Polybinaphthyls incorporating chiral (R) or (S)-2,2′-binaphthyland oxadiazole moieties by Stille reaction

Chiral polymers P-1 and P-2 were prepared by the polymerization of (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-1) and (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-1) with 2,5-bis[(4-tributylstannyl)phenyl]-1,3,4-oxadiazole (M-2) via Pd(PPh₃)₄ catalyzed Stille coupling reaction. 1,3,4-Oxadiazole unit not only has high electron affinity, high thermal and oxidative stability, but also serves as a good chromophore. Polymers have strong blue fluorescence due to the efficient energy migration from the extended π-electronic structure of the polymers to the chiral binaphthyl core and can be expected to have potential application in the materials of fluorescent sensors. Circular dichroism (CD) spectra of polymers P-1 and P-2 are almost identical except that they gave opposite signals at each wavelength. The long wavelengths CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and a high rigidity of the polymer backbone.     

Controlled synthesis and characterizations of amphiphilic poly[(R,S)-3-hydroxybutyrate]-poly(ethylene glycol)-poly[(R,S)-3-hydroxybutyrate] triblock copolymers

Well-defined biodegradable amphiphilic triblock copolymers consisting of atactic poly[(R,S)-3-hydroxybutyrate] (PHB) and poly(ethylene glycol) (PEG) as the side hydrophobic block and middle hydrophilic block were synthesized via ring opening polymerization of (R,S)-β-butyrolactone from PEG macroinitiators and characterized using NMR, GPC, FT-IR, XRD, DSC and TG analyses. The controlled synthesis was made possible by the facile synthesis of pure PEG macroinitiators through a TEMPO-mediated oxidation. Constituting 40-70 wt% of the copolymer content, PHB blocks grown were amorphous while PEG formed crystalline phase when segment was sufficiently long. While hindering PEG crystallization, atactic PHB mixed well with amorphous PEG to give single T_g in all the copolymers. The copolymers exhibited two-step thermal degradation profile starting with PHB degradation from 210 to 300 °C, then PEG from 350 to 450 °C.     

(R,R)-salen/salan-based polymer fluorescence sensors for Zn detection

(R,R)-salen-based polymer fluorescence sensor P-1 could be synthesized by the polymerization of 5,5′-(isoquinoline-5,8-diylbis(ethyne-2,1-diyl))-bis(3-tert-butyl-2-hydroxybenzaldehyde) (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via nucleophilic addition-elimination reaction, and (R,R)-salan-based polymer sensor P-2 could be obtained by the reduction reaction of P-1 with NaBH₄. The fluorescence response behaviors of two chiral polymers P-1 and P-2 on Zn²⁺ were investigated by fluorescence spectra. The fluorescence intensities of P-1 and P-2 can exhibit gradual enhancement upon addition of Zn²⁺. Compared with other cations, such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺, Cr³⁺ and Pb²⁺, Zn²⁺ can lead to the pronounced fluorescence enhancement as high as 22.8-fold for P-1 and 3.75-fold for P-2, respectively. The results show that P-1 and P-2 incorporating (R,R)-salen/salan moieties as receptors in the polymer main chain backbone can exhibit high sensitivity and selectivity for Zn²⁺ detection.     

Biocatalytic separation of (R, S)-1-phenylethanol enantiomers and fractionation of reaction products with supercritical carbon dioxide

The continuous kinetic resolution of (R, S)-1-phenylethanol via enzymatic transesterification was chosen as a benchmark reaction for the study of a complete reaction/separation process using supercritical carbon dioxide. Phase equilibrium data for binary and ternary systems was acquired as a starting point to determine the best conditions of operation. Total conversion of the (R)-isomer of the alcohol was achieved using a 10% molar excess of vinyl laurate. Three separators operating at given temperatures and pressures allowed the recovery of (S)-1-phenylethanol with a purity of 86%. The phase equilibrium data obtained indicates that an additional separation step should allow the recovery of both (S)-1-phenylethanol and (R)-1-phenylethylaurate with over 95% purity. Due to the low solubilities of the target compounds, CO₂ from the outlet gas stream of the last separator must be recycled to ensure the technical viability of the integrated reaction/separation of (R, S)-1-phenylethanol.     

