Grijpma, Dirk Wybe

English

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   University of GroningenHigh impact strength poly(lactide) tough biodegradable materials.Grijpma, Dirk WybeIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1993Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Grijpma, D. W. (1993). High impact strength poly(lactide) tough biodegradable materials. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 08-06-2022SuvvnRyThe development of  b iodegradable polymers for  use in surgical  appl icat ions hasreceived considerable at tent ion in recent  years.  Especia l ly  poly(c-hydroxy-acids)  have been ut i l ized in sutures,  drug re lease systems and bone f racturef ixat ion.  In load bear ing surgical  devices I ike bone plates and screws, goodmechanical  propert ies (st rength,  toughness) of  the mater ia l  are essent ia l  i ft he  imp lan t s  a re  t o  be  used  sa fe l y  and  success fu l l y .  l n  o rde r  f o r  t he  po l ymerto hydrolyze and degrade tn v i .vo wi thout  e l ic i t ing adverse secondary t issuereact ions,  low crystal l ine or  amorphous polymers are the preferred mater ia ls.This thesis descr ibes the synthesis and propert ies of  several  copolymers ofL- lact ide.  The ef fect  of  the nature of  the comonomer and the copolymercomposi t ion on the thermal-  and mechanical  propert ies has been evaluated.Fu r t he rmore ,  t he  l ow  impac t  r es i s t ance  o f  amorphous  po l y ( l ac t i de )  can  berelated to the re lat ively low entanglement densi ty in the mel t .  The toughnessof  these br i t t le  mater ia ls can be substant ia l ly  improved by block copoly-mer izat ion and blending wi th b iodegradable rubbers.The preparat ion of  b iodegradable elastomeric implant  mater ia ls is  descr ibed inchapter 2.  High molecular  weight  copolymers of  L- lact ide and e-caprolactonewere prepared in the monomer mel t  by r ing opening polymerizat ion wi th stannousoctoate.  The 50, /50 mole, /mole L- lact ide, /e-caprolactone copolymers show anon-random distr ibut ion of  monomer sequences,  resul t ing in the presence ofcrystal l izable L- lact ide sequences.  These crystal l ine domains account for  thegood mechanical  propert ies of  the mater ia l ,  the tensi le st rength is  34 Mpa andthe elongat ion at  break 5oo 7. .  These favourable propert ies make th is copolymera sui table mater ia l  for  use in b iomedical  appl icat ions such as nerve guides,were a degradable,  e lastomeric implant  mater ia l  is  required.  The degradat ionproducts of  these L- lact ide/e-caprolactone copolymers are non-toxic,  incontrast  to those of  the f requent ly used medicai  grade,  MDI contain ingpolyurethanes.In chapter 3 the ef fect  of  the polymerizat ion temperature on the propert ies ofL- lact ide and e-caprolactone copolymers is  invest igated.  In the r ing openingcopolymerizat ion of  these lactones,  the large di f ference in react iv i ty  betweenthe monomers leads to tapered copolymers wi th b locky structures.  Less blockycopolymers are formed at higher temperatures due to the increased occurrenceof t ransester i f icat ion react ions and a less pronounced di f ference inreact iv i ty  of  , the monomers.  The average monomer sequence lengths,  readi lymeasured by ^"c NMR, have a large ef fect  on the thermal-  and mechanicalcharacter is t ics of  the copolymers.  copolymers synthesized at  go oc wi threlat ively long average monomer sequence lengths and pronounced phaseseparat ion were much st i f fer  and stronger than copolymers prepared at  11o oc.chapter 4 deals wi th routes to improve the impact  resistance of  as-polymerizedpoly(L- lact ide).  I t  was shown that  as-polymerized poly(L- lact ide) has a muchhigher impact  st rength than af ter  compression moulding and rapid ly cool ing tobelow room temperature.  The toughness can great iy  be increased by bulkpolymeriz ing of  l - - lact ide in the presence of  carbon f ibres.  These modelcomposi tes possess an unnotched impact  st rength upto s ix t imes higher thannascent poly(L- lact ide).  As-polymerized copolymers of  L- lact ide wi th smal lamounts of  t r imethylene-carbonate showed a very sharp maximum in impactstrength versus the copolymer composi t ion,  most  l ikely re lated to thehomogenei ty and morphology of  the obtained mater ia l .  