Effect of chain compositions on interpolymerspecific interaction in solutions

Yuhua Wang, Guorong Qi *, Huiling Li, Shilin Yang

Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China

Received 8 May 2001; received in revised form 25 September 2001; accepted 19 November 2001

Abstract

An interpolymer specific interaction of polymers with complementary proton donor units and proton acceptor units

was studied with viscometry. In this study, poly(styrene-co-octyl acrylate-co-acrylic acid) as proton donating polymer

(PDP) and poly(styrene-co-octyl acrylate-co-4-vinylpyridine) as proton accepting polymer (PAP) with different mac-

romolecular chain compositions were prepared by emulsion copolymerization. Complexed solutions formed by PDP

and PAP were studied with a novel interaction criterion ka based on viscosity enhance factor. The effects of macro-

molecular chain compositions on the ability to interpolymer interaction and complex stoichiometry were discussed. The

results showed that long chain alkyl acrylate units play an important role in the interpolymer specific interac-

tion. � 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Specific interaction; Proton donor; Proton acceptor; Complexation; Viscometry

1. Introduction

Due to incorporation of functional groups in the

polymer chains, interpolymer specific interaction has

long been known to result in unusual behavior and

material properties that are dramatically different from

the nonfunctional parent polymers. These specific in-

teractions include ion–ion Coulombic interaction, hy-

drogen bonding and transition metal complexation [1].

In low-polarity solvents specific interactions between

polymers usually accompany aggregation or association

of the component polymer chains, resulting in solution

viscosity variation compared to polymer blend without

specific interaction [2]. For studying interpolymer spe-

cific interaction, viscometric technique becomes a rela-

tively reliable and simple method providing information

as to polymer–polymer and polymer–solvent interaction

as compared with such demanding and time-consuming

techniques as DSC [3,4], neutron scattering [5], light

scattering and nonradiative energy transfer fluorospec-

troscopy [6], etc.

There are some viscometric methods employed to

study interpolymer interaction. (1) Viscosity enhance-

ment factor. Weiss and Lu [7] studied the solution vis-

cosities of blends of lighted sulfonated polystyrene (SPS)

and poly(styrene-co-4-vinylpyridine) (PSVP) with the

viscosity enhancement factor. The metal salts of SPS

were used resulting in higher solution viscosities than

comparable blends containing non-metal salts, which

was attributed to the interaction occurring between the

electron-deficient nitrogen of the vinylpyridine group

and the electron-rich oxygen of the sulfonate anion. Pan

et al. [8,9], using the same method as Weiss did, reported

the improved solution viscosities for blends of carb-

oxylated poly(phenyl oxide) (CPPO) and PSVP where

the interaction occurred between carboxyl and vinyl-

pyridine attached to CPPO and PSVP chains, respec-

tively. (2) Combined parameters DB or Db criterion

[10–13]. Combined parameter b, the product of Huggins

constant k0 and ½g�2, is used to study polymer–polymer

interaction. Under the ideal instance for a ternary system

European Polymer Journal 38 (2002) 1391–1397

www.elsevier.com/locate/europolj

* Corresponding author. Tel.: +86-571-87952131/8209; fax:

+86-571-87951773.

E-mail address: qiguorong@cmsce.zju.edu.cn (G. Qi).

0014-3057/02/$ - see front matter � 2002 Elsevier Science Ltd. All rights reserved.

PII: S0014-3057 (02 )00007-1

(polymer1–polymer2–solvent) where there is no ther-

modynamic interaction between both components, b12, aparameter characterizing the interactions of unlike

polymer molecules, should be an arithmetic or geometric

mean value of b11 and b22 pertaining to binary system

consists of polymer–solvent, respectively. Thus, the de-

viation of measured b12 from ideal value, i.e. DB or Db[DB ¼ b12 � 0:5ðb1 þ b2Þ and Db ¼ b12 � ðb1b2Þ1=2] mayreflect the magnitude of interaction between both com-

ponents. (3) a criterion: Cragg and Bigelow [14] studied

the interpolymer interaction in solution by Huggins

constant in ternary system in the absence of strong in-

terpolymer interaction that would encourage complex-

ation. Based on Cragg and Bigelow’s study, Sun et al.

