Synthesis of poly(N-vinyl carbazole)-based block copolymers by sequential polymerizations of RAFT-ATRP

- A variety of unique difunctional haloester-xanthate inifers were prepared and successfully subjected to sequential RAFT polymerization of N-vinylcarbazole (NVK) and ATRP of styrene and methyl methacrylate.
- In the presence of small amounts of bromoxanthate inifers, a rational side reaction of acid-catalyzed NVK dimerization was conceivably proposed through a cationic mechanism.
- Based on the significant results of model reactions, other two chloroxanthate inifers provided first-order kinetic plots on RAFT polymerization of NVK and obtained well-defined PNVK macroinitiators (Mn = 6k-40k; Mw/Mn < 1.35).
- Using a proper ATRP-initiating groups and optimization of the reaction conditions, well-defined BCPs of PNVK-b-PSt (Mn = 5k-12k; Mw/Mn < 1.5) and PNVK-b-PMMA (Mn = 46k-100k; Mw/Mn < 1.35) were thus obtained.

Poly(N-vinylcarbazole) (PNVK) is one of the extensively studied photoconductive polymers because of its wide ranges of applications. Through the reversible addition-fragmentation chain transfer/macromolecular design via the interchange of xanthates (RAFT/MADIX) polymerizations, in this study we investigated the syntheses of PNVK-based block copolymers (BCPs) with styrene (St) and methyl methacrylate (MMA). A variety of difunctional haloester-xanthate inifers were prepared and subjected to sequential polymerizations through RAFT and ATRP. In the presence of small amounts of bromoxanthate inifers, the 1H NMR spectra showed nearly complete consumption of the NVK monomer, but without formation of PNVK. The bromoxanthate inifer could act as acidic moieties that protonated the highly basic NVK monomer. Through 1H NMR and MALDI-TOF spectroscopic analyses, the structures of byproducts were indentified and a plausible mechanism for their formation was proposed. Alternatively, RAFT/MADIX polymerizations of NVK with two chloroxanthate inifers S-[1-methyl-4-(6-chloropropionate)ethyl acetate] O-ethyl dithiocarbonate and S-[1-methyl-4-(6-chloroisobutyrate)ethyl acetate] O-ethyl dithiocarbonate) provided first-order kinetic plots and well-controlled PNVK-Cl MIs (Mn ≈ 6000-40,000; Mw/Mn < 1.35). Using a suitable ATRP-initiating groups and optimization of the reaction conditions, the BCPs PNVK-b-PSt (Mn ≈ 4900-12,800; Mw/Mn < 1.5) and PNVK-b-PMMA (Mn ≈ 46,000-100,000; Mw/Mn < 1.35) were obtained.

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