Simultaneous Formation of Polyhydroxyurethanes and Multicomponent Semi-IPN Hydrogels

Abstract

This study introduces an efficient strategy for synthesizing polyhydroxyurethane-based multicomponent hydrogels with enhanced rheological properties. In a single-step process, 3D materials composed of Polymer 1 (PHU) and Polymer 2 (PVA or gelatin) were produced. Polymer 1, a crosslinked polyhydroxyurethane (PHU), grew within a colloidal solution of Polymer 2, forming an interconnected network. The synthesis of Polymer 1 utilized a Non-Isocyanate Polyurethane (NIPU) methodology based on the aminolysis of bis(cyclic carbonate) (bisCC) monomers derived from 1-thioglycerol and 1,2-dithioglycerol (monomers A and E, respectively). This method, applied for the first time in Semi-Interpenetrating Network (SIPN) formation, demonstrated exceptional orthogonality since the functional groups in Polymer 2 do not interfere with Polymer 1 formation. Optimizing PHU formation involved a 20-trial methodology, identifying influential variables such as polymer concentration, temperature, solvent (an aprotic and a protic solvent), and the organo-catalyst used [a thiourea derivative (TU) and 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU)]. The highest molecular weights were achieved under near-bulk polymerization conditions using TU-protic and DBU-aprotic as catalyst-solvent combinations. Monomer E-based PHU exhibited higher Mw¯ than monomer A-based PHU (34.1 kDa and 16.4 kDa, respectively). Applying the enhanced methodology to prepare 10 multicomponent hydrogels using PVA or gelatin as the polymer scaffold revealed superior rheological properties in PVA-based hydrogels, exhibiting solid-like gel behavior. Incorporating monomer E enhanced mechanical properties and elasticity (with loss tangent values of 0.09 and 0.14). SEM images unveiled distinct microstructures, including a sponge-like pattern in certain PVA-based hydrogels when monomer A was chosen, indicating the formation of highly superporous interpenetrated materials. In summary, this innovative approach presents a versatile methodology for obtaining advanced hydrogel-based systems with potential applications in various biomedical fields.

Keywords: IPN; NIPU; PHU; SIPN; cyclic carbonates; functional polymers; interpenetrated networks; porous materials; rheological properties.

Figure 1

Main routes for the synthesis of polyurethanes.

Scheme 1

Synthesis of polyhydroxyurethanes (PHUs) from bis(cyclic carbonate)s and diamines.

Scheme 2

Synthetic scheme for the preparation of monomer A and PHU-A_DETA. (a) Propargyl bromide, TEA, MeCN, 0 °C → r.t., 5 h; (b) bis(trichloromethyl) carbonate, pyridine, CH₂Cl₂, —55 °C → r.t., overnight; (c) diazide 3, sodium ascorbate, CuSO₄, ^tBuOH-H₂O 2:1, r.t., 19 h; (d) The preparation of PHU-A_DETA from bis(cyclic carbonate) from MA and DETA were conducted under several reaction conditions that are summarized in Table S1.

Scheme 3

Synthetic scheme for the preparation of monomer E and PHU-E_DETA and PHU-E_HMDA. (a) DMPA, CH₃OH, UV 365 nm, r.t. (b) The polymerizations were conducted under several reaction conditions that are summarized in Table S2.

Figure 2

¹H NMR of monomer A (500 MHz, CDCl₃) and the PHU formed by reaction with DETA [PHU-A_DETA, 500 MHz, CD₃OD, (entry 15, Table S1)].

Figure 3

FT-IR spectra of monomer A (green) and PHU-A_DETA (black) (Table S1, entry 13).

Figure 4

A unified approach for single-step multicomponent hydrogel synthesis.

Figure 5

ATR-FTIR spectra of (a) monomer E; (b) PVA used in fabrication of PVA-based SIPNs; (c) multicomponent hydrogel IPN6 [PHU-E_DETA/PVA].

Figure 6

Comparative studies of the rheological properties of PVA-based SIPN and its blank. Evolution of storage modulus, $G^{\prime },$ and loss modulus, $G^{″}$ with the frequency for SIPN hydrogels prepared by aminolysis of bisCC monomers A or E in colloidal solutions of PVA in DMSO-H₂O 1:1. The figure legends describe the constituents of Polymer 1 (PHU) formed within the colloidal solution of Polymer 2 (PVA). DETA: diethylenetriamine; HMDA: 1,6-hexamethylenediamine; A: monomer bisCC A; E: monomer bisCC E.

Figure 7

Comparative studies of the rheological properties of PVA-based co-IPN and its blank. Evolution of storage modulus, $G’,$ and loss modulus, $G”,$ with the frequency for co-IPN hydrogels prepared by the aminolysis of bisCC monomers A and E in colloidal solutions of PVA in DMSO-H₂O 1:1. The figure legends describe the constituents of Polymer 1 (PHU) formed within the colloidal solution of Polymer 2 (PVA). DETA: diethylenetriamine; A: monomer bisCC A; E: monomer bisCC E.

Figure 8

Comparative studies of the rheological properties of gelatin-based IPN and its blank. Evolution of storage modulus, $G’$, and loss modulus, $G”$, with the frequency for IPN hydrogels prepared by aminolysis of bisCC monomers A (IPN7 [PHU-A_DETA/gelatin]) or E (IPN1 [PHU-E_DETA/gelatin]) in colloidal solutions of gelatin in DMSO-H₂O 1:1. The figure legends describe the constituents of Polymer 1 (PHU) formed within the colloidal solution of Polymer 2 (gelatin). DETA: diethylenetriamine; A: monomer bisCC A; E: monomer bisCC E.

Figure 9

SEM images of bulk samples from monomer A-based multicomponent hydrogels. (a) IPN8 [PHU-A_DETA/PVA]; (b): IPN7 [PHU-A_DETA/gelatin]. Magnification 1.63 K, 5.00 K, and 1.50 K, respectively.

Figure 10

SEM images of bulk samples from ME-based SIPN (freeze-dried samples). (a) IPN4 [PHU-E_DETA/PVA]; (b): IPN5 [PHU-E_HMDA/PVA]; (c) IPN2 [PHU-E_HMDA/gelatin]. Magnification 264, 293, and 641, respectively.