Influence of the content of hard segments on the properties of novel urethane-siloxane copolymers based on a poly(ε-caprolactone)-b-poly(dimethylsiloxane)-b-poly(ε-caprolactone) triblock copolymer

Abstract

A series of novel thermoplastic urethane-siloxane copolymers (TPUSs) based on a α,ω-dihydroxy-[poly(ε-caprolactone)-b-poly(dimethylsiloxane)-b- -poly(ε-caprolactone)] (α,ω-dihydroxy-PCL-PDMS-PCL) triblock copolymer, 4,4'-methylenediphenyl diisocyanate (MDI) and 1,4-butanediol (BD) was synthesized. The effects of the content (9-63 mass %) of hard urethane segments and their degree of polymerization on the properties of the segmented TPUSs were investigated. The structure, composition and hard segment degree of polymerization of the hard segments were examined using 1H- and quantitative 13C-NMR spectroscopy. The degree of crystallinity of the synthesized copolymers was determined using wide-angle X-ray scattering (WAXS). The surface properties were evaluated by measuring the water contact angle and water absorption. In the series of the TPUSs, the average degree of polymerization of the hard segments was varied from 1.2 to 14.4 MDI-BD units. It was found that average values from 3.8 to 14.4 MDI-BD units were effective segment lengths for crystallization of hard segments, which resulted in an increase in the degree of microphase separation of the copolymers. Spherulite-like superstructures were observed in copolymer films by scanning electron microscopy (SEM), which are believed to arise from the crystallization of the hard segments and/or PCL segments, depending on the content of the hard segments. The surface of the copolymers became more hydrophobic with increasing weight fraction of PDMS. The synthesized copolymers based on a PCL-PDMS-PCL segment showed good thermal stability, which increased with increasing content of soft PDMS segments, as was confirmed by the value of the starting temperature of thermal degradation.

U ovom radu prikazana je struktura i neka svojstva serije novih termoplastičnih uretan-siloksanskih kopolimera (TPUSs) na bazi α,ω-dihidroksi-[poli(ε-kaprolakton)-b-poli(dimetilsiloksan)-b-poli(ε-kaprolakton)] triblok kopolimera (α,ω-dihidroksi-PCL-PDMS-PCL), 4,4'-metilendifenildiizocijanata (MDI) i 1,4-butandiola (BD). Ispitan je uticaj sadržaja uretanskog tvrdog segmenta (9-63 mas. %) i njegove dužine, tj. stepena polimerizacije, izražene preko broja MDI-BD ostataka, na svojstva segmentiranih TPUSs. Struktura, sastav i stepen polimerizacije tvrdog segmenta su ispitani pomoću 1H- i kvantitativne 13C-NMR spektroskopije. Stepen kristaliničnosti kopolimera je određen metodom difrakcije X-zraka na velikim uglovima (WAXS). Površinska svojstva kopolimera su ispitana određivanjem kontaktnih uglova sa vodom i merenjem apsorpcije vode. U seriji kopolimera dužina tvrdog segmenta izražena preko broja ponavljajućih MDI-BD jedinica je varirana od 1,2 do 14,4. Utvrđeno je da tvrdi segmenti sa 3,8 do 14,4 ponavljajućih MDI-BD jedinica efikasno kristališu, što je rezultovalo u povećanju stepena mikrofazne separacije kopolimera. SEM analiza je pokazala prisustvo sferulitne strukture u kopolimernim filmovima, koja najverovatnije potiče od kristalizacije tvrdih i/ili PCL segmenata, zavisno od sadržaja tvrdih segmenata. Hidrofobnost površine kopolimera je rasla sa povećanjem masenog udela PDMS-a u odgovarajućem uzorku. Sintetisani poliuretani na bazi PCL-PDMS-PCL pokazuju povećanje termičke stabilnosti sa povećanjem sadržaja mekih PDMS segmenata, što je potvrđeno porastom početne temperature degradacije, određene TG analizom.