Isotactic polypropylene‐compatible block copolymer

Chain-level mixing in polyolefins is investigated for blends of polyisobutylene (PIB) and polyethylene-co-1-butene (PEB). Previous reports suggest that PIB exhibits unusual mixing behavior in certain saturated blends relative to other polyolefins, even though it is immiscible with most. Variabletemperature 1 H, 2 H, 13 C, and 129 Xe NMR experiments are used to characterize local PIB chain dynamics in blends with PEB in which the concentration of 1-butene comonomer units is 23 or 66 wt %. Results from 1D and 2D solid-state 13 C exchange experiments, 1 H relaxation measurements, and 2 H line shape analysis indicate that local conformational dynamics of the PIB CH2 group in the polymer backbone increase significantly in blends with PEB copolymers containing 66 wt % butene comonomer (PEB-66). Even though the PEB-66 is a higher Tg polymer than PIB, PIB exhibits a lower effective Tg when the blend is formed relative to its pure state. Similar perturbations are not observed in the PIB/PEB-23 blend, indicating that this blend is not miscible at the chain level. These results are directly relevant to the length scale of glass transitions in polyolefins, indicating that local interchain packing plays an important role in the conformational dynamics that occur within a chain, and are suggestive of local configurational entropy contributions to mixing. Although 1 H spin-diffusion experiments could not reveal quantitative length scales of mixing in the these blends due to insufficient contrast between the constituents, 129 Xe NMR experiments showed that the PIB/PEB-66 blend was homogeneous on a 50 nm length scale. In agreement with the heterogeneous morphology indicated by the dynamic NMR experiments, 129 Xe NMR showed two resolved peaks for the PIB/PEB-23 blend, indicative of phase separation on a 50 nm length scale. The compilation of all the data, most of which was obtained at natural abundance, indicates that the PIB/PEB-66 blend exhibits intimate chain-level mixing on a length scale much shorter than Rg (ca. 8 nm). More importantly, the data show that reduced chain packing constraints occur in the miscible blend and suggest that local entropic contributions are the driving force for miscibility.

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Polyolefin Miscibility: Solid-State NMR Investigation of Phase Behavior in Saturated Hydrocarbon Blends

Wolak¹,

Jia²,

Gracz³

et al. 2003

“…A different approach to the exploration of the thermodynamics of i-PP blends has been taken by our group. 8,9 Previous experimental work 31 and the conformational asymmetry theory 30 described by eqs 3 and 4 both suggest that the excess free energy of mixing of a polyolefin blend will be minimized when ) 1. Guided by these results, we developed model polyolefins in homopolymer and block copolymer architectures that are compatible with i-PP.…”

Section: Introductionmentioning

confidence: 99%

Phase Behavior of Isotactic Polypropylene−Poly(ethylene/ethylethylene) Random Copolymer Blends

Weimann¹,

Jones²,

Hillmyer³

et al. 1997

Self Cite

The melt-state phase behavior of isotactic polypropylene (i-PP) blended with a series of poly(ethylene/ethylethylene) random copolymers has been investigated using small-angle neutron scattering (SANS). These PEExx copolymers, where xx is the percentage of ethylethylene (EE) units, were prepared by hydrogenation of anionically polymerized polybutadienes with controlled amounts of 1,2 addition. Random phase approximation (RPA) fits to the scattering data for blends of i-PP with a deuterated, low molecular weight PEE90 at 180 °C indicate a statistical segment length for i-PP that is 10% less than that reported previously. Scattering from blends of i-PP with higher molecular weight PEE90 and PEE73 at 180 °C can be quantitatively fit using the RPA theory with χ as the only adjustable parameter, indicating melt miscibility. PEE46 and PEE62 are strongly and marginally immiscible, respectively, with i-PP at 180 °C. These results establish a “window” in EE content in which these random copolymers can form single phase mixtures with i-PP.

“…P(S- b -EE) is a symmetric copolymer (50 wt % polystyrene) with one block containing, randomly, 70% ethyl ethylene (hydrogenated 1,2-butadiene) and 30% ethylene (hydrogenated 1,4-butadiene), and the other block was PS. Both blocks have molecular weight of 50 000, with narrow molecular weight distribution: M w / M n = 1.05 . Bates et al have shown that the EE block of this BCP is miscible in polypropylene .…”

Section: Methodsmentioning

confidence: 99%

“…Both blocks have molecular weight of 50 000, with narrow molecular weight distribution: M w / M n = 1.05 . Bates et al have shown that the EE block of this BCP is miscible in polypropylene . The other two copolymers were P(S- b -MMA) with M w = 85 000, and P(S- b -E) with M w = 40 000 .…”

Section: Methodsmentioning

confidence: 99%

Shearing of Polymer Drops with Interface Modification

Levitt

Macosko

1999

The influence of block copolymers (BCP) and interfacial reaction on the deformation of 30-100 µm polymer drops inside an immiscible polymer matrix was visualized in a parallel plate, counterrotating apparatus. Symmetric diblock copolymers were blended into polypropylene (PP), poly(methyl methacrylate) (PMMA), and polyethylene (PE) homopolymers. These were dispersed as drops in a polystyrene (PS) matrix. Addition of BCP significantly increased the amount of area the deforming drop generates when subjected to simple shear flow. Polymers with terminal amine groups (PMMA and PS) were coupled with maleic anhydride functional PS and PE. This reaction results in the formation of graft copolymer at the interface. These reactive pairs appear to be even more effective than BCP at generating interfacial area. The enhancement in area may be attributed to reduction in interfacial tension or to reduction in slip, but more likely a combination of both and a gradient in interfacial tension.