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    ENGINEERING TASK ENGLISH

    Name : Harris Nur Hidayat

    NIM : 2010440009

    Chapter 2

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    Molecular weight and polymer solution

    2.1 Weight average molecular weight and number average molecular weight

    Molecular weight is a variable that is particularly important because direct contact with the physical

    properties of polymers. In general, polymers with higher molecular weight are more powerful, but (as

    will be shown in the net chapter! that is too high molecular weight bias causes difficulties in

    processing. "ow to define a molecular weight of the polymer in #uestion and the epected

    application. In this chapter will be presented the definitions of molecular weight and molecular weight

    distribution determination method in a polymer sample. We will provide a discussion of the molecular

    structure of the polymer, because the solubility is a prere#uisite for the determination of molecular

    weight.

    Mentioned that the polymers are compounds with high molecular weight, but we must start with the

    #uestion, how do we interpret the high molecular weight$ %ntil that limit rendan molecular weightand molecular weight ranging how high$ &ot easy to answer, because what constitute the molecular

    weight of the 'low', for eample, for a sample of polyethylene, may be ideal for polyamide samples.

    Moreover, some polymers deliberately made with a low molecular weight (even as oligomers! to

    facilitate the initial process, the molecular weight increases the level of the net process. ut in

    general, the polymers are considered as having a molecular weight ranging from thousands to

    millions, with the optimum molecular weight depends on the chemical structure and its application.

    )inyl polymers that have commercial value usually has a molecular weight between 1*+ to 1*.

    -olymers having functional groups are very polar, such as polyamides, may have a low molecular

    weight ranging from 1+,*** to 2*,***.

    o define the molecular weight compounds are simple (nonpolimeri/!, we use the techni#uescommonly /nown as mass spectrometry, the free0ing point depression (/rios/op!, the boiling point

    elevation (ebulliometri! and when present functional groups are suitable, titration (for eample,

    neutrali0ation, or saponification!. "owever, the determination of the molecular weight of the

    polymers is much more comple by the following two basic reasons. irst, in a polymeri0ation

    process, in fact it would not be possible if all of the growing polymer chain ends (berterminasi! with

    vesar or similar chain length therefore one needs to treat the average molecular weight. (3ome natural

    polymer having a molecular weight typically have a legal eception to this!. 3econd, the techni#ues of

    /rios/opi, ebulliometri, and titration only effectively applied to polymers with relatively low

    molecular weight methods must be more sophisticated to polymers with higher molecular weight of

    4*,***. Conventional techni#ues of mass spectrometry is not much more used in the field beyond thecharacteri0ation of polymer5related products of polymer degradation products because of the

    re#uirements for sample measurement is volatile. 6ately it has been found ebberapa eciting new

    developments in the

    field desorption mass spectrometry has epanded into the area of macromolecules. "owever, such

    developments are still in the early phase (growth! and do not have regular use of the methods in a

    more traditional molecular weight determination.

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    he techni#ues are more commonly used for polymer molecular weight determination is osmometri,

    light scattering (light scattering!, and ultracentrifugation, although titration (end group analysis!,

    /rios/opi, and ebulliometri also used in some applications. 1.2 he most convenient method for

    routine determination of molecular weight measurement involves vis/opsitas solution, but this is not

    an absolute method and can only be used in con7unction with any of the techni#ues of measurement of

    absolute molecular weight.

    Molecular weight values obtained depend on the magnitude of the si0e of the measurement method.

    he method relies on the analysis of end groups or colligative properties (free0ing point depression,

    the boiling point elevation, osmotic pressure! results in what is /nown as the average molecular

    weight of numbers or a number because the number of molecules of each of the respective weight of

    the sample is calculated. he total weight of a polymer sample,w, is the total weight of each species

    of molecules that eist8

    where & and M, respectively show the number of moles and molecular weight of each species i.

    9verage molecular weight number,Mn, is the sample weight per mole8

    or eample, suppose we have a sample of a polymer consisting of : mol molecular weight of ;*,***

    and + mol molecular weight of +*,***, then

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    theMw= Mn. &arrower molecular area valuesMwandMnhis closer, and thus the ratioMw =Mn can be

    used as an indication of the width of the molecular weight of a polymer sample. his ratio is called

    the index polidispersiias and systems that have a region depends on the molecular weight of the

    polymer solubility and interaction 5 solvent.

