Research Article

Synthesis and Styrene Copolymerization of Dimethyl and Dimethoxy Ring-Substituted Isopropyl Cyanophenyl Propenoates

Rachel Pride L, Alana MacDonald, Emma McCarthy E, Aashi Modi N, Evan Mucciolo H, Alexa Schinderle L, Shawn Trewartha, Joseph Tylka D, Michael Wade, Jacob Wat S, William S Schjerven and Gregory Kharas B*

Department of Chemistry, DePaul University, USA

Submission: August 13, 2019; Published: August 22, 2019

*Corresponding author: Gregory Kharas B, Department of Chemistry, DePaul University, USA

How to cite this article: Gregory K B, Rachel P L, Alana MD, Emma MC E, Aashi M N,et al. Synthesis and Styrene Copolymerization of Dimethyl and Dimethoxy Ring-Substituted Isopropyl Cyanophenyl Propenoates. Academ J Polym Sci. 2019; 3(1): 555602. DOI: 10.19080/AJOP.2018.02.555602

Abstract

Novel trisubstituted ethylenes, dimethyl and dimethoxy ring-substituted isopropyl 2-cyano-3-phenyl-2-propenoates, RPhCH=C(CN)CO₂CH(CH₃)₂ (where R is 2,3-dimethyl, 2,4-dimethyl, 2,5-dimethyl, 2,6-dimethyl, 3,4-dimethyl, 3,5-dimethyl, 2,3-dimethoxy, 2,4-dimethoxy, 2,5-dimethoxy) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-disubstituted benzaldehydes and isopropyl cyanoacetate and characterized by CHN elemental analysis, IR, 1H- and 13C-NMR. All the ethylenes were copolymerized with styrene in solution with radical initiation (ABCN) at 70C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and ¹³C-NMR, GPC, DSC, and TGA. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200-500oC range with residue (3.8-5.6% wt.), which then decomposed in the 500-800 oC range.

Keywords: Trisubstituted ethylenes; Radical copolymerization; Styrene copolymers

Introduction

Ring–functionalized trisubstituted ethylenes (TSE), esters of 2-cyano-3-phenyl-2-propenoic acid, R1PhCH=C(CN)CO2R2 continue to attract attention as compounds with interesting properties and as comonomers for modification of commercial polymers. Thus, methoxy ring-substituted methyl ester of 2-cyano-3-phenyl-2-propenoate, MCPP was used in synthesis of pyridotriazines and triazolopyridines [1]. Dimethylamino ring substituted MCPP was examined among other cyanovinylheteroaromatics in relation to organic nonlinear optics [2]. There are a number of applications of ethyl 2-cyano-3-phenyl-2-propenoate, ECPP and its ring-substituted derivatives which include studies of catalysis [3] and potential antimicrobial and antioxidant agents [4]. 2, 4-Dimethoxyphenyl ECPP was used in design, synthesis and study of anticancer activity of novel benzothiazole analogues [5], in synthesis of thiazacridine derivatives as anticancer agents against breast and hematopoietic neoplastic cells [6] and in DABCO-catalyzed Knoevenagel condensation using hydroxy ionic liquid as a promoter [7]. This ECPP was involved in catalysis study of N, N’- dialkylimidazolium dimethyl phosphates [8], in synthesis and study of antimicrobial activity of some cyanoacrylates [9], as well as in synthesis of antiproliferative active 2- aminobenzimidazole derivatives [10].

We have reported synthesis and styrene copolymerization of a number of dimethyl and dimethoxy ring-substituted esters of cyanophenylpropenoates (CPP): methyl ester of CPP [11,12], ethyl CPP [13,14], propyl CPP [15], and butyl CPP [16]. In continuation of our exploration of novel isopropyl CPP compounds [17-20] with the objective to synthesize novel structures with a various functional groups and explore the feasibility of their copolymerization with styrene we have prepared some dimethyl and dimethoxy ring-disubstituted isopropyl 2-cyano-3-phenyl-2-propenoates (ICPP), RPhCH=C(CN)CO₂CH(CH₃)₂, where R is 2,3-dimethyl, 2,5-dimethyl, 2,6-dimethyl, 3,4-dimethyl, 2,3-dimethoxy, 2,4-dimethoxy, 2,5-dimethoxy, 2,6-dimethoxy 3,4-dimethoxy, 3,5-dimethoxy. To the best of our knowledge, there have been no reports on either synthesis of these isopropyl 2-cyano-3-phenyl-2-propenoates, nor their copolymerization with styrene.

Experimental

Materials

2,3-dimethyl, 2,5-dimethyl, 2,6-dimethyl, 3,4-dimethyl, 2,3-dimethoxy, 2,4-dimethoxy, 2,5-dimethoxy, 2,6-dimethoxy 3,4-dimethoxy, 3,5-dimethoxybenzaldehydes, propyl cyanoacetate, piperidine, styrene, 1,1’-azobiscyclohexanecarbonitrile, (ABCN), and toluene supplied from Sigma-Aldrich Co., were used as received.

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. Tg 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 800oC at 20oC/ 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 1.0mL/ min; Phenogel 5μ Linear column at 25oC and Viscotek 302 detector. 1H- and 13C-NMR spectra were obtained on 10-25% (w/v) monomer or polymer solutions in CDCl3 at ambient temperature using Avance 300MHz spectrometer. Elemental analyses were performed by Midwest Microlab, LLC (IN).

Results and Discussion

Synthesis of monomers

The dimethyl and dimethoxy ring-substituted isopropyl 2-cyano- 3-phenyl-2-propenoates (ICPP) were synthesized by Knoevenagel condensation [21] of a ring-substituted benzaldehyde with isopropyl cyanoacetate, catalyzed by base, piperidine (Figure 1).

The preparation procedure was essentially the same for all the monomers. In a typical synthesis, equimolar amounts of isopropyl cyanoacetate and an appropriate ring-substituted benzaldehyde were mixed in equimolar ratio in a 20mL vial. A few drops of piperidine were added with stirring. The product of the reaction was isolated by filtration and purified by crystallization from 2-propanol. The condensation reaction proceeded smoothly, yielding products, which were purified by conventional techniques.

Isopropyl 2-cyano-3-(2,3-dimethylphenyl)-2-propenoate

Yield 92%; mp 114°C, ¹H-NMR δ 8.3 (s, 1H, CH=), 7.8, 7.2, 7.0 (m, 3H, Ph), 5.1 (m, 1H, OCH), 2.3 (d, 6H, CH₃) 1.3 (d, 6H, CH(CH₃)₂); ¹³C-NMR δ 166 (C=O), 152 (HC=), 133, 131, 130, 126, 125 (Ph), 116 (CN), 104 (C=), 68 (OCH), 22 (CH(CH₃)₂), 20, 16 (CH₃); FTIR (cm^-1): 3028-2837 (m, C-H), 2226 (m, CN), 1728 (s, C=O), 1596 (C=C), 1246 (s, C-O-C), 968, 842 (s, C-H out of plane). Anal. Calcd. for C₁₅H₁₇NO₂: C, 74.05; H, 7.04; N, 5.76; Found: C, 72.32; H, 6.96; N, 5.91.

Isoropyl 2-cyano-3-(2,4-dimethylphenyl)-2-propenoate

Yield 84%; mp 55°C, 1H-NMR δ 8.4 (s, 1H, CH=), 7.5, 7.0, 6.9 (t, 3H, Ph), 5.1 (m, 1H, OCH), 2.3 (d, 6H, CH₃) 1.3 (d, 6H, CH(CH₃)₂); ¹³13C-NMR δ 166 (C=O), 152 (HC=), 131, 130, 127, 126, 125 (Ph), 116 (CN), 104 (C=), 68 (OCH), 22 (CH(CH₃)2), 21, 22 (CH₃); FTIR (cm^-1): 3122-2802 (m, C-H), 2224 (m, CN), 1724 (s, C=O), 1592 (C=C), 1273, 1268 (s, C-O-C), 923, 839 (s, C-H out of plane). Anal. Calcd. for C₁₅H₁₇NO₂: C, 74.05; H, 7.04; N, 5.76; Found: C, 73.76; H, 6.96; N, 5.91.

Isopropyl 2-cyano-3-(2,5-dimethylphenyl)-2-propenoate

Yield 87%; mp 33°C, 1H-NMR δ 8.5 (s, 1H, CH=), 7.5 - 7.0 (m, 3H, Ph), 5.3 (m, 1H, OCH), 2.3 (d, 6H, CH₃) 1.3 (d, 6H, CH(CH₃)₂); 13C-NMR δ 166 (C=O), 152 (HC=), 136, 133, 131, 130 (Ph), 116 (CN), 104 (C=), 68 (OCH), 22 (CH(CH₃)2), 21, 20 (CH₃); FTIR (cm- 1): 3052-2847 (m, C-H), 2224 (m, CN), 1724 (s, C=O), 1558 (C=C), 1279 (s, C-O-CH₃), 935, 844 (s, C-H out of plane). Anal. Calcd. for C₁₅H₁₇NO₂: C, 74.05; H, 7.04; N, 5.76; Found: C, 72.30; H, 7.02; N, 5.69.

Isopropyl 2-cyano-3-(2,6-dimethylphenyl)-2-propenoate

Yield 91%; mp 46°C, 1H-NMR δ 8.5 (s, 1H, CH=), 7.5 - 7.0 (m, 3H, Ph), 5.3 (m, 1H, OCH), 2.3 (d, 6H, CH₃) 1.3 (d, 6H, CH(CH₃)₂); 13C-NMR δ 166 (C=O), 152 (HC=), 136, 133, 131, 130 (Ph), 116 (CN), 104 (C=), 68 (OCH), 22 (CH(CH₃)2), 21, 20 (CH₃); FTIR (cm- 1): 3052-2847 (m, C-H), 2224 (m, CN), 1724 (s, C=O), 1558 (C=C), 1279 (s, C-O-CH₃), 935, 844 (s, C-H out of plane). Anal. Calcd. for C₁₅H₁₇NO₂: C, 74.05; H, 7.04; N, 5.76; Found: C, 71.39; H, 6.92; N, 5.66.

Isopropyl 2-cyano-3-(3,4-dimethylphenyl)-2-propenoate

Yield 79%; mp 83°C, 1H-NMR δ 8.6 (s, 1H, CH=), 8.2 - 7.0 (m, 3H, Ph), 5.3 (m, 1H, OCH), 2.3 (d, 6H, CH3) 1.3 (d, 6H, CH(CH₃)₂); 13C-NMR δ 166 (C=O), 154 (HC=), 137, 136, 131, 130, 125 (Ph), 116 (CN), 104 (C=), 68 (OCH), 22 (CH(CH₃)2), 19 (CH₃); FTIR (cm- 1): 3164-2850 (m, C-H), 2222 (m, CN), 1722 (s, C=O), 1602 (C=C), 1245 (s, C-O-CH₃), 849 (s, C-H out of plane). Anal. Calcd. for C₁₅H₁₇NO₂: C, 74.05; H, 7.04; N, 5.76; Found: C, 72.83; H, 7.14; N, 5.69.

Isopropyl 2-cyano-3-(3,5-dimethylphenyl)-2-propenoate

Yield 82%; mp 72°C, 1H-NMR δ 8.2 (s, 1H, CH=), 7.3 - 7.0 (m, 3H, Ph), 5.3 (m, 1H, OCH), 2.4 (d, 6H, CH3) 1.3 (d, 6H, CH(CH₃)₂); 13C-NMR δ 166 (C=O), 154 (HC=), 137, 136, 131, 130, 125 (Ph), 116 (CN), 104 (C=), 68 (OCH), 22 (CH(CH₃)₂), 19 (CH₃); FTIR (cm- 1): 3164-2850 (m, C-H), 2224 (m, CN), 1720 (s, C=O), 1610 (C=C), 1249 (s, C-O-CH₃), 835 (s, C-H out of plane). Anal. Calcd. for C₁₅H₁₇NO₂: C, 74.05; H, 7.04; N, 5.76; Found: C, 72.66; H, 6.95; N, 5.67.

Isopropyl 2-cyano-3-(2,3-dimethoxyphenyl)-2-propenoate

Yield 96%; mp 66°C, 1H-NMR δ 8.6 (s, 1H, CH=), 7.9-6.9 (m, 3H, Ph), 5.1 (m, 1H, OCH), 3.8 (d, 6H, CH₃O), 1.3 (d, 6H, CH(CH₃)₂); 13C-NMR δ 166 (C=O), 152 (HC=), 152, 127, 126, 121 (Ph), 116 (CN), 111 (C=), 68 (OCH), 60, 56 (OCH₃), 22 (CH(CH₃)2); FTIR (cm- 1): 3120-2790 (m, C-H), 2224 (m, CN), 1724 (s, C=O), 1615 (C=C), 1250 (s, C-O-CH₃), 810, 762 (s, C-H out of plane). Anal. Calcd. for C₁₅H₁₇NO₄: C, 65.44; H, 6.22; N, 5.09; Found: C, 63.89; H, 6.19; N, 4.95.

Isopropyl 2-cyano-3-(2,4-dimethoxyphenyl)-2-propenoate

Yield 87%; mp 62°C, 1H-NMR δ 8.6 (s, 1H, CH=), 7.6-6.9 (m, 3H, Ph), 5.1 (m, 1H, OCH), 3.8 (d, 6H, CH₃O), 1.3 (d, 6H, CH(CH₃)₂); 13C-NMR δ 166 (C=O), 152 (HC=), 152, 131, 106, 98 (Ph), 116 (CN), 96 (C=), 68 (OCH), 56, 55 (OCH₃), 22 (CH(CH₃)₂); FTIR (cm- 1): 3982-2867 (m, C-H), 2224 (m, CN), 1723 (s, C=O), 1607 (C=C), 1286 (s, C-O-CH₃), 842 (s, C-H out of plane). Anal. Calcd. for C₁₅H₁₇NO₄: C, 65.44; H, 6.22; N, 5.09; Found: C, 67.37; H, 6.64; N, 5.65.

Isopropyl 2-cyano-3-(2,5-dimethoxyphenyl)-2-propenoate

Yield 77%; mp 87°C, 1H-NMR δ 8.7 (s, 1H, CH=), 7.9-6.6 (m, 3H, Ph), 5.2 (m, 1H, OCH), 3.9 (d, 6H, CH3O), 1.3 (d, 6H, CH(CH₃)₂); 13C-NMR δ 166 (C=O), 152 (HC=), 152, 131, 106, 98 (Ph), 116 (CN), 96 (C=), 68 (OCH), 56, 55 (OCH₃), 22 (CH(CH₃)₂); FTIR (cm- 1): 3095-2807 (m, C-H), 2222 (m, CN), 1718 (s, C=O), 1611 (C=C), 1264 (s, C-O-CH₃), 854 (s, C-H out of plane). Anal. Calcd. for C₁₅H₁₇NO₄: C, 65.44; H, 6.22; N, 5.09; Found: C, 65.51; H, 6.31; N, 5.06.

Homopolymerization

An attempted radical homopolymerization of the ICPP monomers in the presence of ABCN did not produce any polymer as indicated by the lack of a precipitate in methanol. The inability of the monomers to polymerize is associated with steric difficulties encountered in homopolymerization of 1,1- and 1,2-disubstituted ethylenes [22]. Homopolymerization of ST under conditions identical to those in copolymerization experiments yielded 18.3% of polystyrene, when polymerized for 30min.

Copolymerization

To the best of our knowledge, there have been no reports on copolymerization of the dimethyl and dimethoxy ring substituted ICPP compounds. Copolymers of the ST and the ICPP monomers were prepared 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 2.44mol/L in 10mL of toluene. The copolymerization was conducted at 70°C. After a predetermined time, the mixture was cooled to room temperature, and precipitated dropwise in methanol. The conversion of the copolymers was kept between 10 & 20% to minimize compositional drift. The composition of the copolymers was determined based on the nitrogen content.

The ST-ICPP copolymers were characterized by nitrogen elemental analysis, FTIR, 1H-&13C-NMR spectroscopies. Thermal behavior was studied by DSC and TGA.

Styrene-isopropyl 2-cyano-3-(2,3-dimethylphenyl)-2- propenoate copolymer

Yield 12%; 1H-NMR δ 7.4-6.5 (8H, Ph), 5.2-5.0 (1H, OCH), 4.0- 3.7 (1H, CHPh –ST), 1.6-1.4 (2H, CH₂), 2.7-2.4 (6H, PhCH₃), 2.7-2.5 (1H, CH-ICPP), 1.5-1.0 (6H, CH(CH₃)₂); 13C-NMR δ 174-165 (C=O), 152-100 (Ph), 118-114 (CN), 68-58 (OCH), 51-41 (CH, CH₂), 24-19 (CH(CH₃)₂), 22-14 (CH₃); FTIR (cm^-1): 3028-2832 (m, C-H), 2246 (m, CN), 1732 (s, C=O), 1248 (s, C-O-C), 978 (s, C-H out of plane). Nitrogen content 2.44%.

Styrene - isopropyl 2-cyano-3-(2,4-dimethylphenyl)- 2-propenoate copolymer

Yield 15%; ^{1_{H-NMR δ 7.5-6.6 (8H, Ph), 5.3-5.1 (1H, OCH), 4.0- 3.6 (1H, CHPh –ST), 1.5-1.3 (2H, CH2), 2.6-2.3 (6H, PhCH3), 2.6-2.4 (1H, CH-ICPP), 1.4-0.9 (6H, CH(CH3)2); 13C-NMR δ 173-164 (C=O), 151-101 (Ph), 119-112 (CN), 68-57 (OCH), 51-40 (CH, CH2), 25-20 (CH(CH3)2), 21-14 (CH3); FTIR (cm-1): 3036-2812 (m,C-H), 2243 (m, CN), 1736 (s, C=O), 1241 (s, C-O-C), 973 (s, C-H out of plane). Nitrogen content 1.97%.}}

Styrene-isopropyl 2-cyano-3-(2,5-dimethylphenyl)-2-propenoate copolymer

Yield 12%; 1H-NMR δ 7.4-6.5 (8H, Ph), 5.2-5.0 (1H, OCH), 4.0- 3.7 (1H, CHPh –ST), 1.6-1.4 (2H, CH2), 2.7-2.4 (6H, PhCH₃), 2.7-2.5 (1H, CH-ICPP), 1.5-1.0 (6H, CH(CH₃)2); 13C-NMR δ 174-165 (C=O), 152-100 (Ph), 118-116 (CN), 68-58 (OCH), 51-41 (CH, CH₂), 24-19 (CH(CH₃)2), 22-14 (CH₃); FTIR (cm^-1): 3028-2832 (m, C-H), 2246 (m, CN), 1732 (s, C=O), 1248 (s, C-O-C), 978 (s, C-H out of plane). Nitrogen content 2.96%.

Styrene-isopropyl 2-cyano-3-(2,6-dimethylphenyl)- 2-propenoate copolymer

Yield 12%; 1H-NMR δ 7.5-6.6 (8H, Ph), 5.3-5.1 (1H, OCH), 4.1- 3.7 (1H, CHPh-ST), 1.5-1.3 (2H, CH₂), 2.8-2.5 (6H, PhCH₃), 2.7-2.5 (1H, CH-ICPP), 1.6-1.1 (6H, CH(CH₃)2); 13C-NMR δ 176-166 (C=O), 151-99 (Ph), 117-115 (CN), 69-58 (OCH), 52-42 (CH, CH₂), 23-18 (CH(CH₃)2), 21 - 14 (CH₃); FTIR (cm^-1): 3045-2822 (m, C-H), 2243 (m, CN), 1738 (s, C=O), 1252 (s, C-O-C), 981 (s, C-H out of plane). Nitrogen content 1.54%.

Styrene - isopropyl 2-cyano-3-(3,4-dimethylphenyl)- 2-propenoate copolymer

Yield 11%; 1H-NMR δ 7.8-6.4 (8H, Ph), 5.3-5.1 (1H, OCH), 4.0- 3.6 (1H, CHPh-ST), 1.5-1.3 (2H, CH₂), 2.6-2.2 (6H, PhCH₃), 2.6-2.4 (1H, CH-ICPP), 1.4-0.9 (6H, CH(CH₃)2); 13C-NMR δ 173-165 (C=O), 151-101 (Ph), 119-114 (CN), 68-57 (OCH), 51-42 (CH, CH₂), 25-21 (CH(CH₃)2), 21-14 (CH₃); FTIR (cm^-1): 3066-2852 (m, C-H), 2241 (m, CN), 1731 (s, C=O), 1247 (s, C-O-C), 977 (s, C-H out of plane). Nitrogen content 2.73%.

Styrene - isopropyl 2-cyano-3-(3,5-dimethylphenyl)- 2-propenoate copolymer

Yield 17%; 1H-NMR δ 7.5-6.5 (8H, Ph), 5.4-5.1 (1H, OCH), 4.1- 3.6 (1H, CHPh-T), 1.6-1.3 (2H, CH₂), 2.5-2.3 (6H, PhCH₃), 2.6-2.3 (1H, CH-ICPP), 1.3-0.9 (6H, CH(CH₃)2); 13C-NMR δ 173-163 (C=O), 153-101 (Ph), 118-114 (CN), 68-58 (OCH), 51-42 (CH, CH₂), 25-21 (CH(CH₃)2), 21-14 (CH₃); FTIR (cm^-1): 3046-2835 (m, C-H), 2246 (m, CN), 1737 (s, C=O), 1244 (s, C-O-C), 978 (s, C-H out of plane). Nitrogen content 2.54%.

Styrene - isopropyl 2-cyano-3-(2,3-dimethoxyphenyl)-2-propenoate copolymer

Yield 13%; 1H-NMR δ 7.7-6.4 (8H, Ph), 5.4-5.1 (1H, OCH), 4.1- 3.6 (1H, CHPh-ST), 3.8-3.6 (6H, CH₃O), 1.5-1.2 (2H, CH₂), 2.6-2.3 (1H, CH-ICPP), 1.4-1.1 (6H, CH(CH₃)2); 13C-NMR δ 173-167 (C=O), 152-101 (Ph), 117-114 (CN), 68-56 (OCH), 60-56 (OCH₃), 52-42 (CH, CH₂), 25-22 (CH(CH₃)2); FTIR (cm^-1): 3062-2856 (m, C-H), 2242 (m, CN), 1738 (s, C=O), 1237 (s, C-O-C), 982 (s, C-H out of plane). Nitrogen content 2.53%.

Styrene - isopropyl 2-cyano-3-(2,4-dimethoxyphenyl)-2-propenoate copolymer

Yield 15%; 1H-NMR δ 7.8-6.5 (8H, Ph), 5.5-5.1 (1H, OCH), 4.2- 3.6 (1H, CHPh-ST), 3.8-3.4 (6H, CH₃O), 1.3-1.2 (2H, CH₂), 2.6-2.4 (1H, CH-ICPP), 1.4-1.2 (6H, CH(CH₃)2); 13C-NMR δ 172-167 (C=O), 152-103 (Ph), 116-114 (CN), 68-58 (OCH), 63-56 (OCH₃), 52-43 (CH, CH₂), 26-22 (CH(CH₃)2); FTIR (cm^-1): 3029-2855 (m, C-H), 2243 (m, CN), 1743 (s, C=O), 1247 (s, C-O-C), 987 (s, C-H out of plane). Nitrogen content 2.26%.

Styrene - isopropyl 2-cyano-3-(2,5-dimethoxyphenyl)-2-propenoate copolymer

Yield 11%; 1H-NMR δ 7.6-6.3 (8H, Ph), 5.4-5.2 (1H, OCH), 4.2- 3.5 (1H, CHPh-ST), 3.9-3.5 (6H, CH₃O), 1.6-1.3 (2H, CH₂), 2.7-2.4 (1H, CH-ICPP), 1.5 - 1.2 (6H, CH(CH₃)2); 13C-NMR δ 174-166 (C=O), 152-100 (Ph), 117-115 (CN), 68-58 (OCH), 60 - 54 (OCH₃), 54 - 41 (CH, CH₂), 25 - 23 (CH(CH₃)2); FTIR (cm^-1): 3077-2869 (m, C-H), 2243 (m, CN), 1740 (s, C=O), 1238 (s, C-O-C), 978 (s, C-H out of plane). Nitrogen content 2.27%.

Copolymerization (Figure 1) of ST and the dimethyl and dimethoxy ring-substituted ICPP resulted in formation of copolymers (Table 1) with weight-average molecular masses 52 to 63kD. Since ICPP monomers do not homopolymerize, the most likely structure of the copolymers would be isolated ICPP monomer units (n=1) alternating with short ST (m=1-4) sequences (Figure 2). The copolymers prepared in the present work are all soluble in ethyl acetate, THF, DMF&CHCl3 and insoluble in methanol, ethyl ether, and petroleum ether. According to the nitrogen elemental analysis, between 13.5 and 31.1 mol% of ICPP monomer is present in the copolymers prepared at ST/ICPP=3(mol), which is indicative of relatively high reactivity of the monomers towards ST.

To qualitatively correlate the observed monomer reactivities, we considered copolymer composition data. The relative reactivity of ST in copolymerization with these monomers can be estimated by assuming applicability of the copolymerization equation (Equation 1) of the terminal copolymerization model [22]:

m /m =[M ](r₁[M₁]+[M₂]([M₁]+r₁[M₁]) (1)

m₁ & m₂ are the mole fractions of ST and ICPP monomer units in the copolymer, respectively, [M₁] & [M₂] are the concentrations of ST and an ICPP in the monomer feed, respectively. The monomer reactivity ratios, r₁ & r₂ are k₁₁/k₁₂ & k₂₂/k₂₁, respectively. In the absence of the self-propagation of ICPP monomers (k₂₂=0, r₂=0), and at the monomer feed ([M₁]/[M₂] = 3), the above equation yields:

r =(m₁ /m₂ -1)/3 (2)

or the equation for the relative reactivity of styrene radical k₁₂/k₁₁ with ICPP monomers

1/r₁ =3/(m₁ /m₂ )-1(3)

Consideration of monomer reactivities according to Equation 3 also involves the assumption of minimal copolymer compositional drift at given conversion. This non-rigorous kinetic treatment [22] allows estimation of the reactivity of a ST-ended polymer radical in reaction with ICPP monomer. The order of relative reactivity (1/r₁) for the ICPP monomers is 2,5-dimethyl (2.48) >3,4-dimethyl (1.88) >2,3-dimethoxy (1.79) >3,5-dimethyl (1.53) >2,3-dimethyl (1.38) > 2,5-dimethoxy (1.31) >2,4-dimethoxy (1.30) >2,4-dimethyl (0.86) >2,6-dimethyl (0.56). More detailed information on the copolymer composition at different monomer feed ratios would be necessary for the application of copolymerization models that would allow prediction of copolymer composition.

Thermal behavior

Thermal transitions of the ST-ICPP copolymers were analyzed by differential scanning calorimetry. All the copolymers were amorphous and show no crystalline DSC endotherm on repeated heating and cooling cycles. The glass transition temperatures T_g of the copolymers were measured by DSC. The second heating results were obtained in all cases so that the samples become drier without “thermal memory”. Table 2 shows glass transition values for the ST-ICPP copolymers prepared in this work with no correlation to the size and position of the ICPP ring substitution apparently due to non-uniform composition, monomer unit distribution, and/or molecular weight and MWD.

A single T_g value was observed for all the copolymers with values higher than polystyrene (104oC). Information on thermal stability of the copolymers was obtained from thermogravimetric analysis (Table 1). Decomposition of the copolymers in nitrogen occurred in two steps, first in the 250-500oC range with residue (3.8-5.6% wt), which then decomposed in the 500-800oC range. The decomposition products were not analyzed in this study, and the mechanism has yet to be investigated.

Conclusion

Novel trisubstituted ethylenes, dimethyl and dimethoxy ring-substituted isopropyl 2-cyano-3-phenyl-2-propenoates were prepared and copolymerized with styrene. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, H1&13C-NMR. The thermal gravimetric analysis indicated that the copolymers decompose in in two steps, first in the 200-500°C range with residue (3.8-5.6%wt), which then decomposed in the 500-800 oC range.

Acknowledgment

The authors are grateful to acknowledge that the project was partly supported by the Coatings Industry Education Fund (CIEF) and Chicago Society of Coating Technology (CSCT).

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