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Optically active N-propargylamides bearing a porphyrin group, (S)-HC&tbd1;CCH2NHCOCH(CH3)OCOR (1) and (S)-HC&tbd1;CCH2NHCOCH(Ph)OCOR (2), where R = 4-(10,15,20-tris(4-tert-butylphenyl)porphyrin-5-yl)phenyl, were polymerized with (nbd)Rh⁺[η⁶-C6H5B^-(C6H5)3] along with analogous monomers (S)-HC&tbd1;CCH2NHCOCH(CH3)OCOC6H4-p-tert-Bu (3) and (S)-HC&tbd1;CCH2NHCOCH(Ph)OCOC6H4-p-tert-Bu (4) for comparison to afford the corresponding polymers with moderate molecular weights (Mn = 17 000−24 000) in 28−76% yields. The ¹H NMR spectra demonstrated that the resulting polymers had fairly stereoregular structures (cis content = 78−97%). CD and UV−vis spectroscopic studies revealed that poly(1)−poly(4) took one-handed helical structure. The relationship between the screw sense of poly(N-propargylamides) and the sign of Cotton effect originating from the main chain was elucidated by comparison of the Cotton effects of either poly(1) and poly(3) or poly(2) and poly(4). It was concluded on the basis of the exciton chirality method along with molecular modeling study that the pendent porphyrins of poly(1) and poly(2) form right-handed helical arrays and that the main chains form a right-handed helix.

Optically active N-alkynylamides (S)-HC&tbd1;C(CH2)aNHCO(CH2)bCH(CH3)CH2CH3 (1:  a = 1, b = 0; 2:  a = 1, b = 1; 3:  a = 1, b = 2; 4:  a = 1, b = 3; 5:  a = 2, b = 0; 6:  a = 2, b = 1; 7:  a = 3, b = 0), having several numbers of methylene spacers between the ethynyl group and chiral carbon or amide group, and (S)-HC&tbd1;C(CH2)2OCOCH2CH(CH3)CH2CH3 (8) were polymerized with (nbd)Rh⁺[η⁶-C6H5B^-(C6H5)3] to afford the corresponding polymers with moderate molecular weights (Mn = 11 000−21 000) in 67−99% yields. The ¹H NMR spectra demonstrated that the resulting polymers had stereoregular structures (cis content = 79−100%). CD, UV−vis, and IR spectroscopic studies revealed that the position of the amide group and chiral center strongly affects the pitch and stability of helical structure of the polymers, and intramolecular hydrogen bonding is formed between the amide groups in CHCl3. By comparison with the results of CD measurements and molecular orbital calculation, the sign of Cotton effect and the relationship between the screw sense of poly(N-propargylamides) was elucidated.

Five novel N-propargylacetamide and -propaneamide monomers [HC&tbd1;CCH2NHCOR; 4:  R = CH2C6H5, 5:  R = CH(C6H5)2, 6:  R = CH2CH2C6H5, 7:  R = CH2CH(C6H5)2, 8:  R = CH2C(C6H5)3] were polymerized with a rhodium catalyst, (nbd)R⁺B^-(C6H5)4 (nbd = 2,5-norbornadiene), to provide polymers in 81−99% yields. Poly(4), poly(5), and poly(8) possessed low molecular weights (Mn = 3100−6100), presumably due to their low solubility in solvents, while poly(6) and poly(7) had moderate Mn's (15 000 and 16 700) and good solubility in several solvents including chloroform. The secondary structures of the five polymers in chloroform were investigated by UV−vis spectroscopy. Poly(4) adopted a helical structure to a certain extent, while poly(5)−poly(7) hardly did not. In contrast, poly(8) exhibited a UV−vis absorption peak around 365 nm, demonstrating that it invariably formed helices under the given conditions. Copolymers of monomer 8 with either chiral monomer 10 [HC&tbd1;CCH2NHCOCH(CH3)CH2CH3] or achiral monomers 1 [HC&tbd1;CCH2NHCOC(CH3)2C6H5] and 9 [HC&tbd1;CCH2NHCO(CH2)5CH3], i.e., poly(8-co-10)s, poly(8-co-1)s, and poly(8-co-9)s, showed good solubility and possessed higher Mn's than that of poly(8). Furthermore, with the increase of unit 8 in poly(8-co-10)s, poly(8-co-1)s, and poly(8-co-9)s, initial blue and then red shifts were observed in the λmax of their UV−vis spectra and further in the CD signal of poly(8-co-10)s, demonstrating that all of these copolymers formed helices with different pitches, which depended on the compositions of the copolymers. Additionally, the sergeants and soldiers rule was observed in achiral/chiral poly(8-co-10)s.

N-Propargylamides with one, two, and three phenyl groups at the α-position of the carboxyl group [HC≡CCH2NHCOR; 1, R = C(CH3)2C6H5; 2, R = CCH3(C6H5)2; 3, R = C(C6H5)3] were polymerized with a rhodium catalyst, (nbd)Rh⁺B^-(C6H5)4 (nbd = 2,5-norbornadiene), to obtain the corresponding polymers in 85−91% yields. Poly(1) possessed a moderate molecular weight (Mn = 6300) and was thoroughly soluble in chloroform and dichloromethane. On the other hand, poly(2) and poly(3) were not totally soluble in the solvents. The Mn's of chloroform-soluble parts were less than 3000. The secondary structure of these three polymers in chloroform was examined by UV−vis spectroscopy with varying temperature. It was found that only poly(1) could adopt helical conformation even at 60 °C. By the copolymerization of either monomer 2 or 3 with HC≡CNH2CO(CH2)4H (4), the solubility of the polymers was effectively improved, and the Mn's were remarkably increased. When the content of unit 4 in poly(2-co-4)s was 25% and above, the copolymers could form helical conformation with different degrees, among which poly(20.40-co-40.60) showed the largest helicity. When the content of unit 4 of poly(3-co-4)s exceeded 95%, the copolymer took helical structure partly.

A variety of novel N-propargylsulfamide monomers (HC≡CCH2NHSO2R) with alkyl (1−4) or aryl groups (5−10) were polymerized with a Rh catalyst, (nbd)Rh⁺B^-(C6H5)4 (nbd = 2,5-norbornadiene), to provide polymers with moderate molecular weights (3000−15 000) in good yields (above 80%). Polymerization of monomer 4 (R = −(CH2)7CH3) at −15 °C yielded a stereoregular polymer whose cis content was nearly 100%, while the cis content remained 79% at 30 °C. Thus, the stereoregularity of the polymer largely depended on polymerization temperature. On the other hand, polymerization solvents hardly affected stereoregularity. Copolymerization of monomer 4 and N-propargylamide monomer 11 afforded copolymers with various compositions in high yields (above 87%), and the cis contents of the resultant copolymers were located between those of the corresponding homopolymers. The presence of intramolecular hydrogen bonding between the neighboring sulfamide groups was confirmed by IR spectroscopy measured in chloroform, suggesting that these types of polymers with appropriate substitutents also have the potential to form helices under suitable conditions like poly(N-propargylamides).

N-Propargylamides with bulky pendent groups [HC&tbd1;CCH2NHCOR, 9:  R = CH2C(CH3)3, 10:  R = C(CH3)3, 11:  R = C(CH3)2CH2CH2CH3, 12:  R = CH(CH2CH3)2, 13:  R = CH(CH2CH2CH3)2] were polymerized with a rhodium catalyst, (nbd)Rh⁺B^-(C6H5)4 (nbd = 2,5-norbornadiene), to obtain the polymers in 80−92% yields. Poly(11) and poly(12) possessed moderate molecular weights (Mn ≥ 10 000) and were totally soluble in a few solvents including chloroform. On the other hand, the Mn values of poly(9), poly(10), and poly(13) were no more than 5000, and these polymers were not completely soluble in any solvents. The conformational transition behavior of these polymers was examined by temperature-variable UV−vis spectroscopy in chloroform solution, which revealed that poly(10)−poly(13) could form dynamically stable helical conformation even at 60 °C. By copolymerizations of monomers 9 and 10 with monomer 4, HC&tbd1;CCH2NHCO(CH2)4H, the solubility of the polymers was effectively improved and almost all the copolymers totally dissolved in chloroform, while the molecular weights of the copolymers increased up to 18 600−45 000. Moreover, the helix contents of poly(40.63-co-90.37) and poly(40.40-co-100.60) were the highest among the two series of (co)polymers, respectively. It is concluded that the copolymerization of 9 and 10 with 4 effectively decreased the steric repulsion between the crowded side chains, which probably allowed the copolymers to take helical conformation efficiently.

N-Propargylamides having pendent groups with different lengths (HC&tbd1;CCH2NHCOR, R = (CH2)nH, n = 1−8) were polymerized in the presence of a Rh catalyst [(nbd)Rh⁺B^-(C6H5)4; nbd = 2,5-norbornadiene] to obtain polymers with moderate molecular weight and high stereoregularity [poly(1)−poly(8)] in high yields. The conformational transition behavior of the resultant polymers was investigated by measuring UV−vis spectra in chloroform solution at different temperatures. Among the examined polymers, poly(5) and poly(6) took a stable helical conformation at relatively high temperatures, and their helical contents were the highest. Poly(2)−poly(4), which bear shorter alkyl pendent chains, did not exist in stable helical conformation owing to the lack of chain flexibility and the intermolecular hydrogen bonding. Poly(1) was not completely soluble in any solvents. Poly(7) and poly(8), which contain longer pendent chains, took helical conformation only at low temperatures because of the lower cis content of the polymer main chain. Both ΔH and ΔS for the conformational transition from random coil to helix assumed negative values, which also greatly depended on the length of the pendent groups. Whereas the helical conformation of poly(5) and poly(6) was readily generated in chloroform, neither THF nor toluene was favorable for helix formation.

Copolymerization of chiral N-propargylamides, (S)-N-propargyl-2-methyldecanamide (1), and either (R)-N-propargyl-3,7-dimethyloctanamide (2) or (1S)-N-propargyl-3-oxo-2-oxa-4,7,7-trimethyl-2-bicyclo[2.2.1]heptan-1-acetamide (3) were conducted with (nbd)Rh⁺[η⁶-C6H5B^-(C6H5)3] catalyst to obtain the corresponding copolymers with moderate molecular weights (Mn = 19 000−56 000) in good yields. The CD spectroscopic study showed that these two types of copolymers with various compositions formed helical structure and underwent a helix−helix transition driven by temperature change. In all cases, the optical activity became zero at certain temperatures, which depended on copolymer composition. The temperature dependence of helix sense of the copolymers allowed the determination of thermodynamic parameters. The helical structure of poly(1-co-2), which has long alkyl pendants, was affected by external stimuli more than poly(1-co-3) was. The thermodynamic parameters of helix inversion were also influenced by solvent polarity.

Achiral N-propargylamides, i.e., N-propargyl-3-methylbutanamide (1), N-propargyl-2-ethylbutanamide (2), and N-propargyl-3,3-dimethylbutanamide (3), were polymerized with (nbd)Rh⁺[η⁶-C6H5B-(C6H5)3] to afford polymers with moderate molecular weights (Mn = 6000−22 000) in good yields. The ¹H NMR and UV−vis spectra demonstrated that the polymers, poly(1)−poly(3), have stereoregular structures (cis = 100%) and equally populated right- and left-handed helical conformation. A predominant helix sense was induced in these polymers by the addition of chiral alcohols or amine, which was confirmed by CD and UV−vis spectroscopies. ¹H NMR and CD spectroscopic studies strongly suggested that the poly(N-propargylamides) interacted with the chiral alcohols by hydrogen bonding at the amide groups of the polymer side chain. Chiral terpenes could also induce single-handed helical conformation. It is likely that hydrophobic interaction led to the one-handed helical conformation in the case of the chiral terpenes because the addition of n-hexane decreased the CD signal.

N-Propargylcarbamates (2, HC&tbd1;CCH2NHCO2R), where R = i-Bu (2a) or (S)-CH2CH(CH3)C2H5 (2b), were polymerized in the presence of a Rh catalyst, [(nbd)RhCl]2−Et3N, in CHCl3, giving stereoregular cis polymers as slightly yellow solids in good yields. The ¹H NMR spectra of poly(2) showed very broad signals at ambient temperature, indicating the limited mobility of the main chain. IR spectroscopic study of the polymers in CHCl3 revealed that most of the pendant carbamate groups participate in intramolecular hydrogen bonds. The chiral polymer from 2b exists in a helical conformation with an excess of one-handed screw sense, which was supported by the very large optical rotation ([α]D = +777°) and intense CD effects ([θ]max = 81 700 deg cm² dmol^-1). A Rh-based polymer from the corresponding chiral carbonate monomer, (S)-HC&tbd1;CCH2OCO2CH2CH(CH3)C2H5 (3), obtained as a viscous oil, showed much poorer chiroptical properties ([α]D = +13.8°), meaning that the intramolecular hydrogen bonds rigidify the polymer backbone and simultaneously induce and stabilize the helical conformation of poly(2). The contribution of the hydrogen bonds to the secondary structure was also supported by variation in the CD and UV−vis spectra of poly(2) upon the addition of methanol.

N-Propargylbenzamides having chiral ester groups on the benzene ring, 1−6, were polymerized with (nbd)Rh⁺[η⁶-C6H5B^-(C6H5)3] to afford soluble polymers with moderate molecular weights (Mn = 34 000−100 000) in good yield. The ¹H NMR spectra demonstrated that the polymers have stereoregular structures (cis = 91−100%). The influence of the substitution position for the chiral ester group on the secondary structure was examined. From the comparison of the CD effects of poly(1)−poly(3), the meta-substituted polymer was proven to possess a one-handed helical conformation. When the chiral center was closer to the benzene ring or chiral ester group was bulkier, the polymers showed more intense chiroptical properties. A variable temperature CD spectroscopic study showed that the helical structure of poly(2) and poly(6) was thermally stable. However, the CD spectra of poly(4) and poly(5) were inverted in sign on temperature change in chloroform or toluene, meaning that the helix inversion took place. The temperature of helix inversion could be controlled by copolymerizing with N-propargylbenzamide (7).

The secondary structure of Rh-based stereoregular cis-poly(N-propargylamides) was proposed on the basis of the UV−vis, CD, and IR spectra, the wormlike touched-bead model theory, and a semiempirical molecular orbital calculation. The IR spectra demonstrated the formation of well-ordered intramolecular hydrogen bonding between the pendant amide groups. The relatively red-shified absorption and the intense CD effects indicate that the main chain twists only slightly from coplanarity to exist in a helical conformation with a large helix pitch. Analyzing the intrinsic viscosity of a polymer, (±)-poly(N-propargyl-2-ethylhexanamide), on the basis of the wormlike touched-bead model theory, showed a large helix pitch per monomer unit (h, 0.2 nm), which also supports the above characteristics that the main chain loosely twists. A semiempirical calculation with the AM1 method showed that the helical conjugated backbone is surrounded by two helically arranged hydrogen-bond strands.

N-Propargylamides having chiral centers at the α-carbon of the amide groups, 1−3, were polymerized with (nbd)Rh⁺[η⁶-C6H5B^-(C6H5)3] to afford polymers with moderate molecular weights (Mn = 6000−32 000) in good yield. The ¹H NMR spectra demonstrated that the polymers have stereoregular structures (cis = 100%). The polymers were proven to take a helical conformation with an excess of one-handed screw sense in CHCl3, which was supported by their intense CD effects and large optical rotations. It was confirmed that the helical structure was stabilized not only by the steric repulsion but also by the intramolecular hydrogen bonds between the pendant groups. CD spectroscopic study showed that the helical structure is more stable than that of the polymers without a branch at the α-position, which allowed the polymers to exist in the helical state in various solvents. The electronic absorption, CD effects, and optical rotations of the polymers closely correlated to the extent of the hydrogen bonding between the pendant amide groups.

Achiral N-propargylalkylamides (1a−1g, HC&tbd1;CCH2NHR) having various alkyl groups (R = CH3, C2H5, C3H7, i-C3H7, i-C4H9, n-C5H11, n-C7H15) were homopolymerized or copolymerized with a chiral comonomer, (R)-N-propargyl-3,7-dimethyloctanamide (2), in the presence of a Rh initiator to establish the relationship between the main-chain conformation and the structure of the pedant groups. ¹H NMR and viscosity measurements of the homopolymers revealed that the structure of the pendant groups markedly influences the rigidity of the polymer backbone and the stability of the helical conformation. The copolymerization using the achiral comonomers having linear or α-branched alkyl groups showed poor or no cooperative effects on the helical conformation, meaning that these polymers exist in a disordered state. On the other hand, a stable helical conformation, i.e., a long persistence length of the helical domain, was attainable for the polymer having β-branched alkyl chains (poly(1e), R = i-C4H9), which was evidenced by a clear, positive nonlinear relationship between the feed ratio of 1e to 2 and the optical rotation of the copolymers. UV−visible spectroscopic studies demonstrated that, in CHCl3, the helical and disordered main chains display absorption centered at 400 and 320 nm, respectively, which resulted in different colors in solution of the helical (yellow) and disordered (achromic) polymers. Thermochromism was achieved by the thermally induced reversible conformational change between helical and disordered states. The thermodynamic parameters (ΔGr, ΔHr, and ΔSr) that govern the stability of the helical conformation of a copolymer were estimated by the temperature dependence of the populations of the helical and disordered states using UV−visible spectra.