High-Performance Nano-Photoinitiators with Improved Safety for 3D

Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES

Letter

High Performance Nano-Photoinitiators with Improved Safety for 3D Printing Yanyang Han, Fei Wang, Chin Yan Lim, Hong Chi, Dairong Chen, FuKe Wang, and Xiuling Jiao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b08399 • Publication Date (Web): 06 Sep 2017 Downloaded from http://pubs.acs.org on September 8, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

High Performance Nano-Photoinitiators with Improved Safety for 3D Printing Yanyang Han,†,⊥ Fei Wang,‡,⊥ Chin Yan Lim,§ Hong Chi,ǁ Dairong Chen,† FuKe Wang,*‡ Xiuling Jiao*† †

School of Chemistry & Chemical Engineering, Shandong University, Jinan 250100, P. R.

China. ‡

Polymeric Materials Department, Institute of Materials Research and Engineering, Agency for

Science, Technology and Research (A*STAR), 2 Fusionopolis Way, #08-03 Innovis, 138634 Singapore. §

Institute of Medical Biology, Agency for Science, Technology and Research (A*STAR), 8a

Biomedical Grove, #06-06, 138648, Singapore. ǁ

Shandong Provincial Key Laboratory of Fine Chemicals, School of Chemistry of

Pharmaceutical Engineering, Qilu University of Technology, Jinan 250353, China.

ABSTRACT: In this work, we report the first hybrid nano-sized photoinitiators with low cytotoxicity and migration by coupling of polyhedral oligomeric silsesquioxanes (POSS) to

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 21

benzophenone derivatives. This new series of photoinitiators were fully characterized and showed many favorable properties such as uniform sizes, extremely low tendency to migrate, less effect on resin viscosity, enhanced thermal stability and mechanical strength, increased photoactivity and significantly lower cell toxicity compared to their corresponding benzophenone molecules. The utility of these hybrid nano-sized photoinitiators in 3D printing was demonstrated in printing of various 3D structures with high resolution and accuracy.

KEYWORDS: photoinitiators, benzophenone, 3D printing safety, printable resin, additive manufacturing, POSS

Three-dimensional (3D) printing, also known as additive manufacturing, is an emerging technology and has started to evolve into the next-generation manufacturing technology.1-5 3D printing is expected to change the whole industry and revolutionize the traditional manufacturing process. Various 3D printing techniques and methods have been developed to build 3D structures and objects. Among these, stereolithography (SLA) technology is the first 3D printing technique to be developed that has sustained utility in additive manufacturing due to its superior resolution, accuracy and good z-axis strength, compared to other printing techniques.6 SLA printing involves layer-by-layer rapid photopolymerization of a light-sensitive liquid resin to solid polymers by UV light or laser,7-9 with free radical photopolymerization (FRPP) of acrylate or methacrylate

being

the

major

technique.10,11

In

FRPP,

radicals

generated

from

photoinitiators upon light excitation are used to initiate the polymerization of acrylate polymers. After photopolymerization, photoinitiators remaining in the polymer matrix can readily migrate out of the matrix with time, due to their fairly low molecular weight, leading to negative consequences. For instance, small photoinitiators of 200-250 Daltons used in food packaging,


2

Page 3 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


such as 4-Methyl Benzophenone (4-MBP) and Isopropyl Thioxanthone (ITX), were found to migrate from the packaging materials into the food, raising significant food safety concerns.12 Undoubtedly, as the 3D printing market and interests shift rapidly from prototyping to end-use product manufacturing and bio-printing, the migration of photoinitiators from printed objects will soon become a critical safety issue. To improve the safety of photopolymers, various polymeric photoinitiators, derived from grafting or condensing low molecular weight photoinitiators to linear,13-15 dendritic,16 or hyperbranched17 polymers, have been developed. Low extractability has been reported for these polymeric photoinitiators, but this is usually accompanied by reduced photoactivity compared to their corresponding low molecular weight analogues. Only a few polymeric photoinitiators with enhanced photoactivity have been reported.13-16 Furthermore, the coupling of photoinitiators to large molecular weight polymers generally leads to significant increases in resin viscosity. The low reactivity and high viscosity of polymeric photoinitiators, as well as inconvenient

