Synthesis and vinyl benzene copolymerization of novel trisubstituted ethylenes: 15. Halogen and methoxy ring-substituted isopropyl 2-cyano-3-phenyl-2-propenoates

ABSTRACT Condensation of isopropyl cyanoacetate and substituted benzoic aldehydes resulted in formation of novel isopropyl esters of 2-cyano-3-phenyl-2-propenoic acid, RPhCH = C(CN)CO2CH(CH3)2 (where R is 2,3,4-trimethoxy, 2,4,5-trimethoxy, 2,4,6-trimethoxy, 3-bromo-4,5-dimethoxy, 5-bromo-2,3-dimethoxy, 5-bromo-2,4-dimethoxy, 6-bromo-3,4-dimethoxy, 2-bromo-3-hydroxy-4-methoxy, 4-bromo-2,6-difluoro, 2-chloro-3,4-dimethoxy, 3-chloro-4,5-dimethoxy, 5-chloro-2,3-dimethoxy, 2,3,6-trichloro, 3-chloro-2,6-difluoro, 2,3,4-trifluoro, 2,4,5-trifluoro, 2,4,6-trifluoro, 3,4,5-trifluoro, 2,3,5,6-tetrafluoro, 2,3,4,5,6-pentafluoro). Copolymerization of the esters with vinyl benzene in solution with radical initiation (ABCN) at 70°C led to formation copolymers. The products were characterized by CHN elemental analysis, IR, 1 H- and 13 C-NMR, GPC, DSC, and TGA.


Instrumentation
Infrared spectra of the TSE monomers and polymers (NaCl plates) were determined with an ABB FTLA 2000 FT-IR spectrometer. The melting points of the monomers, the glass transition temperatures (T g ), of the copolymers were measured with TA (Thermal Analysis, Inc.) Model Q10 differential scanning calorimeter (DSC). The thermal scans were performed in a 25 to 200ºC range at heating rate of 10ºC/min. The thermal stability of the copolymers was measured by thermogravimetric analyzer (TGA) TA Model Q50 from ambient temperature to 800ºC at 20ºC/min. The molecular weights of the polymers were determined relative to polystyrene standards in THF solutions with sample concentrations 0.8% (w/v) by gel permeation chromatography (GPC) using an Altech 426 HPLC pump at an elution rate of 1.0 mL/min; Phenogel 5μ Linear column at 25ºC and Viscotek 302 detector. 1 H-and 13 C-NMR spectra were obtained on 10-25% (w/v) monomer or polymer solutions in CDCl 3 at ambient temperature using Avance 300 MHz spectrometer. Elemental analyses, CHN (wt%) for ICPP compounds, and nitrogen (wt%) for the copolymers were determined accurately to 0.3% for analysis by Midwest Microlab, LLC (IN).

Homopolymerization
The IPCA compounds did not homopolymerize on ABCN initiation at 70ºC for 48 h with no polymer precipitated in methanol. Vinyl benzene (VB) polymerization (30 min) resulted in 18.3% yield of polyethenybenzene.

Copolymerization
Copolymers of the vinyl benzene (VB) and the ICPA monomers were prepared at VB/ICPA = 3 (mol) the monomer feed with 0.12 mol/L of ABCN at total monomer concentration 2.44 mol/L in 10 mL of toluene at 70ºC. Polymerization time was 8 h. To stop reaction the mixture was cooled and precipitated in methanol. Nitrogen elemental analysis was used to determine composition of the copolymers. The yield of copolymers was kept low to decrease copolymer compositional drift.
Copolymerization (Sch. 1) of VB and the ring-substituted ICPA resulted in the formation of copolymers (Table 1)  According to elemental analysis, between 9.4 and 35.2 mol% of ICPA monomer is present in the copolymers prepared at VB/ICPA = 3 (mol), which is indicative of relatively high reactivity of the monomers towards ST.
The copolymers were all soluble in ethyl acetate, THF, DMF and CHCl 3 and insoluble in methanol, ethyl ether, and petroleum ether.

Monomer relative reactivity
Relative reactivities of VB and the ICPA monomers in the copolymerization can be estimated by application of the copolymerization equation for the terminal copolymerization model [10].
where m 1   formed homopolymers, (k ICPA-ICPA = 0, r 2 = 0) [10], Eq. (1) yields These relative reactivity values can be used to predict specific copolymer composition as function of the comonomer feed. Additional research will be needed to correlate effect of phenyl ring substitution with reactivity of ICPA monomers in radical copolymerization.

Thermal behavior
Thermal transitions of the VB-ICPA copolymers were analyzed by differential scanning calorimetry (DSC). The second heating results were obtained in all cases so that the samples become more dry and without 'thermal memory'. DSC analysis confirmed amorphous morphology of the EB-ICPA copolymers showing glass transition temperatures T g and absence of crystalline endotherm on repeated heating and cooling cycles ( Table 2). A single T g value was observed for all the copolymers with values close to or higher than polystyrene (104ºC) [25]. Introduction of trimethoxy and bromo-dimethoxy phenyl substitution does not change significantly T g which is related to segmental mobility [26], whereas chloro-dimethoxy, trifluoro, tetrafluoro, and pentafluro phenyl substitution in VB-ICPA copolymer lead to decrease of segmental mobility in the polymer chain. More precise correlation of the segmental mobility to the size and position of the ICPA ring substitution is difficult apparently due to non-uniform composition, monomer unit distribution, and/or molecular weight and MWD of the copolymers.
Thermogravimetric analysis (TGA) provided information on thermal stability of the copolymers ( Table 2). Thermal stability of the P(VB-co-ICPA) copolymers is lower than that of poly(vinylbenzene, PVB) [27], the onset of decomposition at 219ºC (PVB 350ºC), 10% weight loss at 301ºC (PVB 425ºC), 50% weight loss at 343ºC (PVB 428ºC). Lower thermal stability of the VB-ICPA copolymers apparently associated with presence of ICPA quaternary carbon in the chain similarly to poly-alpha-methylstyrene [28]. TGA showed that the copolymers decomposed in nitrogen in two steps, first Table 2. Thermal Behavior of VB -ICPA copolymers.

Conclusions
Novel isopropyl esters of ring-substituted 2-cyano-3-phenyl-2-propenoic acid were prepared and copolymerized with vinyl benzene. The compositions of novel copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, H 1 and 13 C-NMR. The thermal gravimetric analysis indicated that the copolymers decompose in two steps, first in the 200-500°C range with a residue, which then decomposed in the 500-800ºC range.