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Natural rubber is a renewable resource with a potential as precursor of a very wide range of novel polymers, including polyisoprene-based surfaces with antifouling (AF) activity. In this work, new ionic and non-ionic coatings were prepared by the photocrosslinking reaction of photosensitive cis -1,4-oligoisoprenes, bearing a variable number of ammonium groups. The photochemical crosslinking was achieved using radical (via acrylate groups) or cationic (via epoxy groups) processes. Surface properties of these coatings were studied by static contact angle measurements and AFM imaging. Assessment of bioactivity demonstrated that most of the resulting coatings showed AF potential against fouling organisms: growth inhibition of marine bacteria ( Pseudoalteromonas elyakovii , Shewanella putrefaciens , Cobetia marina , Polaribacter irgensii , Vibrio aestuarianus ) and fungi ( Halosphaeriopsis mediosetigera , Asteromyces cruciatus , Lulworthia uniseptata , Zalerion sp., Monodictys pelagica ); decreased adhesion of microalgae ( Navicula jeffreyi , Cylindrotheca closterium , Chlorarachnion globosum , Pleurochrysis roscoffensis , Exanthemachrysis gayraliae , Amphora coffeaeformis ); inhibition of attachment and/or germination of spores of Ulva intestinalis . The best AF activity was obtained with the ionic surfaces. These new coatings prepared from precursors obtained from natural rubber are in essence active by contact. As the biocidal functions are fixed covalently to the polymer chain, detectable release of biocidal products in the marine ecosystem is prevented so that a valuable environment-friendly alternative for new AF coatings is hereby proposed.

Metathetic degradation of synthetic cis-1,4-polyisoprene (PI) and styrene–butadiene copolymer (SBR) was performed with cis-1,4-diacetoxy-2-butene (DAB) as chain transfer agent (CTA) using Grubbs II catalyst. Well-defined acetoxy telechelic polyisoprene structures were obtained in a selective manner with a wide range of targeted average molecular weights from 350 g mol −1 to 98,000 g mol −1 , with a polydispersity index of around 2. Starting from SBR, a similar structure control was obtained with a range of M n from 1400 g mol −1 to 65,000 g mol −1 . It was found that precise selection of catalyst concentration and solvent is the major factor to obtain targeted products with high M n control. Moreover, preliminary tests using such a procedure have shown its efficiency starting from waste tyre. This methodology thus suggests the possibility to recycle such rubber waste leading to high value liquid rubber.

The photoinitiated polymerization of epoxidized hydroxytelechelic cis-1,4-polyisoprene and of a dual system (epoxidized/ acrylated) telechelic cis-1,4-polyisoprene in the presence of 2,2-dimethyl-1,2-hydroxyacetophenone or/and hexafluoro-phosphate triar- ylsulfonium salt has been studied by real-time infrared spectroscopy. The synthesis of photosensitives oligoisoprenes was achieved by chemical modifications of hydroxytelechelic cis-1,4-polyisoprene obtained by controlled degradation of high molecular weight cis-1,4- polyisoprene. Then, the effect of light intensity, photoinitiator concentration, addition of reactive diluent and concentration of func- tional groups on the photopolymerization process was evaluated. Concerning the cationic process, the results showed that the kinetic profile improves when photoinitiator concentration and light intensity increase. The optimum concentration of triarylsulfonium salt used as photoinitiator was determined as 5% (w/w) and the optimum light intensity was 50 mW cm � 2 . Reactive diluent (3-ethyl-3- hydroxymethyl oxetane) addition greatly improves the ultimate conversion and the polymerization rate. Subsequently, the photopoly- merization kinetic of a dual epoxidized/acrylated system was studied. The results obtained using different photoinitiator mixtures and different intensity of irradiation showed that the crosslinking of acrylate functions at the chain-end prevents the progression of the cationic process at the oxirane groups along the chain. Thus, the mobility of the cationic reactive centers was restricted by the cross- linking at the high conversion of the acrylate double bonds. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000-000, 2012

