Yanjing Gao

Self-floating ability and initiating gradient photopolymerization of acrylamide aqueous solution of a water-soluble polysiloxane benzophenone photoinitiator

Three water-soluble polysiloxane benzophenone photoinitiators (W-Si-HBP2-A/B/C) with various silicon content used for preparing a gradient polymer were synthesized based on the traditional photoinitiator 4-hydroxybenzophenone (HBP) and aminopolysiloxane. The structures were confirmed by proton nuclear magnetic resonance (1H NMR), and gel permeation chromatography (GPC). The water solubility of the photoinitiators, the effect of the silicon content on their triplet state lifetimes and photopolymerization property and the self-floating ability in the water system, and the internal connection between the surface morphology and property of the gradient polymer and film initiated by the photoinitiators were investigated. All three photoinitiators showed relatively good solubility in water, and longer triplet lifetimes and a smaller rate constant than HBP. It is found that the photoinitiator with the highest silicon content had the best floating capability due to lower surface tension and energy of polysiloxane. By using this photoinitiator, the gradient polymer with a significant molecular weight gradient was obtained. In addition, the polysiloxane-based photoinitiators can decrease the dispersion surface energy of the gradient polymer, and the increase of photoinitiator content can change the microstructure of the gradient polymer film. The new green method for preparing gradient polymeric material by using the polymerization technology and the water-soluble polysiloxane-based photoinitiators may have potential applications in the green chemical industry.

A study of nanogels with different polysiloxane chain lengths for photopolymerization stress reduction and modification of polymer network properties

This paper reports a series of nanogel compositions synthesized with methacrylate-modified polysiloxanes of different chain lengths, urethane dimethacrylate (UDMA) and isobornyl methacrylate (IBMA) at molar ratios of 10 : 20 : 70 in the presence of a thiol chain transfer agent. The nanogel structures were characterized by proton nuclear magnetic resonance (1H-NMR), Fourier transform-infrared spectroscopy (FT-IR), gel permeation chromatography (GPC) and transmission electron microscopy (TEM). From simultaneous measurement of real-time kinetics and shrinkage stress during photopolymerization, the nanogel additives showed a significant delay in the onset of stress and further reduce the overall photopolymerization stress without compromising the mechanical properties of the corresponding polymers. Most importantly, it is also proved that thermostability, flexibility and hydrophobic properties were improved by the introduction of polysiloxane-based nanogels into UV-curable materials due to high temperature resistance, excellent flexibility and low surface energy associated with the polysiloxane component.

Hydrosoluble hybrid and multifunctional polysiloxane-based photoinitiators for initiating gradient photopolymerization of acrylamide aqueous solution

A novel hydrosoluble hybrid polysiloxane photoinitiator (W–Si–HBP2–HHMP2) and a hydrosoluble four-functional polysiloxane benzophenone photoinitiator (W–Si–HBP4) were synthesized based on 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl propan-1-one (HHMP), 4-hydroxybenzophenone (HBP) and aminopolysiloxane, and their structures were confirmed by 1H NMR, 13C NMR, 29Si NMR and FTIR. The solubility in water, the photochemical properties, and the self-floating ability of the photoinitiators were evaluated. Both the photoinitiators exhibited great water solubility, high hydrogen abstraction rate constant (more than 7.0 × 109 M−1 s−1), excellent photoinitiating efficiency and relatively good self-floating ability. The initiating efficiency of the polysiloxane photoinitiators was improved by appropriate increase of photosensitive groups in the molecules, but without compromise to the self-floating ability. Remarkably, the hybrid photoinitiator W–Si–HBP2–HHMP2 efficiently initiated photopolymerization without an amine coinitiator due to the interaction between the HBP and HHMP groups. This led to the reduction of the dosage of the amine coinitiator, and even no amine coinitiator, thereby mitigating the harm to materials and the environment derived from the amine coinitiator. Therefore, W–Si–HBP2–HHMP2 has great potential for application in green chemical industry. Moreover, gradient properties, involving molecular weight, glass transition temperature (Tg), and thermostability, of the polyacrylamide (PAM) rods prepared by using W–Si–HBP2–HHMP2 and W–Si–HBP4 were explored by GPC, differential scanning calorimetry (DSC) and thermogravimetry (TG).

Intramolecular-initiating photopolymerization behavior of nanogels with the capability of reducing shrinkage

A series of nanogels possessing both benzophenone and hydrogen-donating groups in the skeleton were synthesized and characterized. The photochemical properties and photoinitiation mechanism of the nanogels were investigated by ultraviolet absorption spectroscopy, real-time infrared spectroscopy, laser flash photolysis and electron spin resonance. The nanogels have a strong absorption characteristic centered at 275 nm. Compared to the bare benzophenone, the nanogels have longer triplet state lifetime that reached up to 1.9 μs. Furthermore, the nanogels can generate both alkyl radicals and amino radicals that can effectively initiate the polymerization of acrylate monomers. More importantly, the nanogels can significantly reduce the volume shrinkage of UV-cured materials and the migration of photolysis fragments. The nanogels should have potential applications for preparing more environmentally friendly materials.

Synthesis and properties of photopolymerizable bifunctional polyether-modified polysiloxane polyurethane acrylate prepolymer

Abstract A UV-curable polyether-modified polysiloxane polyurethane acrylate prepolymer PESiUA that can be used for polyvinyl chloride leather finishing agents has been synthesized and characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and gel permeation chromatography. The prepolymer exhibited excellent compatibility with acrylate monomers, satisfying photopolymerization efficiency and good yellowing resistance. The influences of the monomers on the properties of the UV-cured film were systematically studied. The results showed that the increase in the functionality of monomers can increase the thermostability, glass transition temperature, tensile strength, tensile modulus, dispersion surface energy, and decrease the contact angle and elongation at break. More significantly, the PVC leather finishing agent designed based on the photopolymerizable polyether-modified polysiloxane polyurethane acrylate prepolymer PESiUA possessed excellent performances and had great application potential, due to the combination of advantages of polysiloxane segment and polypropylene glycol segment as well as photopolymerization technique.

Synthetic Strategy and Performances of a UV-Curable Poly Acryloyl Phosphinate Flame Retardant by Carbene Polymerization

GRAPHICAL ABSTRACT A route to synthesize poly ethyl (4-acrylamidebenzyl) phosphinate (PPAC) was discussed and the optimal route was determined. Diethyl benzylphosphonate was synthesized by Arbuzov reaction, then, a nitryl was introduced onto the aromatic ring by the nitration reaction of ethyl benzylphosphonate. Subsequently the carbene polymerization of the product was carried out. Finally, the nitryls were reduced and amidated to introduce the acryloyl group into the prepolymer to obtain the target product (PPAC). PPAC can rapidly photopolymerize under UV light irradiation. The addition of PPAC decreased the smoke production rate (SPR), CO2 production (CO2P), and CO production (COP) of the UV-cured resin.

Reducing volumetric shrinkage of photopolymerizable materials using reversible disulfide-bond reactions

We introduce a new strategy for reduction in volumetric shrinkage of free radical photopolymerization. Our strategy is based on the reversible reaction of disulfide bonds under UV irradiation. Here, we synthesized 2,2′-dithiodiethanol diacrylate (DSDA), an acrylate monomer with disulfide bonds. The homolytic photocleavage of DSDA under UV irradiation generates thiyl radicals that can initiate polymerization. Volumetric shrinkage can decrease to 0.1% through a repeated “contraction–expansion–contraction” volume-adjustable process. We identified the mechanism that underlies volumetric shrinkage reduction. The photocleavage rate of DSDA under UV irradiation is slower than that of the added photoinitiator. Moreover, in the presence of the photoinitiator, most of the generated thiyl radicals undergo restoration and exchange reactions instead of polymerization initiation or chain termination. The free volume and structure of the polymer network are effectively tuned by the dynamic and reversible processes of gradual disulfide-bond homolysis and recombination during fast photopolymerization.

Photocured Materials with Self-Healing Function through Ionic Interactions for Flexible Electronics

Photocured materials with self-healing function have the merit of long lifetime and environmentally benign preparation process and thus find potential applications in various fields. Herein, a novel imidazolium-containing photocurable monomer, (6-(3-(3(2-hydroxyethyl)-1 H-imidazol-3-ium bromide)propanoyloxy)hexyl acrylate, IM-A), was designed and synthesized. Self-healing polymers were prepared by fast photocuring with IM-A, isobornyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, and 2-hydroxyethyl acrylate as the monomers. The mechanical and self-healing properties of the polymers were tuned by varying the contents of IM-A and other monomers. The as-prepared self-healing polymer IB7-IM5 exhibited a tensile strength of 3.1 MPa, elongation at break of 205%, healing efficiency of 93%, and a wide healing temperature range from room temperature to 120 °C. The self-healing polymer was also employed as a flexible substrate to fabricate a flexible electronic device, which could be healed and completely restore its conductivity after the device was damaged.