Differential scanning calorimetry (d.s.c.) measurements were performed on a series of ethylene-vinyl chloride (E–V) copolymers for the purpose of studying the dependence of their thermal transitions upon their microstructure. The method of preparation, via reductive dechlorination of poly(vinyl chloride) with tributyltin hydride, resulted in a series of E–V copolymers differing only in comonomer content, sequence distribution and stereoregularity of adjacent V units. Chain length distribution and branching frequencies were identical for each member of the series.Extrapolation of glass transition temperatures, Tg, measured for our E–V copolymers to pure polyethylene (PE) predicted a Tg = ?85°C ± 10°C for amorphous PE. E–V copolymers with greater than 60 mol% E units exhibited melting endotherms characterized by melting temperatures from 20°C to 128°C and degrees of crystallinity from 12 to 63%. Observed melting temperatures were plotted against the composition of the E–V copolymers and compared to Flory's equation for melting point depression of random copolymers containing one crystallizable and one non-crystallizable monomer unit. The melting point depressions observed for our E–V copolymers were in agreement with Flory's theory, if the CH2CH2 moiety is considered to be the crystallizable unit and theCHmoiety is assumed to prevent the CH2CH2 units attached on either side from being incorporated into the crystal. This implies that among all possible comonomer triad sequences only the EEE triad may crystallize. Therefore only those E–V copolymers with average lengths of consecutive E units greater than 2 exhibit crystallinity. 相似文献
The results of adiabatic compressibility measurements for two copolymers, acrylic acid-vinyl pyrrolidone (AA—VP) and N-dimethylaminoethyl methacrylate-vinyl pyrrolidone (DAM—VP), in three different solvents, namely, water, methanol, and dioxane, have been described. The molecular weight of copolymers was determined by the light scattering method and the IR and NMR spectra of the polymers and copolymers were examined to establish that the alternating acrylic acid–vinyl pyrrolidone and N-dimethylaminoethyl methacrylate–vinyl pyrrolidone structure exists in the copolymers. The AA—VP copolymer behaves as a slightly weaker acid than the homopolymer of acrylic acid, while DAM—VP copolymer is very feebly basic and has the same strength as that of the homopolymer of N-dimethylaminoethyl methacrylate. The reduced viscosity for the two copolymers in aqueous solution is very low (~0.08 dL/g for AA—VP copolymer). In methanol solution AA—VP and DAM—VP copolymers show a decrease of øK°2 and øV°2 by 61.6 × 10?4 cc/bar/mol and 8.0 cc/mol, and 191.0 × 10?4 cc/bar/mol and 20.0 cc/mol, respectively, over that of the values of aqueous solution. The void space around the solute is smaller in methanol than in water, and accordingly this decrease has been attributed to geometric effect. Only one copolymer, DAM—VP is soluble in dioxane, and the values are seen to have increased in this solution by 71.0 × 10?4 cc/bar/mol and 18.7 cc/mol, respectively, compared to the values obtained from aqueous solution. The experimentally determined øK°2 and øV°2 for AA—VP and DAM—VP copolymer are 0.6 × 10?4 cc/bar/mol, and 102.4 cc/mol and ?61.0 × 10?4 cc/bar/mol, 94.4 cc/mol, respectively, in aqueous solution, and ?12.0 × 10?4 cc/bar/mol, 211.0 cc/mol and ?203.0 × 10?4 cc/bar/mol, 191.0 cc/mol, respectively, in methanol solution. In dioxane solution the values for DAM—VP copolymer are 59.0 × 10?4 cc/bar/mol and 229.7 cc/mol, respectively. These experimentally determined values for AA—VP copolymer show an increase by 0.04 × 10?4 cc/bar/mol, 4.4 cc/mol and 28.3 × 10?4 cc/bar/mol, 8.0 cc/mol in aqueous and methanol solution, respectively, compared to calculated values determined on the basis of no interaction between acid and the pyrrolidone group. In contrast, the DAM—VP copolymer shows a decrease of 27.6 × 10?4 cc/bar/mol and 10.3 cc/mol, 149.3 × 10?4 cc/bar/mol and 20.2 cc/mol, and 23.0 × 10?4 cc/bar/mol and 4.1 cc/mol in aqueous, methanol, and dioxane solutions, respectively. In aqueous solution these differences between calculated and observed values have been attributed to a change of water structure around the copolymer chain. A similar effect is responsible for the difference of the values in the methanol solution also. In the dioxane solution the difference is rather small, and the solvent structure has probably not altered much due to the presence of the DAM unit in the chain. 相似文献
The surface tensions of fluorinated polysiloxanes prepared by hydrosilylation of unsaturated perfluoroalkyl esters derived from undecylenic acid [CH2?CH? (CH2)8? COO? CH2? CH2? RF, with RF = C6F13, C8F17, and C8F17? (CH2)10COO? CH2? CH2? CH?CH2] by methylhydrodimethylsiloxane copolymers of various Si? H contents have been measured. The critical surface tensions, γc, and the solid surface tensions, γDs, were deduced from n-alkane and water contact angle data. They decrease as the perfluoroalkyl graft content of the copolymers increases. Some of them, which are in the range of the lowest surface tension fluoro polymers known, are observed when the fluorinated segments are self-organized at the interface, i.e. when the polymers are mesomorphous or crystalline at room temperature. 相似文献
Comb-branched copolymers containing ethylene amine side chains of the general structure -NH(CH2CH2NH)x? H with x=1, 2, 3 and 4, were prepared by the reaction of poly(monoalkyl-codialkyl itaconate)s, using an excess of the appropriate diamine in the presence of dicyclohexylcarbo-diimide. Incorporation of ethylene amine units in the itaconate copolymers resulted in an increase in the glass transition temperature (Tg) and in the complex modulus of the modified copolymers above Tg. Both effects were proportional to the ethylene amine content of the copolymers. Chemical modification also occurred when samples were heated to about 450 K when imide formation was detected. 相似文献