New photosensitive oligoisoprenes were synthesized by controlled degradation of high molecular weight cis-1,4-polyiso- prene and successive chemical modification of the chain-ends. Oligomers with diacrylate extremities were synthesized, characterized, and used in photocrosslinking reactions in different conditions. The photoinitiated polymerization of the diacrylate oligoisoprenes was carried out using 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as initiator and the reaction was monitored by photoca- lorimetry-DSC and real time FTIR spectroscopy. The influence of oxygen, photoinitiator concentration, light intensity, diluting agent, and oligomers molecular weight on the reaction rate was investigated. It was found that the presence of oxygen does not influence the photopolymerization kinetics of the diacrylate oligoisoprenes. Maximum conversion was obtained for a photoinitiator concentra- tion of 5% (w/w) and for a light intensity of 13.5 mW/cm 2 . Decreasing the formulation viscosity by addition of a diluent (1,6-hexa- nediol diacrylate) raised the photopolymerization rate, by increasing the reactive species mobility. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000-000, 2012

Presently, the disposal of thousands of tons of waste tyres produced every year in the whole world is a major environmental problem. Since tyre rubbers do not decompose easily on account of crosslinking and stabilizers, the processing of the waste tyre rubber constitutes a significant technical challenge. This work describes the use of periodic acid for the controlled one-pot oxidative cleavage of carbonyl telechelic cis -1,4-oligoisoprenes (CTNR) and natural rubber (NR) as model compounds and the application of this method to the degradation of ground waste tyre rubber. Average molecular weight analysis of the degraded material indicates that the reaction time and the periodic acid quantity can be used to control the degree of breakdown; we obtained materials in the average molecular weight range of 700–5000 g mol −1 . The processed material shows ketone and aldehyde groups at the chain ends. Degradation studies of waste tyre rubbers were also carried out using this oxidative cleavage by periodic acid, to achieve carbonyl telechelic oligomers. Well-defined structures were obtained with an average molecular weight from 3000 to 7000 g mol −1 according to the periodic acid/waste tyres rubber ratio used.

A new trithiocarbonate functionalized cis-1,4-polyisoprene was obtained from oxidative degradation of natural rubber followed by reductive amination and amidation. The structure of the resulting functionalized cis-1,4-polyisoprene was confirmed by a combination of 1H NMR spectroscopy, 13C NMR spectroscopy, MALDI-TOF mass spectrometry and FTIR spectroscopy. 1H NMR spectroscopy showed that the trithiocarbonate functionality was equal to one. The well-defined trithiocarbonyl-end functionalized cis-1,4-polyisoprene was used as a macromolecular chain transfer agent (macroCTA) to mediate the RAFT polymerization of t-BA using AIBN as the initiator ([t-BA]0/[macroCTA]0/[AIBN]0 = 250/1/0.2) in toluene at 60 °C. The resulting PI-b-P(t-BA) diblock copolymer presents an unimodal SEC trace shifted toward higher molecular weight in comparison with the SEC trace of the macroCTA, indicating that the polymerization of the second block is effective. The characteristics of the copolymer were determined by SEC ( M ¯ n = 26,000 g mol−1, PDI = 1.76) and 1H NMR spectroscopy ( DP ¯ n (PI) = 62 and DP ¯ n (P(t-BA)) = 87).

Novel flexible polyurethane foams were successfully prepared from a renewable source, hydroxytelechelic natural rubber (HTNR) having different molecular weights (1000–3400 g mol−1) and variation of epoxide contents (EHTNR, 0–35% epoxidation) by a one-shot technique. The chemical and cell structures as well as physico-mechanical, thermal, and acoustic properties were characterized and compared with commercial polyol analogs. The obtained HTNR based foams are open cell structures with cell dimensions between 0.38 and 0.47 mm. The HTNR1000 based foam exhibits better mechanical properties but lower elongation at break than those of commercial polyol analog. However, the HTNR3400 based foam shows the best elastic properties. In a series of EHTNR based foams, the tensile and compressive strengths show a tendency to increase with increasing epoxide content and amount of 1,4-butanediol (BD). The HTNR based foams demonstrate better low temperature flexibility than that of the foam based on commercial polyol. Moreover, the HTNR based polyurethane foams was found to be an excellent absorber of acoustics. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

International audience; This work describes the influence of silica fillers on the thermomechanical properties of diglycidyl ether of bisphenol A/triethylenetetramine (DGEBA/TETA) epoxy resins during ageing under electron beam irradiation. Whatever be the silica filler (pure micrometric ground and spherical silicas, nanometric silicas and coupling agent treated silicas), the glass transition temperature of the epoxy resins decreases with increasing irradiation dose, meaning that the main effect of the irradiation is chain scission. No influence of the silica fillers has been detected from the changes in the glass transition temperature with the increase in the irradiation dose. The disappearance of the cooperativity of the ? relaxation, the decrease of the a relaxation and the decrease of the elastic modulus at the rubbery plateau observed by dynamic mechanical analyses involve a decrease in the crosslink density of the epoxy resins. The occurrence of chemical reactions between the epoxy resin and the silica surface at high irradiation doses has been shown. Moreover, we show evidence that chemical reactions between the epoxy resin and the silica surface occur at high irradiation dose.

The study of the chemical modifications of model compounds of the diglycidyl ether of bisphenol A/triethylene tetramine (DGEBA/TETA) epoxy resins under electron irradiation is described. The reaction of butylamine and N , N′ -diethylethylene diamine with DGEBA afforded model compounds of the DGEBA/TETA structure. Nanometric silica was used as filler for these model compounds. 1 H and 13 C NMR analyses allowed identification of the chemical structures before and after irradiation. C–O and C–N scissions were observed with the formation of phenolic and methyl-ketone ends and of primary and secondary amines. For the model compounds containing the 1,2-diaminoethylene structure, the scission of the C–N bond is followed by the formation of an enamine end. The mechanisms of the different bond scissions are proposed. The presence of the nanometric silica fillers allows the protection of some C–N bonds. The reaction of the chemical species formed by electron irradiation with the reactive functions at the silica surface is proposed to explain the chemical modifications observed on the irradiated filled model compounds.

Carbonyl telechelic cis-1,4-oligoisoprene (CTPI) obtained from high molecular weight polyisoprene through an oxidative chain cleavage reaction have been chemically modified. Thus, new well defined amino telechelic cis-1,4-oligoisoprenes have been obtained in a mass range of 1600–2300 g/mol according to two different pathways. The first approach involved a standard mesylate displacement by sodium azide followed by smooth reduction using triphenylphosphine. The second pathway implied a reductive amination sequence. Primary or secondary amine functions have thus been selectively obtained at both oligomer chain-ends depending on reaction conditions. Peculiar NMR experiments conducted on these functional oligomers confirmed a precise control of functionality during the chemical modification. Moreover, their abilities to react with toluene diisocyanate or bis(succinimidyl)carbonate have been investigated.

Degradation studies of cis-1,4-polyisoprene were carried out using first and second generation Grubbs catalysts to achieve end-functionalized acetoxy oligomers in both an organic solvent and a latex phase at room temperature. Well-defined acetoxy telechelic polyisoprene structures were obtained in a selective manner with arange of M n from 10 000 to 30 000, with a polydispersity index of around 2.5.

Depolymerization of 20% epoxidized cis-1,4-polybutadiene was carried out through alkenolysis of the butadiene repeat units (B) using 4-octene as depolymerizing agent (DA) and bis(tricyclohexyl phosphine)benzylidene ruthenium (IV) dichloride (1) as catalyst. The average molecular weight of the depolymerization products was determined by NMR, and SEC, and their constituents were identified by GC MS. Cis-4-octene was found more efficient in performing the depolymerization as compared to its trans isomer. Besides dodeca-4,8-diene and hexadeca-4,8,12-triene, 2,3-di[3-heptenyl]-oxirane with a cis oxirane configuration was clearly characterized. Beside the DA to B mole ratio, the catalyst to double bond mole ratio was observed as the major factor controlling the molecular weight of the depolymerization products and the 2,3-di[3-heptenyl]-oxirane yields.

