Structure of poly-ω-dodecalactam obtained in bulk by an anionic mechanism

Eur. P&n. J. Vol. 33, No. 8, pp. 1377-1382, 1997 8 1997 ElsevierScience Ltd. All rights reserved

Pergamon

Printed in Great Britain PII: SOO14-3057(96)00222-4

0014-3057197 $17.00 + 0.00

STRUCTURE OF POLY-co-DODECALACTAM OBTAINED IN BULK BY AN ANIONIC MECHANISM R.

MATEVA’, 0. DELEV’ and S. ROUSSEVA*

‘University of Technology, K1. Ohridski Blvd. 8, 1756 Sofia, Bulgaria *Central

Laboratory of Physico-Chemical Mechanics, Bulgarian Academy “Acad. G. Bonchev” Str., BI. 1, 1113 Sofia, Bulgaria

and of Science,

(Received 14 August 199.5; accepted in final form 13 May 1996)

Abstract-The

nascent structure of poly-w-dodecalactam, nylon-12 (PA-12), obtained during bulk polymerization of o-dodecalactam by an anionic mechanism has been investigated. The w-dodecalactam polymerization and PA-12 crystallization proceed in a successive manner. The influence of the type and concentration of the initiators and activators or modifiers on polymerization rate, molecular weight of the obtained PA-12, crystallinity degree, crystal size, alteration of melting temperature and enthalpy, and crystal lattice parameters has been studied. The structural changes in PA-12 depending on polymerization conditions are studied by means of infrared spectroscopy, differential scanning calorimetry, wide-angle X-ray scattering and polarized light optical microscopy. It is established that the type of initiator and activator or modifier as well as their concentration exert a substantial effect on the formation of the supermolecular structure of the obtained modified PA-12. 0 1997 Elsevier Science Ltd

INTRODUCTION Polyamides

(PA)

with

the

general

formula

are obtained by la&am [(CH& - I-CO-CN], polymerization and are also called Z-polyamides [l, 21. Their characteristic feature is that polymer chains can be parallelly and antiparallelly oriented in the crystal lattice [l-5]. It has been proved by X-ray investigations that various crystallographic modifications exist: G(,/I, y, the o!modification being typical for polyamides with an uneven number of repeated segments n as well as for polyamides with an even n possessing a short length methylene chain. The y modification is observed in PA with a long methylene chain [l-5]. Two polymorphous modifications, t( and y are known for PA-12 (poly-w-dodecalactam). Both forms are characterized by a monocline elementary cell with different parameters, the y modification being the more stable one for PA-12. The y form is usually called pseudohexagonal [l-5]. The transition from y to c( form proceeds under strictly specified conditions [6-131. A variety of the t( modification t(* has been established, characterized by an elementary cell containing four monomer units. The crystal lattice parameters of the c(* modification differ substantially from those of the GLone [8]. Galeski established that the conditions of the polymerization process affect to a great extent the Table I. Some parameters

characterizing

rate of nuclei formation and of thickness growth of lamellae, which is considered to regulate the rate of secondary nuclei formation [4]. It is reasonable to assume that these factors will exert a significant influence on PA-12 structure formation during the anionic polymerization process. The investigation of the effect of various initiators and different types of activation and modification additives on the kinetics and thermodynamics of the polymerizing system is of special interest. The study of the chemical and physical structure as well as of the crystallinity degree of PA-12, obtained in bulk by anionic mechanism is also of great importance. Similar investigations were not found in reference literature.

EXPERIMENTAL The w-dodecalactam (o-L) is a product of Fluka (Switzerland). It was purified twice by distillation in vacuum (T, = 152°C) and kept under a nitrogen atmosphere in a desiccator. Na-caprolactam (Na-CL) was obtained and purified using the method described in ref. [2]. The [OC[CIHs]sNAI(OCH2CHIOCH~)~]Na dilactamate (DL) produced in Czechia was used without additional purification [14]. Al-acetylcaprolactam was produced in Dimitrovgrad (Bulgaria) and purified through distillation under vacuum. SL, BL and LC (Scheme 1) were obtained and purified according to the procedure described in ref. [6].

the polymer PA-12 samples obtained shown intiators

in the presence of the &r,,, ,

EPJ 33;8-G

Initiator (I mol%) Na-CL DL

AH*

LWM

Mv

V& (%/min)

@al/g)

55200 54800

2.20 4.54

17.70 7.43

1377

(A)

WAXS [71

(Oh) DSC

223.0 61.8

39.40 20.76

17.7 7.43

1378

R. Mateva

el crl.

