed only by the rate constant ratio. The (TTD)_p/(TVD)_p and (TTD)_t/(TVD)_t ratios remain constant during degradation, independently of the decreases in volume and molecular weight of the reacting polymers and this tendency agrees fairly well with the kinetic expectation. This result suggests that back-biting depends only on the local motion of the reacting chain ends. The ratios between the abstractions of the same type of hydrogen from different macroradicals are expressed by the product of the rate constant ratio and the integrated macroradical concentration ratio ([R]/[R]). The observed values of (TTD)_p/(TTD)_t and (TVD)_p/(TVD)_t decrease with reaction time. This decrease results from the decrease in macroradical concentration.     

Reverse Atom Transfer Radical Polymerization of Methyl Methacrylate using a New Catalyst,Copper(II) N,N′‐Butyldithiocarbamate

Summary: The homogeneous bulk reverse ATRP using AIBN/Cu(SC(S)N(C₄H₉)₂)₂/bpy as the initiating system has been successfully carried out for methyl methacrylate. Well‐controlled polymerizations with low polydispersities ( = 1.10–1.30) have been achieved. The revised number‐average molecular weights ( 's) increased linearly with monomer conversion and were close to the values. The polymerization rate followed the first‐order kinetics in monomer, while it is about 2.0 order in initiator concentration and 1.15 order in Cu(II) concentration. The k values for the homogeneous bulk reverse ATRP of MMA initiated by AIBN/Cu(SC(S)N(C₄H₉)₂)₂/bpy (1:2:6) at 80, 90, 100 and 110 °C were 0.402 × 10^?4, 1.021 × 10^?4, 2.952 × 10^?4, and 3.687 × 10^?4 (s^?1), respectively. On the basis of the Arrhenius plot, the apparent activation energy was calculated to be ΔE = 87.1 kJ/mol. The obtained PMMA was functionalized with an ultraviolet light sensitive ω‐SC(S)N(C₄H₉)₂ group characterized by means of ¹H NMR spectroscopy, and which was also proved by its chain extension with fresh MMA under UV‐light irradiation at room temperature. A polymerization mechanism for this novel initiation system is proposed.

Dependence of and on the monomer conversion for the homogeneous bulk reverse ATRP of MMA at different concentration of catalyst.     

Effects of Residual Nuclei on Crystals and Equilibrium Melting Points of Dual Crystals in Poly(ethylene 2,6‐naphthalene‐dicarboxylate)

Summary: The crystal structures and possible transformations in poly(ethylene naphthalate) (PEN) were examined using differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD). The crystal cells (α‐ and β‐form) were dependent on several factors related to their thermal histories. For PEN subjected to T_max = 280 °C (where T_max is the maximum melt temperature at which the samples were treated before crystallization), only the α‐form developed regardless of the temperature of crystallization or cooling rate. However, for PEN subjected to T_max = 300 °C, PEN developed mixed dual crystals, with greater fractions of the α‐form at low temperatures of crystallization (220 °C or lower) or higher cooling rates, but higher β‐form fractions at higher crystallization temperatures (>230 °C). The difference in the relative stability of these two crystals was utilized to prepare PEN containing only the α‐form or only the β‐form. The equilibrium melting temperatures of these two crystal forms in PEN were then measured separately. For PEN containing only the β‐form, T (289.3 °C) was found by using the Hoffman‐Weeks technique, while for PEN containing only the α‐form, T was determined using the same technique but was found to be lower (282.6 °C).

Comparison of Hoffman‐Weeks extrapolations for the α‐crystal and β‐crystal, respectively, in PEN.     

Flash‐Heating‐Enhanced Ring‐Opening Polymerizations of ε‐Caprolactone under Conventional Conditions

Summary: Flash conventional heating (FCH) and microwave heating (MH) were matched in their effects on the ROP of ε‐CL catalyzed by Sn(Oct)₂. The temperature of the ROP, heated by a hot salt bath, increased from room temperature to 215 °C within 3 min, which rose a little faster than that by MH (213 °C at 6 min), and the way of heating was considered as FCH. The kinetic results indicate that the chain propagation of PCL was significantly accelerated under FCH conditions and the ratio of the chain propagation rate constant by FCH to that by MH (k/k) was 4.48, if the concentrations of their propagating species were the same. The largest number‐average molar mass ( ) of PCL obtained by FCH was 13.0 × 10⁴ g · mol^?1 at 6 min, but that by MH was 4.1 × 10⁴ g · mol^?1 at 15 min. The ratio of the concentrations of propagating species under the two conditions was around one‐fifth at 4, 6, and 8 min.

Thermal and kinetic behavior of the ROP of ε‐CL.     

Thermodynamics of 2,2-dimethyltrimethylene carbonate,of its bulk polymerization process and of poly(2,2-dimethyltrimethylene carbonate) from 0 to 470 K at standard pressure

In the present work the thermodynamic properties of 2,2-dimethyltrimethylene carbonate (DTC) and poly-2,2-dimethyltrimethylene carbonate (PDTC) were studied by precise calorimetry. In adiabatic and dynamic vacuum calorimeters the temperature dependence of the heat capacity of DTC and PDTC was studied between 5 and 470 K. Temperature and enthalpies of physical transitions were determined, and in an isothermal calorimeter energies of combustion of the above compounds were measured. From the results the thermodynamic functions C(T), H°(T)–H°(0), S°(T), G°(T)–H°(0) were calculated for various physical states of the monomer and the polymer from 0 to 470 K. The standard enthalpies of combustion and thermochemical parameters of formation ΔH, ΔS, ΔG of the objects studied were estimated at T =298,15 K and p = 101,325 kPa. The zero entropy S(0) and configurational entropy S of PDTC in the glassy state and the difference in zero enthalpies of the polymer in the glassy and crystalline states H(0)–H(0) were estimated. The results were used to calculate the thermodynamic parameters of the bulk polymerization of DTC (ΔH, ΔS, ΔG) in the range of 0 to 420 K. It was established that for the process DTC → PDTC, ΔG < 0 if the polymer is crystalline and ΔG > 0 in the case of amorphous PDTC (glassy or liquid). The ceiling temperature is T = 500 K.     

Luminescent characteristics of tris(2,2′-bipyridine)-ruthenium(II) adsorbed in a silk fibroin membrane

The emission characteristics of the excited state of tris(2,2′-bipyridine)ruthenium(II), Ru(bpy), adsorbed on a silk fibroin membrane is studied. The life time of the excited state of the adsorbed Ru(bpy) is unusually longer (1 000 ns) than that of Ru(bpy) in aqueous solution (598 ns). The excited state of the adsorbed Ru(bpy)₃²⁺ is quenched by oxygen when dipped in methanol, but not in water. The quenching by oxygen in methanol follows the Stern-Volmer equation. The luminescent characteristics of the adsorbed Ru complex is discussed in terms of binding in hydrophobic domains composed of tyrosine residues of the protein.     

Stabilizer‐Free Dispersion Copolymerization of Maleic Anhydride and Vinyl Acetate. II. Polymerization Features

Summary: The polymerization features of the novel stabilizer‐free dispersion copolymerization of MAn and VAc were studied. It was found that the dispersion copolymerization of MAn/VAc is a fairly rapid process, which starts from a slow solution polymerization (below 10% conversion, Stage I) and follows a drastic increase of polymerization rate (10–80% conversion, Stage II) due to the known gel effect. Such process was accompanied by the increase of molecular weight of the copolymer formed ( from 1.2 × 10⁴ to 3.8 × 10⁴ g · mol⁻¹) and the broadening of the molecular weight distribution ( from 2.4 to 8.0). E_a of Stage I was determined to be 76.7 kJ · mol⁻¹, while the value of Stage II was 64.7 kJ · mol⁻¹. The lower E_a in Stage II than that in Stage I suggests that there exists a shift of polymerization locus from the solution phase to the particle phase. Moreover, we found that the initial rate of polymerization increased with monomer concentration as well as initiator concentration, following the relationship (R_p)_i ∝ [MAn + VAc] · [BPO]. This further implies that the dispersion copolymerization mainly proceeds as a solution polymerization in the very early stage.

Evolutions of the stabilizer‐free dispersion copolymerization of MAn and VAc with butyl acetate as reaction medium and the solution copolymerization with methyl propyl ketone as solvent.     

Monomolecular and bimolecular termination in the polymerization of di(meth)acrylates

The termination mechanism in the polymerization of a series of analogous di(meth)-acrylates differing only by the type of the heteroatom (S or O) in the ester group was investigated. The experimental method was based on differential scanning calorimetry measurements of photochemically initiated polymerization. The ratio of the bimolecular termination and propagation rate constants k/k_p and/or the monomolecular termination rate constant k were determined according to three termination models (monomolecular, bimolecular, and mixed). Statistical techniques were used for choosing between the models to find out by which mechanism (monomolecular, bimolecular or mixed) the termination occurs. The results obtained prove than monomolecular reaction is an important termination way in the polymerization of multifunctional monomers and must be taken into account when kinetic constants are determined, even at low degree of conversion. The sulfur-containing monomers are characterized by much lower k values than the analogous sulfur-free monomers.     

Novel Possibilities by Cationic Ring‐Opening Polymerisation of Cyclodextrin Derivatives: Preparation of a Copolymer Bearing Block‐Like Sequences of Tri‐O‐methylglucosyl Units

Summary: Equimolar mixtures of O‐permethylated and O‐perdeuteromethylated cyclodextrins were submitted to cationic ring‐opening polymerisation (CROP) with Et₃OPF₆ or BF₃ · Et₂O as initiator in dichloromethane. Reaction started after an incubation time and yielded a polymeric product, which was partially degraded again during competing chain transfer reaction. Average block length was determined by ESI‐MS after partial methanolysis and was found to be close to the theoretical value of 14 for β‐cyclodextrin in the early stage of the reaction, but decreased to 2–5 during further chain transfer reactions accompanied by an equilibration of α‐ and β‐configurated glucosidic linkages to a ratio of 64:36. Molecular weight was estimated from end group analysis and GPC to reach about 29 000 as a maximum. From ³¹P NMR spectra of the initiator it was obvious that PF is partly hydrolysed to PO₂F under participation of the glass surface.

     

Synthesis of Novel Polycations Using the Chemistry of Ionic Liquids

Summary: In this work, we report the synthesis of a great variety of polycations with varying counter‐anions. These new polymers were obtained by a simple anion exchange reaction facilitated by the phase separation of the resulting products. This strategy has been successfully applied to three different polycations, poly(1‐vinyl‐3‐ethylimidazolium bromide) poly(ViEtIm⁺Br^?), poly(1‐ethyl‐4‐vinylpyridinium bromide) poly(ViEtPy⁺Br^?), and poly(methacryloyloxyethyltrimethylammonium chloride) poly(EMTMA⁺Cl^?), with seven counter‐anions such as PF, CF₃SO, (CF₃SO₂)₂N^?, (CF₃CF₂SO₂)₂N^?, dodecylbenzenesulfonate, toluene‐4‐sulfonate, and bis(2‐ethylhexyl) hydrogen phosphate. The solubility range of the new polymeric ionic liquids becomes very broad, including apolar organic solvents and ionic liquids, depending on the nature of the counter‐anion. Thermogravimmetric experiments showed that the thermal stability of the PILs also depends on the nature of the counter‐anion improving in the order CF₃SO > (CF₃CF₂SO₂)₂N^? > C₁₂H₂₅C₆H₄SO > PF > Br^? > C₁₆H₃₄PO.

A simple anion exchange procedure similar to the reaction used in ionic liquids chemistry is used to the synthesis of new polymeric ionic liquids (PILs).     

Effect of molecular weight distribution of the original polymer on separation characteristics in successive solutional fractionation

An attempt has been made to clarify the effect of molecular weight distribution (MWD) in the original polymer on the separation characteristics in successive solutional fractionation (SSF) and comparisons were made with successive precipitational fractionation (SPF). Polymers with Schulz-Zimm distribution and Wesslau distribution of the degree of polymerization (ratio of the weight- to number-average degree of polymerization, X?/X? = 2 to 5) were brought into solution, and cooled to cause precipitation according to the modified simulative procedure of Kamide and Sugamiya, based on the Flory-Huggins's theory of dilute solutions of polymers. No double-peak distributions were observed in the fractions obtained by SSF under the conditions which give double-peak distributions in the case of SPF. The minimum value of X?_w in the fractions obtained in a given run is almost the same for SSF and SPF, the minimum increasing with decreasing X?/X? (the suffix zero denoting the original polymer). The ratio X?_w/X?_n in the fractions is not greatly influenced by X?/X? except for the first few fractions. The standard deviation σ′ of the MWD in the fractions decreases with increasing X?/X? in an initial stage, while this situation is reversed in the later stages. In general SSF furnishes sharp fractions regardless of X?/X?.     

Influence des traitements thermiques à l'état fondu sur les cinétiques de cristallisation du poly(oxyméthylène)

The influence of the temperature of the melt T₁ on the kinetics and the morphology of a semicrystalline polymer (poly(oxymethylene)) was investigated using thermal analysis and optical microscopy. The thermodynamic melting point T and the enthalpy of melting at thermodynamical equilibrium ΔH were determined by extrapolation of the graphs T_f = f(T_c) and ΔH_f = f(T_c); (T = 198°C, ΔH = 251 J/g). For different temperatures of the melt (T₁ = 185°C, 195°C, 205°C), isothermal and non-isothermal crystallizations were analysed using the Avrami and Ozawa equations. Nucleation and spherulitic growth in this polymer were studied by using optical microscopy at elevated temperatures. Using different analyses, we observed initial nucleation followed by spherulite growth with the following influence of the temperature of the melt on the distribution and the number of spherulites: T₁ < T produces many small spherulites; T₁ > T gives rise to few large spherulites.     

Accessing Chain Length Dependent Termination Rate Coefficients of Methyl Methacrylate (MMA) via the Reversible Addition Fragmentation Chain Transfer (RAFT) Process

Summary: The RAFT‐CLD‐T methodology is demonstrated to be not only applicable to 1‐substituted monomers such as styrene and acrylates, but also to 1,1‐disubstituted monomers such as MMA. The chain length of the terminating macromolecules is controlled by CPDB in MMA bulk free radical polymerization at 80 °C. The evolution of the chain length dependent termination rate coefficient, k, was constructed in a step‐wise fashion, since the MMA/CPDB system displays hybrid behavior (between conventional and living free radical polymerization) resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The obtained CLD of k_t in MMA polymerizations is compatible with the composite model for chain length dependent termination. For the initial chain‐length regime, up to a degree of polymerization of 100, k_t decreases with α (in the expression k = k · i^−α) being close to 0.65 at 80 °C. At chain lengths exceeding 100, the decrease is less pronounced (affording an α of 0.15 at 80 °C). However, the data are best represented by a continuously decreasing non‐linear functionality implying a chain length dependent α.

     

Polymerizability of Cycloalkenes in “Living” Ring‐Opening Metathesis Polymerization Initiated by Schrock Complexes, 2. Effect of Initiator Structure

The kinetics of ring‐opening metathesis polymerization of norbornene were investigated in cyclohexane using several Schrock complexes as initiators. Three different Schrock complexes were used: Mo(CHC(CH₃)₂Ph)(NAr)(O‐t‐Bu)₂ (NAr = Ph) ( I ), Mo(CHC(CH₃)₂Ph)(NAr)(OC(CF₃)₂CH₃)₂ (NAr = Ph) ( II ) and W(CH‐t‐Bu)(NAr)(O‐t‐Bu)₂ (NAr = Ph) ( III ). The presence of alkoxy‐fluorinated ligands on II and on the corresponding propagating species enhances the polymerizability of norbornene and modifies the kinetic scheme compared to that of polymerizations initiated by the tert‐butoxy complex. The greater electropositive character of II compared to that of I results in a majority of metalla‐alkylidenic growing species being complexed to monomer; therefore, the coordination of the monomer is not the rate‐determining step for the process. In contrast, the major part of growing species, which are derived from the tert‐butoxy complex are in a non‐coordinated state and, thus, the ability of the initiator to complex the monomer is decisive. In addition, this study allows to quantify the stronger reactivity of W‐based complexes compared to that of Mo‐based ones. These results were all corroborated by prior theoretical studies using ab initio calculations.     

The spontaneous polymerization of methyl methacrylate, 7. External heavy atom effect on the initiation

A dimeric biradical ^?M plays a central role in the initiation of the spontancous polymerization of methyl methacrylate (M₁). Besides the initiation step by chain transfer reaction, a change of the multiplicity of ^˙M seems to be of importance. Evidence is given by heavy atoms in the solvent or in an inert gas atmosphere, leading to an acceleration of the overall polymerization rate. The observed effect is related to the atomic number of the respective heavy atom. Measurements of the temperature dependence of the effect for carbon tetrachloride show that — as expected — no activation energy is needed for this reaction step. The results are summarized in a reaction scheme for the initiation mechanism of the spontaneous polymerization of methyl methacrylate.