[15] suggested a thermodynamic coefficient a to reflect

the interaction between unlike polymer molecules. a mayin fact be referred to as the deviation of measured

Huggins constant of polymer blend (k0m;exp) from theo-

retical value (k0m;cal) calculated from the following Eq.

(1):

k0m;cal ¼k01w

21½g�

21 þ 2ðk01k02Þ

1=2w1w2½g�1½g�2 þ k02w22½g�

22

½g�2m;calð1Þ

½g�m;cal ¼ ½g�1w1 þ ½g�2w2 ð2Þ

where k01 and k02 are Huggins constants, ½g�1 and ½g�2 arethe intrinsic viscosities and w1 and w2 are the weight

fractions of the two polymers in polymer blend, re-

spectively. ½g�m;cal is the theoretical intrinsic viscosity of

the blend obtained from weight average of component 1

and 2, as shown in Eq. (2). Intrinsic viscosity data for

ternary system have been also employed to evaluate

the interaction between unlike polymers [16–18]. But the

effect of specific interaction on intrinsic viscosity of the

polymer blend is complicated due to such influencing

factors as molecular weight, the structure and shape of

the blends as well as solvent power. Not only positive

deviation but also negative deviation of experimental

intrinsic viscosity of the blend, ½g�m;exp, from ½g�m;cal werereported in references.

Generally, the methods mentioned above have more

or less limits for the evaluation of interpolymer inter-

action. Combined parameters DB, Db criterion and acriterion, based on Huggins equation, are applicable at

sufficiently low concentrations and must be employed in

a theoretical premise that there is no considerable de-

viation of ½g�m;exp from ½g�m;cal. In our experiments, how-

ever, in addition to the deviation of ½g�m;exp from ½g�m;cal,the dependence of reduced viscosity gsp=c on polymer

concentration c are curved even in dilute region due to

strong interpolymer specific interaction. Under the cir-

cumstances, Huggins equation cannot be used to depict

the solution behavior. Therefore, a novel criterion was

proposed to estimate interpolymer specific interaction in

this work.

To date, there are few studies concerned with inter-

polymer specific interaction between long chain alkyl

acrylate copolymers. In the present study, poly(styrene-

co-octyl acrylate-co-acrylic acid) and poly(styrene-

co-octyl acrylate-co-4-vinylpyridine) with different

macromolecular chain compositions were used as pro-

ton donating polymers (PDP) and proton accepting

polymers (PAP), respectively. The effect of copolymer

chain composition on interpolymer interaction was

studied by the viscometric technique.

2. Experimental

2.1. Materials

PDP and PAP were prepared through emulsion

copolymerization with potassium persulfate as the ini-

tiator and sodium lauryl as the emulsifier. The carboxyl

content in PDP was determined by titration of PDP in

toluene/methanol (4/1,v/v) solution to a phenolphthalein

end point with methanolic sodium hydroxide. The VP

content in PAP was determined by element analysis with

an ThermoQuest EA 1110. The contents of styrene (St)

and octyl acrylate (OA) in copolymers were obtained

from JEOL FX90Q 1HNMR analysis in CDCl3 at 30

�C.

2.2. Viscosity measurements

Blend solutions with various weight ratio of PDP to

PAP were prepared by blending the two corresponding

polymer solutions. Reduced viscosities of polymer com-

ponents and their polymer blends were measured at 300:05 �C with a Ubbelohde viscometer in toluene. The

kinetic energy corrections were carried out.