    2.2 3olution polimer;

    >issolving a polymer is not the same as dissolving compound having a low molecular weight because

    of the dimensions are very different between the solvent and the polymer molecules. >issolution of

    the polymer occurs in two stages. 9t first solvent molecules diffuse across the polymer matri to form

    a mass called a bulging and solvated gel. (9 student who closes a flas/ containing organic solvents

    with a rubber cap surely see for yourself the effects of development coupled with gel formation !. In

    the second stage, the gel brea/s (divorce5divorce! and the molecules are dispersed into a true solution.

    >issolution is often a slow process. While some types of polymers can be dissolved rapidly in certain

    solvents, other polymers may re#uire long periods of heating near the melting point of the polymer.&etwor/ polymers can not be dissolved, but usually swollen (ballooned! in the presence of solvent.

    ?ven some linear polymers can not be dissolved in any manner whatsoever, hence the lac/ of

    solubility of the polymer does not necessarily mean that the person concerned is a type of polymer

    networ/.

    "ow does one choose a solvent$ he easiest way is to chec/ on a polymer handbook, in which

    accumulated abundant list of solvents and nonpelarut for various types of polymers. 4a detailed study

    of the solubility of the polymer using the principles of thermodynamics have melhir/an semiempiris

    relationships to predict solubility. 9 dissolution process is governed by the free energy relationship.

    @A "5 3

    When a soluble polymer with a spontaneous, free energy solution, @, is negative. ?ntropy solution,

    3, always has a positive value that occurs as a result of the increase in conformational mobility of

    the polymer chains. herefore, the magnitude of the enthalpy of solution, ", will determine the sign

    of @. It has been proposed that the hot miture "miBfor a binary system parameters related to the

    concentration and energy through the e#uation where )miis the total volume of the miture,V1 and V2

    is the molar volume (molecular weight =

    49

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    density! of the two components, is the volume fraction, and ?1and ?2 and are the

    energy evaporation. 3cale meeting called cohesive energy (rapat energi kohesif!. If

    replaced with a symbol, then the above e#uation is written more simply8

    symbol called the solubility parameter. Clear that, in order to dissolve the polymer (

    negative!, the mi should be small. In other words, , must have a value that is

    approimately the same. When , solubility at all only influenced by the effects of entropy.

    herefore, predictions based on the discovery of the solubility of the solvent and the polymer

    solubility parameters were comparable, who need a way (tool! to establish a cohesive energy meeting.

    Meeting cohesive energy is the energy re#uired to move a molecule from its nearest neighbors, thus

    analogous to the heat of vapori0ation per volume for a compound that is volatile (easily evaporated!.

    or the solvent, can be calculated directly from the latent heat of vapori0ation ( ! using therelationship

    Where is the ideal gas constant, and is the absolute temperature in Delvin. hus

    ecause polymers have negligible vapor pressure, the easiest method is to use to determine the molar

    attraction constant of the cluster. he constants derived from the results of a study of compounds withlow molecular weight that gave birth to numeric values for the various groups of molecules based on

    the consideration of intermolecular forces. wo sets of these numeric values (denoted by G! have been

    proposed, one by 3mall, + which is derived from the heat of vapori0ation, and the other by "oy,

    which is based on the vapor pressure measurements. Gvalues are given in able 2.1 is typical. It is

    clear that there is a significant difference between the values proposed by 3mall and "oy. 3ets which

    are used are usually determined by the method used to determine the value of the solvent.

    he values of @ is in addition to a certain tru/tur, and lin/ed to by the e#uation

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    Where d is the type of M is the molecular weight. 9s an eample for polystyrene has a density

    (obtained from handhboo/4b! 1.*+ and re51*4 mass units, as well as the structure

    Calculated, using the values of G3mall, as

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    reduced, it becomes more important intramolecular interactions, which cause shrin/age of the

    hydrodynamic volume.

    It is easy to epress r and s by the following two factors8

    ied dimensions (r* ataus*! and the epansion factor (E!. hus,

    ied dimension refers to the si0e of the macromolecule eclusive solvent effects. "e arose from the

    combination of free rotation and intramolecular steric interactions and polar interactions.

