Segmented Polyester Thermoplastic Elastomers

4

Segmented Polyester Thermoplastic Elastomers

W. K. WITSIEPE

1

Downloaded by EAST CAROLINA UNIV on March 7, 2017 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0129.ch004

E . I. du Pont de Nemours and Co., Inc., Elastomer Chemicals Department, Experimental Station, Wilmington, Del. 19898

The

preparation

and physical properties

polyether-polyester

of a group of

copolymers are described.

Where the

polyester component has a high homopolymer melting point, the resulting copolyesters are tough, resilient, thermoprocessable elastomers.

Polymer hardness and modulus character-

istics may be varied from a fairly soft elastomer to an impact-resistant plastic by varying the relative amounts of polyether (soft segment) and polyester (hard segment).

The

general characteristics of these polymers suggest that these materials have a continuous amorphous polyether

phase

tied together with crystalline hard segment domains.

Prop-

erties such as tear strength, flex resistance, and oil resistance may be modified

by incorporating

a second ester

component; in these latter polymers, the crystalline phase contains one, but not both, of the hard segment ester components.

Melting

points of the copolymers depend

upon

the mole fraction of crystallizable hard segment.

n p h i s r e p o r t deals w i t h t h e synthesis a n d c h a r a c t e r i z a t i o n o f c o p o l y esters d e r i v e d f r o m p o l y a l k y l e n e ether glycols, a r o m a t i c d i c a r b o x y l ates, a n d s h o r t - c h a i n a l i p h a t i c diols.

M o d i f i c a t i o n of p o l y e t h y l e n e tere-

p h t h a l a t e b y use of u p to 20 w t % of h i g h - m o l e c u l a r - w e i g h t ether

glycol

w a s first r e p o r t e d

S n y d e r ( 2 ) to y i e l d p o l y m e r i c

independently fibers

(J)

and

having improved d y e receptivity

a n d m o i s t u r e r e g a i n , as w e l l as greater unmodified polymer.

polyethylene

by Coleman

flexibility,

compared

with the

M e l t i n g p o i n t a n d t e n a c i t y of the m o d i f i e d p o l y

mers w e r e s i m i l a r to those o f u n m o d i f i e d p o l y m e r s .

C o l e m a n ( 3 ) also

r e p o r t e d that t h e p o l y e t h e r d i d n o t interfere w i t h t h e c r y s t a l l i n i t y of polyethylene

terephthalate, a n d that t h e p o l y e t h e r

resided wholly i n

Present address: E. I. du Pont de Nemours and Co., Inc., Elastomer Chemicals Dept., P.O. Box 1378, Louisville, Ky. 40201 1

39 Platzer; Polymerization Reactions and New Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

40

POLYMERIZATION REACTIONS A N D N E W POLYMERS

280 O 240 < 200 I X ~ 160

Plastic Flow

I-

z


£l20 e> § 80 UJ 5 40 _l_

0 10 20 30 40 50 60 70 80 90 100 POLYETHYLENE TEREPHTHALATE HARD SEGMENT, Wt.% Figure 1. Melting point (x-ray) of segmented polyesters having a 4000 M polyether glycol soft segment and a polyethylene terephthalate hard segment (5) n

a m o r p h o u s regions of t h e s e m i c r y s t a l l i n e

fibers.

Copolymers containing

30% p o l y e t h e r h a d l i m i t e d elasticity. J . C . Shivers ( 4 , 5 ) b r o a d e n e d this a p p r o a c h to i n c l u d e other p o l y a l k y l e n e ether glycols a n d polyester h a r d segments.

C h a r a c t e r i z a t i o n of

p o l y m e r s h a v i n g a m u c h b r o a d e r range of ether content s h o w e d that a w i d e v a r i e t y of p r o d u c t s — r a n g i n g f r o m h a r d plastics to s e m i c r y s t a l l i n e elastomers a n d , at h i g h ether content, to soft elastic g u m s — c o u l d b e obtained

(Figure 1).

T h e elastomers d e s c r i b e d b y Shivers w e r e r e

p o r t e d to h a v e excellent stress decay a n d tensile r e c o v e r y w h e n tested as d r a w n

fibers.

S u b s e q u e n t l y , other w o r k e r s i n v e s t i g a t e d t h e use of

p o l y e t h e r esters i n various 8, 9, 10).

fiber,

film,

a n d adhesive a p p l i c a t i o n s (6, 7,

C e r t a i n c h a r a c t e r i s t i c properties of a r o m a t i c polyesters s u c h

as h i g h m e l t i n g p o i n t , i n s o l u b i l i t y i n most solvents, excellent m e l t sta b i l i t y , a n d h i g h strength m a k e t h e m of interest as h a r d segments i n thermoprocessable

elastomers.

