Summary: Hydrogels, the elastic chains of which are constituted of a short central poly(1,3‐dioxolane) (PDXL) block surrounded by two hydrophilic poly(ethylene oxide) (PEO) blocks, were obtained by free radical homopolymerization of α,ω–methacryloyloxy PEO‐block‐1,3‐PDXL‐block‐PEO macromonomers. The central PDXL block is known to be sensitive to acidic degradation due to the presence of acetal groups. Once swollen to equilibrium, these hydrogels were characterized for their equilibrium swelling degree and their mechanical properties and network degradation studies were carried out.
Representation proposed for the breaking of a PEO‐block‐PDXL‐block‐PEO block copolymer. 相似文献
Intelligent hydrogels were first obtained by copolymerization of telechelic poly(1,3-dioxolane) (pDXL) with acrylic acid, acrylamide, N-isopropylacrylamide respectively. The synthesis and characterization of the networks were discussed. The swelling behavior of the hydrogel was dependent on the solubility parameter of the solvents and hydrogels. The networks containing polyacetal segments (pDXL) can degrade by acid in different solvents. DXL and few other cycle molecules measured by GC-MS analysis were formed after degradation. According to the degradation products, the polymerization mechanism can be testified. 相似文献
The onset of decomposition of poly(4-methyl-1,3-dioxolane) was lowered to 70°C by 0.1 wt% p -toluene sulfonic acid from 170°C in the absence of acid to produce more than 81% yield of monomer. Protonation forms cyclic oxonium ion followed by depolymerization. Minor products are isomers of hydroxymethyl-2-hydroxyl-2-methyl ethyl ether and bis(2-hydroxyl-2-methyl ethoxyl)methane from rearrangements of the oxonium ions. The first order rate constant of acidolysis of poly(4-methyl-1-1,3-dioxolane) is about 8.5 kcal mol?1, which is much smaller than about 17 kcal mol?1 for the acidolysis of poly(1,3-dioxolane). 相似文献
1,3-Dioxolane was polymerized in the presence of ethylene glycol in order to prepare α,ω-dihydroxylated polymers which, upon reaction with pluriisocyanates yielded networks swellable in water. The crosslinks were made of urethane groups, which are bulky and hydrophobic. In order to expand the scope of the networks that can be envisioned, we have studied the replacement of the two end-standing hydroxylic groups by unsaturated polymerizable groups. Several methods are presented which allow successfully the quantitative endowment of the polymer endings with methacryloyl- or styryl- or vinylether-type groups. α,ω-dihydroxylated poly(1,3-dioxolane) was also metallated and used as a macroinitiator for the polymerization of ethylene oxide: the α,ω-dihydroxylated triblock copolymer obtained is made of a central poly(1,3-dioxolane) block flanked by two poly(ethylene oxide) ones. Several methods are also shown to be efficient in the characterization of the hydroxylic end-standing functions of the polymer. 相似文献
Mean-square dipole moments 〈μ2〉0 for the (atactic) poly(4-methyl-1,3-dioxolane) chain [CH2OCH(CH3)CH2O? ] were determined from dielectric-constant measurements carried out on two fractions dissolved in benzene. Simple examination of the chain structure leads to the predictions that this polymer should have a significantly larger value of 〈μ2〉0 than poly(1,3-dioxolane) itself, but that 〈μ2〉0 should be nearly independent of stereochemical structure. The first expectation is confirmed by the experimental results obtained, and the second by calculated results based on rotational isomeric state theory. 相似文献
We report here a novel strategy for fabrication of SiO2 hollow microspheres with urchin-like structure based on templates from directed assembly of block copolymer, poly(2-cinnamoyloxyethyl
acrylate)-block-poly(acrylic acid-co-styrene) (PCEA-b-P(AA-co-Sty)). The structures of template from directed assembly of copolymers as well as that of as-obtained hollow SiO2 microspheres were observed by a combination technique of optical microscope, scanning electron microscope, and transmission
