Structure, crystallization and morphology of poly (aryl ether ketone ketone)*

Transcription

1 Structure, crystallizatin and mrphlgy f ply (aryl ether ketne ketne)* KennCrwin H Gardner?~, Benjamin S Hsia, Rbert R Mathesn Jr~ and Barbara A Wd N Central Research and Develpment, Fibers and Plymers, I DuPnt de Nemurs, xperimental Statin, Wilmingtn, Delaware , USA (Received 1 May 1991; revised 24 July 1991; accepted 19 August 1991) The structure, crystallizatin and mrphlgy f ply (aryl ether ketne ketne)s (PKKs) prepared frm diphenyl ether (DP), terephthalic acid (T) and isphthalic acid (I) and having different T/I ratis have been investigated As prepared, these cplymers can be thught f as cnsisting f 'phthalate diads' cntaining -DP-T DP-T- (TT) and/r-dp T-DP-I- (TI) Melt-crystallized PKKs (all T/I ratis) frm a structure similar t that bserved in ther ply(aryl ether ketne)s (frm 1 ; a = 0769 nm, b = 0606 nm and fibre axis c = 1016 nm) Hwever, depending n cmpsitin, bth TT and TI crystals were bserved All PKK materials grw in the frm f spherulites having negative birefringence The incrpratin f isphthalyl mieties is bserved t increase the chain flexibility and decrease the rate f crystallizatin The equilibrium melting temperatures f varius PKKs were estimated using the Hffman Weeks apprach, and shwed a linear crrelatin with the meta ismer cntent In cntrast t ther ply(aryl ether ketne)s, a frm 2 crystalline mdificatin (a = 0393 nm, b = 0575 nm and c = 1016 nm) can be induced either by expsure t slvents r by cld crystallizatin The tw crystalline mdificatins differ frm each ther in the placement f the chains and, cnsequently, the interchain interactins (Keywrds: ply(ether ketne ketne); structure; crystallizatin; mrphlgy; eplymer; X-ray diffractin; thermal analysis; electrn micrscpy) INTRODUCTION High-temperature, high-perfrmance thermplastic ply- (aryl ether ketne) s are f scientific interest The chemical structure and linkage cmpsitin f sme members f the ply(aryl ether ketne) family are given in Table 1 These plymers are members f a family that can be schematically represented as -P-Li- where P is a 1,4- r 1,3-1inked phenyl grup and Li signifies either an ether r a ket linkage The effect f ket cntent n the crystallizatin f ply(aryl ether ketne)s has been discussed ~ ~ ther linkages have a relatively shallw rtatinal cnfrmatin energy barrier and thus are mre flexible than a ket linkage 5 The additin f ket linkages inevitably increases the stiffness f the mlecule, as reflected by the increase f glass temperature 6 An increase f ket linkages als enhances the packing efficiency f the unit-cell structure, thereby prducing a larger crystal binding (r chesive) energy r a higher melting temperature 1 (Figure 1) Pwder diffractin patterns f three family members are shwn in Figure 2 The diffractin patterns fr ply (aryl ether ether ketne) (PK), ply (aryl ether ketne) (PK) and ply (aryl ether ketne ketne) (PKK(T/I = 100/0)), all crystallized frm the melt, are similar in kind but exhibit a small * Paper presented at 'Plymer Physics', 3-5 April 1991, Bristl, UK t T whm crrespndence shuld be addressed Central Research and Develpment Fibers II Plymers shift in peak psitins t lwer angle with increase in ket cntent This shift is reflected in the systematic changes in the unit-cell parameters (Figure 3) The crystalline structures f ply (phenylene xide) (PPO), PK and PK have been previusly described 1 4,7-~ ~ The ply(aryl ether ketne) that has previusly received the mst attentin is ply(aryl ether ether ketne) PK can be crystallized frm dilute slutin, frm the melt, r frm quenched samples expsed t lwmlecular-weight slvents Slutin-crystallized PK has recently been studied by Lvinger et al ~2 They cncluded that similar mrphlgies were fund fr slutin-crystallized and melt-crystallized specimens Bth rutes prduce spherulites with narrw, elngated lamellae, that grw radially in the crystallgraphic b-axis directin In this structure, the c axis lies parallel t the spherulite plane and the a axis lies vertical t the plane Since the anistrpy f plarizability f a PK chain is psitive (ac > ab) 16, the abve mlecular arrangement shuld prduce a negative birefringence in spherulites This is cnsistent with many experimental bservatins ~3'a6 The mrphlgy f melt-crystallized PK specimens depends strngly n the thermal histry, the mlecular weight and the degree f crsslinking ~3-~7 This behaviur is similar t that f ther semicrystalline plymers PK exhibits a lwer degree f crystallinity (less than ca 40%) than plymers such as plyethylene r plyxymethylene, pssibly due t the high rigidity f the chain ~s /92/ Butterwrth-Heinemann Ltd POLYMR, 1992, Vlume 33, Number