Ortho alkyl substituents effect on solubility and thermal properties of fluorenyl cardo polyimides

Five fluorenyl cardo diamines containing different alkyl substituents were synthesized and characterized. A series of fluorenyl cardo polyimides were prepared by polycondensation of these cardo diamines with 4,4′-oxydiphthalic anhydride (ODPA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 3,3′,4,4′-biphenyl tetracarboylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA). Most of fluorenyl cardo polyimides exhibited excellent solubility in common organic solvents such as m-cresol, chloroform, tetrahydrofuran (THF), N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAC) etc. and intrinsic viscosity in N,N-dimethylacetamide (DMAC) ranged from 0.31 to 0.92 dl/g. T_g of polyimides based on ODPA decrease with the number and size of alkyl substituents on fluorenyl cardo diamine. The results show that the incorporation of noncoplanar structure led by the introducing alkyl substituents on fluorenyl cardo diamines improves the solubility of cardo polyimides in organic solvents without sacrificing thermal properties.     

Solution‐processable colorless polyimides with ultralow coefficients of thermal expansion for optoelectronic applications

This work reports colorless polyimides (PIs) that are applicable as plastic substrates in image display devices, which produce an ultralow coefficient of thermal expansion (CTE) by solution casting without thermal imidization and mechanical stretching. An effective monomer molecular design is proposed for this purpose. Chemical imidization (CI) process compatibility is the key factor in attaining the target properties. We focused on a PI system derived from 1,2,3,4‐cyclobutanetetracarboxylic dianhydride (CBDA) and a novel para‐amide‐linked diamine (AB‐TFMB) with CF₃ groups as it has great potential as an ultralow CTE material, although it offers no CI process compatibility because of its poor solubility. The CBDA/AB‐TFMB system was modified by copolymerizing with 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride. This approach drastically improved CI process compatibility. The CTE of the PI films linearly decreased with increasing CBDA content. At a CBDA content of 70 mol%, the PI achieved an ultralow CTE of 7.3 ppm K^?1, non‐coloration/non‐turbidity, a very high glass transition temperature of 329 °C and sufficient ductility. The ultralow CTE results from the highly oriented main chains along the X–Y direction during the casting process as supported by the very high birefringence exceeding 0.1. Thus, our materials almost achieved the target properties required for novel coating‐type high‐temperature plastic substrate materials. © 2016 Society of Chemical Industry     

Polybinaphthyls incorporating chiral 2,2′-binaphthyl and isoquinoline moieties by Sonogashira reaction

Polymers P-1, P-2, P-3, P-4 and P-5 were synthesized by the polymerization of 5,8-bis(ethynyl)isoquinoline (M-1) with (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-2), (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-2), (R)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-3), (S)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-3), and rac-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl (M-4) under Sonogashira reaction, respectively. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. CD spectra of polymers P-1 and P-2, P-3 and P-4 are almost identical except that they gave opposite signals at each wavelength. The long wavelength CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and the helical backbone in the polymer chain. All five polymers have strong blue-green fluorescence due to the efficient energy migration from the extended π-electronic structure of the repeating unit of the polymers to the chiral binaphthyl core and are expected to provide understanding of structure-property relationships of the chiral conjugated polymers.     

Optical isomers of 3,13-dimethylheptadecane: Sex pheromone components of the western false hemlock looper,Nepytia freemani (Lepidoptera: Geometridae)

(3S, 13R)-3, 13-Dimethylheptadecane [(3S, 13R)-3, 13-dime-17Hy] is the major pheromone component of the western false hemlock looper (WFHL),Nepytia freemani. In comparative gas chromotographic-electroantennographic detection (GC-EAD) analyses of stereoselectively synthesized isomers, 1 pg of (3S, 13R)-dime-17Hy elicited significantly stronger electrophysiological responses by male WFHL antennae than did 1 pg of separately injected (3R, 13R)-, (3R, 13S)- or (3S, 13S)-3, 13-dime-17Hy. In field experiments with individually tested stereoisomers. (3S, 13R)-3, 13-dime-17Hy was the only stereoisomer to attract males, but the four-stereoisomer blend was 3.6 times more attractive. Quaternary and all binary combinations of (3S, 13R)-3, 13-dime-17Hy with the other stereoisomers were equally attractive, suggesting that synergisytic behavioral activity in WFHL resided with either one of (3R, 13R)-, (3R, 13S)-, or (3S, 13S)-3, 13-dime-17Hy. Because optical isomers of (di)methylhydrocarbons do not separate on currently available columns, it remains unknown whether female WFHL also produce a four-stereoisomer pheromone blend. Substitutionality of pheromone stereoisomers without loss of behavioural activity has not previously been reported, but favorably compares with the concept of pheromone redundancy that was first suggested for the multiple pheromone component blend of the cabbage looper moth,Trichoplusia ni.     

The influence of multiple ortho-substituted phenylenes on the nature of poly(ether imide)s

The new ortho-aminophenyl diamine 1,2-bis(2′-aminophenoxy)benzene has been synthesized and polymerized with 1,2-bis(3′,4′dicarboxyphenoxy)benzene dianhydride to yield a poly(ether imide) with four ortho-catenated phenylenes per structural repeat unit. The polymer has been characterized by gel permeation chromatography and MALDI-TOF mass spectrometry and shown to contain a large proportion of oligomers. The oligomers have been found to be primarily macrocyclic oligomers with two to 10 repeat units. The results are contrasted with the high-molecular-weight polyimides formed from corresponding para-aminophenoxy diamines. It is concluded that either the ortho-aminophenoxy moiety or the large sequence of ortho-catenated phenylene rings gives a high propensity for ring closure and macrocycle formation in competition with propagation.     

Polyimides from 2,3,3′,4′-biphenyltetracarboxylic dianhydride and aromatic diamines

A series of new polyimides were prepared from the reaction of 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) with various aromatic diamines. The properties of the a-BPDA polyimides were compared with those of polyimides prepared from the reaction of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) with the same aromatic diamines. Films of the a-BPDA polyimides had higher glass transition temperatures (T_gs) and less color than the corresponding s-BPDA polyimide films. Light transmission at 500 nm, solar absorptivity, and thermal emissivity were determined on certain films. Films of similar polyimides based upon a-BPDA and s-BPDA containing meta linkages and others containing para linkages were each cured at 250, 300, and 350 °C. The films were characterized primarily by T_g, color, optical transparency, tensile properties, dynamic mechanical thermal analysis, and coefficient of thermal expansion. The a-BPDA meta linked polyimide films had tensile strengths and moduli higher than films of the a-BPDA para linked polyimide. The same phenomenon was not observed for the s-BPDA meta and para linked polyimides. The chemistry, mechanical, and physical properties of the polymers and films are discussed.     

Hydrolytic degradation of poly[(R)-3-hydroxybutyric acid] in the melt

Poly[(R)-3-hydroxybutyric acid] [R-P(3HB)] was hydrolyzed in high-temperature and high-pressure water at the temperature range of 180-300 °C and for a period of 360 min. The formation, racemization, and decomposition of 3-hydroxybutyric acids (3HBs) and molecular weight change of R-P(3HB) were investigated. The highest yield of (R)-3-hydroxybutyric acid (R-3HB), ca. 80%, was obtained at 200 °C in the hydrolytic degradation periods of 240-360 min. Too-high hydrolytic degradation temperature such as 300 °C induced the decomposition and racemization of formed 3HBs, resulting in decreased yield of R-3HB. The hydrolytic degradation of R-P(3HB) proceeds homogeneously and randomly via a bulk erosion mechanism. The molecular weight of R-P(3HB) decreased exponentially without formation of low-molecular-weight specific peaks originating from crystalline residues. The hydrolytic degradation rates in the melt estimated from M_n changes were lower for R-P(3HB) than for poly(l-lactide) (PLLA) in the temperature range of 180-220 °C. The activation energy for the hydrolytic degradation (ΔE_h) of R-P(3HB) in the melt (180-250 °C) was 30.0 kcal mol⁻¹, which is higher than 12.2 kcal mol⁻¹ for PLLA in the melt in the temperature range (180-250 °C). This study reveals that hydrolytic degradation of PHB in the melt is an effective and simple method to obtain (R)-3HB and to prepare R-P(3HB) having different molecular weights without containing the specific low-molecular-weight chains, because of the removal of the effect caused by crystalline residues.     

