Synthesis of poly(phenylgermanosilanes) and poly(phenylgermanocarbosilanes)

Phenyl-substituted poly(germanosilanes) and poly(germanocarbosilanes) have been synthesized through the Wurtz-Kipping reaction via dechlorination of mixtures of dichlorophenylsilanes (PhSi(R)Cl₂, where R = H, Ph, or vinyl) with diphenyldichlorogermane in the presence of an ultradisperse sodium suspension. The polymers thus synthesized have been investigated by X-ray fluorescence analysis; FTIR and UV spectroscopy; and ¹H, ¹³C, and ²⁹Si NMR spectroscopy. The peak maxima in the UV spectra of the polymers dissolved in THF are in the wavelength range of 300–375 nm. Under the effect of UV irradiation with a wavelength of 320–380 nm, photoluminescence emission peaking in the range of 380–470 nm is observed. Size exclusion chromatography indicates that all the (co)polymers under examination are characterized by a narrow GPC curve and their polydispersity indexes are no larger than 1.5. According to dynamic TGA data, the weight loss of the polymers reaches 80% even at 500°C. Owing to formation of branched structures in vinyl-substituted copolymers, the GPC curves widen (the polydispersity index is ～6), while the yield of an inorganic residue at 900°C amounts to 40%.     

Degradation of poly(methylphenylsilylene) and poly(di-n-hexylsilylene)

Degradation of poly(methylphenylsiylene) and poly(di-n-hexylsilylene) was studied by chemical and mechanical methods at ambient and higher temperatures. Purely thermal degradation in solid state starts as a slow process at 150°C and provides soluble and insoluble products which include cyclosilanes as well as various siloxanes. Sonication at ambient temperatures leads to the mechanical degradation of high molecular weight polymers by homolytic cleavage induced by shear forces. No cyclics are formed under these conditions. Polysilanes in the presence of strong nucleophiles degrade exclusively to cyclic oligomers. Rate of this back-biting chain reaction depends on substituents at silicon atom, alkali metal, solvents, and temperature. Electrophiles degrade polysilanes to various α,ω-difunctional oligosilanes. © 1993 John Wiley & Sons, Inc.     

Sulfonated poly(pyromellitimides) and poly(naphthylimides)

A comparative synthesis of poly(imides) based on benzidine-2,2′-disulfonic acid and dianhydrides of pyromellitic and naphthalene-1,4,5,8-tetracarboxylic acids via the high-temperature polycyclocondensation in m-cresol in the presence of triethylamine has been performed for the purpose of designing proton-exchange membranes for fuel cells. The polymers are shown to be water-soluble with poly(naphthylimide) showing by a much higher hydrolytic stability than poly(pyromellitimide). To render poly(naphthylimide) insoluble in water, copoly(naphthylimide) has been synthesized using 4,4′-bis(4-aminophenoxy)diphehyl sulfone as a comonomer. Copoly(naphthylimides) combine solubility in organic solvents with insolubility in water. These polymers demonstrate high viscosity characteristics and excellent film-forming behavior. They combine excellent thermal stability and hydrolytic resistance with proton conductivity, which is higher than the proton conductivity of Nafion commercial membranes in wide temperature and relative conductivity ranges.     

Preparation of poly(fumaric acid) from poly(di-t-butyl fumarate) and poly(di-trimethylsilyl fumarate)

Polymerization conditions of di-t-butyl fumarate and di-trimethylsilyl fumarate were studied in detail. They cannot be polymerized by either anionic or coordination initiators, but radical and radiation polymerizations are successful. Characterization of poly(di-t-butyl fumarate), obtained thereby, with ¹H-NMR spectrum suggests that the backbone of the chain is stiff. From analysis of thermal properties of poly(di-t-butyl fumarate), it is found to be completely converted to poly(fumaric acid) by pyrolysis around 200°C. Poly(di-trimethylsilyl fumarate), on the other hand, can be quantitatively hydrolyzed with acid to the same polyacid, too. The preliminary measurement of the dissociation behaviors of poly(fumaric acid) was done by potentiometric titration, which shows that the titration curves of poly(fumaric acid) are different from those of poly(acrylic acid) and poly(maleic acid).     