Telechelic cis-1,4-oligoisoprenes were prepared by the selective cleavage of weak epoxidized units (E) in epoxidized cis-1,4-polyisoprenes (EPIs) and by the random cleavage of isoprenic units (I) in cis-1,4-polyisoprene (PI). In both cases, cleavage by periodic acid (H 5 IO 6 ) in tetrahydrofuran led to aldehydic and ketonic chain ends. Through variations in the E/(I + E) molar percentage (E%) in the cleavage of EPI and through variations in the H 5 IO 6 /I molar percentage (PA%) in the cleavage of PI, a polydispersity index near 2 and a number-average molecular weight of 2 - 20 × 10 3 were obtained. The correlation of the degree of scission with E% and PA%, combined with kinetic, led to the proposal of a two-step mechanism for the H 5 IO 6 cleavage of double bonds.

ROMP of the optical pure monomer of the title compound (1) was performed successfully using the classical WC1 6 /SnMe 4 catalyst. Beside the stereoregularity (σ c = 0.70), the 13 C NMR spectrum of the resulting polymer (P 1 ) evidenced a noticeable directional regularity (B = (HT + TH)/(HH + TT) = 1.6) which can be due to sterically induced regiospecificity in the norbornenyl ring opening during propagation. Significant optical activities were observed for P 1 and for poly(norbornene-2-carboxylic acid) (P 2 ) resulting from LiOH hydrolysis of P 1 is probably due to the homochiral pantolactonyl side chain and the (S) C 2 backbone carbon.

By chemical modification of natural rubber, it is possible to modify its basic properties (for instance, improvement of gas permeability, resistance to oils or fire resistance) or to prepare new polymeric materials for specific applications (for instance, photocrosslinkable rubbers and rubbers support of active molecules). The purpose of the present paper is to give an overview of recent works carried out in the field of new rubber derivatives for specific applications, especially dealing with natural rubber degradation and products derived from liquid rubbers of type 1,4-polyisoprene (liquid natural rubbers, synthetic polyisoprenes) and/or their epoxidized forms. A reflexion on the perspectives of researches on natural rubber or its derivatives is given in conclusion. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1461–1477, 2000

Resume Un caoutchouc synthetique (CK) et deux caoutchoucs naturels liquides (CF et Cf) ont ete selectionnes en fonction de leur teneur en extremites phenylcetone (EP) et methylcetone (EM). L’oxydation acceleree est conduite par barbotage d’oxygene dans de solutions (benzene) de concentration constante en polyisoprenes (10 g l−1) et de concentration variable en phenylhydrazine (20 mmol l−1

N-[n-(4-cyanobiphenyl-4′-yloxy)alkyl]-7-oxanorbornene-5,6-exo-dicarboximide (CBON2–CBON8) with increasing number of methylene groups in the alkyl part (n = 2–8) were synthesized by Mitsunobu condensation between the appropriate alcohols (CBA2–CBA8) and 7-oxanorbornene-5,6-exo-dicarboximide (ON). The conditions for the ring opening metathesis polymerization of CBONn giving acceptable molecular weights and molecular distributions were established. Characterization of the resulting polymers (P2–P8) by 1H- and 13C-NMR has shown a high trans content. Differential scanning calorimetry and optical microscopy analysis have shown that the alcohols CBAn are thermotropic with some variations between the first and second heating-cooling cycles, the monomers CBONn melt with no evidence of any mesomorphic state, the polymers Pn show only the glass transition, and the glass transition temperature (Tg) decreases with increases in the spacer length. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2807–2821, 1998

New copolyethers were prepared by chemical modification of polyepichlorohydrin and poly(3,3-bis(chloromethyl)oxetane) with the sodium salt of either 4-hydroxy-4'-nitrostilbene or 4-hydroxy-4'-cyanoazobenzene, employing the concept of having the nitrostilbene or cyanoazobenzene species serve concomitantly as both the nonlinear optical (NLO) chromophore and the mesogenic moiety in the polymer. Their thermal behavior was established by means of differential scanning calorimetry (DSC) and optical microscopy. The NLO properties of two nematic copolyethers were studied. The NLO mesogenic groups were oriented by the standard corona poling technique and the degree of axial ordering was determined as a function of poling conditions. The second harmonic coefficients d 31 and d 33 were measured. The results showed that liquid crystallinity enhances field-induced polar ordering. The ratio d 33 /d 31 was found to be much larger than 3, in agreement with the theoretical models for electric field poling of liquid crystals. We were able to obtain d 33 values up to 130 pm/V at λ = 1,064 μm, thus exceeding many values previously reported for second harmonic generation measurements on isotropic polymers containing similar side chain chromophores.

Optimal conditions for distannoxane catalyzed transesterification of methyl esters with benzylic alcohols were established by studying the polycondensation of hex-3-ene-1,6-bis(methyl oate) (1) with 1,4-bis(hydroxymethyl)benzene (2). α,ω-Dicarbomethoxy-1,4-oligobutadiene (3) was obtained by cross metathesis between cycloocta-1,5-diene and 1. The synthesis of 1,4-bis[4-(hydroxymethyl)cinnamoyl]-benzene (4) were conducted starting from 4-(diethoxymethyl)benzaldehyde (5) and 1,4-diacetylbenzene. Finally the organosoluble polyester (PE3/4) were synthesized by reacting 3 with 4 and the occurrence of crosslinkings by UV irradiation was checked.

Low-molecular-weight organosilane polymers were prepared by sodium and potassium/sodium coupling of dichloromethylphenylsilane (1) with chlorotrimethylsilane (2). Size exclusion chromatography (SEC), IR, UV and NMR (1H, 13C and 29SI) analysis of the crude α,ω-bis(trimethylsilyl) oligo(methylphenylsilane) (3) were performed and compared with those of the isolated shortest oligomers. According to an anionic mechanism, the solvent and alkali-metal effects on the yield and the oligomer distribution (SEC-resolved) allow an optimisation for the synthesis of the shortest oligomers (trisilane and tetrasilane).

The thermal reaction between N-phenylmaleimide and 2-allylphenol was taken as a model reaction in order to obtain information about chain extension and crosslinking mechanisms of the thermal curing of bismaleimides with diallylbisphenol A. Isolation (preparative HPLC) and characterization ( 1 H and 13 C NMR, FT-IR, HPLC/SM) of a monoadduct and two original triadducts (principally low molecular weight products of the reaction) and studies as a function of time (0-6 h) of this thermally induced reaction (160-250 o C) with equimolar quantities of N-phenylmaleimide and 2-allylphenol, as well as with an excess of N-phenylmaleimide, give direct evidence of the occurrence of an ene-reaction and further Diels-Alder and retro Diels-Alder reactions with rise in temperature

The coupling of dichloromethylphenylsilane (1) with chlorotrimethylsilane (2) by lithium is considered for the synthesis of low-molecular-weight organosilane polymers 3 and for the preparation of heptamethylphenyl-2-trisilane (3a) and octamethyldiphenyl-2,3-tetrasilane (3b). Size-exclusion chromatography, ultraviolet and infrared spectroscopies and nuclear magnetic resonance (1H, 13C and 29Si NMR) analyses of the crude product 3 were performed and compared with those of 3a and 3b. According to the spectroscopic characteristics of heptamethyltetrakis(trimethylsilyl)-3,4,5,6-cyclohex-1-enyl-2-trisilane (4), and the observed silylation of the trisilane 3a when it is submitted to the action of a (CH3)3SiCl/Li/tetrahydrofuran system, the silylation of the phenyl ring during the reductive condensation of the chlorosilanes is supported by NMR identification of 4-like structures.

Owing to its origin, Natural Rubber exhibits more variation than synthetic polymers. If, over the years, NR specifications have evolved from mere visual inspections towards the more complex Technically Specified Rubber (TSR) schema, industrial practice shows that, even for typical TSR grades, significant variations still exist within each shipment, especially in regard to processability. It follows that mastication is quite systematically needed in industrial operations, without or with processing aids or so-called peptizers. Typical NR compounding operations consume therefore time and mixer capacity, a situation, which obviously calls both better characterization methods of (gum) natural rubber and eventually improved grades. There are nowadays promising new techniques to analyze and characterize polymer materials, some of which are a priori attractive for a better specification of NR grades. One such technique is the so-called Fourier Transform rheometry, a dynamic testing method to investigate both the linear and the non-linear viscoelastic domains of polymer materials. Other are spectroscopic methods like solid Nuclear Magnetic Resonance (NMR), either liquid or solid, whose results might be complemented by Size Exclusion Chromatography with special detection techniques, e.g. SEC-MALS, and Differential Scanning Calorimetry (DSC). The purpose of the work reported here was to investigate a series of gum NR grades using such techniques, with the objectives not only to demonstrate their interest but also to cross-validate their results. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

We investigate the one-pot synthesis of a new α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene (Pip) via metathesis degradation from natural rubber (NR) in the presence of the Grubbs second generation catalyst (GII) and a bistrithiocarbonyl-end functionalized olefin as a chain transfer agent (CTA). When the metathesis degradation of the NR of 2 × 10 6 g mol ―1 molecular weight is performed in toluene at 25 °C using the ratio of [Ip] 0 /[GII] 0 /[CTA] 0 = 100/1/1 (Ip = isoprene units), a cis-1,4-polyisoprene of 14000 g mol ―1 after 4 h is obtained. The functionality estimated by 1 H NMR spectroscopy is equal to 1.5 ± 0.1. The structure of telechelic cis-1,4-polyisoprene was confirmed by combination of 1 H NMR. 13 C NMR spectroscopy and FTIR. The influence of the CTA concentration was investigated. It was found that using higher concentrations of CTA ([Ip] 0 /[GII] 0 /[CTA] 0 of 100/1/2 and 100/1/5) lead to form a perfectly telechelic cis-1,4-polyisoprene with a functionality of 2 with no significant difference in M n values (approximately 6400 g mol ―1 ) and in polydispersity indices (∼1.70). The new well-defined α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprenes were used successfully as macromolecular chain transfer agents (macroCTAs) to mediate the RAFT polymerization of t-BA using AIBN as the initiator ([t-BA] 0 /[macroCTA] 0 /[AIBN] 0 = 500/1/0.4) in toluene at 60 °C leading to well-defined P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers.

Telechelic oligoisoprenes were successfully prepared by the selective controlled degradation of natural rubber, a renewable source, via epoxidation and cleavage reactions. The molar mass of the oligoisoprene product obtained depends on the degree of epoxidation of the starting materials. The chemically modified structures obtained via epoxidation, hydrogenation, and ring opening of epoxide groups were also studied, and the chemical structures and thermal properties of the oligoisoprene products were determined. Moreover, the preliminary study of preparation of hydroxytelechelic natural rubber (HTNR)-based polyurethane foam was performed. A novel HTNR-based polyurethane foam was successfully prepared and its thermal properties were investigated and the results indicated that the HTNR-based polyurethane foam has a good low temperature flexibility. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The first [4 + 2] inverse electrodemand heterocycloaddition between hydroxytelechelic oligoisoprenes and the benzylidene pyruvic methyl ester promoted by tin tetrachloride is described. A partial hydrogenation of hydroxytelechelic oligoisoprenes was necessary to selectively promote the cycloaddition.

New telechelic cis -1,4-polyisoprene oligomers bearing an hydroxyl group at the end of the polyisoprene backbone and possessing controlled molecular weights were used as soft segments in the elaboration of polyurethane elastomers. Besides, the well defined hydroxytelechelic cis -1,4-polyisoprene (HTPI) structure obtained through a controlled methodology, was chemically modified leading to hydrogenated and epoxidized oligomers based polyurethanes. The influence of the structural changes of these precursors on the polyurethanes properties have been studied. Thus, mechanical parameters as well as glass transition and mechanical transition temperature measurements indicated an increase in PUs hardness when the length of soft segment decreases and when the degree of epoxidized and hydrogenated isoprenic moieties increases. Moreover, based on thermogravimetric analysis (TGA), a linear relationship was established between the weight loss in the urethane stage degradation and the amount of hard segments in the PUs. Otherwise, the hydrogenated soft segments were found more thermally stable than the epoxidized and the non modified ones. By comparison with similar investigations developed from commercial oligodienes (PBHT R20 LM ® and EPOL ® ), this study mainly showed that the PUs based on hydrogenated hydroxytelechelic cis -1,4-polyisoprenes were more thermally stable and softer than the EPOL ® based analogues.