purification

procedures,

have

thus

far

limited

their

applications

in

stereolithography-based 3D printing technology, which requires fast solidification and low resin viscosity. Here we report a new series of nano-sized photoinitiators generated by coupling benzophenone derivatives to polyhedral oligomeric silsesquioxanes (POSS). POSS was chosen in this work for its well-defined nano-structures, facile chemical modification, biocompatibility, and the commercial availability of various useful precursors for modification.18-20 For example, POSSbased proton donor21 and acrylate monomers22 have been developed and tested in photopolymerization. In our strategy, new photoinitiators can be facilely obtained by simple coupling of the hard nano-sized POSS core with commercially available photoinitiators.


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 21

Characterization of structures, thermal stability, photoactivity and evaluation of effects on resin viscosity and migration property were conducted on the as-obtained hybrid photoinitiators. The cytotoxicity of the new hybrid photoinitiators was demonstrated by cell proliferation assays with photopolymerized structures initiated by hybrid photoinitiators and their corresponding low molecular weight parent photoinitiators. Benzophenone (BP) derivatives are low-cost and highly efficient photoinitiators that have become the preferred choice for industrial uses.23,24 In this work, three easily available BP derivatives with different initiating absorption wavelengths were selected as parent photoinitiators. A hydroxyl group in the parent photoinitiators was included for coupling with the POSS nanoparticle. As shown in Scheme S1 (Supporting Information), benzophenone type photoinitiators, 4-hydroxylacetophenone (HAP), 4-hydroxylbenzophenone (HBP), and 4hydroxyl(dimethylamino)-benzophenone (HDBP) with initiating wavelengths at 277, 290, and 345 nm, respectively, were coupled to mono(bromopropyl)-substituted POSS (POSS-Br). As HDBP is not commercially available, it was synthesized in the lab with high yield through the reaction of corresponding amide with N,N-dimethylaniline in the presence of phosphoryl chloride (Scheme S2, Supporting Informaition).25 POSS-Br was prepared from trisilanocyclohexyl POSS, and its purity and structure was confirmed by the proton nuclear magnetic resonance (1H-NMR) spectrum (Figure 1). The triplet at d = 3.43 ppm was assigned to -CH2Br in the bromopropyl group. The coupling of the small molecular photoinitiators with POSS-Br was achieved through the reaction of POSS–Br with benzophenone derivatives containing hydroxyl group in the presence of potassium carbonate and a catalytic amount of 18-crown-6 as the phase transfer agent.26 The new POSS-coupled photoinitiators, named as POSS-AP, POSS-BP, and POSS-DBP, were successfully obtained


4

Page 5 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with high yield after the coupling reactions and purification by silica gel chromatography. The chemical structures of these new photoinitiators were confirmed by NMR (Figure S3-S4, Supporting Information), with the spectrum for POSS-DBP shown as an example in Figure 1. A new triplet appearing at d = 4.0 ppm was attributed to the -CH2 group that links POSS to the phenol ring in HDBP. In the low field region (6.7–7.8 ppm), characteristic peaks of aromatic protons on the DBP ring appeared with slight downfield shift as compared with the pristine HDBP (Figure S1, Supporting Information). These new photoinitiators showed better solubility than their corresponding polar BP derivatives in organic solvents such as chloroform, THF, hexane, and toluene, mainly due to the coupled hydrophobic POSS moiety, which contains seven cyclohexyl groups.


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 21

Figure 1. Comparison of the 1H-NMR spectra of starting materials HDBP, POSS–Br and the product POSS–DBP. R substituent on POSS here represents the cyclohexyl group, and the small peak at δ = 0.83 ppm is attributed to hexane residue.