2 Structure, crystallizatin and mrphlgy f PKK: K H Gardner et al Table 1 Chemical structures f members f the ply(aryl ether ketne) family and their ket cntents Structure Name Ketne (%) - -- PPO 0 c-- PK 33 L> -C> -O-' In this wrk, we discuss sme general aspects f the crystallizatin and mrphlgy f PKKs having different T/I ratis Tw issues will be addressed One is the characterizatin f the tw crystal structures Anther is the effect f T/I rati n features f the crystallizatin behaviur such as melting temperature, duble-melting behaviur, crystallizatin kinetics and recrystallizatin This wrk is based n X-ray diffractin and thermal analysis studies Mrphlgy will be discussed in terms f the spherulitic structure btained frm the melt as revealed by electrn micrscpy fllwing permanganic etching, ptical micrscpy and small-angle light scattering The thermal histry effect n the mrphlgy will als be discussed t_ ~ 200 f Tm B XPRIMNTAL Materials and preparatin PKK samples used were develpmental grade plymers made by Du Pnt The plymers were prepared frm diphenyl ether (DP), terephthalic acid (T) and isphthalic acid (I) in a tw-step prcess and have a generalized chemical structure as fllws, but differ frm each ther by their para/meta phenyl ismer ratis, ie 100 i i i % Ket Figure 1 Plt f transitin temperatures vs ket cntent The full symbls represent transitin temperatures fr all-para ply(aryl ether ketne)s taken frm the literature The pen symbls represent transitin temperatures fr PKK samples with different T/I ratis Nn-crystalline PK specimens can be crystallized by expsure t interactive slvents such as methylene chlride The presence f slvents increases chain mbility and s facilitates crystallizatin The crystalline phase bserved in slvent-crystallized PK is apparently identical t that derived frm melt r slutin a9-23 A unique member f the high-perfrmance ply- (aryl ether ketne) family is ply(aryl ether ketne ketne)22 26, PKK, which is prepared frm diphenyl ether (DP), terephthalic acid (T) and isphthalic acid (I), has a higher percentage f ket linkages (67%) than ther ply(aryl ether ketne)s The all-part-linked plymer (T/I rati 100/0) has a high glass transitin temperature (Tg ~ 165 C), but melts t clse t its thermal degradatin temperature t be f practical use By incrprating meta linkages int the PKK structure via the isphthalyl mieties, the melting temperature can be lwered int a usable range while retaining a high glass temperature (Figure 1) Unlike PK, which has a single crystalline mdificatin, PKK shws tw stable crystalline plymrphs : frm 1, the cnventinal structure, and a new structure (frm 2) btained by slvent crystallizatin r cld crystallizatin22'23'27 >- I-- (/3 Z - L,I t-- Z _J J I I I I SCATTRING ANGL Figure 2 X-ray pwder diffractin patterns f melt-crystallized PK, PK and PKK(T/I = 100/0) 2484 POLYMR, 1992, Vlume 33, Number 12

3 Structure, crystallizatin and mrphlgy f PKK: K H Gardner et al T/I rati: 'r i ~--~,~,~,, ~_~ m_~,,~dc-i i-t3-_, i L T TrI 1 Six T/I ratis were prepared fr this wrk: 100/0, 90/10, 80/20, 70/30, 60/40 and 50/50 Because f the synthetic rute, these plymers can be thught f as cplymers f the 'diads' cntaining -DP-T-DP T (TT) and/r -DP T-DP-I- (TI) The plymer cmpsitins, in terms f TT and T! diads, are given in Table 2 This pint f view makes it apparent that T/I ratis f 100/0 and 50/50 result in hmplymers In all cases the isphthalate units are separated by a minimum f five phenyl grups II II II II 0 C C 0 C C L T T J,, l 0 _O O O O_ ] T I J All f the plymers have number-average mlecular weights (Mn) and weight-average mlecular weights (M w) f abut and , respectively Samples were vacuum dried at 120 C fr 24 h prir t all experiments Thin films (ca 5#m) fr ptical micrscpy and small-angle light scattering studies were prepared by pressing pwder specimens at abut 30 C abve the melting temperature Samples fr X-ray diffractin experiments, 125 #m thick, were made using this prcedure fllwed by a water quench Psttreatments t the X-ray samples included expsure t methylene chlride (anhydrus grade), annealing at 200 C, remelting and isthermal crystallizatin at 200 r 300 C as already reprted in a preliminary accunt 23 PKK plaques were prepared under varius thermal treatments fr transmissin electrn micrscpy (TM) f surface replicas fllwing permanganic etching These treatments included slw cling (abut 5 C rain- 1 ) and annealing at a high (30 C belw Tin) and a lw (100 C belw Tin) temperature The permanganic etching was perfrmed as fllws, which is slightly different than that prpsed fr PK a 5 A slutin cntaining 50 ml cncentrated sulphuric acid, 30 ml 85% phsphric acid and 2 g f grund ptassium permanganate was prepared and then l0 ml f distilled water was added The specimen was immersed in this slutin fr abut 1 h in an ultrasnic bath t prevent redepsitin f degraded plymer 28 Recvered specimens were then rinsed with water and air dried tched specimens were expsed t a carbn-platinum vapur Table 2 T/I rati The plymer 'diad' distributin in PKK TT/TI 100/0 100/0 80/20 60/40 70/30 40/60 6O/40 20/80 5O/5O 0/100 at lw angle inside a vacuum evapratr, cated with ply(acrylic acid) slutin, and allwed t dry The dry replica was stripped and was vacuum evaprated with carbn The ply(acrylic acid) cating was disslved by vernight saking nt the surface f water in a Petri dish The remaining replica was picked up n cpper mesh grids, dried and transferred t the micrscpe Characterizatin techniques X-ray diffractin X-ray diffractmetry scans were cllected in the symmetrical transmissin mde using an autmated Philips diffractmeter (curved crystal mnchrmatr, 1 divergence and receiving slits, sample rtating) and Cu K~ radiatin Data were cllected in a fixed time mde with a step size f 005 and run frm 20 = 4 t 65 Data prcessing was accmplished in