The effect of annealing at 135°C for 5 hours on the tensile properties of mechanically mixed and then injection molded high density polyethylene (HDPE) and polypropylene (PP) blends has been investigated. Both the tangent elastic modulus and the tensile strength at yield exhibit a non-linear behavior versus blend composition with a minimum of properties typical for incompatible blends. Annealing substantially improves mechanical properties of pure components and blends (20 percent increase in the yield strength of pure components and blends and the modulus of pure components, and ~40 percent increase in the modulus of 50/50 blends) but the property behavior versus composition is still nonlinear. Scanning electron microscopy studies of fracture surfaces of blends seems to indicate some improvement in bonding between phases as a result of annealing, Both the elastic modulus and yield strength fit extremely well to the modified “rule of mixtures” equation in the general form: Mb = MPEφPE + MPPφPP + ΔMPE/PPφPEφPP where Mb is the blend property, MPE and MPP are properties of pure PE and PP components, φPE and φPP are weight fractions of PE and PP, and ΔMPE/PP is the interaction term being a measure of the deviation from simple additivity. 相似文献
Several different series of rigid and flexible polyesters with main chain liquid crystalline units were prepared and their properties were examined in relation to their structures. The first group of polymers were rigid aromatic copolyesters with mesogenic groups based on either chloro or methyl hydroquinone terephthalate units combined with varying amounts of different types of bisphenol terephthalate units The bisphenol comonomers used contained the structure: in which X was none, ? C(CH3)2? , ? CH2? , ? O? , ? S? , and ? So2? . It was observed that the bisphenols with the bulkier X group were more efficient in destroying thermotropic liquid crystallinity of the resulting copolymers. The second group of polymers studied were flexible polyesters consisting of various types of mesogenic units which were connected together by different lengths of polymethylene flexible spacers. The liquid crystalline behaviours of these polymers, particularly their transition temperatures, were correlated with their structures. A brief review of previous studies on the synthesis of thermotropic liquid crystalline polyesters is included. 相似文献
From a consideration of the work required for expansion of a liquid, the following relationship between viscosity η, pressure P and temperature T is put forward. For unassociated liquids with molecules which are not too large, V* is taken as the parachor, log10 (η* in Ns/m2) is ?3.88, P* is 8.58 × 106 N/m2, R is the gas constant, and T* is a constant characteristic of each liquid. The equation can be applied to polymeric liquids if V* and η* are taken as disposable constants. For example, for polystyrene V* is found to be 3 × 10?3 m3 mol?1 and log10 (η* in Ns/m2) to be 3.4 log10M?w ?10.2 where M?w is the weight-average molecular weight (kg/mol) from 5 kg/mol upwards. In the equation, the same constants serve for the variation of viscosity with pressure and with temperature. The viscosity under a high pressure can therefore be estimated from viscosities all measured at normal pressures but at different temperatures. The viscosities of a number of polymers have been measured over a range of temperature and pressure and the results support the equation. Support is found for the view that segments are involved in the flow of polymeric liquids and V* gives a measure of the volume of the segment. The size of the segment seems to increase as the flexibility of the polymer chain decreases. The lowest values for V* are found for polysiloxanes in which the segment seems to be only four atoms long. Larger values of V* are found for polymers with units of the type –CH2–CHR-. Larger values still of V* are given by polymers with units of the type –CH2-CR1R2- and even larger V* values are found for those polymers with benzene rings constituting a major part of the main chain. As V* rises the viscosity of the polymeric liquid becomes much more dependent upon pressure and temperature. Thus whilst the polysiloxanes have viscosities which are relatively insensitive to pressure and temperature, the aromatic polysulphones and poly(2,6-dimethylphenylene oxide) have viscosities which are very sensitive to pressure and temperature. 相似文献
Polysiloxanes with oligo-oxyethylene side chains of the type —O(CH2CH2O)7CH3 and —(CH2)3O(CH2CH2O)nCH3 (average n ≈ 7 and 11) were synthesized from poly(hydrogenmethylsiloxane) and characterized by 1H n.m.r., 29Si n.m.r., i.r. and g.p.c. Cyclic analogues were used as model compounds and synthesized from tetramethylcyclotetrasiloxane. Polymer electrolyte complexes were made from the comb polymers and LiClO4 by solvent-casting from THF, and their conductivities measured as a function of temperature and studied by differential scanning calorimetry and correlated with their conductivity behaviour. Maximum conductivities close to 10?4S cm?1 were achieved at room temperature and at ethylene oxide units to Li+ ratios of about 25. Cross-linking or blending with high molecular weight poly(oxyethylene) lowers the conductance somewhat but vastly improves the mechanical properties of the complexes, and the blends with PEO can be cast into thin, flexible and tough films with good conducting properties. 相似文献