Enantioselective separation of R,S-phenylsuccinic acid by biphasic recognition chiral extraction

A new process has been developed to separate phenylsuccinic acid (H₂A) enantiomers, based on the oppositely preferential recognition of hydrophobic and hydrophilic chiral selectors in organic and aqueous phases, respectively, which is named as biphasic recognition chiral extraction (BRCE). BRCE system is established by adding hydrophobic l-iso-butyl tartrate in organic phase and hydrophilic β-cyclodextrin (β-CD) derivative in aqueous phase, which preferentially recognize S-H₂A and R-H₂A, respectively. The studies performed involve two enantioselective extractions in a biphasic system, where H₂A enantiomers form four complexes with β-CD derivative in aqueous phase and l-iso-butyl tartrate in organic phase, respectively. Here it is shown that the efficiency of the extraction depends, often strongly, on a number of process variables, including the types of organic solvents and β-CD derivatives, iso-butyl tartrate configurations, the concentrations of the extractants and H₂A enantiomers, pH and temperature. Phase-equilibria in BRCE systems is governed by the complex chemical equilibria in both the organic and aqueous phases. By changing the monophasic recognition chiral extraction (MRCE) system into BRCE system, the enantioselectivity increases from 1.501 to 2.862. The maximum enantioselectivity for H₂A enantiomers is obtained at pH≤2.5 and the ratio of 2:1 of [l-(+)-iso-butyl tartrate] to [HP-β-CD]. The experimental results show that BRCE is of much stronger chiral separation ability than MRCE, which is due to utilization of the separation abilities of both tartrate and β-CD derivative. It may be very helpful to optimize the extraction systems and realize the large-scale production of pure enantiomers.     

Dolichodial: A New Aphid Sex Pheromone Component?

The sex pheromones of many aphid species from the subfamily Aphididae comprise a mixture of the iridoids (cyclopentanoids) (1R,4aS,7S,7aR)-nepetalactol and (4aS,7S,7aR)-nepetalactone. In this paper, we investigate whether other chemicals, in addition to nepetalactol and nepetalactone, are released from Dysaphis plantaginea (rosy apple aphid) oviparae as part of their sex pheromone. Four compounds present in an air entrainment sample collected from D. plantaginea oviparae feeding on apple (Malus silvestris c.v. Braburn) elicited electrophysiological responses from male D. plantaginea. Active peaks were tentatively identified by gas chromatography (GC) coupled with mass spectrometry, with identification confirmed by peak enhancement with authentic compounds on GC columns of different polarities. The electroantennography-active chemicals were (1R,4aS,7S,7aR)-nepetalactol, (4aS,7S,7aR)-nepetalactone, (1S,2R,3S)-dolichodial, and phenylacetonitrile. (1S,2R,3S)-Dolichodial elicited a behavioral response from male D. plantaginea and naïve-mated female parasitoids, Aphidius ervi. This is the first report of electrophysiological and behavioral responses from any aphid morph to (1S,2R,3S)-dolichodial. Whether or not (1S,2R,3S)-dolichodial is a third component of the aphid sex pheromone is discussed.     

Synthesis and nonvolatile memory characteristics of thermally, dimensionally and chemically stable polyimides

A series of soluble poly(amic acid) precursors were prepared from a new carbzole-containing monomer, 3,3′-bis[9-carbazole(ethyloxy)biphenyl]-4,4′-diamine (HAB-CBZ) by polycondensation with four different aromatic dianhydrides: pyromellitic dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-diphenylethertetracarboxylic dianhydride (ODPA), and 3,3′,4,4′-diphenylsulfonyltetracarboxylic dianhydride (DSDA). From the precursors, nanoscale thin films of polyimides (PIs) were prepared by spin-coating and subsequent thermal imidization. All the PIs exhibited excellent thermal and dimensional stability. In particular, the PIs based on the PMDA and BPDA units revealed excellent chemical resistance to organic solvents, in addition to the high thermal and dimensional stability, which are required for the fabrication of high performance memory devices in three-dimensionally multi-stack structure. Devices fabricated with nanoscale thin PI films exhibited excellent unipolar write-once-read-many-times (WORM) memory behavior with a high ON/OFF current ratio of up to 10¹⁰. The active PI films were found to operate at 2.2-3.3 V, depending on the chemical structures. This study found that the imide rings as local charge trap sites are necessary to enhance the memory performance in addition to carbazole moiety. All the results collectively indicate that the thermally, dimensionally and chemically stable PIs of this study are a promising material for the mass production at low cost of high performance, programmable nonvolatile WORM memory devices that can be operated with low power consumption in unipolar switching mode.     

