Controlled Synthesis of Poly(vinylamine)-Based Copolymers by

Article pubs.acs.org/Macromolecules

Controlled Synthesis of Poly(vinylamine)-Based Copolymers by Organometallic-Mediated Radical Polymerization Mathilde Dréan,†,‡ Philippe Guégan,‡ Christophe Detrembleur,† Christine Jérôme,† Jutta Rieger,‡ and Antoine Debuigne*,† †

Center for Education and Research on Macromolecules (CERM), Department of Chemistry, University of Liege (ULg), Sart-Tilman, Allée de la Chimie 3, Bat. B6a, B-4000 Liège, Belgium ‡ UPMC Univ Paris 06, CNRS, Institut Parisien de Chimie Moléculaire (IPCM), UMR 8232, Team Chimie des Polymères (LCP), Sorbonne Universités, 4 Place Jussieu, F-75005 Paris, France S Supporting Information *

ABSTRACT: Living/controlled polymerization methods have enabled the synthesis of numerous (co)polymers with defined compositions and architectures. However, the precision design of poly(vinylamine)-based copolymers remains challenging despite their extensive use in various fields of applications and the clear benefits to finely tune their properties. Here, we report on a two-step strategy for the synthesis of tailor-made poly(vinylamine) derivatives through the organometallicmediated radical (co)polymerization (OMRP) of N-vinylacetamide and/or N-methylvinylacetamide followed by acid hydrolysis of the acetamide groups. A series of well-defined homopolymers as well as statistical and block copolymers with pendant primary and/or secondary amines having controlled molar masses, compositions, and low dispersities were produced accordingly. The reactivity ratios of the comonomers as well as the composition drift along the chain were determined in order to have a precise idea of the polymer structures. These advances represent a significant step toward an efficient platform for synthesis of this important class of amino group-containing (co)polymers.

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INTRODUCTION Because of its widespread use in various fields of applications like surfaces and interfaces engineering,1,2 water purification,3 paper additives,4−6 and many more huge efforts have been devoted to the development of straightforward synthetic routes to the simplest primary amine functional polymer, i.e., poly(vinylamine) (PVAm).7 The basic characteristics of this polymer that makes it such a success are metal binding capacity,8,9 polyelectrolyte complexation,10 water solubility, and pH-responsiveness.11 However, the inherent instability of vinylamine, which is involved in a tautomeric equilibrium with the corresponding imine, prohibits its direct polymerization.12 As a consequence, the synthesis of PVAm necessarily consists of a multistep process. It can notably be produced by polymerization of acrylamide followed by the Hoffman rearrangement generating the pendant primary amines.13 Nevertheless, in this case, significant quantities of carboxyl and urea groups contaminate the PVAm backbone.14 A more efficient synthetic route is based on the free radical polymerization (FRP) of N-vinyl monomers followed by deprotection and release of the masked amino functions. For example, PVAm with high density of amines can be produced either by hydrazinolysis of poly(N-vinylphthalimide) (PNVPi)15 or by polymerization of acyclic N-vinylamides, namely N-vinyl© XXXX American Chemical Society

formamide (NVF) or N-vinylacetamide (NVA), and subsequent hydrolysis of the pendant amide groups.16−20 On the other hand, controlled radical polymerization (CRP) has enabled the synthesis of numerous polymers with predictable molecular parameters, compositions, architectures, and functionalities. However, the controlled synthesis of poly(vinylamine)s remains challenging so far despite the benefits that can arise from fine adjustment of its macromolecular parameters. Indeed, producing the well-defined precursors of PVAm by CRP is not trivial because of the lack of resonance stabilization and the high reactivity of the propagating radicals deriving from nonconjugated N-vinyl monomers.21 The reversible addition−fragmentation chain transfer (RAFT) polymerization based on xanthate- and dithiocarbamate-type chain transfer agents, also called MADIX (macromolecular design via the interchange of xanthates),22,23 allows good control of the N-vinylphthalimide (NVPi) polymerization and the formation of well-defined PVAms after hydrazinolysis.15 Polystyrene-b-PNVPi and PNVPi-b-poly(N-isopropylacrylamide) block copolymers were Received: May 13, 2016 Revised: June 16, 2016

A

DOI: 10.1021/acs.macromol.6b00992 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Table 1. Preparation of Well-Defined PNVA by Photochemically Initiated OMRP and Conversion into PVAm by Acid Hydrolysis PNVA

PVAm

entry

[NVA]0/[VA-86]0/[Co(acac)2]0

time (h)

conv (%)

Mn (g/mol)

Đ

1 2 3

110/2/1 220/2/1 440/2/1

4 7.5 7.5

5 23 39

21900 56300 128500

1.14 1.18 1.56

a

b

c

d

e

hydrolysis level (%)

Mnf (g/mol)

91 94 94

12000 30100 68700

a Polymerization time at room temperature after 4 h irradiation at 0 °C. bDetermined by 1H NMR. cDetermined by SEC DMF equipped with a MALLS detector, dn/dc = 0.06. dDetermined by SEC DMF using a PS calibration. eDetermined by elemental analysis (see Table S1 for crude EA analysis and calculations). fMolar mass for the nonprotonated PVAms calculated from the Mn of the PNVA precursor and the level of hydrolysis of the amide moieties.

(PrSH) (99%, Aldrich), dichloromethane (CH2Cl2) (p.a.), and methanol (MeOH) (p.a.) were degassed by bubbling argon for 30 min. The alkyl−cobalt(III) adduct initiator ([Co(acac)2-(CH(OAc)CH2)98%, TCI), cobalt(II) acetylacetonate (Co(acac)2) (97%, Aldrich), 2,2′-azobis(4-methoxy2,4-dimethylvaleronitrile) (V-70, t1/2 = 10 h at 30 °C) (>98%, Wako), and 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propioamide] (VA-086, t1/2 = 10 h at 86 °C) (>98%, Wako) were used as received. NMethylvinylacetamide (NMVA) (>98%, Aldrich) and vinyl acetate (>99%, Aldrich) were purified by distillation under reduced pressure and degassed by freeze-drying cycle under vacuum. Propanethiol B

DOI: 10.1021/acs.macromol.6b00992 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules power input at 150 W) for 4 h at 0 °C. After irradiation was stopped, the medium was allowed to return to room temperature (∼20 °C), and the polymerization proceeded for 7 h 30 min. A sample was picked out of the reactor, quenched by TEMPO, and used for determining the conversion by 1H NMR (23%) and the molar mass of the polymer by SEC analyses. In order to quench the reaction as reported elsewhere,45 degassed 1-propanethiol (1.4 mL, 15.8 mmol) was added with a syringe under inert atmosphere to the reaction medium which became instantaneously dark black. The medium was stirred overnight at room temperature. The reaction medium was eluted through a Celite allowing removing any black residues. The polymer was purified by three successive precipitations in acetone and dried under vacuum. Methanol was used for dissolving the polymer between each precipitation. The polymer was further purified by dialysis against water for 2 days. After lyophilization, an off-white solid was obtained and characterized by SEC, NMR, and ICP (dn/ dcPNVA in DMF = 0.06, Mn,SEC DMF MALLS = 56 300 g/mol, Mn,SEC DMF cal PS = 48 100 g/mol, ĐSEC DMF cal PS = 1.18, Mn,SEC H2O cal P2VP = 31 000 g/ mol, ĐSEC H2O cal P2VP = 1.27) (see Table 1, entry 2). The cobalt content in the nonpurified polymer was evaluated at 13 623 ppm considering the initial amounts of cobalt and NVA as well as the monomer conversion. The cobalt content in the PNVA purified by treatment with propanethiol and precipitation measured by ICP was equal to 111 ppm (