Primary Polymer Chains Research Articles

Novel Amphiphilic Network Polymers Consisting of Polar, Short Primary Polymer Chains and Nonpolar, Long Cross-link Units Obtained by Free-Radical Cross-linking Monomethacrylate/Dimethacrylate Copolymerizations

Solution copolymerizations of 2-hydroxyethyl methacrylate (HEMA), a polar monomer having a hydroxyl group, with 5 mol % (corresponding to 35.7 wt %) heneicosapropylene glycol dimethacrylate (PPGDMA-21), a nonpolar monomer having a poly(oxypropylene) unit, were carried out in MeOH at a dilution of 2/3 in the presence of different amounts of lauryl mercaptan as a chain transfer agent, providing novel amphiphilic vinyl-type network polymers consisting of polar, short primary polymer chains and nonpolar, long cross-link units. The vinyl-type network polymers formed via highly branched prepolymers have abundant dangling chains as their characteristic feature, especially when the primary polymer chain length is short, because both terminal parts of primary polymer chain would be dangling chains. The amphiphilicity of the resulting gels was checked by measuring their swelling ratios in the mixed solvents consisting of nonpolar tert-butylbenzene (t-BB) and polar MeOH; thus, with an increase in the MeOH volume percent, the gels shrank to the smallest swelling ratio at the start point (i.e., in pure t-BB), swelled gradually and then rather sharply beyond 20 vol %, reached the maximum swelling at about 70 vol %, and then shrank gradually up to a rather high swelling ratio at the terminal (i.e., in pure MeOH). The profiles of the solvent component dependencies of the swelling ratios are characteristic of novel amphiphilic gels. The conversion dependency of the characteristic swelling behavior suggests that the response of the gel obtained at an earlier stage of gelation was sharper than that of the gel obtained at a late stage of gelation. The influence of H2O on the characteristic swelling behavior of resulting amphiphilic gels was examined by measuring their swelling ratios in the mixed solvents consisting of MeOH/H2O or acetone/H2O in order to collect information about the role of cross-link units on the swelling behavior of amphiphilic gel.

Influence of structural parameters on the degradation of ultrahigh-molecular-weight vinyl-type network-polymer precursors during elution through size exclusion chromatography columns

Network-polymer precursors obtained in various crosslinking monovinyl/divinyl copolymerization systems, including benzyl methacrylate/1,6-hexanediol dimethacrylate, benzyl acrylate (BzA)/1,6-hexanediol diacrylate (HDDA), and vinyl benzoate/divinyl adipate, were subjected to degradation during elution through size exclusion chromatography (SEC) columns, although the copolymerizations were conducted under specified conditions where the factors for the greatly delayed gelation from the Flory–Stockmayer gelation theory were reduced. The most remarkable degradation was observed for the BzA/HDDA copolymerization, which provided prepolymers with the most flexible backbone chains. Thus, the BzA/HDDA precopolymers were chosen, and their degradation behavior during elution through SEC columns was explored in detail as one of the representatives of vinyl-type network-polymer precursors. The results were correlated with the structural parameters of network-polymer precursors, including primary polymer chain length, branched structure, and multiple crosslink or network structure. The degradation became more remarkable with decreased primary polymer chain length, that is, the increment of branching, whereas reduced degradation was observed with the incorporation of loop and network structures into the prepolymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 577–582, 2003

Effect of hydrogen bonds on gelation by introduction of carboxyl groups in the free-radical crosslinking copolymerization of butyl methacrylate with 1,6-hexanediol dimethacrylate

The preliminary study of the effect of physical crosslinking on the gelation in monovinyl/divinyl copolymerizations is described. Thus, mono(2-methacryloyloxyethyl) succinate was added to the crosslinking copolymerization of butyl methacrylate with 1,6-hexanediol dimethacrylate and the gelation was explored in terms of the effect of hydrogen bonds formed between carboxyl groups introduced into the primary polymer chain.

Microgel formation in emulsion copolymerization: 2. Seeded polymerization

Microgel formation in seeded emulsion copolymerization of methyl methacrylate and ethylene glycol dimethacrylate is investigated both experimentally and theoretically. By introducing seed latex, the network structure development can be changed significantly. Even when the crosslinking density development takes a similar pattern as the crosslinking copolymerization in homogeneous media, the molecular weight development shows both types of behavior that is characteristic of emulsion polymerization without seed latex and of homogeneous polymerization, depending on the primary polymer chain length and the mole fraction of the divinyl monomer used. Once the microgels are formed, the weight-average molecular weight increases just linearly with conversion due to a very small locus of polymerization. The present investigation reveals important characteristics of gelation phenomena in a limited space. © 1996 John Wiley & Sons, Inc.

