Synthesis and characterization of ABA-triblock copolymers with polystyrene and main-chain liquid crystalline polyester segments

This paper reports on the synthesis and characterization of polystyrene-block-poly(2,2′-dimethyl-4,4′-biphenylene phenylterephthalate)-block-polystyrene. The ABA-triblock copolymers were synthesized by condensation reactions of telechelic poly(2,2′-dimethyl-4,4′-biphenylene phenylterephthalate) with anionically prepared ω-hydroxy polystyrenes. Three different lengths of the liquid-crystalline polyester (M?_n = 2650, 5 500, 10 100 g/mol) were used as central block B. The number-average molecular weight M?_n of the polystyrene segments was varied in the range of 690 to 10 000 g/mol. The liquid crystalline behavior and the transition temperatures are discussed with respect to the molecular weight of the polystyrene segments and the block copolymer composition. A comparison with the corresponding polymer blends is given and first results on the morphology of the block copolymers are presented.     

Molecular weight determination of isotactic polypropylene by high-sensitivity ebulliometry

The use of a new differential ebulliometer and the determination of the number average molecular weight of unfractionated isotactic polypropylenes is described; the results were reproducible and of satisfactory accuracy. Application of a thermopile with 150 junctions and of suitable devices for the regularity of boiling allowed measurements of number average molecular weights M?_n up to 100000 in good agreement with results obtained by other methods. In this way it is possible to measure M?_n directly, e.g. for reliable determinations of M?_w/M?_n also for polymer samples with low molecular weights and/or wide molecular weight distributions.     

Synthesis and properties of well-defined multiblock copolymers: poly(4,4′-isopropylidenediphenyl carbonate)-block-polystyrene

Well-defined poly(4,4′-isopropylidenediphenyl carbonate)-block-polystyrene multiblock copolymers, PC-b-PS, were prepared by condensation of PC prepolymers having chloroformyl end-groups with PS prepolymers having hydroxyl end-groups. Both prepolymers had narrow molecular weight distribution (PC prepolymer: M?_w/M?_n ≤ 1,31, PS prepolymer: M?_w/M?_n ≤ 1,03). The course of the polycondensation reaction depends on the molecular weight of the prepolymers used as substrates. After fractionation, the obtained multiblock copolymers are homogeneous in chemical composition and have a narrow molecular weight distribution. The mechanical properties of the copolymers depend on the weight fraction of the PS blocks. All copolymers exhibit two glass transition temperatures, close to those of the parent homopolymers.     

Characterization of non-homogeneous polymers with size-exclusion chromatography by implementing an on-line viscometer

The viscosity distribution of a polymer sample can be obtained by using an on-line viscometer as a detector in size-exclusion chromatography. This newly defined viscosity distribution is closely related to the molecular weight distribution and expresses weight fraction times intrinsic viscosity of species i as a function of the corresponding molecular weight times intrinsic viscosity (w_i[η_i] vs. M_i[η_i]). The intrinsic viscosity ([η]) and number-average molecular weight (M?_n) can be obtained directly from a viscosity distribution. If the Mark-Houwink exponent a is known (or approximately known) for non-homogeneous polymer the M?_w/M?_n can be estimated from the viscosity distribution when the molecular weight distribution is approximated with a known distribution function. These estimates are independent of any other detector and are valid even for non-homogeneous polymer samples. The relation between the moments of the viscosity distribution and the M?_w/M?_n is presented for two widely used distribution functions, the Log-Normal and the Generalized Exponential Distributions. Polymer characterization based on the viscosity distribution is shown to be a robust technique. It is particularly attractive in characterizing non-homogeneous polymers since it is solely obtained from on-line viscometer.     

