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What would be the number average molecular weight of the polymer formed from the condensation polymerization of 6-aminohexanoic acid (MW131) and the cyclic amide caprolactam (MW 113) where from both nylon 6 if the reaction were carried out to 99.9% reaction conversion? (Choose from the following four possibilities)

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שאלה #36988

		131,000 and 113,000
		113,000 and 95,000
done		113,000 and 113,000
		113,000 and 131,000

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מיין לפי דירוג חדש ישן

Free radical polymerization of olefins general forms polymers with a broad range of molecular weights. To overcome this and to form polyolefins having a narrow range of molecular weight by a free radical polymerization which of the following approaches has been successful?

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שאלה #36989

done		Reversibly blocking the growing chain end with a group that associates and dissociates. .
		b) Adding radical transfer agent
		Controlling the initiation step by using initiators with high efficiency.
		Ensuring that the rate of initiation is equal to the rate of termination.

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מיין לפי דירוג חדש ישן

The difference in mechanical properties between low density polyethylene and high density polyethylene is due to which of the following? (Choose from the following four possibilities)

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שאלה #36990

done		Low density PE has side chains and is amorphous while high density is none branched and can form crystallites
		Low density polyethylene has added plasticizers to reduce density but high density PE does not have added plasticizers
		Low density PE have side chains which enhance crystallite formation, while high density is none branched and amorphous
		None of the above.

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מיין לפי דירוג חדש ישן

Which of the following statements on polymerization mechanisms is correct? (Choose from the following four possibilities)

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שאלה #36991

		In chain reaction polymerization by peroxide or azo initiators the termination step can be easily controlled to achieve a narrow molecular weight range
		Step polymerization reactions such as the reaction of di-isocyanates with di-alcohols always have a reaction by-product in the polymerization reaction
done		In step condensation and step addition polymerization as close as possible to exact Vstoichiometry of reactive groups is needed for achieving high molecular weight.
		None of the above

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מיין לפי דירוג חדש ישן

Olefin polymers made by complex metal coordination catalysts generally can have better mechanical properties than the same polymers made by free radical or cationic polymerization. The reason for this is (Choose from the following four possibilities)

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שאלה #36992

		The coordination catalysts introduce polar groups resulting in stronger polymer chain interactions
		Metal coordination of the growing polymer chain changes the chemical structure of the monomer as it is added to the growing chain end to give a polymer with stronger non covalent chain interactions
done		Metal coordination of the growing polymer chain allows for steric orientation of the monomer addition and enhances final polymer crystallization.
		Coordination catalysts formpolymers with a crosslinked network that improves mechanical strength.

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מיין לפי דירוג חדש ישן

The polydispersity of a particular polymer sample is 1.8 and the molecular weight (MW) determined by light scatter was 126,000 what MW would a membrane osmometry measurement determine?

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שאלה #36993

		140,000
done		70,000
		35,000
		17,500

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מיין לפי דירוג חדש ישן

If a polyvinylchloride (PVC) polymer sample elutes on a gel permeation chromatograph column at the same volume as a polystyrene sample that has a molecular weight of 20,000 and an intrinsic viscosity of 2.3 dL/g and the PVC polymer has an intrinsic viscosity of 4.8 dL/g what is the molecular weight of the PVC polymer sample?

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שאלה #36994

		583 1
		1916
		38332
done		9583

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מיין לפי דירוג חדש ישן

The following polymers were synthesized: (I) polyvinyl alcohol, (II) polyacrylonitrile, (III) polyamide and (IV) polyacrylic acid. What are the different types of inter-chain secondary interactions in each of the polymers? (Choose from the following four possibilities)

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שאלה #36995

done		I-hydrogen bonding, II polar, III-Hydrogen bonding, (IV)-ionic
		I-covalent, II van der Waals, III-hydrogen bonding. (IV)-polar
		I- hydrogen bonding, II ionic, III-polar, (IV)-ionic
		I-hydrogen bonding, II polar, III-Van der Waals, (IV)-ionic

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מיין לפי דירוג חדש ישן

A new polymer has been synthesized with the structure - (CH2-CHR)n- where R contains the groups of -C(=O), and -C6H5. The group attraction constants G [(cal cm3)1/2 mol-11 are for -CH2- is 133, and for -C=O it is 275, and for -CH-it is 28, and for -C6Hs it is 735. Using the equation for solubility parameters of polymers o[(cal cm)1/2] =DEG/M where M is the molecular weight 132, d is the density of 1.2 determine which of the following solvents will most likely dissolve the polymer? (Choose from the following four possibilities)

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שאלה #36996

		Hexane d= 7.5
done		Chloroform d= 9.65
		Dimethyl formamide d= 12.4
		Ethyl alcohol d= 13.1

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מיין לפי דירוג חדש ישן

Three different methods are used to determine molecular weight distribution by separating the different molecular weight fractions. These methods are Fractional solution (FS), fractional precipitation (FP) and gel permeation chromatography (GPC): Which of the following statements on the sequence in which the different molecular weights are separat d by each method is true? (Choose from the following four possibilities)

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שאלה #36997

		The low molecular weight fra tion is first separated in each of the method (FS, FP and GPC)
		The low molecular weight fraction is removed first in GPC, FP but not in FS.
done		The low molecular weight fraction is removed first in FS but not in GPC, FP.
		The low molecular weight fraction is removed first in FP but not in GPC or FS.

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מיין לפי דירוג חדש ישן

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