摘要:

AbstractRing‐opening polymerization of ε‐caprolactone has been carried out by using rare earth coordination catalysts for the first time. The rare earth compounds, RE(acac)3.3H2O, Nd(P204)3, Nd(P507)3, Nd(naph)3, Nd(BA)3.2H2O, etc. (where RE = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Lu, Y; acac = acetylacetone; BA = benzoylacetone), combined with trialkyl aluminum, greatly increased the degree of conversion and the molecular weight of poly(ε‐caprolactone) (PCL). The influence of reaction conditions on the polymerization of ε‐caprolactone catalyzed by the Nd (acac)3.3H2O‐AlEt3system has been examined in detail. The kinetics indicates that the polymerization rate has the first‐order in monomer and a half‐order in catalyst. The overall activation energy of the ring‐opening polymerization amounts to 59.4 kJ/mol. By IR and UV‐Vis spectra,1H‐ and13C‐NMR data, it is assumed that the ring‐opening polymerization of ε‐caprolactone catalyzed by the Nd(acac)3.3H2O‐AlEt3system proceeds via complexation of monomer to catalyst, acyl‐oxygen cleavage insertion propagation mecha

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320401

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe exit or desorption of free radicals from latex particles is an important kinetic process in an emulsion polymerization. This article unites a successful theory of radical absorption (i.e., initiator efficiency), based on propagation in the aqueous phase being the rate determining step for entry of charged free radicals, with a detailed model of radical desorption. The result is a kinetic scheme applicable to true “zero‐one” systems (i.e., where entry of a radical into a latex particle already containing a radical results in instantaneous termination), which is still, with a number of generally applicable assumptions, relatively simple. Indeed, in many physically reasonable limits, the kinetic representation reduces to a single rate equation. Specific experimental techniques of particular significance and methods of analysis of kinetic data are detailed and discussed. A methodology for both assessing the applicability of the model and its more probable limits, via use of known rate coefficients and theoretical predictions, is outlined and then applied to the representative monomers, styrene and methyl methacrylate. A detailed application of the theory and illustration of the methodology of model discrimination via experiment is contained in the second article of this series. © 1994 John Wiley&Son

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320402

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractIn emulsion polymerizations, desorption (exit) from latex particles of monomeric radical species that arise from transfer can be an important determinant of the overall kinetics. An examination of various methodologies for the testing of postulated free radical exit mechanisms is made. These utilize the model descriptions for the exit process presented in the accompanying article of Casey et al., employing data consisting of conversion as a function of time for the approach to steady state polymerization conditions. Experimental data are presented on the exit rate coefficients as a function of such experimental parameters as: particle size, monomer concentration, and aqueous‐phase free‐radical concentration for a series of styrene polymerizations at 50°C, where the average number of free radicals per particle (n̄) never exceeds 0.5. It is demonstrated for these systems that while the conversion/time dependence from a single run, under conditions sensitive to exit, is insensitive to mechanistic assumptions as to the fate of desorbed free radicals, the variation of the exit rate coefficient with particle size so obtained suggests a second order dependence onn̄, implying complete re‐entry of desorbed free radicals under all conditions studied. Once the monomeric radicals have re‐entered, they are more likely to remain inside the particle where they will either propagate or undergo termination rather than re‐escape. The article also presents an estimate for the rate coefficient at 50°C of the first propagation step of the monomeric radical subsequent to transfer. The conclusions drawn here for seeded systems should prove useful for study of particle nucleation mechanisms, when exit is particularly likely in small, newly formed, particles. © 1994 John W

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320403

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractA series of fully aromatic, thermotropic polyesters based on 1,1′‐binaphthyl‐4,4′‐diol, BND, was prepared by the melt polycondensation method and characterized for their thermotropic behavior by a variety of experimental techniques. The homopolymer of BND with terephthalic acid formed a nematic melt at 353°C. In contrast, the polyester from BND and 2,6‐naphthalenedicarboxylic acid had a melting transition,Tm, above 400°C, so it was not possible with the equipment available to determine whether it formed a nematic melt. All of the copolymers of BND formed nematic melts at much lowerTmvalues than those of its respective homopolymers, as expected, because of the copolymerization effect of the added monomer. Moreover, all of the copolymers had higher glass transition temperatures,Tg, than those of other liquid crystalline polyesters and higher thermal stabilities. © 1994 John W

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320404

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractSyndioselective propylene polymerization has been promoted byrac‐2,2‐dimethylpropylidene (1‐η5‐cyclopentadienyl) (1‐η5‐fluorenyl) dichlorozirconium (1). The active catalytic species were generated using either triphenylcarbenium tetrakis (pentafluorophenyl) borate (2) (Zr+method) or methylaluminoxane (MAO method). The former exhibited much higher activity than the latter, especially at low polymerization temperatures (Tp). Syndiotactic poly (propylene) (s‐PP) obtained at Tp= −20°C has Tmapproaching 160°C, [rrrr] pentad fraction of 0.92 to 0.95, and 45% crystallinity (Xc). It crystallized in two antichiral unit cells B and C. The C structure is favored by low temperature of polymerization, slow crystallization from melt, and annealing. Thes‐PP hasM̄w/M̄nranging from 3.6 to 4.4, which can be separated into stereoregular fractions soluble in heptane and hexane and stereoirregular fractions soluble in pentane, ether, and acetone. Therefore, this system cannot be considered to be a single‐site catalyst. A parallel study was made on the isopropylidene (1‐η5‐cyclopentadienyl) (1‐η5‐fluorenyl) dichlorozirconium (3)/MAO catalyst. Molecular mechanics calculations were performed for all combinations of the configuration of asymmetric centers. The steric energy favors syndiotactic enchainment for both catalysts1and3, with1forming the more syndioselective ca