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    With r*2E2 obtained

    Which can be rearranged into

    ecause r* andM is constant, with regard

    hen

    9t the theta temperature, E A 1 and

    or conditions other than the theta temperature, the e#uation has the form

    Where a is a constant which changes depending on the polymer, solvent, and temperature. Dnown as

    theMark-ouwink e!uation-"akurada, this e#uation is important that, as we will see later in 3ection

    2.+, is used to connect the viscosity of the a#ueous solution with molecular weight.

    In addition to the determination of molecular weight, practical considerations are important to muncil

    of solubility effects. When someone moves in the direction of solvent 'good' to 'bad', and

    intramolecular forces become more important, the polymer molecules shrin/ in volume. his

    compactness rising birth reduced 'shrin/age' and therefore the solution viscosity becomes lower. he

    chemists in the field of paints especially once associated with solvent effects due to viscosity is a

    basic re#uirement in the application of spray or brush5application of paint or solvent5based lac#uer.

    he manufacturer of fiber can also reduce the cost of energy used in spinning fibers from solution (see

    Chapter 4! by reducing the viscosity of the solution.

    2.; Measurement of the molecular weight of the average number of

    2.;. 1 9nalysis of end groups Ha, :a, 1*a

    9verage molecular weight of the amount of a linear polymer having end groups that can be Measured

    by the methods of chemistry or physics could theoretically determined if the method of measurement

    is #uite sensitive. ut it must be remembered that the end groups are present in very low

    concentration of. he techni#ues available today 9llows the upper limit of the measurement of

    molecular weight to about +*,***. 3everal methods in the determination of end groups muta/ir

    include (1! titration, using either an indicator or -otentiometric techni#ues(2! analysis of end groups

    elements containing certain elements, (;! measurement of end groups which are radioactive and (4!

    5"

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    %) spectroscopic determination of end groups that have a chromophore nuclear magnetic (&M! has

    a more limited use.

    he things that must be considered in the application of analysis of end groups are as follows8

    1 his method can not be applied to branched polymers ecept if the number of branches is /nown

    with certainty thus this method in practice is limited to linear polymers.

    2 In a linear polymer end groups are sebanbya/ two linear molecules.

    ; If the polymer contains different groups at each end of the chain and the measurement is only

    carried out on one of the end groups that can di/ara/terisasai, the number of types of end groups is

    e#ual to the number of polymer molecules.

    4. measurement molecular weight by end group analysis only has meaning if the initiation and

    termination mechanism is well understood.

    9s a typical eample, let us consider the unsaturated polyester (Chapter 12!. -olyester is a linearpolymer with a relatively low molecular weight that they provide cross (crosslin/ing!, carboyl

    groups and hydroyl end groups can diditrasi with standard methods. :a In case /arbo/sl, the polymer

    sample was weighed, dissolved in a suitable solvent such as acetone and titrated with standard base to

    the end point fenolfatelin. or hydroyl, samples acetylated with ecess acetic anhydride and acetic

    acid release, along with the carboy end groups diditrasi the same way.

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    3chematic representation of an osmometer shown in igure 2.2 Memberam semipermeable usually

    constructed of polymeric materials such as rubber, nitrocellulose, cellulose acetate, and poly (vinyl

    alcohol!. he osmotic pressure can be determined by ma/ing

    system reaches /setimbangan and measure hydrostatic pressure arising. his way is classified as a

    static e!uilibrium method. 9lternatively, one can apply bac/ pressure to the first measuring tubeusually re#uires a long period of time to reach e#uilibrium, the dynamic method is preferred.

    )arious dynamic membrane osmometer has been produced, which usually includes a hori0ontal

    membrane separator solution and solvent cells. he type is shown schematically in igure 2.;

    measures the osmotic pressure directly through the strain gauge transducer connected to a fleible

    diaphragm in the solvent cell.

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    Where is the ideal gas teatpan *.*H2 mol 651 atm D1 ([email protected]! or H.;14 mol51 D51 (3I! is the

    temperature in Delvin C is the concentration, in grams per liter p is the solvent density, in grams per

    cubic centimeter g is the acceleration of gravity *,:H1 m = s2 is the height difference between the

    solvent and the solution, in centimeters and 92 is the second virial coefficient (a measure of the

    interaction between the solvent and polymer!.