6

Page 7 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. Comparison of the UV-vis spectra of benzophenone photoinitiators before and after coupling with POSS. UV-vis spectral analysis of the new photoinitiators in methylene chloride showed that the coupling of benzophenone initiators with POSS nanoparticles had only slight effects on their respective major absorption wavelengths, suggesting little impact on their optical properties. As shown in Figure 2 and Table 1, no major absorption changes before and after coupling to POSS were observed for HDBP, while HAP and HBP showed only slight red shifts of less than 10 nm after coupling to POSS. Interestingly, we found that the absorption coefficients of the new photoinitiators were all larger than that of their corresponding small molecule analogues, suggesting that these new photoinitiators may exhibit higher photoactivity.


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 21

Table 1. Comparison of the physical properties of new photoinitiators and their corresponding parent molecules.

Molecular Weight

HAP

POSS-AP

HBP

POSS-BP

HDBP

POSSDBP

136

1147

198

1209

241

1252

207

280

246

278

265

344

272

277

280

290

345

345

1.02

1.38

1.06

1.41

2.49

2.94

Thermal stability (Td, °C) λmax (nm)

ε (L·mol-1·cm-1) × 10

4

The thermal stability of the new photoinitiators were studied by thermal gravimetric analysis (TGA)

under

nitrogen

atmosphere.

Remarkably

enhanced

thermal

stability

was

found for these new POSS-coupled photoinitiators compared to their corresponding small molecular analogues (Table 1 and Figure S5-S7, Supporting Information). For instance, the decomposition temperature (Td) of HDBP was found to be at 265 °C, while Td of POSS-DBP was increased to 344 °C. The enhancement of thermal stability after introduction of the POSS moiety had been observed in our previous studies,26 and was attributed to the greater thermal barrier capability of POSS due to its low thermal conductivity. The enhanced thermal stability of the new POSS-coupled photoinitiators indicates these initiators can be used within a broader range of working temperatures compared to traditional benzophenone initiators. The photoactivity of the new photoinitiators was investigated by photopolymerization conversion of methyl methacrylate (MMA) or methacrylate (MA) under air atmosphere with triethanolamine (TEA) as coinitiator in a Luzchem photoreactor. For simplicity, the results for


8

Page 9 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


only POSS-BP, POSS-DBP and their corresponding small benzophenone photoinitiators were listed in Table 2 as POSS-AP performed similarly to POSS-BP. As shown in Table 2, both new POSS-coupled

photoinitiators

showed

enhanced

photoactivity

compared

to

their

corresponding small molecular benzophenone analogues. POSS-BP showed a 150-230% increase in polymer conversion over HBP, while POSS-DBP showed 20-30% more polymer conversion than HDBP. It is interesting to note that POSS-DBP and POSS-BP have different concentration dependent effects. POSS-DBP showed a concentration dependent manner, a higher POSS-BP concentration resulted in a lower photoactivity enhancement effect. At low initiator concentration (10 µmol/g), a 22% increase of polymer conversion (entries 1, 2) was observed for POSS-DBP compared to HDBP, and further enhancement (32%) was observed when the initiator concentration was doubled (entries 3, 4). By contrast, while low POSS-BP concentration (10 µmol/g) greatly enhanced polymer conversion (227%, entries 5-6) over HBP, the positive enhancement effect was reduced to 158% (entries 7, 8) upon doubling the concentration of POSS-BP. The greater photoactivity of the POSS-coupled initiators observed was likely due to the high steric effect of POSS, as illustrated by computer simulation (Figure S9, Supporting Information). This was in line with the well-established concept that free radicals can be stabilized by high steric structures or hyperconjugation.26-28 Since the benzophenone and POSS moieties were not conjugated in the POSS-coupled photoinitiators, stability of the radical would primarily be conferred by the steric effect of POSS. The large-sized POSS core and cyclohexyl-substituted periphery shield the benzophenone moiety, thus extending the half-life of the generated radicals, and giving rise to enhanced photoactivity.


