Investigation of the effect of the α-CH3-group on low-temperature postpolymerization in devitrifying matrices leads to the following conclusions. 1. The low-temperature postpolymerization in supercooled alcohol solutions (Tg ~ 102 K) is quite efficient with acrylic monomers. Inactivity of their methacrylic analogues under these conditions is attributed to steric screening of the unpaired electron in the growing radicals. 2. As the temperature is raised and the CH3-group vibration intensity increases, the screening effect fades. Thus in devitrifying water-alcohol solutions of NaAA and NaMAA, at higher temperatures the postpolymerization is efficient in both cases. Data on copolymerization of NaAA and NaMAA indicate that at ~ 170 K the steric limitations due to the CH3-group are eliminated. 3. In a glycerine matrix (), all the acrylic and methacrylic monomers studied show efficient polymerization over virtually the same temperature range. It is concluded that the a-CH3-group in methacrylic monomers appreciably affects their polymerization activity only at low temperatures, where steric screening of the growing polymer radical becomes important. 相似文献
A comparative study of mechanical and dielectric relaxation behaviour in the glassy region of some acrylic polymers containing 1,3-dioxane rings in the side chain is reported. Earlier results for similar polymers containing cycloaliphatic rings are used to interpret the results obtained. This study suggests that simple mechanisms based on chair-to-chair inverse conformational transitions are not able to explain in a unified way the responses of these polymers in the glassy region to mechanical and electric perturbation fields. 相似文献
The kinetics of high-energy radiation initiated polymerization of acrylate and methacrylate monomers were studied in dilute cyclohexane solutions. The absorption spectra of the intermediates were obtained by pulse radiolysis with optical detection. In solutions of acrylates at longer times after the pulse the presence of oligomer radicals was observed. In solutions of methacrylates the beginning of the oligomerization reaction was detected at higher monomer concentrations. From the kinetic curves the rate coefficients of termination were calculated. 相似文献
The cationic polymerization of 2-vinyl-1,3-dioxane initiated with triethyloxonium tetrafluoroborate was studied with particular emphasis on elucidation of the structure of the polymer. The polymer was a light yellow powdery material with a molecular weight of several thousands which was soluble in most organic solvents. The infrared and NMR investigations on the polymer, together with chemical analyses, showed that the polymer consisted of the three structural units I, II, and III, the contents of which were estimated to be 5–10%, 20–25%, and 65–70%, respectively. The formation of the structural units I and II was discussed in detail. 相似文献
The synthesis and structure determinations of (2,2-dimethyl-1,3-dioxolan-4-yl)-methyl acrylate, 4-(2,2-dimethyl-1,3-dioxolan-4-yl)methyl itaconate, and [(2,2-dimethyl-1,3-dioxolan-4-yl)methyl] methyl fumarate are described. Reactivity ratios in the copolymerization of these monomers with other comonomers are reported and the Alfrey-Price Q and e values calculated. The post-polymerization study of the effects of ultraviolet light and heat on these polymers and copolymers is presented. The 1,3-dioxolane group when appended to the polymer chain performs as an internal ultraviolet sensitizer. A mechanism is offered to explain the crosslinking behavior of these polymers when treated with ultraviolet light. 相似文献
Ten fluoromonomers of structure (RFO)2P(O)OCH2CH2OC(O)CRCH2 were made in 30-64% yield by treating the chloridates (RFO)2P(O)Cl with HOCH2CH2OC(O)CRCH2 in chloroform in the presence of triethylamine [RF=CF3CH2, C2F5CH2, C3F7CH2, C4F9CH2, C4F9CH2CH2 or C6F13CH2CH2; R H or Me]. The chloromonomer (CCl3CH2O)2P(O)OCH2CH2OC(O)CHCH2 was obtained analogously in 29% yield. Polymerisation of the acrylate monomers, but not the methacrylate monomers, could be effected using α-azoisobutyronitrile as a radical initiator. Acrylic polymers having CF3CH2O, CCl3CH2O and C6F13CH2CH2O side-chains were obtained as translucent rubbers. Specimens of cotton fabric were treated with solutions of the polymers, and average water and oil repellency ratings measured. Fabric coated with the polymer with the C6F13CH2CH2O side-chain afforded protection from penetration of the test liquids. Treated fabrics were subjected to the limiting oxygen index (LOI) test according to BS EN ISO 4589-2 (1999): this test determines the point at which a material just burns in a volumetric flow of oxygen and nitrogen. The treated fabrics were more fire-resistant (LOI 22-29%) than the untreated fabric (LOI 18%). Fabric coated with the CCl3CH2O-based polymer can be considered fire-retardant (LOI 29%). The fluoromonomers were tested for anti-acetylcholinesterase activity and were found to be poor enzyme inhibitors; they are predicted to possess low acute toxicity. 相似文献
