23

Kevlar is an A,B co-polymer where the monomers are terephthalic acid and 1,4-diaminobenzene. The amide linkage, together with the aromatic rings in the polymer, makes a very rigid polymeric structure that stacks the chains in an organized way, maximizing the effectiveness of hydrogen bonding between amide linkages, together with pi-stacking of the rings: ...


13

You have a possible answer to your question in proteins, an example which includes some long polymer chains. Intramolecular interactions - while not necessarily the driving force for formation of a collapsed protein globule (usually argued to be due to the hydrophobic effect, requiring intermolecular interactions) - are the basis for higher order structure ...


10

First, it's important to define what you mean by "nylon", a term which is often used generically to refer to many different aliphatic polyamides. The most common are "nylon 6" and "nylon 6,6". Nylon 6 is the polymer of 6-aminohexanoic acid (aka 6-aminocaproic acid), while nylon 6,6 is from alternating units of 1,6-diaminohexane (aka hexamethylene diamine) ...


10

You can combine materials in two ways: chemically and mechanically. On average, if you want to the desired physical properties to add up, you want to go mechanical way, not the chemical one. Once the reaction takes place, the there is absolutely no reason to assume the product preserves properties of both precursors. It might sometimes, but more often than ...


7

No, neither C nor Si have to be present in a polymer. IUPAC defines polymer simply as A substance composed of macromolecules. In turn, there is no limitations on the elements the macromolecules may consist of. In fact, there is an extensive class of inorganic polymers free of carbon and silicon.


7

Sodium is included in the name because it was essential in the chain polymerization that forms the rubber. Sodium served as the initiator for the anionic polymerization.


7

You are starting out with amino groups on one monomer and carboxylate groups on the other monomer. As William R. Ebenezer states in the comment, these combine via condensation (to form an amide, which is written as -NHCO- or -CONH- in condensed formulas). The linkages in the answer choices between repeating units are not visible until you write another ...


7

Well, this is a rather obvious development (in retrospect, that is). We had an $sp^3$ carbon with tetrahedral bonds, and it made diamond. We had an $sp^2$ carbon with trigonal bonds, and it made graphite. What if we just had a linear $sp$ carbon? Such thoughts have been around for more than quite a while. Theorists swarmed around that non-existent tree. No ...


6

I hope this is not a homework question. Suppose your polymer has $n$ reapeating units and capped with methyl groups at the end as you described. Thus, it should looks like following figure: Thus it has $n$ $\ce{(-CH2CH2-)}$ units and $2$ $\ce{(-CH3)}$ units. Thus your $\ce{(-O-CH2-)}$ signal is accounted for $4n$ protons while $\ce{(-O-CH3)}$ signal ...


6

Actually, polyethylene is still an alkane as it fits IUPAC definition perfectly fine [1, p. 1313]: alkanes: Acyclic branched or unbranched hydrocarbons having the general formula $\ce{C_nH_{2n+2}}$, and therefore consisting entirely of hydrogen atoms and saturated carbon atoms. Smaller alkane molecules you are referring to, are oligomers. IUPAC defines ...


5

First, note that formazine structure attached from PubChem is a different compound; note that there are also, related, formazan $\ce{HN=N-CH=N-NH2}$ and “formaldazine” $\ce{CH2=N-N=CH2}$ (dimethylidenehydrazine); formazin (polymer) does not necessarily has to have cage-like structure, as this characterization belongs to hexamethylenetetramine in the quoted ...


5

A classic hygrometer consists of bundle of a dozen or so human hairs (blonde are supposedly best, because they're typically thinnest, i.e. react fastest to humidity changes), stretched between a metal spring with a pointing device and a fixed point. A uniaxial effect is much easier to record precisely, and hair is thin (=fast) and far more mechanically ...


4

There are non-enzymatic methods for removing the three glucose moieties of stevioside 1. Unfortunately, dilute mineral acid hydrolysis not only removes the glucose entities but also effects Wagner-Meerwein rearrangement of the aglycone steviol 2 to isosteviol 3.1 While vinegar (5% aqueous acetic acid) is a weaker acid than hydrochloric acid, I am certain ...


4

As propylene glycol can dissolve plastic... This claim is absurd. Propylene glycol cannot dissolve poly(olefin) polymers especially polypropylene or polyethylene. It is possible for glycols to cause paneling of containers made to such, but not dissolve; and certainly wouldn't happen in the amount of time it takes to perform an injection.


4

Is temperature of crystallization same as melting point temperature for polymers? In a word: NO. If you undrestand what the glass transition, crystallization and melting temperatures are it will make sense why they are not the same. This paper does an excellent job at explaining the three concepts but I will summarize. The glass transition temperature is ...


4

Acrylates/Beheneth-25 Methacrylate Copolymer is an INCI name for a copolymer … formed from the ester of 2-methylpropenoic acid and docosanol, ethoxylated, 25 mol EO (average molar ratio) and one or more monomers of acrylic acid, methacrylic acid or one of their simple esters (Source: cosmetics.specialchem.com) Also known by the trademark Aculyn™ 28. Dow ...


4

This table indicates that polyethylene (HD/LD not specified) "melts at" 135°C, decomposes in the range 335-450°C, and produces vapors that will ignite between 341-357°C. I'm sure melting/softening temperature is more complex than that, but I'm not sure that you should expect much decomposition into toxic gases at temperatures below 260°C. However, if you'...


3

Note: I was employed at DuPont in the 1990's, and my understanding of Teflon(R) cookware manufacturing is based on proximity to product research and development and not from hands-on experience with PTFE formulations. Teflon(R) polytetrafluoroethene coated materials are manufactured in several steps. The PTFE coating is specially formulated as a waterborne ...


3

There is at least a fair degree of consensus (there will always be naysayers) that the results that were performed back in the 80s and 90s by Berner and Landis were false positives that could not be confirmed by further investigations. A good historical account of this can be found for instance in Nick Lane's book "Oxygen" (first published in 2002). Quoting ...


3

It's rather molecular mass concept. According to normatives, MM of polyethylene is from tens of thousands units to several million. So molecule must weight at least 10000 to be considered polyethylene (otherwise it can be named as oligomer of ethylene). But I should mention that there are no precise "threshold" like "10-100 monomers = oligomer, 100+ - ...


3

As reported in Gooch JW (Jan W. Encyclopedic Dictionary of Polymers. Springer; 2011. doi:10.1007/978-1-4419-6247-8. Poly(N-methyl methacrylamide) has a refractive index of 1.5398


3

Running the calculation without imposing symmetry constraints should give the same ground energy as one with them because the true electronic ground state of the system (within the Born-Oppenheimer approximation) always has the same symmetry as the nuclei. The variational principle always puts an upper bound on your ground state energy, so in principle it ...


3

You got the answer you have looking for in Karsten Theis' answer. However, your statement of "as far as I know, there should be double bonds present at the ends of the repeating unit" is not entirely correct for all polymers in general (see A.K.'s comment). Yes, some have double bonds within the chain and at the end. But, most polymers forms without ...


3

First off, lets understand how densities of poly(ethylene) are differentiated. The prototypical polyethylene is often represented as a simple repeating ethylene monomer units as shown below: This is what high-density polyethlyene (HDPE) is constructed of; simple linear monomer units that form closely packed crystal structures. This polymer is synthesized by ...


3

Many hygroscopic materials have this behaviour but sometimes they might have some "memory" of the previous swellings cycles, or the swelling might vary depending on the arrangments of the polymers chains, making them often not so reliable for such a device. You might want to do some testing on Nylon which is hygroscopic (more detail in the link). Also, ...


3

I think the meaning of the word "bulk" — as it is used in English language — is preserved here despite chemical context. I suspect that it's been used to stress some aspects or features of the surface chemistry: thin film is a 2D object, whereas bulk polymer is a 3D object (e.g. continuous in three directions) possessing a significant volume. From IUPAC's ...


2

Not polyethylene, but I recall doing an experiment in school where hexamethylenediamine and adipic acid were poured carefully so one was layered on top of the other. They did not mix in bulk, but reacted at the contact surface to form a Nylon-type polymer barrier. We poked a rod in to pull the polymer out (enabling more reaction) and wind it around the rod!...


2

"Strength" is a dubious quantity. The E-modulus will rise, and as the material swells with more and more monomer diffusing in, it will at some point rupture when the brittle network cracks. Like a fruit gum that was put in water overnight. I have no idea if the two networks actually stay separated, or if they interconnect more and more. I suspect the latter,...


2

The standard way is to solve for the eigenvectors of your Fock matrix. Since you have a single electron, that's your Hamiltonian. Any number of programming languages have algorithms for this implemented. Each of your coefficients would correspond to an entry in the eigenvector.


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