Primena reaktivnih siloksanskih pretpolimera za sintezu poli(ester-siloksana) i poli(ester-etar-siloksana)

Thermoplastic poly(ester-siloxane)s (TPES) and poly(ester-ether-siloxane)s, (TPEES), based on poly(butylene terephthalate) (PBT) as the hard segment and different siloxane-prepolymers as the soft segments, were prepared. The TPES and TPEES were synthesized by catalyzed two-step transesterification from dimethyl terephthalate, (DMT), 1,4-butanediol, (BD) and a siloxane-prepolymer. Incorporation of dicarboxypropyl- or disilanol-terminated poly(dimethylsiloxane) s (PDMS) into the polar poly(butylene terephthalate) chains resulted in rather inhomogeneous TPES copolymers, which was a consequence of a prononuced phase separation of the polar and non-polar reactants during synthesis. Two concepts were employed to avoid or reduce phase separation: 1) the use of siloxane-containing triblock prepolymers with hydrophilic terminal blocks, such as ethylene oxide (EO), poly(propylene oxide) (PPO) or poly(caprolactone) (PLC) when the terminal blocks serve as a compatibilizer between the extremely non-polar PDMS and the polar DMT and BD, and 2) the use of a high-boiling solvent (1,2,4-trichlorobenzene) during the first phase of the reaction. Homogeneity was significantly improved in the case of copolymers based on PCL-PDMS-PCL.U okviru ovog rada su sintetisani termoplastični poli(estar–siloksani) (TPES) i poli(estar–etar–siloksani) (TPEES), sa tvrdim segmentima na bazi poli(butilentereftalata) (PBT) i mekim segmentima na bazi različitih siloksanskih pretpolimera. TPES i TPEES su sintetisani katalizovanom reakcijom dvostepene transesterifikacije, iz dimetilterftalata (DMT), 1,4-butandiola (BD) i odgovarajućeg siloksanskog pretpolimera. Pri ugradnji dikarboksipropil- ili disilanol-terminiranih poli(dimetilsiloksana) (PDMS) u polarne poli(butilentereftalatne) lance dobijeni su prilično nehomogeni TPES kopolimeri, što je bila posledica loše menjivosti reaktanata tokom odigravanja reakcije. Primenjena su dva koncepta da bi se izbeglo ili smanjilo fazno razdvajanje reakcione smene tokom sinteze organo–siloksanskih kopolimera: 1) primena siloksanskih triblok-pretpolimera kod kojih su hidrofilni terminalni blokovi, izgrađeni od etilenoksida (EO), poli(propilenoksida) (PPO) ili poli(kaprolaktona) (PLC), imali funkciju kompatibilizatora između nepolarnog PDMS-a i polarnih reaktanata, DMT-a i BD-a i 2) primena rastvaranja visoke temperature ključanja (1,2,4-trihlorbenzena) za vreme izvođenja prve faze reakcije. Značajno povećanje homogenosti postignuto je kod kopolimera na bazi PCL–PDMS–PCL segmenata

Degradation behaviour of PCL/PEO/PCL and PCL/PEO block copolymers under controlled hydrolytic, enzymatic and composting conditions

Short-term hydrolytic and enzymatic degradation of poly(epsilon-caprolactone) (PCL), one series of triblock (PCL/PEO/PCL) and the other of diblock (PCL/PEO) copolymers, with a low content of hydrophilic PEO segments is presented. The effect of the introduction of PEO as the central or lateral segment in the PCL chain on copolymer hydrolysis and biodegradation properties was investigated. FUR results revealed higher hydrolytic degradation susceptibility of diblock copolymers due to a higher hydrophilicity compared to PCL and triblock copolymers. Enzymatic degradation was tested using cell-free extracts of Pseudomonas aeruginosa PAO1, for two weeks by following the weight loss, changes in surface roughness, and changes in carbonyl and crystallinity index. The results confirmed that all samples underwent enzymatic degradation through surface erosion which was accompanied with a decrease in molecular weights. Diblock copolymers showed significantly higher weight loss and decrease in molecular weight in comparison to PCL itself and triblock copolymers. AFM analysis confirmed significant surface erosion and increase in RMS values. In addition, biodegradation of polymer films was tested in compost model system at 37 degrees C, where an effective degradation of block copolymers was observed

Uticaj sadržaja tvrdog segmenta na svojstva novih uretan-siloksanskih kopolimera na bazi poli(e-kaprolakton)-b-poli(dimetilsiloksan)-b-poli(e-kaprolaktona)

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

Synthesis and characterization of biodegradable poly(butylene succinate-co-butylene adipate)s

A series of high molecular weight polyesters, poly(butylene succinate-co-butylene adipate)s was prepared from dimethyl succinate, dimethyl adipate and 1,4-butanediol by catalyzed transesterification in the melt. The structure, average molecular weights and physical properties of the resulting random aliphatic copolyesters were characterized by H-1 NMR, solution viscosity, gel permeation chromatography, differential scanning calorimetry and X-ray analysis. The effect of copolymer composition on the physical and thermal properties, as well as enzymatic degradation was investigated. The enzymatic degradation was performed in a buffer solution with Candida cylindracea lipase at 30 degreesC. The highest enzymatic degradation rate was observed for the copolyester containing 50 mol.% butylene succinate units (PBAS-50). This copolyester has the lowest crystallinity and these results suggest that degree of crystallinity has a strong influence on the enzymatic degradation rate

Synthesis and characterization of thermoplastic copolyester elastomers modified with fumaric moieties

