Modification of linear prepolymers to tailor heterogeneous network formation through photo-initiated polymerization-induced phase separation

Abstract

Polymerization-induced phase separation (PIPS) was studied in ambient photopolymerizations of triethylene glycol dimethacrylate (TEGDMA) modified by poly(methyl methacrylate) (PMMA). The molecular weight of PMMA and the rate of network formation (through incident UV-irradiation) were varied to influence both the promotion of phase separation through increases in overall free energy, as well as the extent to which phase development occurs during polymerization through diffusion prior to network gelation. The overall free energy of the polymerizing system increases with PMMA molecular weight, such that PIPS is promoted thermodynamically at low loading levels (5 wt%) of a higher molecular weight PMMA (120 kDa), while a higher loading level (20 wt%) is needed to induce PIPS with lower PMMA molecular weight (11 kDa), and phase separation was not promoted at any loading level tested of the lowest molecular weight PMMA (1 kDa). Due to these differences in overall free energy, systems modified by PMMA (11 kDa) underwent phase separation via Nucleation and Growth, and systems modified by PMMA (120 kDa), followed the Spinodal Decomposition mechanism. Despite differences in phase structure, all materials form a continuous phase rich in TEGDMA homopolymer. At high irradiation intensity (Io=20mW/cm2), the rate of network formation prohibited significant phase separation, even when thermodynamically preferred. A staged curing approach, which utilizes low intensity irradiation (Io=300µW/cm2) for the first ~50% of reaction to allow phase separation via diffusion, followed by a high intensity flood-cure to achieve a high degree of conversion, was employed to form phase-separated networks with reduced polymerization stress yet equivalent final conversion and modulus.

Rapid, Template‐Less Patterning of Polymeric Interfaces for Controlled Wettability via in Situ Heterogeneous Photopolymerizations

“…In addition to comonomers, each formulation also included a varying amount (based on wt%) of a nonreactive, thermoplastic, fluoropolymer: poly(vinyl diene) fluoride (PVDF). Previous studies of phase‐separating polymerizations have often turned toward the use of a nonreactive additive to increase overall free energy of a polymerizing resin and thus promote the formation of heterogeneous structure through diffusion of incompatible phases . Here, PVDF is chosen as the nonreactive additive due to the favorable properties it imparts on the resulting coating.…”

“…Previous studies of phase-separating polymerizations have often turned toward the use of a nonreactive additive to increase overall free energy of a polymerizing resin and thus promote the formation of heterogeneous structure through diffusion of incompatible phases. [13,[25][26][27][28] Here, PVDF is chosen as the nonreactive additive due to the favorable properties it imparts on the resulting coating. This includes resistance to solvents, mechanical strength, and rigidity, as well as low surface energy.…”

Long-Range Surface-Directed Polymerization-Induced Phase Separation: A Computational Study

“…Szczepanski et al [ 30 ] investigated the photo-polymerization of triethylene glycoldimethacrylate (TEGDMA) modified by poly(methyl methacrylate) (PMMA), which induced the phase separation and formed the heterogeneous network. The obtained tan delta profile showed the formation of two separated phases, one rich in TEGDMA, and the other rich in TEGDMA/PMMA.…”

Manipulating the Surface Structure of Hybrid UV Curable Coatings through Photopolymerization‐Induced Phase Separation: Influence of Inorganic Portion and Photoinitiator Content

“…One of the most important concerns about incorporating nonreactive inorganic moiety into a photopolymerizing formulation is their tendency to undergo polymerization‐induced phase separation (PIPS). [1b,3] The Gibbs free energy of mixing thermodynamically determines the advancement of phase separation in a multicomponent mixture …”

“…Increasing the molecular weight of the nonreactive part not only promotes PIPS but also changes the mechanism of phase separation. Samples with a high molecular weight nonreactive part undergo phase separation through spinodal decomposition while samples with low molecular weight polymer additives undergo phase separation through nucleation and growth . Other studies have revealed that miscibility and crosslink density can affect the final morphology.…”