On-demand, readily degradable Poly-2,3-dihydrofuran enabled by anion-binding catalytic copolymerization

Abstract

Copolymerization with cleavable comonomers is a versatile approach to generate vinyl polymer with viable end-of-life options such as biodegradability. Nevertheless, such a strategy is ineffective in producing readily degradable 2, 3-dihydrofuran (DHF) copolymer with high-molecular-weight (>200 kDa). The latter is a strong and biorenewable thermoplastic that eluded efficient cationic copolymerization synthesis. Here, we show that an anion-binding catalyst seleno-cyclodiphosph(V)azanes enable the efficient cationic copolymerization with cyclic acetals by reversibly activating both different dormant species to achieve both high living chain-end retention and high-molecular-weight. This method leads to incorporating low density of individual in-chain acetal sequences in PDHF chains with high-molecular-weight (up to 314 kDa), imparting on-demand hydrolytic degradability while without sacrificing the thermomechanical, optical, and barrier properties of the native material. The proposed approach can be easily adapted to existing cationic polymerization to synthesize readily degradable polymers with tailored properties while addressing environmental sustainability requirements.

Fig. 1. Cationic (co)polymerization of DHF.

a Cationic polymerization of DHF towards high-molecular-weight PDHF. b Proposed anion-binding catalytic cationic copolymerization strategy for synthesizing high-molecular-weight while readily degradable DHF copolymer. Inset: a The cationic copolymerization process between DHF and ideal cyclic acetal comonomer. b The features of PDHF material produced by anion-binding catalyst.

Fig. 2. Anion-binding catalytic cationic copolymerization of DHF with CA.

a Synthesis of PDHF-CA copolymer. b The structures of catalyst, cationogen, and comonomers used.

Fig. 3. Anion-binding catalytic cationic copolymerization of DHF with DMDOP.

a ¹H NMR spectra of PDHF and P(DHF-co-DMDOP) in CDCl₃ (Table 1, entry 5). b DOSY NMR spectra of P(DHF-co-DMDOP) in CDCl₃ (Table 1, entry 5). c Polts of M_n,SEC and Đ (M_w/M_n) as a function of M_n,calcd. (calculated by monomer conversion). Inset: Overlay of SEC profiles at varied DHF and DMDOP conversions. Copolymerization conditions: [DHF]₀:[DMDOP]₀:[ICCI]₀:[1a]₀ = 200:200:1:1 at −40 °C in DCM. d SEC profiles of the copolymers obtained by sequential monomer addition experiment (Table 1, entry 6-8).

Fig. 4. The degradation of PDHF copolymer.

a The SEC profiles of P(DHF-DMDOP_2.6) and P(DHF-DMDOP_6.9) in response to HCl treatment after 10 minutes. b ¹H NMR spectra of P(DHF-DMDOP_6.9) and its degradation product after acidic hydrolysis in CDCl₃. c MALDI-TOF-MS of P(DHF-DMDOP_6.9) degradation product. d The photos of rectangle-shaped specimens of P(DHF-DMDOP_2.6) treated with camphorsulfonic acid solution after different degradation times. e The SEC profiles of accelerated degradation of oligomer. f The molecular weight change of oligomer during accelerated oxidative degradation.

Fig. 5. Physical properties of PDHF copolymers.

a DSC curves of PDHF and P(DHF-co-DMDOP). b TGA curves of PDHF, P(DHF-DMDOP_2.6) and P(DHF-DMDOP_6.9). c Stress-strain curves of native PDHF (σ_PDHF = 64.9 MPa, ε_PDHF = 17.9%, M_n,MALLS = 295.2 kg/mol) and P(DHF-DMDOP_2.6) (σ_b = 43.9 MPa, ε_b = 39.0%, M_n,,MALLS = 265.2 kg/mol). d PDHF copolymers showed comparable permeability for O₂ and e Water Vapor with native PDHF. Data are presented as mean ± SD (standard deviation) and collected from three independent experiments. The compared WVTR values for PET and LDPE were from recent article. f Adhesive property comparison for PDHF and P(DHF-DMDOP_2.6). Data are presented as mean ± SD and collected from four independent experiments. The compared adhesive strength for PVAc was from reported article.