In order to enhance the delivery of drugs with limited absorption due to poor solubility/dissolution, approaches are being developed to improve the dissolution rates and solubility of drug molecules. These approaches include identification of water-soluble salts of parent drugs, preparation of stable amorphous drug formulations, inclusion of solubility-enhancing agents in the dosage form, and particle size reduction. Technologies to reduce drug particle size to sub-micrometer range are being applied to product development more frequently. Electrospinning is being considered as one of the technologies which can produce nanosized drugs incorporated in polymeric nanofibers. In vitro and in vivo studies have demonstrated that the release rates of drugs from these nanofiber formulations are enhanced compared to those from original drug substance. This technology has the potential to be used for enhancing the oral delivery of poorly soluble drugs.

The radiopacifying organobismuth monomer p-styryldi(p-tolyl)bismuth was synthesized in 40% yield by means of a three-step process using 4-bromotoluene, 4-bromostyrene and bismuth trichloride as starting compounds. The product is a crystalline solid of at least 95% purity, unlike the earlier reported styryldiphenylbismuth which could only be obtained in a very impure form. Radical or anionic polymerization yields a soluble homopolymer, and copolymers were made with styrene and methyl methacrylate. The products were characterized by standard techniques. Data are reported on their solubility, blending and radiopacity. The latter property, expressed in mm of aluminium per mm resin, is a linear function of the molar bismuth concentration in the polymer specimens.

Thermotropic liquid crystalline polymers containing bis(p-oxybenzoyl terephthalate) (Triad) mesogen units linked by flexible polymethylene units were prepared by melt and solution polymerization reactions. Analogous Triad polymers based on a central isophthalate group were also prepared, but these polymers, which contained non-linear rigid segments, did not exhibit liquid crystalline behaviour. Copolymers composed of a mixture of linear and non-linear Triad units were also evaluated. In addition, a series of random Triad copolymers that contained butylene terephthalate (BT) units were also synthesized in solution. The liquid crystalline behaviour of these copolymers depended on the relative number of BT moieties present.

A series of novel thermotropic block copolyesters based on poly(tetramethylene 4,4'-(terephthaloyldioxy)dibenzoates) (Triad-4) and poly(butylene terephthalate) (PBT) were synthesized by high-temperature polycondensation in solution to minimize sequence randomization by transesterification. Three different schemes were examined in order to facilitate the systematic variation of block length and block content. All reaction schemes predict the formation of tetramethylene 4-(terephthaloyloxy)benzoate (Diad-4) moieties in the block copolymers. Diad-4 homopolymer and its block copolymers with PBT were synthesized and characterized and were compared to Triad-4-co-PBT block copolymers. The compositions of all block copolymers were determined from H-1 NMR spectroscopy. The DSC thermogram of a typical block copolymer revealed the presence of two major melting transitions, corresponding to the separate melting of PBT and Triad-4 domains. During the cooling cycle separate and distinct crystallization exotherms were also observed. Polarizing optical microscopy showed that all block copolymers were liquid crystalline and exhibited a nematic texture.

Alternating, block, and random copolymers of the rigid moiety terephthaloyl bis(4-oxybenzoyl) (Triad) with-either ethylene terephthalate (ET) or butylene terephthalate (BT) flexible units were prepared by polycondensation in solution. The Triad mesogen was incorporated using either terephthaloyl bis(4-oxybenzoyl chloride) (TOBC) or alpha,omega-bis[(4-hydroxybenzoyl)oxy]butane (T4). Use of the latter monomer resulted in the formation of terephthaloyl (4-oxybenzoyl) (Diad) moieties in the copolymer. The block copolymers exhibited nematic liquid crystalline texture, whereas the behavior of the random and alternating copolymers depended on the flexible alkylene terephthalate content and method of synthesis.

Carbamoyl phosphonate derivatives of methacrylic acid and alpha-methyl styrene were synthesized in good yield by reacting dimethyl and diethylphosphite with isocyanato ethylmethacrylate (IEM) or with meta-isopropenyl-alpha,alpha-dimethylbenzylisocyanate (m-TMI). The IEM derivatives yield soluble homopolymers with common radical initiators. The m-TMI carbamoyl phosphonates were copolymerized with styrene and with acrylates yielding soluble materials with better than 50 mol % incorporation of the phosphonate monomer. The side chain carbamoyl phosphonate group drastically lowers the T(g) relative to those of the parent polymers. Thermogravimetric studies suggest the NHC (O) - P (O) (OR)2 bond to be stable to about 225-degrees-C. The radiopacifying salt UO2(NO3)26 H2O yields transparent films with the phosphonate-containing polymers. The T(g) increases with uranyl content.