A series of poly(ether-ester)s derived from dimethyl terephthalate (DMT), dimethyl fumarate (DMF), 1,4-butandiol (BD) and poly(tetramethylene oxide) (PTMO, M̄n = 1000 g/mol) was synthesized in a two stage process involving transesterification and polycondensation in the melt. The mole ratio of the starting components was selected to result in copolymers with a constant hard:soft segment wieght ratio (56:44). The amount of DMF was 10 mol %, referred to the total amount of the esters used. The synthesis was optimized in terms of both the concentration of catalyst, tetra-n-butyl-titanate, Ti(OBu)4 and thermal stabilizer N,N'-diphenyl-p-phenylenediamine, DPPD, as well as the temperature. The composition and structure of the synthesized poly(ether-ester)s were characterized by 1H-NMR. The number average molecular weights of the polymers calculated from the 1H-NMR spectra were compared with the corresponding values of the inherent viscosity (ηinh) in m-cresol and the complex dynamic viscosity (η*). The effect of the content of fumaric residues on the thermal properties of the synthesized copolyesters was also investigated using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA)

Synthesis, structure and properties of thermoplastic poly(ester-siloxane) elastomers

Two series of thermoplastic poly(ester-siloxane) elastomers (TPES), with hard segments based on poly(butylene terephthalate) (PBT) and soft segments based on poly(dimethylsiloxane) (PDMS), were synthesized by high-temperature, two-step transesterification reaction in the melt. In series I, the mass ratio of hard and soft segments was kept constant (57:43), while the length of the segments was varied, whereas in series II, the mass ratio of hard and soft segments was varied in range from 70:30 to 40:60, with a constant length of the soft segments. The segmented structure of the poly(ester-siloxane) copolymers was verified by 1H-NMR spectroscopy of the soluble and insoluble fractions, obtained after extraction of the samples with chloroform. The influence of the structure and composition of the TPES on the melting temperatures and degrees of crystallinity was investigated by differential scanning calorimetry (DSC). The rheological properties were investigated by dynamic mechanical analysis (DMA)

Thermoplastic Copolyester Elastomers

In this chapter the preparation, structure and properties of thermoplastic copolyester elastomers, TPEE, are presented. TPEEs are multiblock copolymers built up from so-called short crystallizable hard segments and long flexible segments. Owing to such chemical structure, TPEEs exhibit unusual combination of thermoplastic and elastomeric behavior. Physical and mechanical properties of these copolymers strongly depend on the chemical composition and the molecular structure of both hard and soft segments. By variation of the hard to soft segment ratio, the length of the soft segments and the degree of crystallinity of the hard segments, TPEEs ranging from soft to the relatively hard elastomers could be obtained. Recent developments in design and application of high-performance engineering TPEE materials and their blends and nanocomposites, as well as biodegradable TPEEs, are presented. Environmental impact, recycling possibilities and the future trends in TPEEs development are also addressed

Semi-interpenetrating polymer networks composed of poly(N-isopropyl acrylamide) and polyacrylamide hydrogels

Three series of semi-interpenetrating polymer networks, baaed on crosslinked poly(N-isopropyl acrylamide) (PNIPA) and 1 wt % nonionic or ionic (cationic and anionic) linear polyacrylamide (PAAm), were synthesized to improve the mechanical properties of PNIPA gels. The effect of the incorporation of linear polymers into responsive networks on the temperature-induced transition, swelling behavior, and mechanical properties was studied. Polymer networks with four different crosslinking densities were prepared with various molar ratios (25:1 to 100:1) of the monomer (N-isopropyl acrylamide) to the crosslinker (methylenebisacrylamide), The hydrogels were characterized by the determination of the equilibrium degree of swelling at 25°C, the compression modulus, and the effective crosslinking density, as well as the ultimate hydrogel properties, such as the tensile strength and elongation at break. The introduction of cationic and anionic linear hydrophilic PAAm into PNIPA networks increased the rate of swelling, whereas the presence of nonionic PAAm diminished it. Transition temperatures were significantly affected by both the crosslinking density and the presence of linear PAAm in the hydrogel networks. Although anionic PAAm had the greatest influence on increasing the transition temperature, the presence of nonionic PAAm caused the highest dimensional change. Semi-interpenetrating polymer networks reinforced with cationic and nonionic PAAm exhibited higher tensile strengths and elongations at break than PNIPA hydrogels, whereas the presence of anionic PAAm caused a reduction in the mechanical properties

High strength thermoresponsive semi-IPN hydrogels reinforced with nanoclays

Two series of nanoclay reinforced, thermoresponsive hydrogels were prepared, one based on poly(N-isopropylacrylamide) (PNIPA) and the other on semi-interpenetrating networks containing PNIPA and poly(N-vinyl pyrrolidone) (PVP), designated as SIPNs. The gels were crosslinked with 1, 3, and 5 wt % inorganic clay (hectorite) and SIPN gels additionally contained 1 wt % of PVP. The hydrogels were tested in the "as-prepared state," i.e., at 10 wt % PNIPA concentration in water and at equilibrium (maximum) swelling. Increasing the concentration of nanoclays increases crosslink density, modulus, tensile strength, elongation (except in equilibrium swollen gels), hysteresis and with decreases in the degree of swelling, broadening of the phase transition region, and a decrease in elastic recovery at high deformations. The presence of linear PVP in the networks increases porosity and the pore size, increases swelling, deswelling rates, and hysteresis, but decreases slightly lower critical solution temperature (LCST), tensile strength, elongation, and elastic recovery. The strongest hydrogels were ones with 10 wt % PNIPA and 5 wt % of nanoclays, displaying tensile strengths of 85 kPa and elongation of 955%. All properties of hydrogels at the equilibrium swollen state are lower than in the as-prepared state, due to the lower concentration of chains per unit volume, but the trends are preserved