Mechanischer Scherabbau von Polymeren in Lösung mittels turbulenter Strömung, 1. Kinetik,Molekulargewichtsabhängigkeit und Frage des Bruchmechanismus

The mechanical shear degradation of poly(decyl methacrylate) with weight average molecular weights 1,0·10⁶ ≤ M?_w ≤ 1,7·10⁶, and molecular polydispersity ratio M?_w/M?_n = 5 in dilute solutions is studied in turbulent flow as a function of molecular weight using a special apparatus consisting of two vessels connected by a capillary. Shear stress and shear rate remained constant during degradation. The rate of degradation was followed up by molecular weight distribution curves using gel permeation chromatography and described by ?dc_i/dt = k_i·cⁿ, i being a high molecular weight species of the distribution. The reaction was found to be of the first order (n = 1) independent of solvent and of capillary length. Rate constants k_i in the molecular weight range from 3,2·10⁶ to 13,5·10⁶ proved to be proportional to the hydrodynamic volume of the polymer molecules expressed in terms of the product of intrinsic viscosity and molecular weight [η]_i·M_i. This corresponds to a linear relationship between k_i and M_i^1,75. Additional experiments show that this type of dependence on molecular weight holds only for turbulent flow; in laminar flow the result of the literature could be confirmed that there is a linear relation between k_i and M_i¹. Both results are independent of capillary length. As to the mechanism of breakage in turbulent flow it seems that in one step each macromolecule is broken simultaneously into several smaller parts.     

Synthesis,dynamic-mechanical and morphological behavior of styrene/butyl methacrylate diblock copolymers

In order to investigate the structure-property relationship of styrene/butyl methacrylate (PS/PBMA) diblock copolymers, two ranges of polymers with M̄_n ≈ 100 000 and M̄_n > 200 000, respectively, with polydispersity indexes M̄_w/M̄_n < 1.15 are synthesized with varying ratios of the block lengths. The molecular weights of these polymers are determined by size exclusion chromatography (SEC). Thermal behavior and morphology are characterized by dynamic-mechanical analysis (DMA) and transmission electron microscopy, respectively. Whereas for unsymmetrical diblock copolymers with an overall molecular weight of M̄_n ≈ 100 000 only one broadened glass transition due to their disordered state is found, nearly symmetrical diblock copolymers show a partial miscibility which can be ascribed to the proximity of the order-disorder transition and the annealing temperature of the samples. In the case of unsymmetrical high molecular weight diblock copolymers a partial miscibility is observed as well. The high molecular weight diblock copolymers with M̄_n > 200 000 at all compositions show microphase-separated structures in contrast to the diblock copolymers with an overall molecular weight of M̄_n ≈ 100 000. Compared with styrene/isoprene diblock copolymers a relatively wide range for lamellar structures is found.     

Protection and polymerization of functional monomers, 26. Synthesis of well-defined poly[4-(3′-butynyl)styrene] by means of anionic polymerization of 4-(4′-trimethylsilyl-3′-butynyl)styrene

Anionic polymerization of 4-(4′-trimethylsilyl-3′-butynyl)styrene ( 2 ) was carried out in THF at ?78°C for 0.5 h with oligo(α-methylstyryl)lithium, -dilithium, and -dipotassium. Poly( 2 )s possessing predicted molecular weights and narrow molecular weight distributions (M?_w/M?_n < 1.11) were quantitatively obtained in all cases. By sequential anionic copolymerization of 2 and styrene, novel block copolymers, polystyrene-block-poly( 2 ) starting either from living polystyrene or living poly( 2 ), were synthesized. After completion of the polymerization, there occurred some gradual deactivation of the propagating carbanion of poly( 2 ) at ?78°C. This deactivation reaction could be almost completely suppressed at ?95°C. The deprotection of poly( 2 ) was performed by treating with Bu₄NF in THF at 0°C for 1 h. The trimethylsilyl protecting group of poly( 2 ) was completely removed to afford a poly[4-(3′-butynyl)styrene] of a controlled molecular structure.     

Chemical-composition distribution of a diblock copolymer

The experimentally determined distribution of the chemical composition of styrene/butadiene block copolymers reported by Kuhn is compared with the results of a model calculation assuming that the constituent blocks have a gamma (Schulz-Zimm) distribution of molecular weights and the ratios of weight- to number-average molecular weights are M?_w/M?_n = 1,025 or M?_w/M?_n = 1,05. A good agreement is found between experimental and calculated distributions.     

Stereo block copolymers of L- and D-lactides

Sequential diblock copolymers composed of L - and D -lactic acid residues were synthesized through a living ring-opening polymerization of L - and D -lactide initiated by aluminium tris(2-propanolate). The composition of the block copolymers was varied by changing the reaction conditions and monomer over initiator ratio and confirmed by ¹H NMR analysis, molecular weight determination and optical rotation measurements. Molecular weights ranged from 1,3 to 2,0 · 10⁴ with 1,2 < M?_w/M?_n < 1,4. Stereocomplex formation in all block copolymers was determined using differential scanning calorimetry showing melting temperatures of about 205°C.     