2.3. Determination of apparent molecular weights of

component polymers

The apparentMw values of component polymers were

determined by static light scattering with toluene as the

solvent. The refractive index increments dn=dc were

measured in toluene at 30 �C with an OPTILAB DSP

interferometic refractometer operating at 633 nm, which

was calibrated with aqueous NaCl solutions. The in-

tensity of scattered light was detected on an 18-angular

DAWN DSP laser photometer using polarized light of

wavelength 633 nm from a He–Ne laser. Toluene was

purified by distilling and filtered through 0.2 lm pore

size Nylon filters prior to use. The solutions were clari-

fied by filtration through 0.5 lm pore size Nylon filters.

Weight average molecular weights were obtained

from Berry plot,

1392 Y. Wang et al. / European Polymer Journal 38 (2002) 1391–1397

ffiffiffiffiffiffiffiffiffiffiKcRðhÞ

s¼ 1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

MwPðhÞp þ A2c

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiMPðhÞ

pð3Þ

where K is an optical constant including dn=dc, c the

polymer solution concentration, RðhÞ the difference be-tween the Rayleigh ratio of the solution and that of the

pure solvent, Mw the apparent weight average molecular

weight, A2 the second virial coefficient, P ðhÞ particle

scattering function.

Compositions, refractive index increments in toluene

and apparent molecular weights of copolymers are

compiled in Table 1. Dx–yOA represents PDP in which

x and y are the contents of AA and OA in wt.%.

Ax–yOA represents PAP in which x and y are the con-

tents of VP and OA in wt.%. D(A)x-St represents binary

copolymer comprising St and functional monomer

(AA,VP), x% is the weight content of functional

monomer by percent.

3. Theoretical consideration

3.1. Viscosity enhancement factor

For a solution of two polymers without specific in-

teractions between the polymers, the specific viscosity of

the blend, gsp;m;cal, can be calculated as a weight average

of the specific viscosities of the individual components

[7], as given by Eq. (4).

gsp;m;cal ¼ ðgsp;1c1 þ gsp;2c2Þ=cm ð4Þ

where c1 and c2 are concentrations of component 1 and2 in the blend solution, gsp;1 and gsp;2 are the specific

viscosities of component 1 and 2 at concentration cm ¼c1 þ c2, respectively. When there are specific interac-

tion in the blend, the solution viscosity of the blend

will generally be different from the value given by Eq.

(4).

Thus, as suggested by Weiss, a viscosity enhancement

factor, R, can be defined as

R ¼ ðgsp;m;exp � gsp;m;calÞ=gsp;m;cal ð5Þ

where gsp;m;exp is the experimentally measured specific

viscosity of the blend solution, gsp;m;cal is given by Eq. (4).

Pan et al. considered R as a measure of the magnitude of

the interpolymer interaction. However, it was found that

some values of R of the blend solutions are lower than

zero in very dilute regions in our experiments; whereas

with the increase of the blend solution concentrations, R

increase gradually and change into the positive value. It

is indicated that the case of R being zero does not indeed

mean no interpolymer specific interaction occurs. Ac-

cordingly, it is required to deduce a general procedure

based on the relationship of R with polymer level in

solution for estimating interpolymer specific interaction.

3.2. Evaluation of interaction for ternary system based on

viscometric parameters

In this study, the dependence of gsp=c on c are curved

for polymer blends as well as components. The rela-

tionship between gsp=c and c may be given by Schulz–

Blaschke equation, as shown in Eq. (6) and Eq. (60) to

depict polymer solution behavior [19],

gsp=c ¼ ½g� þ kSB½g�gsp ¼½g�

1� kSB½g�cð6Þ

cgsp

¼ 1

½g� � kSBc ð60 Þ

where [g] is intrinsic viscosity, c is solution concentrationand kSB is Schulz–Blaschke constant. Theoretically,

Schulz–Blaschke constant kSB, similar to Huggins con-

stant, can provide information as to hydrodynamic and

thermodynamic interactions between polymers. Corre-

sponding to Eq. (6) for a single component, Schulz–

Blaschke equation can be applied to a ternary system

(polymer1–polymer2–solvent),

gsp;mc

¼ ½g�m1� km½g�mc

ð7Þ

where km is Schulz–Blaschke constant of the blend so-

lution, gsp;m is the specific viscosity and ½g�m is intrinsic

viscosity of blend solution. For the blend solution

without specific interaction between component poly-

mers, similar to Eq. (4), the reduced viscosity can be

expressed by weight additivity of both components:

Table 1

Chain compositions, refractive index increments in toluene and molecular weights of copolymers

Copolymer OA unit (wt.%) St unit (wt.%) AA unit (wt.%) 4-VP unit (wt.%) dn=dc Mw 10�4

D2.2-54OA 53.9 43.9 2.2 – 0.050 97

D2.2-15OA 15.3 82.5 2.2 – 0.081 77

D3-St – 97 3.0 – 0.11 74

A5.3-47OA 47.3 47.4 – 5.3 0.046 438

A5.8-16OA 16.2 78.0 – 5.8 0.093 353

A6.1-St – 93.9 – 6.1 0.11 320

Y. Wang et al. / European Polymer Journal 38 (2002) 1391–1397 1393

gsp;m;calcm

¼ ½g�1w1

1� k1½g�1cmþ ½g�2w2

1� k2½g�2cm

�½g�m;cal

1� km;cal½g�m;calcmð8Þ

where cm is the sum of concentration of the two com-

ponents, wi, ki and ½g�i are the weight fraction, Schultz–Blaschke constant and intrinsic viscosity of individual

components in the polymer blend, respectively. Sub-

scripts 1 and 2 correspond to components 1 and 2. The

theoretical intrinsic viscosity of the blend, ½g�m;cal, is

obtained from Eq. (2) and km;cal is the theoretical

Schultz–Blaschke constant of the polymer blend ap-

proximating to an average calculated from Eq. (9)

km;cal ¼k1½g�21w1 þ k2½g�22w2

ð½g�1w1 þ ½g�2w2Þ2ð9Þ

If the relationship between the reduced viscosity and

concentration follow well the Schultz–Blaschke equation

for both polymer components and complexed blend

system, viscosity enhancement factor R defined by Eq.

(5) can be related to the theoretical specific viscosity of

the blend solution, gsp;m;cal, by an expression as follows:

1

Rþ 1¼

½g�m;cal½g�m;exp

� kagsp;m;cal ð10Þ

where ½g�m;exp is experimentally measured intrinsic vis-

cosity of the blend solution and ka, the extent to which R

increases with gsp;m;cal, is related to theoretical and ex-

perimental Schultz–Blaschke constant and intrinsic vis-

cosity by

ka ¼ km;exp � km;cal½g�m;cal½g�m;exp

ð11Þ

The product kagsp;m;cal thus expresses the extent of in-

terpolymer interaction and ka value can therefore be

considered as a contribution expressing the ability to

interpolymer interaction in a given complexed system.

4. Results and discussion

4.1. Effect of macromolecular chain composition on the

ability to interpolymer interaction

The plot of reciprocal of gsp=c versus c should yield astraight line with intercept and slope corresponding to

[1=g] and negative Schulz–Blaschke constant, respec-

tively. These results and ka parameters calculated from

equations mentioned above are summarized in Table 2.

The c values are correlation coefficients in linear re-

gression analysis and almost equal to unity, which shows

the experimental values follow the typical linear rela-

tionship of the Schultz–Blaschke equation.

Fig. 1(a)–(c) shows the variation of ka in toluene as a

function of FAA for the polymer blends with different

macromolecular chain compositions (FAA is the molar

fraction of AA groups calculated through dividing the

moles of carboxylic group by the total moles of VP

group and carboxylic group in the blend, as given in Eq.

(12)).

FAA ¼ wPDP AA%=72

wPDP AA%=72þ wPAP VP%=105ð12Þ

where wPDP and wPAP are weight fraction of PDP and

PAP, AA% and VP% are AA content and VP content in

respective component copolymers by weight.

As is the result of interpolymer specific interaction,

the values of ka are larger than zero in the range of FAAstudied. Generally, it can be seen that when the com-

position of PDP is fixed and the OA content in PAP is

changed at constant FAA the values of ka of blend solu-

tions increase with OA content in PAP. It provides an

indication of OA units playing an important role in the

interpolymer interaction between PDP and PAP. In the

opinion of Malik and Mashelkar [20], intermolecular

interaction between randomly distributed VP and AA

groups on the complementary chains in the presence of

long chain alkyl acrylate cannot be visualized without

considering the overlapping (Van der Waals force) be-

tween side chains of long chain alkyl acrylate on two

types of chains. But the interaction between VP and AA

groups in the absence of long chain alkyl acrylate can

also be visualized in our experiments although the in-

teraction strength is not as strong as in the presence of

long chain alkyl acrylate. Therefore, we think the pres-

ence of long chain alkyl acrylate makes it realized to

form a larger and more stable gel-like structure of in-

terpolymer complex.

Fig. 2(a)–(c) shows D½g�m=½g�m;cal (D½g�m ¼ ½g�m;exp�½g�m;cal) as a function of FAA for the blends with different

macromolecular chain compositions in toluene. D½g�m=½g�m;cal represents the extent to which ½g�m;exp deviates

from ½g�m;cal, which is in fact the value of R at zero

concentration. By comparing Figs. 1 and 2, one can find

that D½g�m=½g�m;cal shows generally the opposite variationtrends to ka as a function of FAA for the same complexed

system. That is, the increase of ka and the decrease of

½g�m=½g�m;cal are shown to be the result of increasing the

interpolymer interaction. When the interpolymer inter-

action is strong restricting motion of chains due to

functional groups matching pairedly, the blend mole-

cules are contracted with the formation of a compact

structure of the complex that leads to a lower intrinsic

viscosity of the polymer blend than weight average value

predicted by Eq. (2). When the interaction is diminished

to some extent, the interpolymer complex gradually

becomes less compact and makes for chain expansion

with the formation of comparatively loose aggregates in

1394 Y. Wang et al. / European Polymer Journal 38 (2002) 1391–1397

solution, which makes D½g�m=½g�m;cal increase and grad-

ually shift towards higher values even up to the positive

value. The similar solution behavior can be found in the

studies of Jiang and coworkers [6].

On the other hand, D½g�m=½g�m;cal of D3-St/A6.1-St

blend system are shown to be much lower than those of

D2.2-54OA/A5.3-47OA and D2.2-15OA/A5.8-16OA.

We conclude it may depend on the solvation of side

chains of octyl acrylate units. Theoretically, intrinsic

viscosity measures the effective hydrodynamic-specific

volume of the polymer molecule. For interaction be-

tween D2.2-54OA and A5.3-47OA, isolated associates

form a structure with some ‘‘free’’ side chains of octyl

acrylate units interacting with solvent molecules. Whereas

in the case of D3-St/A6.1-St, associates form a denser

structure than D2.2-54OA/A5.3-47OA due to no solva-

tion of side chains, which results in a stronger contrac-

tion of the component polymer chains and accordingly

the decrease of intrinsic viscosity of the blend solution to

a larger extent.