Negative in-plane CTE of benzimidazole-based polyimide film and its thermal expansion behavior

Non-stretched polyimide films based on 5,4′-diamino-2-phenyl benzimidazole (DAPBI) show curious thermal expansion properties: the in-plane CTE value of PI film is negative when cured at 350 °C (contract upon heating). However, the value of CTE turns positive when cured at 400 °C. In-plane and out-of-plane CTE of PI films annealed at various temperatures have been measured to study the annealing effect on thermal expansion feature. The in-plane CTE value increases from negative to positive as the raise of the annealing temperatures (T_anneal), while the out-of-plane CTE decreases as a function of T_anneal. Morphologies of PI films change from amorphous to semi-crystalline accompanied with the change of in-plane CTE from negative to positive. Mechanism of the thermal expansion behavior of DAPBI-based PI films is proposed: negative in-plane CTE is generated under the combination of the more preferential thermal expansion in the out-of-plane direction and the amorphous structure when the films are cured at lower temperatures; while thermal expansion in the in-plane and out-of-plane directions are both available for semi-crystallized PI films, affording positive in-plane CTE values.     

Homo- and R/S-copolymerizations of chiral methylpropargyl esters carrying pyrene moieties, and optical properties of the formed polymers

Pyrene-functionalized chiral methylpropargyl esters, (R)-3-butyn-2-yl-1-pyrenebutyrate [(R)-1], (S)-3-butyn-2-yl-1-pyrenebutyrate [(S)-1], (R)-3-butyn-2-yl-1-pyrenecarboxylate [(R)-2], and 3-butyn-2-yl-1-pyrenecarboxylate [(R,S)-2] were polymerized with (nbd)Rh⁺[η⁶-C₆H₅B⁻(C₆H₅)₃] to obtain the corresponding polymers with moderate molecular weights (M_n: 10?500-66?500) in good yields (82-97%). All the polymers were soluble in CHCl₃, CH₂Cl₂, and THF. The polarimetric and CD spectroscopic data indicated that poly[(R)-1], poly[(S)-1], and poly[(R)-2] existed in a helical structure with predominantly one-handed screw sense in these solvents. The helical structure of poly[(R)-1] and poly[(S)-1] was stable upon heating and addition of MeOH, while that of poly[(R)-2] changed upon MeOH addition. The copolymerization of (R)-1 with (S)-1 was also conducted to obtain the copolymers satisfactorily. Poly[(R)-1], poly[(S)-1], and poly[(R)-2] emitted fluorescence smaller than the corresponding racemic copolymers. The fluorescence intensity was tuned by the addition of MeOH to THF solutions of the polymers.     

Identification of Epoxyhenicosadiene and Novel Diepoxy Derivatives as Sex Pheromone Components of the Clear-Winged Tussock Moth Perina nuda

Four EAG-active components (A–D) were found in the solvent extract of virgin females of the clear-winged tussock moth, Perina nuda. The most abundant component (B, ca. 250 ng/female) was identified as (3Z,6S,7R,9Z)-6,7-epoxyhenicosa-3,9-diene by GC-MS analyses of the extract, chemical derivatization, and comparative chiral HPLC. Minor components also elucidated were (3Z,9Z)-cis-6,7-epoxyicosa-3,9-diene, (A); (3R,4S,6S,7R,9Z)-3,4-6,7-diepoxyhenicos-9-ene, (C); and its 3S,4R,6S,7R isomer, (D); with amounts of 0.4, 5, and 8 ngt/female, respectively. Component B showed weak attractiveness to male moths in the field. The attractiveness was significantly enhanced by addition of component(s) C and/or D. No males were captured with either the antipode of component B or its mixtures with the minor components. In this field test, noctuid Hypocala rostrata males were also attracted with the synthetic P. nuda pheromone.     

Synthesis and properties of polyimides derived from cis- and trans-1,2,3,4-cyclohexanetetracarboxylic dianhydrides

Cis-1,2,3,4-cyclohexanetetracarboxylic dianhydride (cis-1,2,3,4-CHDA) was synthesized. It was found that under such conditions as heating or boiling in acetic anhydride, cis-1,2,3,4-CHDA could be converted to its trans-isomer. The process of thermal isomerization was monitored by ¹H NMR spectra and the mechanism of conversion was proposed. Their absolute structures of cis- and trans-1,2,3,4-CHDAs were elucidated by single crystal X-ray diffraction. The polycondensations of cis- and trans-1,2,3,4-CHDAs with aromatic diamines such as 4,4′-oxydianiline (ODA), 4,4′-methylenedianiline (MDA), 4,4′-diamino-3,3′-dimethyldiphenylmethane (DMMDA), 4,4′-bis(4-aminophenoxy)benzene (TPEQ), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) were studied. It is easy to obtain higher molecular weight polyimides from trans-1,2,3,4-CHDA using conventional one-step or two-step methods. However, higher molecular weight polyimides derived from cis-1,2,3,4-CHDA could not be prepared by the usual methods (solid content ca. 10%) owing to the trend of forming cyclic oligomers. Increasing the concentration of monomers could give higher molecular weight cis-polymers. All of the cis-polyimides were soluble at room temperature in aprotic polar solvents and phenolic solvents and some of them even soluble in chloroform and tetrahydrofuran, while the corresponding trans-polymers showed poor solubility as compared to cis-polymers. All of the polyimides showed good thermal stability with the 5% weight loss temperatures in air over 415 °C. Furthermore, polyimides derived from cis-1,2,3,4-CHDA have higher glass transition temperatures (T_gs) than corresponding trans-polyimides. The flexible polyimide films possessed a tensile modulus range of 2.1-3.6 GPa, a tensile strength range of 42-116 MPa, an elongation at break of 4-18%. These polyimides exhibited cutoffs at wavelengths around 270 nm and were entirely colorless. All the polyimides showed amorphous pattern according to Wide angle X-ray diffraction measurements. The differences of polymerization and properties were explained by the structural changes resulted from isomerism.     

Chirality of synergistic sex pheromone components of the western hemlock looperLambdina fiscellaria lugubrosa (HULST) (Lepidoptera: Geometridae)

Bakers' yeast reduction of (2E)-3-(2-furanyl)-2-methyl-2-propenal yielded the synthetic intermediate, (2S)-3-(2-furanyl)-2-methylpropanol, of high chiral purity (>97% ee) for the synthesis of the enantiomers of 2,5-dimethylheptadecane and 7-methylheptadecane, two synergistic sex pheromone components of the western hemlock looper (WHL),Lambdina fiscellaria lugubrosa Hulst. In electrophysiological bioassays, (7S)- but not (7R)-7-methylheptadecane elicited strong antennal responses by male WHL antennae. In field trapping experiments, addition of (7S)- but not (7R)-7-methylheptadecane to (5R,11S)-5,11-dimethylheptadecane, the major sex pheromone component of WHL, increased attraction. Attraction to (5R,11S)-5,11-dimethylheptadecane in combination with (7S)-7-methyiheptadecane was further enhanced by the addition of (5S)- but not (5R)-2,5-dimethylheptadecane. Similarly, attraction to (5R,11S)-5,11-dimethylheptadecane combined with (5S)-2,5-dimethylheptadecane increased when 7S- but not (7R)-7-methylheptadecane was added as a third component. We conclude that (7S)-7-methylheptadecane and (5S)-2,5-dimethylheptadecane are the synergistic sex pheromone components of WHL. The synthetic methodology described is applicable to the synthesis of chiral methyl-branched pheromones in other orders of the Insecta, particularly Coleoptera, Diptera and Orthoptera.