13715156

7/26/2019 13715156

1/7

Radiation Physics and Chemistry 63 (2002) 185191

Radiation synthesis of poly(2-vinylpyridine) gels

and their swelling characteristics

N. Acar*

Department of Chemistry, Faculty of Science & Letters, Technical University of Istanbul, 80626 Maslak, Istanbul, Turkey

Received 19 June 2000; accepted 17 March 2001

Abstract

The effect of irradiation under vacuum on thermal properties, and swelling behaviour on Poly(2-vinylpyridine)

(P2VP) has been investigated with respect to their swelling properties and network structures. The gel percent of the

irradiated P2VP samples was determined by Soxhlet extraction, and UV spectroscopy was used to determine sol

percent. The change in glass transition temperature (Tg) was followed by Differential Scanning Calorimetry before and

after soxhlet extraction.# 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Irradiation; Poly(2-vinylpyridine); Gel; Characterization

1. Introduction

A gel is a crosslinked polymer or copolymer, which is

capable of imbibing a considerable quantity of liquid up

to swelling equilibrium. The final liquid content depends

on the chemical composition and also, in the majority

cases, on the crosslinked density (Huglin and Zakaria,

1986). Interest in the preparation of gels with various

properties has increased considerably in recent years,

due to their applications in many fields (Dole, 1986).

Crosslinked gels are generally prepared from monomer

with or without comonomers, in the presence of

crosslinking agents or treating the polymer with radia-tion. This technique is generally termed a clean

technique, not requiring any extra chemicals or leaving

some unwanted residues (G .uuven and Sen, 1991; Huglin

et al., 1987).

Polyvinylpyridines have drawn much attention in the

past and gained wide practical use because of their

properties (Reilly Report, 1983).The vinylpyridine mono-

mers are similar to styrene except the presence of

nitrogen atom on the pyridyl ring. P2VP would be

expected to combine high radiation resistance with its

thermal properties because of its aromatic content.

Knowledge of the changes in thermal properties of the

polymer on irradiation is important for its application in

many fields such as advanced composites and as an

insulating materials for wire and cables in nuclear power

plants.

In the present work P2VP samples were irradiated and

their thermal properties were determined after irradia-

tion. The gels prepared were characterised with respect

to their swelling properties and network structures.

2. Experimental

2.1. Materials

P2VP was purchased from Polyscience Inc. The

measured value of the limiting viscosity number in

methanol at 298 K (114.99 dm3 kg1), in conjuction with

the MarkHouwink constants gave a molecular weight

of 28.4 104 gmol1 (Fuoss et al., 1958). P2VP was

dissolved in ethanol and then solvent cast in a petri dish

to give thin film of P2VP. However, the film thus formed

strongly adhered to the petri dish and it was very brittle

*Fax: +90-212-285-6386.

E-mail address:[email protected] (N. Acar).

0969-806X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.

PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 2 3 1 - 6

7/26/2019 13715156

2/7

so that it could not be separated from the petri dish

without fracturing. For this reason, it was impossible to

prepare uniform strip specimen. Powdered P2VP sam-

ples were dried in vacuum at 343 K before irradiation.

2.2. Irradiation

The glass ampoules (7 cm in length and 3 cm in

diameter) which contained P2VP samples were put on a

vacuum rig and evacuated for 4 h, after which they were

sealed. The glass ampoules were irradiated at a 4.5 MeV

Dynamitron electron accelerator at Isotron plc. to six

different doses (0.20; 0.61; 1.03; 1.43; 1.84; 2.19 MGy).

There was no discernible increase in temperature during

the process, with each of the samples receiving a 32 kGy

per pass. The ampoules were at room temperature

before entering the irradiation cell for each pass.

