摘要:

AbstractLong‐term compositional changes were observed whenn‐hexane plasma polymers were stored in air at ambient temperature. These post‐deposition changes were monitored over periods exceeding one year using XPS, grazing angle FTIR, and SEM. A rapid initial increase in the oxygen content was followed by a slower oxygen uptake, which continued for many months. In contrast to the reported autocatalytic acceleration of the oxidation of polyolefins, the rate of oxidation ofn‐hexane plasma polymers was found todecreasecontinuously, and it did not proceed to the same extent toward higher oxidation states. The plasma polymer coatings did not show physical manifestations of oxidative degradation such as cracking, reduction in thickness, or loss of physical integrity. Comparison of the XPS and FTIR data suggested that the top few nanometers of the plasma polymer coatings oxidized at a faster rate than the “bulk.” The experimental data were interpreted using a model comprising reactions known from the oxidative degradation of polyolefins: carbon‐centered radicals, trapped in the course of the plasma deposition, combine with atmospheric oxygen to form metastable peroxy radicals and hydroperoxides, which decompose to generate a variety of stable product groups such as hydroxyl, carbonyl, and carboxylic groups. There was broad agreement between the XPS data and the time dependence of particular species in model calculations. © 1994 John W

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320801

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPoly[4‐(4‐hydroxyphenoxy) benzoic acid] was prepared by the bulk polycondensation of 4‐(4‐acetoxyphenoxy) benzoic acid. Polycondensation was conducted at 350°C for 3 h under a reduced pressure of 0.1 mmHg and gave a polymer with X̄n of 255. The polymer was characterized by elemental analysis, IR spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray measurement. The crystal/nematic and nematic/isotropic phase transition temperatures of polymer, which depend on the molecular weight, were observed at about 300°C and 410°C, respectively. The polymers with low molecular weights showed nematic textures above 300°C. This nematic/isotropic phase transition temperature is lower than that of poly (4‐hydroxybenzoic acid). This thermal behavior of polymer comes from ether units, which increase the flexibility (the rotation or torsion of skeletal bonds) of the polymer chain. © 1994 J

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320802

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractChain transfer constants (Ctr) for thiuram disulfide (TD) groups, included in the backbone of polydimethylsiloxane (PDMS) of different chain lengths, in methyl methacrylate (MMA) and styrene (St) were determined from measurements of the degree of polymerization. Two methods were used. The first consisted of using the initiation and transfer properties of the thiuram disulfides groups, and the second, of using a more efficient free radical initiator than TD groups, in which case the former behaves only as a transfer agent. In both the methods, theCtrof TD was evaluated in bulk polymerization of MMA at 60, 70, 80, and 90°C. Using the first method, theCtrof TD was measured also in solution polymerization of MMA in toluene at 100°C and, with the second one, in bulk polymerization of styrene at 60, 80, and 90°C. PDMS‐based macrothiuram disulfide (macroiniferter) behaves as an “azeotropic” transfer agent for MMA and styrene at 125°C and 110°C, respectively. © 1994 John Wile

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320803

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractLatexes of 100 nm diameter were synthesized by emulsifier‐free copolymerization of styrene, sodium styrenesulfonate, and 1–5 wt% divinylbenzene using persulfate initiator at 91°C. A shot growth method was used to incorporate a high density of sulfonate groups. Coefficients of variation of particle size were 0.04–0.08 without resort to seed growth polymerization. Redox initiation at 40–50°C produced larger, more polydisperse, and less colloidally stable crosslinked latexes. © 1994 John Wiley

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320804

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPolymerization of lipid assemblies may be usefully employed to alter the properties of the assemblies. The possible locations of the reactive group in the lipids include (1) the chain terminus, (2) the head group, and (3) near the lipid backbone. The third strategy yields polymerized assemblies which retain their head group functionality and lipid chain motion. We have designed and synthesized new members of this later category by the use of 2‐methylene‐substituted acyl chains. The main transition temperature (Tm) from gel to liquid crystalline phase of hydrated bilayers of 1‐palmitoyl‐2‐(2‐methylene)palmitoyl‐sn‐glycero‐3‐phosphocholine (1) and the disubstituted 1,2‐bis(2‐methylenepalmitoyl)‐sn‐glycero‐3‐phosphocholine (2) were 33.6 and 25.3°C, respectively. TheTmof the mono‐substituted 1‐oleoyl‐2‐(2‐methylene)palmitoyl‐sn‐glycero‐3‐phosphocholine (3) bilayers was detected in a range from −15 to −10°C by x‐ray diffraction. Hydrated bilayers of each individual lipid were successfully polymerized with a water‐soluble initiator, azobis(2‐amidinopropane) dihydrochloride (AAPD). These results indicate the lipid 2‐methylene groups are accessible to the water interface. Thermal polymerization of the mono‐substituted lipids in aqueous suspensions with AAPD, yielded oligomers. However the bis‐2‐methylene PC (2) was successfully polymerized

