polyamides , polyimides , and their copolymers are certainly one of the most useful classes of high - performance polymers , which have found many applications in industries as discussed by mittal   and abade .
aromatic polyimides are an important class of heterocyclic polymers with remarkable heat resistance and superior mechanical and electrical properties , and also durability as discussed by banihashemi and abdolmaleki , ghosh and mittal   and wilson et al . .
various efforts have been focused on the preparation of soluble and/or thermoplastic polyimides , while still maintaining the excellent thermal and mechanical properties .
typical approaches that have been employed to improve the processability of them include the incorporation of flexible links as discussed by tamai et al . , bulky pendant or cardo groups as discussed by hsiao and li   and mller and ringsdorf , kinked or asymmetric structures as discussed by li et al . , and spiro skeletons as discussed by reddy et al .   into the polymer chain .
these modifications lower the melting temperature and lead to soluble and amorphous polymers . in general ,
amorphous polymers have a lower softening temperature ( tg ) and improved solubility with respect to their crystalline analogues .
some of the block copolymers composed of polyethers and polyamides have already been commercialized as thermoplastic elastomers as discussed by legge et al . .
a number of synthetic routes for polyether - polyimide block copolymers have been known as discussed by noshay and mcgrath .
the synthesis and application of optically active polymers is a considerable topic , which has been paid more attention recently as discussed by hajipour et al . .
most of the natural polymers are optically active and have special chemical activities , such as catalytic properties that exist in genes , proteins , and enzymes .
some other applications are construction of chiral media for asymmetric synthesis , chiral stationary phases for resolution of enantiomers in chromatographic techniques as discussed by akelah and sherrington , aglietto et al .
okamoto and yashima , and soai and niwa , chiral liquid crystals in ferroelectrics and nonlinear optical devices as discussed by wulff   and fontanille and guyot .
these synthetic polymers based on optically pure amino acids can induce crystallinity with their ability to form higher ordered structures that exhibit enhanced solubility characteristics as discussed by birchall et al . .
these properties have caused them to be good candidate for drug delivery systems , biodegradable macromolecules , biomaterials , and also as chiral purification media as discussed by mallakpour et al . .
recently , we have synthesized optically active polymers by different methods as discussed by mallakpour et al .
l - lysine with good functionalities has been used to prepare some polytartaramides as discussed by bou and muoz - guerra   and maj et al . .
in this research , we report the synthesis and characterization of some pas and pis from an inexpensive starting material through polycondensation in refluxing dmf .
these polymers showed good optical activity ( 28.12 to 48.56 ) and because of the presence of pendent ester moiety they can potentially be ion exchangeable as discussed by mller and ringsdorf . in pi2 because of the presence of benzophenone moiety , this polymer can potentially be photolabile .
the photolabile polymers can potentially be used as affinity columns for protein purification as discussed by guo et al . .
the outstanding characteristics of these polymers include thermal stability , good solubility , optical activity , semicrystallinity , potentially being photolabile and ion exchangeable .
h nmr spectra were recorded on 300  mhz ( bruker avance ) instrument , using dmso - d6 as solvent and tetramethylsilane as shift reference ( tube diameter , 5  mm ) .
ir spectra were recorded on a shimadzu ft - ir-680 instrument , using kbr pellets .
thermogravimetric analyses ( tga ) were recorded on a mettler tga-50 with heating rate of 10c  min under air atmosphere .
inherent viscosities of polymers were measured by a standard procedure using a kpg cannon fenske routine viscometer at 25c using dmf as solvent .
elemental analyses were preformed in a heraeus chns - rapid instrument . in a 50  ml round - bottomed flask equipped with a reflux condenser and a stirring bar , 8  ml of thionyl chloride
was added dropwise to the stirring absolute ethanol ( 2.5  ml ) at 10c .
l - lysine hydrochloride ( 7.3  g , 0.04  mol ) was added to the mixture and refluxed for 6 hours .
the solvent was evaporated under reduced pressure and the residue was washed with diethyl ether for three times .
yield : 87% ; m.p . : 136 - 137c ; ir ( cm ) : 3421 , 33502514 , 2019 , 1740 , 1603 , 1583 , 1501 , 1217 , 851 , 740 ; h - nmr ( d2o , ppm ) : 1.07 ( 3h ) , 1.29 ( 2h ) , 1.49 ( 2h ) , 1.76 ( 2h ) , 2.78 ( 2h ) , 3.91 ( 1h ) , 4.08 ( 2h ) ; elemental analysis for c8h18n2o22hcl , calculated : c ( 38.87% ) , h ( 8.16% ) , n ( 11.33% ) , found : c ( 38.62% ) , h ( 8.31% ) , n ( 11.40% ) . for the general procedure in a 25  ml round - bottomed flask equipped with a reflux condenser and a stirring bar ,
a mixture of dianhydride ( 0.001  mol ) , ethyl l - lysine dihydrochloride ( 0.001  mol ) , et3n ( 0.002  mol ) , and dmf ( 5  ml ) were placed . the mixture was stirred at r.t . for 2 hours and then at refluxing temperature for 5 hours .
the white precipitate was filtered off , washed with water , and dried under vacuum condition . 


pi1 ( using pyromellitic dianhydride)yield : 75% ; inh ( dl  g ) = 0.42 ; [ ]d = 30.68 ; uv ( max ) : 263 ; ir ( cm ) : 29802894 , 2858 , 17741680 , 1495 , 14581386 , 1244 , 1120 , 1023 , 719 , 496 ; h nmr ( dmso - d6 , ppm ) : 1.26 ( 2h ) , 1.41 ( 3h ) , 1.761.83 ( 2h ) , 2.33 ( 2h ) , 3.74 ( 2h ) , 4.23 ( 1h ) , 4.87 ( 2h ) , 8.068.29 ( 2h ) . elemental analysis for c18h16n2o5 : calculated : c ( 63.52% ) , h ( 4.73% ) , n ( 8.23% ) , found : c ( 63.42% ) , h ( 4.80% ) , n ( 8.11% ) .
wide - angle x - ray diffraction patterns of this polymer in the region of 2 = 570 at room temperature indicate 2030% of crystallinity . 
 
yield : 75% ; inh ( dl  g ) = 0.42 ; [ ]d = 30.68 ; uv ( max ) : 263 ; ir ( cm ) : 29802894 , 2858 , 17741680 , 1495 , 14581386 , 1244 , 1120 , 1023 , 719 , 496 ; h nmr ( dmso - d6 , ppm ) : 1.26 ( 2h ) , 1.41 ( 3h ) , 1.761.83 ( 2h ) , 2.33 ( 2h ) , 3.74 ( 2h ) , 4.23 ( 1h ) , 4.87 ( 2h ) , 8.068.29 ( 2h ) .
elemental analysis for c18h16n2o5 : calculated : c ( 63.52% ) , h ( 4.73% ) , n ( 8.23% ) , found : c ( 63.42% ) , h ( 4.80% ) , n ( 8.11% ) .
wide - angle x - ray diffraction patterns of this polymer in the region of 2 = 570 at room temperature indicate 2030% of crystallinity . 


pi2(using 3,3,4,4-benzophenone tetracarboxylic-3,3,4,4-dianhydride)yield : 80% ; inh ( dl  g ) = 0.15 ; [ ]d = 48.56 ; uv ( max ) : 265 , 290 ; ir ( cm ) : 2938 , 17761715 , 1669 , 1619 , 1441 , 1385 , 1294 , 1246 , 1184 , 1157 , 1096 , 1024 , 859 , 726 ; h nmr ( dmso - d6 , ppm ) : 1.26 ( 2h ) , 1.44 ( 3h ) , 1.751.82 ( 2h ) , 2.34 ( 2h ) , 3.73 ( 2h ) , 4.24 ( 1h ) , 4.87 ( 2h ) , 7.998.23 ( 6h ) .
elemental analysis for c25h20n2o6 : calculated : c ( 67.55% ) , h ( 4.54% ) , n ( 6.30% ) , found : c ( 67.46% ) , h ( 4.77% ) , n ( 6.16% ) . 
 
yield : 80% ; inh ( dl  g ) = 0.15 ; [ ]d = 48.56 ; uv ( max ) : 265 , 290 ; ir ( cm ) : 2938 , 17761715 , 1669 , 1619 , 1441 , 1385 , 1294 , 1246 , 1184 , 1157 , 1096 , 1024 , 859 , 726 ; h nmr ( dmso - d6 , ppm ) : 1.26 ( 2h ) , 1.44 ( 3h ) , 1.751.82 ( 2h ) , 2.34 ( 2h ) , 3.73 ( 2h ) , 4.24 ( 1h ) , 4.87 ( 2h ) , 7.998.23 ( 6h ) .
elemental analysis for c25h20n2o6 : calculated : c ( 67.55% ) , h ( 4.54% ) , n ( 6.30% ) , found : c ( 67.46% ) , h ( 4.77% ) , n ( 6.16% ) . 

 pi3(using 4,4-(hexaflouroisopropylidene ) diphthalic anhydride)yield : 70% ; inh ( dl  g ) = 0.18 ; [ ]d = 28.26 ; uv ( max ) : 280 ; ir ( cm ) : 2941 , 17791719 , 1442 , 1385 , 1297 , 1255 , 1210 , 1140 , 1105 , 722 ; h nmr ( dmso - d6 , ppm ) : 1.051.12 ( 2h ) , 1.22 ( 3h ) , 1.531.58 ( 2h ) , 2.11 ( 2h ) , 3.49 ( 2h ) , 4.01 ( 1h ) , 4.65 ( 2h ) , 7.607.99 ( 6h ) .
elemental analysis for c27h20n2o5f6 : calculated : c ( 57.24% ) , h ( 3.56% ) , n ( 4.95% ) , found c ( 57.10% ) , h ( 3.64% ) , n ( 4.86% ) . 
 
yield : 70% ; inh ( dl  g ) = 0.18 ; [ ]d = 28.26 ; uv ( max ) : 280 ; ir ( cm ) : 2941 , 17791719 , 1442 , 1385 , 1297 , 1255 , 1210 , 1140 , 1105 , 722 ; h nmr ( dmso - d6 , ppm ) : 1.051.12 ( 2h ) , 1.22 ( 3h ) , 1.531.58 ( 2h ) , 2.11 ( 2h ) , 3.49 ( 2h ) , 4.01 ( 1h ) , 4.65 ( 2h ) , 7.607.99 ( 6h ) .
elemental analysis for c27h20n2o5f6 : calculated : c ( 57.24% ) , h ( 3.56% ) , n ( 4.95% ) , found c ( 57.10% ) , h ( 3.64% ) , n ( 4.86% ) .
in a 25  ml round - bottomed flask equipped with a reflux condenser and a stirring bar , a mixture of aromatic acid dichloride ( 0.001  mol ) , ethyl l - lysine dihydrochloride ( 0.001  mol ) , et3n ( 0.004  mol ) and dmf ( 5  ml ) were placed .
the white precipitate was filtered off , washed with water , and dried under vacuum conditions . 


pa4(using terephthaloyl dichloride)yield : 65% ; inh ( dl  g ) = 0.31 ; [ ]d = 28.12 ; uv ( max ) : 265 ; ir ( cm ) : 3423 , 2963 , 17271615 , 1505 , 1439 , 1410 , 1276 , 1197 , 1118 , 1018 , 727 ; h nmr ( dmso - d6 , ppm ) : 1.12 ( 2h ) , 1.231.26 ( 3h ) , 1.32 ( 2h ) , 1.381.60 ( 2h ) , 1.82 ( 2h ) , 2.96 ( 2h ) , 3.29 ( 1h ) , 4.30 ( 1h ) , 4.47 ( 2h ) , 7.658.16 ( 4h ) , 11.42 ( 1h ) .
elemental analysis for c16h20n2o3 : calculated c ( 66.65% ) , h ( 6.99% ) , n ( 9.71% ) , found c ( 66.54% ) , h ( 7.07% ) , n ( 9.66% ) . 
 
yield : 65% ; inh ( dl  g ) = 0.31 ; [ ]d = 28.12 ; uv ( max ) : 265 ; ir ( cm ) : 3423 , 2963 , 17271615 , 1505 , 1439 , 1410 , 1276 , 1197 , 1118 , 1018 , 727 ; h nmr ( dmso - d6 , ppm ) : 1.12 ( 2h ) , 1.231.26 ( 3h ) , 1.32 ( 2h ) , 1.381.60 ( 2h ) , 1.82 ( 2h ) , 2.96 ( 2h ) , 3.29 ( 1h ) , 4.30 ( 1h ) , 4.47 ( 2h ) , 7.658.16 ( 4h ) , 11.42 ( 1h ) .
elemental analysis for c16h20n2o3 : calculated c ( 66.65% ) , h ( 6.99% ) , n ( 9.71% ) , found c ( 66.54% ) , h ( 7.07% ) , n ( 9.66% ) . 


pa5(using isophthaloyl dichloride)yield : 60% ; inh ( dl  g ) = 0.17 ; [ ]d = 30.22 ; uv ( max ) : 265 ; ir ( cm ) : 3422 , 2962 , 17221685 , 1431 , 1312 , 1288 , 1251 , 11311077 , 724 ; h nmr ( dmso - d6 , ppm ) : 1.12 ( 2h ) , 1.231.26 ( 3h ) , 1.39 ( 2h ) , 1.401.79 ( 2h ) , 2.97 ( 2h ) , 3.25 ( 1h ) , 4.42 ( 2h ) , 7.648.56 ( 5h ) .
elemental analysis for c16h20n2o3 : calculated c ( 66.65% ) , h ( 6.99% ) , n ( 9.71% ) , found c ( 66.48% ) , h ( 7.10% ) , n ( 9.62% ) . 
 
yield : 60% ; inh ( dl  g ) = 0.17 ; [ ]d = 30.22 ; uv ( max ) : 265 ; ir ( cm ) : 3422 , 2962 , 17221685 , 1431 , 1312 , 1288 , 1251 , 11311077 , 724 ; h nmr ( dmso - d6 , ppm ) : 1.12 ( 2h ) , 1.231.26 ( 3h ) , 1.39 ( 2h ) , 1.401.79 ( 2h ) , 2.97 ( 2h ) , 3.25 ( 1h ) , 4.42 ( 2h ) , 7.648.56 ( 5h ) .
elemental analysis for c16h20n2o3 : calculated c ( 66.65% ) , h ( 6.99% ) , n ( 9.71% ) , found c ( 66.48% ) , h ( 7.10% ) , n ( 9.62% ) .
ethyl l - lysine dihydrochloride was prepared with the reaction of a mixture of etoh and thionyl chloride with l - lysine hydrochloride .
l - lysine hydrochloride was added to the mixture dropwise at 10c and then refluxed for 6 hours .
the dark solid was washed three times with diethyl ether to leave a bright white solid ( 87% ) .
ft - ir spectroscopy shows a strong and broad peak at 33502514  cm corresponding to the amonium n  h stretchings and a strong peak at 1740  cm corresponding to the c = o stretchinng of ester moiety .
h - nmr ( d2o , ppm ) spectroscopy shows the corresponding peaks such as 3.91 ( 1h ) due to the chiral center and 1.07 ( 3h ) and 2.78 ( 2h ) peaks due to the ethyl moiety .
solution polymerization in dmf in the presence of et3n was applied to prepare the polymers from ethyl l - lysine dihydrochloride and the other corresponding monomers ( schemes 1 and 2 ) .
but in preparing the pis the mixture was refluxed to turn the amic acid groups to imide .
et3n was used to release the amino group of the l - lysine derivative and also to scavenge the released hcl in amidation .
we also found that using an ionic liquid ( 1-methyl-3-propyl imidazolium bromide ) as the solvent of polymerization can cause some difficulties in purification , so it is an unsuitable polymerization media .
all of the very probable atactic polymers were obtained from an inexpensive starting material in quantitative yields with moderate inherent viscosities ( 0.150.42  dl  g ) and optical rotation ( 28.12 to 48.56 ) . as there is no obvious regioselectivity between alpha and epsilon amino groups of the lysine ester during the polymerisation step
then random orientation of lysine moieties along the polymer backbone can be predicted and the concept of  tacticity " can not be addressed in this research .
head - to - tail regiorandomness may likely affect some physical properties of the polymers such as crystallinity .
the formation of pis was confirmed by ir and h nmr spectroscopy and elemental analysis . as an example , the ir of pi1 showed the c = o asymmetric stretching of imide group , the c = o symmetric stretching of imide and ester groups at 17741680  cm , c 
n stretching at around 1386  cm , and c  o stretching at 1120  cm .
all of these pis exhibited strong absorption at around 1380 and 720  cm , which shows the presence of the heterocyclic imide groups ( figure 1 ) .
as an example the h nmr spectrum of pi1 is presented in figure 2 which shows peaks that confirmed its chemical structure ( h nmr ( dmso - d6 , ppm ) : 1.26 ( 2h ) , 1.41 ( 3h ) , 1.761.83 ( 2h ) , 2.33 ( 2h ) , 3.74 ( 2h ) , 4.23 ( 1h ) , 4.87 ( 2h ) , 8.068.29 ( 2h ) ) .
the formation of pas was confirmed by ir and h nmr spectroscopy and elemental analysis . as an example , the ir of pa4 showed the n  h stretching of amide group at 3423  cm , the c = o stretching of amide and ester and also the n 
h bending of amide groups at 17271615  cm and the c  o stretching at 1118  cm ( figure 3 ) . as an example
the h nmr spectrum of pa4 is presented which shows peaks that confirmed its chemical structure ( figure 4 ) .
the elemental analyses results are also in good agreement with calculated / expected percentages of carbon , hydrogen , and nitrogen contents in the polymer - repeating units .
the resulting homogenous glassy compound films were isolated by adding methanol / h2o ( 80  :  20 ) and triturating , followed by filtration .
transparent , flexile , and tough films of these polymers were obtained which showed good mechanical strength of the films and consequently high molecular weight .
wide - angle x - ray diffraction patterns of pi1 in the region of 2 = 570 at room temperature indicate 2030% of crystallinity .
tga technique shows moderate to good thermal stability for these polymers ( table 1 ) .
for example the tga / dtg spectrum of pi1 presents t5% and t10% at around 240c and 310c , respectively .
these polymers can be partially hydrolyzed to present the pendent carboxylic acid groups ( ion - exchangeable polymers ) .
one of the major objectives of this work is to study the solubility and the versatility of these polymers by incorporating the soft segment in the polymer backbone .
the solubility of these polymers was tested qualitatively in various solvents and the results are summarized in table 2 .
five new chiral polyamides and polyimides incorporating ethyl l - lysine ester have been synthesized from an inexpensive starting material by usual solution polycondensation method .
the resulting polymers are identified spectroscopic methods such as ft - ir , uv - vis and h nmr spectroscopy and elemental analysis .
the polymers are characterized by yield of reaction , inherent viscosity , wax diffraction , and specific rotation .
 ethyl l - lysine dihydrochloride was reacted with three different dianhydrides to yield the poly ( ethyl l - lysinimide)s ( pi13 ) ; it was also reacted with two different diacyl chlorides to yield the poly ( ethyl l - lysinamide)s ( pa4 - 5 ) . 
 the resulting polymers have inherent viscosities in the range of 0.15 to 0.42  dl  g1 . 
 these polymers are prepared from an inexpensive starting material and are optically active , potentially ion exchangeable , semicrystalline , thermally stable , and soluble in polar aprotic solvents such as dmf , dmso , nmp , dmac , and sulfuric acid . 
 all of the above polymers were fully characterized by ft - ir and 1h nmr spectroscopy , elemental analysis , wax diffraction , tga , inherent viscosity measurement , and specific rotation . 
1. Introduction
2. Material and Methods
3. Results and Discussion
4. Conclusions