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In the copolymerization of Monomer 1 (M1)-and monomer 2 (M2) the reactivity ratios are ri = 0.05, r2 = 0.01, and in another case Monomer 1 (M1)-and monomer 3 (M3) the reactivity ratios are r = 20.0, r3 = 0.05. What type of copolymers would expect after 10% monomer conversion into polymer for Mı reacting with M2 and M1 reacting with M3, respectively? (Choose from the following four possibilities)

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שאלה #36998

		An block copolymer for Mi with M2 and in the second case of Ml and M3 a polymer mostly of Mi without M3
		A random copolymer for Mi with M2 and in the second case of M1 and M3_a alternating copolymer of Mi reacting with M3
done		An alternating copolymer for M, with M2 and in the second case of M1 and M3 a mostly homopolymer of My with a small amount of monomer M3 in the polymer
		A homo polymer of M; for Mwith M2 and in the second case of M1 and M3 a alternating copolymer of M1 reacting with M3

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מיין לפי דירוג חדש ישן

Which of the following polymers is most likely to have the highest glass transition points (Tg) (Choose from the following four possibilities)?

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שאלה #37075

		A vinyl polymer with side chains such as -CH3, -CH2CH3, -OCH3
		Aliphatic polyamides
		Aliphatic polyester
done		Polymers with rigid aromatic backbone segments

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מיין לפי דירוג חדש ישן

If I want to synthesize a polymer to act as a compatibilizers for two non compatible polymers which would be the best type of polymer to make (Choose the best answer from the following four possibilities)?

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שאלה #37076

		A random copolymer where each of the two monon ers has a solubility parameter similar to at least one of the incompatible polymers.
done		A block copolymer where each of the blocks has a solubility parameter similar to the Solubility of one of the incompatible polymers.
		An alternating copolymer where each of the two monomers has a solubility parameter similar to the solubility of one of the incompatible polymers.
		A graft copolymer where both the graft and the polymer backbone have the same solubility parameter as one of the incompatible polymers.

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מיין לפי דירוג חדש ישן

For mechanical properties measured by the tensile modulus (stress/strain) as a function of temperature which of the following statements is correct? (Choose from the following four possibilities)

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שאלה #37077

		Above the Tg the modules for amorphous polymers drops to a plateau and stays constant until its Tm where it falls sharply again
		ncreasing temperatures above the Tg for polycrystalline polymers the tensile modules has a sharp drop that after the Tm also drops but not as sharply
		rosslinked amorphous polymers drop in tensile modulus above the Tg and have the same profile after the Tg as non crosslinked amorphous polymers.
done		Increasing temperature above the Tg but below the Tm, the tensile modules drops strongly for amorphous polymers but does not decrease as much for polycrystalline polymers.

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מיין לפי דירוג חדש ישן

To study stereo regular placement of the groups in the polymer chains and how it affects the Tg and Tm which combination of methods would you chose? (Choose from the following four possibilities)

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שאלה #37078

done		Differential Scanning Calorimetry (DSC) and Nuclear magnetic resonance (NMR)
		X-ray diffraction (WAXS and SAXS) and Nuclear magnetic resonance (NMR)
		Transmission electron microscopy (SEM) combined with Electron Spectroscopy for Chemical analysis (ESCA)
		Pyrolysis-gas chromatography and Raman spectroscopy

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מיין לפי דירוג חדש ישן

Though both cellulose and starch are both made from glucose monomers they have very different mechanical and solubility properties. This difference is due to which of the following. (Choose from the following four possibilities)

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שאלה #37079

		The cellulose polymer has a coiled helical structure with internal hydrogen bonding which holds the polymer together as compared to starch which is linear
		The structure of starch allows it to be highly crystalline and cellulose is amorphous
		Cellulose is a covalently crosslinked linear molecule through the -OH groups to form - O- bonds, while starch is crosslinked by non covalent H-binding interactions.
done		None of the above.

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מיין לפי דירוג חדש ישן

The synthesis of polypeptides by the Merrifield processes is much simpler than the synthesis polynucleotides for which of the following reasons: (Choose from the following four possibilities)

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שאלה #37080

		Peptides are held together by amide bonds which are easier to form than phosphate bonds.
		Polynucleotides are less stable than peptides and this requires better control over the reaction conditions
done		In peptide synthesis there are fewer groups to protect than in nucleotide synthesis
		The amine base components of the nucleotide often interfere with the coupling reactions and this lowers the yield.

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מיין לפי דירוג חדש ישן

Under what polymerization conditions can a polymer be synthesized where the ratio of the weight average to number average molecular weights (Mw/Mn) approaches 1.0. (Choose from the following four possibilities)

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שאלה #37081

		Condensation polymerization under exact stoichiometric conditions of the reactive groups
		Polymerizations where the termination and chain transfer rates are high as compared to initiation and propagation
sentiment_very_satisfied		Free radical polymerization where the growing chain end is protected from termination or chain transfer
		Anionic polymerization where propagation and termination occur at the same rates.

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מיין לפי דירוג חדש ישן

A certain monomer is polymerized by benzoyl peroxide labeled in the benzene ring with carbon-14. Analysis by carbon counting shows that the polymer contains on average 1.9 labeled phenyl groups per molecule. Assuming no chain transfer occurred what does this indicate about the mechanism of termination? (Choose from r the following four possibilities)

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שאלה #37082

		Most of the termination occurred by disproportionation and a small fraction by chain coupling.
done		Most of the termination occurred by coupling and a small fraction of by disproportionation
		Termination occurred mainly by reaction with coupling of the propagating chains to radicals generated by the benzoyl peroxide
		None of the above.

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מיין לפי דירוג חדש ישן

Stress vs. strain curves which are measured when the polymer material has been deformed at a constant rate may be characterized by which of the following characteristics? Which of the following statements is correct? (Choose from the following four possibilities)

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שאלה #37083

		In glassy polymers small forces are needed to obtain large strain (deformations)
		If material breaks under a small strain it is said to be tough
		A material is brittle when it breaks under a large strain (deformation)
mood		Factors which influence toughness are MW, crystallinity and intermolecular forces

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מיין לפי דירוג חדש ישן

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