2.3. Gel determination

Each irradiated sample was weighed into a soxhlet

thimble (Winitial) and extracted with ethanol for 15 h to

determine the insoluble part in the samples gravime-

trically (Wgel). This procedure was also used for the

unirradiated samples. After extraction, amount of

polymer dissolved in ethanol (Wsol) was determined

spectrophotometrically (Champbell and White, 1989;

Skurlatov et al., 1982). P2VP can be detected by UV

spectrophotometry (Molyneux, 1982). P2VP had an

absorbance peak at 264 nm. The absorbance of series

of standard solutions of P2VP was measured at this

wavelength by using a Hewlett-Packard 8452 A UV

Spectrophotometer and found to obey the Lambert

Beer Law. The extinction coefficient was determined to

233.9 m2 mol1. At the end of the experiment, the sum of

Wgel andWsol was equal to Winitial. After extraction, the

gel percent in the irradiated samples was calculated as

follows:

Gel% wi=wo100; 1

where wo represents the weights of dry irradiated

samples (before Soxhlet extraction that contains both

sol and gel part) andwi represents the dry insoluble (gel)

part.

2.4. Swelling measurements

To measure swelling properties of powdered P2VP

samples tea bags were used. First the tea bag was wetted

with ethanol and blotted quickly with absorbent paper,

then dried P2VP sample (contains only gel part) of

known weight, was put into a tea bag. The tea bag that

contained P2VP sample was immersed in ethanol. The

swelling proceeded at 208C. At various times the tea

bags were removed, blotted quickly to remove ethanol

attached to the surface and weighed in a stoppered

weighing bottle. Equilibrium was reached after 24 h,

then tea bags were removed, the surface dried and

the sample weighed. The ethanol uptake percent was

calculated as follows:

Ethanol uptake% ws wd

ws

100; 2

where Wd and Ws represents the weights of dry and

swollen irradiated samples, respectively.

For a P2VP gel, swelling data from the gravimetric

analysis were used to calculate the volume fraction, V2m,

and equilibrium degree of swelling, qv, of polymer in a

given gel sample swollen to equilibrium in ethanol

(Baysal et al., 1997; Sen et al., 1999).

qv 1 r qw 1

d

; 3

whereqwis the ratio of the weights of the network in the

swollen state and dry state, r and dare the densities ofP2VP and ethanol, respectively. The equilibrium degree

of swelling, qv, was defined as qv 1=V2m. Using thevalues ofr 0:95gml1 andd 0:786gml1,qvvalueswere calculated.

2.5. Measurements of glass transition temperatures

DSC measurements were carried out using DSC

Mettler TA 3000. Samples of20 mg of the irradiated

P2VP were used for measurements. Indium, zinc and

nickel standards were utilised to calibrate the tempera-

ture scale. The measurements were carried out in N2atmosphere at a heating rate of 10 deg min1. Tg of

irradiated and unirradiated samples was determined.

After soxhlet extraction all samples were dried under

vacuum at 318 K andTg was determined in the gel part.

3. Results and discussion

3.1. Gel determination

The formation of intermolecular crossslinks is one of

the most important changes brought about radiation,

since crosslinking of polymers leads to beneficialchanges in some of their properties, such as heat

resistance etc. Therefore, the gelled part, i.e. the

insoluble part, in the samples having different degrees

of crosslinking was determined. Results are given in

Fig. 1, that shows the relation between the gel percent

and irradiation dose for P2VP samples in Fig. 1 error

bars at 1 standard deviation are shown. Initially, the gel

percent increase with increasing irradiation dose up to

0.61 MGy, at higher doses increase in gel percent is

small.

