Chapter 3
Polybutylene Terephthalate Modified with Diamide Segments 1
Downloaded by UNIV OF GUELPH LIBRARY on September 6, 2012 | http://pubs.acs.org Publication Date: January 28, 1999 | doi: 10.1021/bk-1998-0713.ch003
R. J . Gaymans and A . C. M. van Bennekom
University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
Studied are the synthesis and thermal degradation of polybutylene terephthalate (PBT) and polybutylene terephthalate modified with diamide segments, [Benzoic acid, 4,4'-(1,4-butanediylbis(imino-carbonyl)]bis - ,dimethyl ester, CAS no 1028 10-33-3. The diamide used is synthesized from butanediamine and dimethyl terephthalate in a toluene/methanol solution with Lithium methanolate as catalyst at 60-90°C, for 7.5 - 40 hours. The diamide has a melting temperature of 265°C. The polycondensation of PBT and PBT with 20 mol% of diamide units is carried out in the melt at 255°C under a high vacuum with Ti(OC H )4 as catalyst. The influence of the concentration Ti-catalyst (0.02-0.28 mol%) and the diamide purity is studied. The concentration of Ti-catalyst has little effect. The presence of Lithium was found to increase the polymerization rate. Lithium thus seems to be an interesting cocatalyst. A decreasing 3
7
purity of the diamide has a lowering effect on the η and the T . A very effective way to obtain a high molecular weight polymer is the use of a short melt polymerization time followed with a solid state post condensation at 220°-230°C. The thermal stability is studied at 255°-270°C, under nitrogen and high vacuum with a stirred melt. The degradation is followed by the change in inh
m
inherent viscosity (η ), carboxylic acid endgroup concentration and amount of ester-amide interchange. The degradation constants for PBT are comparable to the literature values. The degradation constants for the P B T with diamide segments as measured by viscometry are the same as P B T but if calculated from the acid endgroup concentrations slightly higher. With degradation time the uniformity of the diamide by ester-amide inter change is lost. inh
Polybutylene terephthalate (PBT) is an important engineering plastic. PBT has excellent mechanical properties combined with a high crystallization rate and an ease of processing. PBT is marketed neat, impact modified, blended with other polymers as polycarbonate and glass fiber reinforced. The PBT has however a relatively low glass transition ( T 45°C) and low melting temperature ( T 220°C). Studied has been the modification of PBT with diamide segments (PBTA). The diamide segment is g
m
1
Current address: GE Plastics, P.O. Box 117, 4600 AC Bergen op Zoom, The Netherlands.
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©1998 American Chemical Society In Solvent-Free Polymerizations and Processes; Long, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
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made separated before it is included in the polymer. The diamide used is synthesized from 1,4 diamino butane and dimethyl terephthalate and is called ([Benzoic acid, 4,4'-(l ,4-butanediylbis(imino-carbonyl)]bis-,dimethyl ester) or abbreviated T4T.dimethyl (1).
H CO-C-^yC-N-(CH2) -N-C-^V-Ç-OCH 3
4
(D
3
T4T.dimethyl It has been found that the T and T can be increased by modification of P B T with diamide segments (T4T.dimethyl) without losing its high crystallization rate, its ease of processing and its thermo-dimensional stability (Table I)(l-4). The rate of
Downloaded by UNIV OF GUELPH LIBRARY on September 6, 2012 | http://pubs.acs.org Publication Date: January 28, 1999 | doi: 10.1021/bk-1998-0713.ch003
g
m
Table I. τ * Diamide T* T, c (mol% ) (°C) (°Q TO PBT 0 222 47 186 PBTAQ2 2 224 51 191 PBTA 10 232 59 201 20 70 249 219 PBTA™ * DSC data measured at 20°C/min heating and cooling ** Water absorption measured after 30 days, 100 RH at 25°C m
1
10
T -T m
TO
36 33 31 30
c
G*i40°c (MPa) 180
Water** (wt %) 0.45
-
-
190 250
0.50 0.85
crystallization of the P B T A ' s seems even to be higher than that of P B T . Also the blends of P B T A with P C have a higher T and a higher crystallization rate of the P B T A and a higher T g of the P C phase due to lower miscibility with P B T A ( 5 , 6 ) . The 1,4-diamino butane in the diamide has a stretched length comparable to the butanediol in the P B T . In spite of the similarity of the structure of the diamide and the ester group, the polyesteramides based on these are non isomorphous( 1,4,7-9). Random copolyesteramides synthesized by co-reaction of a monomer mixture of diol, diamine and dicarboxylic acid (or esters thereof), have a low order and poor properties(7-9). Thus for P B T A with good properties it is important that the diamide segments in the polyester are uniform in length. Other uniform segments that have been incorporated in polyesters are a diimide in PBT(10), a diamide in PET(4,11), diamide in polyhexamethylene terephthalate(12) and diamides and diurethanes in aliphatic polyesters(13). A special case of polyesters with diamide segments are the alternating polyesteramides(14-18). These copolymers all have a high order and a high crystallization rate. The faster crystallization of the P B T A (with uniform diamide segments) we expect to be due to a preordering of diamide segments in the melt (self assembling), forming very thin lamellae. These nano crystalline regions are nuclei for the crystallization of the ester segments, which follow by adjacent ordering (Figure 1)(4). The polyesteramide with P B T and 20 m o l % diamide ( P B T A ) has an average repeat length of the ester unit (x) in (2) of four. m
20
C-
> DMT + 7 4 + 4 7 4 + 7 4 7 + 7 4 7 4 + oligomers + CH OH 3
(4)
The first precipitate (white suspension) was formed after 1 hour. On further reaction the yield increased from 65% after 7.5 hours to 85% after 40 hours total reaction time. The hot filtered mixture consisted of T4T.dimethyl, precipitated sideproducts (T4T4 and higher) and soluble products ( D M T , T4) which had precipitated during the hot filtration step. B y extraction or washing with hot toluene the soluble products like DMT-residues were removed. The impurity of the T4T.dimethyl after extraction/washing as measured by C N M R was 4-6%, T m = 253°-260°C, A H m = 110-145 J/g. Further purification by recrystallization from hot N M P resulted in an impurity content of