three steps First, a smth backgrund was remved frm each raw diffractgram using a cubic spline functin defined by pints with 20 < 10 and 20 > 60 Secndly, the diffractin pattern frm a nn-crystalline sample f the same cmpsitin was scaled and subtracted frm the semicrystalline pattern The residual pattern represents the crystalline cmpnent f the riginal diffractgram The crystallinity index is defined as the rati f the area under the residual pattern divided by the ttal scattering in the riginal pattern (see ref 23) Reflectin psitins were defined by decnvluting the residual pattern int a series f Gaussian peaks Differential scanning calrimetry Tw different thermal analysis statins were used: a Du Pnt 990 DSC t measure mst thermal scans, and a Perkin lmer DSC7 t study the crystallizatin kinetics and scanning rate effect (2 t 150 C rain- 1 ) All samples were equilibrated at abut 10 C abve their equilibrium melting temperatures fr 10 min prir t measurements The dsc heating rate was 10 C min- 1, unless therwise specified All thermal scans were cnducted under nitrgen Fr the crystallizatin kinetics study, the specimens were cled at a rate f 320 C rain-1 frm the temperature f an equilibrated melt state t the desired temperature The isthermal crystallizatin peak time was recrded t characterize the crystallizatin rate Micrscpy and ptical techniques The electrn micrscpy wrk was carried ut n a JOL 2000FX transmissin instrument Images were btained at 100 kv accelerating vltage and recrded n film The ptical micrscpe used was a plarizing Nikn Optipht-PDL mdel equipped with a 35 mm camera and a Mettler FP82 HT ht stage A first-rder red tint plate was used t determine the birefringent sign f the spherulite under crssed plars The small-angle light scattering apparatus included a He-Ne unplarized laser, tw plarizers and a Plarid 55 camera, and was used t characterize the spherulite dimensins and als the birefringent sign f the spherulite RSULTS X-ray diffractin Melt-crystallized PKK The pwder diffractin f melt-crystallized PKK(100/0) is shwn in Figure 2 The diffractin pattern is similar t that f ther all-para ply(aryl ether ketne)s Hwever, the reflectins are shifted t lwer angles because f the higher ket cntent POLYMR, 1992, Vlume33, Number

4 Structure, crystallizatin and mrphlgy f PKK" K H Gardner et al The diffractin pattern can be indexed by a tw-chain rthrhmbic unit cell with dimensins a = 0769 nm, b = 0606 nm and fibre axis c = 1016 nm (see Figure 3) ffect f I n the crystalline phase Figure 4a shws the diffractin patterns f melt-crystallized PKK with six different T/I ratis (100/0, 90/10, 80/20, 70/30, 60/40, 50/50) The reflectin psitins are unaffected by the change in plymer cmpsitin, indicating that the O 130' 120 " 110' 100' 90' 80 70" 60" Figure 3 cntent c axis a axis b axis PK PK PKK, I,,,,,, Ketne Cntent (%} Unit-cell parameters f ply(aryl ether ketne)s vs ket unit-cell parameters are unchanged There is, hwever, a change in the intensity f the reflectin (20 = 206 ) (with respect t the 1 10 reflectin (20 = 185 )) with increasing isphthalate cntent Since PKK (100/0) and (50/50) are hmplymers, the / 1 10 intensity rati in their respective diffractin patterns represents the extremes f ttal inclusin (50/50) int and ttal exclusin (100/0) f I frm the crystalline phase Fr intermediate cmpsitins, if bth T and! are included in the crystal withut prejudice then a linear relatinship shuld exist between the 1 1 1/1 1 0 intensity rati and percentage ft (full line in Figure 5a) Deviatins frm a linear relatinship wuld suggest sme degree f exclusin Ttal exclusin wuld result in a step functin similar t that indicated by the brken line in Figure 5a The 1 1 1/1 1 0 intensity rati is pltted in Figure 5a against the percentage f T While PKK (60/40) and (90/10) have intensity ratis cnsistent with inclusin, PKK(80/20) and (70/30) have ratis well abve the expected values, indicating that sme! units are excluded frm the bulk f the crystal The data suggest that up t 20% f the 'wrng' diad can be incrprated int each structure The general shape f the intensity relatinship leads us t cnclude that the crystalline phase in PKK(50/50) and (60/40) mainly cnsists f TI diads, while PKK cmpsitins with higher T cntent mainly cnsist f TT diads ,,144 i it ,,, b /0 90/10 >- I-- O3 Z i,i I-- Z >- I-- O0 Z i,i I-- Z 80/20 70/30 Figure 4 10 I I I I SCATTRING ANGL SCATTRING ANGL X-ray diffractin patterns f (a) melt-crystallized and (b) slvent-crystallized PKK with different T/I ratis POLYMR, 1992, Vlume 33, Number 12

5 Structure, crystallizatin and mrphlgy f PKK K H Gardner et al n,- "i'- 05" c 200 _= 100 Cm0,ete r--i ; xclusi n '~i i ~e TI J TT ' ' ~k'rule ~ f Mixing Inclusin / i Cmplete / i i i i %T Intensity (110) Figure 5 Plts f (a) the 11 ]/1 ] 0 peak ratis vs percentage f T and (b) the intensity f the 200 reflectin vs the intensity f the 110 reflectin fr melt-crystallized PKK samples The intensity f the reflectin is pltted against the intensity f the reflectin fr different T/I ratis in Figure 5b The linear crrelatin between the intensities f these tw equatrial reflectins indicates that the TT and TI structures lk the same in prjectin dwn the chain axis Slvent-crystallized and cld-crystallized PKK PKK can als be crystallized by expsing quenched nncrystalline films t methylene chlride The diffractmerry scans f the six T/I cmpsitins f slventcrystallized PKK are shwn in Figure 4b All f the patterns shw a new reflectin at ca 20 = 156 that is nt bserved in melt-crystallized materials The simplest explanatin fr this reflectin is that it is the reflectin f a ne-chain (metrically) rthrhmbic unit cell (a = 0393 nm, b = 0575 nm and c = 1016 nm) that has been designated as frm 2 Attempts were made t imprve the crystallinity and perfectin f this crystalline phase by thermal treatments, and sme imprvement has been achieved Hwever, high-temperature annealing prduces a cnversin t a structure indistinguishable frm that f melt-crystallized material (frm 1) The I I a reflectin psitins fr frm 2, like frm 1, are relatively unaffected by the incrpratin fisphthalyl mieties Schematic diagrams f the chain packing mdes fr frm 1 and frm 2 that predict diffractin patterns cnsistent with thse we bserve are shwn in Figure 6 Pssible interchain interactins are limited t alignment f weak diples and phenyl-phenyl interactins These phenyl-phenyl interactins are edge-t-face in frm 1, but face-t-face in frm 2 The diffractin patterns f nn-crystalline, quenched, PKK samples that have been heat treated at 200 C shw that bth frm 1 and frm 2 are present 22'2a The transitin temperature f the different crystalline phases and their dependence n T/I cmpsitin are discussed belw Melting and crystallizatin behaviur Figure 7 reprts the X-ray diffractin patterns and dsc, traces fr PKK(50/50) specimens prepared by melt crystallizatin and cld crystallizatin at 200 C The X-ray diffractin patterns shw that cld crystallizatin prduces a mixture f frm 1 and frm 2, while the melt crystallizatin prduces nly frm 1 The difference between the tw dsc, scans indicates that the endtherm at abut 280 C is assciated with the melting f frm 2 while the endtherms at abut 300 and 330 C are assciated with the melting f frm 1 Bth dsc, scans exhibit a small endtherm at abut 220 C This peak is attributed t duble-melting behaviur and will be discussed later Different preparatin prtcls prduce different mrphlgies Fr example, the dsc, scan f a slventcrystallized PKK(50/50) specimen having nly the frm 2 structure is shwn in Figure 8 (tp curve) This scan is similar t that f a cld-crystallized specimen in Figure 7, but sme differences can be fund: a sharp extherm appears at 290 C and a small endthermic peak at 220 C disappears The sharp extherm at 290 C might be assciated with the cnversin (at least partial) f frm 2 t frm 1 In the dsc, scan f a quenched, amrphus specimen (secnd curve) an extherm at 225 C appears This extherm is attributed t the cld crystallizatin, which prduces a mixture f frm l and frm 2 as discussed previusly The dsc, scan f a slw cled PKK(50/50) specimen (third curve) differs frm the previus tw The 280 C peak is cmpletely eliminated and replaced by tw peaks at 300 and 330 C The X-ray pattern shws that this specimen cntains nly frm 1 structure; therefre, these tw peaks are related FORM 1 (dge t Face Phenyl Packing) Figure 6 frm 2 2 C ~~d -'-"0 FORM 2 (Face t Face Phenyl Packing) C:-O",-'3 C--'l~-'b Schematic drawing f chain packing mdes in frm 1 and POLYMR, 1992, Vlume33, Number

6 Structure, crystallizatin and mrphlgy f PKK" K H Gardner et al k- Z LU k- z_ J U I-- ~ 0 1! Crystallizatin M ii '~'"J i " " :'"" ~ Melt Crystallizatin "*'*-*'-,' ' 1 I l I f I SCATTRING ANGL uj -r ~ -lp- I 0 "- ': V " z, -j I f I I I I l TMPRATUR ( C) Figure 7 (a) X-ray diffractin and (b) dsc, scans f PKK(50/50) specimens having different crystal frms Bth melt-crystallized and cld-crystallized specimens were held at 200 C fr 6 h t the melting f frm 1 Finally, annealing at 270 C (bttm curve) prduces a small endtherm at 280 C This is nt due t the melting f frm 2 (verified by the X-ray diffractin) It has always been bserved that an endtherm ccurs abut 10 C abve the isthermal annealing temperature Such behaviur is called the duble-melting behaviur and has been seen in PK and ther semicrystalline plymers 14'17'18'29 Althugh the exact cause is nt yet prven, there is increasing evidence that this peak is assciated with the melting f a secndary structure within the spherulite 17'3 Figures 9a-c shw dsc, traces f PKK(90/10), (80/20) and (70/30), respectively, annealed at several temperatures fr 30 min The dsc, traces f PKK (60/40) and (50/50) annealed at several temperatures fr 1 h are shwn in Figures loa and lb It is apparent that PKK(90/10), (80/20) and (70/30) shw the straightfrward duble-melting behaviur while PKK (60/40) and (50/50) melt in a mre cmplicated manner with an additinal high-temperature peak at abut 330 C Amng these samples, (50/50) has the mst cmplicated melting behaviur This is ratinalized by the fllwing argument The additin f isphthalate units increases the chain flexibility (see discussin), but PKK (50/50) is als a hmplymer while the rest are randm -j a b cplymers Therefre, (50/50) cnsists f nt nly the highest chain flexibility but als the highest chain regularity amng the five specimens cntaining isphthalate residues These tw factrs may inevitably cmplicate the crystallizatin and melting behaviur We have studied the effect f dsc, scanning rate n the thermal behaviur f the annealed (50/50) and (60/40) specimens The results are shwn in Figures lla and llb It is nted that the annealing-induced lwtemperature peak and the middle endtherm are invariant in magnitude fr all heating rates and, therefre, are due t the melting f tw thermdynamically (recta)stable states In cntrast, the size f the high-temperature peak des depend n the heating rate At rates larger than 100 Cmin -1, this peak is cmpletely eliminated, suggesting that this transitin may be due t a recrystallizatin r rerganizatin prcess The middle peak (at abut 310 C), therefre, represents the melting f frm 1 We have interpreted this peak t signal the nminal melting temperature Hffman-Weeks plts using the melting temperatures retrieved frm Figures 9 and 10 are shwn in Figure 12 The equilibrium melting temperature is extraplated frm the interceptin f the brken line and the Tm= T line It is clear that the increase f isphthalate cntent decreases the equilibrium melting temperature We have pltted the equilibrium melting temperature vs the terephthalate cntent, which shws a linear relatinship (Figure 13) Anther interesting aspect f the crystallizatin is the crystallizatin kinetics This is studied by the isthermal dsc, crystallizatin half-time methd Hwever, it is difficult t measure the half-time if the crystallizatin rate is fast An alternative methd is t study the crystallizatin peak time (time that has a maximum heat flw), as shwn in Figure 14 We find that the crystallizatin rate increases with decreasing isphthalate cntent, except fr (50/50), which crystallizes faster than (60/40) A difference in crystallizatin behaviur is bserved fr TI structures, (50/50) and (60/40), versus TT structures with exclusin, (70 / 30 ) and (80 / 20), versus TT structures with inclusin, (90/10) and (100/0) v ~ if_ "1" cz,,=, 5 ~ I, L O0 10 C/min cling annealed at 270 C fr 30 min I I I ] I Temperature ( (3) Figure 8 Dsc scans f fur different PKK(50/50) specimens The treatment cnditins are as specified 2488 POLYMR, 1992, Vlume 33, Number 12

7 Structure, crystallizatin and mrph/gy f PKK: K H Gardner et al 325 C 335 C " ~ 345 C ~_ 355 c,~ 365 C I 01 IT I uj 280 C 290 C 300 C a 100 1; a00 10 C/MIN 220 C, lhr f i 'O I I I I I I [ I I Temperature (~C) V 240 C, lhr 260 C, lhr Figure 9 Dsc scans f PKK specimens annealed at different temperatures fr 30 min: (a) PKK(90/10), (b) PKK(80/20), (c) PKK(70/30) $ C, lhr 290 C, 1 hr 300 C, lhr 310 C, lhr 320 C, 1 hr C vv 1 I I I I I r Mrphlgy A typical ptical micrgraph f the melt-crystallized PKK spherulites is shwn in Figure 15a These spherulites are all negatively birefringent as identified by a plarizing ptical micrscpe equipped with a quarterwave plate al and a small-angle light scattering device 32'a3 The small-angle light scattering patterns (Vv and Hv) are shwn in Figure 16 The H v scattering shws a fur-leaf-clver pattern with the maximum intensity alng the 45 azimuthal angle; the Vv scattering shws a vertical tw-fld symmetric pattern The vertical V v pattern suggests that the anistrpy f plarizability is tangential within the spherulite, which is a clear indicatin f the negative sign f birefringence Since the anistrpy f plarizability f PKK chains is psitive (ac > ab), the unit-cell c axis must lie alng the tangential directin f the spherulite and the b axis must be parallel t the radial (r grwth) directin A TM image f an etched melt-crystallized PKK specimen surface (Figure 15b) shws a sheaf-like spherulitic structure having fine lamellar features Such a structure is quite cmmn in many crystalline plymers 34'35 and is certainly indistinguishable frm that f PK 15'17 The spherulite is initiated frm a sheaf-like frmatin f lamellae and then develps by infilling grwth The etching technique has revealed fine lamellar details f the spherulite In Figure 15b, stacks f lamellae with a peridicity f abut 15 nm are clearly seen This dimensin is quite clse t the lng perid determined by small-angle X-ray scattering, as will be discussed elsewhere Figures 17 and 18 shw TM images f replicas f the etched spherulite mrphlgy f PKK(60/40) and (70/30) having different thermal histries Figures 17a c are micrgraphs f (70/30) prepared under the fllwing cnditins: (a) fast cled at 50 C rain-1 rate, (b) slw cled at 5 C rain -1 rate and (c) annealed at 300 C fr 30 min In the case f fast cling, the specimen is partially crystallized (abut 20% crystallinity) Figure POLYMR, 1992, Vlume 33, Number

8 Structure, crystallizatin and mrphlgy f PKK" K H Gardner et al ca m +2 _ LU 1 02 N a 1 1 I I I I r C 260 C 270 C 280 C 290 C 295 C b i i i i i I Figure 10 Dsc scans f PKK specimens annealed at different temperatures fr 1 h: (a) PKK(60/40), (b) PKK(50/50) 17a thus represents the structure develped during the early stage f crystal grwth (r the primary crystallizatin stage) The sheaf-like skeletn lamellar frmatin is seen, which has ften been fund in the early stage f PK spherulite grwth 12"13'Is'Iv The lamellae are prly defined, pssibly because the predminant amrphus material was eaten away during the etching, leaving behind the initial crystalline structure The TM images in Figures 17b and 17c are quite different frm that in Figure 17a, which has nly brad, indistinct lamellar layers Hwever, Figures 17b and 17c differ frm each ther in the appearance f impinging spherulite bundaries Figure 17b shws relatively diffuse bundaries and Figure 17c shws distinct straight bundaries This difference is even mre dramatic in Figures 18a and 18b, where TM images f (60/40) under tw different thermal treatments are shwn These treatments included : (a) a slw cling at 2 C min- 1 rate and (b) an annealing at 260 C fr an hur The slw-cled specimen (Figure 18a) reveals a distinct lamellar structure, whereas the annealed specimen shws a brad and indistinct ne DISCUSSION X-ray diffractin studies 1-4'v :1 supprt the fllwing generalizatins: (1) Regardless f chemical structure, ply (aryl ether ketne )s appear t pack int a tw-chain rthrhmbic unit cell with tw phenyl grups (and tw linkage grups) in the crystallgraphic repeat (2) The chains are arranged at the crner and centre f the unit cell, (0, 0, Z) and t~, [1 ~, 1 "~ 7'] J' (3) The chains adpt a fully extended cnfrmatin and have adjacent phenylene grups rtated ut f the plane f the linkage grups by the angle +V, where y varies frm 30 t 50 (4) The apparent space grup, Pbcn (n 60), requires that all f the phenyl grups and all f the linkage grups be symmetrically related and therefre identical There are tw pssible explanatins fr the bservatin f a crystallgraphic repeat that is shrter than the chemical repeat and fr the super-symmetry First, the bserved cell culd be a sub-cell f the true unit cell, ie the electrn density difference between the ether and ket grups is s small that reflectins crrespnding t the true repeat are nt bserved If this is the crrect mdel, the ket linkages are expected t be segregated frm the ether linkages The secnd mdel is ne in which the chains are randmly shifted past each ther The result f such a shift wuld prduce a 'nn-segregated' structure with ether grups packing adjacent t ket grups and vice versa This mdel wuld lead t the bservatin f an' averaged' tw-phenyl crystallgraphic repeat where a given linkage culd lie at any linkage site in the crystal In bth mdels the 'average' linkage grup depends n the plymer cmpsitin Indeed, Figure 2 displays a plt f the unit-cell parameters versus the ket cntent in the 'average' linkage fr different ply(aryl ether ketne) structures taken frm the literature 1-4'7-11'36 There is a single, simple linear dependence f the cell parameters n the ket cntent The c and b cell parameters increase with increasing ket cntent, the frmer because f the increased stiffness f the ket grup and the latter because f the ket grup's larger bulk The third parameter, a, decreases t preserve the density f the system This study has investigated the effect f incrprating meta linkages (via isphthalyl mieties ) n the structure and crystallizatin f the particular family member dented PKK It was fund fr all T/I ratis that melt-crystallized PKKs frm a structure similar t ther ply(aryl ether ketne)s, ie frm 1 Hwever, a clear difference is seen between cmpsitins with high and 2490 POLYMR, 1992, Vlume 33, Number 12

9 Structure, crystallizatin and mrphlgy f PKK: K H Gardner et al 10 C/min 10 C/min 20 C/min 20 C/min 40 C/min 40 C/min c ~ < 80 C/min 100 C/min - J~ _ 60 C/min 80 C/min LLI 140 C/min t-- "5 1D t- IJJ 100 C/min 140 C/min a I F! i Figure 11 (a) Dsc scans f an annealed PKK(60/40) specimen (held at 260 C fr 60 min) at different heating rates (b) Dsc scans f an annealed PKK(50/50) specimen (held at 270 C fr 60 rain) at different heating rates 75 b P I I P I I q [ Figure 12 T/I ratis -,"-",~'~,~-~- -f J/ PKK (50/SO) D ~~e" / " " " PKK (60/40) PKK (70/30) PKK (80/20) PKK (90/10) PKK (100/0) i u i i, T c ( C) The Hffman-Weeks plt f PKKs having six different lw isphthalate cntent PKKs cntaining ~<30% isphthalate cntent pack in a structure that cnsists mainly f TT diads In cntrast, PKKs cntaining 40 and 50% isphthalate cnsist f TI diads The rate-dependent high melting peak that is bserved in samples cntaining TI crystals (at 330 C, as seen in P ' I Tm Tg 100,, m i i %T n Figure 13 The extraplated equilibrium melting temperature and glass transitin temperatures vs T cntent Figure llb) is assciated with a recrystallizatin r rerganizatin prcess This behaviur can be explained by the increase f chain flexibility in PKK(50/50), which may result in rearranging the crystal structure t a mre perfect ne after premelting We suspect that this I 100 POLYMR, 1992, Vlume33, Number

10 Structure, crystallizatin and mrphlgy f PKK: K H Gardner et al 102 Vv Z5 101, ~ PKK (100/0) "~, -, PKK (90/10) "-~ [] PKK (80/20) ~'--'-'-"~'~ PKK (70/30) PKK (60/40) PKK (50/50) i 200 i 250 i 300 u,, 350 Figure 14 Plt f crystallizatin peak time vs temperature fr six different P K K s Hv 5 Figure 16 Small-angle light scattering patterns (Vv and Hv) f a crystallized P K K ( 7 0 / 3 0 ) specimen 10 um 400 nm Figure 15 Tw micrgraphs f the P K K spherulite : (a) a plarized ptical micrscpic image and (b) a TM image f a replica surface The specimen is a PKK(60/40) sample annealed at 280 C fr abut 30 min 2492 POLYMR, 1992, Vlume 33, Number 12 transitin crrespnds t the cnversin f a structure cntaining randm shifts f the chains past each ther t a structure where the isphthalate grups are segregated Figure 19 shws the lcal cnfrmatin abut a terephthalate grup and tw pssible cnfrmatins abut an isphthalate grup The tw 'isphthalate' cnfrmatins differ in the relative rtatins f the phenyl rings n each side f the isphthalate unit It is clear that the verall shape and therefre ptential packing interactin is different fr the tw phthalyl mieties Cnsequently, the presence f the isphthalate miety in the crystal can be viewed as a symmetry r entrpic defect It is cnceivable that, upn annealing r premelting, these defects can segregate t prduce a mre stable state Hwever, ur evidence is nt cnclusive Further experiments, including neutrn scattering, are planned t prbe this pssiblity In general, the incrpratin f meta ismers affects tw aspects f the crystallizatin in P K K First, it intrduces a symmetry (r entrpy) defect in the chain within the crystal unit cell, as we have inferred frm the crystallgraphic data Secndly, it increases the chain flexibility in the melt An increase f chain flexibility can be inferred by the bservatin that

11 Structure, crystallizatin and mrphlgy f PKK: K H Gardner et al III II 5 ~m Figure 18 TM micrgraphs f replica surfaces f etched PKK(60/40) specimens Samples were prepared under: (a) slw cling (5 C min -1 ) and (b) annealing at 260 C fr 30 min T I' I" C~ >O Figure 17 TM micrgraphs f replica surfaces f etched PKK(70/30) specimens Samples were prepared under different treatments: (a) fast cling (50 C min- 1), (b) slw cling (5 C rain- 1 ) and (c) annealing at 300 C fr 30 rain C~ Figure 19 Mlecular cnfiguratin f PKK chains having I ismers in the crystalline phase POLYMR, 1992, Vlume33, Number

12 Structure, crystallizatin and mrphlgy f PKK: K H Gardner et al the increase f meta ismer cntent decreases the glass transitin temperature (Figure 13 ; PKK (100/0) Tg = 165 C, PKK(50/50) Tg = 155 C) The crystallizatin rate is als affected by chain flexibility As the meta ismer cntent decreases, the chain becmes stiffer and the crystallizatin rate generally increases If we cmpare hmplymers, PKK(100/0) crystallizes faster than PKK(50/50) Fr cplymers, the crystallizatin rate increases in the rder (60/40) < (70/30) ~ (80/20) < (90/10) The mlar heat f fusin fr the meta and para ismers are abut the same, since there is n difference between the maximum heat f fusin fr the lw and high T/I rati PKKs The cmparable heats f fusin and the diffractin data suggest that neither the exclusin mdel nr the inclusin mdel 38 fr predicting the cplymer melting pint is apprpriate fr describing the meltingpint depressin in PKK The PKK cplymers appear t behave in a manner intermediate between the extreme assumptins f the tw theries, ie bth cmpnents (para and meta) are capable f crystallizing with the same heat f fusin, but have different entrpy change during crystallizatin The annealing-induced endtherm in the dsc, thermgram has been attributed t the melting f a secndary structure within the spherulite This was studied by the thermal, ptical and small-angle light scattering methds, which shwed that, after the first melting (annealinginduced endtherm), the spherulite size remained cnstant but the integrated transmitted light intensity decreased The integrated transmitted light intensity is partially assciated with the ttal degree f crystalline rdering within the spherulite Therefre, the decrease f intensity indicates that the rdering within the spherulite may be reduced In additin, the secndary crystallizatin cnsists f crystallizatin frm tw different aspects : ne cntributes t the crystal perfectin such as lamellar thickening; and anther ne cntributes t the crystal imperfectin such as lamellar subsidiary branching and lw-mlar-mass crystallizatin The melting f imperfect crystals certainly will ccur at a lw temperature and may prduce an annealing-induced endtherm Our TM wrk has revealed a difference between the micrstructure f fast- and slw-cled PKK specimens Structure was develped during the initial primary crystallizatin stage, which shwed nly a single endtherm in the dsc, scan This endtherm ccurred at a high temperature, which indicates that the primary structure cnsists f mre perfect crystals We have als nticed that the primary structure has a less defined lamellar feature than that f a slw-cled r annealed specimen This is because the specimens d nt underg a lamellar thickening prcess during fast cling but they have ample time t thicken the lamellae during slw cling In the case f PKK(80/20) r (50/50), the melt-crystallized specimen shws a similar spherulite structure, at least by ptical techniques The mrphlgical appearance is nt a direct functin f the isphthalate cntent but depends strngly n the thermal histry and the crrespnding crystallizatin rate Finally, ur bservatin f the different spherulitic bundary mrphlgy is pssibly assciated with the diffusin prcess f the lw-mlar-mass cmpnents and/r impurities during crystallizatin In the isthermal crystallizatin, these cmpnents may be excluded frm the spherulite and segregated t the bundaries, leaving a distinct bundary mrphlgy after etching In the nn-isthermal crystallizatin, they may be trapped within the spherulite, leaving behind diffuse bundaries In cntrast t the rest f the ply(aryl ether ketne) family, PKK specimens, regardless f T/I rati, can be induced t shw a secnd crystalline mdificatin, frm 2, either by slvents r cld crystallizatin We attribute its existence t the high ket cntent in PKKs The tw packing mdes fr PKK are similar t thse bserved in the armatic plyamide, ply(p-phenylene terephthalamide) 37 (Blundel127 has recently reprted the bservatin n a 'new' structure fr PKK While indexed differently, his structure crrespnds t the phase we have labelled frm 2) In the case f PKK(50/50), frm 2 has a lwer melting temperature (abut 280 C), and may be able t cnvert int frm 1 after melting In this case, frm 2 is thermdynamically less stable than frm 1 and requires less mbility t frm CONCLUSIONS Many PKK characteristics can be understd as typical f the family f ply(aryl ether ketne)s, eg frm 1 structure, Tg and Tin We have investigated the crystallizatin, melting and mrphlgy f PKK having different para/meta ismer ratis In cntrast t related ply (aryl ether ketne )s, PKK has tw different crystal structures: a cnventinal frm 1 structure, the same as that bserved in PK and PK, which is usually develped frm melt crystallizatin, and a new frm 2 structure, which can be develped frm slvent crystallizatin r cld crystallizatin Frm 1 has a tw-chain rthrhmbic unit cell (a = 0769 nm, b = 0606 nm and fibre axis c = 1016 nm) while frm 2 has a ne-chain (metrically) rthrhmbic unit cell (a = 0786 nm, b = 0575 nm and c = 1016nm) The frm 2 structure is capable f cnverting int frm 1 after melting The additin f the meta ismer (isphthalate miety) decreases the equilibrium melting temperature and the crystallizatin rate, but increases the chain flexibility and the recrystallizatin ability It has little effect n the unit-cell dimensins and the entrpy f fusin r the ttal degree f crystallinity In fact, in the unit cell, the terephthalate and isphthalate grups are crystallgraphically ismrphus The meta linkage can be viewed as creating 'symmetry r entrpy defects' in the unit cell and these defects are respnsible fr the equilibrium melting-temperature depressin The extent f crrelatin between these defects (if any) cannt yet be quantified It may depend n crystallizatin kinetics The crrelatin can be prbed by neutrn scattering f PKK specimens having the isphthalate segment deuterated The diffractin data indicate that cmpsitins with high isphthalyl cntent, PKK (50/50) and (60/40), cnsist f TI diads and cmpsitins with high terephthalyl cntent, PK K (70 / 30 ) t ( 100 / 0 ), are made up f TT diads This mdel is supprted by the crystallizatin data The dsc, scans shw a duble-melting behaviur fr TT crystals (Figure 9) and a triple-melting behaviur fr TI crystals (Figure 10) In additin, the crystallizatin rate is very different fr TT and TI crystals (Figure 14) 2494 POLYMR, 1992, Vlume 33, Number 12

13 Structure, crystallizatin and mrphlgy f PKK" K H, Gardner et al ACKNOWLDGMNTS The authrs wish t thank J Freida, J P McKewn, R Kveleski and W Wright fr their excellent technical assistance The PKK specimens were supplied by T Carney, K L Farn and W J Libbey Jr RFRNCS 1 Radhakrishnan, S and Nadkarni, V W Plym J Mater 1985, 2, 93 2 Dawsn, P C and Blundell, D J Plymer 1980, 21,577 3 Fratini, A V, Crss, M, Whitaker, R B and Adams, W W Plymer 1986, 27, Hay, J N and Kemmish, D, J Plym Cmmun 1989, 30, 77 5 Abraham, R J and Hawrth, I S Plymer 1991, 32, Jg, JP andnadkarni, VMJ Appl Plym Sci 1986,32, Rueda, D R, Ania, F, Richardsn, A, Ward, I M and Balta Calleja, F J Plym Cmmun 1983, 24, Wakelyn, N T Plym Cmmun 1984, 25, Yda, O Plym Cmmun 1984, 25, Hay, J N, Kemmish, D J, Langfrd, J I and Rae, A I M Plym Cmmun 1984, 25, Hay, J N, Kemmish, D J, Langfrd, J I and Rae, A I M Plym Cmmun 1985, 26, Lvinger, A and Davis, D D Macrmlecules 1986, 19, Lvinger, A and Davis, D D J Appl Phys 1985, 58, Blundell, D J and Osbrn, B N Plymer 1983, 24, Olley, R H, Bassett, D C and Blundell, D J Plymer 1986, 27, Kumar, S, Andersn, D P and Adams, W W Plymer 1986, 27, Bassett, D C, Olley, R H and AI Raheil, I A M Plymer 1988, 29, Chang, S Z D, Ca, M Y and Wunderlich, B Macrmlecules 1986, 19, Mensitieri, G, Del Nbile, M, Apicella, A, Niclais, L and Garbassi, F J Mater Sci 1990, 25, Graysn, M, and Wlf, C J Plym Sci, Plym Chem dn 1987, 25, Stber, J, Seferis, J C and Keenan, J D Plymer 1984, 25, Mathesn, R R, Chia, Y T, Avakian, P and Gardner, K H ACS Plym Prepr 1988, 29, Avakian, P, Gardner, K H and Mathesn, R R J Plym Sci, Plym Lett dn 1990, 28, Chang, I Y SAMP Q 1988, 19, Sauer, B B, Avakian, P, Starkweather, H and Hsia, B S Macrmlecules 1990, 23, Hsia, B S, Chang, I Y and Sauer, B B Plymer 1991,32, Blundell, D J and Newtn, A B Plymer 1991, 32, Ghil, R M and Phillips, P J Plymer 1986, 27, Lee, Y and Prter, R S Maermlecules 1988, 21, Marand, H persnal cmmunicatins, Meeten, G H 'Optical Prperties f Plymers', lsevier Applied Science, New Yrk, Stein, R S and Rhdes, M B J Appl Phys 1960, 31, Samuels, R J Plym Sei (A-2) 1971, 9, Wunderlich, B 'Macrmlecular Physics', Academic Press, New Yrk, 1976, Vl 2 35 Bassett, D C 'Principles f Plymer Mrphlgy', Cambridge University Press, Cambridge, Bn, J and Magre, P Makrml Chem 1969, 126, Flry, P J Trans Faraday Sc 1955, ill, Sanchez, I C and by, R K J Res NBS 1973, 77, 353 POLYMR, 1992, Vlume33, Number