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 21

Table 2. The photoactivity studies of the new photoinitiators.a PI content Time (h)

Convn (%)c

10

5

22.7%

POSS-DBP

10

5

27.8% (+22%)

0.5 mL MMA

HDBP

20

3

21.1%

4

0.5 mL MMA

POSS-DBP

20

3

27.8% (+32%)

5

0.5 mL MMA

HBP

10

5

21.6%

6

0.5 mL MMA

POSS-BP

10

5

70.7% (+227%)

7

0.5 mL MMA

HBP

20

3

9.7%

8

0.5 mL MMA

POSS-BP

20

3

25% (+158%)

9

0.5 mL MA

HDBP

10

5

28.6%

10

0.5 mL MA

POSS-DBP

10

5

35.8% (+25%)

11

0.5 mL MA

4-HBP

10

5

25.7%

12

0.5 mL MA

POSS-BP

10

5

72.0% (+180%)

Entry

Resin

Initiator

1

0.5 mL MMA

HDBP

2

0.5 mL MMA

3

(µmol/g) b

a

total light density used: 200 cd•sr/m2. b mole number of photoinitiators per gram of photopolymer resin. c value in bracket indicate the conversion enhancement ratio of new photoinitiators comparing to their corresponding small molecular analogues.


10

Page 11 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (a) HeLa cells grown in 0.75X HBP media (top row) or POSS-BP media (bottom row) for the first 1, 5 and 13 hours. (b-d) Confluence plots showing growth rates of HeLa cells in different concentrations of photoinitiator media for 144 hours (6 days). (e) Amount of photoinitiators extracted from cured PEGDA and HDDA polymers.


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 21

The cytotoxicity of the new POSS-coupled photoinitiators was evaluated by cell toxicity tests conducted

on

cured

polyethylene

(glycol)

diacrylate

(PEGDA),

which

was

photopolymerized by using either the POSS-coupled photoinitiator, POSS-BP, or its corresponding small molecular initiator, HBP.29 The cured polymer sheets of 1 mm thickness were cut into 10 x 10 mm squares and incubated in 1mL of HeLa cell media (Dulbecco’s Modified Eagle Medium supplemented with 10% fetal bovine serum) for 72 hrs at 37 °C. The conditioned media was harvested and centrifuged for 10 min to remove particulates and diluted to appropriate concentration with normal media before adding to cells. HeLa cells were seeded at 12,000 cells/well in 24-well plates, one day before addition of conditioned media to achieve a density of ~10-15% confluence at the start of experiment. After addition of conditioned media, cellular growth was monitored using the IncuCyte Live Cell Analysis System (Essen Bioscience) by measuring the percentage confluence every 2 hrs over 6 days. Every treatment was carried in triplicate wells in 3 independent replicate experiments. As shown in Figure 3a, at 1 hr post treatment, little toxicity was observed for cells cultured in 0.75X HBP and POSS-BP media. However, after 5hrs of incubation, obvious cell death was observed in the HBP media, while cells in POSS-BP media remained viable. After 13 hours incubation, almost all cells in the HBP media were dead. These initiators also showed a dose-dependent toxicity. The survival and growth of HeLa cells in different concentrations of HBP and POSS-BP media was assessed for 6 days as shown in Figure 3 (b-d). At 0.75X, 0.5X, and 0.25X concentrations, POSS-BP media showed significantly lower cell toxicity compared to HBP. We attributed this improved safety of the POSS-coupled photoinitiators predominantly to their low migration property, as well as the intrinsic biocompatibility of the POSS core. Migration was a diffusion-controlled process and the speed


12

Page 13 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of diffusion was, in general, inversely correlated to the molecular weight. Since POSS-coupled photoinitiators had much higher molecular weights than their small molecular analogues (Table 1) because of the cage-like nano-structured POSS moieties,16,18 migration of these photoinitiators is expected to be considerably reduced. To confirm this, the migration potential of the initiators from the polymer matrix was assessed by extraction of the photoinitiators from a square polymer sheet with the help of ultrasonication in ethanol. Extraction of POSS-BP and HBP photoinitiators was carried out on cured PEGDA and hexanediol diacrylate (HDDA) polymers. As shown in Figure 3e, the extractability of POSS-BP was indeed significantly reduced compared to HBP in both types of polymer matrices due to its low mobility in the polymer matrix. POSS is a hard nanoparticle that has been widely used as nano-fillers in nanocomposites reinforcement.19 To test the effect of POSS-coupled BP photoinitiators on the mechanical strength of cured polymers, dynamic mechanical analysis (DMA) of cured HDDA polymers containing different weight percentages of HBP and POSS-BP photoinitiators was carried out. We found that both the storage modulus and the polymer glass transition temperature (Tg) increase correspondingly with increasing amounts of photoinitiators (Figure S10, Supporting Information). These observations may be attributed to increased photopolymer conversion and greater degree of crosslinking at higher photoinitiator content. Notably, the storage moduli of HDDA resin cured with POSS-BP were consistently greater than that cured with HBP, especially at higher photoinitiator content. These results demonstrate the dual capacities of these POSS-coupled photoinitiators, functioning as highly efficient photoinitiators as well as mechanical reinforcement nanofillers.


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 21

The new POSS-coupled photoinitiators thus exhibit many advantageous qualities such as improved safety and biocompatibility, enhanced photoactivity and better mechanical properties, which make them highly suitable for applications in stereolithography-based 3D printing. To demonstrate their potential applications, HDDA resin was mixed with POSS-coupled initiators and printed on a digital light processing (DLP) printer (Brand: LittleRP) with a DLP projector as light source (Brand & model: Acer P1283 ).30 The viscosity of the HDDA resin (η = 8.726 ± 0.35 mm2/s) was measured before and after mixing with the POSS-coupled photoinitiators, and a slight increase of < 2% in viscosity was observed upon the addition of approximately 3 wt% of photoinitiators (η = 8.741 ± 0.26 mm2/s). The surprisingly small effect on resin viscosity by the high molecular weight POSS-coupled initiators may be attributed to the spherical structure of POSS,

which

confers

low

resistance

to

the

flow

of

liquid.

Printing

conditions were optimized with cure depth analyses and prototypes of different 3D structures were printed on the DLP 3D printer controlled by Creation Workshop software (Figure 4). With the successful printing of various 3D structures with high resolution and accuracy, we have thus demonstrated the utility of these newly synthesized POSS-coupled photoinitiators in 3D printing. We propose that this new type of photoinitiators will be very useful in various 3D printing applications, such as consumer products printing and bio-printing, which require high safety, photo-efficiency, and mechanical strength.


14

Page 15 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Pictures of 3D printed objects by POSS-DBP photoinitiator using a DLP printer with HDDA resin containing 3 wt% POSS-coupled photoinitiators and 0.05 wt% of photo-absorbers. In summary, a new series of POSS-coupled benzophenone photoinitiators with different initiating wavelengths (270-350 nm) was designed and synthesized. These new nano-sized photoinitiators were characterized by NMR and thermal analysis. Compared to their corresponding benzophenone small molecules, the POSS-coupled photoinitiators showed many advantageous properties such as large molecular weight with uniform sizes, extremely low migration tendency, small effect on resin viscosity, enhanced thermal stability and mechanical strength and greater photoactivity. Particularly, the hybrid photoinitiators exhibited lower cell toxicity than their corresponding small molecular weight parent photoinitiators, making them high-potential candidates for dental- and bio-printing. Their application in 3D printing was demonstrated on a DLP printer with high resolution and accuracy. This class of POSS-coupled photoinitiators, with its many favorable characteristics, will thus have significant potential applications in future 3D printing of end-use products and food-related UV coating.

ASSOCIATED CONTENT Supporting Information.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 21

Supporting Information Available: Experimental details, full characterization of the photoinitiators, thermal analysis of the photoinitiators, Photopolymerization efficiency test, Computer optimized structure, and Mechanical tests (PDF). This material is available free of charge via the Internet at http://pubs.acs.org. Corresponding Authors *[email protected] and [email protected] ORCID FuKe Wang: 0000-0002-6980-5857; Xiuling Jiao: 0000-0002-4358-7396. Author Contributions ⊥

These authors contributed equally.

Acknowledgements We acknowledge financial support of this work from the Science and Engineering Research Council (Grant 1325504107) of Agency for Science, Technology and Research of Singapore. References 1. Horvath, J. Mastering 3D Printing; Apress: Berkeley, CA, 2014. 2. Council, A.; Petch, M. 3D Printing: Rise of the Third Industrial Revolution; Gyges 3D.com, 2014. 3. Gibson, I.; Rosen, D.; Stucker, B. Additive Manufacturing Technologies: 3D Printing, Rapid Prototyping, and Direct Digital Manufacturing; Springer-Verlag New York: New York, 2015.


16

Page 17 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4. Wang, F.; Wang, F. K. Liquid Resins Based Additive Manufacturing. J. Mol. Eng. Mater. 2017, 5, 1740004. 5. Balasubramanian, A.; Bettinger, C. J. Shape Recovery Kinetics in Vascularized 3D-Printed Polymeric Actuators. Adv. Eng. Mater. 2015, 17, 1287-1293. 6. Liska, R.; Schuster, M.; Inführ, R.; Turecek, C.; Fritscher, C.; Seidl, B.; Schmidt, V.; Kuna, L.; Haase, A.; Varga, F.; Lichtenegger, H.; Stampfl, J. Photopolymers for Rapid Prototyping. J. Coat. Technol. Res. 2007, 4, 505-510. 7. Decker, C. In Processes in Photoreactive Polymers; Krongauz, V. V., Trifunac, A. D., Eds.; Springer US: New York, 1995; Chapter 2, pp 34-55. 8. Belfield, K. D.; Crivello, J. V. Photoinitiated Polymerization; American Chemical Society: Washington DC, 2003. 9. Green, W. A. Industrial Photoinitiators A Technical Guide; CRC Press: Boca Raton, FL, USA, 2010. 10. Schuster, M.; Turecek, C.; Kaiser, B.; Stampfl, J.; Liska, R.; Varga, F. Evaluation of Biocompatible Photopolymers I: Photoreactivity and Mechanical Properties of Reactive Diluents. J. Macromol. Sci. 2007, 44, 547-557. 11. Fouassier, J. P.; Lalevée, J. Photoinitiators for Polymer Synthesis: Scope, Reactivity, and Efficiency, Wiley, VCH: Weinheim, Germany, 2012. 12. Lago, M. A.; De Quirós, A. R.; Sendón, R.; Bustos, J.; Nieto, M. T.; Paseiro, P. Photoinitiators: A Food Safety Review. Food Addit. Contam. A 2015, 32, 779-798.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 21

13. Wei, J.; Wang, H. Y.; Jiang, X. S.; Yin, J. Novel Photosensitive Thio-Containing Polyurethane as Macrophotoinitiator Comprising Side-Chain Benzophenone and Co-initiator Amine for Photopolymerization. Macromolecules 2007, 40, 2344-2351. 14. Angiolini, L.; Caretti, D.; Rossetti, S.; Salatelli, E.; Scoponi, M. Radical Polymeric Photoinitiators Bearing Side-chain Camphorquinone Moieties Linked to The Main Chain Through a Flexible Spacer. J. Polym. Sci. Pol.Chem. 2005, 43, 5879-5888. 15. Sarker, A. M.; Lungu, A.; Neckers, D. C. Synthesis and Characterization of a Novel Polymeric System Bearing a Benzophenone Borate Salt as a New Photoinitiator for UV Curing. Macromolecules 1996, 29, 8047-8052. 16. Jiang, X. S.; Yin, J. Deandritic Macrophotoinitiator Containing Thioxanthone and Coinitiator Amine. Macromolecules 2004, 37, 7850-7853. 17. Chen, Y.; Loccufier, J.; Vanmaele, L.; Frey, H. Novel Multifunctional Hyperbranched Polymeric Photoinitiators With Buit-in Amine Coinitiators for UV Curing. J. Mater. Chem. 2007, 17, 3389-3392. 18. Baney, R. H.; Itoh, M.; Sakakibara, A.; Suzuki, T. Silsesquioxanes Chem. Rev. 1995, 95, 1409-1430. 19. Cordes, D. B.; Lickiss, P. D.; Rataboul, F. Recent Developments in the Chemistry of Cubic Polyhedral Oligosilsesquioxanes. Chem. Rev. 2010, 110, 2081-2173. 20. Wang, F. K.; Lu, X. H.; He, C. B. Some Recent Developments of Polyhedral Oligomeric Silsesquioxane (POSS)-based Polymeric Materials. J. Mater. Chem. 2011, 21, 2775-2782.


18

Page 19 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


21. Sencevik, R. G.; Tasdelen, M. A. Poly(methyl methacrylate)/POSS Hybrid Networks by Type ⅡPhotoinitiated Free Radical Polymerization. Polym. Compos. 2014, 35, 1615-1620.

22. Tegou, E.; Bellas, V.; Gogolides, E.; Argitis, P. Polyhedral oligomeric silsesquioxane (POSS) acrylate copolymers for microfabrication: properties and formulation of resist materials. Microelectronic Engineering 2004, 73-74, 238-243. 23. Yagci, Y.; Jockusch, S.; Turro, N. J. Photoinitiated Polymerization: Advances, Challenges, and Opportunities. Macromolecules 2010, 43, 6245-6260. 24. Lalevée, J.; Blanchard, N.; El-Roz, M.; Graff, B.; Allonas, X.; Fouassier, J. P. New Photoinitiators Based on the Silyl Radical Chemistry: Polymerization Ability, ESR Spin Trapping, and Laser Flash Photolysis Investigation. Macromolecules 2008, 41, 4180-4186. 25. Shah, R. C.; Deshpande, R. K.; Chaubal, J. S. Condensation of Benzanilides and pDialkylanilines With Phosphorus Oxychloride as Condensing Agent, and the Mechanism of the Reaction. J. Chem. Soc. 1932, 642-650. 26. Chi, H.; Mya, K. Y.; Lin, T. T.; He, C. B.; Wang, F. K.; Chin, W. S. Thermally Stable Azobenzene Dyes Through Hybridization With POSS. New J. Chem. 2013, 37, 735-742. 27. Hirano, T.; Li, W.; Abrams, L.; Krusic, P. J.; Ottaviani, M. F.; Turro, N. J. Supramolecular Steric Effects as the Means of Making Reactive Carbon Radicals Persistent. Quantitative Characterization of the External Surface of MFI Zeolites through a Persistent Radical Probe and a Langmuir Adsorption Isotherm. J. Org. Chem. 2000, 65, 1319-1330.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 21

28. Bhunia, K.; Sablani, S. S.; Tang, J.; Rasco, B. Migration of Chemical Compounds from Packaging Polymers during Microwave, Conventional Heat Treatment, and Storage. Compr. Rev. Food Sci. F. 2013, 12, 523-545. 29. Bail, R.; Patel, A.; Yang, H.; Rogers, C. M.; Rose, F. R. A. J.; Segal, J. I.; Ratchev, S. M. The Effect of a Type I Photoinitiator on Cure Kinetics and Cell Toxicity in ProjectionMicrostereolithography. Procedia CIRP 2013, 5, 222-225. 30. Wang, F.; Chong, Y. T.; Wang, F. K.; He, C. B. Photopolymer Resins for Luminescent Three-dimensional Printing. J. App. Polym. Sci. 2017, 134, 44988.


20

Page 21 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Graphic for the Table of Contents:

High Performance Nano-Photoinitiators with Improved Safety for 3D Printing Yanyang Han,†,⊥ Fei Wang,‡,⊥ Chin Yan Lim,§ Hong Chi,ǁ Dairong Chen,† FuKe Wang,*‡ Xiuling Jiao*†


21

High-Performance Nano-Photoinitiators with Improved Safety for 3D

Recommend Documents