    -lot reduction osmotic pressure, J = C, versus concentration (igure 2.4! with a linear shaped cut point

    is e#ual to = Mn and the gradient is e#ual to 92. F%nit for J = C is dyne 6 g51 cm51 ([email protected]! or /g51

    (3I!.G ecause K is a measure of the solvent5polymer interaction, the gradient becomes 0ero at theta

    temperature. hus the osmotic pressure measurements can be used to determine the theta conditions.

    he main causes of errors in osmometri membrane arising from species with low molecular weight

    diffuses across the membrane. his eplains why the molecular weight obtained is usually lower thanthe value obtained through measurement pengu/urang5other colligative properties in which all species

    are present calculated.

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    In these e#uations C is the concentration in grams per cubic centimeter is the free0ing point or

    boiling point of the solvent in Delvin % is the gas constant p is the density of the solvent

    successive latent heat of fusion and evaporation of solvent per gram Mis the average

    molecular weight and the number of 9 is the second virial coefficient. he molecular weight

    determined from plots versus concentration, as in the case of analog osmometri.

    he main limitation of /rios/opi and ebulliometri lies in the sensitivity of the methods of measuring

    the free0ing point or elevation of boiling point, when the molecular weight increases

    more and more small such that even with the most sensitive thermistor (of which is sensitive

    to 1 1*54 L C, upper limit of measurable molecular weight range of 4*,***. would but this method,

    together with the vapor pressure osmometri method (discussed below!, it is better to use if the

    molecular weight below 2*,***.

    2.;.4

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    and nois the solvent refractive inde, is the wavelength of

    light that occurred, and nois 9vogadroBs number. ribe dn = dc referenced as a specific increase in

    refraction, obtained by measuring the refractive inde gradient as a function of concentration, and its

    value but for the polymer, solvent, and temperature. Deti/e large molecular si0e approaches thewavelength achaya, corrections must be made for the interference between the scattered light that

    comes from the parts of different molecules.

    o define the molecular weight, the e#uation for turbidity rewritten as

    Where - (*! is a function of the angle * at time is measured, this function depends on the shape of

    the molecule in solution. 92 is the second virial coefficient. hen, turbidity was measured at different

    concentrations as well as the different angles, the latter is to compensate for variations in molecular

    shape,

    hen the eperimental data etrapolated to 0ero concentration and 0ero angle, where - (*! be e#ual to

    1 double ?trapolation hus, as shown in igure 2.+, is called)imm plot(from

    runo imm, who pioneered this method! factor k oada 7iirdubat flat (coordinate ! is any constant.

    he point of intersection with the y5ais according to 1Mw*.

    he main problem in the light scattering method is to get the solutions that really clear and free of

    dust. his is usually done by ultracentrifugation or filtration caution. >espite such difficulties arise,

    the light scattering method is widely used to obtain the weight average molecular weight of between

    1*,*** and 1*,***,***. 6ight scattering photometer5photometer longer use high pressure mercury

    lamp and filters to obtain monochromatic light beam. his photometer has been replaced with a laser

    light source. 6aser light scattering photometer scheme is given in igure 2.

    2.4.2 ultracentrifugation Hc, 1;, 14a

    %ltrasentrifug so far is the instrument of the most complicated and epensive for molecular weight

    determination. his method is not used as much as or osmometri ray scattering method in determining

    the molecular weight synthetic polymers, but it is widely used for natural polymers, especially

    proteins. he techni#ue is based on the principle that molecules, under the influence of strong

    centrifugal field, distribute themselves according to the magnitude of the perpendicular to the ais

    putarm a process called sedimentation, and its speed is proportional to the mass of the molecule.Centrifugation carried out in an open hole in a cell in the rotor circuit, given both windows so that

    optical methods, such as measurement of refractive inde or interferometry, can be used to observe

    changes in the concentration of the polymer solution is concerned. he basic components of a

    ultrasentrifug shown in igure 2.N

    5!

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    here are two approaches to obtain the molecular weight with ultrasentrifug.

