Photoresponsive Coumarin Polyesters That Exhibit Cross-Linking and Chain Scission Properties

Maddipatla, Murthy V. S. N.; Wehrung, Daniel; Tang, Chuan; Fan, Weizheng; Oyewumi, Moses O.; Miyoshi, Toshikazu; Joy, Abraham

doi:10.1021/ma400584y

Cited by 85 publications

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“…We have previously shown that coumarin polyester films demonstrate this dual photochemistry−undergoing primarily cross-linking at 350 nm and chain scission at 254 nm ( Figure 1). 31 This dual behavior enabled the fabrication of complementary micropatterned surfaces by irradiation at 350 or 254 nm. In this work to clearly understand the reactions, we utilize thin films of the virgin coumarin containing polyester (CA11) and irradiate either at 350 nm to enable polymer crosslinking, or at 254 nm to induce chain scission.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…31 A decrease in the absorbance coefficient, α, is expected for the cross-linked products due to the change from a coumarin chromophore to a benzenoid chromophore after cross-linking. However, chain scission, which is the minor product at 350 nm, is not expected to show a decrease in α because this does not cause a change in the structure of the chromophore.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Kinetics of UV Irradiation Induced Chain Scission and Cross-Linking of Coumarin-Containing Polyester Ultrathin Films

et al. 2014

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Photoresponsive thin films are commonly encountered as high performance coatings as well as critical component, photoresists, for microelectronics manufacture. Despite intensive investigations into the dynamics of thin glassy polymer films, studies involving reactions of thin films have typically been limited by difficulties in decoupling segregation of reacting components or catalysts due to the interfaces. Here, thin films of coumarin polyesters overcome this limitation where the polyester undergoes predominately cross-linking upon irradiation at 350 nm, while chain scission occurs with exposure to 254 nm light. Spectroscopic ellipsometry is utilized to track these reactions as a function of exposure time to elucidate the associated reaction kinetics for films as thin as 15 nm. The cross-linking appears to follow a second order kinetic rate law, while oxidation of the coumarin that accompanies the chain scission and enables this reaction to be tracked spectroscopically appears to be a first order reaction in coumarin concentration. Because of the asymmetry in the coumarin diol monomer and the associated differences in local structure that result during formation of the polyester, two populations of coumarin are required to fit the reaction kinetics; 10−20% of the coumarin is significantly more reactive, but these groups appear to undergo chain scission/oxidation at both wavelengths. These reaction rate constants are nearly independent (within 1 order of magnitude) of film thickness down to 15 nm. There is maximum rate at a finite thickness for the 254 nm exposure, which we attribute to constructive interference of the UV radiation within the polymer film, rather than typical confinement effects; no thickness dependence in reaction rates is observed for the 350 nm exposure. The utilization of a single polymer with two distinct reactions enables unambiguous investigation of thickness effects on reactions. ■ INTRODUCTIONFor nearly two decades, 1 the physical properties of polymer thin films have been investigated with an emphasis predominately on the glass transition temperature 2−4 as a function of film thickness. In many cases, a thickness dependent glass transition temperature (T g ) is found with the deviations from the bulk T g generally associated with the interfaces, 5 where T g is depressed 6,7 at a free interface (surface) and increased 8,9 at an attractive hard interface. The interactions of the polymer film with the underlying substrate or capping layer as well as the processing history 10−12 can impact the observed changes in T g . However, other physical properties of polymers under confinement can vary inconsistently with intuitive expectations based on the observed T g changes, 13−17 where typical relationships for polymers appear to breakdown for thin films, in particular for mechanical properties. This inconsistency leads to challenges in understanding a priori how polymers will behave when confined to thin films. For example, the rubbery compliance of ultrathin polymer films appears to decrease s...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Kinetics of UV Irradiation Induced Chain Scission and Cross-Linking of Coumarin-Containing Polyester Ultrathin Films

et al. 2014

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“…The synthesis of the monomers and polymer has been described in our earlier publication. 27 In brief, the coumarin polyester CA11 ( Figure 1A) is synthesized by the carbodiimide mediated polymerization of the coumarin diol (250 mg, 1 mmol, 1 equiv) with adipic acid (146 mg, 1 mmol, 1 equiv). The above diol and diacid are taken in an evacuated and N 2 filled round bottomed flask along with 4-(N,Ndimethylamino)pyridinium-4-toluenesulfonate (DPTS, 117 mg, 0.4 mmol, 0.25 equiv) and N,N-diisopropylcarbodiimide (DIC, 470 mL, 3 mmol, 3 equiv).…”

Section: Methodsmentioning

confidence: 99%

“…27 This design enables the polymer to demonstrate dual photoreactive properties. Irradiation at 350-365 nm results in polymer chain crosslinking as a result of a [2 + 2] cycloaddition reaction between the coumarin units.…”

Section: Introductionmentioning

confidence: 99%

Micropatterned Coumarin Polyester Thin Films Direct Neurite Orientation

McCormick

Maddipatla²,

Shi

et al. 2014

ACS Appl. Mater. Interfaces

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Guidance and migration of cells in the nervous system is imperative for proper development, maturation, and regeneration. In the peripheral nervous system (PNS), it is challenging for axons to bridge critical-sized injury defects to achieve repair and the central nervous system (CNS) has a very limited ability to regenerate after injury because of its innate injury response. The photoreactivity of the coumarin polyester used in this study enables efficient micropatterning using a custom digital micromirror device (DMD) and has been previously shown to be biodegradable, making these thin films ideal for cell guidance substrates with potential for future in vivo applications. With DMD, we fabricated coumarin polyester thin films into 10×20 μm and 15×50 μm micropatterns with depths ranging from 15 to 20 nm to enhance nervous system cell alignment. Adult primary neurons, oligodendrocytes, and astrocytes were isolated from rat brain tissue and seeded onto the polymer surfaces. After 24 h, cell type and neurite alignment were analyzed using phase contrast and fluorescence imaging. There was a significant difference (p<0.0001) in cell process distribution for both emergence angle (from the body of the cell) and orientation angle (at the tip of the growth cone) confirming alignment on patterned surfaces compared to control substrates (unpatterned polymer and glass surfaces). The expected frequency distribution for parallel alignment (≤15°) is 14% and the two micropatterned groups ranged from 42 to 49% alignment for emergence and orientation angle measurements, where the control groups range from 12 to 22% for parallel alignment. Despite depths being 15 to 20 nm, cell processes could sense these topographical changes and preferred to align to certain features of the micropatterns like the plateau/channel interface. As a result this initial study in utilizing these new DMD micropatterned coumarin polyester thin films has proven beneficial as an axon guidance platform for future nervous system regenerative strategies.

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“…Subsequent irradiation of the coumarin dimer at λ<300 nm induces cleavage of the cyclobutane ring and the monomer coumarins reform. Various coumarin-functionalized polymer materials, in particular, photo-cross-linking polymers have been reported thus far [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Chujo et al reported photocontrollable swelling behavior of hydrogel films obtained from polyoxazoline having a coumarin moiety [1].…”

Section: Introductionmentioning

confidence: 99%

Macroscopic Photoinduced and Reversible Sol-Gel Conversions of Polymer Materials Containing Photoreactive Coumarin Moieties

Moriyama

Okano

Ono

et al. 2015

Trans. Mat. Res. Soc. Japan

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Hydrophilic copolymers containing N-isopropylacrylamide and acrylate with coumarin or 4-methylcoumarin moieties have been synthesized. We reveal that the copolymers with a very small content of coumarin and 4-methylcoumarin units exhibit macroscopic photoinduced and reversible sol-gel conversions. UV light (λ>310 nm) irradiation of aqueous solutions for the copolymers causes the increase in viscosity and the formation of hydrogels, based on photodimerization of coumarin moieties. Subsequent irradiation with UV light (λ=254 nm) of the hydrogels induces the return of fluidity and the change to sol state, due to the decomposition of coumarin dimers. The amount of crosslink structures in the copolymers can be regulated by the reversible photoreaction of coumarin moieties.

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Photoresponsive Coumarin Polyesters That Exhibit Cross-Linking and Chain Scission Properties

Cited by 85 publications

References 50 publications

Kinetics of UV Irradiation Induced Chain Scission and Cross-Linking of Coumarin-Containing Polyester Ultrathin Films

Kinetics of UV Irradiation Induced Chain Scission and Cross-Linking of Coumarin-Containing Polyester Ultrathin Films

Micropatterned Coumarin Polyester Thin Films Direct Neurite Orientation

Macroscopic Photoinduced and Reversible Sol-Gel Conversions of Polymer Materials Containing Photoreactive Coumarin Moieties

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