3D Printing/Vat Photopolymerization of Photopolymers Activated by Novel Organic Dyes as Photoinitiators
, Tao Gong 1,* and Pu Xiao 2,*Round 1
Reviewer 1 Report
The manuscript is a mini-review that describes what was discovered within the last one and half years (i.e., 2021 - mid 2022) in the area of photoinitiators or photoinitiating systems applicable for 3D printing by free radical photopolymerization. It is written in understandable English, though some improvement of grammar could be beneficial for the paper. Nevertheless, minor grammatical errors or some improper wording do not hinder understanding the paper contents, so those are acceptable in the case of non-native English speakers. However, there are also some meritorious errors that need correction to make the manuscript acceptable for publication. The following is wrong and needs to be corrected:
1. Free radical generation from photoinitiators does not necessarily occur from singlet excited states. In many cases triplet excited states are involved. For example, benzophenone never reacts from singlet excited state. Hence, using 1PI (h ) symbol in the equations (r1) and (r2) that implies singlets is misleading. Moreover, it is not clear what (h ) means in the reactions (r1)-(r3). I recommend replacing that symbol with PI*, which is commonly used to denote excited states regardless of their multiplicity.
2. Reaction (r4) is wrong, because the radical Ar2I∙ is not an intermediate in the reaction sequence (i.e., it was never detected by EPR nor other techniques, though some people tried hard). This means that Ar2I∙ is only a transient that decomposes immediately into an aryl radical and an aryl iodide. Consequently the reaction (r4) should be written as:
PI* + Ar2I+ → PI●+ + Ar● + ArI
where PI* denotes PI excited state of any multiplicity. Moreover, the reaction (r3) can be simplified to the following form:
PI + photon → PI*
3. Tables 1-5: The wavelength symbol "lambda" (λ) is not visible neither in PDF nor in printout. Lambda from the "Symbol" font set has to be used to avoid problems.
4. Table 2: Structures of OXE-M, OXE-V and OXE-P are wrong (i.e., nitrogen atom is missing from the oxime ester groups).
5. lines 180/181: The statement: "Subsequently, the decarboxylation reaction eliminate the potential back electron donation,..." makes no sense, because there is no electron transfer involved in the reaction mechanism shown in Fig. 2a, so the "back electron donation" is not possible.
6. The title of right vertical axis in Figure 3b is missing.
7. line 282: there is a reference to wrong figure.
8. It is well known that trimethylolpropane triacrylate (TMPTA) does not polymerize to higher than 80 % conversions of acrylic groups, for steric reasons. Hence, the conversion data exceeding 90% , taken from the ref. 63 and collected in Tables 4-5 are not reliable. Either the original authors of ref.63 ill-determined those conversions or the monomer they used was not TMPTA. Erroneous data should not be discussed in a review, because a review presents an opinion of the review authors, not the opinion of the original authors cited in the review. Hence, the final conversions reported in Tables 4-5 may be left just to indicate that something like that was investigated, but the erroneous numbers from the tables should not be repeated in the discussion in lines 298-332. In such case, the photoinitiator performance can be compared only in relative terms without reference to the erroneous absolute conversions.
9. line 327: Full chemical name of the monomer "TA" should be reported before first use of the TA acronym, while adding TA in parenthesis after the name, because it is not obvious what TA was. Same applies to the other acronyms used in the review.
10. When type of the photocatalyst (PC) is not specified in Figures 7b-c (i.e., whether PC is ionic or neutral), the product of electron transfer from excited state of PC to the polymer terminal group should be denoted as a radical cation (i.e., as PC●+, not as PC+) to keep the electron and charge balance.
11. The statement in lines 458-460 is unclear, because of grammar.
12. Conclusions section should contain main conclusions (i.e., what new was found), not what was done. What was done is appropriate for an abstract. Consequently, the statements in lines 530-541 are not conclusions.
