摘要:

AbstractThe authors' kinetic models for network formation in free radical polymerization both for pre‐ and post‐gelation periods are re‐examined and extended to include high mole fractions of divinyl monomer. Network formation in free radical polymerization is a non‐equilibrium process, namely, it is kinetically controlled, and therefore, the crosslinking density of a primary polymer molecule depends on its history. The crosslinking process is responsible for a distribution of crosslinking density with crosslinking density a function of the birth time of a primary polymer molecule. The crosslinking density distribution is an important feature of network formation in free radical polymerization. Under special rather limiting conditions the present kinetic models reduce to Flory's theory of network formation in which an equilibrium system is assumed. These kinetic approaches provide great insight into the phenomena of network formation, and they can readily be applied to emulsion polymer

ISSN:0258-0322    

DOI:10.1002/masy.19900350113

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA stochastic model for evaluating Molecular Weight Distribution (MWD) and Chain Composition Distribution (CCD) of copolymers prepared in emulsion is applied to a “zero‐one‐two” binary system, i.e. with no more than two active chains per particle. Model predictions are compared with those by widely applied literature models based on bulk polymerization equations for evaluating CCD and on simplifying approaches for MWD (Refs. 5 and 6). For the particular system under examination, the range of reliable applicability of these approximated models is limited to high molecular weights (average degrees of polymerization larger than about 500 units), while for shorter chains the model here reported has to

ISSN:0258-0322    

DOI:10.1002/masy.19900350114

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThin layer chromatography with flame ionisation detection (TLC/FID) was applied to determine the chemical composition distribution (CCD) of styrene‐methyl acrylate (S‐MA) emulsion copolymers. The reliability of this method was determined using a well defined high conversion S‐MA solution copolymer. The influence of conversion and monomer water ratio on the emulsion copolymer CCD could successfully be described by a model that uses r values determined in solution, and takes into account the monomer partitioning. The samples were prepared in the presence of 1‐dodecanethiol in order to reduce the molecular mass of the copolymer formed. Not only the conversion part of the total copolymer CCD but also the instantaneous (statistical) part appeared to be im

ISSN:0258-0322    

DOI:10.1002/masy.19900350115

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effect of various monomer addition policies on the copolymer composition during the seeded copolymerization of methyl acrylate and vinyl acetate in a semicontinuous reactor was investigated. Four policies were considered. In the first, which is called optimal policy, the reactor was initially charged with all of the less reactive monomer (vinyl acetate) plus the amount of the more reactive monomer (methyl acrylate) needed to initially form a copolymer of the desired composition. Then, the addition of the remaining methyl acrylate was made at a flow rate that ensured the formation of a copolymer of the desired composition. In the second, the initial charge is the same as in the previous case but the time dependent addition rate of methyl acrylate was decomposed into three periods of constant feed rate. In the third, the initial charge is the same as in the previous policies but the remaining methyl acrylate was added at a constant feed rate. In the forth, both monomers were added under starved conditions. In order to calculate the optimal addition policy, the time evolution of the average number of radicals per particle, ñ, is required. The calculation of ñ involves rate parameters which values are usually unknown. Therefore, a semi‐empirical method for the calculation of the time evolution of ñ was developed. It was found that ñ was always greater than 2. For the experimental conditions used in this work, this result suggested that termination in the polymer particles was affected by gel effect. A gel effect function was estimated and then the optimal addition policy was calculated. Comparison between the different processes showed that, for a fixed process time, the copolymer obtained through the optimal addition policy was more homogeneous than that formed when the methyl acrylate was fed in three periods of constant feed rate and even better than the one obtained using a constant feed rate throughout the process. The copolymer quality of the later process is similar to that of the copolymer formed by means of the starved process. Nevertheless, a more homogeneous copolymer composition can be obtained through the starved process when longer process times are

ISSN:0258-0322    

DOI:10.1002/masy.19900350116

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractAccurate kinetic investigations of emulsion copolymerization of monomers of different polarity have allowed to derive reliable mechanisms which appeared to be more complex than usually expected: polymerization in the water phase seems quite general; the solid content ‐ i.e. monomer/water ratio ‐ or, even the pH(when copolymerizing ionogenic monomers) modify the reactivity ratios in emulsion copolymerization; monomer partition is an upmost parameter. However, it is believed that what may be the monomers and the polymerization process, it is possible to model emulsion copolymerization and to develop simulation softwares. These computer simulations then allow to quantitatively compare theoretical behaviour with experimental data and to improve our knowledge of emulsion process. Furthermore, these programs give the sequence distribution of emulsion copolymers and can predict some important properties like the glass transition, which is closely related to copolymer microstructure and hetero‐geneity. Modelling and simulation have been applied to a lot of emulsion copolymerizations and terpolymerizations of various monomers, including some functional mon

ISSN:0258-0322    

DOI:10.1002/masy.19900350117

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractSmall angle neutron scattering studies have been carried out on copolymer latices prepared using acrylonitrile and styrene. These showed that when one of the monomers was deuterated good contrast in scattering was obtained between the two polymers. In the case of poly(acrylonitrile) ‐ poly(styrene) particles evidence was obtained for a core shell morphology with the poly(acrylonitrile) forming the outer shel

ISSN:0258-0322    

DOI:10.1002/masy.19900350118

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractSubmicron‐size composite polymer particles consisting of two kinds of polymers were produced by seeded emulsion polymerization. Since most polymer pairs are not compatible, phase separation of the polymers proceeds throughout the polymerization and results in unique morphologies. Factors having a great influence on the formation of such morphology were clarified. Special properties can be obtained by controlling the morphology, as demonstrated using examples. Some anomalous composite particles were produced using this metho

ISSN:0258-0322    

DOI:10.1002/masy.19900350119

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA survey of the recent literature is given concerning the synthesis and characterization of functionalized latex particles. Two main methods have been particularly considered and discussed: first, the functionalization of latexes by copolymerization of a basic monomer with adding small amount of a monomer bearing a chemical reactive group, with a special emphasis on the kinetics, the distribution of the functional monomer, the surface morphology of latex particles and the optimization of processes; secondly, the use of surface‐active monomers in such reactions which may confer potential advantages (low level of water‐soluble polymers, control of surface charge density) in comparison with the former ones, provided further information can be obtained on their kinetic behavior in emulsion polymerizat

ISSN:0258-0322    

DOI:10.1002/masy.19900350120

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractIn the emulsifier‐free emulsion polymerization of styrene/potassium persulfate (KPS) system, due to larger particle size and ionic chain ends, the polymerization only occurs in the shell part of the polymer particles (the shell‐growth mechanism). For the styrene/comonomer/KPS system, the hydrophilicity and ionic characteristic of the comonomer play a dominant role in the nucleation and growth mechanisms. If a nonionic comonomer is used, the shell‐growth mechanism also follows. If an ionic comonomer having sufficient cross‐propagation with the monomer is used, the particle size is small and the polymerization occurs uniformly within the particles as in the conventional case. If it has insufficient cross‐propagation, then shell‐growth mechanism o

ISSN:0258-0322    

DOI:10.1002/masy.19900350121

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA reactive latex Styrene (S) ‐ Butyl Acrylate (BuA) functionalized with methyl acrylamidoglycolate methyl ether (MAGME) has been synthesized in emulsion and characterized, which can be further crosslinked with other adapted reactive latices. This work deals mainly with kinetics and location of the monomers and with a comparison between experimental and simulated data based on monomer partition and reactivities. The three stages polymerization of hydrophilic MAGME has been quantitatively explained. From the change in overall propagation rate constants and DSC thermograms, it is concluded that particles are structured with a core richer in S and a shell richer in BuA, a huge amount of MAGME being polymerized in the water phase as hydrosoluble polymer strongly adsorbed onto particles and forming a reactive ultimate laye

ISSN:0258-0322    

DOI:10.1002/masy.19900350122

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY