Abstract
A key for the preparation of polyacrylate-based polyurethane is the synthesis of hydroxyl-terminated polyacrylate. To our knowledge, exactly one hydroxyl group of every polyacrylate chain has not been reported. The hydroxyl-terminated poly(butyl acrylate) (PBA) has been successfully synthesized by degenerative iodine transfer polymerization (DITP) of the n-butyl acrylate (n-BA) using 4,4′-azobis(4-cyano-1-pentanol) (ACPO) and diiodoxylene (DIX) as initiator and chain transfer agent, respectively, and subsequently substituted reaction of the iodine-terminated PBA with β-mercaptoethanol in alkaline condition. The latter reaction was highly efficient, and the terminal iodine at the end of polymer chains were almost quantitatively transformed to a hydroxyl group. 2,2′-Azobis(isobutyronitrile) (AIBN) and ACPO were used as initiators in the DITPs of n-BA. The results demonstrated that they had a significant influence on the terminal groups of the formed polymer chains. The structure, molecular weight, and molecular weight distribution of the hydroxyl-terminated PBA have been studied by 1H, 13C NMR, and GPC results. The components of hydroxyl-terminated PBA were determined by MALDI-TOF MS spectra, and their formation is discussed. The broad molecular weight distribution of the PBA and the difference in the polymerization behaviors from typical living radical polymerization are explained based on the results of 1H NMR and MALDI-TOF MS spectra. The hydroxyl-terminated PBA has been successfully used in the preparation of PBA-based polyurethane dispersions (PUDs). The aqueous PUDs were stable, and based on the DSC results it can be said that the miscibility of hard segments with PBA chains was improved.
Highlights
Polyurethane dispersions (PUDs) are generally synthesized by the condensation polymerization of oligomer polyols, diisocyanate, chain extender, and hydrophilic comonomers
To prepare low-molecular-weight poly(butyl acrylate) (PBA) with both ends capped with hydroxyl groups via degenerative iodine transfer polymerization (DITP), the first issue is the design of an appropriate polymerization system
According to previous reports [18,32], hydroxyl-terminated polyacrylate could be prepared by the DITP of acrylates using diiodoxylene (DIX) and AIBN as di-functional chain transfer agent and initiator, respectively, and this patent claimed that the end-functionalized polymers were useful as reactive intermediates in condensation polymerization, chain polymerization, and heterogeneous polymerization
Summary
Polyurethane dispersions (PUDs) are generally synthesized by the condensation polymerization of oligomer polyols, diisocyanate, chain extender, and hydrophilic comonomers. Preparation of the waterborne polyurethane–polyacrylate hybrid emulsions has been reported, low compatibility between the polyurethane and the polyacrylate has limited its applications [12,13,14,15,16] This problem can be solved by using the polyacrylate as soft segments of aqueous PUDs. The key issue for achieving this purpose is the synthesis of the oligomer polyacrylate diol. Many studies have demonstrated that the DITP is a feasible method for the synthesis of low-molecular-weight polyacrylate (Mn = 2000–6000 g mol− 1 ), but the ratio of iodine-end-capped functional groups cannot reach 100% (mostly only 50–80%). The purpose of the study reported is to synthesize a well-defined α,ω-di(hydroxy)poly(nbutyl acrylate) with relatively low molecular weight, and to use it in the synthesis of PUDs with polyacrylate as soft segment
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