Percentage of Rigid Chain Length, a New Concept for Predicting

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Macromolecules 1992,25, 6646-6650

6646

Percentage of Rigid Chain Length, a New Concept for Predicting Glass Transition Temperatures and Melting Points of Polyfaryl ether ketone)s and Poly(ary1 ether su1fone)s V. Carlier,' J. Devaux, and R. Lepas Unit6 de Physique et de Chimie des Hauts PolymBres, Universith Catholique de Louvain, 1, Croix d u Sud, 1348 Louvain-la-Neuve, Belgium

P. T. McGrail ICI Wilton Materials Research Centre, P.O. Box 90,Wilton, Middlesbrough TS6 WE, Great Britain Received December 26, 1991; Reoked Manuscript Received August 3, 1992

ABSTRACT Molecular design, microstructure, and physical properties of polymers are etrongly related to each other. A better understanding of their interdependence will give the polymer chemist useful ideas for the synthesis of new macromolecules. The present paper aime to compare the thermal behavior of aryl polycondensatea baaed on ether, sulfone, and ketone links. Ultimately the objective is to design a new polymer combining, for example, the glass transition (T,) of poly(ether sulfone)s and the crystallinity of poly(ether ether ketone)s. By the use of anew concept,thepercentage of rigidchainlength,it is demonstrated that one can predict T, and T, of poly(ary1ether ketone)s and T,of poly(ary1ether 8ulfone)s. The feasibility of crystalline poly(ary1 ether sulfone)s is also discussed on the basis of the BBme principle. Introduction Poly(ary1ether ketone)s (PEEK, PEK, etc.) and poly(aryl ether sulfone)s (PES, PEES, etc.) exhibit complementary properties which have often been emphasized.'+ The former types of polymer are semicrystallinebut their fairly low Tis are often consideredto be a limitation. The latter typee of polymer are characterizedby high Tis(often above 200 "C),but, since they fail to crystallize, their solvent resistance is often very poor. Many attempts to synthesize polycoadensates including both types of linkages (ketone and sulfone) or copolymers have not led to practicalsolutions. Nevertheless,joining together the best thermal properties of both families in a unique material is a challenge. A better understanding of the factors which give rise to thia situation is the objective of this study. To facilitate this understanding, the glass transition temperatures and melting points of a wide range of poly(aryl ether ketonels and poly(ary1 ether sulfone)s have been examined. A group contribution principle has been deduced from this preliminary study.

I. Glass Transition Study A. Poly(ary1 su1fone)s. It is well known that the Tg of a polymer depends on both chain rigidity and polarity. In Table I, a series of poly(ary1ether sulfone)eis presented which exhibit high Tgdue to their chain rigidity (C6H4, C&41l0) are needed to hinder the crystallization.

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Macromolecules, Vol. 25, No. 24, 1992

Table 111 Crystallizability Study on Polymers Containing C-S Links

Tg( O C )

T, ("(2)

steric hindrance due to SO2

valence angle difference (deg) 0

*O

ref 5, 9 20 1,12,13 21 20 20 29

+20 +20 *20 +20 *11

Table IV PRCLn, for the Poly(ary1ether su1fone)s Listed in Table I

66 61 63 67 67 49

383 393 398 389 408

sequence

csH4 csE4csH4 CsH4G&I4+H4

CG0-C C-0-C

c-sorc

Table V Calculation Data length (A) % rigidity valence angle (deg) 100 2.79 100 7.08 100 11.37 1.5-1.5 33 124 1.36-1.36 0 124 100 105 1.73-1.73

Thermodynamically,these two conditions correspond, through a lower compaction within the crystalline unit cell, to a lower A H m , leading to a lowering of T,. As simultaneously the sulfone link strongly rigidifies the polymer chain, the glass transition temperature is increased. Therefore, the Tm - Tgdifference decreases and the crystallization rate is very low. This observation is confiied by the cryatallizabilityof PEES when a lowering of Tgis induced by a solvent.21 A solution to the problem of the crystallization of poly(aryl ether sulfone)s from the melt can be found by increasing rigidification of the chain by a means other than the sulfone link. This will lead to a large decrease of the entropy of the melt without any corresponding decrease of the enthalpy (no increase of steric hindrance nor in valence angle difference). The melting point will remain fairly high. This solution has been realized by Stanilands through the use of biphenyl and terphenyl groups, which can be considered aa rigid due to the *-conjugation. Five poly(aryl ether sulfone)s of that structure are presented in Table I. It is possible to calculate PRCL,, the contribution to the PRCL of all the rigid groups except the sulfone link (C6H4, CsH4-CsH4, and CsH4-CsH4-CsHd, for all the polysulfones in Table I. From Table IV it can be seen that the lower limit of this contribution lies around 61% in order to get a melt-crystallizablechain structure. The

P

c

*

h mu0 U t 6

Figure 7. Repeat unit of a modelpoly(ether ketone-co-sulfone).

only exception is (OC6H4C6H4S02Ca&)., which requires reexamination. That limit of 61% of PRCL, contribution seems to constitute a necessary condition to synthesize a crystallizable poly(ary1 ether sulfone).

III. Calculation Procedure The repeat unit is written in ita extended form. Each sequencelength is then calculated from the values reported in Table V16*26p27 and projected onto the main axis of the molecule, taking into account the valence angles (Table V). The rigid length is then calculated by multiplication of the projected length of each rigid segment by ita percentage of rigidity (see Table V). Finally, the percentage of rigid chain length is calculated aa the ratio of the rigid length on the full length of the repeat unit. An example of calculation is given below for a model poly(ether ketone-co-sulfone) (Figure 7). Example: Lfifid = 3LC,H4 cos 28'

+

x 100% + LC,H4