electron microscopy. It is shown that the hollow microspheres consist of aligned SiO2 “spines” radially growing from the core which are induced a favorable growth by the structures of the template from directed
assembly of PCEA-b-P(AA-co-Sty). The “spine” density of the hollow SiO2 sphere can be tuned by controlling the structure of the copolymer with different hydrolysis degree of poly(tert-butyl-acrylate) to PAA, and the ultimate size of the resultant SiO2 hollow sphere can be adjusted by solvent and temperature in the sol–gel process, etc. 相似文献
Four different routes for the production of polyacetal containing networks are described : (1) free radical copolymerization of α,ω-(meth)acrylate terminated polyacetals, (2) hydrosilylation reactions of α,ω-allyl terminated poly- (1,3-dioxolane) with a multifunctional silane, (3) modification of α,ω-hydroxy terminated poly(1,3-dioxepane) through reaction with 3-isocyanatopropyl-triethoxysilane and subsequent cross-linking under influence of H2O and (4) cross-linking of multifunctional hydroxy-terminated polyacetals by reaction with a diisocyanate. 相似文献
Polymerization of three cyclic ketene acetals: i.e., 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), 2-methylene-4-phenyl-1,3-dioxolane (MPDO) and 4, 7-dimethyl-2-methylene-1, 3-dioxepane(DMMDO) were carried out in the presence ofethyl α-bromobutyrate/CuBr/2, 2'-bipyridine respectively. The structures of poly(BMDO), poly(MPDO) and poly(DMMDO)were characterized by ~1H and ~(13)C-NMR spectra. The effects of monomer structure on the behavior of atom transfer freeradical ring-opening polymerization were investigated and the mechanism of controlled free radical ring-openingpolymerization was discussed. 相似文献
The preparation and characterization of the crystalline inclusion complexes between a polymeric guest, poly(1,3-dioxolane) (PDXL), and small-molecular hosts, cyclodextrins (CDs) are reported. It is observed that the polymer guest can form crystalline inclusion complexes with three kinds of cyclodextrins, which may be attributed to the high oxygen atom density in PDXL chain. The crystalline inclusion complexes were characterized with FTIR , TGA, X-ray diffraction, SEM, 1H NMR and 13C CP/MAS NMR spectroscopes. It was found that the crystalline inclusion complexes have higher temperature stability than the pure CDs. The X-ray powder diffraction patterns of the crystalline inclusion complexes proved that they have columnar structures. 13C CP/MAS NMR spectra of the crystalline inclusion complexes indicate that CDs adopt a more symmetrical conformation in the complexes, while pure CDs assume a less symmetrical conformation in the crystal without a guest inside their cavities. The morphology of the crystal was 相似文献
The cationic ring-opening polymerization of trioxane and 1,3-dioxolane was found to be initiated by CO+CIO4? groups on a carbon black surface, which were introduced by the reaction of COCI groups with AgCIO4. The activation energy of the ring-opening polymerization of trioxane was estimated to be 15.5 kcal/mol. In the polymerization system, poly(oxymethylene) and poly(1,3-dioxolane) formed were effectively grafted onto carbon black depending upon the propagation of these polymers from the carbon black surface; for instance, the grafting ratio of poly(oxymethylene) onto carbon black increased with an increase in conversion and went up to about 180%. Although the grafted chain of poly(oxymethylene) was subject to stepwise thermal depolymerization from the chain ends, the thermal stability of poly(oxymethylene)-grafted carbon black was improved by acetylation of hemiformal end groups. The molecular weight of ungrafted poly(oxymethylene) formed in the polymerization was determined to be 1.8–2.0 × 104. Furthermore, the copolymerization of trioxane with 1,3-dioxolane, styrene, and other comonomers initiated by CO+CIO4? groups and the thermal stability of these acetal copolymer-grafted carbon black were investigated. 相似文献