Moreover, the following replacements or deletions will improve some of the improper wording:
line 10: there is: on -> there should be: of
line 11: delete: been
line 12: act as -> play
lines 13/14: photocatalysts in literature during 2021-2022 -> photocatalysts, reported in literature during 2021-2022,
line 35: Emitted -> Emitting
line 16,229: of -> with
line 20: knowledges of -> reports on
lines 28/29: prototyping -> prototyped
line 41: their proper -> its
line 49: by absorbing light. Charges could -> upon absorption of light, charges can
lines 50/51: delete: in order to form the catalytic cycle
line 53: achieved -> involved
lines 60/61: the benchmark monomers converted as a -> the monomer conversion to a
line 61: delete: benchmark (because the equation 1 applies to all kind of monomers, not only to the benchmark ones)
lines 67,70,87,91,120,179,279: were -> are
line 79: photochemical -> thermal (because if PIs showed high photochemical stability, they would not be photoinitiators)
line 80,442: are -> were
lines 85,89: following -> by the following
lines 88,116-117,121,127,139: N-naphthalimide ester -> N-hydroxynaphthalimide esters ; delete: derivatives
line 94: combine -> are combined ; amine -> ethyl 4-dimethylaminobenzoate (EDB)
line 105: photo-RAFT -> photo-RDRP
line 115: using -> used
line 134,137,420: is -> was
line 147: of -> to ; in -> for
lines 150/151: delete: which can be proved by the highest occupied molecular orbitals (HOMO) (because it is unclear)
lines 151/152: photobleachable -> photobleaching
line 153: after -> upon
line 156: deep as 32 mm in thickness -> depth of 32 mm
line 164,165,175,188,212: delete: derivatives.
line 165,188,212: ester -> esters
line 167: delete: without oxime ester group
line 169: on -> within
line 179/180: occurred by excitation of ground states OXEs -> occurring upon excitation of OXE
line 185: can be observed by the characterization of optical microscopies -> was observed
line 186: Meanwhile -> Moreover
line 189: high -> highly
line 197: Continue from -> While continuing
line 198: delete: (Column B-F) (because there is no those columns in the review)
line 205: the truths of -> the fact that the ; delete also the other: that
line 206: were -> was
line 223/224: numerical optical microscope -> digital microscope
line 208: in 16s -> within the first 16 s
line 212: performed -> studied
line 237: step mechanisms -> mechanism
line 235: photocatalysis -> photocatalyst
line 247: modifying with -> modifying benzophenone with
line 250: noted dye 1-5 -> noted as dyes 1-5
lines 256/257: to enhance the -> with enhanced
line 264: irradiation -> photopolymerization
line 268: be used in -> to initiate
line 270: for photopolymerization as Type II photoinitiators -> as Type II photoinitiators for photopolymerization
line 272: chemical function -> functional
line 289: has -> have
line 297: delete: as presented in the literature (redundant)
line 301: photopoymerization -> photopolymerization
line 356: inti -> in ; TMTPA -> TMPTA
line360: truth -> fact
line 361: delete: groups
line 364: photopolymerization and photocuring -> photopolymerization (because photocuring has the same meaning as photopolymerization)
line 370-371: delete: for (3x)
line 382-384, 498: showed -> shown
line 413,423: contained -> containing
line 423: different crosslinker -> different amounts of crosslinker
line 427: delete: different crosslinker
line 461: irradiated by -> carried out under
line 470: as the -> used in
line 488,493,544: delete: been
line 491: only few -> little
line 498,503: serves -> serve
line 499,501: could -> can
line 501: delete: (or monomers)
line 512: monomer -> polymerization
line 514: usage -> use
Author Response
Recently our manuscript entitled as “3D Printing/Vat photopolymerization of photopolymers activated by novel organic dyes as photoinitiators” was submitted to Catalysts, and we are very thankful for your kindly help as well as the referees’ professional and valuable comments and suggestions. The actual version has been changed and all the comments were taken into account. The details of revision as a point-by-point response to the comments made by the first referee are given in the following parts. We have highlighted the answers in the revised manuscript with red font.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript ‘3D Printing/Vat photopolymerization of photopolymers activated by novel organic dyes as photoinitiators’ by k. Sun et al.is a review paper on newly synthesized photoinitiators/photocatalysts molecules appeared in literature during 2021-2022, discussing the photochemistry and the performance of these photoinitiators in several systems. The manuscript is well written with very good coverage of the literature published during 2021-2022. I am happy to recommend publication of the article which will certainly be of interest to the readership of Catalysts after addressing the following minor points.
A) Some points in the manuscript have different font size i.e line 136-138, 142, 244-245 e.t.c
B) The structures of the molecules in the tables have different font sizes in the letters of the atoms.
C) The figures 2a, 3, 4 seem blurred.
Author Response
Recently our manuscript entitled as “3D Printing/Vat photopolymerization of photopolymers activated by novel organic dyes as photoinitiators” was submitted to Catalysts, and we are very thankful for your kindly help as well as the referees’ professional and valuable comments and suggestions. We have highlighted the changes in the revised manuscript. The details of revision as a point-by-point response to the comments made by the referee 2 are given in the associated document.
Author Response File: Author Response.pdf