-6

c=o

/”

/\ (CH,),-N+gSi-R

trialkylsilylcaprolactam

(SL)

\R -6

-6

/“T”P

(CH),-N-C+aCl-

-6

(CH,&-

“,s

caprolactamcarbonylchloride

-6

-6

C -N+? -6

Bis-caprolactamcarbonyl

(CH,),

K” ii

N-acetylcaprolactam

Polymer samples mechanically ground and extracted with methanol were used for the DSC-2 and WAXS investigations and for determination of viscosity-average molecular weight. Before investigation the samples were dried over PZOS at 40°C until constant mass was obtained. The initiation of the polymerization and the elimination of unreacted products from the polymers is presented in detail in ref. [6]. The structural changes in the obtained PA-12 were investigated by means of Philips X-ray diffractometer with a voltage of 30 kV, 30 mA and scanning speed of 1%/min WAXS [7]. The IR spectra were recorded on a Specord MS0 in KBr tablets. The PA-12 samples were ground in a disintegration mill with liquid nitrogen. The polarization microscope photographs were made on thin layers using an Opton Karl Zeiss apparatus. The viscosity-average molecular weight was determined according to ref. [15]. The DSC were obtained on a Perkin-Elmer-2 at a heating rate of 10 K/min. The degree of crystallinity c( was determined by DSC-2 and WAXS:

AH, is the experimentally determined enthalpy of melting. AH, is the enthalpy of melting of 100% crystalline PA-12. AH = 32.05 Cal/g [16].

S,, is the area of the reflex of the crystalline phase, S,, is the area of the amorphous phase. S,, and .S,, are measured according to ref. [17].

Activator

(Imol%) 0 AL BL SL CL

of PA-12

VI”>,,,” (%+nin)

10.0 15 12.5 IS.1 15.0

polymer

The polarized light micrographs of the polymers obtained with the two kinds of initiators show the existence of different types of positive spherolites (Fig. 1a.b). The crystallinity degree and the crystallite size, determined from DSC and WAXS. respectively (Fig. 2a,b), are considerably higher and larger for the polymers obtained with a Na-CL than with DL initiator (Table I).

RESULTS

2)

350 700 920 850 610

148.4 175.4 170. I 168.3 163.3

AND DISCUSSION

The analysis of the presented experimental data (Table 1) leads to the conclusion that the considerably higher rate of polymerization by DL causes a decrease in the crystallinity degree and size of the spherolites as well as of defectivity degree, while the influence on the degree of polymerization, M,, is not so marked. Taking into consideration the fact that according to the mechanism of activators action they do not only accelerate the polymerization reaction but are also incorporated in the polymer chain [I& 191, it should be expected that they will substantially change the polymer structure too. Activation additives of different chemical structure and degree of activity (Scheme 1) were investigated in order to understand their influence.

samples activators

MV

(AL)

1

Scheme

2. Characteristics

(BL)

-6

(CH&--N+rC-CH,

Table

(LC)

obtained

H Wk) 88 IO.1 IO.8 8.53 6.31

with a DL initiator

l"lC (Oh) 21.46 31.51 33.70 20.37 19.69

ZUA\S 20.7 80 82 89 86

and various

LWAXS A 38 42 40 39

Poly-w-dodecalactam

obtained

1379

in bulk

b Fig. I. Polarized

light micrographs:

(a) PA-12

obtained

by Na-CL;

(b) PA-12 obtained

by DL.

(b)

2 S-

on 2i

J

E 0.4 0.2

0

23

21

19

I 17

c

I 80

20” Fig. 2. Difiractograms

(a) and DSC-grams (b) of PA-12 samples obtained Na-CL. (b) 1. Na-CL; 2. DL.

I 120

I 160

1 _ 200

“C

with initiators:

(a) 1. DL; 2.

R. Mateva

et al

(b) t

I

I

I

I

23

21

19

17

*

28”

Fig. 3. WAXS (a) and DSC-grams (b) of PA-12 samples obtained with DL initiator and the following types of activators: (a) I. CL; 2. SL; 3. BL; 4. no activator, only DL. (b) 1. BL; 2. AL; 3. CL; 4. SL.

Scheme

The experimental data from the WAXS and DSC tests show that considerable changes are observed (Fig. 3a,b). The applied activators of the w-DL polymerization decrease the crystallinity degree inall cases. This decrease is most significant for caprolactam carbonylchloride (CL) and most negligible for acetyl caprolactam (Table 2). It is obvious that for the DLjCL system the large volume substitute Cl in the side group by N has a special influence. The computer aided calculations Table 3. d-values of the crystal lattice of PA-12 samples obtained with various catalyst systems Activator I. 2. 3. 4.

CL SL BL AL

dl (A)

dz

4.01 4.44 4.083 4.14

3.99 4.01 4.03 3.95

[I] = [DL] = 1 mol%.

2

and those obtained by computer programme conformations of the PA-12 chains for the cases of different activators visually show that the volume of the side substituted by the N atom in the caprolactam molecule has a substantial effect on the packing and arrangement of the PA-12 chains as well as on the protonic interaction between -C=O and NH bonds of two polymer chains [20]. This is of considerable importance for the chain arrangement in the crystal lattice (Scheme 2). Table 4. d-values of the crystal lattice of samples PA-12 and a copolymer of o-DL/20% SL Activator

d, 3.94 3.95 3.86

1. 2. 3 4.

I% SL 5% SL 10% SL 2O%SL

di (A)

dz

d,

dd

4.66

4.17 4.15 4.13 4. I78

4.15 4.12 4.08 4.13

3.99 3.93 3.95 3.99

[I] = [DL] = I mol%.