A clear effect of Lewis acids, such. as scandium trifluoromethanesulfonate [Sc(OTf)3], on stereocontrol during the radical polymerization of a designed monomer, benzyl α-(methoxymethyl)acrylate was found. This Lewis acid also influenced the stereochemistry in the radical polymerization of methyl methacrylate giving a less syndiotactic and more isotactic polymer, although many Lewis acids were not effective. A catalytic amount of Lewis acids, such as Y(OTf)3 and Yb(OTf)3, also significantly enhanced isotactic-specificity during the radical polymerization of acrylamide and its derivatives, N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide. Obvious solvent and temperature effects on tacticity were observed in these polymerizations, and poly(NIPAM) with >80% triad isotactic content has been obtained in the presence of Lewis acids. 相似文献
The polymerization of acrylic and methacrylic esters of 2-allyphenol with different anionic, cationic and coordination catalysts was studied. The polymerization occurs exclusively or predominantly through (meth)acrylic C?C double bonds in all the studied cases. With anionic catalysts the allylic groups are not polymerizable and the polymers have linear structure. Polymerization with catalysts based on dialkylaluminum chloride (alone or associated with some metal salts) yields soluble or partially crosslinked polymers, depending on the reaction conditions. The crosslinking is due to the participation of allylic groups in the polymerization reactions. Copolymers of acrylic and methacrylic esters of 2-allylphenol with styrene, acrylonitrile, methyl methacrylate, N-vinylcarbazole and 1,3-pentadiene were synthesized by copolymerization in the presence of anionic catalysts and of systems based on dialkylaluminum chloride. 相似文献
Vinyl-type monomers containing the pyrrole ring, such as 2-vinylpyrrole (2-VPyrr), N-(pyrrol-2-yl)methylacrylamide (PMA), N-methyl, N-(pyrrol-2-yl)methylacrylamide (MPMA), 2-allylpyrrole (2-AP), β-(pyrrol-1-yl)ethyl vinyl ether (PEVE), 2-diallyl-aminomethylpyrrole (DAMP), and 3-(2-pyrrolylmethyleneimino)propene-1 (PIP) were synthesized by various reactions involving characteristic properties of the pyrrole ring. Radical homopolymerizations and copolymerizations of these monomers were studied. In the homopolymerization of conjugated monomers such as 2-VPyrr and PMA, chain transfer to the pyrrole-containing monomer was remarkable but not degradative. The copolymerization parameters, that is, the values of r1, r2, Q1, and e1 of 2-VPyrr, were determined to be 0.066, 0.69, 5.53, and ?1.36, respectively in the copolymerization of 2-VPyrr (M1) with MMA (M2). The Q and e values of the monomers containing a heteroaromatic ring such as 2-vinylpyrrole, 2-vinylfuran, and 2-vinylthiophene were evaluated by the molecular orbital theory. The e value of PMA was found to be negative (?0.64) in the copolymerization with styrene, although e for acrylamide derivatives is generally positive. This may be explained by the intermolecular hydrogen bonding between the carbonyl group and NH group of PMA. That is, attraction or polarization of π-electrons in the vinyl group of PMA is weakened by such hydrogen bonding. From the results of copolymerization of 2-AP with various comonomers, the comonomers could be classified into three categories: class a monomers, in which both Q and e values are largely positive, can copolymerize with 2-AP; class b monomers, having small e values, homopolymerize and can not copolymerize with 2-AP; class c monomers, in which both Q and e values are small. The Q and e values of the comonomer must be largely positive in order to permit copolymerization with an allyl-type monomer. 相似文献
The synthesis is described of four new chiral liquid crystalline monomers (M2–M5) and their corresponding side‐chain homopolysiloxanes (P2–P5) containing menthyl groups. Chemical structures were characterised using FT‐IR or 1H NMR spectra, and specific optical rotations were evaluated with a polarimeter. The phase behaviour and mesomorphic properties of the new compounds were investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy, UV/visible/NIR spectrocopy and X‐ray diffraction. The monomers and homopolymers with more aryl segments showed noticeably lower specific optical rotation value. The monomers M2–M5 formed a cholesteric or blue phase when a flexible spacer was inserted between the rigid mesogenic core and the terminal menthyl groups by reducing the steric effect. M2–M5 revealed enantiotropic cholesteric phase. Moreover, M2 also exhibited a monotropic smectic A (SmA) phase, and M4 also exhibited a cubic blue phase on cooling. The selective reflection of light shifted to the long wavelength region with increasing rigidity of the mesogenic core for M2–M5. P2–P5 exhibited SmA phases, and the mesogenic moieties were ordered in smectic orientation with their centres of gravity in planes. Melting or glass transition temperature and the clearing temperature increased, and the mesophase temperature range widened with increasing rigidity of the mesogenic core. 相似文献