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320805

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe cationic nonlinear polymerization of diglycidyl ether of Bisphenol A (DGEBA) in the presence of a diluent γ‐butyrolactone (BL) was initiated by the BF3‐4‐methoxyaniline (MA) complex. The reaction was studied by size exclusion chromatography, DSC, and dynamic mechanical analysis. Reaction mechanism involves a fast formation of adducts of DGEBA with MA released from the initiator. Formation of spiro orthoesters (S) by reaction of BL with DGEBA and homopolymerization of DGEBA as well as copolymerization with S follow. Gelation occurs at 60°C within a few minutes at conversion of epoxy groups (ξE)c= 0.20–0.45. The networks cured under optimum conditions show high glass transition temperature,Tα= 178°C. The mechanism‐structure‐property relations are discussed. © 1994 Joh

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320806

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractKinetics of methyl methacrylate polymerization initiated by a redox system [cumene hydroperoxide (CHP)/copper saccharinate] were studied in bulk at 20°C in the presence of accelerators such asN,N‐dimethyl‐p‐toluidine (DMPT) ando‐benzoic sulphimide (saccharin). Assuming a steady‐state concentration of propagating radicals, the polymerization rate depends on the square root of the initiation rate and the kinetic orders with respect to each compound in the initiation step may be deduced. Initiation is first‐order in CHP, copper saccharinate, and saccharin and second‐order in DMPT. A reaction scheme consistent with these orders is proposed. The main features are the following: (1) CHP reduces rapidly Cu(II) to Cu(I); (2) a small fraction of Cu(I) is complexed with DMPT; (3) the complexed ions (Cu+, DMPT2) are strong reductants with respect to CHP whereas uncomplexed Cu+are almost inactive; (4) the decomposition of CHP is strongly catalyzed by saccharin (protonated CHP is 13000 times more reactive than free CHP). Thus both accelerators are necessary to get high polymerization rates. © 1994 John

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320807

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe role ofN,N‐dimethyl‐p‐toluidine (DMPT) and saccharin as accelerators in the polymerization of methyl methacrylate initiated by the redox decomposition of cumene hydroperoxide (CHP) in the presence of iron saccharinate has been kinetically investigated. DMPT reduces ferric ions to ferrous ions, so that an equilibrium is established between the two oxidation states. With the assumption of a steady‐state concentration of propagating radicals, the rate of initiation was deduced from the rate of polymerization and the kinetic orders with respect to each compound involved in the initiation step have been determined. The reaction is first‐order in CHP, iron saccharinate, and saccharine and second‐order in DMPT. In a proposed scheme, Fe2+ions, complexed by two DMPT molecules, are much more reactive than uncomplexed Fe2+and saccharin activates the decomposition of CHP by protonation of the OO bond. This mechanism, similar to that proposed in the case of copper saccharinate, explains the synergistic effect of both accelerators. © 1994 John W

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320808

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractSeven imidodicarboxylic acidsII‐1 to 5,II‐10, andII‐11 were prepared from trimellitic anhydride and ω‐amino acids, such as glycine, β‐alanine, 4‐aminobutyric acid, 5‐aminopentanoic acid, 6‐aminohexanoic acid, 11‐aminoundecanoic acid, and 12‐aminododecanoic acid. Several aliphatic‐aromatic poly(amide‐imide)s were prepared by triphenyl phosphite promoted polycondensation reaction from the combination of 3‐(4‐carboxyphthalimido)propionic acid (II‐2) or 6‐(4‐carboxyphtalimido)hexanoic acid (II‐5) with various aromatic diamines and of all the imidodiacids withp‐phenylenediamine or 4,4′‐oxydianiline. All poly(amide‐imide)s were characterized by inherent viscosity, gel permeation chromatography (GPC) measurements, solubility, tensile test, wide‐angle X‐ray scatting patterns, differential scanning calorimetry (DSC) measurements, and thermogravimetric (TGA) analyses. Effects of structural changes such as polymethylene length and diamine moieties on the properties of poly(amide

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320809

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractEmulsion polymerizations were used for preparing fluorescent‐labeled polymers. The labeled polymers were analyzed by gel permeation chromatography (GPC) using both fluorescence (FL) and refractive index (RI) as detectors. The uniformity of polymer labeling was measured by the ratio between FL and RI signals, calculated by a computer software, on the basis of each GPC chromatogram. It was found that in emulsion polymerizations, the semicontinuous process can produce a more homogenous dye distribution in the host polymer molecules than the batch method. Uniform labeling of a polymer with various dyes can be achieved by the semi‐continuous process. However, experimental conditions for polymerization, such as initiator concentration and the presence of surfactant or chain transfer agent, may influence the uniformity of dye distribution. © 1994 John Wiley&Sons,

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320810

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY