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

Abstract

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...