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    igure 2.N 3chematic of a ultrasentrifug. From

    abe/, Hc copyright 1:H* ewritten by

    permission of ohn Wiley O 3ons, 6td.G

    Where dr = dt is the sedimentation velocity, m is mass, and f is the friction coefficient. or random coil

    polymers, f associated with the diffusion coefficient, > at infinite dilution by the e#uation

    he average molecular weight can then be obtained from e#uation

    his type of measurement is most effective on monodispersi systems such as proteins, and synthetic

    polymers for polidispersi can be obtained only approimate.

    2.4.; he field desorption mass spectrometry (>M3!

    ield desorption is a method of separating molecular ions directly from a solid to a gaseous state

    without de/omposisi.1+ or eample, the sample plimer superimposed upon filament5filament

    Carbon anodes are tied to the sharpened tip (sharp5edged! at the entrance of a mass spectrometer.

    hese samples were then sub7ected to an electric field is very strong (with the 1*+ volt level

    persentimeter!. When the anode is heated, molecular ions out of the sample and analy0ed by the

    spectrometer. hus the mass spectrum gives the calculation of various molecular masses are present in

    a sample polidispersi. @ood usability of the >M3 (,ield esorption Mass "pectrometry! lies in its

    ability to measure M andMwas well in addition to molecular weight distribution. 1 >M3 can

    almost be sure will have a better advantage if the instrumentation developed for uses more routine.

    2.+ viscometry

    )iscosity measurements of dilute solutions provide the simplest techni#ues and most widely used for

    determination of molecular weight on a regular basis. Hf, :e 14b. )iscometry method is not absolute each

    polymer system must first be calibrated with the determination of absolute molecular weight (usually

    with a light scattering method! were run on samples fractionated polymer. )iscosity measured at a

    concentration of about *.+ g = 1** ml solvent flow by setting the length of a volume of solution

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    through the capillary length is fied. 6amanbya flow in seconds is recorded as the time for the

    meniscus passed between two boundary signs on the viscometer. )iscosity5viscosity set at a constant

    temperature, usually ;*.* P *.*1 *C.

    wo typical viscometer is shown in igure 2.H. etween them, the type %bbelohde easier to use

    because it does not need to have the eact volume to obtain results that can be proven again.Moreover, additional solvent can be added (assuming that the reservoir is large enough!

    concentration can thus be reduced without having to empty and refill the viscometer. Whichever type

    is used, the polymer solution needs to be filtered into the viscometer because dirt particles affect the

    length of the flow. iltration easily solved with micro filter units that replace hypodermic needle on a

    syringe.

    @ambar 2.H )is/ometer /apiler8 (9! %bbelohde (! Cannon5ens/e

    he modules are controlled by a computer viscometer is now available commercially. his tool

    measures the time in the capillary flow of the photoelectric and held dilution and miing

    automatically in addition to the viscosity value calculation and planning.

    )iscosity can be, epressed in several ways (able 2.2!. &ow these common names are more widely

    used than the names recommended by I%-9C .1N (he names of the more recently appointed by

    I%-9C to avoid inconsistencies arising from the designation of 'viscosity' that there is no unit!.

    elative viscosity (viscosity ratio! (nre! is the ratio (ratio! solution viscosity is proportional to the

    viscosity of the solvent with the first approach for dilute solutions of time5time to the ratio of the

    corresponding flow. %nit viscosity (usually epressed with poise! or flow time divided into various

    epressions of viscosity. 3pecific viscosity (&3-! is an increase in the fraction (part! in the viscosity.

    oth nreland nsp both dimensionless. When the concentration increases, the viscosity was increased.

    herefore, to eliminate the effect of the concentration, the specific viscosity divided by the

    concentration and etrapolated to 0ero concentration to give intrinsic viscosity, FnG. 3ometimes the

    viscosity determined at a single concentration and inherent viscosity (ninh! is used as an indication of

    the approach of molecular weight. Inherent viscosity menge/trapolasi to FnG are the same.

    Concentration, C, in the above epression is epressed in grams per 1** ml of solvent or in grams per

    cubic centimeter, and the initial unit more commonly used. hus the inherent viscosity and intrinsic

    viscosity5have units of grams per deciliter or, which is the ta/e gumum, cubic centimeters per gram.