Experimental C a t a l y s t . M a g n e s i u m m e t a l (1.41 grams, 0.058 gram-atom) is a d d e d to 300 m l of d r y 1-butanol a n d the b u t a n o l refluxed f o r a b o u t f o u r hours i n t h e absence of moisture. T h e m a g n e s i u m reacts to f o r m a gelatinous mass after; 36.0 grams (0.106 m o l e ) of t e t r a b u t y l t i t a n a t e is t h e n a d d e d a n d reflux c o n t i n u e d f o r a n a d d i t i o n a l h o u r . T h e r e s u l t i n g h o m o g e n e ous s o l u t i o n is c o o l e d a n d b o t t l e d u n t i l r e q u i r e d .

Platzer; Polymerization Reactions and New Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1973.


4.

WITSIEPE

Polyester Thermoplastic

41

Elastomers

P o l y m e r i z a t i o n . T h e s e materials are p l a c e d i n a 3 0 0 - m l d i s t i l l a t i o n flask fitted for d i s t i l l a t i o n : p o l y t e t r a m e t h y l e n e ether g l y c o l ( P T M E G ) , n u m b e r - a v e r a g e m o l e c u l a r w e i g h t a b o u t 1000 (35.0 grams, 0.035 m o l e ) ; 1,4-butanediol ( 4 G ) (25.0 grams, 0.28 m o l e ) ; d i m e t h y l t e r e p h t h a l a t e ( D M T ) (40.0 grams, 0.21 m o l e ) ; s y m - d i - / ^ n a p h t h y l - p - p h e n y l e n e d i a m i n e (0.15 g r a m ) . A stainless-steel stirrer w i t h a p a d d l e cut to c o n f o r m w i t h the i n t e r n a l r a d i u s of the flask is p o s i t i o n e d about % i n c h f r o m the b o t t o m of the flask a n d a g i t a t i o n is started. T h e flask is p l a c e d i n a n o i l b a t h at 2 0 0 ° C , a g i t a t e d for five m i n u t e s , a n d 0.3 m l of catalyst is a d d e d . M e t h a n o l d i s t i l l a t i o n starts almost i m m e d i a t e l y , a n d d i s t i l l a t i o n is p r a c t i c a l l y c o m p l e t e i n 20 m i n u t e s . T h e t e m p e r a t u r e of the o i l b a t h is m a i n t a i n e d for one h o u r after the a d d i t i o n of catalyst. T h e t e m p e r a t u r e of the b a t h is t h e n increased to 2 6 0 ° C d u r i n g about 30 m i n u t e s . T h e pressure o n the system is t h e n r e d u c e d to 0.5 m m H g or less ( a b o u t 0.1 m m H g m e a s u r e d w i t h a M c L e o d gauge at the p u m p ) a n d d i s t i l l a t i o n at r e d u c e d pressure is c o n t i n u e d for about 90 m i n u t e s . T h e r e s u l t i n g viscous, m o l t e n p r o d u c t is s c r a p e d f r o m the flask i n a n i t r o g e n ( w a t e r a n d o x y g e n - f r e e ) atmosphere a n d a l l o w e d to cool. M a t e r i a l s . E x c e p t for the s h o r t - c h a i n d i o l s , a l l of the reagents w e r e of c o m m e r c i a l q u a l i t y a n d u s e d as r e c e i v e d . T h e s h o r t - c h a i n diols ( E a s t m a n ) w e r e d i s t i l l e d f r o m a s m a l l q u a n t i t y of s o d i u m before use. T e s t M e t h o d s . Inherent viscosities w e r e d e t e r m i n e d at a c o n c e n t r a t i o n of 0.1 g / d l i n m-cresol at 3 0 ° C a n d are r e p o r t e d i n d l p e r g r a m . M e l t i n g points a n d glass t r a n s i t i o n temperatures w e r e d e t e r m i n e d i n the u s u a l w a y b y use of a d i f f e r e n t i a l s c a n n i n g c a l o r i m e t e r ( D u p o n t M o d e l 900). H e a t i n g rate was 11° C / m i n . T o d e t e r m i n e m e c h a n i c a l properties, unless otherwise n o t e d , a l l specimens w e r e pressed at a b o u t 2 0 ° C a b o v e t h e i r m e l t i n g p o i n t , h e l d at this t e m p e r a t u r e , a n d t h e n c o o l e d u n d e r pressure over five to 10 minutes to r o o m t e m p e r a t u r e . T h e y w e r e t h e n c o n d i t i o n e d at 24 ° C a n d 50% r e l a t i v e h u m i d i t y for at least t w o days before testing. T e s t methods u s e d w e r e : A S T M D2240 A S T M D412

