Poly block copolymer impact strength

The use of core-shell impact modifiers combined with styrene-hydrogenated poly butadiene block copolymers in sPS is described by Rohm and Haas [24]. The core of the former type is of polybutadiene or its copolymer, the shell consists predominately of polystyrene. Rohm and Haas found that a synergistic effect is present and that the Izod notched impact strength is higher when both rubber types are used instead of only one. 

X HE IMPORTANCE AND UTILITY of multiphase copolymer systems have been well documented in the literature (1-4), with emphasis on their unique combination of properties and their potential material applications. Or-ganosiloxane block polymers are a particularly interesting type of multiphase copolymer system because of the unusual characteristics of poly siloxanes, such as their stability to heat and UV radiation, low glass transition temperature, high gas permeability, and low surface energy (i, 2, 5). The incorporation of polysiloxanes into various engineering polymers offers an opportunity for many improvements, such as lower temperatures for the ductile-to-brittle transitions and improved impact strength. 

As discussed earlier, ethylene propylene rubber (EPR or EPM) has been blended with PP and PE to improve the impact strength and to render the materials softer. Recently, metallocene catalysts or postmetallocene catalysts provide new pathways to generate elastic copolymers that can replace EPR. These pathways possess cheaper manufacturing cost and generate new materials with better compatibility to PP or PE. Such new materials included ethylene-propylene random copolymers with dominant ethylene component (33-34) or propylene-dominant component (35 1), propylene-ethylene block copolymer (42), ethylene-octene copolymer (43), poly(propylene-co-ethylene) (44), ethylene-hexene copolymer (45), ethylene-butene copolymer (46), low isotactic PP (47), and stereoblock PP (48). These materials are generally compatible with PP or PE, thus can be used to tailor the toughness (or the softness) of... 

Glycidyl methacrylate copolymers Ethylene/butyl acrylate/maleic anhydride copolymers Styrene/ethylene-butylene/styrene block copolymer Poly(amide) (PA), MgO Silicone rubber and aminosilane Liquid crystalline polymers Improved impact strength Improved impact strength" Improved impact strength Improved electrical properties, in glass fiber applications" Improved mechanical properties" Viscosity reduction" ... 

In order to improve the low-temperature notched impact strength of polycarbonate while still maintaining the transparency, new polycarbonate-poly(dimethyl siloxane) block copolymers were developed (Maruvada et al. 2005). These PC-siloxane block copolymers were transparent as long as the siloxane block length was kept short (<10 units), so that fine siloxane rubber domains (10-40 nm) were... 

However, for homopolymer poly(TMC) and PLA blends, the corresponding wt% of mbber phase did not improve the notched Izod impact strength. Joziasse et al. (1998) have investigated blends of PLA homopolymer with poly(trimethylene carbonate) (poly(TMC)) mbbery copolymers. They found that the samples with 21 wt% of the mbber block of poly(TMC) in PLA did not break in an unnotched impact test. Diblock copolymers of L-lactide and caprolactone (P(LA/CL)) were also blended with PLA to determine their influence on the mechanical properties. The addition of 20 wt% of diblock copolymer improved the unnotched impact strength of the blend from 5 kJ/m to 50 kJ/m. ... 

Random copolymer addition to binary blends involving copolymers with structural units equal or similar to the blend components or with specific interacting groups capable of non-reactive interaction with one of both the blend components comprises another ternary polymer addition approach. An early example involved EPR (ethylene-propylene rubber) addition to HDPE/PP blends, where synergistic impact strength was observed. In some cases, the random copolymers have been compared to block copolymers comprised of the same units. The compatibihzation of LLDPE/PMMA and LLDPE/poly(MMA-co-4-vinyl pyri-dine(4VP)) blends with poly(ethylene-co-methacrylic acid) (EMAA) addition were compared [47]. Modest improvements in LLDPE/PMMA dispersion and strength were observed. The specific acid-base interaction allowed for much larger improvements with EMAA addition to LLDPE/PMMA-CO-4VP blends. 

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