4.2. Effect of chain composition on complex stoichiometry

Jiang and coworkers [6] regarded the carboxyl com-

position corresponding to minimum in R at concentra-

tion obviously less than c�, at which the chains overlap

threshold, as the fixed mean stoichiometry of the com-

plex. In this study, the molar fraction of AA groups in

the blend corresponding to the minimum in D½g�m=½g�m;calcan be regarded as the complex stoichiometry. Efforts

were made to find the effect of long chain alkyl acrylate

unit content in polymer components on complex stoi-

chiometry. It can be seen from Fig. 2(a) that when the

composition of PDP is fixed and OA content in PAP is

Table 2

Experimental and theoretical viscometric data for PDP/PAP systems

Polymer blend FAA km;exp km;cal ½g�m;cal ½g�m;exp ka D½g�m=½g�m;cal c

D2.2-54OA/A5.3-47OA 0.167 0.824 0.352 4.29 3.95 0.442 �0.080 0.9999

0.231 0.934 0.355 4.16 3.64 0.528 �0.126 0.9981

0.376 0.901 0.361 3.91 3.64 0.513 �0.070 0.9968

0.475 0.867 0.363 3.76 3.44 0.470 �0.085 0.9994

0.644 0.687 0.365 3.53 3.55 0.324 0.005 0.9999

D2.2-54OA/A5.8-16OA 0.156 0.781 0.364 4.47 4.09 0.383 �0.084 0.9978

0.217 0.849 0.368 4.32 3.92 0.444 �0.093 0.9985

0.356 0.785 0.373 4.03 3.84 0.394 �0.048 0.9998

0.580 0.666 0.374 3.65 3.57 0.283 �0.023 0.9991

D2.2-54OA/A6.1-St 0.149 0.658 0.354 5.06 4.45 0.255 �0.121 0.9991

0.208 0.687 0.360 4.85 4.22 0.273 �0.130 0.9999

0.345 0.77 0.370 4.43 3.88 0.347 �0.124 0.9996

0.513 0.689 0.377 4.00 3.76 0.287 �0.061 0.9998

0.612 0.641 0.378 3.79 3.68 0.252 �0.028 0.9996

D2.2-15OA/A5.3-47OA 0.223 0.658 0.370 4.24 3.95 0.261 �0.068 0.9999

0.365 0.839 0.389 3.80 3.46 0.412 �0.089 0.9990

0.534 0.824 0.405 3.36 3.15 0.392 �0.062 0.9997

0.649 0.784 0.412 3.10 2.93 0.349 �0.053 0.9994

0.697 0.623 0.414 3.00 2.97 0.205 �0.011 0.9865

D2.2-15OA/A5.8-16OA 0.260 0.611 0.394 3.93 3.79 0.203 �0.035 0.9979

0.346 0.750 0.403 3.69 3.48 0.321 �0.059 0.9991

0.513 0.683 0.416 3.29 3.27 0.264 �0.006 0.9994

0.679 0.594 0.420 2.97 3.09 0.191 0.043 0.9988

D3-St/A5.3-47OA 0.291 0.767 0.383 4.10 3.81 0.355 �0.071 0.9996

0.451 0.896 0.411 3.59 3.32 0.451 �0.076 1.0000

0.552 0.954 0.428 3.29 3.10 0.500 �0.056 0.9993

0.720 0.747 0.451 2.81 2.99 0.323 0.063 0.9995

D3-St/A6.1-St 0.382 0.502 0.411 4.05 3.65 0.046 �0.099 0.9990

0.489 0.695 0.433 3.65 3.06 0.179 �0.161 0.9996

0.550 0.776 0.444 3.43 2.95 0.259 �0.141 0.9933

0.617 0.766 0.455 3.21 2.74 0.234 �0.144 0.9968

0.738 0.702 0.470 2.82 2.51 0.175 �0.108 0.9972

Conditions: measured at 30 0:05 �C in toluene.

Y. Wang et al. / European Polymer Journal 38 (2002) 1391–1397 1395

changed, FAA corresponding to the minimum in D½g�m=½g�m;cal are about 0.23, 0.22 and 0.21 for D2.2-54OA/

A5.3-47OA, D2.2-54OA/A5.8-16OA and D2.2-54OA/

A6.1-St, respectively. This indicates that the complex

stoichiometry is relatively insensitive to the composition

of PAP. As regards the effect of chain composition of

PDP on complex stoichiometry, it was further studied by

changing OA content in PDP. It can be seen from Fig.

2(b) and (c) that the complex stoichiometry increases

with decreasing OA content in PDP and gradually ap-

proaches to 0.5 when D3-St is used as PDP.

In a complexed system, as Weiss proposed, it would

be expected that there exist two types of competitive

interactions: (1) interpolymer complex interaction be-

tween the carboxylic groups and VP groups and (2) in-

tra-association of carboxyl. The latter interaction

depends strongly on the solvent nature and is favored in

very dilute region. The dependence of complex stoichi-

ometry on chain composition of PDP, we conclude, is

the result of the combination of steric hindrance of side

chains of OA units in PDP with intra-association of

carboxyls. In the case of D2.2-54OA as the PDP, side

chains of OA units in PDP affect the interactions of

carboxyl with other functional groups on unlike mac-

romolecular chains, making carboxyls more apt to intra-

association. In order to destroy intra-association of

carboxyls, a large excess of VP groups is needed to

achieve a maximum in interpolymer complexation. As

steric hindrance of side chains of OA units diminishes

due to the decrease of OA content in PDP, AA groups

prefer to interacting with VP groups. In the case of D3-

St as the PDP, due to without steric hindrance of side

chains of OA units in PDP completely and the strength

of intra-association of carboxyls not comparable to in-

teraction between carboxyl and VP, large excess of VP

groups is unnecessary to achieve a maximal interpoly-

mer complexation. As a result, the interaction between

D3-St and A6.1-St shows good agreement with the case

of ideal acid–base interaction, where the complex stoi-

chiometry approaches to the base value, i.e. 0.5.

5. Conclusion

Effect of copolymer chain compositions on inter-

polymer interactions between long chain alkyl acrylate

copolymers bearing proton donor and proton acceptor,

respectively, were studied with the interaction criterion

ka. The increase of ka and decrease of D½g�m=½g�m;cal arethe result of increasing the interpolymer specific inter-

action. General ability to interpolymer interaction be-

tween poly(styrene-co-octyl acrylate-co-acrylic acid) and

poly(styrene-co-octyl acrylate-co-4-vinylpyridine) was

increased with long chain alkyl acrylate unit content in

Fig. 1. ka as a function of molar fraction of AA groups for

blends of ( ) D2.2-54OA/A5.3-47OA, ( ) D2.2-54OA/A5.8-

16OA, ( ) D2.2-54OA/A6.1-St, ( ) D2.2-15OA/A5.3-47OA,

( ) D2.2-15OA/A5.8-16OA, ( ) D3-St/A5.3-47OA, ( ) D3-

St/A6.1-St.

Fig. 2. D½g�m=½g�m;cal as a function of molar fraction of AA

groups for blends of ( ) D2.2-54OA/A5.3-47OA, ( ) D2.2-

54OA/A5.8-16OA, ( ) D2.2-54OA/A6.1-St, ( ) D2.2-15OA/

A5.3-47OA, ( ) D2.2-15OA/A5.8-16OA, ( ) D3-St/A5.3-

47OA, ( ) D3-St/A6.1-St.

1396 Y. Wang et al. / European Polymer Journal 38 (2002) 1391–1397

component copolymers due to Van der Waals force

between side chains of alkyl acrylate unit on unlike

macromolecular chains. Because of steric hindrance of

side chains of octyl acrylate unit together with intra-

association of carboxyl in PDP, complex stoichiometry

expressed by molar fraction of AA increases gradually

up to 0.5 as OA content decreases in PDP and relatively

insensitive to chain composition of PAP.

Acknowledgements

The authors are indebted to the National Natural

Science Foundation of China for financial support of

this research. The number of financial item is no.

59973016.

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