H a r d n e s s , Shore T e n s i l e strength E l o n g a t i o n at b r e a k Tensile modulus T e a r strength

A S T M D412, D i e C A S T M D412 A S T M D 1 9 3 8 at 50 i n . / m i n

Torsional modulus (Clash-Berg)

A S T M D1043

C o m p r e s s i o n set

A S T M D395-55, method B , 22 h r / 7 0 ° C

Brittle point

A S T M D746

Discussion The

copolyesters

may be

considered

as h a v i n g b e e n d e r i v e d

r a n d o m l y j o i n i n g , h e a d - t o - t a i l , soft a n d h a r d segments.

by

A generalized

structure is:


42

POLYMERIZATION REACTIONS A N D N E W POLYMERS

(0—CH CH CH CH ) OC—AR—C-2

2

2

2

x

II 0

--0D0—C—AR—CII o

N o


Soft Segment

II o

H a r d Segment

A R = the a r o m a t i c m o i e t y of the d i c a r b o x y l a t e D = the a l k y l e n e p o r t i o n of a s h o r t - c h a i n d i o l x = the n u m b e r of t e t r a m e t h y l e n e ether units i n the p o l y t e t r a m e t h y l e n e ether g l y c o l Copolyesters h a v e b e e n p r e p a r e d f r o m d i m e t h y l terephthalate, p o l y tetramethylene

ether

glycol

(molecular

weight,

1000)

and

various

s h o r t - c h a i n d i o l s , e s p e c i a l l y 1,4-butanediol a n d ethylene g l y c o l .

With

1,4-butanediol, the c r y s t a l l i n e h a r d segments ( w h i c h p r o d u c e the h i g h modulus tie-point domains)

consist of consecutive units of t e t r a m e t h

y l e n e t e r e p h t h a l a t e ( 4 G T ) ; w i t h ethylene g l y c o l , these segments consist of ethylene t e r e p h t h a l a t e ( 2 G T ) .

T h e a m o r p h o u s phase contains units

of p o l y t e t r a m e t h y l e n e ether g l y c o l t e r e p h t h a l a t e ( P T M E G - T ) . Copolyesters

containing two

b e e n s y n t h e s i z e d , too.

aromatic carboxylate

residues

have

F o r e x a m p l e , 1,4-butanediol has b e e n u s e d w i t h

d i m e t h y l t e r e p h t h a l a t e i n c o m b i n a t i o n w i t h a n u m b e r of d i m e t h y l esters, i n c l u d i n g d i m e t h y l phthalate ( 4 G P ) , d i m e t h y l isophthalate ( 4 G I ) , d i m e t h y l sebacate ( 4 G 1 0 ) ,

and dimethyl m-terphenyl-4,4"-dicarboxylate

(4GTP). F o r convenience, p o l y m e r compositions w i l l b e specified a c c o r d i n g to t h e i r h a r d segment w e i g h t p e r c e n t a g e a n d soft segment c o m p o s i t i o n . F o r e x a m p l e , 44% 4 G T / P T M E G - T

is a r a n d o m segmented

copolymer

c o n t a i n i n g 44% b y w e i g h t of t e t r a m e t h y l e n e terephthalate segments a n d 56% b y w e i g h t of p o l y t e t r a m e t h y l e n e ether terephthalate.

U n l e s s other

w i s e specified, a l l d a t a refer to p o l y t e t r a m e t h y l e n e ether g l y c o l h a v i n g a n u m b e r - a v e r a g e m o l e c u l a r w e i g h t of 980.

Synthesis T h e p o l y e t h e r esters are m a d e b y t y p i c a l m e l t p o l y m e r i z a t i o n p r o cedures. A p r e p o l y m e r is first p r e p a r e d b y i n t e r c h a n g e of t h e m e t h y l ester of one or m o r e a r o m a t i c d i c a r b o x y l i c acids w i t h a m i x t u r e of a p o l y m e r i c d i o l a n d e n o u g h s h o r t - c h a i n d i o l for a n o v e r a l l 50% excess of h y d r o x y l f u n c t i o n a l i t y ( F i g u r e 2 ) . A titanate catalyst is g e n e r a l l y u s e d . M e t h a n o l is f r a c t i o n a t e d f r o m the r e a c t i o n m i x t u r e to a v o i d loss of


4.

WITSIEPE

Polyester Thermoplastic

0

0

11

/ ^ \ 'I

43

Elastomers

3H0R0H

2MeOC-/ O )-C0Me A

•

2 0 0 ° C , catalyst

0

0


HOROC-^(^LO

COROH

250°C,

ii TT^VII

H

+

4MeOHf

Segmented Polyester Thermoplastic Elastomers

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