    Clear that the units of concentration must be specified when reporting data vis/oitas.

    able 2.2 >istribution of solution viscosity encer*

    61

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    9mong the various types of viscosity, intrinsic viscosity is the most helpful and easy to use because it

    can be lin/ed to the molecular weight by the Mar/5"ouwin/ e#uation53a/urada8

    Where Mv is the weight average molecular viscosity, which is defined as8

    3et D and 9, respectively, the intersection and the gradient of the plot of log FnG versus log Mw or Mn

    log of a series of polymer samples were fractionated. 3uch plots be linear (ecept at the low molecular

    weight! for the linear polymers, thus

    6og FnG A log. P a log M

    Weight average molecular viscosity lies between the polymer Mw and Mn are concerned, but closer to

    Mw. will therefore obtained results are better if the D and 9 are determined by

    fractionated samples with Mw values are /nown. o evaluate D and a re#uire considerable

    manipulation, but now it has published a wide area that shows the value of a wide spectrum of the

    polymer, solvent and temperature 4e. or most plimer general, the value of a varies between *.+ (for

    random coil polymers in a theta solvent! and *.H whereas for long5chain polymers that more

    resembles the stem where hidrodinami/anya relatively large volume, the value of a may be 1.*, a state

    where Mv A Mw. D values generally vary between 1*5; and *.+. 3ome peresentatif values of a and D

    are given in able 2.;.

    he factors that can disrupt the application of e#uation Mar/5"ouwin/Q3a/urada is chain branching,

    molecular weight distribution is too wide in the samples used to determine the value of a and D,

    solvation of polymer molecules, and the presence of a series of alternations or bloc/s in the polymer

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    bac/bone . he state of the polymer chain that wraps usually not a problem on solutions highly

    diluted such that, unless very large molecular weight.

    ypes of other viscosity measurements were based on the principles of shifting me/ani/14b also

    performed, the most common is the polemic solutions of concentrated or insoluble polymer however

    these methods can be applied to the flow properties of polymers (Chapter ;!, not for the determinationof molecular weight. 9nother Moetode to assign based on the molecular weight of the polymer

    fractionation and will be discussed in the following pasa.

    2. he molecular weight distribution

    9 molecular weight distribution of the polymer characteristics are important because, as well

    mole/ulm weight can greatly affect the properties of the polymer. 9s low molecular weight

    polystyrene shows the different properties of high molecular weight polystyrene, a polystyrene sample

    that has a narrow molecular weight area will show the different properties of polystyrene which has abroad molecular weight region, although the mean molecular weight the average of the two samples

    are the same.

    6"

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    In general, the techni#ues for the determination of the molecular weight distribution of polymer

    samples involving fractionation and comparison of fractions obtained with samples having an

    absolute molecular weight is already /nown through some calibration procedures. In this regard,

    various methods have been developed.

    2..1 gel permeation chromatography (@-C! Hg, 1H, 14c, 1:a

    %ntil now, @-C (@el -ermeation Chromatography! is the most widely used method for determination

    of molecular weight distribution. 9s a column chromatographic techni#ue. @-C may be used as a first

    step to obtain fractions of narrow molecular weight. 3eparation is done in a column filled with a

    material very ais that separates polymer molecules according to si0e, a phenomenon that is often

    epressed as molecular sieving (molecular sleving!. (9 common techni#ue is sometimes called si0e

    eclusion chromatography!. hought to later stated that the separation was based on the

    hydrodynamic volume of the molecule rather than the molecular weight per se.2* molecules able to

    diffuse into the aes (small holes! column filled (pac/ed! more efficiently, and therefore they pass

    through the column more slowly. hus the first to be eluted are fractions with higher molecular

    weight.

    he basic form of gel permeation chromatography are shown in igure 2.:. iller materials (pac/ing!

    column included in a variety of forms, but most commonly they consist of small grains and a half of

    soft bonded polystyrene cross5lin/ed with divinylben0ene and bulging with solvent, or from grains

    dan/ shaft eras of glass or silica. >etection of polymer fractions in the elution, most commonly done

    with a refractive inde detector or spectroscopic (ultraviolet and infrared!. Instruments5instruments

    that are commercially available do sample in7ection and fraction collection automatically, by the rapid

    flow of high5pressure pumps, and treatment data with computer aided. Which is closely related to

    @-C gel filtration chromatography (@-C!, a techni#ue that in principle be used to characteri0e the

    natural polymers in a#ueous solution. @C columns pac/ed with hydrophilic gels, which are usuallyin the form of detran5detran crosslin/ed or crosslin/ed polyacrylamide. 9s in the case of @-C,

    @C column separation also occurs via molecular filtration, however, adsorption, ion of echange and

    ion eclusion also play a role.

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    9 typical gel permeation

    chromatogram (igure 2.1*!

    will plot the detector response

    to the volume of dilute polymer solution is passed through the column (elution volume, )r!. o obtain

    molecular weights at a particular retention volume, the chromatogram may be compared to a reference

    chromatogram obtained with fractions with average molecular weight is /nown in the same solvent

    and at the same temperature. to ob7ectives benchmar/ing purposes, ribbon (band! elution divided into

    'columns' with height above the baseline is proportional to the amount of polymer (&1M1! were

    eluted.

    9 ma7or problem in calibrating the @-C column for a typical polymer is that the standard samples are

    slightly narrower molecular weight distribution available commercially. -olystyrene standards have

    polydispersity inde close to one available with a broad molecular weight region (**52,+7uta! and is

    often used but when someone treats polymers other than polystyrene, molecular weight obtained at

    best are approimate and may, in some cases, a wrong value. o avoid this difficulty, use the universal

    calibration method.

    %niversal calibration based on the observation that obervasi215viscosity product (bilanganvis/ositas

    barrier! and the molecular weight does not depend on the type of polymer. his product, FnG M, called

    the universal calibration parameters. 9s shown in igure 2.11, the plot of log (FnG M! versus elution

    volume and the solvent tetrahydrofuran ("! produces a single curve, shaped almost linear, for

    groups of polymers are manifold. hus log (FnG M! can be considered as a constant for all polymersfor columns, temperature and elution volume is concerned. If it is considered that the reference

    polymer (eg, polystyrene! are polymer 1 and polymer is a polymer difra/si/an 2, then apply

    (FnG 1M1! A (FnG 2M2!

    from the e#uation Mar/5"ouwin/53a/urada,

    FnG1 A.1M1a

    FnG2 A.2M2a

    Combining these e#uations and solve for the log M2, obtained

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    o define the molecular weight (M2! at a certain retention bolume,

    9t first column must be calibrated with standard polystyrene fractions (same solvent, and the same

    temperature!. It will provide a lin/ with the type as shown in igure 2.12. 3emilogarithmic calibration

    plots thus usually be linear over a wide molecular weight region, with deviations due to the linearity

    which occurs in a high molecular weight low, especially at high molecular weight. Constants D and a

    can usually be obtained from a polymer handboo/. 4e substitution M1 values for specific retention

    volume of the calibration plots and the values of D and a in the above e#uation, will soon be able to

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    determine the value of M2. @-C thereby providing a rapid and practical method to obtain the

    molecular weight distribution if a suitable calibration5calibration can be arranged.

    2..2 6eaching fraction Hh, 22

    In its simplest form, it may involve etraction fraction dissolving the polymer in a 3olhet type tool to

    dissolve the fractions of molecular weight increased with the passage etraction. o be practical, this

    method has been adapted to /rematografi procedure. Chromatography column filled with an inert

    material such as glass or grains of fine sand coated with polymer. 9 nonpelarut fluid flowed through

    the column, followed by increasing the amount of solvent that is mied with the li#uid nonpelarut. 9t

    first, a low molecular weight polymer will dissolve, followed by fractions with higher molecular

    weight. his is in contrast with

    igure 2.12 -lot of typical semilogarithmic calibration of molecular weight versus retention volume

    @-C, therefore, the first to be eluted fractions are low molecular weight. ypical combination

    between solvent and nonpelarut are consecutive 25butanone to polystyrene and ylene (ylene! and

    15propanol for politetilena. ernal applications gradient along the column chromatography method

    called gradient solvent 5 is a variation of the dissolution fractions.

    2..; deposition fraction Hh 22

    ?ssentially this is the opposite of dissolving fraction. he procedure is umu is by adding a small

    amount nonpelarut to dilute homogeneous solution of polymer polidispersi to materials with high

    molecular weight settles. he precipitate was ta/en by filtration or decantation and then add the

    remaining solubility nonpelarut once again. his procedure is repeated many times as long as

    necessary to get the desired fractionation and all polymers have been retrieved.

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    used type of coating that macroporos!. he absorption based on the competition between solvent and

    solute for penyerapnya materials primarily a function of the chemical structure of the deposition

    involves fractionation by molecular weight he is the main mechanism in determining the molecular

    weight distribution.

    here are ; ways to hold while /eeping 6C fractionation have been attached to the polymer (1!solvent miture and homogeneous nonpelarut used as an elution medium. When the solvent limit goes

    above the chip, /omposisisnya changed due to a combination of different absorption and evaporation.

    When the solvent limit be filled with non5solvent, fractions with high molecular weight began to

    settle. (2! nonpelarut first used, and the solvent is added to the amount of the increase during elution.

    ractions with low molecular weight initially moves will increase move, followed by fractions with

    higher molecular weight. (;! the solvent initially used to move the entire patch (dot! polymer, then

    added nonpelarut with increasing amounts which causes the fractions with high molecular weight

    will settle first.

    >efinite advantage of 6C is its low cost and simplicity. 9lso, he has the ability as a routine method

    for the initial screening of polymer samples or to monitor polymeri0ation processes paper

    chromatography has also been studied as a method to establish the molecular weight distribution, 2N

    but its users are less etensive.

    2..+ ultracentrifugation 1;

    his method involves observations of the boundary during sedimentation velocity eperiments

    performed sedimentation (centrifugation at high speed!. 3edimentation boundary is moving boundary

    caused by the movement of solvent penetrating the polymer during centrifugation. he limit is

    widened, partly due defusi and partly due to the polydispersity, and this widening can be attributed to

    the molecular weight distribution. his techni#ue provides the advantage with the ability to decipher

    fractions with very narrow area, but the drawbac/ is the high cost of e#uipment and compleity.

    6!

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    eferences

    1 [email protected] Weissberg, 3.oothman, and M. Wales. In 9nalytical Chemistry of polymers, -art 2 (@M

    Dline, ed.!, Wiley5Interscience, &ew Ror/, 1:2 Chap.1

    2 &. C. illingham, Molar Mass Measuraements in -olymer 3cience, "alsted -ress, &ew Ror/, 1:NN.

    ; ". Morawet0, -olymers in 3olution, 2nd ed., Wiley5Interscience, &ew Ror/, 1:N+

    4 . randrup and ?" Immergut (eds.! -olymer "andboo/m 2nd ed., Wiley5Interscience, &ew Ror/,

    1:N+8 (a! e//er, &ew Ror/, 1:N1.

    1:. 6.". ung (ed!, ractionation of 3ynthetic -olymers, >e//er, &ew Ror/, 1:NN8 (a! 6" ung and

    .C. Moore, Chap. (b! "[email protected] ?lias Chap. 4 (c! ". Inaga/i, Chap, N.

    69

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    2*. .C. Moore, in 6i#uid Chromatography of -olymers and elated Materials, -art ; (. Ca0es, ed!,

    >e//er, &ew Ror/, 1:H1, p. 1ff.

    21. , @rubisic, -. empp, and ". enoit, . -olymer. 3ci., +, N+; (1:N!.

    22. .M. 3ecreaton, in &ewer Methods of -olymer characteri0ation (. De, ed!, Wiley5Interscience,

    &ew Ror/, 1:4, Chap. 11

    2;. ?- .C., 1:N;, -++.

    24. [email protected] enen/ii and ?.3. @an/ina, . chromatog. ev., 141, 1;, (1:NN!.

    2+ >W 9rmstrong and D.". ul, 9nal, Chem., +4, N* (1:H1!.

    2. ". Inaga/i, . Doto/a, and .5I. min, -ure 9ppl. Chem., 4.1 (1:N!.

    2N. 3iling M. I., ). Ra. Dovner, Ru. -vyrs/y, and

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    of the titration. What is the molecular weight of the average number of the polyester$ Is this method

    suitable for the determination of any polyester$ ?plain.

    1* What is the >- (degree of polymeri0ation! of a sample of polyester made from 45hydroyben0oic

    acid if the acid number, which is determined by a standard D