Organobismuth monomers containing the Ph3Bi moiety were synthesized and polymerized to obtain homogeneous X-ray constrast polymers. Styryldiphenylbismuth (I), α-methylstyryldiphenylbismuth (II), tris(α-methylstyryl) bismuth (III) and (p-diphenylbismuthphenyl)vinyldimethylsilane (IV) were prepared via a Grignard reaction with BiPh2Cl. Monomers I and II are contaminated with significant amounts of Ph3Bi and divinyl compounds. Monomer I can be homo- and copolymerized radically and anionically, II can only be copolymerized, while IV did not polymerize at all. In anionic polymerization the carbanion also attacks the PhBi bond of I and II. Glass transition temperatures were determined as a function of bismuth comonomer content for styrene and acrylate copolymers, and the thermal decomposition was also studied. Radiopacities in millimetres of aluminium per millimetre of polymer were found to be proportional to the molar bismuth content of the transparent copolymer specimens.

Styrvl- and alpha-methylstyryldiphenylbismuth (I and II, respectively), and styryl and alpha-methylstyryltriphenyllead and the two corresponding tin-containing monomers (III, IV, V and VI, respectively) were synthesized. Compounds III through VI were obtained pure, but I and II contain substantial quantities of Ph3Bi and di- and tri-vinyl derivatives. Homopolymers of I, III and V, as well as copolymers with methyl acrylate were synthesized radically. Monomers III, V, and VI yielded narrow MWD polymers with anionic initiators such as the potassium salt of the alpha-methylstyrene dimer carbanion in THF at -80-degrees-C, while I gave a broad, bimodal MWD. Monomers II and IV did not polymerize under these conditions due to side reactions with the initiator. Glass transition temperatures, thermal stabilities and radiopacities of a number of the polymers were determined.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermal aging of tetraalkyl ammonium doped polyacetylenesFrancis Ignatious and Claude MathisCite this: Macromolecules 1990, 23, 1, 70–77Publication Date (Print):January 1, 1990Publication History Published online1 May 2002Published inissue 1 January 1990https://doi.org/10.1021/ma00203a014Request reuse permissionsArticle Views69Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (934 KB) Get e-Alertsclose Get e-Alerts

The doping kinetics of Shirakawa polyacetylene (PA), involving bulky R4N+ like Bu4N+, Hep4N+ and Dodec4N+, was undertaken. From the drastic influence of dopant concentration and film thickness on the kinetics, the interfibrillar diffusion of the dopant was identified as the rate-limiting step. However, a minimum value of 10−15cm2s2−1 was estimated for the intrafibrillar diffusion constant. The relaxation of the narrow electron spin resonance line, produced during a short heterogeneous doping of cis-PA, was critically examined in the case of each of the above cations. The relaxation times were found to decrease in the order Bu4N+ < Hep4N+ < Dodec4N+.

The kinetics of the chemical insertion of tetraalkylammonium cations into Shirakawa polyacetylene films is entirely controlled by the interfibrillar diffusion of the dopant. The maximum doping level Ymax achieved at the end of the reaction is limited not only by the redox potential of the reductor used, but also by the size of the inserted cation and the chemical stability of the doped sites. Homogeneously doped films can be prepared by chemical doping using thermodynamic control of the doping level, or by an ion-exchange technique.

The maximum conductivities of cis and trans Shirakawa polyacetylene doped with three different tetra-alkyl ammonium doping agents are reported. Utilizing one system, the conductivity was investigated as a function of the cation size. A linear relationship between log σ and the size of the R 4 N + ions is deduced. The influence of THF on the measured conductivities was examined and compared to the effect of the solvation of the cations in the alkali-metal-doped PA. The study was extended to other solvents like DMF, DME, dioxane, cyclohexane, etc. The temperature dependence of the conductivity of films doped with various R 4 N + cations was determined and the activation energies were calculated. They were found to be much higher than those of the alkali-metal-doped PA having the same dopant concentration.

The different methods of chemically inserting organic cations in polyacetylene are discussed. The most efficient among them was exploited quantitatively to insert tetraalkyl ammonium ions (R4N+) of well defined size. The influence of the size of (R4N)+ ions on the maximum doping levels, room temperature conductivities and ESR band widths of the doped products was demonstrated.