Kinetics of polyelectrolyte network formation in free-radical copolymerization of acrylic acid and bisacrylamide

Recently, a research/development program has been initiated to investigate the kinetics of synthesis, characterization and applications of polyelectrolyte networks. The research on crosslinking involves both theoretical development and experimentation. Herein, is provided a summary of this work. In the experimental polymerization done to date, acrylic acid (AA)/N.N'-methylenebisacrylamide (BAM) was studied in considerable detail. The polymerization conditions were: temperature, 50°C; initial monomer concentration, 5 wt%, of which 1.0 mol% is BAM; K2S2O8(KPS) as the initiator, 10−3 mol/L; pH range, 1 − 13; sodium chloride concentrations up to 3.1 mol/L. Measurements included: monomer conversion, polymer composition, sol/gel fraction, swelling ratio, and the densities of primary cyclization, secondary cyclization and crosslinking. It was found that the effect of polymerization parameters on the resulting polymer network microstructure was dramatic, and in particular, the pH and ionic strength of the reaction medium were important parameters. In the theoretical studies, the Tobita-Hamielec kinetic gelation model was extended to incorporate the concept of ion pair interaction and the divinyl loop formation. The system was treated as a multi-component polymerization of acrylic acid, acrylate ion, acrylate ion pair and bisacrylamide. The model permits one to investigate the development of the crosslinking density distribution among primary polymer chains during the course of polymerization as a function of pH and ionic strength.

Kinetics of polymeric network synthesis via free‐radical mechanisms ‐ polymerization and polymer modification

AbstractThe kinetics of polymeric network formation via free radical mechanisms is an attractive research area because there are many phenomena which are not well understood and in addition, the commercial potential for crosslinked systems is great. Recently, a large research/development program was initiated at the McMaster Institute for Polymer Production Technology (MIPPT) to investigate the fundamentals and applications of polymeric network, in particular, the kinetics of synthesis via free‐radical mechanisms and network characterization. The research on crosslinking involved both theoretical developments and experimentation. Herein is provided a comprehensive summary of this work.In the experimental polymerization, two comonomers, methyl methacrylate (MMA) / ethylene glycol dimethacrylate (EGDMA) and acrylamide (AAm) / N,N‐methylene bisacrylamide (Bis), as model systems were studied in considerable detail. Measurements included: monomer conversions, radical concentrations, sol/gel fractions, crosslink densities (equilibrium swelling and swollen‐state 13C‐NMR) over the entire range of divinyl monomer levels as a function of polymerization time. In the polymer modification, high density polyethylenes were crosslinked using peroxides and γ‐radiation. For this system, crosslinking and chain scission occur simultaneously.In the theoretical studies, it was shown that in general, network formation by free‐radical mechanisms is highly irreversible requiring that the classical equilibrium gelation theories after Flory/Stockmayer be generalized. The general model which was developed using the pseudo‐kinetic rate constant method predicts the existence of a crosslink density distribution (crosslink density of a primary polymer chain depends on its birth time) with a variance which can vary widely depending on network synthesis conditions.

Influence of cross-link density distribution on network formation in free-radical copolymerization of vinyl/divinyl monomers

The influence of the cross-link density distribution on polymer network formation in free-radical copolymerization of vinyl/divinyl monomers was investigated using the Tobita-Hamielec kinetic model coupled with the Macosko-Miller statistical gelation model. The properties investigated were molecular weight development of sol, the gelation point, the sol/gel fraction, and properties of primary polymer chains. Errors involved in neglecting the cross-link density distribution (or assuming a zero variance for the distribution) were correlated with an index of distribution variance in the gelation equations

Study of diallylisophthalate polymerization by DSC and PMR methods

The radicapolymerization of diallylisophthalate was studied, in the presence of three initiators, with continuous temperature change up to 200°C. Three heat-evolution peaks were observed, connected with initiator decomposition. Monomer consumption and double bond conversion were followed in the course of the polymerization. Changes in the content of double bonds and in the number of inter-crosslink units were determined from DSC and PMR data. The polymerization process consists of two stages: quasilinear polymerization and structurization. Monomer is consumed to produce the primary polymer chains, whereas structurization is characterized by the formation of secondary polymer chains by was of double bond consumption.

The kinetics of block and graft copolymerization of acrylonitrile

AbstractThe polymerization of a monomer in the presence of a preformed polymer with suitable structural features gives rise to block or graft copolymers, which, in favorable circumstances, may be isolated as well‐characterized materials. For preparing block copolymers a primary polymer with amine endgroups can be used as a macromolecular transfer agent. Graft copolymers may be prepared by using a primary polymer with terminal double bonds which copolymerize with the second monomer. We have studied the kinetics of block and graft copolymerization based on these methods with particular references to the systems in which the second monomer is acrylonitrile. All transfer agents reduce the rate of heterogeneous polymerization of acrylonitrile since the reduction in molecular weight leads to a diminution in the mean degree of occlusion of the propagating radicals and a consequent increase in the effective termination coefficient. We have found the effect of macromolecular transfer agents on the rate to be greater than that of simple amines. This behavior is attributed to the fact that the radicals produced by transfer are attached to primary polymer chains which are present in solution; as propagation proceeds the growing radicals remain in solution until a comparatively late stage in their growth on account of the solubilizing action of the primary polymer chains. The termination coefficient for these radicals is therefore relatively high and the rate of polymerization correspondingly low. The solubilization of polymer radicals in graft polymerization is less marked than in block copolymerization; this is shown to be consistant with the mechanism of solubilization suggested.