Sinteza, struktura i svojstva segmentiranih poli(uretan-urea-siloksana)

Abstract

Segmentirani poli(uretan-urea-siloksanski) kopolimeri (PUUS), na bazi 4,4'–metilendifenildiizocijanata (MDI) i etilendiamina (ED) kao komponeti tvrdog segmentai α,ω–dihidroksipropil-poli(dimetilsiloksana) (PDMS, Мn = 1000 g mol-1) kao mekogsegmenta, sintetisani su postupkom dvostepene poliadicije u rastvoru, uz kalaj-oktoatkao katalizator. Eksperimentalni uslovi za sintezu PUUS kopolimera su optimizovanivariranjem temperature, odnosa korastvarača, koncentracije katalizatora, početnekoncentracije monomera i vremena druge faze reakcije poliadicije. Za sintezu sukorišćene dve različite smeše rastvarača: tetrahidrofuran/N,N-dimetilacetamid(THF/DMAc) i tetrahidrofuran/N-metilpirolidon (THF/NMP), pri konstantnommolarnom odnosu monomera (PDMS:MDI:ED=1:2:1). Pokazano je da polarnijaTHF/NMP smeša predstavlja bolju reakcionu sredinu za sintezu PUUS. Nađeno je da suoptimalni reakcioni uslovi sledeći: temperatura 40 °C, koncentracija katalizatora 0,05mol. % (u odnosu na PDMS), koncentracija monomera u reakcionoj smeši 25 mas. % ivreme druge faze reakcije 3 h, pri zapreminskom odnosu korastvarača THF/NMP=1:9.Serija PUUS kopolimera sa različitim sadržajem tvrdih segmenata sintetisana je podoptimalnim reakcionim uslovima, u THF/NMP smeši sa velikim udelom polarnog NMPrastvarača, što je omogućilo dobru rastvorljivost rastućih polimernih lanaca i dobijanjekopolimera relativno velike molarne mase. Molarni odnos PDMS-a, MDI-a i ED-a jevariran od 1:2:1 do 1:6:5, što je odgovaralo promeni masenog udela tvrdih segmenata ukopolimerima od 36 do 64 mas. %. Struktura i sastav PUUS kopolimera su potvrđeni 1HNMR i FTIR spektroskopijom. Prosečna dužina sekvenci mekih i tvrdih segmenata, kaoi raspodela sekvenci tvrdih segmenata u seriji PUUS kopolimera, dobijena jekorišćenjem 13C NMR i dvodimenzionalne korelacione NMR spektroskopije.Kopolimeri sa manjim sadržajem tvrdih segmenata su imali nasumičnu raspodelu tvrdihi mekih segmenata duž kopolimernih lanaca, dok su se kopolimeri sa udelom tvrdihsegmenata većim od 55 mas. % ponašali kao multiblok-kopolimeri. Detaljna analizastrukture je pokazala da se prosečna dužina sekvenci tvrdih urea segmenata povećavalaod 2,2 do 4,9 sa povećanjem njihovog masenog udela od 38 do 65 mas. %. Na osnovurezultata termičke i mehaničke analize, zatim analize rasipanja X-zraka na malimuglovima (SAXS), kao i FTIR analize vodoničnog vezivanja, utvrđeno je da sintetisaniPUUS kopolimeri pokazuju mikrofazno razdvojenu strukturu i velike vrednosti zateznečvrstoće. Globularne superstrukture, zapažene u filmovima uzoraka kopolimera pomoćuskenirajuće elektronske mikroskopije (SEM) i mikroskopije atomskih sila (AFM), bilesu posledica mikrostrukturne organizacije MDI–ED segmenata, zavisno od njihovogudela i dužine. Velike vrednosti početnih elastičnih modula i zatezne čvrstoće su bileposledica prisustva veoma jakih bidentatnih urea vodoničnih veza. PUUS kopolimeri supokazali veliku otpornost na vodu, pri čemu se hidrofobnost i hrapavost njihovepovršine neznatno povećavala sa povećanjem masenog udela PDMS segmenta, što činiove materijale pogodnim za potencijalnu biomedicinsku primenu...

Segmented poly(urethane-urea-siloxane) copolymers (PUUS), based on 4,4′-methylenediphenyl diisocyanate (MDI) and ethylene diamine (ED) аs the hard segmentcomponents and α,ω-hydroxypropyl-poly(dimethylsiloxane) (PDMS, Mn= 1000 g mol-1)as the soft segment were prepared by a two-step polyaddition procedure in a solution inthe presence of stannous octoate as a catalyst. The experimental conditions for thesynthesis of PUUS copolymers were optimized by varying the temperature, the cosolventsratio, the concentration of the catalyst, the initial monomer concentration andthe time of the second step of the polyaddition reaction. Two different solvent mixtures:tetrahydrofuran/N,N-dimethylacetamide (THF/DMAc) and tetrahydrofuran/Nmethylpyrrolidone(THF/NMP) were used for the synthesis, at constant molar ratio ofthe monomers (PDMS:MDI:ED = 1:2:1). It was demonstrated that the more polarTHF/NMP mixture was a better reaction medium for the synthesis of PUUSs. Thefollowing conditions were optimal: a temperature of 40 °C, a catalyst concentration of0.05 mol % (calculated to PDMS), a monomer concentration in the reaction mixture of25 wt. % and a reaction time for the second step of 3 h, at the co-solvent ratio ofTHF/NMP = 1:9. A series of PUUS copolymers with different hard segment contentwas synthesized under optimal reaction conditions, in THF/NMP mixture with a largeproportion of polar NMP solvent, which provided good solubility of the growing chains,thus ensuring copolymers of relatively high molecular weight. The molar ratio ofPDMS, MDI and ED was varied from 1:2:1 to 1:6:5, which resulted in thepredetermined content of the hard segments from 36 to 64 wt. %. The structure andcomposition of the PUUSs were confirmed by 1H NMR and FTIR spectroscopy. Themean sequence length of the soft and hard segments, as well as the sequencedistribution of the hard segments in the PUUS series, were obtained by 13C NMR andtwo-dimensional correlation spectroscopy. The copolymers with lower hard segmentcontent were random, while the others with the hard segment content higher than ~ 55wt. % were multi-block copolymers. Detailed structural analysis showed that the meansequence length of the hard urea segments increased from 2.2 to 4.9 with increasinghard segments content from 38 to 65 wt. %. Thermal, mechanical, small-angle X-rayscattering (SAXS) and hydrogen bonding analyses by FTIR indicated the formation ofthe microphase-separated copolymers with high tensile strength. Globularsuperstructures observed in the copolymer films by scanning electron microscopy(SEM) and atomic force microscopy (AFM) were probably arisen from themicrostructural organization of the MDI–ED segments, depending on their content andlength. The high initial elastic modulus and high values of tensile strength of the PUUSsare the consequences of the presence of a very strong urea bidentate hydrogen bonding.The PUUS copolymers showed high water resistance, their surface became morehydrophobic and the values of the surface roughness slightly increased with increasingthe weight fraction of the PDMS segment, which suggested a great promise for thepossible use of PUUS copolymers in potential biomedical applications...