A. Galukhin et al.
Reactive and Functional Polymers 165 (2021) 104956
(>99.5%, EKOS-1), hydrochloric acid (>35%, Component-Reagent),
Na2SO3 (anhydrous, > 99%, Chimmed), Na2SO4 (anhydrous, > 99.5%,
Chimmed), SiO2 (60 Å, 0.04–0.063 mm, Machery-Nagel), P2O5 (>98%,
Vekton), and isopropanol (99.8%, REACHEM) were purchased and used
as received. Acetone (>98%, TatChemProduct) was purchased and
additionally distilled over P2O5.
Target dicyanate ester 4 was obtained according to the synthetic
procedure presented in Fig. 2.
1,3-dibromoadamantane 2 and 1,3-bis(4-hydroxyphenyl)adaman-
tane 3 were synthesized according to known synthetic protocols
[22,23].
Synthesis of 1,3-bis(4-cyanatophenyl)adamantane 4. 1,3-bis(4-
hydroxyphenyl)adamantane 3 (2.0 g, 6 mmol), cyanogen bromide
(2.7 g, 25 mmol), and 30 mL of acetone were added to a round bottom
flask with a magnetic stirrer. The reaction mixture was cooled to ꢀ 20◦С,
and then triethylamine (3.5 mL, 25 mmol) was added dropwise. The
synthesis was carried out for an hour under continuous stirring and
cooling. Then solvent was removed from reaction mixture under
reduced pressure and obtained residue was dissolved in dichloro-
methane and washed several times with deionized water. Obtained
organic solution was dried over anhydrous Na2SO4 and target compound
was separated by column chromatography (dichloromethane as an
eluent). The resulting product 4 was purified by recrystallization from
the mixture of CH2Cl2 and hexane. The final yield of pure product was
1.8 g (81%). Mp: 122 ◦C. 1H NMR, CDCl3-d1, δ (ppm): 1.83 (s, -CH2-,
2H), 1.97–2.00 (m, -CH2-, 8H), 2.38 (s, -CH-, 2H), 7.27 (d, ArH, 4H, J =
8.4 Hz), 7.47 (d, ArH, 4H, J = 8.4 Hz). 13C NMR, δ (ppm): 29.32, 35.47,
37.22, 42.11, 49.02, 108.98, 115.02, 126.98, 149.19, 150.97. Crystal
Data. C24H22N2O2, Mr = 370.43, triclinic, P-1 (No. 2), a = 7.3404(3) Å,
Fig. 1. Schematic illustration of the effect of the polymer Tg value on the
reactivity of a monomer. Dashed lines represent variation of Tg with conversion
(α), solid lines represent α-T plots obtained at the heating rate β. Circles show
intersection points of the corresponding α-T and Tg-α curves.
having higher Tg is more likely to encounter vitrification at earlier stages
of the reaction progress.
In all, we hypothesize that incorporation of adamantane into the
structure of cyanate resin as a rigid bridging fragment should increase
the glass transition temperature and thermal stability of the resulting
polymer. Also we expect that the reactivity of the monomer should be
affected by vitrification as described above. To explore this hypothesis
we have synthesized adamantane-based dicyanate ester, which is sub-
jected to thermal polymerization. We have studied the obtained mono-
mer reactivity by both conventional and temperature-modulated DSC
under nonisothermal conditions and parameterized its polymerization
kinetics with the aid of isoconversional methodology [19]. We have also
applied thermogravimetry to test the thermal stability of the polymeri-
zation product and compared it with that of the polymers produced from
commercially available dicyanate esters of similar structure. It should be
noted that although adamantane-based cyanate esters are known since
the middle of the last decade [20,21] the kinetics of their polymerization
has never been studied before.
b = 10.5239(6) Å, c = 12.9183(6) Å,
α
= 107.619(4)◦, β = 104.129(4)◦,
γ = 93.734(4)◦, V = 911.86(8) Å3, T = 100.0(2) K, Z = 2, Z’ = 1,
μ(Cu
Kα) = 0.686, 10,248 reflections measured, 3681 unique (Rint = 0.0297)
which were used in all calculations. The final wR2 was 0.1182 (all data)
and R1 was 0.0409 (I > 2(I)). CCDC number 2065109.
2.2. Methods
2.2.1. Methods for the determination of the structure and purity of target
monomer
Data set for single crystal of the monomer was collected on a Rigaku
XtaLab Synergy S instrument with a HyPix detector and a PhotonJet
microfocus X-ray tube using Cu Kα (1.54184 Å) radiation at low tem-
perature. Images were indexed and integrated using the CrysAlisPro
data reduction package. Data were corrected for systematic errors and
absorption using the ABSPACK module: numerical absorption correction
based on Gaussian integration over a multifaceted crystal model and
empirical absorption correction based on spherical harmonics according
to the point group symmetry using equivalent reflections. The GRAL
module was used for analysis of systematic absences and space group
determination. The structure was solved by direct methods using
SHELXT and refined by the full-matrix least-squares on F2 using SHELXL
[24,25]. Non‑hydrogen atoms were refined anisotropically. The
hydrogen atoms were inserted at the calculated positions and refined as
2. Experimental section
2.1. Materials
Iron powder (≥99%, Sigma-Aldrich), bromine (99.6%, Acros Or-
ganics), adamantane (>99%, Sigma-Aldrich), triethylamine (>99%,
Sigma-Aldrich), cyanogen bromide (97%, Acros Organics), phenol
(99.5%, Acros Organics), ethanol (95%, RFK), trichloromethane
(>99.5%, EKOS-1), dichloromethane (>99.5%, EKOS-1), hexane
Fig. 2. Scheme of synthesis of target dicyanate ester.
2