~

of

Fig. 4. WAXS in the amount

(a) and DSC-grams (b) of PA-12 samples obtained in the presence of various activators of up to 1 mol%. (a) 1. 0.1% SL; 2. 5% SL; 3. 10% SL; 4. 20% SL. (b) 1. 0.1% SL; 2. I% SL; 3. 2% SL; 4. 10% SL; 5. 20% SL.

I I 4600 4000

IY

I

3000

26002000

1500

I

I

1000

750

)

cm-’

Fig. 5. IR spectrum

I-& 6. Polarized

of PA-12

hght micrographs

samples

in KBr samples:

of PA-12 samples

obtained

1381

I. SL = 0%; 2. SL = I%.

with: (a) 1% SL; (b) 5% SL; (c) 10% SL.

1382

R. Mateva

The decreased density of protonic bonds leads to a decrease in the crystallinity degree [20]. The activator/initiator combination affects the crystal lattice type of PA-12. The changes in the crystal lattice parameters for the different types of activator/initiator systems are shown in Fig. 3(a) and Table 3. The influence of the activator on PA-12 structure is determined by two factors: (i) changes in the rate of the polymerization and crystallization processes. The anionic polymerization in bulk of w-dodecalactam is characterized by successive crystallization, i.e. it is preceded by the polymerization; (ii) changes in the chemical structure due to activator incorporation in the polymer chain [18, 191. In fact, copolymers are obtained when the activator content exceeds 2 mol%. Thus, activators may be regarded as structural and chemical modifiers. which is very distinctly expressed in the case of SL activator. It is reasonable to expect that the increase of SL concentration will result not only in decrease of the crystallinity degree (Fig. 4) but also in the formation of a new a modification together with the basic 7 modification. This is shown by WAXS and DSC investigations (Fig. 4) and by IR spectroscopy data (Fig. 5). The changes in the crystal lattice parameters become very significant with the increase of the incorporation degree of the SL additive in the PA-12 chain. The data from the WAXS investigation are shown in Tables 3 and 4. The larger amount of SL additive causes great disturbance of the crystal lattice (Table 4) and considerable morphological changes (Fig. 6). The results presented lead to the conclusion that the type of the initiator/activator system exerts a substantial effect on the processes of polymerization and successive crystallization of PA-12. The crystallinity degree may be regulated in a broad interval by variation of the quantity of adequately selected activators and modifiers. The regulation of the chemical and physical structure provides the opportunity to obtain a variety

et rrl.

of physico-mechanical polymers.

properties

of the investigated

REFERENCES

Deschant, L., Irzfrakmsnaja Spectroskopia Polimerov. Chimia, Moscow. 1976. 2. Simeonovitch, T. and Chranova, T.. Physicochimia I.

Polimrror.

JK,

Kiev.

1985. 3, 86.

3 Kasarian. G.. Zesina, A. and Pavlov, N., Vysokomol. Soed. V.A.. 1987. XXIX, 949. 4. Galeski. H.. Argin, A. and Coehen, R.. Macromol. Chem.. 1982, 188, 1195. 5. Wunderlich. B., Macromol. Phys., N. Y.. Moscow, 1973. VI, 16. 6. Mateva, R. and Delev, 0.. Journal qf Polymer Science of Japan, 1987; Mateva. R. and Delev, O., BG P. 7942411987. 7. Hermans, P. H. and Weidinger. A.. Macromol. Chem.. 1961. 44-46, 24. C. and Malta, V., 8. Cojazri. G., Fischera, A., Gorbuglio. Macromol. Chem.. 1987, 188, 2745. 9. Inoue, K. and Hoshimo, S.. Journal of’Po/ymer Science Ph,xic.r Ed.. 1973, 11, 1077. H., Japanese Journal qf’ Applied Science, IO. Hiiikawa. 1982, 21(4),

659.

T. and Nagdi, S., Journal of Polymer Scicxcr Phvsics Ed., 1979. 18(2), 1414. Mateva. R., Krasteva, V. and Ivanova. M., Act. Po/ymer.. I99 I, 5(42), 240. Northolt, M., Ishikawa, K. and Aertsen, J., Journal of‘ Polymer Science. 12. 10. 191. Horsky, J.. Kubanek, V., Kubanek. J., Marek, J. and Kravlicek. J., Chrm. Promysl., 1982. 11, 599. Ivanova, S. J., Kulichkin, S. G.. Akaeva, 0. and Akumushina, N., Vysokomol. Soed., 1978, B.20, 12. Puffr, R., Stechlicek, J. and Sebenda, J., Macromol.

11. Ishikawa. 12. 13. 14. 15. 16.

Swtp.,

1992. 60, 219.

17. Sekiguchi, H., in Ring Opening Polymerizarion, Vol. 2, ed. K. J. Ivin and T. Saegusa. Elsevier, London, 1982. p. 833. 18. Privalko, W. P., Physical Chemistry qf Polymers, Kiev, 1984, 2, 242.

19. Dimitrova, Conformation,

T.,

Computer

Programmes

for

Polymer

Chimia i Industria, Sofia, 2. 20. Mateva, R. and Delev, O., Journal of Applied Polymer Scirnce (in press).