Degradation of Ultrahigh Molecular Weight Poly(styrene-co-m-divinylbenzene)s as Network-Polymer Precursors in SEC Columns

Abstract

KEY WORDSDegradation / SEC Column / Styrene / m-Divinylbenzene / Ultrahigh Molecular Weight / Network-Polymer Precursor / As an extension of our continuing studies concerned with the mechanistic discussion of the three-dimensional network formation in the freeradical polymerization and copolymerization of multivinyl compounds, 1 the preceding article 2 dealt with the crosslinking copolymerization of styrene (St) with m-divinylbenzene (m-DVB) as a most typical monovinyl/divinyl system. Thus, the reasons for the greatly delayed gelation from Flory-Stockmayer gelation theory (FS theory) 3 have been discussed extensively in order to clarify the crosslinking polymerization mechanism of multivinyl compounds. 1 The actual gel point should be close to the theoretical one if the experiment were done under the polymerization conditions in which the polymer concentration, at the theoretical gel point, would be high enough to reduce the significance of a thermodynamic excluded volume effect as a primary factor and, furthermore, the intramolecular crosslinking preceded by the intermolecular crosslinking could be suppressed. Our interpretations are verified for monomethacrylate/dimethacrylate, 4, 5 monoacrylate/diacrylate, 6 and St/m-DVB 2 copolymerizations, in which the results obtained are discussed in terms of ideal network formation according to FS theory.In a series of these investigations, the detailed pursuit of the variation of molecular-weight distribution (MWD) curves with conversion is inevitable for a full understanding of crosslinking polymerization because the MWD curves should rapidly broaden towards a higher molecular weight side with conversion as a result of exclusive occurrence of intermolecular crosslinking reaction leading to ideal network formation. 3,7,8 Here it is worthy to note that a size-exclusion chromatography (SEC) is commonly used to determine † To whom correspondence should be addressed. the molecular weight and the MWD of resulting prepolymers. However, as a technique it is not always applicable to our crosslinking polymerization systems because the structure of prepolymer changes from a linear to a branched form with progressing polymerization and, moreover, the content of ring or loop structure introduced into the linear portion or primary chain and the content of multiple crosslink or network structure in the branched form depend on the polymerization conditions. On the other hand, SEC equipped with a multiangle laser light scattering (MALLS) device (SEC-MALLS) is expected to be a very useful and efficient tool in characterizing our prepolymers because the use of MALLS, as an absolute detector, enables the molecular weight and MWD to be determined directly without any calibration. 5 During the progress of our investigation, we noticed that the degradation of poly(St-co-m-DVB) prepolymer of ultrahigh molecular weight obtained at the conversion close to the gel point occurred significantly in SEC columns. That is, the molecular weights determined by both SEC-MALLS and light scattering (LS) me...

Free-radical crosslinking polymerization of unsymmetrical divinyl compounds, 1 Gelation in the polymerization of allyl methacrylate

“…[10] In this connection, microgelation was demonstrated to have a small A 2 value of less than 10 -5 mol cm 3 g -2 in the EDMA polymerization. [7,8]…”

“…As part of our previous work, microgelation was pursued directly by light scattering for the polymerization of ethylene dimethacrylate (EDMA) and its copolymerization with methyl methacrylate (MMA). [7,8] In this connection, the crosslinking polymerization of allyl methacrylate (AMA) as an unsymmetrical divinyl compound was explored for comparison: Because AMA has two different types of double bonds, i. e., conjugated methacryloyl and unconjugated allyl groups, and the reactivity of the methacryloyl group relative to the allyl group is quite high, the preferential polymerization of methacryloyl group leading to the formation of prepolymer having abundant pendant allyl groups occurs at an early stage of polymerization. [4] With the progress of polymerization, the intermolecular and intramolecular crosslinking reactions occurs gradu-Full Paper: As an extension of our continuing studies concerned with the free-radical crosslinking polymerization of multivinyl compounds, this article deals with the gelation in the polymerization of allyl methacrylate (AMA) as a typical unsymmetrical divinyl compound containing two types of vinyl groups such as methacryloyl and allyl ones having quite different reactivities.…”

Mechanistic discussion of cationic crosslinking copolymerizations of 1,2‐epoxycyclohexane with diepoxide crosslinkers accompanied by intramolecular and intermolecular chain transfer reactions

“…The slopes of the correlation lines of M w versus elution volume shifted a bit upward with conversion but any specific correlation lines were not observed al all as opposed to the case of the cationic crosslinking ECH/BECHMA(80/20) copolymerization, especially at the conversion close to the gel point. Moreover, the M w value of the ECH/BECHMA(80/20)‐NPP obtained at 49.1%, very close to the gel‐point conversion of 49.6%, was estimated to be only 5.0 × 10 5 , although the exclusion limit of SEC was much higher at 2 × 10 7 ; this will be discussed later in connection with the degradation of ultrahigh‐molecular‐weight NPPs during elution through SEC columns 51, 52…”

“…Our previous articles51, 52 dealt with the free‐radical crosslinking monovinyl/divinyl copolymerizations as an extension of our continuing studies concerned with the mechanistic discussion of the three‐dimensional network formation in crosslinking multivinyl polymerization 1. During the detailed pursuit of the variation in molecular weight distribution curves with conversion by SEC‐MALLS, we noticed by chance that the degradation of an ultrahigh‐molecular‐weight NPP obtained at a conversion close to the gel point occurred significantly during elusion through SEC columns.…”

Construction of Crosslink‐System‐Materials Utilizing Designed Network‐Polymer‐Precursor Modules

“…[17] During the progress of our investigation, we noticed by chance that the degradation of NPPs with ultrahigh molecular weight obtained at a conversion close to the gel point occurred significantly during elution through SEC columns. [18,19] That is, the molecular weights determined by both SEC-MALLS and light scattering (LS) measurements were compared in detail. Although both results were in a good agreement within experimental errors for NPPS of moderate molecular weight less than one million, the discrepancy between both measurements became greater with further increment of molecular weight, i.e., with the progress of polymerization.…”