Synthesis and Styrene Copolymerization of New Halogen and Methoxy Ring-Trisubstituted Propyl Cyanophenylpropenoates

New ring-trisubstituted propyl cyanophenylpropenoates, RPhCH=C(CN)CO2C3H7 (where R is 2-bromo-3-hydroxy-4-methoxy, 5-bromo-2,3-dimethoxy, 5-bromo-2,4-dimethoxy, 6-bromo-3,4-dimethoxy, 2-chloro-3,4-dimetoxy, 5-chloro-2,3-dimetoxy, 4-bromo-2,6-difluoro, 3-chloro-2,6-difluoro, 4-chloro-2,6-difluoro) were prepared by the piperidine catalyzed Knoevenagel condensation of ring-trisubstituted benzaldehydes and propyl cyanoacetate and characterized by CHN elemental analysis, IR, H and C-NMR. The propenoates formed copolymers with styrene in solution with radical initiation (ABCN) at 70C. The copolymers were characterized by nitrogen elemental analysis, IR, H and C-NMR, DSC. Decomposition of the copolymers in nitrogen (TGA) occurred in two steps, first in the 200-500oC range with residue (4.2 -8.1% wt.), which then decomposed in the 500-800oC range.


General Procedures
IR spectra of the PCPP compounds and polymers (NaCl plates) were determined with an ABB FTLA 2000 FT-IR spectrometer.The melting points of the PCPP compounds and 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 200º C range on second heat at heating rate of 10º C/min.T g was taken as a midpoint of a straight line between the inflection of the peak's onset and endpoint.The thermal stability of the copolymers was measured by thermogravimetric analyzer (TGA) TA Model Q50 from ambient temperature to 800º C at 20º C/min in the flow of nitrogen (20 mL/min).The molecular weights of the polymers was determined relative to polystyrene standards in THF solutions with sample concentrations 0.8% (w/v) by gel permeation chromatography (GPC) using a Altech 426 HPLC pump at an elution rate of 1.0 mL/min; Phenogel 5μ Linear column at 25ºC and Viscotek 302 RI detector. 1H-and 13 C-NMR spectra were obtained on 10-25% (w/v) PCC or polymer solutions in CDCl 3 at ambient temperature using Bruker Avance 300 MHz spectrometer.Elemental analyses of were performed by Midwest Microlab, LLC (IN).
The cyanophenylpropenoates were prepared by mixing equimolar amounts of propyl cyanoacetate and an appropriate benzaldehyde, together with 0.2 g of piperidine.The product was recrystallized in propyl alcohol.No stereochemical analysis of the novel ring-trisubstituted PCPP was performed since no stereoisomers (E or/and Z) of known configuration were available.

Synthesis of Styrene -PCPP Copolymers
ST and the PCPP monomers were mixed in 25-mL glass screw cap vials at ST/PCPP = 3 (mol) the monomer feed using 0.12 mol/L of ABCN at an overall monomer concentration 2.44 mol/L in 10 mL of toluene.The mixture was heated at 70º C for 5 hours followed by precipitated in methanol forming white flaky precipitates.The new synthesized PCPP compounds copolymerized readily with ST under free-radical conditions (Scheme 2).The conversion of the copolymers was kept between 10 and 20% to minimize compositional drift (Table 1).Nitrogen elemental analysis showed that between 18.4 and 32.2 mol% of PCPP is present in the copolymers, which is indicative of relatively high reactivity of the PCPP monomers towards ST radical.We showed that the PCPP monomers do not homopolymerize under these conditions, therefore the most likely the copolymers' structure would be PCPP centered triads, ST-PCPP-ST separated by short ST sequences (Scheme 2).

Structure and Thermal Properties
The ST-PCPP copolymers were characterized by IR and NMR spectroscopy.The spectra of the monomers were compared with those of copolymers and polystyrene thus providing evidence that the reaction between the PCPP monomers and ST is a copolymerization.The C-H stretch vibrations are observed in 3200-2800 cm -1 region.PCPP showed absorptions at 2244-2233(w, CN), 1748-1725 (s, C=O) (s, C=O), and 1256-1212 cm -1 (s, C-O).Vibrations at 1500-1400 cm -1 as well as a doublet 800-700 cm -1 are associated with ST and PCPP rings stretching bands, as well as with C-H out-of-plane deformations.
ST-PCPP copolymers microstructure analysis is based on 1 H-and 13 C-NMR spectroscopy (DEPT, HETCOR, NOESY and JMODXH) of ST copolymers with 2-phenyl-1,1-dicyanoethene (Kharas, Murau, Watson, & Harwood, 1992) which showed the formation of both head-to-tail and head-to-head alternating monomer structures, as well as short ST sequences.A broad double peak in a 5.0-7.5 ppm region in the 1 H-NMR spectra of the ST-PCPP copolymers corresponds to phenyl protons.Head-to-tail and head-to-head structures, which might form via the attack of ST-ended radical on both sides of PCPP monomer or/and participation of both free monomers and monomer donor-acceptor complexes (Odian 2004) might be associated with broadening of the NMR signals.The IR and NMR data showed that these are true copolymers, composed of both TSE and ST monomer units.
DSC analysis confirmed amorphous morphology of the ST-PPCA copolymers showing glass transition temperatures T g and absence of crystalline endotherm on repeated heating and cooling cycles (Table 2).
Thermogravimetric analysis provided information on thermal stability of the copolymers (Table 2).Thermal stability of the P(ST-co-PCPP) copolymers is lower than that of polystyrene, PS (Ellison et al., 2005, Petrson et al., 2001), the onset of decomposition at 202 -291º C (PS 350º C), 10% weight loss at 275 -297º C (PS 425º C), 50% weight loss at 337 -380º C (PS 428º C).Lower thermal stability of the copolymers apparently associated with presence of PCPP quaternary carbon in the chain similarly to poly-alpha-methylstyrene (Lina et al., 2012).Information on the degradation of

Table 1 .
Molecular characteristics of P(ST-co-PCPP) copolymers a The methyleneoxy protons of propyl ester in both head-to-tail (H-T) structure and head-to-head (H-H) structure are observed in 4.4-4.0ppmregion.The methylene protons of H-T structures and methine protons of ST in H-H structures as well as methine protons of PCPP in both structures are represented by broad overlapping resonances at 4.0-2.7 ppm.Methoxy protons of PCPP absorb in 4.0-3.5 ppm.The methine and methylene protons of ST monomer sequences as well as to PCPP ester methylene protons are attributed to a broad resonance peak in 2.0-0.8ppmrange, whereas methyl groups of PCPP propyl ester are represented by the absorption in 1.0-0.4ppm.In 13 C-NMR spectra of the copolymers, the carbonyl of the PCPP propyl ester group is associated with the peak in 162-157 ppm range.Absorptions in 120-115 ppm range are assigned to nitrile carbon, whereas phenyl carbon resonances of ST and PCPP are observed in 147-120 ppm range.Absorption of methyleneoxy carbon of propyl ester in both H-T and H-H alternating ST-PCPP structures is observed at 68-63 ppm.Methoxy carbons of PCPP monomer unit are assigned to resonance in 57-52 ppm range.Signals for PCPP quaternary and methine carbons in H-H structure B are assigned to overlapping absorptions at 55-52 ppm.ST methylene and methine carbons are observed at 48-33 ppm.Methylene carbons of propyl group and methyl carbon result in signals at 23-19 ppm and at 10 ppm, respectively.