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320405

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

Abstracttert‐Butyl substituted poly (aryl ether ketone)s with relatively high molecular weights were prepared by the Ni‐catalyzed polymerization oftert‐butyl substituted aromatic dichlorides containing ether ketone unit. These polymers were amorphous and soluble in common organic solvents, such as THF, dichloromethane, and chloroform. De‐tert‐butylation of the polymer by the treatment of trifluoromethanesulfonic acid in the presence of toluene proceeded smoothly and produced crystalline poly (aryl ether ketone). © 1994 John Wiley

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320406

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractSeveral series of multifunctional silicon‐containing epoxide monomers and oligomers have been prepared using rhodium catalyzed hydrosilation reactions. Dialkyl and diarylsilanes can be condensed with vinyl epoxides to give high yields of the desired diepoxides while the hydrosilation of alkyl and aryl silanes yields a mixture of di and tri epoxy substituted products. The condensation of αω,SiH difunctional compounds with vinyl epoxides can be carried out regioselectively to give α‐hydrogen‐ω‐epoxy intermediates, which can be further reacted with di and tri olefins bearing terminal double bonds to give a series of well characterized epoxy functional oligomers. An investigation of the photoinitiated cationic polymerization of the monomers and oligomers, which were prepared during the course of these studies, was carried out. © 1994 John

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320407

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPlasma‐oxidized polyethylene (O‐PE) was derivatized with various chemicals and the advancing and receding contact angles with water, formamide, and tricresylphosphate were measured. The contact angles were used to evaluate the surface free energy (SFE) components in terms of the Lifshitz‐van der Waals‐acid base (LW‐AB) model. The derivatization was directed to couple alkyl chains to carbonyl, hydroxyl, and carboxyl groups generated on the surface of O‐PE. Carbonyl groups were treated with hydrazine and then reacted with dodecanoyl chloride. Hydroxyl groups were first reacted with reactive dicarboxylic acid dichlorides or cyanuric chloride, respectively, and then with alkylamines because the direct bonding of long‐chain alkyl carboxylic acid chlorides proceeds slowly and is, therefore, completed by surface restructuring. Carboxyl groups were chlorinated and in a second step reacted with alkylamines. The bonding of C12‐alkyl chains can be sensitively detected by the LW part of the SFE. Concerning the receding contact angles, it is pointed out that the carbonyl groups are present on the surface in a higher concentration than hydroxyl and carboxyl groups. The combination of contact angle goniometry (CAG) and chemical derivatization reactions supplies semiquantitative information about functional groups in the uppermost surface layer. In this way, a major shortcoming of CAG can be overcome. © 1994 John

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320408

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe new acrylate monomers 4‐(ω‐acryloyloxyalkyloxy)‐N‐(9‐methyl‐2‐carbazolylmethylene) anilines containing from 2 to 11 methylenic units in their alkyl group and a carbazolyl group in the mesogenic unit were synthesized and polymerized by azobisisobutyronitrile (AIBN) as radical initiator and by low‐energy electron beam (EB) initiation. The thermal properties of the resulting polymers were examined using differential scanning calorimetry and thermal optical polarizing microscopy. The polymer prepared by AIBN with a hexamethylene spacer exhibited a nematic phase from 73 to 170°C and with an undecamethylene spacer exhibited a smectic phase from 55 to 202°C. The isotropization temperature of the polyacrylates increased with increasing the number of carbons of the methylenic spacer. The yield of the resulting polymer was changed by EB irradiation temperature from 4.5 to 41%. The highest yield was obtained when the monomer was polymerized in a liquid‐crystalline phase. The same tendency was observed in the molecular weight of the resulting polymers. © 1994

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320409

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPolyarylates derived from 4,4″‐dihydroxy‐meta‐terphenyl (DHmTP) were prepared by the phase‐transfer catalyzed, two‐phase polycondensation with aromatic diacid chlorides. The resulting polymers were crystalline, solvent resistant, and produced brittle films. Copolymers with bisphenol‐A were also synthesized using isophthaloyl diacid chloride. At low to moderate levels of DHmTP in the copolymers (25–75%), the materials had high glass transition temperatures (186–201°C), good solvent resistance, and gave tough, clear films. Terpolymers of DHmTP and BPA with 50:50 isophthaloyl and terphthaloyl diacid chloride were prepared with not much improvement over Ardel D‐100®. All the DHmTP‐polyarylates had good thermal stability (5% weight loss in air>415–460°C) and had a high % char (20–48%).

ISSN:0887-624X    

DOI:10.1002/pola.1994.080320410

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY