Rigid rod polymers with flexible side chains
`Synthesis, structure and phase behaviour of
`po ly(3-n-a I kyl-4-oxybenzoate )s*
`
`R. Stern, M. Ballaufft. G. Lieser and G. Wegner
`Max-Planck·fnstitut fiir Polymerforschung, Postfach 3148, 65 Mainz, Germany
`(Received 26 February 1990; revised 31July1990; accepted 31 July 1990)
`
`The synthesis of poly{3·n-alkyl·4·oxybenzoate)s (PAOB·n) with n= 3-18 is reported. The sulllcient solubility
`of these comb-like polymers with stiff.chain backbones allows the determination of the Kuhn length
`(l00-200A). The unit cells could be determined for PAOB·11 with n=3 and 5. All PAOB·n form
`thermotropic mcsophases. For n=3 a nematic phase is found. For n=S there is a transition from a
`smectic·like, layered mesophase to a nematicmesophase. PAOB-n with n~6 solely form layered mesophases.
`Except for n=3, all PAOB-n exhibit a transition to the isotropic state. The transition temperature is
`lowered monotomically with increasing n.
`
`(Kt)'llords: rigid rod polymer; synch~ls; pb•se heha\iour)
`
`The synthesis of the mono1ners, the 3-n-alkyl-4-
`hydroxybenzoic acids (I-11), proceeds along the following
`lines: the monomer bearing the propyl substituent (1-3,
`11=3) is easily available from the 3-allyl-4-hydroxybenzoic
`acid 9 through catalytic hydrogenation at atmospheric
`pressure. The monomers bearing longer 11-alkyl chains
`(1-5 to 1-18) are obtained through a Fries rearrange(cid:173)
`ment 10 of the respective 0-acylated 4-hydroxybenzoic
`acids (2-n) and subsequent Clemmensen reduction of the
`ketones 3-11 (Schen1e 1). The polycondensatiori of the
`monomers 1-11 is performed by heating the monomer
`with an excess of acetic anhydride (cf. ref. 3).
`
`EXPERIMENTAL
`/>.faterials
`All chemicals were purchased from Merck or Fluka.
`They were used without further purification unless
`otherwise stated. All solvents used were of p. a. quality;
`1, 1,2,2-tetrachloroethane, phenol and o-dichlorobenzenc
`e1nployed as solvents for viscosity measurements were
`distilled prior to use.
`
`Synthesis of nwnon1ers
`J,3-Propyl-4-hydroxybenzoic acid (l-3). The 3-allyl-4-
`hydroxybenzoic acid was synthesized through Claiscn
`rearrangement of ethyl-4-allyloxybcnzoate which was
`prepared from ethyl-4·hydroxybcnzoate9
`• Hydrogenation
`using palladium on charcoal as catalyst and subsequent
`saponification in 30°/o aqueous sodium hydroxide solution
`led to 3-propyl~4-hydroxybenzoic acid. The monomer
`
`INTRODUCTION
`Rigid rod polymers usually exhibit very low solubility
`and melting points far above the temperatures of thermal
`decomposition. In a number of recent publications it has
`been shown that flexible side chains appended to the rigid
`backbones lower the melting point and increase the
`solubility in a systematic fashion 1
`• Most of the fully
`aromatic systen1s studied so far are ·composed of rather
`synlmetric repeating units, i.e. the different conformers
`of these polymers exhibit nearly the same shape. Asym~
`metric monomers, on the other hand, should cause a
`further disturbance of crystallization because of the vast
`number of shapes generated by different confonncrs. In
`this work we present a con1prehensive study of the
`poly (J-11-alk y 1-4-ox y bcnzoa te )s( PA 0B·11)
`
`as an example of a comb-like polymer composed of
`asymntetric repeating units. The number of carbon aton1s
`n in the side chains is varied between 3 and 18, thus
`PAOB-12 is poly(J-dodecyl-4-oxybenzoate). The choice
`of poly(4-oxybenzoate) as the stiff backbone derives from
`the fact that this polymer has already been the subj~t
`7
`of a number of exhaustive studies 2-
`• Hence the influence
`of the side chains on the structure can be asse!i!ied in
`detail by comparing the results found here with the data
`obtained on the unsubstituted poly(4-oxybcnzoate). To(cid:173)
`gether \Vi th a previous investigation 8 of defined oligomcrs
`of PAOB-3 the present study aims at a full understanding
`of the structure and the phase behaviour of these
`comb·like polyesters.
`
`• Part of the PhD Thesis of R. Stern
`t To whom oorrespondence should be addressed. Present addrcs.s:
`Polymer-Institut der UniVersitiil Karlsruhe, Kaiserslr. 12, 7500
`Karl>ruhe, Gennany
`0032-3861/91/112096--10
`© 1991 Bucterworth-Heinemann Ltd.
`2096 POLYMER, 1991, Volume 32, Number 11
`
`Sch~me I
`
`OH ~
`rAY -R
`Y' 21 NoO~ '9'
`
`o-tR'
`~ OAtCt
`
`COOEt
`
`COOH
`
`,
`
`OH
`Zo/HCI &R
`
`Hg Y'
`
`COOH
`
`Roxane Labs., Inc.
`Exhibit 1023
`Page 001
`
`

`

`T1ble I Melting point~ and elemental analyses of the 3-n-alky!-4-
`hydroxy~nzoic acids (l-n)
`- - - - - - ------------
`Cale.
`Found
`--
`-
`fl(%)
`
`C(%)
`
`H {o/o)
`
`-
`Cl%)
`
`Melting
`point
`CC)
`
`3
`
`'
`
`6
`10
`12
`14
`16
`18
`
`~------
`
`115-118
`126-127
`100---lOl
`103-104
`98-99
`JO! -!02
`100-102
`100---101
`
`666-l
`69.20
`70.23
`73.33
`74.45
`75.39
`76.18
`76.86
`
`6.73
`7.76
`8.18
`9.43
`9.89
`10.26
`10.58
`10.86
`
`66.58
`69.39
`70.11
`73.46
`74.38
`75.53
`76.31
`76.91
`
`6.76
`7.75
`8.14
`9.26
`9.77
`10.14
`10.36
`10.77
`
`1H n.m.r. (acetone): J=0.89 (t, CH 1Cl::h), J .2-1.7 (m, ·(CthJ,-), 2.69
`(t, Ar-CU 1-), 6.93, 7.72 (d, Ar-8), 7.82 (s, Ar-UJ
`
`T•bl:e 2 11elting points and elemental analyses of the 3-(n-alkyl-2-
`one)-4-hydro:q·benzoic acids (3--u)
`
`t.telting
`point
`('C)
`
`191-193
`185-187
`179-180
`174-176
`173-175
`168-170
`
`"
`6
`10
`12
`14
`16
`18
`
`Elemental analysis
`
`Cale.
`
`Found
`
`C(%)
`
`H ('%)
`
`C(%)
`
`H (%)
`
`-----------~-
`
`66_08
`69.82
`71.20
`72.36
`73.35
`74.20
`
`6.84
`8.29
`8.82
`9.27
`9.66
`9.98
`
`66.13
`70.00
`71.32
`72.22
`73.57
`73.07
`
`6.71
`8.13
`8.70
`9.13
`9.53
`9.90
`
`1H n.m.r. [trifluoro:u:etic acid): ,)=0.95 (t, CH 1C!:J 3 ), 1.2-2.2 (m,
`-1Clj 1 ).--). J.24 (t, COCU 1CH 2 ). 7.18 and 8.34 (d, Ar-tl). 8.81 (s.
`Ar-8)
`
`1-3 was purified from H 20 and dried carefully prior to
`use. The overall yield of the four-step reaction was 45o/o.
`The melting point and the cle1nental analysis of l ·3 is
`given in Table I.
`
`Synthesis of 1110non1ers 1-5 to 1-18. The ethyl-4~
`alkanoyloxybenzaotcs 2-5 to 2--18 were prepared by
`reacting ethyl-4-hydroxybenzoatc with an excess of the
`respective acid chloride according to
`the standard
`procedures given in the literature 11 . The Fries rcarrange(cid:173)
`ntent of 2-11 was achieved in the following way {cf. ref.
`10): 0.3 mol of 2-11 was dissolved in 500 ml CS 2 and
`1.2 n1ol AICl3 were added in small portions leading to a
`slightly exothern1ic reaction and evolution of HCJ. After
`the last addition the mixture was refluxed for 3 h. Then
`the solvent was distilled off and the remainder heated to
`140-160°C followed by evolution of HCl and strong
`foatning. After 2 h and cooling to roo1n temperature
`800 ml H 20 were added and subsequently 160 g NaOH
`with caution. The n1ixture dissolved upon heating to
`1 l0-120°C and the resulting ketone 3-11 could be isolated
`by acidification with 400 ml concentrated HCI. Purifica(cid:173)
`tion was achieved through recrystallization from ethanol,
`toluene or chlorofonn (yields 40-45°/o). Table 2 shows
`the melting points and the elemental analyses of 3-5 to
`3-18.
`The Clemmensen reduction was carried out in the usual
`way fo!lowing references 10 and 11: 0.1 mol 2-11 was
`refluxed for 24 h in 350 nil of a mixture of H 20/ethano!jHCl
`(1:1:2) with zinc amalgan1 prepared from 200g zinc
`powder 11
`• During this time 10 n1l of concentrated HCI
`were added several tin1es. The resulting 1-n was isolated
`
`Rigid rod polyn1ers: R. Stern et al.
`
`from the cold mixture by extraction with diethyl ether.
`Analysis by 1 H nuclear magnetic resonance (n.tn.r.)
`spectroscopy demonstrated that the raw materials still
`contained a side product having a double bond in the a
`position of the alkyl side chain. For further purification
`20 g of the raw material were dissolved in 300 111\ ethanol
`and hydrogenated after addition of 0.5 g palladium on
`charcoal (10°/o) at 50°C for 24-30 h. Then the catalyst
`was filtered off and the mono1ners J-11 were recrystallized
`three tilnes from CH 30H/H 20 or CHJOH (yields
`50-75%).
`
`Poly1nerization {cf. ref. 3)
`For the poly1ncrization reaction, 1.5-3.0 g of l-11 were
`added to 1.2 equivalents of acetic anhydride and refluxed
`under an atinosphere of argon at l 80~c for 30 min. Then
`the condenser was taken off and the acetic acid ren1oved
`by a slow stream of argon. \Vhile raising the temperature
`to 260"'C the evolution of acetic acid started again at
`-245"C. By variation of the reaction time from 45 min
`to 7 h poly1ners with different molecular weights could
`be obtained (Table 3). Purification of PAOB-3 was
`carried out by refluxing the polymer with acetone;
`polyesters with longer side chains were dissolved in hot
`chloroform and precipitated fron1 methanol. All poly1ners
`reported in this investigation gave satisfactory elemental
`analyses when taking into account the measured molecular
`weights and the respecti\•e end groups.
`
`Deterlllill(Jlion of 1110/eni/ar 11·eiyht throuf!h end group
`analysis
`According to Kricheldorf and Schwarz3
`, 20-30 mg of
`the polyester PAOB-11, -200 ntg 40°/o NaOD in 0 20
`and 500 n1g CD 30D were weighed carefully in a n.m.r.
`
`Table 3 Char.icterization of the PAOB-n
`
`Reaction time
`(min)
`180°C/260"'C
`Polymer
`--~- ------- --
`PAOB-3,I
`30/45
`PAOB-3,2
`30/60
`PAOB-3,3
`30/160
`PAOB-3,4
`30/240
`PAOB-3,5'
`30/240
`30/240
`30/360
`30/240
`30/360
`
`PAOB-6,1
`PAOB·6,2
`
`PAOB-5,I
`PAOB-5,2
`
`PAOB·lO,l
`PAOll-10,2
`
`PAOB-12,\
`PAOB-12,2
`
`PAOB-14,l
`PAOB·l4,2
`PAOB·\6,1
`PAOB-16,2
`PAOB-16.3
`PAOB·\6,4
`PAOB-16,5
`PAOJl.J6,6
`
`PAOB-18
`
`30/240
`30/360
`
`30/150
`30/300
`
`30/240
`60/240
`3-0/60
`30(120
`30/180
`J0/240
`30/360
`30/420
`60/180
`
`,,, ..
`
`2650
`3600
`6350
`20000
`12100
`4450
`7650
`
`3350
`1600
`4500
`10750
`3800
`24300
`6400
`8600
`2950
`5650
`7550
`7800
`!{)lllO
`13900
`13100
`
`0.3\0l'
`0.4<JOI
`1.620"
`0.8601
`
`0.096'
`0.180'
`0.290'
`0.350'
`0.485'
`
`DP"
`
`16
`
`"
`
`39
`123
`74
`23
`40
`16
`J7
`
`17
`41
`13
`84
`20
`27
`8
`16
`
`"
`
`23
`JO
`40
`
`"
`
`'Determine-ct by 11{ n.m.r. end-group analysis
`~ }.{easured in phcnol/o-dichlorobenzene (I:\) at 50°C
`'Measured in tet1achloroethane/o--<lichlorob<:nzenr (\:!)at 5-0'C
`4 Polymerized l'oith addition of 5 mnl"/~ 4-methoxyl-3-propylbenzoic
`acid
`
`POLYMER, 1991, Volume 32, Number 11 2097
`
`Roxane Labs., Inc.
`Exhibit 1023
`Page 002
`
`

`

`Rigid rod polymers: R. Stern et al.
`
`tube and heated to 50-60°C. The solution obtained was
`analysed by 300 MHz or 400 MHz 1H n.m.r. spectroscopy
`to yield the an1ount of end groups quantitatively (see
`below).
`
`Afetliods
`1H n.m.r. spectra were recorded with 80 MHz con·
`tinuous wave, 300 MHz Fourier transfonn (F1) and
`400 MHz FTspcctron1eters (Bruker A \V 80, AC 300 and
`\VM 400). Vapour pressure osmon1ctry (v.p.o.) was done
`at 50°C using toluene as a solvent (\Vescan 232 A,
`Corona). The concentration of the polyn1er was 2-10 g 1- 1•
`For polarizing n1icroscopy a Zeiss Fotomikroskop III
`equipped with a Leitz hot stage was used. Differential
`scanning calorimetry (d.s.c.) was done with a Perkin(cid:173)
`Elmer DSC-7 calibrated with indium and tin. Thermo(cid:173)
`gravimetric data were obtained by means of a TG 50 of
`Mettler under an atmosphere of oxygen or nitrogen
`e1nploying a heating rate of 10 K min- 1
`• The intrinsic
`viscosity of the polyesters was determined using an
`Ubbe!ohde capillary viscosimeter. All data arc mean
`values of at least four measurements corrected 1 3 according
`to Hagenbach. High performance liquid chrotnatography
`(h.p.J.c.) was carried out on Li Chrosorb RP 18 or Li
`Chrosorb diol columns (Knauer) using a 1nixturc of
`diethyl acetate and n-hcptane (1: 1) with ultraviolet (u.v.)
`detection at).= 254 nm. For gel permeation chromatog(cid:173)
`raphy (g.p.c.) 1011m Styragel columns (!Os, 103 and
`10 2, Polymer Laboratories) with
`tetrahydrofuran
`(1 ml inin- 1) as the inobile phase (u.v. detection at
`A.= 254 nn1) were used. \Vide-angleX-ray analysis (\VAXS)
`was performed using Ni-filtered CuKa radiation in
`reflection mode on a Siemens D 500 diffracton1etcr
`equipped with a hot stage. All diffractogran1s are
`uncorrected. Electron diffraction was done using a
`Philips EM 300 calibrated with thallium chloride. The
`density of polymer films and fibres was determined in a
`density gradient set up from 1nixtures of H 20 and
`Ca(N0 3h at room temperature.
`
`RESULTS AND DISCUSSION
`All polymers investigated were synthesized by the acetoxy
`method 3
`, i.e. by reaction of the unsubstituted hydroxy(cid:173)
`bcnzoic acid with acetic anhydride. Since the 1naxi1nun1
`ten1perature applied in the course of the polycondensation
`did not exceed 260°C, no side products as discussed by
`Economy and co-workers1 have been observed. The
`satisfactory degrees of polymerization achieved and the
`absence of any by-products to be detected in the analysis
`of the saponificated polyesters arc furthermore indicative
`of the absence of side reactions. Special care has been
`taken to remove the evolving acetic acid as well as excess
`acetic anhydride by a slow strca1n of argon. During the
`reaction small atnounts of a solid material sublimed out
`of the mixture. Analysis by infra-red (i.r.) and n.1n.r.
`spectroscopy unambiguously demonstrated this substance
`to be identical with the acctylated monon1er. In the c-ase
`of short side chains (11=3, 5, 6) the melt turned turbid
`after 40--120 min indicating the formation of a mesophase.
`For monon1ers having longer side chains the resulting
`n1elt became increasingly viscous during polycondensation
`but only turned turbid when cooled to te1nperatures
`below 200°c. As is obvious from Table 3 the degree of
`polymerization (DP) can be adjusted by the length of the
`
`2098 POLYMER, 1991, Volume 32, Number 11
`
`reaction time. The present data indicate that even higher
`molecular weights could be obtained if desired. However,
`raising the DP beyond the values given here resulted in
`difficulties when determining the molecular weight by
`end-group analysis (sec below).
`In contrast to the unsubstituted poly(4-oxybenzoate)3
`the PAOB-3 already exhibits sufficient solubility in
`mixtures like o-dichlorobenzene with tetrachloroethane
`or phenol. Polyesters bearing longer side chains 1nay be
`dissolved in toluene or chloroforn1. Therefore purification
`can be achieved through dissolution in these solvents
`and reprecipitation into n1ethanol. This finding is in
`accordance with observations on a number of other rigid
`rod polymers being sin1ilarly substituted by flexible side
`chains 1
`• It indicates that the side chains act as a 'bound
`solvent'. However, investigations of solutions of PAOB-
`16 in solvents like toluene lead to the conclusion that
`these polyesters still have a strong tendency for association
`in solution. This fact 1nay be also inferred from the
`fornullion of gels by these solutions at room tcn1pcraturc.
`Mixtures of strong polar solvents like o-dichlorobenzene
`and tetrachloroethane prevent the formation of such gels
`if the concentration is not too high. Up to now attempts
`to determine the molecular weight and the radius of
`gyration by light scattering have failed because of either
`strong association or s1nall refractive index incren1ent.
`Thus the DP of the polyn1ers had to be determined by
`1 H n.m.r. end-group analysis according to Kricheldorf
`and Schwarz3 . For this the magnitude of the triplet of
`the CH 2 group neighbouring the aromatic core of the
`monomer is compared to the signal of the acetic acid
`anion after saponification with Na0D/D 20. \Vhen
`evaluating the magnitude of the latter signal, a small
`triplet resulting from partial H-D exchange on the acetic
`acid has to be taken into account. By this method the
`nu1nber average DP could be obtained within 10% error
`for smaller molecular weights; higher DPs are determined
`with less accuracy. For PAOB-16 the DP thus 1neasured
`compares favourably with data derived from v.p.o. The
`DPs given by the latter n1ethod arc in general higher by
`10-15o/o which certainly can be assigned to association
`in solution. Therefore only DPs derived from end-group
`analysis are used in this work (cf. Table 3).
`It has been observed that substitution of the poly(4-
`oxybenzoate) backbone n1ay lower the thermal stability
`of the resulting poly1ners considerably 14
`• Thern1ogravi(cid:173)
`metric measuren1ents on the PAOR-11 conducted in
`nitrogen (10 K 1nin- 1 heating rate) showed these polymers
`to be stable up to ,..., 350°C. A residual weight loss at
`lower ten1peraturcs can be traced back to the onset of
`further polycondensation. Nevertheless the oxidative
`degradation of the side chains represents a severe
`constraint for the stability at elevated temperatures in
`the presence of oxygen. All thermogravimetric data
`obtained so far indicate the upper limit for \ong-ter1n
`stability in air to be at temperatures between 160°C and
`220°C. Polyesters having longer side chains are more
`susceptible to degradation. Hence, measurements at
`elevated te1nperatures have to be conducted in an inert
`atmosphere or in vacuo.
`Another point of great interest is the stiffne-ss of the
`1nain chain. Since the unsubstituted polyester is not
`soluble in any known solvent there are no experin1ental
`data on its persistence length. Calculations by Erman
`et a1. 1s using the rotational isomeric state model lead to
`the prediction of a rather rigid chain \Vith a persistence
`
`Roxane Labs., Inc.
`Exhibit 1023
`Page 003
`
`

`

`(':';,_)'
`
`lo I
`
`1SO
`
`soo
`
`ISO
`
`0
`
`+
`
`0
`
`+ +
`
`so
`
`100
`
`1SO
`
`100
`
`Figure l Bohdanecky plot of the intrinsic viscosities of PAOB-J 101
`and PAOB-16 ( +)
`
`length of the order of 700 A. However, these authors
`ren1ark that such a high value has to be regarded as an
`upper limit since torsional fluctuation about the ester
`bonds should lower it appreciably 16
`• Molecular dynamics
`calculations performed by Jung and Schtirmann 11 lead
`to a much smaller value of the persistence length ( -60 A)
`for this reason. Experimental data on similar polyamidcs
`are of limited use for settling this question since the values
`for the persistence length of these systems given by
`various methods arc not conclusive1. 1s. By virtue of their
`in1proved solubility in aprotic solvents the PAOR-11 arc
`n1uch better candidates for an expcriinental tesl of the
`above conflicting predictions. In the absence of reliable
`1neasuremcnts of the radius of gyration by light scattering
`data, the intrinsic viscosity [11] 1nay serve as a first
`estimate of the chain stiffness. Thus [11] has been
`measured for PAOB-3 in phenoljo-dichlorobenzcnc and
`for PAQB.16 in tetrachloroethane/o·dichlorobcnzene at
`50°C (cf. Tal1le 3). The dependence on temperature as
`well as the dependence on concentration is well-behaved
`for these systen1s \vhereas solutions of PAOB-16 in
`toluene and in chloroform did not lead to reproducible
`results (sec above). The resulting t\fark-Houwink relations
`aro ([>1] in di g- '):
`[>1]=6.95x 10- 2 M~· 06
`PAOB-3
`in phenol/o-dichlorobenzene at SO''C
`PAOB-16 [11]=2.87x l0- 2Af!· 1
`6
`in tetrachloroethane/o-dichlorobenzene at S0°C
`A quantitative interpretation of the data for [11] 1nay be
`given in tenns of the worm-like chain n1odel developed
`by Yan1akawa and Fujii 19
`• Based on this
`theory,
`Bohdanecky 20 has recently given a simple procedure for
`data evaluation leading to the following relation:
`(i\1 2 /[t/]) 113 =A"+ B,At 111
`
`where A" is a quantity depending on the hydrodynamic
`diameter d of the chain and B" is expressed by
`B"= Bo<I>O.!f l((r2 )o/Af);, i12
`where (r 2
`) 0 is the mean-square end-to-end distance, and
`the subscript oo indicates that the (r 2 )/M value obtained
`fro1n 8" is the random coil value.
`The quantity <1>0 ."" is the viscosity function for infinite
`chain length (¢ 0 ,.,, = 2.86 x 1023
`20
`• The quantity 8 0
`)
`varies between 1.10 and LOO and may be set to a 1nean
`
`Rigid rod polymers: R. Stern et al.
`
`value of I.OS at the present level of accuracy. Figure I
`shows a Bohdanecky plot of the present data. The weight
`a\•eragc 1nolecular weights ha\'e been calculated fron1 the
`data given in Table 3 by assuming a 1nost probable
`distribution.
`The Kuhn length is calculated as /K=(r 2)/N/u where
`N=Af/Afu with A1u and lu being the mass per unit length
`and the length of the monomer unit, respectively. The
`latter quantity is given by 6.2 A in good approximation
`(see below). From these data and the slope of the
`respective curves in Figure J, /K is -90 A for PAOB-3
`and -190 A for PAOD-16. The intercept A may be used
`to yield first esti1nates of the hydrodyna~ic radius r
`20
`according 10
`:
`d'
`A'
`0
`where tl,=<i/IK is the reduced hydrodynamic radius and
`tl:/A 0 is related to <1, by 2o
`ln(d; I A0 )=0.! 73 + 2.158 ln(d,)
`!s approximated 7 unity, we obtain for PAOB-3 a value
`If the partial specific volun1e ii of the polymer in solution
`
`=(4'1>0 .. :c1.21 SnJ\f A)(ii/A~)B!
`
`, and for PAOB-1611-13A. Similar
`111 the range 7-8
`values have been found recently for substituted cellulose
`polyn1ers 21 and seem to be quite reasonable. One has to
`bear in n1ind that these values have been derived under
`20
`a number of stringent assu1nptions 19
`. On the molecular
`•
`level the poly1ner chain is approximated by a cylinder
`which 1nay be rather questionable when looking at the
`structure of PAOB-11 with 11 > 6. Hence, these data should
`be only regarded as rough estimates and the present
`investigation of chain stiffness 1nust be certainly supple-
`1nented by other methods.
`Despite t~ese proble1ns it is clear that our findings data
`arc inore 1n support of the prediction of Jung and
`Schtirmann 17
`• Krigbaum and Tanaka 22 recently found
`IK. values of similar n1agnitude for poly(phenyl p·
`phenyleneterephthalate) by a variety of methods. Thus
`the present data indicate that the stiffness of the fully
`aron1atic polyester chain is significantly smaller than
`anticipated by the calculations neglecting the effect of
`bond-angle fluctuations. The surprising fact that the
`stiffness seems to increase with increasing length of the
`side chains 1nay be explained 23 by the notion that steric
`interactions between bulky side chains lead to a significant
`rise in IK. In the absence of further information on the
`shape of the PAOB-11 chain as revealed by small angle X-ray
`or neutron scattering no finn conclusions can be drawn.
`
`Phase behaviour of PAOB·3
`In the following it will beco1nc obvious that the phase
`behaviour of PAOD-3 is significantly different from the
`phase behaviour of PAOR-11 bearing longer side chains.
`In the case of PAOB-3 the n1ain chains control the
`structure and thcnnal transitions. For longer side chains
`the vohunc fraction of the main chains is decreasing and
`the most favourable arrangement of the side chains
`detennincs the packing of the polyn1er in the solid state
`as well as in the mesophase.
`
`Solid state. Figure 2 shows the \VAXS patterns of
`PAOB-3 recrystallized from the n1ell (Figure 2a) and
`fro1n dioxane {Figure 2b ). From this it is evident that
`two different modifications have been forn1ed through
`
`POLYMER, 1991, Volume 32, Number 11 2099
`
`Roxane Labs., Inc.
`Exhibit 1023
`Page 004
`
`

`

`Rigid rod polymers: R. Stern et al.
`a
`
`---~
`
`2 a JO
`
`10
`
`15
`
`10
`
`15
`
`b
`
`" c
`" -e
`" ?:'
`" c • c
`
`5
`
`10
`
`15
`
`20
`
`25
`
`JO
`
`18
`
`Figure 2
`\Vidc·angle X-ray diffractograms (uncorr.xted) of PAOB-3
`recrystalli1.ed from the melt (a) and from dioxarte (b)
`
`Figure 3 X-ray fibre diagram of PAOD-3 drawn from the melt
`(modifications Ta and lb). The Miller indires are gh·en in Table 4
`
`the different conditions of crystallization. The \VAXS
`patterns furthermore show both modifications to have a
`high degree of crystallinity. Melt-crystallized san1ples
`(referred to as modification I fibres) with a high degree
`of orientation 1nay be drawn. The resulting fibre diagram
`is shown in Figure 3.
`The distance between the layer lines demonstrates
`that the identity period along the chain consists of two
`oxybenzoate monomer units. This is in accordance with
`the crystal structure of the din1eric model compound 8 in
`which the planes of subsequent benzene rings are rotated
`through an angle of 90° with respect to each other. The
`
`2100 POLYMER, 1991, Volume 32, Number 11
`
`absence of meridional reflections with odd 1 indices
`indicates a 21 or a 42 helical structure of the main chain.
`An additional feature is the presence of two series of
`reflections on the different layer lines leading to two
`hyperbolas per layer. This can be seen tnost clearly from
`the splitting of the 002 reflection. Variations of the
`c-parameter within a range of 12.4-12.9 A were observed
`in earlier work on poly(4-hydroxybcnzoic acid) and were
`shown to be a function of the DP 3
`• All reflections found
`in this work nuiy be indexed satisfactorily in tenns of
`two tetragonal modifications, Ia and lb, which differ only
`with regard to tbc c vector of the unit cell. Tcible 4 gives
`the Bragg distances and their respective indices.
`The presence of two very sin1ilar 1nodifications Ia and
`
`Titble 4 Calculated and ob>erved X-ray refleetions of modifications
`la, lb and rl of l•AOB-3
`
`Reflection
`index
`(h kl)
`
`Calculated
`~,\icing
`
`Observed
`spacing
`{A)
`
`Position/modific.ation
`
`Tetragonal modifications Ia and lb, a=b= 16.95 A, c= 12.36 A (la),
`c=t2.86A (lb)
`I JO
`020
`
`11.99
`8.48
`
`Equator (a, b)
`
`I 1.99(vs)
`8.47(vs)
`7.16(vw)
`5.96(vw)
`5.34(s)
`4.70(s)
`4.24(,·s)
`4.12(m)
`3.99(s)
`3.78(m)
`3.34(w)
`
`5.99
`5.36
`4.70
`4.24
`4.11
`4.00
`3.79
`3.32
`
`6.46
`4.92
`4,39
`
`5.17
`4.42
`4.02
`3.6-1
`3.22
`
`6.18
`5.81
`4.79
`4.05
`
`6.43
`5.!2
`4.JS
`
`120
`130
`230
`040
`140
`·330
`240
`150
`I 2 I
`13 I
`231
`OJI
`2 JI
`041
`24 I
`I 5 I
`001
`0 I 1
`112
`131
`002
`032
`222
`0 I J{a}
`OJJ/113(b)
`02 )(a)
`023/123(b)
`004
`
`4.0(a)
`4.16/4.M(b)
`J.71(o)
`3.83/J.7J{b)
`3.0'J(a)
`3.22(b)
`- - - - - - -
`Reflection
`Ca!C1Jlated
`index
`s~acing
`(hkl)
`{)
`
`6.SO(n\')
`4.86(m)
`4.28{m)
`
`5.ll{m)
`4.50(m)
`4.03(vw)
`3.68(w)
`3.19(vw)
`
`6.18{s)
`5.85(w)
`4.69(w)
`3.95(\'\\')
`6.43(s)
`5.0S(vw)
`4.50(\'W)
`
`4.06(m)
`
`!st layer line: a
`
`1st la}·cr line: b
`
`2nd layer line: a
`
`2nd la)·er line: b
`
`3.77(m)
`
`3rd !a)'er line
`
`3.ll(w)
`
`4th layer line
`
`Observed spacing (A)
`
`X-ray
`
`Ekctron diffraction
`--------
`
`Orthorhombic modification JI
`a= 14.20 A, b=9.60A,c=12.48 A
`110
`7.95
`7.94(s)
`200
`7.10
`7.07(m)
`002
`6.24
`6.24{w)
`
`020
`310
`220
`420
`
`4.80
`4.25
`3.98
`2.85
`
`4.72(w')
`4.22(s)
`3.96(s)
`
`7.99(s)
`7.l2(s)
`
`4.83(w)
`4.25(s)
`4.00(s)
`2.87(w)
`
`•Shoulder of 3 I 0 reflection
`Abbreviations: vs. \'erystrong;s, strong; m, medium; w, weak; vw, \·cry
`wc.ak
`
`Roxane Labs., Inc.
`Exhibit 1023
`Page 005
`
`

`

`Rigid rod polyrners: R. Stern et al.
`
`by material with lower degrees of polymerization. Since
`crystallites of stiff polyn1crs usually have dimensions
`which arc n1uch larger in the direction perpendicular
`rather than parallel to the chains4
`, these crystallites will
`lie ft.at on the 00 l surface. Thus with this geometry
`(electron beam perpendicular on the crystal surface) only
`Ii k 0 reflections will be monitored. Figure 5 shows the
`result whereas Table 4 gives the d-spacings of modification
`[J which can be indexed by an orthorhon1bic unit cell
`(a~ 14.20 A, b ~ 9.60 A, c ~ 12.48 A, four chains per unit
`cell). The 6.24 A reflex which is only visible in the \VAXS
`diffractogran1 (Figure 2b) is interpreted as the 002 reflex
`in analogy to modification I. The length of the repeating
`unit (12.48 A) is the mean value of the data derived from
`the ds and tra11s chains (see above). The X·ray density
`(l .27 g cni- 3 ) is similar to values (l .2-1.3 g cm - 3 ) found
`for the solution.crystallized oligomers 8 •
`
`Elevated ten1peral11res. All PAOB·3 samples exhibit a
`broad bimodal n1elting peak with temperatures depending
`on molecular weight. Since the specimens ha,·ing a
`smaller DP still contain reactive end groups, heating up
`in
`leads
`to further polycondensation. Second runs
`consequence exhibit higher melting temperatures. If the
`materials arc annealed at the temperature of the lower
`1nelting peak a second run only gives a single sharp
`melting transition at T=294°C and no indication of a
`glass transition (Figure 6).
`This value nearly coincides with the melting point of
`the oligomers extrapolated to infinite molecular weight 8
`•
`It is thus concluded that the crystallinity in the annealed
`1naterial is very high. This finding is already obvious from
`the fibre diagra1ns of melt·drawn specimens. In this
`context it is interesting to note that the heat of fusion
`) is approxi1nately equal to the value found 3 for
`{36 J g- 1
`the high temperature solid-solid transition (38 J g- 1 ) of
`the unsubstituted poly(4·oxybcnzoatc). \VAXS dilfracto(cid:173)
`grams and polarizing microscopy however, revealed that
`PAOB-3 is transforn1ed into an ordinary nematic phase.
`No transition to the isotropic fluid occurred within the
`accessible range of ten1perature. The extrapolation of the
`transition
`temperatures obtained from oligo1ners
`to
`infinite nlolecular weight indicates8 the Tn1 of the polymer
`to be located at ,...,4]0''C, i.e. where thermal decomposition
`pre\•ails.
`
`" 100
`E
`' ~
`.9
`
`50
`
`o.o~~-~-~~-~-~-~___,
`lOO
`0
`100
`200
`300
`
`T/°C
`Figure 6 Differential £canning calurinietry ana\y~is of an annealed
`sample of PAOB-J at 20 K min-· i
`
`POLYMER, 1991, Volume 32, Number 11
`
`2101
`
`cis chain
`
`Figure 4 Representation of the trans and cis conformers of the
`p·oxybenlOate backbone together with the cakula!ed c values (modifi·
`cations la and lb)
`
`Figure 5 Elet:lron diffraction of PAOfJ.J recrystallized from dioxane
`(modifirntion H). Talile 4 gh·es the Miller indi~s
`
`lb 1nay be due lo the formation of crystals with different
`conformalion of the n1ain chains (Figure 4). The length
`of the identity period along the c direction can be
`calculated fro1n the bond lengths and angles derived from
`the crystal structure or the dimer. This leads to 12.60
`or 12.36 A for the trans and cis chains, respectively.
`The values derived fron1 the analysis of the fibre diagram
`(Ia: 12.36; lb: 12.86) compare favourably with these
`deductions if the slightly higher value of c found for
`lb is explained in tenns of s1nall distortions of bond
`angles. Also the mean value of the theoretical density
`(1.190 g cm·· 3 ) is in accordance with the experitnental
`result (1.!83gc1n- 3
`). The only reflection not being
`indexed by the above unit cell corresponds to a Bragg
`distance of 7. l 6 A and is the strongest one of a series of
`reflections (21.3, 10.7, 7.1 ). The rnost probable explanation
`is the assun1ption of a third orthorhotnbic
`for this
`modification le which scen1s to be forn1ed during solid
`state polycondcnsation (cf. ref. 4 for similar observations
`on the unsubstituted polyester).
`In the case of solution-crystallized san1ples {er. Figure
`2b) the corresponding structure may be elucidated by
`electron diffraction applied to srnall crystallites formed
`
`Roxane Labs., Inc.
`Exhibit 1023
`Page 006
`
`

`

`Rigid rod polymers: R. Stern et al.
`
`along the chain consists of two monomer units. However,
`there is no splitting into cis or trans segments, the chains
`seem to contain both fonns in statistical sequence. A
`con1parison with modification II of PAOB·3 shows the
`nlagnitude of b to be identical. From Table 5 and Figure
`7b it is obvious that the gradual loss of long-range
`correlation does not allow an una1nbiguous assignment
`of the unit cell o\ving to the absence of 1nixed reflections.
`On the other hand, all reflections of PAOB-6 can be
`satisfactorily indexed in terms of modification III (cf.
`Table 5). No new feature appears in the fibre diagran1s
`
`Table 5 Calculated and observed X-rny reflectiom of orthorhombic
`mo<lific.ation III (PAOB-5 to PAQB.J8) a=· ·. b=9.6 A, c"' 12.6 A
`
`Reflection
`inde~
`(hk I)
`
`PAOB-5
`JOO
`200
`300
`400
`020
`220
`33 0
`
`Calculated
`sp~cing
`<A>
`
`17.80
`8.90
`5.93
`4.45
`4.80
`4.22
`2.82
`
`02 1/3 11
`221
`321/4 I I
`002
`012/202
`212
`302
`022/312
`022/122
`004
`4.6 A {\'W,d): halo
`PAOB-6
`JOO
`200
`300
`400
`500
`
`4.5/4.6
`4.0
`3.6/3.8
`6.3
`5.3/5.1
`4.5
`4.3
`3.8/3.9
`3.8/J.7
`3.15
`
`19.80
`9.90
`6.60
`4.95
`196
`
`021/401
`lll
`002
`11 2
`004
`4.6 A {w,dl: halo
`
`4.5/4.6
`4.1
`6.2.5
`5.10
`
`3.15
`
`PAOB-10
`100
`200
`400
`500
`
`26.80
`13.40
`6.70
`5.36
`
`002
`
`6.25
`
`004
`4.1:5A (w,d): halo
`
`3.15
`
`Obsen'ed
`spacing
`(A)
`
`17.75(vs)
`8.90(m)
`5.92(m)
`4.43(m)
`4.80(s)
`4.34(s)
`2.86(w)
`4.45(w,d)
`
`4.6(m)
`4.0{vw)
`3.7(vw)
`
`6.3(s)
`5.2{vw)
`4.7(m)
`4.3{vw)
`3.9(m)
`3.7(vw)
`3.l{m)
`
`19.SO{vs)
`9.91{vw)
`6.60{w)
`4.96(m)
`4.00(vw)
`4.47(m,d)
`4.60(w)
`4.0