Control of Intermolecular Crosslinking by Long-Chain Alkyl Groups in the Free-Radical Crosslinking Copolymerizations of Alkyl Methacrylates with Trimethylolpropane Trimethacrylate

抄録

This article deals with the further discussion of the steric effect of long-chain alkyl groups on the network formation in the free-radical crosslinking copolymerizations of alkyl methacrylates including hexyl methacrylate (HMA), lauryl methacrylate (LMA), and stearyl methacrylate (SMA) with trimethylolpropane trimethacrylate (TMPTMA), especially focused on the control of intermolecular crosslinking leading to gelation. The MWD curves were broadened toward higher molecular weight side with conversion for HMA/TMPTMA copolymerization as a reflection of the occurrence of intermolecular crosslinking induced by a lessened steric hindrance of shortened alkyl groups. On the other hand, the opposite results were observed when LMA was replaced by SMA having a longer alkyl group. Then, the solvent effect on the gelation in LMA/TMPTMA copolymerization was discussed because the steric effect of long-chain alkyl groups on the intermolecular crosslinking leading to gelation would be influenced by the change of the conformation or the interpenetration of polymer chains in various solutions caused by the difference in their solvent powers. The delay of gelation from theory became smaller in dioxane than in benzene, whereas it was reversed in cyclohexane/benzene (9/1 v/v), suggesting that the steric effect of long-chain alkyl groups on gelation was reduced or enhanced in a tight-coiled or rather extended conformation, respectively. The interpenetration of polymer chains was enhanced in dioxane as reflected on the MWD curves broadened toward higher molecular weight side with conversion.