Synthetic procedures for the preparation of 1-bromo-3-butyn-2-one and 1,3-dibromo-3-buten-2-one are given. These compounds are prepared from 2-bromomethyl-2-vinyl-1,3-dioxolane, which can readily be prepared from 2-ethyl- 2-methyl-1,3-dioxolane. The synthetic routes are as follows: 2-bromomethyl-2-vinyl-1,3-dioxolane is converted to 2-(1,2-dibromoethyl)-2-bromomethyl-1,3-dioxolane. Double dehydrobromination with tBuOK affords 2-ethynyl-2-bromomethyl-1,3-dioxolane. Formolysis with formic acid gives 1-bromo-3-butyn-2-one. Deacetalized 2-bromoethyl-2-vinyl-1,3-dioxolane was treated with Br2 and Li2CO3/12-crown-4 in tetrahydrofuran to give 1,3-dibrom-3-buten-2-one in moderate yield. 相似文献
2-Methyl-2-phenyl-4-methylene-1,3-dioxolane ( IIa ), 2-ethyl-2-phenyl-4-methylene-1,3-dioxolane ( IIb ), 2-phenyl-2-(n-propyl)-4-methylene-1,3-dioxolane ( IIc ), 2-phenyl-2-(i-propyl)-4-methylene-1,3-dioxolane ( IId ), 2-(n-heptyl)-2-phenyl-4-methylene-1,3-dioxolane ( IIe ), 2-methyl-2-(2-naphthyl)-4-methylene-1,3-dioxolane ( IIf ), and 2,2-diphenyl-4-methylene-1,3-dioxolane ( IIg ) were prepared and polymerized in the presence of a radical initiator. IIa–IIf were found to undergo vinyl polymerization with ring-opening reaction accompanying the elimination of ketone groups in bulk. IIg was found to undergo the quantitative ring-opening reaction accompanying the elimination of benzophenone in solution to obtain polyketone without any side reaction. 相似文献
A series of thermosensitive and fast-response poly(vinyl alcohol) (PVA)/poly(N-isopropylacrylamide) (PNIPA) hydrogels were prepared by incorporating PVA into cross-linked PNIPA to form a semi-interpenetrating polymeric network (semi-IPN). Compared to the conventional PNIPA hydrogel, the semi-IPN hydrogels thus prepared exhibit significantly faster response rates and undergo full deswelling in 1 min (lose about 95% water within 1 min) when the temperature is raised above their lower critical solution temperature, and have larger equilibrium swelling ratios at room temperature. These improved properties are attributed to the incorporation of PVA, which forms water-releasing channels and results in increased hydrophilicity, into the PNIPA hydrogel networks. 相似文献
The catalytic reduction of acetophenone, methyl α-acetamidocinnamate, and dimethyl itaconate with alcohol-modified sodium borohydride was studied in the presence of complexes CoCl2·L2 (L2 are chiral C2-symmetric diamines: (4S,5S)-2,2-dimethyl-4,5-bis(aminomethyl)-1,3-dioxolane, (4S, 5S)-2,2-dimethyl-4,5-bis(methylaminomethyl)-1,3-dioxolane, (4S, 5S)-2,2-dimethyl-4,5-bis(dimethylaminomethyl)-1,3-dioxolane, and (4S, 5S)-2,2-dimethyl-4,5-bis(diphenylaminomethyl)-1,3-dioxolane). The maximum enantiomeric excess of (S)-1-phenylethanol was 24%, that of dimethyl α-methylsuccinate was 38%.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 342–347, February, 2005. 相似文献
Thermosensitive membranes were prepared by radiation-induced graft copolymerization of monomers on PET fabrics. A binary mixture of N-isopropyl acrylamide (NIPAAm) and acrylic acid (AA) was grafted on polyester fabric as a base material to introduce thermosensitive poly(N-isopropyl acrylamide) pendant chains having LCST slightly higher than 37 °C in the membrane. The influence of ferrous sulfate, radiation dose and monomer composition on the degree of grafting was studied. The structure of the grafted fabric was characterized by thermogravimetric analysis, differential scanning calorimetry and scanning electron microscopy. The thermosensitive nature of the fabric was monitored by swelling at different temperatures. The graft copolymerization of AA with NIPAAm enhanced the LCST of the resultant membrane to ∼37 °C. The moisture vapor transmission rate (MVTR) and air permeability of the fabric decreased slightly, may be due to the slight blocking of the fabric pores. The immobilization of tetracycline hydrochloride as the model drug and its release characteristics at different temperatures were monitored. 相似文献