Synthesis and properties of polyetheretherketone–polydimethylsiloxane block copolymers

Polyetheretherketone-polydimethylsiloxane (PEEK–PDMS) block copolymers were synthesized from the condensation of dimethylamino terminated PDMS and hydroxy terminated PEEK oligomers in 1-chloronapthalene. Yields for block copolymers synthesised from low molecular weight PDMS oligomers were good but yields were significantly reduced when higher molecular weight PDMS oligomers were used. This was related to the limited solubility of higher molecular weight PDMS in the reaction solvent. Differential scanning calorimetry (DSC) studies indicated that phase separation of the block copolymers occurred at very short segment length (M?_n < 4000). A depression in the crystallinity of both the PEEK and PDMS phases in the block copolymer was observed. Thermogravimetric analysis (TGA) studies indicated that the PEEK–PDMS block copolymers displayed insufficient thermo-oxidative stability to be melt-processed successfully in PEEK based blends.     

Synthesis and properties of polyethersulphone–polydimethyisiloxane block copolymers

High molecular weight alternating block copolymers of polyethesulphone (PES) and polydimethylsiloxane (PDMS) were prepared by the condensation of dimethylamino-terminated PDMS oligomers and hydroxy-terminated PES oligomers in 1,2-dichlorobenzene. Microphase separation of the block copolymers at exceptionally short block lengths was observed by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The Si? O? C intersegment linkage in these materials appeared to display poor hydrolytic stability which is contrary to results obtained for other block copolymers.     

Synthesis of 4-vinylbiphenyl–isoprene block copolymers and their characterization by gel-permeation chromatography

4-Vinylbiphenyl–isoprene ABA block copolymers were prepared by initiating 4-vinylbiphenyl with n-butyllithium in benzene, adding isoprene, and coupling the resulting AB anion with phosgene. Preliminary coupling experiments with a polyisoprene anion have shown that virtually quantitative coupling could be achieved provided the phosgene was added extremely slowly. The block copolymers could be quantitatively analyzed by gel-permeation chromatography from a knowledge of the ratio of the refractive index increments of the two homopolymers and the overall composition.     

Theory of block copolymers. I. Domain formation in A–B block copolymers

Microphase separation occurs in many block copolymers to give domain structures. In this first paper in a series dealing with domain formation and the consequences there of, a theory is presented for the formation of spherical domains in A-B block copolymers. The theory establishes criteria for the formation of domains and their size in terms of molecular and thermodynamic variables. It is shown that the considerable loss in configurational entropy due to the constraints on the spacial placement of chains in a domain structure requires that the critical block molecular weights required for domain formation are many-fold greater than required for phase separation of a simple mixture of the component blocks. The relation between domain radius R and molecular dimensions is obtained from the requirement that space in the domain must be filled with a constant density of segments. Segment densities are evaluated from solutions of the diffusion equation, treating the constraints on chain placement as boundary value problems. This gives the relationship R = 4/3 <L²>^1/2, where <L²>^1/2 is the root-mean-square end-to-end chain length. Because of chain perturbations in a domain system, <L²>^1/2 is larger than the unperturbed value $ < {\rm L}^2 > _0^{1/2}$ normally expected for bulk polymers. A means to evaluate the perturbations is shown. The agreement between the predictions of the present theory and the limited published experimental information appears quite satisfactory.     

Multiblock copolymers of styrene and isoprene. I. Synthesis and characterization

An anionic polymerization procedure for preparing multiblock copolymers of styrene and isoprene is described. The process is based on the initial specific incorporation of isoprene when mixtures of styrene and isoprene are polymerized with butyllithium in hydrocarbon solution. As examples, linear (AB)₃ block copolymers have been prepared by interrupting styrene polymerization by step additions of isoprene at times programmed according to the reactivity ratios and the rate constants for styrene and isoprene propagations. The products were characterized by means of osmometry, light scattering, gel-permeation chromatography, and density-gradient ultracentrifugation. The analyses showed that the multiblock copolymers are free from polymeric impurities and reasonably homogeneous in molecular weight and composition. The polystyrene segment lengths were analyzed by means of GPC after the oxidative degradation of the polyisoprene moieties in the copolymers. The results suggest that the polyisoprene blocks contain a nonnegligible amount of styrene but that this monomer is incorporated as very short segments. On the other hand the polystyrene blocks produced at the end of the copolymerizations appear to have narrow molecular weight distributions.     

Glass transition temperature of low molecular weight styrene–isoprene block copolymers

Different series of poly(styrene–isoprene) diblock and poly(styrene–isoprene–styrene) triblock copolymers were prepared. In each series, the low molecular weight polystyrene block was kept constant, and the molecular weight of the polyisoprene block varied. The glass transition behavior of these polymers was studied and their glass transition temperatures compared with those of the random copolymers of styrene and isoprene. It is concluded that some low molecular weight styrene-isoprene block copolymers form a single phase. Krause's thermodynamic treatment of phase separation in block copolymers was applied to the data. One arrives at a polystyrene–polyisoprene interaction parameter χ1,2 ≈ 0.1. The experimental and theoretical limitations of this result are discussed.     

Multiblock copolymers of styrene and isoprene. II. Microstructure and dilute solution properties

Dilute solution properties of linear (SI)₃ six-block copolymers of styrene and isoprene are compared to those of random, two-block, and three-block copolymers of the same system. All the copolymers were prepared with sec-butyllithium in benzene. The microstructure of the polyisoprene blocks is close to that of homopolyisoprene prepared under the same conditions. In contrast, the random copolymer shows a larger amount of trans-1,4 isoprene units. The intrinsic viscosities of the copolymers in methylisobutyl ketone, a poor solvent for both polystyrene and polyisoprene, and in toluene, a good solvent for both homopolymers, are examined on the basis of the Fox–Flory relation for homopolymers. All the copolymers behave similarly in each solvent. In methylisobutyl ketone, the viscosity results indicate a random coil conformation with a small expansion owing to the extra repulsive interactions between the dissimilar units. In all cases, the heterocontact repulsive interactions are small and can be characterized by an interaction parameter χ_ab close to 0.025. In toluene, the perturbation caused by the heterocontacts becomes negligible and the expansion factor α_η can be predicted from a weighted average of those of the parent homopolymers of the same molecular weight as the copolymer.     

Synthesis and solution properties of anionic linear–dendritic block amphiphiles

The design and synthesis of novel linear–dendritic diblock amphiphiles with linear poly(acrylic acid) (PAA) as the hydrophilic block and dendritic poly(benzyl ether) as the hydrophobic block are described. The synthetic process consisted of two steps: a poly(methyl acrylate) (PMA)–poly(benzyl ether) dendrimer series were synthesized with atom transfer radical polymerization, and through the hydrolysis of linear PMA block into PAA, amphiphilic block copolymers, the PAA–poly(benzyl ether) dendrimer series, were obtained. The copolymers were characterized by ¹H NMR, Fourier transform infrared, and size exclusion chromatography and exhibited well‐defined architectures and low polydispersities. When the generation number of the dendritic block (G_i) less or equal to 3 and the degree of polymerization of the linear chain (n) was greater than 10, the amphiphiles were water‐soluble. The solution intrinsic viscosity increased with both the length of linear chain and the generation number of the dendritic block. The results obtained demonstrate that dendritic blocks play an unusual role in aqueous solutions of amphiphiles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4282–4288, 2000     

Synthesis and characterization of polymethylphenylsilane–polystyrene block copolymers

Block copolymers of polymethylphenylsilane (PMPS) and polystyrene (PS) have been successfully prepared by the condensation of α,ω-dichloro-polymethylphenylsilane with polystyryl-lithium. These new materials have been characterized by UV spectroscopy, ²⁹Si-NMR, and size exclusion chromatography. These block copolymers show a good emulsifying activity to compatibilize blends of the two homopolymers (PMPS and PS). © 1993 John Wiley & Sons, Inc.     

Solution properties of polystyrene–polybutadiene block copolymers

Dilute solution viscosity and osmotic pressure measurements were performed on polystyrene (PS), polybutadiene (PB), polystyrene–polybutadiene (SB) diblock and polystyrene–polybutadiene (SBS) triblock copolymers. Anionic polymerization was used in such a way that the molecular weight of the PS block was kept constant (ca. 10 000), while the molecular weight of the PB block varied from 18000 to 450000. The measurements were carried out at a fixed temperature of 34.20°C in three solvents, namely toluene, a good solvent for PS as well as for PB, dioxane, which is a good solvent for PS and almost a theta solvent for PB, and cyclohexane, which is nearly a theta solvent for PS and a good solvent for PB. The compositions of SB and SBS, as derived from kinetic data agree with ultraviolet measurements in CHCl₃ solutions. The viscosity and osmotic pressure results indicate that the properties of SB and SBS are similar. Their intrinsic viscosities and second virial coefficients can be calculated from their chemical compositions, molecular weight, properties of parent polymers, and values of the interaction parameter \documentclass{article}\pagestyle{empty}\begin{document}$\bar \beta _{{\rm SB}}$\end{document} between styrene and butadiene units, for molecular weights not exceeding approximately 10⁵. The magnitude of \documentclass{article}\pagestyle{empty}\begin{document}$\bar \beta _{{\rm SB}} $\end{document} varies with the solvent. The results suggest that the domains of the PS and PB blocks overlap to a great extent.     

Dilute solution properties of styrene–acrylonitrile and styrene–methyl methacrylate copolymers. I. Intrinsic viscosity–molecular weight relations

Styrene–acrylonitrile (St–AN) copolymers of three compositions—27.4 mole-% (SA₁); 38.5 mole-% (SA₂); and 47.5 mole-% (SA₃) acrylonitrile—and styrene–methyl methacrylate (St–MMA) copolymer (SM) of 46.5 mole-% methyl methacrylate were prepared by bulk polymerization at 60°C with benzoyl peroxide as the initiator, and were then fractionated. The molecular weights of unfractionated and fractionated samples were determined by light scattering in a number of solvents. The [η] versus M?_w relations at 30°C were established for SA₁, SA₂, SM, and polystyrene (PSt) in ethyl acetate (EAc), dimethyl formamide (DMF), and γ-butyrolactone (γ-BL), and for SA₃ in methyl ethyl ketone (MEK), DMF, and γ-BL. Second virial coefficients A₂ and the Huggins constant were determined. From values of A₂ and the exponent a of the Mark–Houwink relation it is seen that the solvent power for samples SA₁, SA₂, and PSt is in the order EAc < γ-BL < DMF, while for sample SA₃ the solvent power is in the order MEK < γ-BL < DMF. The solvent power decreases with an increase in AN content. The solvent power of the three solvents used for SM copolymer sample is practically the same within experimental errors. From the a values it is concluded that in a given solvent the copolymer chains are more extended than the corresponding homopolymers.     

Synthesis and characterization of styrene/isoprene/ethylene oxide block copolymers

Poly(ethylene oxide/isoprene/styrene/isoprene/ethylene oxide) block copolymers were synthesized using potassium–napthalene catalyst in tetrahydrofuran. The dynamic and thermal properties and water absorption of these tri-block copolymers were determined and related to their bulk morphology.     

Structures and properties of block copolymers in solution

Structures and properties of block copolymers in solution depend on the total block length, the block length ratio, the block sequence and the solvent quality. The supramolecular structures formed by core/shell or flower-like micelles in the concentrated solution region are examined by dynamic light scattering to ascertain some of the conditions which can enhance the formation of open associated structures using a triblock copolymer in a selective solvent for the middle block.     

Synthesis and properties of p-nitrophenylacetylene–phenylacetylene copolymers

Copolymers of phenylacetylene (PA) and p-nitrophenylacetylene (pNPA) with various monomers ratios were prepared and characterized. The solubility of copolymers is dependent on the number of PA units in the chain. They show a good degree of stereoregularity and the M_W s are in the 10³–10⁵ a.m.u. range, depending on the monomers and catalyst molar ratios. The soluble samples exhibit film-forming properties and the film-surface morphology may be varied by using different solvents. The copolymers give good electrical response to relative humidity variations. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 93–102, 1998     

Surface properties of styrene–ethylene oxide block copolymers

Hydrophobic–hydrophilic block copolymers were prepared by “living” anionic polymerization. They consist of polystyrene and poly(ethylene oxide) blocks, and are soluble in water. Their interfacial properties were investigated, employing aqueous solutions. The block copolymers lowered the surface tension of water in analogy with the low molecular weight surfactants such as sodium lauryl sulfate and heptaethylene oxide n-dodecyl ether. Their aqueous solutions exhibited solubilization properties differing from those of polyethylene glycol. Therefore, it is thought that the polystyrene blocks produce solubilization phenomena. In samples of the same styrene content, the precipitation temperature of a high molecular weight copolymer in water was lower than that of a low molecular weight copolymer at the same concentration in the same solvent. The surface tension and precipitation temperature of aqueous solutions seem to be influenced by molecular weight and composition.     

Styrene‐vinylferrocene random and block copolymers by TEMPO‐mediated radical polymerization

TEMPO‐mediated free radical polymerization was employed for homo‐ and copolymerization of vinylferrocene (Vfc). Homopolymerization of Vfc resulted in relatively narrow polydispersities (M_w/M_n = 1.24–1.8), however, molecular weights were limited to 4 800. Copolymerization with styrene afforded random copolymers with molecular weights (M_n) up to 10 000, narrow polydispersity (1.2 > M_w/M_n > 1.4) and up to 42 mol‐% Vfc. Block copolymers with PS block and P(S‐co‐Vfc) block with molecular weights (M_n) in the range of 9 000 to 17 600 (M_w/M_n > 1.3) were also prepared with up to 17 mol‐% vinylferrocene. DSC revealed two glass transition temperatures (T_g) evidencing phase separation.     

Synthesis and photophysical characterization of amphiphilic dendritic–linear–dendritic block copolymers

Amphiphilic dendritic–linear–dendritic triblock copolymers based on hydrophilic linear poly(ethylene oxide) (PEO) and hydrophobic dendritic carbosilane were synthesized with a divergent approach at the allyl end groups of diallyl‐terminated PEO. Their micellar characteristics in an aqueous phase were investigated with dynamic light scattering, fluorescence techniques, and transmission electron microscopy. The block copolymer with the dendritic moiety of a third generation could not be dispersed in water. The block copolymers with the first (PEO–D ‐Si‐1G) and second (PEO–D ‐Si‐2G) generations of dendritic carbosilane blocks formed micelles in an aqueous phase. The critical micelle concentrations of PEO–D ‐Si‐1G and PEO–D ‐Si‐2G, determined by a fluorescence technique, were 27 and 16 mg/L, respectively. The mean diameters of the micelles of PEO–D ‐Si‐1G and PEO–D ‐Si‐2G, measured by dynamic light scattering, were 170 and 190 nm, respectively, which suggests that the micelles had a multicore‐type structure. The partition equilibrium constants of pyrene in the micellar solution increased with the increasing size of the dendritic block (e.g., 7.68 × 10⁴ for PEO–D ‐Si‐1G and 9.57 × 10⁴ for PEO–D ‐Si‐2G). The steady‐state fluorescence anisotropy values (r) of 1,6‐diphenyl‐1,3,5‐hexatriene were 0.06 for PEO–D ‐Si‐1G and 0.09 for PEO–D ‐Si‐2G. The r values were lower than those of the linear polymeric amphiphiles, suggesting that the microviscosity of the dendritic micellar core was lower than that of the linear polymeric analogues. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 918–926, 2001     

Synthesis and characterization of polysiloxane–polyamide block and graft copolymers

The synthesis of copolymers constituted of a central polydimethylsiloxane (PDMS) block flanked by two polyamide (PA) sequences is described. α, ω-diacyllactam PDMS, when used as macroinitiator of lactam polymerization, gives rise to the expected triblock copolymer. Likewise, PDMS-g-PA graft copolymers are obtained from acyllactam containing polysiloxanes. NaAlH₂(OCH₂CH₂OMe)₂ turns out to be the best suited activating agent for the polymerization of ?-caprolactam, in the experimental conditions required for the synthesis of polysiloxane–polyamide copolymers. The nucleophilic species formed by reaction of NaAlH₂(OCH₂CH₂OMe)₂ with ?-caprolactam—2-[bis(methoxyethoxy) aluminumoxy]-1-azacycloheptane sodium—is indeed nucleophilic enough to bring about the growth of PA chains and mild enough to stay inert towards PDMS. © 1993 John Wiley & Sons, Inc.     

Conformational behavior of styrene–dymethylsiloxane block copolymers in dilute solution

To determine the behavior of a copolymer is dilute solution, a viscosity study has been performed on a polystyrene–polydimethylsiloxane block copolymer in three solvents presenting different thermodynamic conditions. The results are discussed in relation to a mixture of homopolymers and a segregated model. The unperturbed dimensions, obtained by the Stock–mayer–Fixman method, are intermediate between those of the parent homopolymers. The intrinsic viscosity measured in a good solvent, toluene, was close to the weighted averages of those of the corresponding homopolymers of equal molecular weight, but higher in decalin and in butanone, θ solvents for PS and PDMS, respectively. According to the low value obtained for the interaction parameter, the chain is slightly expanded as a result of the interactions between the unlike monomer units. Both segregation and random conformation would probably occur, depending on the quality of the solvent.