Morphology of (methoxyethoxy/trifluoroethoxy)phosphazene copolymers

Block copolymers were synthesized by the anionically initiated copolymerization of (CH₃OCH₂CH₂O)(CF₃CH₂O)₂P? NSi(CH₃)₃, followed by the addition of (CF₃CH₂O)₃P? NSi(CH₃)₃. Random copolymers were made by simultaneous polymerization of these monomers. These copolymers exhibit a linear dependency on the mole fraction “m” of the repeating units bearing a methoxyethoxy pendant side group as well as on molecular weights. The thermal and morphological characteristics of the block copolymers are different from those of the random copolymers of analogous “m” and molecular weight. All copolymers undergo a mesophase T(1) transition for a range of temperatures depending upon “m” and molecular weights of the copolymers. Morphological and structural features essentially resemble those of the low molecular weight (trifluoroethoxy)phosphazene homopolymer. Upon heating and cooling the solution cast copolymer specimens through T(1), most of them transform into an orthorhombic form with the unit cell dimensions a = 2,060 nm, b = 0,940 nm and c = 0,486 nm from their initial monoclinic form with a = 1,003 nm, b = 0,937 nm, c = 0,486 nm and γ γ 91°. These unit cell dimensions agree completely with those of the low molecular weight PBFP. Complicated morphologies comprised of square and globular shapes that depend upon the copolymer composition were obtained from dilute tetrahydrofuran/p-xylene copolymer solutions. Electron microscopy directly reveals that chain extension occurs for the meltcrystallized copolymer specimen. The non-crystallizable minor component in the block copolymers is rejected from the crystal lattice. In the random copolymers, the methoxyethoxy pendant side group enters into the crystal lattice and influences their morphological and structural features.     

Viscoelastic properties of mixtures of polystyrene with low-molecular-weight poly[oxy(2,6-dimethyl-1,4-phenylene)]

A series of poly[oxy(2,6-dimethyl-1,4-phenylene)]s (PPE) (trivial names: polyphenylenether, polyoxyxylene, polyphenyleneoxide) with narrow molecular weight distribution were prepared by polymerization of 4-bromo-2,6-dimethylphenol and subsequent fractionation. The molecular weight dependence of the glass transition temperature obeys the Fox-Flory equation. Polystyrene (PS)/PPE blends (PS: number-average molecular weight M?_n = 144 000, ratio of weight- to number-average molecular weight M?_w/M?_n = 1,05) were prepared using PPE samples with molecular weights below the entanglement spacing of PPE, in order to obtain information about the influence of specific interactions on the linear viscoelastic properties in the plateau and terminal region. The iso-free-volume state turned out to be the most appropriate reference state to compare samples of various compositions. Low-molecular-weight PPE essentially acts as a solvent for polystyrene. The concentration dependence of the zero-shear viscosity η₀ is proportional to ?^3,6_PS, ?_PS being the volume fraction of PS, and the temperature dependence of the logarithmic shift factor log a_T indicates that interactions, which are responsible for the thermodynamic miscibility in this system, do not alter the linear viscoelastic properties of PS. The concentration dependence of the plateau modulus (G⁽⁰⁾_N ∝ ?^1,2 for PS/PPE-1500) blends is explained by an additional small elastic contribution of the short PPE chains to the plateau modulus at higher frequencies.     

Synthesis and characterization of aliphatic-aromatic poly(ether amide)s

Four aromatic diamines containing aliphatic spacers and Meta and para oriented oxyphenylene rings, and their corresponding hydrochlorides, were combined with isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC) to give high molecular weight polyamides by interfacial and low-temperature solution methods. The synthesis and characterization of monomers and polymers are reported, and the differences observed in polycondensation yields, molecular weights and molecular weight distributions, as a function of the method of synthesis, are discussed. Values of number-average molecular weight (M?_n) up to 8 × 10⁴ g/mol and weight-average molecular weight (M?_w) up to 1 × 10⁵ g/mol could be measured by gel permeation chromatography using aromatic polyamide standards, and values of M?_n up to 2 × 10⁵ g/mol and M?_w up to 3.6 × 10⁵ g/mol by using polystyrene standards.     

Über die quantenausbeute der kettenspaltung von polystyrol in lösung bei bestrahlung mit wellenlängen λ ≧ 270 nm

Values of the mean number of chain scissions per macromolecule and the quantum efficiency of chain scission processes are presented for systems studied in our previous works, in which the photodegradation of polystyrene in solutions irradiated with mercury light (λ ≧ 270 nm) was investigated and changes of the weight-average molecular weight M?_w were considered to be a measure for chain scission. The presented values of the number of scissions were obtained as follows: the molar mass distributions were determined for the investigated polystyrene samples by dynamic (quasielastic) light scattering experiments, before and after irradiation, the number-average molecular weight values M?_n were calculated from these distributions and the mean number of scissions was obtained from the changes of the M?_n values.     

Living cationic polymerization of styrene by 1-chloroethylbenzene/tin(IV) chloride in chloroform

Living cationic polymerization of styrene in the presence of 1-chloroethylbenzene (1-CEB)/SnCl₄ as an initiating system has been investigated in chloroform at -15 to +20°C. The best results were obtained at -15°C. Under these conditions, the number-average molecular weight (M?_n) of the products increases linearly with increasing monomer conversion. The molecular weight of the polymer produced could be further increased by adding additional monomer. The molecular weights are in good agreement with the calculated values assuming that one living polymer chain is formed per one 1-CEB molecular. The molecular weight distributions of the polymers obtained are narrow (ratio of weight- to number-average molecular weights 1,07 ≤ M?_w/M?_n ≤ 1,17). The living character of these polymerizations depends on the polarity of the solvent and on temperature.     

Mechanical shear degradation of polymers in solution by turbulent flow, 3. The influence of chemical constitution and thermodynamic quality of the solvent on shear degradation

Mechanical shear degradation of polyisobutylene, polystyrene, poly(vinyl chloride), poly(methyl methacrylate), poly(decyl methacrylate), poly(methyl acrylate), and 1,4-polybutadiene in dilute solutions of tetrahydrofuran (THF) are studied under turbulent flow conditions through a capillary, in order to study the effect of the chemical constitution on shear degradation. In addition the influence of solvent quality on shear degradation is investigated. The changes of the molecular weight distribution curves were followed by gel permeation chromatography (GPC), in order to determine the degradation constants k_i for the corresponding molecular weight distribution fractions M?_i. GPC calibration via the concept of universal calibration, Mark-Houwink relations for polyisobutylene, poly(methyl methacrylate), poly(methyl acrylate), 1,4-polybutadiene, and poly(dimethylsiloxane) in THF as solvent had to be established for this purpose. Substantial differences in the rate constants k_i were observed as a function of M?_i, whereas a master curve resulted for all polymers except 1,4-polybutadiene when k_i was plotted against the number of main chain carbon atoms n?_i for each molecular weight M?_i. From this the shear degradation of C? C single bond polymers can be represented by k_i = C · n?, C being independent of the chemical nature of the C? C single bond polymer, and a varying from 1,7 to 2,6. This means that in addition to the shape of the deformed macromolecule to be degraded not only its hydrodynamic volume (in rest) but also its chain length plays an important role. As to the influence of solvent quality, the degradation constants were found to increase with decreasing solvating power of the solvent. Mechanical shear degradation of the type discussed here takes place in drag reduction by polymers.     

Synthesis of degradable terpolymers responding to external stimuli such as pH,ionic strength and temperature

Degradable copolymers which respond to external stimuli such as pH, ionic strength, and temperature were successfully prepared by direct polycondensation of L -lactic acid (LA), D ,L -mandelic acid (MA), and 3-(p-hydroxyphenyl)propionic acid (HPPA) without the use of a catalyst at 200°C by bubbling nitrogen through the solution. The molecular weights of the copolymers obtained were relatively low because of the low polymerizability of MA and HPPA, e. g., number-average molecular weight M?_n ≦ 2100 and weight-average molecular weight M?_w ≦ 4100. Poly{(L -lactic acid)-co-(D ,L -mandelic acid)-co-[3-(p-hydroxyphenyl)propionic acid]} (poly(LA/MA/HPPA)) with a composition of the monomeric units (in mol-%) LA:MA:HPPA = 80:10:10 showed rapid degradation after a lag time of 5 h within 48 h from the start of the test, in M/15 phosphate buffer solution (pH 7,2) at 37°C. With increasing pH and temperature, the rate of degradation was markedly accelerated.     

Preparation and co-catalytic properties of amphiphilic diblock copolymers consisting of polystyrene and ionene

Well defined amphiphilic diblock copolymers, consisting of an oligomeric quaternary ammonium block, a so-called ionene, and a polystyrene block, were synthesized. The route started with the preparation of monofunctionalized polystyrene by anionic polymerization, using 3-(dimethyl-amino)propyllithium as initiator. The polystyrene was obtained with relatively narrow molecular weight distributions (M?_w/M?_n = 1,2–1,4). This polystyrene was coupled stepwise with a number of different monodisperse oligomer units of 2,4-ionene, having reactive end-groups, resulting in a monodisperse 2,4-ionene block. End-group titration, size exclusion chromatography, thin-layer chromatography and infrared spectroscopy were utilized to characterize the polymers. Additionally the block copolymer in combination with tetrasodium phthalocyaninatocobalt(II)tetrasulfonate (CoPc(NaSO₃)₄) was tested as co-catalyst in the phase-transfer-catalyzed autoxidation of 1-dodecanethiol. Very high catalytic activities (775 mol O₂/(mol Co · s)) were achieved, 40 times higher as compared with the polymer-free system, due to a combination of the formation of the most active species and hydrophobic interaction with the hydrophobic thiol. This hydrophobic interaction resulted in an enhancement of the autoxidation rate by a factor 2,5, compared with the analogous hydrophilic homopolymer 2,4-ionene.     

Incréments d'indice de réfraction de polymères en solution: Étude des lois de mélange. Influence de la masse moléculaire et de la structure

The variation of the refractive index increment (dn/dc) with the molecular weight and the structure of series of linear and branched well-defined polystyrenes dissolved in benzene was studied. Testing the Lorenz-Lorentz and Onsager-Böttcher mixture rules, we were able to show that:

• 1 Below a critical molecular weight of about 2·10⁴, the linear correlation dn/dc=f(1/M_n) is well explained by the influence of chemical heterogeneities included in the polymer chain (end-groups, branching points etc.).
• 2 These rules do not account for specific polymer-solvent interactions and are not quite rigorous.
• 3 The variations of (dn/dc) and the partial specific volume of the polymer, v?_p, observed already for molecular weights higher than 2·10⁴ are accompagnied by a change in the partial specific refractivity. These effects are related to the influence of intramolecular segment density in the interior of the linear or branched coil.

A homologous series of polyoxyethylene-glycols (α-hydro-ω-hydroxypoly(oxyethylene)s) in benzene presents the same behaviour.     

Uncrosslinked epoxide-amine addition polymers, 44. Linear arylamine/2,2-bis[4-(2,3-epoxypropoxy)phenyl]-propane addition polymers — synthesis and properties

The addition polymerization of aromatic disecondary diamines and 2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane (DGEBA) leads to linear high molecular weight epoxide-amine addition polymers with number-average molecular weights ranging from 10 000 to 20 000 g/mol. Depending on the amine structure, their glass transition temperatures were estimated between 80 and 140°C. The fractionation of the high molecular weight addition polymers allows the separation of cyclic oligomers and the separation of polymers with narrow molecular weight distribution (M?_w/M?_n = 2.4–2.8). In dilute solution, predominantly cyclic oligomers were formed. Hence, they were prepared in such solutions and isolated by means of column chromatography. Their cyclic structure is proved by combination of M? values and ¹³C NMR spectra.     

Polymerization of acrylates by atom transfer radical polymerization. Homopolymerization of glycidyl acrylate

Atom transfer radical polymerization (ATRP) was applied to the homopolymerization of glycidyl acrylate (GA). This functionalized monomer can be polymerized to high conversions and high molecular weights using halogenated initiators and CuBr/4,4′-bis(5-nonyl)-2,2′-bipyridine (dNbipy) as the catalyst. The polymerizations exhibit first order kinetics and molecular weights increase linearly with conversion. The M?_n of the products is controlled by the ratio Δ[M]₀/[I]₀. The polymers obtained showed narrow molecular weight distributions, M?_w/M?_n = 1.25.