摘要:

AbstractParticle nucleation in the polymerization of styrene microemulsions was found to take place throughout the polymerization as indicated by measurements of the particle number as a function of conversion. A mechanism based on the nucleation in the microemulsion droplets was proposed to explain the experimental findings although homogeneous nucleation and coagulation during polymerization were not completely ruled out. A thermodynamic model was developed to simulate the partitioning of monomer in the different phases during polymerization. The model predicts that the oil cores of the microemulsion droplets were depleted early in the polymerization (4% conversion). Due to the high monomer/polymer swelling ratio of the polymer particles, most of the monomer resides in the polymer particles during polymerization. The termination of chain growth inside the polymer particles was attributed to the chain transfer reaction to monomer. The lown̄(less than 0.5) of the microemulsion system was attributed to the fast exit of monomeric radicals

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300501

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA mathematical model was developed to simulate the polymerization kinetics of styrene oil‐in‐water microemulsions. Nucleation of particles in microemulsion droplets was assumed to account for the number of particles generated. It was found that the entry rate coefficient of radicals into microemulsion droplets is much smaller than the entry rate coefficient into monomer‐swollen particles. All particles contain at most one growing radical. Various radical entry mechanisms were evaluated using the simulation. The possibility of flocculation between particles during the later stages of the polymerization and the high desorption rate of monomeric radicals was suggested by the simulation results. The likelihood of re‐entry of desorbed radicals was den on

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300502

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractStereoregular polyamides containing two chiral backbone carbons in the repeating unit were prepared by polycondensation of bis(pentachlorophenyl) 2,3‐O‐methylene‐L‐tartrate with 1,9 and 1,12‐alcanediamines activated asN,N′‐bis(trimethylsilyl) derivatives. The polymers were characterized by elemental analysis, IR, and1H‐NMR spectroscopy, and differential scanning calorimetry. Both viscosimetry and GPC were used to estimate the molecular weights which ranged between 6000 and 44000. These polytartaramides were readily soluble in chloroform, displayed moderate optical activity in solution, and formed highly cr

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300503

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractNovel bismaleimides (BMIs) were prepared from functional monomaleimides and diglycidyl ether of bisphenol A (DGEBA) and some of them were shown to have good processibility and improved water resistance while retaining characteristic thermal stability of polyimide. Functional monomaleimides were synthesized via the condensation reaction of maleic anhydride with either aminobenzoic acid or aminophenol. Crosslinking reaction of thus obtained BMIs was carried out with or without catalyst at the temperature range of 100–250°C. The type of the functional group species and their position in monomaleimides significantly affected the crosslinking behavior of the resulting BMIs and the thermal property of their crosslinked products. BMIs with meta linkage, obtained from meta monomaleimides, exhibited much faster thermal crosslinking behavior than corresponding para BMIs. When the molecular weight of BMI was larger, the crosslinking density became smaller andTgwas lower as expected, while the viscosity started to increase at a higher temperature. Glass transition temperatures of the crosslinked resins were in the range of 160–250°C and these resins showed excellent thermal stability up to

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300504

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA model for evaluating the instantaneous degree of polymerization distribution of homopolymers produced in emulsion, based on the mathematics of the Markov chains, is developed. The model accounts for any number of active chains per particle, as well as for the two fundamental mechanisms of chain termination: mono‐ and bi‐molecular, both by combination and by disproportionation. The core of the model is the so called subprocessmain process treatment, which allows us to correctly evaluate the degree of polymerization of the chains growing in the polymer particles, by distinguishing between the events experienced by the polymer chain which imply a change of its degree of polymerization (subject transitions) and those which imply only a change in the particle state (environment transitions). This is obtained by properly defining the one‐step transition probability matrix of the relevant Markov process. Once this is done, the evaluation of the distribution of the degrees of polymerization reduces to a few simple operations among matrices. Explicit expressions for the instantaneous probability density functions and the relative cumulative distributions are obtained. The application of such relationships is facilitated by the numerical procedures reported in the Appendices. The results of the model developed in this work are in agreement with those of earlier models in the range of parameter values of practical interest. In the limit of very low molecular weights, only the model developed in this work provides the correct answer. Moreover, a much more significant result is its applicability to the case of emulsion copolymerization, as it is shown in Pa

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300505

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA model for evaluating instantaneous degree of polymerization distribution and the chain composition distribution of copolymers produced in emulsion is developed. The approach adopted is based on the mathematics of Markov processes and represents an extension of the one developed for homopolymers in Part I. As in the homopolymer case, the main aspect of the theoretical treatment is the definition of the proper one step transition probability matrix through the so called subprocess‐main process procedure. The model accounts for monomolecular and bimolecular termination (both by combination and disproportionation) and, in principle, it can be applied to any number of reacting monomer species as well as to any number of active chains per particle. However, only the 0–1–2 and 0–1–2–3 emulsion copolymerization systems are discussed in detail. In the case of the chain composition distribution, the model allows the calculation of its moments only, through the method of the Generating Function associated with the probability density function. The expression obtained for the instantaneous probability density functions, as well as for the corresponding cumulative distributions, are all in explicit form and involve only algebraic operations among matrices. Efficient numerical procedure for their application are reported in the Appendix. Illustrative calculations are reported for a 0–1–2–3 copolymerization system, simulating the copolymer styrene–methylmethacrylate. The effect of the various termination mechanisms on the distribution of degrees of polymerization and on the first two moments of the chain composition distribution is discussed in detail. Finally, the three dimensional overall distribution function of both chain length and composition is shown under the assumption of Gaussian type chain compo

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300506

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractBlock copolymers, composed of a hydrophobic block [poly(N‐t‐butylbenzoyl ethylenimine) or poly(N‐lauroyl ethylenimine)] and a hydrophilic block [poly(N‐propionyl ethylenimine)], synthesized by cationic ring‐opening polymerization of 2‐substituted Δ2‐oxazolines, were selectively deacylated by acid hydrolysis. The hydrolysis process was monitored by using1H‐NMR. The results show that the propionyl groups could be removed from the hydrophilic block of the polymer chain without touching the hydrophobic block, if appropriate reaction cond

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300507

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effect of crosslinked poly(methacrylic acid) (c‐PMAA) on the polymerization ofN‐vinylimidazole in aqueous solution was studied using UV, calorimetry, SEM, and TEM. It was established that synthetic lightly crosslinked PMAA samples behaved intermediate between rigid crosslinked PMAA particles functioning as microreactors, and linear conventional PMAA, where template and conventional polymerization in the surrounding solution are integrated. A modified calorimetric technique was used to measure monomer conversion, and to correct for the rapid adsorption process. Rate enhancements up to a factor of 4 were obtained for the c‐PMAA's, which were lower than those obtained for linear conventional PMAA, and which slightly decreased with increasing crosslink density of the samples. Template complexes possessed a platelet‐like morphology similar to template complexes obtained for line

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300508

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe polymerization of 4‐vinyl‐1‐cyclohexene (4VCHE) with Ziegler–Natta catalysts was studied. The polymerization of 4VCHE by the vinyl group took place with TiCl3–aluminum alkyls catalysts, while vinylene group of 4VCHE did not participate in the reaction, but it affected the polymerization rate of 4VCHE. The effects of aluminum alkyl and type of TiCl3on the polymerization were examined. The overall activation energy for the polymerization was estimated to be 41.9kJ/mol. Monomer‐isomerization copolymerization of 4VCHE andtrans‐2‐butene occurred with the TiCl3‐(i‐C4H9)3Al catalyst to give copolymers consisting of 4VCHE

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300509

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractSide‐chain liquid crystalline (SCLC) silphenylene‐siloxane polymers with a phenyl benzoate mesogenic group and polymethylene spacers were prepared and characterized, and their properties were compared with those of equivalent SCLC polymers, SCLCPs, with a biphenyl mesogenic group. With identical spacers and terminal substituents, the melting temperatures of the former were much lower, but the isotropization temperatures were lowered to a lesser extent, than those of the latter, and, consequently, a more thermally stable nematic phase was obtained for the former. Both types of SCLCPs formed nematic phases, while polymethylsiloxanes with the same side‐chain mesogens exhibited smectic phases with wider temperature ranges. The lower thermal stability of the mesophases in the silphenylene‐siloxane SCLCPs compared to those of the SCLC polymethylsiloxanes can be attributed to both the rigidity of the backbone and the greater separation of the side‐chains along the main chains of t

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300510

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY