Analysis of association constant for ground‐state dye‐electron acceptor complex of photoinitiator systems and the association constant effect on the kinetics of visible‐light‐induced polymerizations

We investigated the formation of ground‐state donor/acceptor complexes between xanthene dyes [rose bengal (RB) and fluorescein (FL)] and a diphenyliodonium (DPI) salt, which is dissolved in 2‐hydroxyethyl methacrylate (HEMA) monomer. To characterize the association constant of the complex, we have suggested a new analysis model based upon the Benesi–Hildebrand model. Because the assumption of the original Benesi–Hildebrand model is that the absorption bands are only due to the presence of the complex and that the absorption by the free component is negligible, the model cannot be applied to our systems, which is a dye‐based initiator system. For each dye, the molar absorptivity of the ground‐state complex was evaluated as a function of wavelength, and this analysis confirmed the validity of the modified Benesi–Hildebrand model. In addition, we observed that the RB/DPI photoinitiator system failed to produce a perceptible polymerization rate but the FL/DPI photoinitiator system provided high rates of polymerization. On the basis of the association constant for these complexes, we concluded that the observed kinetic differences arise from the different association constant values of the ground‐state dye‐acceptor complex, resulting in back‐electron transfer reaction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1429–1439, 2009     

Photochemistry and initiation behavior of phenylethynyl onium salts as cationic photoinitiators

Phenyl(phenylethynyl)iodonium hexafluorophosphate and diphenyl(phenylethynyl)sulfonium hexafluorophosphate were synthesized for application as cationic photoinitiators using simple, straightforward methods. Quantification of the purity of the counterion was determined by FTIR analysis with subsequent mathematical peak deconvolution. Photodecomposition products for direct irradiation were determined in steady state photolysis experiments yielding diphenyl sulfide and phenyl(phenylethynyl) sulfide or iodobenzene, respectively, as main products. Heterolytic cleavage was proposed as main photodecomposition pathway because low yields of phenylacetylene radical recombination products and no photoproducts generated by phenyl radicals, including benzene, were detected. High activity as photoinitiators was verified by photo‐DSC experiments in direct irradiation and in photosensitized initiation using 9,10‐dibutylanthracene, 2‐isopropylthioxanthone, and surprisingly also benzophenone as sensitizers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3419–3430, 2009     

Novel amphiphilic triblocks fitted with photocrosslinkable termini,and their photocrosslinking to conetworks

Two new telechelic amphiphilic triblock copolymers, HE₃‐PEG‐b‐PDMS‐b‐PEG‐HE₃ and HE₃‐PEG‐b‐PDMS‐b‐PEG‐HE₃, i.e., sequence‐reversed triblocks of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polydimethylsiloxane (PDMS) segments fitted with photocrosslinkable tri[2‐(3,4‐cyclohexane oxide)ethyl‐dimethylsiloxy]silane (HE₃) termini, were synthesized, characterized, photocrosslinked to amphiphilic conetworks (APCNs), and the properties of the APCNs were analyzed. APCNs in which the crosslinking sites are located in the hydrophobic domains exhibited significantly better mechanical properties than those in which the crosslinks were in the hydrophilic domains. The stiff domains formed of the UV‐crosslinkable HE₃ chain‐end substituents provide not only crosslinking but reinforcement as well. The crosslinking/reinforcement efficiency was greatly enhanced by the addition of excess HE₃. Water‐swollen APCNs were optically clear and exhibited mechanical properties appropriate for biomedical application. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 174–185, 2008     

PMMA光盘基片光致聚合反应复制法工艺研究

本文通过测量ＰＭＭＡ基片在光致聚合反应法复制过程中的形变和收缩应力，由此对其产生的机理作了一定的理论分析。通过在凝胶化后施加一定的压力能够减小形变和收缩应力。本文不仅描述了采用二阶段加压法工艺复制的ＣＤ唱片，还描述了用ＳＥＭ观察复制信息的微观形貌。     

Photoinitiation of acrylamide polymerization using the dianions of rhodizonic and croconic acids

Polymerization of acrylamide has been initiated by the photochemical reactions of the dianions of croconic acid (1,2-dihydroxycyclopentenetrione) and rhodizonic acid (1,2-dihydroxycyclohexenetetrone) in the presence of various acceptor molecules. Photoinitiation was most efficient with croconic acid where a maximum quantum yield for polymerization of 2 x 10³ was observed in neutral solution. Kinetic studies using this initiator showed that the rate of polymerization was a linear function of the concentration of monomer and proportional to the square root of the light absorbed by the croconate dianion. The rate of initiation of radicals calculated from the rate of polymerization was compared with the rate of production of radicals calculated from previous studies of the photochemistry of the croconate dianion and the mechanism of photoinitiation is discussed. © 1992 John Wiley & Sons, Inc.     

Synthesis and cationic photopolymerization of new silicon‐containing oxetane monomers

The cationic photopolymerization of oxetane‐based systems containing silicon monomers was investigated. For this purpose, three new silicon‐containing oxetane monomers were synthesized through a simple and straightforward synthetic method. The silicon‐containing monomers were added to a typical oxetane resin, 3,3′‐[oxydi(methylene)]bis(3‐ethyloxetane), in concentrations of 1–5 wt %. They exploited a certain surface tension effect without affecting the rate of polymerization. Enrichment only on the air side was achieved, which induced hydrophobicity in the photocured films, depending on the monomer structure and concentration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1415–1420, 2004     

Polymerization of a Photocleavable Monomer Using Visible Light

The polymerization of the photocleavable monomer, o‐nitrobenzyl methacrylate (NBMA), is investigated using photoinduced electron/energy transfer reversible addition‐fragmentation chain transfer polymerization. The polymerizations under visible red (λ _max = 635 nm, 0.7 mW cm⁻²) and yellow (λ _max = 560 nm, 9.7 mW cm⁻²) light are performed and demonstrate rational evidence of a controlled/living radical polymerization process. Well‐defined poly(o‐nitrobenzyl methacrylate) (PNBMA) homopolymers with good control over the molecular weight and polymer dispersity are successfully synthesized by varying the irradiation time and/or targeted degree of polymerization. Chain extension of a poly(oligo(ethylene glycol) methyl ether methacrylate) macro‐chain transfer agent with NBMA is carried out to fabricate photocleavable amphiphilic block copolymers (BCP). Finally, these self‐assembled BCP rapidly dissemble under UV light suggesting the photoresponsive character of NBMA is not altered during the polymerization under yellow or red light. Such photoresponsive polymers can be potentially used for the remote‐controlled delivery of therapeutic compounds.

     

Gradient polymer networks formed by photopolymerization with self‐floating polysiloxane‐containing nanogel

Polysiloxane‐containing nanogels can be used as a fast, convenient and environmentally friendly method to control gradient photopolymerization and to obtain gradient polymer network because of its self‐floating feature. The chain length of polysiloxane is a key factor that influences the self‐floating capability of the polysiloxane‐containing nanogel. This paper reports a series of nanogels compositions synthesized with methacrylate‐modified polysiloxanes with different chain lengths, urethane dimethacrylate (UDMA) and isobornyl methacrylate (IBMA) at a molar ratio of 10:20:70 in the presence of a thiol chain transfer agent. The effect of polysiloxane chain length on self‐floating capability of the nanogel and gradient polymer network was researched. The results show that polysiloxane chain length is the main driving force for the self‐floating capability of the nanogels. The nanogel with long polysiloxane chain length exhibits good self‐floating capability in the monomer–polymer matrix because of the lower surface tension of polysiloxane. Furthermore, the gradient polymer network containing the nanogel with long polysiloxane chain length presents lower dispersion surface energy and greater hardness and thermostability. Copyright © 2016 John Wiley & Sons, Ltd.     

Solvent effects on the intramolecular charge transfer character of N,N-diaryl dihydrophenazine catalysts for organocatalyzed atom transfer radical polymerization

The nature of intramolecular charge transfer (CT) of N,N-diaryl dihydrophenazine photocatalysts (PCs) in different solvents is explored in context of their performance in organocatalyzed atom transfer radical polymerization (O-ATRP). PCs having a computationally predicted lowest energy excited state exhibiting CT character can operate a highly controlled O-ATRP in a wide range of solvent polarities, from non-polar hexanes to highly polar N,N-dimethylacetamide. For PCs having a computationally predicted lowest energy excited state not possessing CT character, their ability to operate a controlled O-ATRP is decreased. This study confirms the importance of CT character in the excited state for N,N-diaryl dihydrophenazine PCs, and a deeper understanding of the activity of CT PCs has enabled the synthesis of polymers of low dispersity (<1.10) in a controlled fashion. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3017–3027