The melt rheological behavior of AB, ABA, BAB, and (AB)n block copolymers with monodisperse aramide segments

The melt rheological behavior of segmented block copolymers with high melting diamide (A) hard segments (HS) and polyether (B) soft segments was studied. The block copolymers can be classified as B (monoblock), AB (diblock), ABA (triblock, diamide end segment), BAB (triblock, diamide mid-segment) and (AB)n (multiblock) block copolymers. Varied were the number of HS in the chain, the HS concentration, the position of the HS (in the chain or at the end of the chain) and the molecular weight of the copolymers. The melt rheological behavior of the copolymers was studied with a plate–plate method. The materials B (monoblock), BAB (triblock, diamide mid-segment), and (AB)n (multiblock) block copolymers had a rheological behavior of a linear polymer and the complex viscosity increased with molecular weight. Surprisingly, the diblock copolymers AB and the triblock copolymers ABA at low frequencies and near the melting temperature of the copolymers had the behavior of a gelled melt. The diamide segments at the chain end seemed to form aggregates, whereas the diamide mid-segments did not. Also, time-dependent rheology of diblock copolymer confirmed the network structure built up in the melt. The block copolymers with H-bonding diamide end segments had a thixotropic behavior. POLYM. ENG. SCI., 2010

Polyurethane tri-block copolymers - Synthesis, mechanical, elastic, and rheological properties

A series of polyurethane tri-block copolymers were synthesized by reacting a 4,4′-methylenebis(phenyl isocyanate) (MDI)-endcapped poly(tetramethylene oxide) (PTMO, Mn = 2,000 g/mol) with a monoamine-diamide (6T6m) hard segment (HS). The concentration of the HS in the copolymer was varied between 9 and 33 wt % by changing the length of the soft mid-block segment. The structure of the copolymers was analyzed by nuclear magnetic resonance, the amide crystallinity was investigated by Fourier transform infra-red and the thermal properties were studied by differential scanning calorimetry. The mechanical and elastic properties of the tri-block copolymer were subsequently explored by dynamic mechanical analysis, compression set and tensile experiments, and the melt rheological behavior was studied by a parallel plate method. The amide end groups displayed a high crystallinity and the modulus of the tri-block copolymers was relatively high. The fracture strain increased strongly with the molecular weight and the copolymers demonstrated a ductile fracture behavior for molecular weights above 6000 g/mol. Good compression set values were obtained for the tri-block copolymers despite their low molecular weight. In the molten state, the tri-block polymers displayed a gelling effect at low frequencies, which was believed to be a result of a clustering of the end-segments. POLYM. ENG. SCI., 2010

Polyurethane triblock copolymers with mono-disperse hard segments. Influence of the hard segment length on thermal and thermomechanical properties

Polyurethane triblock copolymers were synthesized by reacting 4,4-methylenebis(phenyl isocyanate) (MDI)-endcapped poly(tetramethylene oxide) (PTMO) with mono-amine-amide (MMA) units. Four different MMA units were used, i.e. no-amide (6m), mono-amide (6B), di-amide (6T6m) and tri-amide (6T6B), based on hexylamine (6m), 1,6-hexamethylenediamine (6), terephthalic acid (T), and benzoic acid (B). The PTMO had a molecular weight of 2000 g/mol. Thermal and thermo-mechanical properties were studied by means of differential scanning calorimetry and dynamic mechanical analysis, respectively. The structure of the carbonyl bond was explored by infra-red analysis and the elastic behavior of the materials by compression set experiments. The triblock polyurethanes with mono-disperse, hard end-segments displayed low molecular weights (3200-3800 g/mol). The crystallinity of the MDI urethane-urea group was found to depend on the structure of the amide. Increasing the number of amide bonds in the mono-disperse hard segment increased the modulus and the hard segment melting temperature, and decreased the compression set values. The low temperature properties were hardly affected by the amide lengt

Tuning of mass transport properties of multi-block copolymers for CO2 capture applications

Polyether and especially poly(ethylene oxide) (PEO) based segmented block copolymers are very well known for their high CO2 permeability combined with a high CO2/light gas selectivity, but most (commercially) available block copolymers have incomplete phase separation between the soft and hard blocks in the polymer leading to reduced performance. Here we present a polyether based segmented block copolymer system with improved phase separation behavior and gas separation performance using poly(ethylene oxide) (PEO) and/or poly(propylene oxide) (PPO) as a soft segment and short monodisperse di-amide (TΦT) as a hard segment.\ud \ud In this work we tune the mass transport properties of such multi-block copolymers for CO2 capture by systematically investigating the effect of the type and length of soft segment in the block copolymer at constant short hard segment. The effect of (1) the length of the PEO soft segment, (2) the type of soft segment (PPO vs. PEO) and (3) the use of a mixture of these two different types of soft segment as a method to tune the gas separation performance and its relation with the thermal–mechanical properties is investigated. The use of such a polyether based segmented block copolymer system as presented here offers a very versatile tool to tailor mass transfer and separation properties of membranes for gas and vapor separation

Tuning of mass transport properties in macromolecular structures

Polyether and especially poly(ethylene oxide) (PEO) based segmented block copolymers are very well known for their high CO2 permeability combined with a high CO2/light gas selectivity, but most (commercially) available block copolymers have incomplete phase separation between the soft and hard blocks in the polymer leading to reduced performance. Here we present a polyether based segmented block copolymer system with improved phase separation behavior and gas separation performance using poly(ethylene oxide) (PEO) and/or poly(propylene oxide) (PPO) as a soft segment and short monodisperse di-amide (TΦT) as a hard segment. In this work we tune the mass transport properties of such multi-block copolymers for CO2 capture by systematically investigating the effect of the type and length of soft segment in the block copolymer at constant short hard segment. The effect of (1) the length of the PEO soft segment, (2) the type of soft segment (PPO vs. PEO) and (3) the use of a mixture of these two different types of soft segment as a method to tune the gas separation performance and its relation with the thermal–mechanical properties is investigated. The use of such a polyether based segmented block copolymer system as presented here offers a very versatile tool to tailor mass transfer and separation properties of membranes for gas and vapor separation