Much effort is expended on measuring the relation-

ship between radiation dose and gel fraction, since this

N. Acar / Radiation Physics and Chemistry 63 (2002) 185191186

7/26/2019 13715156

3/7

determines the efficiency of crosslinking, the G value of

crosslinking, Gx and the G value of scission, Gs. In

many instances, radiation induces simultaneous cross-

linking and scission reactions. In these cases, the yields

for each reaction can be determined by Charlesby

Pinner relationship (Charlesby and Pinner, 1959).

s s1=2 50N

MnGx

1

D

GS

Gx; 4

where s=sol fraction of the irradiated polymer,

Mn=number average molecular weight of polymer

prior to irradiation, D=absorbed dose, Gs=scission

yield and Gx=crosslinking yield. To permit the calcula-

tion of crosslink yields, a determination of scission

concurrent with crosslinking is necessary. Results are

shown in Fig. 2 and Table 1. In Fig. 2, s s1=2 is plotted

against 1/dose for irradiated P2VP samples. Extrapola-

tion to 1/dose=0 gives value for Gs=Gx, the scission to

crosslinking ratio, of 0.279 for irradiated P2VP samples.Extrapolation to complete solubility (s s1=2 2)

permits an estimate of the gel points. For a calculation

of both crosslinking and scission yields, the gel point

dose, rg, and the scission to crosslinking ratios may be

substituted in Eq. (5) (Charlesby, 1960).

w

Mw rg Gx

Gx

2

5

in which w=molecular weight of repeating unit,

rg=6.855 103 MGy, Mw=28.4 10

4 gmol1. Substi-

tuting Gs=Gx 0:279 gives: w=Mw rg 0:861Gx andGx is found 0.063. The scission yield is Gs=0.279

(0.063)=0.018. In literature, polystyrene (PS) was

chosen for the study because it was easy to prepare

and characterize as a linear polymer and it crosslinked

by radiation with few side reactions (Graessley, 1964).

On the basis of some literature values for Gx and Gs,

namely, approximately 0.043 and 0, respectively, for

irradiation in vacuum, Gx decreased from 0.043 in

vacuum to 0.022 in air, there being a concominant

increase in Gs from 0 to 0.022 (ODonnell et al., 1979).

In theg-radiation induced crosslinking of PS in vacuum,

Shimizu and Mitsui (1979) investigated that the gel

fraction increased with increasing irradiation time by the

irradiation beyond the critical time for incipient gel

formation and the rate of gel formation decreased with

time. They found that at 308C, Gx 0:035 and Gs 0:01 when temperature was increased to 708CGx andGsvalues were 0.042 and 0.051, respectively. Parkinson

et al. (1965) described measurements of crosslinking in

PS with g-radiation and with the mixed g-neutron field

Fig. 1. Influence of dose on gel percent of P2VP (The solid

curve is the best fitting curve to the experimental data).

Fig. 2. Solubility of irradiated samples in ethanol as a function

of the reciprocal of dose.

Table 1

Determination of solgel fractions of irradiated samples by UV spectroscopy

Sample no. Dose (MGy) 1/Dose wsol (g) wgel (g) (wsol wgel)a (g) ssol fraction s

1=2 s s1=2

1 0.196 5.102 0.031 0.410 0.441 0.071 0.267 0.338

2 0.614 1.629 0.035 0.562 0.597 0.059 0.243 0.302

3 1.027 0.973 0.029 0.473 0.501 0.057 0.239 0.297

4 1.432 0.698 0.027 0.469 0.496 0.055 0.233 0.288

5 1.841 0.543 0.026 0.472 0.498 0.052 0.229 0.281

6 2.188 0.457 0.021 0.383 0.404 0.052 0.228 0.280

a

=initial weight of sample.

N. Acar / Radiation Physics and Chemistry 63 (2002) 185191 187

7/26/2019 13715156

4/7

of a reactor. G value for crosslinking PS is smaller than

the value for P2VP. It shows that PS is a more radiation

resistant polymer than P2VP.

The vinylpyridine monomers are somewhat more

reactive than styrene; this observation is consistent with

the methyl affinities of the respective monomers. Methyl

affinity (relative reactivity of monomer towards methylradical) of styrene, 2-vinylpyridine and 4-vinylpyridine is

792,1360 and 1360, respectively. This can explain why

polystyrene is more resistant to irradiation than poly-

vinylpyridines although their similar chemical structure

(Encyclopedia of Polymer Science and Engineering,

1989; Davidson, 1984).

3.2. Swelling measurements

Fig. 3 represents the ethanol uptake of P2VP as a

function of dose. It can be seen that the ethanol uptake

decreases with increasing dose in accordance with theincreasing degree of crosslinking, which normally results

in lower degree of swelling (Graessley, 1964; Hegazy

et al., 1995).

3.3. Determination of Mc values of gels

The gels thus prepared were characterized with respect

to their swelling properties and network structures. One

of the basic parameters that describes the structure of a

gel network is the molecular weight between crosslinks,

Mc for swollen networks. This describes the average

molecular weight of polymer chains between twoconsecutive junctions. These junctions may be chemical

crosslinks, physical entaglements, crystalline regions or

even polymer complexes (Peppas, 1991; Peppas and

Klier, 1991; Philippova et al., 1996). Several theories

have been proposed to calculate the molecular weight

between crosslinks in a gel. Probably the most widely

used of these theories is that of Flory and Rehner (Flory

and Rehner, 1943a,b). This theory describes the

equilibrium swelling characteristics of a crosslinked

polymer system where the polymer chains have reacted

in a solid state. The theory deals with neutral polymer

chains within the polymer gel. From the swelling

expression (Eq. (3)), the average molecular weightbetween consecutive crosslinks, Mc can be expressed

by Eq. (5). This equation has been widely used to

characterize a variety of networks. It was used when the

network was prepared from polymer, not from mono-

mer or monomer mixtures.

1

Mc

2

Mn %vv=V1

ln 1 V2m V2m wV22m

V1=32m V2m=2

: 6

Here, Mc is the number average molecular weight of

starting polymer, %vvis the specific volume of polymer, V1

is the molar volume of the swelling agent, V2m is thepolymer volume fraction in the equilibrium-swollen

system and w is the Flory polymer-solvent interaction

parameter. wis 0.487 for P2VP-ethanol system andV1 is

58.3gcm3 for ethanol. The Mc values thus determined

from Eq. (5) are given in Table 2. The results obtained

show that the average molecular weight between cross-

links decreases by increasing dose.

When a non-ionic polymeric network is placed in a

swelling agent, there are two contributions to the free

energy of the system, mixing and elastic-retractive free

energies as expressed as DGmix and DGel, respectively

(Flory, 1953). It is assumed that the change in total free

energy is the sum ofDGmix and DGel, thus,

DG DGmix DGel: 7

The state of equilibrium is obtained when the two

changes balance each other. Mathematically this state is

expressed as:

@DG

@n1

T;P

@DGmix

@n1

T;P

@DGel

@n1

T;P

0; 8

where n1 is the number of molecules of swelling agent,

subscripts T,P indicate that the differentiantions made at

constant temperature and pressure.

Fig. 3. Effect of dose on the percentage swelling of P2VP gels in

ethanol (the solid curve is the best fitting curve to the

experimental data).

Table 2

Values ofMc for gel systems

Dose (MGy) Mc (g mol1) qv

0.20 46382.35 16.83

0.61 18005.07 8.44

1.03 15232.79 7.58

1.43 7448.20 5.03

1.84 4487.86 4.32

2.19 3650.66 3.89


7/26/2019 13715156

5/7

Performing the differentiations indicated in Eq. (7):

ln1 V2m V2m wV22m

V1r

McV

1=32m V2m=2 0

9

or, adopting the terminology

V1r

Mc N1 10

where N is the number of segments in a network chain,

r is the density of polymer network.

ln1 V2m V2m wV22m N

1V1=32m V2m=2: 11

The left hand member in this equation represents the

lowering of the chemical potential owing to mixing of

polymer and swelling agent; that on the right gives the

increase from the elastic region of the network. As

expressed before, at swelling equilibrium, 1=V2m may be

replaced byqv. At large Mc values of 10,000 or more, qvin a good solvent will exceed 10. Then, V2m=2 isconsiderably smaller than V

1=32m and can be neglected.

Also higher terms in the series of expansion of the first

term member of Eq. (8) may be neglected. The swelling

equilibrium equation may then be solved for V2m

1=qv. The FloryRehner equation relating volumeswelling ratio to density of crosslinks has been simplified

by Charlesby to the form Charlesby, 1953):

q5=3v Mc 0:5 w

rV1: 12

Since Mc

is proportional to the reciprocal of dose,

a loglog plot ofqv vs 1/dose should have a slope of 0.6.

The data are presented in this manner in Fig. 4 with the

line constrained to a slope of 0.64.

3.4. Glass transition temperature measurements

Glass transition temperature of P2VP samples were

measured before and after Soxhlet extraction. The

results in Table 3 shows that Tg for P2VP shifts to

higher temperature with dose. Boyer (1963) suggested

that Tg is related to the chemical structure of polymers.

In general, factors that increase the energy required for

the onset of molecular motion increase Tg [such as

intermolecular forces (Boyer, 1954), bulky stiff side

groups (Gibbs, 1956), interchain steric hidrance (Karazsand MacKnight, 1968)]; that decrease the energy

reqirements lower Tg [such as flexible side groups

(Dunham et al., 1963; Rogers and Mandelkern, 1957)

and symmetrical substitution (Barb, 1959)]. Tg is also

governed by the presence and absence of crosslinks

(Glans and Turner, 1981; Sasuga et al., 1987; Hegazy

et al., 1992; Seguchi et al., 1999). In this study, the

increase in Tg with dose suggests that crosslinking is

probably important mechanism in P2VP.

Tg is an important property of polymeric systems,

which determine their temperature range of applicabil-

ity. The Fox equation has been proposed for predictingTg dependence on composition for polymer blends

(Fox, 1956), the equation used here for calculations

Table 3

Changes in Tg of irradiated P2VP samples with gel percent, before and after Soxhlet extractiona

Dose (MGy) Gel % Tgm (8C) Tg1 (8C) Tg1 (Calcd.)b (8C) DTg1

c (8C)

0 0 103.96 } } }

0.196 92.91 0.03 105.98 105.60 106.14 0.54

0.614 94.10 0.02 105.72 107.55 105.83 1.72

1.027 94.27 0.04 106.10 109.61 106.23 3.38

1.432 94.55 0.01 108.53 110.05 109.37 0.68

1.841 94.78 0.02 109.79 111.33 110.12 1.21

2.188 94.83 0.01 109.79 111.51 110.11 1.40

aError limits were estimated using standard deviations with the statistical parameter t=% 95 (Skoog et al., 1992).bCalculated by Foxs Equation.c

DTg1 Tg12

Tg1 (Calcd.).

Fig. 4. The loglog plot of the equilibrium volume swelling

ratio qv of the P2VP gels vs. reciprocal of dose.


7/26/2019 13715156

6/7

of Tg values of samples before and after Soxhlet

extraction.

1

Tgm

w1

Tg1

w2

Tg2; 13

where Tgm is the Tg of irradiated sample beforeseparation of gel and sol part, Tg1 is theTg of irradiated

P2VP sample after Soxhlet extraction (contains only gel

part), Tg2 is the Tg of original P2VP sample before

irradiation (139.68C),w1 andw2 refer to weight fraction

of gel and sol part, respectively. Results are shown in

Table 3. As shown from table, the observed Tg1 values

for samples, except first sample, were higher than the

calculated values. This increase is proportional to the

number of specific interactions existent in gel part and

can be interpreted as the contribution of the effective

crosslinks (Kwei, 1984).

4. Conclusions

In this study, P2VP samples were irradiated under

vacuum and the effect of irradiation on Tg and swelling

behaviour was investigated. Tg shifts to higher tempera-

ture with dose and the gelled part increases with dose

resulting in lower swelling degree. The average mole-

cular weight between two consecutive crosslinks was

determined by swelling experiments according to Flory

Rehner equation. The results obtained showed that

the average molecular weight between crosslinks was

decreased with increasing dose.

References

Barb, W.G., 1959. Effect of chemical structure on softening

points of substituted polystyrenes and related materials.

J. Polym. Sci. 37, 515532.

Baysal, B., Okay, O., Kayaman, N., 1997. Phase transition of

polyacrylamide gels in PEG solutions. Polym. Gels Networks

5, 167184.

Boyer, R.F., 1954. Relationship of first to second order

transition temperatures for crystalline high polymers.

J. Appl. Phys. 25, 825829.

Boyer, R.F., 1963. The relation of transition temperatures to

chemical structure of high polymers. Rubber Chem. Technol.

36 (5), 13031421.

Champbell, D., White, J.R., 1989. Polymer characterization

(Physical techniques). Chapman & Hall, London, pp. 4849

(Chapter 4).

Charlesby, A., 1960. Atomic radiation and polymer. Pergamon

Press Inc., New York, p. 172.

Charlesby, A., 1953. Swelling properties of polystyrene cross-

linked by high-energy radiation. J. Polym. Sci. 11, 521529.

Charlesby, A., Pinner, S.H., 1959. Analysis of the solubility

behaviour of irradiated polyethylene and other polymers.

Proc. Royal. Soc. (London) A 249, 367386.

Davidson, N.S., 1984. g-Irradiation of polystyrene. Soxhlet

extraction with toluene. Ph.D. Thesis, University of Strath-

clyde, UK.

Dole, M., 1986. In: Seymour, R.B., Cheng, T., (Eds.), History

of Olefins. Reidel, Boston, p. 71.

Dunham, K.R., Vanderberghe, J., Faber, J.W.H., Costois,

L.E., 1963. Effect of side chain structure on poly-a-olefinproperties. J. Polym. Sci. A 1, 751762.

Flory, P.J., Rehner, J., 1943a. Statistical mechanics of cross-

linked polymer networks. I. Rubberlike elasticity. J. Chem.

Phys. 11, 512520.

Flory, P.J., Rehner, J., 1943b. Statistical mechanics of cross-

linked polymer networks. II. Swelling. J. Chem. Phys. 11, 521.

Flory, P.J., 1953. Principles of Polymer Chemistry. Cornell

University Press, Ithaca, New York.

Fox, T.G., 1956. Influence of diluent and copolymer composi-

tion on the glass transition temperature of a polymer system.

Bull. Am. Phys. Soc. 1, 123.

Fuoss, R.M., Berkowitz, J.B., Yamin, M., 1958. The Flory

constants for poly(4-vinylpyridine) in ethanol. J. Polym. Sci.28, 69.

Gibbs, K.R., 1956. Nature of the glass transition in polymers.

J. Chem. Phys. 25, 185186.

Glans, J.H., Turner, D.T., 1981. Glass transition elevation of

polystyrene by crosslinks. Polymer 22 (11), 15401543.

Graessley, W.W., 1964. The measurement of molecular weight

distribution in polymers by crosslinking solubility methods.

J. Phys. Chem. 68, 22582263.

G .uuven, O., Sen, M., 1991. Preparation and characterisation of

poly(n-vinyl 2-pyrolidone) hydrogels. Polymer 32,

24912495.

Hegazy, E.A., Sasuga, T., Seguchi, T., 1992. Irradiation effects

on aromatic polymers: 3. changes in thermal properties byg-irradiation. Polymer 33, 29112914.

Hegazy, E.A., Abdel-Maksoud, A., Osman, M.B.S., Mostafa,

A.B., 1995. Preparation and thermal characterization of graft

copolymer obtained by radiation grafting of individual and

binary monomer systems. Polym. Int. 36, 4756.

Huglin, M.B., Zakaria, M.B., 1986. Swelling properties of

copolymeric hydrogels prepared by gamma irradiation.

J. Appl. Polym. Sci. 31, 457475.

Huglin, M.B., Mahmoud, M.A., Rehab, M.A., 1987. Mechan-

ical and thermodynamic properties of butylacrylate-N-

vinylpyrilidone hydrogels. Polymer 28, 22002205.

Karazs, F.E., MacKnight, W.J., 1968. Influence of streoregu-

larity on the glass transition temperatures of vinyl polymers.Macromolecules 1 (6), 537540.

Kwei, T.K., 1984. The effect of hydrogen bonding on the glass

transition temperatures of polymer mixtures. J. Polym. Sci.

Polym. Letters Ed. 22, 303313.

Mark, H.F., Bilakes, N.H., Overberqer, C.G., Menqes, G.,

Kroschwitz, J.I., Encyclopedia of Polymer Science and

Engineering, Vol. 17, 1989, Wiley, New York, p. 569.

Molyneux, P., 1982. Water Soluble Synthetic Polymers;

Properties and Behaviour. CRC Press Inc., Florida, p. 51.

ODonnell, J.H., Rahman, N.P., Smith, C.A., 1979. Cross-

linking and scission yields for polystyrene subjected to

gamma irradiation in vacuo. J. Polym. Sci. Polym. Chem.

Ed. 17, 40814088.


7/26/2019 13715156

7/7

Parkinson, W.W., Bopp, C.D., Binder, D., White, J.E., 1965.

A comparison of fast neutron and gamma irradiated

polystyrene. J. Phys. Chem. 69, 828833.

Peppas, N.A., 1991. Physiologially responsive hydrogels. J.

Bioact. Compat. Polym. 6, 241246.

Peppas, N.A., Klier, J., 1991. Structure and swelling

behaviour of polyethylene glycol/poly(methacrylic acid)complexes. Stud. Polym. Sci. 8 (Absorbent Polym. Technol.),

147-169.

Philippova, O.E., Karybiants, N.S., Starodoubtsev, S.G.,

Khokhlov, A.R., 1996. Conformational transitions in poly

(methacrylic acid) gel/poly(ethylene glycol) complexes. Effect

of the gel cross-linking density. Macromol. Chem. Phys. 197,

23732378.

Reilly Report, 1983. Reilly Report, in Linear Polyvinylpyr-

idines, Properties and Applications. Reilly Industries Inc.,

Indianapolis, USA.

Rogers, S.S., Mandelkern, L., 1957. Glass formation in

polymers. I. The glass transitions of the poly(n-alkylmetha-

crylates). J. Phys. Chem. 61, 985990.

Sasuga, T., Hayakawo, N., Yoshida, K., 1987. Electron beam

irradiation effects on mechanical relaxation of aromatic

polysulphones. Polymer 28, 236240.

Seguchi, T., Sasuga, T., Hirade, T., Hama, Y., 1999. Radiation

effects of aromatic thermoplastic polyimide (new-TPI).

Polymer 32, 24992504.

Sen, M., Yakar, A., G.uuven, O., 1999. Determination of average

molecular weights between crosslinks (Mc) from swelling

behaviours of diprotic acid-containing hydrogels. Polymer

40, 29692974.

Shimizu, Y., Mitsui, H., 1979. Gamma irradiation induced

crosslinking of polystyrene. J. Polym. Sci. Polym. Chem. Ed.

17, 23072316.

Skoog, D.A., West, D.M., Holler, F.J., 1992. Fundementals

of Analytical Chemistry. Saunders, Florida, p. 734

(Chapter 2).

Skurlatov, Y.I., Kokorin, A.I., Travin, S.O., Kirsh, Y.E.,

Purmal, A.P., 1982. The effect of pH on Cu2+ complex

formation with poly(4-vinylpyridine). Polym. Sci. USSR 24

(9), 21432148.


13715156

Documents

Transcript of 13715156