ESR spectroscopic evaluation of void parts in microheterogeneously crosslinked monomethacrylate/dimethacrylate resins by using copper(II) tetraphenylporphyrin spin probe

2000

Macromol. Mater. Eng.

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ESR spectroscopic studies on the microheterogeneity of crosslinked polymers were extended to the attempt on a detailed void evaluation of microheterogeneously crosslinked monomethacrylate/dimethacrylate resins by measuring ESR spectra at lower temperatures, utilizing the interactions between spin probes and side chains. That is, the mobility of copper(II) tetraphenylporphyrin (CuTPP), a spin probe useful for the evaluation of void parts in crosslinked resins, excluded from densely crosslinked network parts to void ones was found to be much restricted at lower temperatures; this provides a useful tool to allow a detailed evaluation of the void parts. Thus, methyl methacrylate (MMA)/ethylene dimethacrylate (EDMA) (mole ratio 70/30) solution copolymerization in toluene at a dilution of 2/3 was chosen as a standard copolymerization system to provide the cured resin with void parts. The effect of introducing polar poly(oxyethylene) units was explored to clarify their interaction with the polar central part of the CuTPP molecule leading to the restricted mobility of CuTPP. The detailed evaluation of void sizes was done by changing the crosslinker content. The polar interaction was prevented by changing the CuTPP spin probe to a nonpolar one; the nonpolar interaction was verified by adding docosyl methacrylate having a long‐chain alkyl group to the MMA/EDMA copolymerization.

“…The ampoule was then immersed in a water bath controlled at 50 l 0.1 8C. The polymerization was proceeded to obtain a completely cured resin for 24 h 6) .…”

Section: Materials and Polymerizationmentioning

confidence: 99%

Section: Esr Spectroscopic Evaluation Of Void Parts In Crosslinked Rementioning

confidence: 99%

Section: Attempt On a Detailed Void Evaluation By Utilizing The Intermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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ESR spectroscopic studies on the microheterogeneity of crosslinked polymers, 3. Attempt to a detailed evaluation of void parts in monomethacrylate/dimethacrylate resins by ESR measurements at lower temperatures

Aota

Nishizawa

2000

Macromol. Mater. Eng.

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“…The clarification of polymerization characteristics of microgel is considered to be significant because microgelation leads not only to delayed gelation, [3][4][5][6][7][8][9][10][11][12][13][14][15][16] but also to the inhomogeneity of network structures of three-dimensional crosslinked polymers as closely related to their properties. [17][18][19][20][21][22][23][24][25][26] EXPERIMENTAL ABz, supplied by Daiso Co., Ltd., as monomer was purified by vacuum distillation under nitrogen. Benzoyl peroxide (BPO) was purified by repeated precipitation from a chloroform solution with methanol.…”

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confidence: 99%

Copolymerization of Poly(allyl methacrylate) Crosslinked Polymer Microspheres with Allyl Benzoate

Fujihashi

Aota

2001

Polym J

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KEY WORDSAllyl Methacrylate / Allyl Benzoate / Microsphere / Crosslinking / Gelation / Microgel / In the preceding article, 1 we have discussed in detail the crosslinking polymerization of diallyl terephthalate (DAT) in the presence of microgel-like poly(allyl methacrylate) microsphere (PAMA microsphere) with abundant pendant allyl groups in order to clarify the polymerization behavior of microgel in the free-radical crosslinking polymerization of multivinyl compounds 2 and, moreover, the reactivity of crosslinked polymer microspheres. In the presence of a small amount of microsphere the wide, free space among microspheres is a main polymerization locus of DAT and, concurrently, a small portion of DAT copolymerizes with the allyl groups present on the surface of microsphere. With the progress of polymerization, the structure of resulting prepolymer in the free space grows to be a more branched form through crosslinking reaction, whereas the number of pendant allyl groups on the surface of microsphere, responsible for crosslinking, increases remarkably through the copolymerization with DAT. Eventually, the polymerization system reaches the critical point at which gelation occurs as a result of the intermolecular crosslinking reaction between microspheres. Thus, the gelation is promoted with an increase in the feed amount of PAMA microsphere. In this connection, the copolymerization with allyl benzoate (ABz) is treated in place of DAT. Because ABz is a monoene counterpart of DAT, the copolymerization of allyl groups present on the surface of PAMA microsphere with ABz reduces the number of allyl groups at the surface of microsphere responsible for crosslinking, leading to the reduced crosslinking reactivity of microsphere with the progress of polymerization as completely opposed to the case of the copolymerization with DAT. The results obtained are in a good agreement with the above mechanistic discussion. † To whom correspondence should be addressed.In the present article, the latter copolymerization with ABz was extended to the further discussion of the characteristic polymerization behavior of PAMA microsphere as reactive crosslinked polymer microsphere or pseudo-microgel. The clarification of polymerization characteristics of microgel is considered to be significant because microgelation leads not only to delayed gelation, 3-16 but also to the inhomogeneity of network structures of three-dimensional crosslinked polymers as closely related to their properties. [17][18][19][20][21][22][23][24][25][26] EXPERIMENTAL ABz, supplied by Daiso Co., Ltd., as monomer was purified by vacuum distillation under nitrogen. Benzoyl peroxide (BPO) was purified by repeated precipitation from a chloroform solution with methanol.Copolymerization was carried out as described previously. 27 After a predetermined time of reaction, the copolymer was precipitated by pouring the reaction mixture into a large excess of cooled hexane containing a small amount of t-butylcatechol as inhibitor. The purification of the soluble copolymer or pre...

Electron spin resonance spectroscopic studies on microheterogeneity of crosslinked polymers. IV. Correlation between void evaluation of crosslinked resin and microgelation in monomethacrylate/dimethacrylate copolymerizations

J of Applied Polymer Sci

Nishizawa

Yamashita

et al. 2001

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ABSTRACT:Electron spin resonance spectroscopic studies on the microheterogeneity of crosslinked polymers were performed to ascertain the correlation of the void evaluation of monomethacrylate/dimethacrylate (DMA) cured resins with the microgel formation before gelation in their crosslinking copolymerizations. Lauryl methacrylate (LMA) was added to methyl MA (MMA)/ethylene DMA (EDMA) copolymerization because the addition of LMA reduces the occurrence of intramolecular crosslinking by the steric hindrance of bulky long-chain alkyl groups, leading to the formation of a less densely crosslinked microgel core and a less microheterogeneously crosslinked resin. Then MMA/vinyl laurate (VL)/EDMA terpolymerization was performed because the polymerizability of conjugated methacryloyl groups belonging to MMA and EDMA is markedly high compared with the unconjugated vinyloxycarbonyl group of VL. Thus, enhanced microheterogeneity for MMA/VL/EDMA terpolymerization would be induced as compared with MMA/EDMA copolymerization. Finally, allyl MA (AMA) and vinyl MA (VMA) crosslinkers were used in place of EDMA because in the polymerizations of AMA and VMA having two types of carbon-carbon double bonds of different reactivities there was no microgelation observed up to the gel-point conversion.