Thermogelling hydrogels of poly(ε-caprolactone-co-D,L-lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-D,L-lactide) and poly(ε-caprolactone-co-L-lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-L-lactide) aqueous solutions

Thermogelling poly(ε-caprolactone-co-D,L -lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-D,L -lactide) and poly(ε-caprolactone-co-L -lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-L -lactide) triblock copolymers were synthesized through the ring-opening polymerization of ε-caprolactone and D,L -lactide or L -lactide in the presence of poly(ethylene glycol). The polymerization reaction was carried out in 1,3,5-trimethylbenzene with Sn(Oct)₂ as the catalyst at various temperatures, and the yields were about 96%. The molecular weights and polydispersities (M_w/M_n) by gel permeation chromatography were in the ranges of 5140–6750 and 1.35–1.45, respectively. The differential scanning calorimetry results showed that the melting temperatures of the poly(ε-caprolactone) components were between 30 and 40 °C. By the subtle tuning of the chemical compositions and microstructures of these triblock copolymers, the aqueous solutions underwent sol–gel transitions as the temperature increased, with the suitable lower critical solution temperature in the range of 17–28 °C at different concentrations. Transesterification in the polymerization process generated the redistribution of sequences, which remarkably affected the sol–gel transition temperature. The amphiphilic copolymers formed micelles in aqueous solutions with a diameter of 62 nm and a critical micelle concentration of about 0.032 wt % at 20 °C. Micelles aggregated as the temperature increased, leading to gel formation. The sol–gel transition was studied, with a focus on the structure–property relationship. It is expected to have potential applications in drug delivery and tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4091–4099, 2007     

Miscibility of poly(butyl methacrylate-CO-methacrylic acid) or poly(styrene-CO-methacrylic acid) with poly(styrene-CO-4-vinylpyridine) or poly(butyl methacrylate-CO-4-vinylpyridine)

The miscibility of blends of copolymers of different compositions of butyl methacrylate-co-methacrylic acid or styrene-co-methacrylic acid with styrene-co-4-vinylpyridine or butyl methacrylate-co-4-vinylpyridine was studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. It was found that these blends were miscible in part as a result of specific favorable interactions between the carboxylic acid and pyridine groups within the polymer chains. Evidence of such interactions was obtained from the single composition-dependent glass transition temperature and the FTIR results.     

The synthesis of poly(hydroxamic acid) from poly(acrylamide)

Poly(hydroxamic acid) in gel or water soluble from was prepared from the reaction of poly(acrylamide) and hydroxylamine in basic aqueous solution (pH > 12) at room temperature. The polymers were composed of 70% hydroxamic acid groups, less than 5% carboxylic acid groups, and 25% unreacted amide groups. The polymers exhibited high affinity to iron(III) and copper(II) in the pH range of 1 to 5 with a high binding rate. A binding of 3 mmol/g for both metals was achieved. Preliminary tests demonstrated the urease inhibitory activity of both linear and crosslinked poly(hydroxamic acids).     

Photochemical behavior of poly(ethylacryloylacetate) and poly(acryloylacetone) films

Films of poly(ethylacryloylacetate) (PEAA) and poly(acryloylacetone) (PAA) were subjected to UV irradiation (λ = 254 nm) at room temperature. The photoinduced structure transfer from cis-enol onto a diketo forms has been investigated. The structure transfer caused by UV light was found to be slower than for the corresponding process in solution. The spectral investigations (UV, IR) showed reversible process of photoketonization. The results were analyzed in terms of the model for the participation of the trans-enol form in the process of the ketonization. Based on the results obtained, some general conclusions were made about the organization of the units in the polymer chain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3683–3688, 1997     

Novel thermooxidatively stable poly(ether-imide-benzoxazole) and poly(ester-imide-benzoxazole)

4-Hydroxy-5-nitrophthalimides were produced via nucleophilic aromatic substitution (NAS) of 4,5-dichloro phthalimide substituents by potassium nitrite. The use of a N-phenyl-phthalimide having a protected 4′-hydroxyl group allows concurrent deprotection and nitro reduction to amine to give the 4-hydroxy-5-amino-N-(4′-hydroxyphenyl) phthalimide. This key intermediate is the precursor to a poly (ether-imide-benzoxazole), and is the condensable monomer for a poly (ester-imide-benzoxazole). Benzoxazole monomer formation via condensation with p-fluorobenzoyl chloride afforded 2-(4′-fluorophenyl)-5,6,-N-[4′(-hydroxyphenyl) imide]-benzoxazole, which was polymerized under NAS conditions to produce a poly(ether-imide-benzoxazole) having an endothermic transition at 454°C with weight retention of 90% at 500°C in both air and nitrogen. Solution polycondensation of the 4-hydroxy-5-amino-N-(4′-hydroxyphenyl) phthalimide monomer with isophthaloyl chloride afforded a poly(ester-amide-imide) which was isolated and thermally cyclodehydrated in the solid state under vacuum to give a poly(ester-imide-benzoxazole) having 95% weight retention at 500°C in both air and nitrogen, with no detectable DSC transitions up to 500°C. © 1994 John Wiley & Sons, Inc.     

The thermal transformation of an aromatic poly (amide), poly (ortho-oxyamide) and poly (benzoxazole)

The thermal behaviour of three aromatic polymers, poly(3,3-dioxy-4,4-diphenylmethane) (POA), poly(2,2-m-phenylene-5,5-dibenzoxazolemethane) (PBO) and a commercial poly-(phenyleneisophthalamide) (Phenylon) was studied by thermal analysis, i.e. DSC and TG. PBO was formed by the progressive thermocyclization of POA. By transforming POA into PBO the thermal stability was increased proportionally to the degree of cyclization, due to the stiffening of the polymer chain. PBO was found to be more thermally stable than Phenylon. The activation energies of the desorption of moisture, cyclization and thermal degradation of the polymers in both nitrogen and air were determined from non-isothermal TG data.     

Synthesis of poly(tert-butoxycarbonyl-p-phenylene): precursor to poly(p-phenylene)

Poly[2-(tert-butoxycarbonyl)-1,4-phenylene] ( 2 ) was prepared by the Ni-catalyzed polymerization of tert-butyl 2,5-dichlorobenzoate ( 1 ). The microstructure of polymer 2 was probably alternating head-to-head and tail-to-tail. This polymer was soluble in dipolar aprotic solvents, chloroform, tetrahydrofuran, and dichloromethane. Polymer 2 was saponified easily by thermal or acid treatment to yield poly[2-carboxy-1,4-phenylene] ( 3 ). Decarboxylation of polymer 3 in quinoline in the presence of copper(II) oxide produced poly(p-phenylene) (PPP) ( 4 ).     

Spectroelectrochemistry of poly(ethylenedithiathiophene)--the sulfur analogue of poly(ethylenedioxythiophene)

Poly(3,4-ethylenedithiathiophene) (PEDTT) is a polythiophene-like conjugated polymer in which each thiophene ring is functionalized with an ethylenedithia bridge. As such, PEDTT is the sulfur analogue of the well-known poly(3,4-ethylenedioxythiophene) (PEDOT). Substituent effects, namely the presence of sulfur atoms in PEDTT replacing the oxygen atoms of PEDOT, do not provide a simple explanation for the different electronic properties of the two polymers in the neutral state. This paper reports the spectroscopic properties of PEDTT, studied by in situ techniques such as IR-, Vis-, and electron spin resonance (ESR) spectroelectrochemistry. The differences observed upon electrochemical oxidation of PEDTT and PEDOT (e.g., the different infrared active vibrational band patterns in IR spectroelectrochemistry as well as the different nature of the charged states) are even more marked than those observed in the neutral state. These results, with AM1 calculations, indicate conformational effects as a possible explanation for the different electronic and spectroscopic properties of PEDTT and PEDOT.     

Fluorescence and viscometry study of complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide)

Interpolymer complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide) was studied by fluorescence spectroscopy and viscometry in dilute aqueous solutions. Changes in chain conformation and flexibility due to the interpolymer association are reflected in the intramolecular excimer fluorescence of pyrene groups covalently attached to the polymer chain. Both poly(acrylamide) and hydrolysed poly(acrylamide) form stable complexes with poly(acrylic acid) at low pH. The molecular weight of poly(acrylic acid) and solution properties such as pH and ionic strength were found to influence the stability and the structure of the complexes. In addition, the polymer solutions mixing time showed an effect on the mean stoichiometry of the complex. The intrinsic viscosity of the solutions of mixed polymers at low pH suggested a compact polymer structure for the complex.     

The morphology of poly(vinylidene fluoride) crystallized from blends of poly(vinylidene fluoride) and poly(ethyl acrylate)

A combined optical and electron microscopical study has been carried out of the crystallization habits of poly(vinylidene fluoride) (PVF₂) when it is crystallized from blends with noncrystallizable poly(ethyl acrylate) (PEA). The PVF₂/PEA weight ratios were 0.5/99.5,5/95, and 15/85. Isothermal crystallization upon cooling the blends from the single-phase liquid region was carried out in the range 135–155°C, in which the polymer crystallizes in the α-orthorhombic unit cell form. The 0.5/99.5 blend yielded multilayered and planar lamellar crystals. The lamellae formed at low undercoolings were lozenge shaped and bounded laterally by {110} faces. This habit is prototypical of the dendritic lateral habits exhibited by the crystals grown from the same blend at high undercoolings as well as by the constituent lamellae in the incipient spherulitic aggregates and banded spherulites that formed from the 5/95 and the 15/85 blends, respectively. In contrast with the planar crystals grown from the 0.5/99.5 blend, the formation of the aggregates grown from the 5/95 blend is governed by a conformationally complex motif of dendritic lamellar growth and proliferation. The development of these aggregates is characterized by the twisting of the orientation of lamellae about their preferential b-axis direction of growth, coupled with a fan-like splaying or spreading of lamellae about that axis. The radial growth in the banded spherulites formed from the 15/85 blend is governed by a radially periodic repetition of a similar lamellar twisting/fan-like spreading growth motif whose recurrence corresponds to the extinction band spacing. This motif differs in its fan-like splaying component from banding due to just a helicoidal twisting of lamellae about the radial direction. © 1993 John Wiley & Sons, Inc.     

Miscibility of poly(vinyl chloride) with poly(methyl-co-hexyl acrylate) and poly(methyl-co-2 ethyl hexyl acrylate)

The miscibility and phase behavior in blends of PVC with poly(methyl-co-hexyl acrylate)[MHA] and poly(methyl-co-2 ethyl hexyl acrylate)[MEH] were studied. It was found that PVC is miscible with MHA copolymers having a HA volume fraction from 0.30 to 0.92 and MEH copolymers having an EH volume fraction from 0.30 to 0.83 at 100°C. By applying the mean field theory to the phase diagrams of these blend systems, segmental interaction parameters which represent the binary interaction between different monomer units were estimated. The calculated values reflect the fact that the miscibility window observed for PVC/MHA and PVC/MEH blend systems was attributed to the effect of repulsion between different monomer units within the copolymer. To investigate the effect of specific interaction on the miscibility for these blend systems, an attempt was also made to describe the blend interaction parameter as a function of polar group concentration in the acrylate copolymer. The blend interaction parameter values exhibit a u-shaped curve as a function of the weight fraction of C?O group in the copolymer, and the lowest blend interaction parameter value appears at about 0.24 C?O weight fraction.     

Miscibility of poly(ϵ-caprolactone) and of poly(styrene-co-acrylonitrile) with poly(styrene-co-acrylic acid)

The miscibility of poly (?-caprolactone) (PCL) with poly (styrene-co-acrylic acid) (SAA) and of poly (styrene-co-acrylonitrile) (SAN) with SAA was examined as a function of the comonomer composition in the copolymers. For PCL/SAA blends it was found that PCL is miscible with SAA within a specific range of copolymer compositions. Segmental interaction energy densities were evaluated by analysis of the equilibrium melting point depression and application of a binary interaction model. The results suggest that the intramolecular repulsion in SAA copolymer plays an important role in inducing the miscibility. Additionally, the critical AA content in SAA for the blend to be homogeneous was predicted by correlating the segmental interaction energy densities with the binary interaction model. For SAN/SAA blends, it was also found that SAA is miscible with SAN within a specific range of copolymer compositions. From the binary interaction model, segmental interaction energy denisties between different monomer units were estimated from the miscibility map and were found to be positive for all pairs, indicating that the miscibility of the blends is due to the strong repulsion in the SAA copolymers.