Segmentirani poli(uretan-urea-siloksanski) kopolimeri (PUUS), na bazi 4,4'–
metilendifenildiizocijanata (MDI) i etilendiamina (ED) kao komponeti tvrdog segmenta
i α,ω–dihidroksipropil-poli(dimetilsiloksana) (PDMS, Мn = 1000 g mol-1) kao mekog
segmenta, sintetisani su postupkom dvostepene poliadicije u rastvoru, uz kalaj-oktoat
kao katalizator. Eksperimentalni uslovi za sintezu PUUS kopolimera su optimizovani
variranjem temperature, odnosa korastvarača, koncentracije katalizatora, početne
koncentracije monomera i vremena druge faze reakcije poliadicije. Za sintezu su
korišćene dve različite smeše rastvarača: tetrahidrofuran/N,N-dimetilacetamid
(THF/DMAc) i tetrahidrofuran/N-metilpirolidon (THF/NMP), pri konstantnom
molarnom odnosu monomera (PDMS:MDI:ED=1:2:1). Pokazano je da polarnija
THF/NMP smeša predstavlja bolju reakcionu sredinu za sintezu PUUS. Nađeno je da su
optimalni reakcioni uslovi sledeći: temperatura 40 °C, koncentracija katalizatora 0,05
mol. % (u odnosu na PDMS), koncentr...acija monomera u reakcionoj smeši 25 mas. % i
vreme druge faze reakcije 3 h, pri zapreminskom odnosu korastvarača THF/NMP=1:9.
Serija PUUS kopolimera sa različitim sadržajem tvrdih segmenata sintetisana je pod
optimalnim reakcionim uslovima, u THF/NMP smeši sa velikim udelom polarnog NMP
rastvarača, što je omogućilo dobru rastvorljivost rastućih polimernih lanaca i dobijanje
kopolimera relativno velike molarne mase. Molarni odnos PDMS-a, MDI-a i ED-a je
variran od 1:2:1 do 1:6:5, što je odgovaralo promeni masenog udela tvrdih segmenata u
kopolimerima od 36 do 64 mas. %. Struktura i sastav PUUS kopolimera su potvrđeni 1H
NMR i FTIR spektroskopijom. Prosečna dužina sekvenci mekih i tvrdih segmenata, kao
i raspodela sekvenci tvrdih segmenata u seriji PUUS kopolimera, dobijena je
korišćenjem 13C NMR i dvodimenzionalne korelacione NMR spektroskopije.
Kopolimeri sa manjim sadržajem tvrdih segmenata su imali nasumičnu raspodelu tvrdih
i mekih segmenata duž kopolimernih lanaca, dok su se kopolimeri sa udelom tvrdih
segmenata većim od 55 mas. % ponašali kao multiblok-kopolimeri. Detaljna analiza
strukture je pokazala da se prosečna dužina sekvenci tvrdih urea segmenata povećavala
od 2,2 do 4,9 sa povećanjem njihovog masenog udela od 38 do 65 mas. %. Na osnovu
rezultata termičke i mehaničke analize, zatim analize rasipanja X-zraka na malim
uglovima (SAXS), kao i FTIR analize vodoničnog vezivanja, utvrđeno je da sintetisani
PUUS kopolimeri pokazuju mikrofazno razdvojenu strukturu i velike vrednosti zatezne
čvrstoće. Globularne superstrukture, zapažene u filmovima uzoraka kopolimera pomoću
skenirajuće elektronske mikroskopije (SEM) i mikroskopije atomskih sila (AFM), bile
su posledica mikrostrukturne organizacije MDI–ED segmenata, zavisno od njihovog
udela i dužine. Velike vrednosti početnih elastičnih modula i zatezne čvrstoće su bile
posledica prisustva veoma jakih bidentatnih urea vodoničnih veza. PUUS kopolimeri su
pokazali veliku otpornost na vodu, pri čemu se hidrofobnost i hrapavost njihove
površine neznatno povećavala sa povećanjem masenog udela PDMS segmenta, što čini
ove 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 segment
components 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 in
the presence of stannous octoate as a catalyst. The experimental conditions for the
synthesis of PUUS copolymers were optimized by varying the temperature, the cosolvents
ratio, the concentration of the catalyst, the initial monomer concentration and
the 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 of
the monomers (PDMS:MDI:ED = 1:2:1). It was demonstrated that the more polar
THF/NMP mixture was a better reaction medium for the synthesis of PUUSs. The
following conditions were o...ptimal: a temperature of 40 °C, a catalyst concentration of
0.05 mol % (calculated to PDMS), a monomer concentration in the reaction mixture of
25 wt. % and a reaction time for the second step of 3 h, at the co-solvent ratio of
THF/NMP = 1:9. A series of PUUS copolymers with different hard segment content
was synthesized under optimal reaction conditions, in THF/NMP mixture with a large
proportion of polar NMP solvent, which provided good solubility of the growing chains,
thus ensuring copolymers of relatively high molecular weight. The molar ratio of
PDMS, MDI and ED was varied from 1:2:1 to 1:6:5, which resulted in the
predetermined content of the hard segments from 36 to 64 wt. %. The structure and
composition of the PUUSs were confirmed by 1H NMR and FTIR spectroscopy. The
mean sequence length of the soft and hard segments, as well as the sequence
distribution of the hard segments in the PUUS series, were obtained by 13C NMR and
two-dimensional correlation spectroscopy. The copolymers with lower hard segment
content were random, while the others with the hard segment content higher than ~ 55
wt. % were multi-block copolymers. Detailed structural analysis showed that the mean
sequence length of the hard urea segments increased from 2.2 to 4.9 with increasing
hard segments content from 38 to 65 wt. %. Thermal, mechanical, small-angle X-ray
scattering (SAXS) and hydrogen bonding analyses by FTIR indicated the formation of
the microphase-separated copolymers with high tensile strength. Globular
superstructures observed in the copolymer films by scanning electron microscopy
(SEM) and atomic force microscopy (AFM) were probably arisen from the
microstructural organization of the MDI–ED segments, depending on their content and
length. The high initial elastic modulus and high values of tensile strength of the PUUSs
are the consequences of the presence of a very strong urea bidentate hydrogen bonding.
The PUUS copolymers showed high water resistance, their surface became more
hydrophobic and the values of the surface roughness slightly increased with increasing
the weight fraction of the PDMS segment, which suggested a great promise for the
possible use of PUUS copolymers in potential biomedical applications...
