Polyurethane microspheres were prepared by polyaddition of ethylene glycol (EG) and tolylene-2,4-diisocyanate (TDI) at 60 °C in cyclohexane as the organic dispersion medium, in the presence of dibutyl tin dilaurate (DBTDL) as catalyst and poly(styrene)-b-poly(ethylene oxide) block copolymers or P-hydroxypolystyrenes as the steric stabilizers. Different parameters such as the manner of addition of the reactants, the concentration, and length of the stabilizer were varied to tune the polyurethane particle size. When P-OH polystyrenes of low molar mass ([`(M)]n\bar M_n =2000-3000 g mol-1) were used as the reactive stabilizers of dispersion, polyurethane particles in a tunable size range of 0.2-5 µm with a narrow size distribution (span = 0.7) could be prepared. 相似文献
The elaboration in a dispersed organic medium of calibrated polyurethane particles with a core-shell structure is presented in this paper. The objective could be achieved by using a series of reactive steric stabilizers of the type ω-(OH)x-poly(n-butyl acrylate), -polystyrene, -polysiloxane or -polybutadiene (x=1 or 2) that play the role of surfmers during the polyaddition reaction between ethylene glycol and tolylene-2,4-diisocyanate, in cyclohexane as a dispersant medium. The final size of the polyurethane particles (0,5-10 μm) was found to be a function of the steric stabilizer characteristics (nature, molar mass and concentration) and of the addition procedure of the different reactants. These novel particles constituted of a polyurethane core and various shells depending on the stabilizer used exhibit specific and original properties. 相似文献
A relatively high-molecular-weight polyurethane based on MDI and ethylene glycol was prepared and characterized. This polymer was metalated with sodium hydride in N,N-dimethylformamide (DMF) at about 0°C. Metalation was confirmed principally by spectroscopic identification of the N-methyl derivative obtained by coupling the metalated polymer with methyl iodide. Under appropriate reaction conditions the metalated polyurethane was used for the anionic graft polymerization of the reactive monomers acrylonitrile and ethylene and propylene sulfides. Attempted anionic graft polymerizations with other monomers, including styrene and ethylene and propylene oxides, were unsuccessful. The polyurethane grafted with acrylonitrile was separated by fractionation from accompanying small amounts of polyacrylonitrile, a low-molecular-weight homopolymer. One sample of polyurethane grafted with acrylonitrile was identified by microanalysis, IR, NMR, and increase in weight and was also characterized by differential thermal analysis. 相似文献
Summary: The free‐radical addition of ω‐functional mercaptans to the vinyl double bonds of 1,2‐polybutadiene‐block‐poly(ethylene oxide) copolymers was used for modular synthesis of well‐defined functional block copolymers. The modification reaction proceeds smoothly and yields quantitatively functionalized block copolymers (1H NMR and FT‐IR spectroscopy) without disturbing the molecular‐weight distribution of the parent copolymer (PDI < 1.09, size exclusion chromatography).
The modular synthetic pathway towards the functional block copolymers reported here. 相似文献
A mixture of homopolymer and graft copolymer was obtained by adding the monomer at 0°C to the polylithiodiene solution. Styrene, methyl methacrylate, and acrylonitrile were used as the monomers. Polylithiodienes were prepared by the metalation of diene polymers, i.e., polybutadiene or polyisoprene, with the use of n-butyllithium in the presence of a tertiary amine (N,N,N′,N′-tetramethylethylenediamine) in n-heptane. The graft copolymers were separated by solvent extraction and were confirmed by turbidimetric titration and elementary analysis. Oxidation of the polybutadiene–styrene grafts revealed that the molecular weight of the side chains was the same as the molecular weight of the free polystyrene formed. The grafting efficiency and grafting percentage were studied for polybutadiene–styrene graft copolymers prepared under various conditions. 相似文献
Well-defined hydroxy end-functionalized poly(n-butyl acrylate)s (PBA-OH and PBA-(OH)2), were prepared by atom transfer radical polymerization (ATRP) and used as reactive stabilizers for the preparation of polyurethane in dispersed medium. PBA-OH was obtained by end-capping the growing poly(n-butyl acrylate) chains with allyl alcohol added in excess at the end of the polymerization. The two hydroxyl functions of PBA-(OH)2 were fixed at one end of the poly(n-butyl acrylate) chains either by initiation or by chain-end functionalization reactions. The latter were protected under the form of cyclic acetal and attached either to the initiator bearing a secondary bromine or to the terminating agent carrying a poorly reactive vinylic unsaturation. PBA-OH and PBA-(OH)2 have been successfully used as reactive stabilizers (surfmers) to prepare core-shell polyurethane particles in dispersed medium. The final particle size was found to be very much dependent to parameters such as the molar mass, concentration and valence of the reactive stabilizer as well as the manner of addition of the reactants during the procedure. 相似文献
A series of α, ω–bishydroxyl terminated PDMS, hydroxypoly(ethylene oxide) propyl–b–polydimethylsiloxane–b–propyl hydroxypoly(ethylene oxide) (HPEO–PDMS–HPEO) was prepared by a hydrosilation reaction of monoallyloxy substituted poly(ethylene oxide) with α,ω–bishydrogen terminated PDMS (HPDMS) that obtained via acid–catalyzed ring–opening polymerization of octamethylcyclotetrasiloxane with 1,1,3,3–tetramethyldisiloxane. Chloroplatinic acid was employed as the catalyst of hydrosilation. The molecular weight of HPEO–PDMS–HPEO could be controlled easily by varying the chain length of HPDMS. FTIR and 1H–NMR spectroscopy were used to identify the structure of HPEO–PDMS–HPEO and HPDMS. The conversion of Si–H bond to Si–C bond was affected by the catalyst amount, reaction time and temperature. It was found that the optimum condition of hydrosilation reaction was the catalyst amount of 22 μg/g and 5 h time at 100°C. Synthesized HPEO–PDMS–HPEO showed good storage stability at ambient temperature. Urethane reaction of OH and NCO group revealed that HPEO–PDMS–HPEO was more reactive toward to diisocyanate than α, ω –bishydroxylbutyl terminated PDMS. 相似文献
A soluble polyurethane was synthesized by a reaction of OH-telechelic, 1,2-rich, low-molecular-weight polybutadiene with toluene 2,4-diisocyanate. To the pendent vinyls of the polybutadiene blocks of the polyurethane, a sterically hindered phenolic antioxidant bearing a sulfanyl group (i.e., 6-sulfanylhexyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate) was added by a free-radical mechanism (in varying degrees of conversion). The self-stabilized polyurethane thus formed, bearing the antioxidant structures as side chains, was mixed in varying concentrations with the original (unstabilised) polyurethane and the thermo-oxidative stability of the mixtures was evaluated by DSC in air. The antioxidant effect of the polymeric stabilizer on the oxidative stability of polyurethane, expressed as the oxidation onset temperature, is approximately the same as that of a low-molecular-weight analogue, the commercial octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate (Irganox 1076), as related to the same molar concentration of the phenolic moiety, but the former is superior to the latter due to its ability to persist in the matrix. In both cases, the onset temperature of oxidation increases with increasing mole ratio of the phenolic structure and the total butadiene units in the mixture. 相似文献