Synthesis and Functionalization of Periodic Copolymers

Abstract

For the copolymerization of non-conjugated olefins and maleimides, it is known that under certain conditions periodic ABA monomer sequences are formed. In this work, such a copolymerization is used to create polymers which have defined (periodic) monomer sequences and can be functionalized after polymerization. The copolymerization of pentafluorophenol (PFP) active esters of 4-pentenoic acid and perillic acid with N-phenyl maleimide (PhMI) was studied in 1,2-dichloroethane (DCE) and 1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol (HFPP). In DCE and for the copolymerization of the PFP ester of 4-pentenoic acid and PhMI in HFPP, polymers were formed where the active esters were separated by at least one PhMI unit. The average number of separating PhMI units can be controlled by varying the feed ratio of the monomers. For the copolymerization of the PFP ester of perillic acid in HFPP, a preference for the formation of periodic copolymers was observed, where active esters were preferably separated from each other by a maximum of two PhMI moieties. Therefore, the copolymerization of said active ester containing monomers with PhMI provides a platform to create polymers in which reactive moieties are distributed along the polymer chain in different fashions. The active esters in the non-conjugated vinyl monomers could be used in a post-polymerization functionalization step to create functionalized polymers with defined monomer sequences in a modular way.

Keywords: alternating copolymer; periodic copolymer; post-polymerization functionalization; sequence control.

Figure 1

Structures of the monomers used in this work.

Figure 2

Copolymer composition found at low conversion for a range of different monomer feed ratios ([M₁]₀/[PhMI]₀ = 1/7, 1/3, 1/2, 1/1, 2/1, 3/1, 7/1) for the copolymerization of (a) PentPFP/PhMI and (b) PerPFP/PhMI with AIBN in DCE at 60 °C. Data points are shown as black dots, the linear-least-square (LLS) fit (dashed lines) is shown as an example.

Figure 3

Generalized structures of the copolymers of (a) PentPFP or (b) PerPFP with PhMI prepared in DCE.

Figure 4

Copolymer composition found at low conversion for a range of monomer feed ratios for the copolymerization of (a) PentPFP/PhMI and (b) PerPFP/PhMI with AIBN in HFPP at 60 °C. Data points are shown as black dots, the linear-least-square (LLS) fits (dashed line) from the terminal and penultimate model respectively are shown as an example of one of the fits.

Figure 5

Generalized structures of the copolymer of PerPFP with PhMI prepared in HFPP.

Figure 6

Predominant pathways in the copolymerization of PerPFP with PhMI in (a) DCE and (b) HFPP.

Figure 7

Schematic representation of the post-polymerization functionalization of P(PentPFP-co-PhMI) with n-hexylamine and benzylamine.

Figure 8

¹H-NMR spectra of (bottom) P(PentPFP-co-PhMI), and after functionalization with (middle) benzylamine or (top) n-hexylamine.