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Various types of soluble crosslinked polymers obtained from the copolymerization of methylmethacrylate (MMA) and p‐divinylbenzene (p‐DVB) in the presence of a transfer agent (CBr4) have been discussed in relation to the variation of the structure during the reaction time. When [p‐DVB]/[MMA] = 1.49 × 10−3 and [CBr4]/[MMA] = 1.28 × 10−4, only linear polymers (primary polymer; Mn = 1.0 × 105) with pendant vinyl groups are formed intially. Considerable branched structure is attained in rather large polymers (Mn = 2.5 × 105), but the number of pendant double bonds is not enough to reach the gelation. As the concentration of the transfer agent becomes high, the intermolecular crosslinking is depressed, and the formed polymers contain loops and short chains. At [p – DVB]/[MMA] = 7.43 × 10−3 and [CBr4]/[MMA] = 1.28 × 10−3, the shape of polymer with the same Mn became compact gradually with increasing reaction time. These results are considered to be useful for the preparation of soluble crosslinked polymer with controlled structure.

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Vinylbenzyl S‐thioacetate (1) was prepared from thioacetic acid and chloromethylstyrene. Although bulk polymerization of 1 afforded a crosslinked polymer, solution polymerization in chlorobenzene afforded a corresponding soluble polymer. The S‐thioacetate group did not react during the radical polymerization of 1. Bulk copolymerization of 1 with styrene afforded a soluble copolymer when the feed ratio of 1 was lower than 30 mol %. Soap‐free emulsion copolymerization of 1, St, divinylbenzene, and 2‐hydroxyethyl methacrylate (66 : 28 : 1 : 5) was carried out in water using 2,2′‐azobis (N,N′‐dimethyleneisobutyramidine) dichloride as an initiator to afford uniform spherical microgel 2, whose average diameter was 135 nm. Aminolysis of 2 with an excess amount of butylamine in the presence of sodium tetrahydridoborate followed by treatment with hydrochloric acid resulted in complete removal of the acetyl group to give a slightly distorted spherical microgel (MG‐SH) bearing mercapto group. The average diameter of MG‐SH was 165 nm. Trans‐esterification of p‐nitrophenyl acetate (3) in the presence of triethylamine was efficiently accelerated by the addition of MG‐SH. The radical polymerization of methyl methacrylate (MMA) in the presence of suspended MG‐SH in chlorobenzene afforded the MMA‐grafted microgel. Although MG‐SH is a crosslinked gel, it acts as a soluble polymer bearing mercapto group. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1443–1451, 1997

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