other means of173toughening,  such as block copolymerizat ion of  L- lact ide wi thL- lact ide, /c-caprolactone rubbers and plast ic izat ion wi th ethyl -acetate,  werealso invest igated,  leading to h igh impact  st rength as-polymerized poly(L-l ac t i de  ) .Chapter 5 describes the synthesis of high molecular weight copolymers ofL- lact ide and glycol ide.  Copolymerizat ion wi th the much more hydrophyl icg l yco l i de  w i l l  dec rease  t he  i n i t i a l  c r ys ta l l i n i t y  o f  t he  copo l ymers  andsimul taneously increase the rate of  hydrolyt ic  degradat ion.  The inf luence ofthe glycol ide content  on the thermal-  and mechanical  propert ies was studied.Excellent mechanical properties and a large melting point depressi.o^n wereobserved. The dyad splitting of the carbonyl carbon atom in the '"C NMnspectrum was used to determine average lengths of monomer sequences. Thesynthesized copolymers did not  reveal  a t ru ly random monomer dist r ibut ion.Hydrolytic degradation experiments in vttro showed that large amounts ofh ighly crystal l ine mater ia l  were st i l l  present af ter  l4O days.  True randomcopolymers,  wi th shorter  L- lact ide sequences should not  d isplay th is largeincrease in crystal l in i ty  and s low mass ioss upon hydrolysis.The synthesis of  a b icycl ic  b is-carbonate and i ts  use in the forrnat ion ofpoly(L- lact ide) networks is  descr ibed in Chapter 6.  Spiro-bis-dimethylene-carbonate proved to be an effective cross-linker for cyclic carbonates as wellas for  lactones.  In the copolymerizat ion wi th L- lact ide,  the high gelpercenta-ges of  upto IOO 7" and the very low gelpoint  of  0.O6 mole % cross- l inker areindicat ive of  the ease wi th which th is cross- l inker copolymerizes wi thL- lact ide.  The molecular  weights between cross- l inks determined f rom swel l ingexperiments were in accordance with those expected from the charged amounts ofmonomer,  indicat ing homogeneous cross- l ink ing to have taken place (atconcentrat ions below 2 mole % spiro-bis-DMc).  A large mel t ing point  depressionand a s igni f icant  reduct ion of  the heat  of  fusion are at ta ined.  The values oftensi le-  and impact  st rength are higher than those of  unmodi f ied as-polymerized poly(L- lact ide).Chapter 7 is  concerned wi th the copolymerizat ion of  L- lact ide wi th severalcycl ic  esters and cycl ic  carbonates.  The thermal  propert ies of  the as-polymerized, nascent copolymers and networks were evaluated with respect tothe nature of  the comonomer.  Comonomers wi th a react iv i ty  equal  to L- lact ideare most effective in decreasing the melting temperature and crystallini^ty.Dur ing long term hydrolysis and accelerated degradat ion exper i rnents at  lOO -C,i t  was shown that  the presence of  crystal l izable L- lact ide sequences in thecopolymers resul ted in long degradat ion t imes before complete loss of  masstakes place.In Chapter 8 the inf luence of  copolymerizat ion of  L- lact ide wi th cycl ic  estersand cycl ic  carbonates on the mechanical  propert ies is  invest igated.  The extentof  crystal l izat ion of  poly(L- lact ide) homo- and copolymers has a Iarge ef fecton their  tensi le-  and impact  propert ies.  Whi le amorphous poly( lact ide) isbr i t t le  in impact  tests,  crystal l ine poly( lact ide) mater ia ls are much tougher.Sharp maxima in the impact strength versus the comonomer composition and theheat of  fusion were obtained,  ref lect ing the important  ro le of  the presence ofa crystal l ine f ract ion in the mater ia l .  The toughest  mater ia ls are obtained atcondi t ions where the entanglement densi ty is  h igh and the interconnect iv i ty  ofthe physical  network due to the presence of  crystal l i tes is  maximaL.Chapter 9 descr ibes the ef fect  of  the (mel t )  entanglement densi ty on theimpac t  s t r eng th  and  t he  d rawab i i i t y  o f  amorphous  and  sem i - c r ys ta l l i neL- lact ide homo- and stereocopolymers.  The molecular  weight  between entangle-ments in amorphous poly(L- lact ide) is  found to be c lose to 1OxlO",  correspon-ding to a character is t ic  rat io Co=12. This value is  much higher than previousdeterminat ions by Flory and coworkers,  they found Co=Z for  poly(L- lact ide).The oPo l y ( l aspiro- tf rom 4draw-rconcentare velentanglChapterrubberspolymerwi th ÍdegradaThe relconvenieThe bl ,severalbr i t t let r imethytoughenibe demelectronweightsv i e l d  c tmethylenABS.The Ápp,thermalsynthesisIncorporrthermal l lthese (rimportanelevatedThe h_vdrpoly( lact iAppendi:iThis b ic;ethers.  Iresul tedmanner,Iactonesb i cyc l i ctone) net 'r74: t ide with)etate, werei - - A  ^ ^ 1 r , í r  -P V I J  \ Lrpolymers ofhydrophylicolymers andinfluence ofwas studied.ression wereihe 13c NMR' n r ! ê n . ê c  T h pdistribution.amounts ofTrue random. .  + L : ^  l ^ - - ^J  L l l r s  l d r  Ë sformat ion ofr-dimethylene-aates as wel lgelpercenta-rss-linker aremerizes withfrom swel l inged amounts ofn  n l r n o  í  a tint depressionThe values ofLmodified as-with severalof the as-th respect toI to L-lactidecrystal l in i ty .r ts  at  100 oC,uences in theIoss of masscyclic estersd. The extent'  l a r o e  e f f e n tr ly( lact ide) ismuch tougher.sition and theLe presence of'e obtained at:onnectivity ofensity on theemi-crystallineveen entangle-- 3I  a n r r p c n ^ n -than previousroly(L- lact ide ) .The observed br i t t le  f racture behaviour of  amorphous poly0act ide) can beexplained by such a high value of  the character is t ic  rat io.Poly( lact ide) networks,  prepared by copolymerizat ion of  L- lact ide wi thspiro-bis-DMC, could be convenient ly  hot-drawn at  temperatures above themelt ing temperature,  or  the glass-t ransi t ion temperature in the case ofamorphous networks,  to g ive very strong,  or iented rods wi th strengths vary ingfrom 4oo to over 8o0 MPa depending on the dnaw-rat io.  The maximum obtainabledraw-rat io is  determined by the entanglement densi ty and the cross- l inkerconcentrat ion.  Semi-crystal l ine,  as-polymerized networks of  poly(L- lact ide)ane very low entangled and could be hot-drawn much fur ther than the moreentangled amorphous L-  and D- lact ide copolymer networks.chapter lo descr ibes the block copolymerizat ion of  star-shaped degradablerubbers wi th poly( lact ide).  Normal ly  amorphous poly(g5,215 L, /D- lact ide)polymers are br i t t le  in tensi le-  and impact  test ,  but  b lock copolymerizat ionwith star-shaped t r imethylene-carbonate/e-caprolactone rubbers and otherdegradable rubbers leads to very tough, impact  resistant  degradable mater ia ls.The re lat ively low sof tening temperatures of  these amorphous mater ia ls a l lowsconvenient  processing by compression moulding.The block copolymerizat ion and blending of  amorphous polyOact ide) wi thseveral  degradable rubbers is  descr ibed in chapter l l .  Rubber toughening ofbr i t t le  amorphous poly( lact ide) matr ices wi th poly( t r imethylene-carbonate) andtr imethylene-carbonate/e-caprolactone rubbers leads to very ef fect ivetoughening.  The presence of  a d iscrete rubber phase in the glassy matr ix  couldbe demonstrated by dynamic mechanical  thermal  analysis and t ransmissionelectron microscopy.  Opt im^al  toughening is  achieved at  rubber(block) molecularweights h igher than 40*10' .  The Izod notched impact  st rength and the tensi ley ie ld stren8th of  poly( lact ide) mater ia ls modi f ied wi th 20 weight  T" r r i -methylene-carbonate/e-caprolactone rubber is even higher than that of HIpS andABS,The Appendices descr ibe prel iminary exper iments concerning the hydrolyt ic-  andthermal  degradat ion of  rubber modi f ied amorphous poly( lact ide),  as wel l  as thesynthesis and copolymerizat ion of  lactones wi th a b icycl ic  b is-ether.Incorporat ion of  carbonate groups in the block copolymer chain resul ts inthermal ly  less stable polymers.  Therefore the thermogravimetr ic  analysis ofthese (rubber)modi f ied lact ide polymers,  descr ibed in Appendix A,  y ie ldsimportant  informat ion concerning the processabi l i ty  of  these mater ia ls ate levated temperatures.The hydrolyt ic  degradat ion of  poly( lact ide) b lock copolymers wi th rubbers andpoly( lact ide) stereo-copolymers of  var ious molecular  weights is  descr ibed inAppendix B.  Áppendix c descr ibes the synthesis of  2,6-dioxa-[3,3]-heptane.This b icycl ic  b is-oxetane was copolymerized wi th several  lactones and cycl icethers.  The cat ionic copolymerizat ion of  e-caprolactone wi th th is cross- l inkerresul ted in networks which could be hot-drawn in a very stra ight forwardmanner,  Ieading to strong mater ia ls.  The in i t ia l  cross- l ink ing react ions oflactones wi th th is cross- l inker,  show that  cat ionic copolymerizat ion wi th abÍcycl ic  b is-oxetane is  a promising al ternat ive method to prepare poly0ac-tone) networks.175

High impact strength poly(lactide) tough biodegradable materials.

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High impact strength poly(lactide) tough biodegradable materials.

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