摘要:

AbstractThe transitions and melting behavior of thermally crystallized poly(ethylene terephthalate) (PET) are studied using a computerized differential scanning calorimeter (DSC). A transition occurs from a structural stage characterized by a strong glass transition and an exothermic crystallization peak to a stage with a barely perceptible glass transition and an endothermic low melting (LM) peak in the DSC thermograms. This transition corresponds to the change from the primary to secondary crystallization process of PET. The exothermic crystallization peak is only observed within the primary crystallization stage. The maximum temperature of the LM peak is a function of annealing temperature and time, and depends on the microstructure of the imperfectly formed crystallites. The high melting peak is the melting of crystallites of higher perfection and is influenced by the recrystallization process of the sample during the scan.

ISSN:0360-8905    

DOI:10.1002/polc.5070710113

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractA copolymer of vinylidene chloride and vinyl chloride containing 13.5% of the latter has been found to form completely miscible blends with atactic and isotactic poly(methyl methacrylate). poly(ethyl methacrylate), poly(n‐propyl methacrylate), and poly(cyclohexyl methacrylate). All but the latter of these blends were shown to exhibit lower critical solution temperature behavior at temperatures below that at which the copolymer rapidly degrades. The copolymer was found to be only partially miscible with poly(isopropyl methacrylate), while no detectable level of miscibility was observed with poly(methyl acrylate), poly(ethyl acrylate), poly(vinyl acetate), poly(vinyl methyl ether), or poly(vinyl methyl ketone). Information about interactions between components in the miscible blends was estimated from melting point data and is discusse

ISSN:0360-8905    

DOI:10.1002/polc.5070710114

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe structures of crystallites formed from a dilute solution of linear polyethylene and of an ethylene‐butene copolymer (hydrogenated polybutadiene) have been studied using several different methods. In addition to the conventional thermodynamic methods, small‐angle x‐ray scattering measurements and analysis of the low‐frequency Raman longitudinal acoustic mode (LAM) were also carried out. The major objectives were to establish the level of crystallinity and to determine the thickness of the crystallite core. The results of these studies were also applied to the analysis of the literature data for isotactic polystyrene crystallites formed from dilute solution. For the linear chains and the isothermally crystallized copolymer the different methods gave essentially the same results. The thickness of the amorphous overlayer for the lamellas formed by the homopolymers was found to be about 25 Å, in agreement with previous conclusions. It represents about 20–30% of the lamellar thickness. For the isothermally crystallized copolymers, the overlayer thickness increases to as much as 60 Å and the level of crystallinity is reduced to about 50%. For the rapidly crystallized, small crystallite size copolymer there is a discrepancy in the sizes obtained by the different methods. Possible reasons for the differences are pointed out However, a rather large overlayer is still deduced. When examined in perspective, it becomes clear that the lamellar‐like crystallites, typical of crystallization from dilute solution, contain a significant disordered overlayer. The relative extent of this overlayer depends on the ch

ISSN:0360-8905    

DOI:10.1002/polc.5070710115

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractQuaternized polyethylenimines exhibit viscosity behavior very similar to that of linear flexible polyelectrolytes and thus evidently swell in dilute salt solutions. This swelling is manifested also in the rate constants for the hydrolysis of chiral or achiral nitrophenyl esters catalyzed by these polymers. Stereoselective preference is exhibited in hydrolyses catalyzed by the quaternized polymers containing covalently linked l‐histidine moieties. Maximum stereoselectivity is manifested at polymer concentrations corresponding to nonswollen conformations. With added cetyltrimethylammonium bromide, the stereoselective preference of the catalyzing polymer can be reversed. A comparison of the effects of added anionic, nonionic, and cationic detergents shows decreases in rate for the first, no significant effect for the second, and substantial changes for the third, depending on the polymer and detergent concentrations. Cationic detergents of different chain lengths and structures show different effects reflecting largely their extent of binding by the polyme

ISSN:0360-8905    

DOI:10.1002/polc.5070710116

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe heat capacity of methylcellulose is determined at various water contents over a wide range of temperatures, down to 125 K. From the data, the partial specific heat capacity of water has been obtained. The results show that water should be considered as a single, mobile phase. No evidence exists for bound water. Near 130 K water becomes immobilized in a glassy state.

ISSN:0360-8905    

DOI:10.1002/polc.5070710117

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe alkaline fusion method for the analysis of the hydrocarbon portion of poly(dimethyl siloxane) gum stock containing pendant vinyl groups has been applied to systems crosslinked with dicumyl peroxide in the presence of near‐UV radiation. Crosslinks made of butyl and propyl chains both with and without aromatic residues were found. Under the conditions of this study the dicumyl peroxide efficiency as a crosslinking agent is slightly greater than one. Owing to the formation of three carbon‐containing crosslinks, the total chemical crosslink density of the system was greater than predicted from simple vinyl‐to‐vinyl a

ISSN:0360-8905    

DOI:10.1002/polc.5070710118

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractIn an effort to elucidate the nature of ionic aggregation and its effect on the primary relaxation (α process) in the Nafion polymers (EW = 1200), underwater and undermethanol stress relaxation tests were conducted at various temperatures (20–70°C). Both semicrystalline and amorphous Nafion‐Na relax faster in the presence of water than in the dry state. In marked contrast to the behavior observed for Nafions in the dry condition, the kind of countercations is insignificant in the underwater stress relaxation. The great similarity in the underwater stress relaxation curves for different cations is attributable to the reduction of ionic interaction between the bound anions and unbound cations, probably associated with the water shielding around the ionic species. This leads to the suggestion that the primary α relaxation may be relevant to the ionic groups rather than to the matrixTg, representing a reversal of the original assignment of the mechanical α and β relaxations. Increased swelling in methanol shows a modulus being one order of magnitude lower than that in the underwater runs. However, little or no difference is seen in the rates of stress relaxation in the underwater and undermethanol stress relaxation experiments. It is postulated that methanol also interacts with the interracial regions or with the fluorocarbon matrix in the Nafions, not just with the ionic

ISSN:0360-8905    

DOI:10.1002/polc.5070710119

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe data of isothermal stretching calorimetry on rubbers at different temperatures above room temperature are presented. Based upon the van der Waals equation of state for rubbers calculations can be fitted to the experimental data obtained by simple elongation whereby the thermoelastic behavior is related to a constant thermal expansion coefficient in the unstrained state and to an invariant temperature coefficient of the end‐to‐end distance of the equivalent freely jointed ch

ISSN:0360-8905    

DOI:10.1002/polc.5070710120

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractAn optically clear sample of undiluted poly(vinyl acetate) (PVAc) has been prepared by UV‐initiated bulk polymerization of monomer at 42°C. Measurements of light‐scattering intensities in the temperature rangeTg− 30°C>T>Tg+ 50°C have been carried out. Photon correlation spectroscopy has been performed in the temperature rangeTg+ 5°C>T>Tg+ 23°C. Intensity data forTδρ2, evaluated using experimental equation‐of‐state information, is found to be in accord with the light‐scattering results. Photon correlation functions are well described by a single Williams–Watts function. Mean relaxation times and associated activation energies are compared with results of other relaxational studies of PVAc. Discrepancies observed are interpreted to be due in part to variability of sample histories as well as to problems in analytical treatment of the pert

ISSN:0360-8905    

DOI:10.1002/polc.5070710121

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractSynthesis of two classes of water‐soluble polydiacetylenes °CR—CC—CRxis presented. Class I has carboxylic acid [R = —(CH2)nCOOH] and their salts as the side group, while the class II has urethane–carboxylic acid [R = —(CH2)nOCONHCH2COOH] and their salts as the side group. Monomers of class I were prepared by oxidation of diacetylenes having R = —(CH2)n+1OH group, while those of class II were prepared by hydrolysis of diacetylenes having R = —(CH2)nOCONHCH2COO(CH2)nCH3group. The monomers polymerize in the solid state either upon thermal annealing or upon exposure to high‐energy radiation. 1HAU, R = —CH2OCONHCH2COOH, polymerizes quantitatively upon thermal annealing. The heat of polymerization (130 kJ/mol) and the activation energy of polymerization (110 kJ/mol) as determined by differential scanning calorimetry are in agreement with those reported

ISSN:0360-8905    

DOI:10.1002/polc.5070710122

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY