摘要:

AbstractFor seeded emulsifier‐free emulsion polymerizations of styrene/potassium persulfate (KPS)/water system using the three sizes of seeds: 1020, 1620, and 1923 Å, analysis on the data of conversion and MWD suggests a shell region polymerization mechanism for the particle growth period as the particle diameter is larger than about 1500–2000 Å. The shell region has thickness of about 100 Å. The occurrence of shell region polymerization is attributed to the higher average number of radicals per particle (n≑ 2−7) for the large particle, causing the polymer radicals (with the sulfate ends anchoring on the particle surface) to be terminated by combination at lower MW. Thus, the radical ends have no chance to arrive at the core of the particles. As the smallest seed is used, the rate of polymerization is of zero order, the same as in the conventional emulsion polymerization. MW of the polymer produced in the cases, in which the shell region polymerization occurs, increases with conversion in the entire process, different from the conventional case in which the MW increases first up to about 60% conversion and then decreases. © 1992 John Wile

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301001

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractImide‐aryl ether ketone block copolymers were prepared and their morphology and thermal and mechanical properties investigated. Two aryl ether ketone blocks were incorporated; the first was an amorphous block derived from bisphenol–A and the second block was a semi‐crystalline poly(aryl ether ether ketone) prepared from a soluble and amorphous ketimine precursor. Bis(amino) aryl ether ketone and aryl ether ketimine oligomers were prepared via a nucleophilic aromaic substitution reaction with molecular weights ranging from 6,000 to 12,000 g/mol. The oligomers were co‐reacted with 4,4′‐oxydianiline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester diacyl chloride inN‐methyl–2‐pyrrolidone (NMP) in the presence ofN‐methylmorpholine. The copolymer compositions, determined by H‐NMR, of the resulting amic ester based copolymers ranged from 8 to 50 wt % aryl ether ketone or ketimine content. Prior to imide formation, the ketimine moiety of the aryl ether ketimine block was hydrolyzed (p‐toluene sulfonic acid) to the ketone form producing the aryl ether ether ketone block. Compositions of this block were maintained low to retain solubility. Solutions of the copolymers were cast and cured to effect imidization, producing clear films with high moduli (ca. 2200 MPa) and elongations (33–100%). The copolymers displayed good thermal stability with decomposition temperatures in excess of 450°C. Multiphase morphologies were observed irrespective of the co‐block type, block length or composition.

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301002

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA molecular composite of an amphiphilic polyanion and cationic surfactants was prepared by treating a terpolymer [consisting of sodium 2‐acrylamido‐2‐methylpropanesulfonate,N‐(1‐adamantyl)methacrylamide, and a small mole fraction ofN‐(1‐pyrenylmethyl)methacrylamide] with didodocyldimethylammonium bromide in aqueous solution. The molecular composite was soluble in organic solvents with a wide range of polarities. Fluorescence spectra indicated that the pyrenyl (Py) residues in the molecular composite experienced polar microenvironments even though the composite was dissolved in nonpolar solvents. Exciplex formation of the Py residue with 4,4′‐dicyanobenzene was strongly suppressed due to the polar microenvironments and steric “protection” of the chromophore. Photoinduced electron transfer (ET) from the Py residue to pyromellitic dianhydride (PMDA) in acetonitrile showed characteristics of long‐range ET between fixed donor and acceptor sites and yielded long‐lived transient Py cation radicals and PMDA anion radicals which persisted for tens of milliseconds. These findings imply that the micellelike structure of the parent amphiphilic polyelectrolyte formed in aqueous solution is retained, to some degree, in the molecular composite dissolved in organic solvents. ©

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301003

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe kinetics of homopolymerization of the monofunctional epoxideN‐methylglycidylaniline in the presence of a tertiary amine or an amino alcohol has been followed by reversed phase high performance liquid chromatography and size exclusion chromatography. The reaction products were identified by mass spectrometry using potassium ionization of desorbed species (K+IDS). 1,3‐Di‐N‐methylanilino‐2‐propanol (P) was the main reaction product and low molecular weight oligomers withMn>600 were also formed. The molecular weight and fraction of oligomers decrease with increasing concentration of the initiator. The suggested complex reaction mechanism involves formation of four stable oligomeric series initiated by reaction of the epoxide with either an OH group of (a) the amino alcohol, (b) product P, (c) traces of water, or (d) the tertiary amine to form ionic species resulting in the ionic propagation. Regeneration of the initiator and formation of new initiating centers during the polymerization are the causes of low molecular weights of oligomers. © 1992 John Wil

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301004

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractMacroporous hydrogels are characterized by large pore sizes, high pore volumes, and high specific surface area. Besides these characteristics, macroporous hydrogels based on thermally reversible polymers respond to temperature changes much faster than hydrogels prepared by a conventional method. Crosslinked poly(N‐isopropylacrylamide) (polyNIPAAm) forms a thermally reversible hydrogel which shows a lower critical solution temperature (LCST) ca. 33°C in aqueous solutions. We have synthesized thermally reversible polyNIPAAm hydrogels having macroporous structures by a new method. These macroporous hydrogels have large pore volumes, large average pore sizes, and faster macromolecule permeation rates in comparison to conventional polyNIPAAm hydrogels synthesized by a conventional method. Compared with conventional polyNIPAAm hydrogels, the macroporous polyNIPAAm hydrogels have higher swelling ratios at temperatures below the LCST and exhibit faster deswelling and reswelling rates. The deswelling rates are especially rapid. These thermally reversible macroporous hydrogels may be very useful in controlled active agent delivery and toxin removal, as well as dewatering of solutions. Peptides or proteins may behave as if they were in bulk solution within the large aqueous pores, and this may reduce their inactivation when such gels are used for their storage and later release. The gels may also be useful in microrobotic devices due to their fast response to temperature. © 1992 John Wiley&Sons,

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301005

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractRecently considerable detail has become available on the initial morphology and the morphological changes that occur for silica based Cr catalysts for ethylene polymerization. These catalysts are produced as a dry powder and may be employed either in gas phase or in slurry processes. MgCl2‐supported Ziegler‐Natta polymerization catalysts are often prepared and employed as slurries. They usually are never dried and thus few studies have employed the spectra of physical techniques common to the characterization of pore structure. In the current study, we have carefully removed the solvent for both ball‐milled and precipitated MgCl2‐supported catalysts. These catalysts are characterized by physical sorption, mercury porosimetry, and electron microscopy both as prepared and during the initial stages of polymerization (to ∼ 100 g of polymer/g of catalyst). We find that the initial catalyst may be represented by a complex agglomerate of small crystallites as contrasted with the branched pore network found in Cr/silica catalysts. As a result, it is concluded that the initial fragmentation of the MgCl2based systems is more uniform as contrasted with the progressive fragmentation of the silica‐based system. This fragmentation mechanism facilitates the retention of greater polymer/catalyst surface during the initial stages of the polymerization. © 1992 John Wil

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301006

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractDifferent poly(tert‐butyl methacrylate) (PTBMA)‐poly(alkyl methacrylate) (PAMA, alkyl=CH3,n‐C4H9) triblock copolymers were synthesized by group transfer polymerization. They were obtained by first preparing “living” PAMA using a difunctional initiator, followed by polymerization of TBMA in THF at room temperature, in the presence of a nucleophilic catalyst. The segment molecular weights and compositions of TBMA segment could be controlled by regulating the feed ratio of two monomers and the ratio of monomer to initiator. As supported by1H‐NMR, IR analysis, and titration, the PTBMA blocks could be quantitatively hydrolyzed into poly(methacrylic acid) (PMAA) blocks whereas the PAMA blocks were not hydrolyzed. The water‐soluble amphiphiles prepared by neutralization of the PMAA block displayed surface‐active behavior in water, which was characterized by a critical micelle concentration. The thermogravimetric analysis demonstrated the loss oftert‐butyl groups. © 1992 Jo

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301007

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractPreparation of copolymer microspheres of diethylene glycol dimethacrylate (2G) with several comonomers by radiation‐induced radical polymerization is described. Ethyl methacrylate (EMA), acrylamide, maleic anhydride, and styrene gave microspheres successively. The copolymerization resulted in gelation more easily than the 2G homopolymerization. The allowed ratio of copolymerization is up to about 0.4 as the mole fraction of comonomer for the solution containing 10 vol % 2G monomer. Copolymerization affected the size of microspheres by keeping its narrow distribution. The size of microspheres was increased by the copolymerization with EMA and styrene and, was decreased with acrylamide. The formation of microsphere strongly depends on the crosslinking ability of monomers. The crosslinking ability and reactivity in the copolymerization cause the change of the size of the microspheres. © 1992 John Wiley&Sons, I

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301008

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA number of diacetylene containing acrylate and methacrylates have been synthesized and the interaction between their propagating radicals and the diacetylene groups was studied by ESR spectroscopy. In the case of polymerization at 70°C using AIBN as an initiator, the propagating radicals of methacrylates are temporarily trapped with the diacetylenes with rapid exchange of the electron, thus showing strong signals of the propagating radicals. Gamma irradiation of the frozen state produces a blue color in samples, and the ESR signals were found to be those of uninteracted acrylate and methacrylates. From a comparison of spectral widths, there seems to exist an intramolecular interaction between the radicals and the diacetylene group at the frozen state. © 1992 John Wiley&Sons, In

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301009

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractCopolymers of 2,4,6‐tribromophenyl acrylate (TBPA) (1) and glycidyl methacrylate (GMA) (2) with different feed ratios are synthesized in toluene using benzoyl peroxide as a freeradical initiator at 70 ± 1°C. The copolymer composition is calculated using1H‐NMR spectroscopy by comparing the intensity of aromatic and aliphatic protons. The copolymers are characterized with FT‐IR and proton decoupled13C‐NMR spectroscopic techniques. The reactivity ratios are calculated by Kelen‐Tüdos method and arer1= 1.08 ± 0.53,r2= 0.52 ± 0.26. Gel permeation chromatography is used for determining theM̄n,M̄wmolecular weights and dispersity index. Thermogravimetric analysis is employed for the determination of thermal stability of homo‐ and copolymers. The glass transition temperatures of the poly(TBPA), poly(GMA), and copoly(TBPA‐GMA) are determined by differential scanning calorimetry. © 1992

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301010

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY